COMPOSITIONS AND METHODS OF TREATMENT OF VISION LOSS THROUGH GENERATION OF ROD PHOTORECEPTORS FROM MIJLLER GLIAL CELLS

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the priority benefit of U.S. provisional application

Nos. 62/654,256, filed April 6, 2018, and 62/654,106, filed April 6, 2018, each of which is incorporated by reference herein in its entirety.

STATEMENT OF FEDERALLY SPONSORED RESEARCH

This invention was made with government support under Grant no.

EY024986, awarded by the National Institutes of Health. The government has certain rights in the invention.

SEQUENCE LISTING

The present specification is being filed with a computer readable form (CRF) copy of the Sequence Listing. The CRF entitled Sequence_Listing.txt, which was created on April 4, 2019 and is 50,002 bytes in size, is identical to the paper copy of the Sequence Listing and is incorporated herein by reference in its entirety.

BACKGROUND

Muller glial cells (MGs) are the primary support cells in the vertebrate retina. In cold-blooded vertebrates such as zebrafish, MGs are a source of stem cells for they can readily re-enter the cell cycle and replenish lost neurons, establishing a powerful self-repair mechanism (Bernardos et al, J. Neurosci. 2007, 27:7028-7040; Fausett and Goldman, J Neurosci. 2006, 26:6303-6313; Fimbel et al, J Neurosci. 2007, 27: 1712- 1724; Qin et al, Proc Natl Acad Sci U S A, 2009, 106:9310-9315; Ramachandran et al, J Comp Neurol. 2010, 518:4196-4212; Thummel et al, Dev Neurobiol. 2008, 68:392-408). In mammals, however, MGs are naturally quiescent and lack regenerative capability (Sahel et al, Exp Eye Res. 1991, 53:657-664). Recent studies suggest that the regenerative machinery still exists in adult mammalian retina, but to restore the stem cell status of MGs, as evidenced by cell cycle re-entry, requires retinal injury such as neurotoxin treatment (Close et al, Glia, 2006, 54:94-104; Dyer and Cepko, Nat Neurosci. 2000, 3:873-880; Karl et al, Proc Natl Acad Sci U S A, 2008, 105: 19508-19513; Ooto et al, Proc Natl Acad Sci U S A, 2004, 101: 13654- 13659). This type of injury would be counterproductive for regeneration as it massively kills retinal neurons including retinal ganglion cells and amacrine cells (Dyer and Cepko, Nat Neurosci. 2000, 3:873-880; Karl et al, 2008; Ooto et al, Proc Natl Acad Sci U S A, 2004, 101 : 13654-13659). The molecular nature of injury- induced signals that activates MG proliferation in mammals remains poorly understood.

Photoreceptors are the most abundant cells in the mammalian retina and they mediate the first step in vision. The death of photoreceptors is a leading cause of vision impairment and blindness in major retinal degenerative diseases including age- related macular degeneration (AMD) and retinitis pigmentosa (RP). Extensive research efforts aimed at restoring the regenerative capability of MGs in mammals have met with little success. Current strategies for MG-derived photoreceptor regeneration rely on retinal injury and treatment of the whole retina with various factors. Retinal injury is a prerequisite for restoring the stem/progenitor cell status of adult mammalian MGs, as evidenced by cell cycle re-entry (Close et al, Glia, 2006, 54:94-104; Dyer and Cepko, Nat Neurosci. 2000, 3:873-880; Karl et al, Proc Natl Acad Sci U S A, 2008, 105: 19508- 19513; Osakada et al, J Neurosci. 2007, 27:4210- 4219; Takeda et al, Invest Ophtalmol Vis Sci. 2008, 49: 1142-1150; Wan et al,

Vision Res. 2008, 48:223-234; Wan et al, Biochem Biophys Res Commun. 2007, 363:347-354). However, retinal injury kills retinal neurons in the first place.

Neurotoxin-induced retinal injury inevitably causes death of amacrine cells and retinal ganglion cells, and therefore could be counterproductive to the aim of restoring regenerative capabilities in the mammalian retina. Global treatment of the entire retina may lead to undesirable side effects in untargeted cells. There is thus a need in the art for an injury-free strategy of restoring photoreceptor function that would not necessitate inflicting a further damage to a diseased retina. The present invention addresses this unmet need in the art.

SUMMARY

In a first aspect, provided herein is a method of treating vision loss or impairment in a subject, comprising: (a) administering to the subject a therapeutically effective amount of a MG cell proliferation agent; and (b) a period of time after the administering of step (a), administering to the subject a therapeutically effective amount of a MG cell differentiation agent.

In a second aspect, provided herein is a method of treating age-related macular degeneration (AMD), diabetic retinopathy, retrolental fibroplasia, Stargardt disease, retinitis pigmentosa (RP), uveitis, Bardet-Biedl syndrome, or an eye cancer, in a subject, comprising: (a) administering to the subject a therapeutically effective amount of a MG cell proliferation agent; and (b) a period of time after the administering of step (a), administering to the subject a therapeutically effective amount of a MG cell differentiation agent.

In a third aspect, provided herein is a method of generating new rod photoreceptors in a retina in a subject, comprising: (a) administering to the subject a therapeutically effective amount of a MG cell proliferation agent; and (b) a period of time after the administering of step (a), administering to the subject a therapeutically effective amount of a MG cell differentiation agent.

In certain embodiments of the first through third aspects, the proliferation agent comprises a nucleic acid encoding a protein selected from the group consisting of beta-catenin, Lin28a, Lin28b, Notch, and Achaete-S cute family basic helix-loop- helix transcription factor 1 (Ascll). In certain embodiments, the proliferation agent comprises a nucleic acid encoding beta-catenin. In certain embodiments, the proliferation agent comprises a nucleic acid encoding Ascll. In certain embodiments, the nucleic acid is operably linked to a promoter, wherein the promoter specifically expresses the nucleic acid in MG cells. In certain embodiments, the promoter is a glial fibrillary acidic protein (GFAP) promoter. In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO: 8.

In certain embodiments of the first through third aspects, the proliferation agent comprises a vector comprising a protein selected from the group consisting of beta-catenin, Lin28a, Lin28b, Notch, and Ascll.

In certain embodiments of the first through third aspects, the proliferation agent comprises a vector, wherein the vector comprises a nucleic acid encoding a protein selected from the group consisting of beta-catenin, Lin28a, Lin28b, Notch, and Ascll. In certain embodiments, the proliferation agent comprises a vector, wherein the vector comprises a nucleic acid encoding beta-catenin. In certain embodiments, the proliferation agent comprises a vector, wherein the vector comprises a nucleic acid encoding Ascll . In certain embodiments, the nucleic acid is operably linked to a promoter, wherein the promoter specifically expresses the nucleic acid in MG cells. In certain embodiments, the promoter is a GFAP promoter. In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO: 8.

In certain embodiments, the vector is a virus or a virus-like particle. In certain embodiments, the vector is an adeno-associated virus (AAV). In certain

embodiments, the AAV is AAV-ShHlO. In certain embodiments, the capsid of the AAV viral vector comprises an amino acid sequence having at least about 85%, at least about 90%, at least about 95%, at least about 98%, at least about 99%, or 100%, amino acid sequence identity to the ShHlO amino acid sequence of SEQ ID NO: 7.

In certain embodiments of the first through third aspects, the proliferation agent comprises a protein selected from the group consisting of beta-catenin, Lin28a, Lin28b, Notch, and Ascll.

In certain embodiments of the first through third aspects, the differentiation agent comprises at least one nucleic acid molecule encoding at least one transcription factor selected from the group consisting of Otx2, Crx, Nrl, Nr2e3, and NueroD. In certain embodiments, the differentiation agent comprises at least one nucleic acid molecule encoding Otx2, Crx, and Nrl. In certain embodiments, the at least one nucleic acid molecule is operably linked to a promoter, wherein the promoter specifically expresses the nucleic acid molecule in MG cells. In certain embodiments, the promoter comprises a GFAP promoter. In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO: 8.

In certain embodiments of the first through third aspects, the differentiation agent comprises a first nucleic acid molecule, a second nucleic acid molecule, and a third nucleic acid molecule, wherein the first nucleic acid molecule encodes Otx2, wherein the second nucleic acid molecule encodes Crx, and wherein the third nucleic acid molecule encodes Nrl. In certain embodiments, the first nucleic acid molecule is operably linked to a first promoter that specifically expresses the first nucleic acid in an MG cell, the second nucleic acid molecule is operably linked to a second promoter that specifically expresses the second nucleic acid in an MG cell, and the third nucleic acid molecule is operably linked to a third promoter that specifically expresses the third nucleic acid in an MG cell. In certain embodiments, each of the first, second, and/or third promoter comprises a GFAP promoter. In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO:8.

In certain embodiments of the first through third aspects, the differentiation agent comprises a first vector, a second vector, and a third vector, wherein the first vector comprises a first nucleic acid molecule, the second vector comprises a second nucleic acid molecule, and the third vector comprises a third nucleic acid molecule, wherein the first nucleic acid molecule encodes a transcription factor selected from the group consisting of Otx2, Crx, Nrl, Nr2e3, and NueroD, the second nucleic acid molecule encodes a transcription factor selected from the group consisting of Otx2, Crx, Nrl, Nr2e3, and NueroD, and the third nucleic acid molecule encodes a transcription factor selected from the group consisting of Otx2, Crx, Nrl, Nr2e3, and NueroD, and wherein each of the first, second, and third nucleic acid molecules encode a different protein. In certain embodiments, the first nucleic acid molecule is operably linked to a first promoter that specifically expresses the first nucleic acid in an MG cell, the second nucleic acid molecule is operably linked to a second promoter that specifically expresses the second nucleic acid in an MG cell, and the third nucleic acid molecule is operably linked to a third promoter that specifically expresses the third nucleic acid in an MG cell. In certain embodiments, each of the first, second, and/or third promoter comprises a GFAP promoter. In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO: 8. In certain embodiments, the first vector is a first virus or a first virus-like particle, the second vector is a second virus or a second virus-like particle, and the third vector is a third virus or a third virus-like particle. In certain embodiments, the first vector is a first AAV, the second vector is a second AAV, and the third vector is a third AAV. In certain embodiments in which the first vector is a first AAV, the second vector is a second AAV, and the third vector is a third AAV, the capsid of each of the first, second, and third AAV comprises an amino acid sequence having at least about 85%, at least about 90%, at least about 95%, at least about 98%, at least about 99%, or 100%, amino acid sequence identity to the ShHlO amino acid sequence of SEQ ID NO:7. In certain embodiments, the first, second, and/or third AAV is AAV-ShHlO. In certain embodiments, the first AAV is AAV-ShHlO, the second AAV is AAV-ShHlO, and the third AAV is AAV-ShHlO.

In certain embodiments of the first through third aspects, the differentiation agent comprises a first vector, a second vector, and a third vector, wherein the first vector comprises a first nucleic acid molecule, the second vector comprises a second nucleic acid molecule, and the third vector comprises a third nucleic acid molecule, wherein the first nucleic acid molecule encodes Otx2, the second nucleic acid molecule encodes Crx, and the third nucleic acid molecule encodes Nrl. In certain embodiments, the first nucleic acid molecule is operably linked to a first promoter that specifically expresses the first nucleic acid in an MG cell, the second nucleic acid molecule is operably linked to a second promoter that specifically expresses the second nucleic acid in an MG cell, and the third nucleic acid molecule is operably linked to a third promoter that specifically expresses the third nucleic acid in an MG cell. In certain embodiments, each of the first, second, and/or third promoter comprises a GFAP promoter. In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO: 8. In certain embodiments, the first vector is a first virus or a first virus-like particle, the second vector is a second virus or a second virus-like particle, and the third vector is a third virus or a third virus-like particle. In certain embodiments, the first vector is a first AAV, the second vector is a second AAV, and the third vector is a third AAV. In certain embodiments in which the first vector is a first AAV, the second vector is a second AAV, and the third vector is a third AAV, the capsid of each of the first, second, and third AAV comprises an amino acid sequence having at least about 85%, at least about 90%, at least about 95%, at least about 98%, at least about 99%, or 100%, amino acid sequence identity to the ShHlO amino acid sequence of SEQ ID NO:7. In certain embodiments, the first, second, and/or third AAV is AAV-ShHlO. In certain embodiments, the first AAV is AAV-ShHlO, the second AAV is AAV-ShHlO, and the third AAV is AAV-ShHlO.

In certain embodiments of the first through third aspects, the differentiation agent comprises Otx2, Crx, and Nrl.

In certain embodiments of the first through third aspects, the differentiation agent comprises a first vector comprising Otx2, a second vector comprising Crx, and a third vector comprising Nrl. In certain embodiments of the first through third aspects, the administering of step (a) is via intraocular, intravitreal, or topical administration.

In certain embodiments of the first through third aspects, the administering of step (b) is via intraocular, intravitreal, or topical administration.

In certain embodiments of the first through third aspects, the period of time of step (b) is at least one week, at least two weeks, at least three weeks, four weeks. In certain embodiments, the period of time of step (b) is two weeks.

In certain embodiments of the first through third aspects, the subject has a condition associated with vision loss or impairment due to photoreceptor loss. In certain embodiments, the condition is AMD, diabetic retinopathy, retrolental fibroplasia, Stargardt disease, RP, uveitis, Bardet-Biedl syndrome and eye cancers.

In certain embodiments of the first through third aspects, the subject is a human.

In a fourth aspect, provided herein is a nucleic acid molecule encoding at least one transcription factor selected from the group consisting of Otx2, Crx, Nrl, Nr2e3, and NueroD, which is operably linked to a promoter, wherein the promoter expresses the nucleic acid in an MG cell. In certain embodiments, the nucleic acid molecule encodes Otx2. In certain embodiments, the nucleic acid molecule encodes Crx. In certain embodiments, the nucleic acid molecule encodes Nrl. In certain embodiments, the promoter specifically expresses the nucleic acid in an MG cell.

In a fifth aspect, provided herein is a vector comprising a nucleic acid of the fourth aspect. In certain embodiments, the vector is a virus-like particle. In certain embodiments, the vector is a virus. In certain embodiments, the virus is AAV. In certain embodiments, the capsid of the AAV comprises an amino acid sequence having at least about 85%, at least about 90%, at least about 95%, at least about 98%, at least about 99%, or 100%, amino acid sequence identity to the ShHlO amino acid sequence of SEQ ID NO:7. In certain embodiments, the AAV is AAV-ShHlO.

In a sixth aspect, provided herein is a composition comprising one or more nucleic acid molecules of the fourth aspect. In certain embodiments, the composition comprises: a first nucleic acid molecule encodes Otx2, a second nucleic acid molecule encodes Crx, and a third nucleic acid molecule encodes Nrl. In certain embodiments, each of the first, second, and third nucleic acid molecules of the composition is operatively bound to a promoter that specifically expresses the nucleic acid in an MG cell. In certain embodiments, each of the first, second, and third nucleic acid molecules of the composition is operatively bound to a GFAP promoter. In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO: 8.

In a seventh aspect, provided herein is a composition comprising one or more vectors of the fifth aspect. In certain embodiments, the composition comprises: a first vector comprising a first nucleic acid molecule encodes Otx2, a second vector comprising a second nucleic acid molecule encodes Crx, and a third vector comprising a third nucleic acid molecule encodes Nrl. In certain embodiments, each of the first, second, and third vectors is a virus-like particle. In certain embodiments, each of the first, second, and third vectors is a virus. In certain embodiments, the virus is AAV. In certain embodiments, the capsid of the AAV comprises an amino acid sequence having at least about 85%, at least about 90%, at least about 95%, at least about 98%, at least about 99%, or 100%, amino acid sequence identity to the ShHlO amino acid sequence of SEQ ID NO:7. In certain embodiments, each of the first, second, and/or third AAV is AAV-ShHlO.

In an eighth aspect, the invention relates to a method for inducing proliferation of a MG cell comprising contacting the MG cell with a composition wherein the composition increases the level or activity of a WNT signaling effector in the cell.

In one embodiment, the method comprises increasing the level or activity of at least one protein selected from the group consisting of b-catenin, Lin28a, and Lin28b.

In one embodiment, the composition comprises at least one nucleic acid molecule encoding at least one protein selected from the group consisting of b- catenin, Lin28a, and Lin28b. In one embodiment, at least one nucleic acid molecule is operationally linked to a promoter for expression in MG cells. In one embodiment, the promoter is the GFAP promoter. In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO: 8.

In one embodiment, the composition is an inhibitor of GSK3B. In one embodiment, the composition is a let-7 anti-miR.

In a ninth aspect, the invention relates to a method of guiding differentiation of cycling MG cells comprising contacting the MG cells with at least one composition wherein the at least one composition increases the level or activity of at least one protein selected from the group consisting of rhodopsin, rod a-transducin, rod arrestin, phosducin, ROM1, retinal cGMP, Guanylate Cyclase-Activating Protein Photoreceptor 2, Tubby Like Protein 1, Retinoschisin 1, G alpha 1, G gamma 1, cGMP PDE gamma, G beta 1, mUNCH9, rod PDE beta, Pleckstrin Homology Domain Retinal Protein 1, Peripherin 2, recoverin, ribeye, bassoon, and CtBP

In one embodiment, the composition comprises at least one transcription factor selected from the group consisting of Otx2, Crx, Nrl, Nr2e3 and NeuroD. In one embodiment, the composition comprises Otx2, Crx, and Nrl.

In one embodiment, the composition comprises at least one nucleic acid molecule encoding at least one transcription factor selected from the group consisting of Otx2, Crx, Nrl, Nr2e3 and NeuroD. In one embodiment, the nucleic acid molecule is operationally linked to a promoter for expression in MG cells. In one embodiment, the promoter is the GFAP promoter. In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO: 8.

In one embodiment, the composition comprises a first nucleic acid molecule encoding Otx2, a second nucleic molecule encoding Crx, and a third nucleic acid molecule encoding Nrl. In one embodiment, the first nucleic acid molecule is operationally linked to a promoter for expression in MG cells, the second nucleic acid molecule is operationally linked to a promoter for expression in MG cells, and the third nucleic acid molecule is operationally linked to a promoter for expression in MG cells. In one embodiment, the promoter is the GFAP promoter. In certain

embodiments, the GFAP promoter comprises the sequence of SEQ ID NO: 8.

In a tenth aspect, the invention relates to a method of treating vision loss or impairment comprising administering to a subject a) a first composition for inducing MG cell proliferation; and b) a second composition for inducing differentiation of proliferating MG cells to rod photoreceptors.

In one embodiment, the first composition increases the level or activity of at least one protein selected from the group consisting of b-catenin, Lin28a, and Lin28b. In one embodiment, the first composition comprises at least one nucleic acid molecule encoding at least one protein selected from the group consisting of b-catenin, Lin28a, and Lin28b. In one embodiment, the at least one nucleic acid molecule is

operationally linked to a promoter for expression in MG cells. In one embodiment, the promoter is the GFAP promoter. In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO: 8.

In one embodiment, the first composition is an inhibitor of GSK3B. In one embodiment, the first composition is a let-7 anti-miR.

In one embodiment, the second composition increases the level or activity of at least one protein selected from the group consisting of rhodopsin, rod a-transducin, rod arrestin, phosducin, ROM1, retinal cGMP, Guanylate Cyclase-Activating Protein Photoreceptor 2, Tubby Like Protein 1, Retinoschisin 1, G alpha 1, G gamma 1, cGMP PDE gamma, G beta 1, mUNCH9, rod PDE beta, Pleckstrin Homology Domain Retinal Protein 1, Peripherin 2, recoverin, ribeye, bassoon, and CtBP

In one embodiment, the second composition comprises at least one transcription factor selected from the group consisting of Otx2, Crx, Nrl, Nr2e3 and NeuroD. In one embodiment, the second composition comprises at least one nucleic acid molecule encoding at least one transcription factor selected from the group consisting of Otx2, Crx, Nrl, Nr2e3 and NeuroD. In one embodiment, at the least one nucleic acid molecule is operationally linked to a promoter for expression in MG cells. In one embodiment, the promoter is the GFAP promoter. In certain

embodiments, the GFAP promoter comprises the sequence of SEQ ID NO: 8.

In one embodiment, the second composition comprises a first nucleic acid molecule encoding Otx2, a second nucleic acid molecule encoding Crx, and a third nucleic acid molecule encoding Nrl. In one embodiment, the first nucleic acid molecule is operationally linked to a promoter for expression in MG cells, the second nucleic acid molecule is operationally linked to a promoter for expression in MG cells, and the third nucleic acid molecule is operationally linked to a promoter for expression in MG cells. In one embodiment, the promoter is the GFAP promoter. In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO: 8.

In one embodiment, the first composition and the second composition are administered substantially concurrently. In one embodiment, the first composition is administered at least one week prior to administration of the second composition.

In an eleventh aspect, the invention relates to a composition comprising an expression vector comprising the ShH-lO backbone sequence and the GFAP promoter for expression of the nucleic acid in MG cells. In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO: 8.

In a twelfth aspect, the invention relates to a composition for inducing proliferation of a MG cell, wherein the composition increases the level or activity of a WNT signaling effector in the cell.

In one embodiment, the composition increases the level or activity of at least one protein selected from the group consisting of b-catenin, Lin28a, and Lin28b. In one embodiment, the composition comprises at least one nucleic acid molecule encoding at least one protein selected from the group consisting of b-catenin, Lin28a, and Lin28b. In one embodiment, the nucleic acid molecule is operationally linked to a promoter for expression in MG cells. In one embodiment, the promoter is the GFAP promoter. In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO:8.

In one embodiment, the composition comprises an inhibitor of GSK3B. In one embodiment, the composition comprises a let-7 anti-miR.

In a thirteenth aspect, the invention relates to a composition for guiding differentiation of cycling MG cells, wherein the composition increases the level or activity of at least one protein selected from the group consisting of rhodopsin, rod a- transducin, rod arrestin, phosducin, ROM1, retinal cGMP, Guanylate Cyclase- Activating Protein Photoreceptor 2, Tubby Like Protein 1, Retinoschisin 1, G alpha 1, G gamma 1, cGMP PDE gamma, G beta 1, mUNCH9, rod PDE beta, Pleckstrin Homology Domain Retinal Protein 1, Peripherin 2, recoverin, ribeye, bassoon, and CtBP

In one embodiment, the composition comprises at least one transcription factor selected from the group consisting of Otx2, Crx, Nrl, Nr2e3 and NeuroD. In one embodiment, the composition comprises at least one nucleic acid molecule encoding at least one transcription factor selected from the group consisting of Otx2, Crx, Nrl, Nr2e3 and NeuroD. In one embodiment, the nucleic acid molecule is operationally linked to a promoter for expression in MG cells. In one embodiment, the promoter is the GFAP promoter. In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO: 8. In one embodiment, the composition comprises Otx2, Crx, and Nrl. In one embodiment, the composition comprises a first nucleic acid molecule encoding Otx2, a second nucleic acid molecule encoding Crx, and a third nucleic acid molecule encoding Nrl. In one embodiment, the first nucleic acid molecule is operationally linked to a promoter for expression in MG cells, the second nucleic acid molecule is operationally linked to a promoter for expression in MG cells, and the third nucleic acid molecule is operationally linked to a promoter for expression in MG cells. In one embodiment, the promoter is the GFAP promoter. In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO: 8. DESCRIPTION OF DRAWINGS

The following detailed description of preferred embodiments of the invention will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings

embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities of the embodiments shown in the drawings.

Figure 1, comprising Figure 1 A through Figure 1K, depicts a time course analysis ofNMDA-induced cell death. Figure 1 A through Figure 1J depict adult mouse retinas collected at 0, 3, 6, 12, 18, 24, 36, 48, 60 and 72 hours after NMD A injection respectively and immunostained with an anti-HuC/D antibody. Confocal images of the retinal ganglion cell layer are presented to show the loss of ganglion and amacrine cells after NMDA damage over time. Scale bar: 20 pm. Figure 1K depicts the number of HuC/D+ cells as a percentage relative to the onset of the treatment. Data are presented as mean±sem, n=4.

Figure 2, comprising Figure 2A through Figure 2J, depicts results of example experiments demonstrating that neurotoxic injury activates Wnt signaling and MG proliferation. Figure 2A depicts a time course analysis of MG proliferation by scoring the number of EdU ⁺ cells/mm ² on retinal flatmount preparations following NMDA- induced neurotoxic injury. Data are presented as mean±sem, n=4. Figure 2B depicts representative images of EdU detection/anti-CyclinD3 or EdU detection/anti- p27 ^kipl immunohistochemistry at each time point. Arrow heads: EdU ⁺ cells were double positive for CyclinD3 or p27 ^{ki l} immunoreactivity. Scale bar: 25 pm. Figure 2C depicts a time course analysis of the RNA levels for Wnt genes, Wnt antagonists Dkkl and WIF-l following NMD A-induced neurotoxic injury. Figure 2D depicts a time course analysis of the RNA levels for Wnt target genes following NMDA- induced neurotoxic injury. Data are presented as mean±sem, n=4. Figure 2E depicts MGs visualized as tdTomato ⁺ cells in Rosa26-tdTomato reporter mice. ONL: outer nuclear layer; INL: inner nuclear layer; GCL: ganglion cell layer. Figure 2F depicts the RNA levels for Wnt genes, Wnt antagonists Dkkl and WIF-l in FACS-purified MGs and non-MGs at 18 hours after neurotoxic injury. Data are presented as mean±sem. n=3. ***p<0.00l, Student’s t test. Figure 2G depicts the RNA levels for Wnt target genes in FACS-purified MGs and non-MGs at 18 hours after neurotoxic injury. Data are presented as mean±sem, n=3. **r<0.01, ***p<0.00l, Student’s t test. Figures 2H and 21 depict inhibition of Wnt signaling suppresses neurotoxic injury- induced MG proliferation. In comparison to NMDA treatment alone (Figure 2H), Wnt inhibitor XAV939 treatment (Figure 21) significantly reduced the number of EdU ⁺ 60 hours after NMDA injection. Scale bar: 50pm. Figure 2J depicts quantification of EdU ⁺ cells after XAV939 treatment. Data are presented as mean±sem, n=4.

***p<0.00l, Student’s t test.

Figure 3, comprising Figure 3 A through Figure 30, depicts results of example experiments demonstrating that ShHlO-GFAP (glial fibrillary acidic protein) promoter-mediated gene transfer is specific for MGs. Transduction of retinal cells by ShHlO-CAG-GFP (Figure 3A - Figure 3C) or ShHlO-GFAP-GFP (Figure 3D - Figure 3F) via intravitreal injections in adult mouse retina at 4-weeks of age. ShHlO-CAG- mediated gene transfer resulted in transduction of NeuN immunoreactive retinal neurons indicated by arrows in Figure 3C. By contrast, ShHlO-GFAP-mediated gene transfer confers MG-specific transduction, eliminating GFP expression in NeuN- labeled cells. Scale bar: 20 pm. Figure 3G - Figure 30 depict ShHlO-GFAP-GFP infected retinas immunostained for MG-specific antigens: glutamine synthase (GS in Figure 3G - Figure 31), r27 ^Mr1 (Figure 3J - Figure 3L), and CyclinD3 (Figure 3M - Figure 30). ShHlO- GFAP mediated gene transfer of GFP was detected in the MG processes indicated by arrows in Figure 31, as well as in the MG nuclei indicated by arrows in Figure 3L and Figure 30. Scale bars: 25 pm. Figure 4, comprising Figure 4A through Figure 4C, depicts results of example experiments demonstrating that ShHlO-GFAP-mediated gene transfer of B- catenin activates the canonical Wnt signaling pathway in MGs. Figure 4A and Figure 4B depicts an assay of Wnt reporter activation in the presence (Figure 4B) or absence (Figure 4A) of b-catenin. Scale bar: 20 pm. Figure 4C depicts gene transfer of b- catenin in MGs activates the expression of Wnt target genes: Ccndl, Lefl, and Axin2. RNA levels were quantified in comparison to ShHlO-GFAP-GFP infected retinas as a control using quantitative PCR at 1, 2, and 4 weeks post-viral infection. Data are presented as mean±sem, n=4. **r<0.01, ***p<0.00l, Student’s t test.

Figure 5, comprising Figure 5 A through Figure 5 Z, depicts results of example experiments demonstrating that MGs re-enter the cell cycle following ShHlO- GFAP- mediated gene transfer of b-catenin without retinal injury. Figure 5 A through Figure 5R depict an analysis of EdU incorporation by immunohistochemistry co-labeling for MG-specific antigens: glutamine synthase (GS in Figure 5A - Figure 5F), CyclinD3 (Figure 5G - Figure 5L), and p27 ^kipl (Figure 5M - Figure 5R). The boxed areas in

Figure 5B, Figure 5H, and Figure 5N are enlarged in Figure 5D - Figure 5F, Figure 5J - Figure 5L, and Figure 5P - Figure 5R, respectively. Arrow heads in Figure 5F,

Figure 5L, and Figure 5R show that EdU signals were detected specifically in MGs. Figure 5S through Figure 5X depict EdU incorporation in the MG-specific reporter mice. The boxed area in Figure 5T is enlarged in Figure 5V - Figure 5X. Arrow heads in Figure 5X show that the EdU signals were detected in the tdTomato-labeled MGs in the ONL. Figure 5Y depicts the distribution of EdU ⁺ cells in retinal layers. ONL: outer nuclear layer; OPL: outer plexiform layer; INL: inner nuclear layer; IPL: inner plexiform layer; GCL: ganglion cell layer. Data are presented as mean±sem, n=38. Figure 5 Z depicts anti-CyclinD3 immunohistochemistry in untreated and b-catenin treated retinas at 2 weeks after viral infection. The number of CyclinD3 ⁺ cells was quantified per lOOpm in retinal sections. Data are presented as mean±sem, n=4. Scale bars in Figure 5C, Figure 50, Figure 51, and Figure 5U: 25 pm; Scale bars in Figure 5F, Figure 5R, Figure 5L, and Figure 5X: 10 pm. Scale bars in Figure 5 Z: 20 pm.

Figure 6, comprising Figure 6A through Figure 61, depicts an analysis of cycle progression of MGs following ShHlO-GFAP-mediated gene transfer of b-catenin in adult mouse retina. Figure 6A- Figure 6D depict co-detection of EdU and cell proliferation antigen Ki67. Figure 6E - Figure 6H depict co-detection of EdU and cell proliferation antigen phospho-histone H3 (PH3). The boxed areas in Figure 6A and Figure 6E are enlarged in Figure 6B - Figure 6D and Figure 6F - Figure 6H, respectively. Figure 61 depicts analysis of the percentage of Ki67 ⁺ cells that were also EdU ⁺ , the percentage of PH3 ⁺ cells that were also EdU ⁺ , and vice versa. Data are presented as mean±sem, n=5. Scale bars in Figure 6A and Figure 6E: 20 pm; Scale bars in Figure 6D and Figure 6H: 5 pm.

Figure 7, comprising Figure 7A through Figure 71, depicts results of example experiments demonstrating that ShHlO-GFAP-mediated gene transfer of b-catenin is highly efficient to stimulate MG proliferation in adult mouse retina. Figure 7A and

Figure 7B depict ShHlO-GFAP-GFP infection itself did not lead to detection of EdU ⁺ cells in the whole retina. Figure 7C and Figure 7D depict many MGs re-entered the cell cycle two weeks after ShHlO-GFAP-mediated gene transfer of b-catenin and GFP (co-infection marker). Figure 7E depicts the number of EdU ⁺ cells/mm ² in each of the four retinal quadrants (Dorasal, Ventral, Nasal, and Temporal) was quantified at 700pm, l400pm, and 2l00pm from the center of the retina. Data are presented as mean±sem. n=2l. Figure 7F depicts quantification of the number of EdU ⁺ cells/mm ² at different distances from the center of the retina. Data are presented as mean±sem, n=2l. *p<0.05, ***p<0.00l, Student’s t test. Scale bar: 1 mm. Figure 7G through Figure 71 depict EdU incorporation analysis performed on retinas that were dissociated two weeks after ShHlO-GFAP-mediated gene transfer of b-catenin and GFP (co-infection marker). Arrowheads: GFP ⁺ cells that were also EdU ⁺ . Scale bar:

20 pm.

Figure 8, comprising Figure 8A through Figure 8N, depicts results of example experiments demonstrating that GSK3B deletion stabilizes b-catenin and activates Wnt signaling in MGs. Adult GSK3B ^loxp/loxp mouse retinas were infected by ShHlO- GFAP-tdTomato (infection marker) in the absence (Figure 8A- Figure 8F) or presence (Figure 8G - Figure 8L) of ShHlO-GFAP-Cre co-infection. Retinal tissues were analyzed two weeks after viral infection by b-catenin immunohistochemistry. The boxed area in Figure 8B is enlarged in Figure 8D -Figure 8F, and the boxed area in Figure 8H is enlarged in Figure 8J - Figure 8L. Arrows in Figure 8K show stabilized b-catenin in transduced MGs labeled by tdTomato (Figure 8J). Figure 8M and Figure 8N depict that GSK3 deletion activates Wnt reporter gene. ShHlO-Wnt- GFP reporter was injected intravitreally into adult GSK2^ ^loxp/loxp mice in the absence (Figure 8M) or presence (Figure 8N) of ShHlO-GFAP-Cre co-infection. Scale bars:

20 pm.

Figure 9, comprising Figure 9A through Figure 9L, depicts results of example experiments demonstrating that GSK3 deletion stimulates MG proliferation without retinal injury. ShHlO-GFAP-Cre was injected intravitreally in adult GSK2^ ^loxp/loxp mice. EdU was injected 10 days after viral infection. Retinal tissues were collected 4 days later for co-detection of EdU and immunohistochemistry for MG-specific antigens. Figure 9A through Figure 9F depict co-detection of EdU and anti- CyclinD3 immunoreactivity in the absence (Figure 9A- Figure 9C) or presence (Figure 9D - Figure 9F) of ShHlO-GFAP-Cre infection. Figure9G through Figure 9L depict co detection of EdU and anti-p27 ^kipl immunoreactivity in the absence (Figure 9G - Figure 91) or presence (Figure 9J - Figure 9L) of ShHlO-GFAP-Cre infection. The boxed areas in Figure 9F and Figure 9L are enlarged to show co-labeling of EdU and MG-specific antigens. Arrows: EdU ⁺ cells were also positive for anti-CyclinD3 (Figure 9F) or anti- p27 ^kipl (Figure 9L) immunoreactivity. Scale bars: 50 pm.

Figure 10, comprising Figure 10A through Figure 10M, depicts results of example experiments demonstrating that ShHlO-GFAP-mediated gene transfer of b- catenin induces Lin28a and Lin28b expression in MGs. Figure 10A depicts gene transfer of b-catenin, or GFP as a control, resulted in an increase in the RNA levels for Lin28a and Lin28b measured by quantitative PCR. Data are presented as mean±sem, n=5. ***p<0.00l, Student’s t test. Figure 10B through Figure 10M depict

immunohistochemistry to detect Lin28a (Figure 10B - Figure 10G) or Lin28b (Figure 10H - Figure 10M) at two weeks after ShHlO-GFAP^-catenin infection. Scale bars:

20 pm.

Figure 11, comprising Figure HAthrough Figure 11X, depicts results of example experiments demonstrating that Wnt^-catenin transactivates Lin28a and Lin28b through direct binding to their promoters in HEK293T cells. Figure 11 A through Figure 11F depict Lin28a-GFP promoter reporter analysis in HEK293T cells transfected with pCAG-tdTomato (transfection marker), in the absence (Figure 11 A - Figure 11C) or presence (Figure 11D - Figure 11F) of pCAG-Flag-B- catenin co- transfection. Figure 11G through Figure 111 depict mutation of the b-catenin binding sites in the Lin28a promoter abolished the reporter activity. Figure 11J through Figure 110 depict Lin28b- GFP reporter analysis in HEK293T cells transfected with pCAG- tdTomato (transfection marker), in the absence (Figure 11 J - Figure 11L) or presence (Figure 11M - Figure 110) of pCAG-Flag^-catenin co-transfection. Figure 11P through Figure 11R depict mutation of the b-catenin binding sites in the Lin28b promoter abolished the reporter activity. Figure 11S and Figure 11T depict schematic illustrations of the putative B- catenin binding sites in the Lin28a (Figure 11S) and Lin28b (Figure 11T) promoter, which were mutated to generate Lin28amut-GFP and Lin28bmut-GFP in the promoter reporter analysis. Figure 11U and Figure 11V depict the results of ChIP analysis, which reveals direct binding of b-catenin to the Lin28a (Figure 11U) or the Lin28b (Figure 11V) promoter. Chromatin, immunoprecipitated with an antibody specific to Flag, was assayed by PCR with primers flanking the putative b-catenin binding sites 1 and 2. Figure 11W and Figure 11X depict quantification of the promoter reporter activity, represented by normalized GFP intensity, for Lin28a (Figure 11W) and Lin28b (Figure 11X). Scale bars: 20 pm. Data are presented as mean±sem, n=4. ***p<0.00l, One-way ANOVA.

Figure 12, comprising Figure 12A through Figure 12T, depicts results of example experiments demonstrating that Wnt^-catenin transactivates Lin28a and Lin28b in MGs in adult mouse retina. Figure 12A through Figure 12F depict Lin28a- GFP reporter analysis in retinas infected with ShHlO-GFAP-tdTomato (infection marker), in the absence (Figure 12A- Figure 12C) or presence (Figure 12D - Figure 12F) of ShHlO- GFAP^-catenin co-infection. Figure 12G through Figure 121 depict mutation of the B- catenin binding sites in the Lin28a promoter abolished the reporter activity. Figure 12J through Figure 120 depict Lin28b-GFP reporter analysis in retinas infected with ShHlO-GFAP-tdTomato (infection marker), in the absence (Figure 12J - Figure 12L) or presence (Figure 12M - Figure 120) of ShHlO-GFAP-b- catenin co-infection. Figure 12P through Figure 12R depict mutation of the b-catenin binding sites on the Lin28b promoter abolished the reporter activity. Scale bars: 20 pm. Figure 12S and Figure 12T depict ChIP analysis which reveals direct binding of b-catenin to the Lin28a (Figure 12S) or the Lin28b (Figure 12T) promoter. Adult mouse retinas were infected with ShHlO-Lin28- GFP or Lin28mut-GFP, in the presence or absence of ShH 1 O-GFAP^-catenin co- infection. Chromatin, immunoprecipitated with an antibody specific to b-catenin, was assayed by PCR with primers flanking the putative b-catenin binding sites 1 and 2.

Figure 13, comprising Figure 13A through Figure 131, depicts results of example experiments demonstrating that Lin28 plays an essential role in MG proliferation in adult mouse retina. Figurel3A through Figure 13C depict Lin28 is sufficient to stimulate MG proliferation without retinal injury. ShHlO-GFAP-mediated gene transfer of Lin28a (Figure 13 A) or Lin28b (Figure 13B) led to proliferative response of MGs, analyzed by EdU incorporation and quantified (Figure 13C) in comparison to b-catenin gene transfer and OdK3b deletion. Figure 13D through

Figure 13F depict eo-deletion of Lin28a and Lin28b abolishes b-catenin -induced MG proliferation, Lin28a ^loxp/loxp ; Lin28b ^loxp/loxp double floxed mice were infected with ShHlO-GFAP-B- catenin, in the absence (Figure 13D) or presence (Figure 13E) of ShHlO-GFAP-Cre co- infection. MG proliferation was analyzed and quantified (Figure 13F) by EdU incorporation. Figure 13G through Figure 131 depict co-deletion of Lin28a and Lin28b largely suppresses NMDA-induced MG proliferation.

Lin28a ^loxp/loxp ; Lin28b ^loxp/loxp double floxed mice were infected with ShHlO-GFAP- GFP (Figure 13G) or ShHlO- GFAP-Cre (Figure 13H) two weeks before NMDA damage. MG proliferation was analyzed and quantified (Figure 131) by EdU incorporation. Scale bars: 50 pm. Data are presented as mean±sem, n=4. ***p<0.00l, Student’s t test.

Figure 14, comprising Figure 14A through Figure 14E, depicts results of example experiments demonstrating that Wnt^-catenin acts through let-7 miRNAs to regulate MG proliferation. Figure 14A depicts ShHlO-GFAP-mediated gene transfer of b-catenin downregulates let-7a, let-7b, and let-7f miRNA levels in the adult mouse retina. Data are presented as mean±sem, n=3. ***p<0.00l, Student’s t test. Figure 14B depicts co-deletion of Lin28a and Lin28b largely neutralizes b-catenin-induced suppression of let-7a, let-7b, and let-7f miRNAs. Data are presented as mean±sem, n=3. ***p<0.00l, One-way ANOVA analysis. Figure 14C through Figure 14E depict co-expression of let- 7b miRNA abolishes b-catenin-mediated effects on MG proliferation, analyzed and quantified (Figure 14E) by EdU incorporation. Scale bar: 25 pm. Data are presented as mean±sem, n=4. ***p<0.00l, Student’s t test. Figure 15, comprising Figure 15 A through Figure 15L, depicts results of example experiments demonstrating that Wnt/Lin28 signaling regulates let-7 miRNAs specifically in MGs. Adult mouse retinas were infected with ShHlO-GFAP-GFP-let-7 miRNA sensor, ShHlO-GFAP-tdTomato (infection marker), and in the absence (Figure 15A - Figure 15C) or presence of ShHlO-GFAP-Lin28a (Figure 15D - Figure 15F), ShHlO-GFAP-Lin28b (Figure 15G - Figurel5I), or ShHlO-GFAP- -catenin (Figure 15J - Figure 15L) co-infection, and analyzed two weeks later by confocal microscopy. Scale bar: 20 pm.

Figure 16 depicts a time course analysis of cell cycle reactivated MGs. Adult mouse retinas infected with ShHlO-GFAP- -catenin, Lin28a, or Lin28b were treated with EdU 10 days after viral infection. Treated retinas were collected at 4, 7, 10 days after EdU injection for analysis in retinal flatmount preparations. Data are presented as mean±sem, n=3.

Figure 17, comprising Figure l7Athrough Figure 17J, wherein each of Figure 17A through Figure 171 comprises four panels demarked as X, X’, X” and X’” with X representing the letters A through I respectively, depicts results of example experiments demonstrating that a subset of cell cycle reactivated MGs express markers for amacrine cells. Adult mouse retinas were treated with EdU at 10 days after infection with ShH 1 O-GFAP-P-catenin. Lin28a, or Lin28b. Treated retinas were dissociated 4 days after EdU treatment and analyzed for EdU incorporation and immunohistochemistry for amacrine cell markers: Pax6, Syntaxinl, and NeuN. Figure 17A through Figure 17C depict co-detection of EdU and the expression of amacrine cell markers in ShH 1 O-GFAP-P-catenin infected retinas. Figure 17D through Figure 17F depict co-detection of EdU and the expression of amacrine cell markers in ShHlO-GFAP-Lin28a infected retinas. Figure 17G through Figure 171 depict co detection of EdU and the expression of amacrine cell markers in ShHlO-GFAP- Lin28b infected retinas. Arrows: EdU positive but marker negative cells. Arrow heads: cells double positive for EdU and marker. Scale bars: 40 pm. Figure 17J depicts an analysis of the percentage of EdU ⁺ cells that were also Pax6 ⁺ , Syntaxinl ⁺ or NeuN ⁺ . Data are presented as mean±sem, n=4.

Figure 18, comprising Figure 18A through Figure 18R, depicts results of example experiments demonstrating that Wnt-activated MGs express amacrine cell markers. Adult mouse retinas infected with ShHlO- GFAP- -catenin (Figure 18A- Figure 18F), ShHlO-GFAP-Lin28a (Figure 18G - Figure 18L), or ShHlO-GFAP- Lin28b (Figure 18M - Figure 18R) were treated with EdU 10 days after viral infection. Treated retinas were collected 4 days after EdU injection for

immunohistochemistry and confocal microscopy analysis. Confocal images of the amacrine cell layer showing that a subset of EdU ⁺ MGs express amacrine cell markers: Pax6 and NeuN. Arrowheads show that EdU ⁺ cells were also Pax6 ⁺ or NeuN ⁺ . Arrows show that EdU ⁺ cells were NeuN-. Scale bar: 20 pm.

Figure 19 depicts a schematic illustration of Miiller glial cell (MG) reprogramming in adult mouse retina. Step 1 : MGs are reprogrammed to become retinal progenitor/stem cells, evidenced by cell cycle re-entry. Step 2: Differentiation of cycling MGs is guided to generate rod photoreceptors using a combination of transcription factors that are essential for photoreceptor cell fate determination during early retinal development.

Figure 20 depicts results of example experiments demonstrating that BrdU labeled MG-derived cells are embedded in the rhodopsin expressing old rods. Left panel, BrdU detection. Middle panel, Rhodopsin immunostaining. Right panel, overlay. Images cited from Ooto S. et al. Proc Natl Acad Sci U S A. 2004, 101: 13654- 13659.

Figure 21, comprising Figure 21 A through Figure 21B, depicts analysis of the rhodopsin-tdTomato reporter by electroporation in neonatal mouse retina. Retinal sections were analyzed at postnatal day 21. Figure 21 A depicts GFP expression driven by a CAG promoter. Figure 21B depicts tdTomato expression driven by a rhodopsin promoter.

Figure 22 depicts a schematic illustration of the two-step rod induction protocol.

Figure 23, comprising Figure 23 A through Figure 231, depicts differentiation stages of MG-derived rod photoreceptors. Figure 23 A through Figure 23C depict the initial stage. Figure 23D through Figure 23F depict the intermediate stage. Figure 23G through Figure 231 depict the terminal stage. Arrow heads: cell soma. Arrows: rod photoreceptor outer segment. Scale bar: 25 pm. Figure 24, comprising Figure 24A and Figure 24B, depicts results of example experiments demonstrating that ShHlO-rhodopsin-tdTomato does not transduce photoreceptors even through the subretinal injection route. Figure 24A depicts co injected AAV2/5-CAG-GFP. Figure 24B depicts ShHlO-rhodopsin-tdTomato.

Figure 25, comprising Figure 25A and Figure 25B, depicts a rate mapping study to trace MG-derived rod photoreceptors. Figure 25A depicts untreated MG fate mapping mice with MGs labeled by tdTomato. Figure 25B depicts MG fate mapping mice treated with the two-step rod induction protocol. Arrow heads: rod soma.

Arrows: rod outer segments. Scale bar: 20 pm.

Figure 26, comprising Figure 26A through Figure 26D, depicts results of example experiments demonstrating that MG-derived rods morphologically resemble native rods, and develop rod specializations for synaptic transmission. Figure 26A depicts regenerated rods labeled by ShHlO-rhodopsin-tdTomato. CtBP

immunoreactivity in green. The boxed area in Figure 26A is amplified in Figure 26B through Figure 26D. Arrow: CtBP expression in the rod synapse. Scale bar in Figure 26A: 25 pm. Scale bar in Figure 26D: 5 pm.

Figure 27, comprising Figure 27A through Figure 27F, depicts results of example experiments demonstrating light-driven translocation of Gnatl (rod a- transducin) in the reconstituted Gnatl : Gnat2 ^cpf13 mice. Figure 27A through Figure 27C depict the localization of Gnatl in the dark. Figure 27D through Figure 27F depict the localization of Gnatl after light stimulation. Green, Gnatl

immunoreactivity. Red, co- expressed ShHlO-rhodopsin-tdTomato. Scale bar: 25 pm.

Figure 28. Generation of rod photoreceptors via reprogramming Muller glial cells (MGs) in the mouse retina a, A schematic illustration of the two-step reprogramming method to generate rod photoreceptors b-j, Characterization of MG- derived rod differentiation through the Initial (b-d), Intermediate (e-g), and Terminal (h-j) stages. Arrowheads: cell soma. Arrows: rod outer segments. Double arrows: synaptic terminals. Scale bar: 25 pm. k-m, Quantification of MG-derived rod differentiation at 1 (k), 2 (1), and 4 weeks (m) after the second injection of ShHlO- GFAP-mediated gene transfer of Otx2, Crx, and Nrl for rod induction n and o,

Lineage analysis of MG-derived rod photoreceptors (n) Untreated MG fate mapping mice with MGs labeled by tdTomato. (o) Treated MG fate mapping mice using the two-step reprogramming method. Arrowheads: rod soma. Arrows: rod outer segments. Scale bar: 20 pm. p-t, Quantification of MG-derived rod photoreceptors in the Doral (p), Nasal (q), Temporal (r), Ventral (s) quadrants of retinal flat-mount preparations at 4 weeks after the second injection for rod induction. Scale bar: 20 pm. Data in (t) show mean ± SEM, n = 4 retinas. Control measurements were combined across quadrants.

Figure 29. MG-derived rod photoreceptors express essential rod genes and are morphologically similar to native rod photoreceptors a-t, MG-derived rods correctly expressed a set of essential rod genes, including Rhodopsin (a-d), Peripherin-2 (e-h), Gnatl (i-l), Recoverin (m-p), and Ribeye (q-t). Arrowheads indicate detection of immunoreactivity in MG-derived rods u-x, MG-derived rods had an enlarged bouton- like synaptic terminal in close apposition to the PKCof rod bipolar cells. Arrowheads indicate rod bipolar dendrites in close proximity to the MG-derived rod terminal.

Scale bars: 20 pm (a, e, i, m, q, u); 10 pm (b-d, f-h, j-l, n-p); 5 pm (r-t, v-x). y-z'", Ultrastructural analysis of MG-derived rods using transmission electron microscopy indicates correct formation of the rod outer segments containing densely packed membrane discs (y), rod inner segments containing long thin mitochondria (z), connecting cilium with microtubule doublets (arrow heads) arranged in a circle (z', z"), and classic triad synapse with horizontal axon terminals (letter H in green) and bipolar dendritic terminal (letter B in brown) (z'"). +, immunogold-labeled MG- derived rods. -, native rods m, mitochondrion. Scale bar: 200 nm.

Figure 30. MG-derived regeneration of rod photoreceptors in adult Gnatl :Gnat2 ^cpf13 mice a-f, Gnatl, detected by immunohistochemistry in Rhodopsin- tdTomato ⁺ MG-derived rods (b, e), translocated from the rod outer segments in the dark-adapted retina (a-c) to the rod inner segments, rod soma, and synaptic terminals (d-f) upon light stimulation. Experiments were performed 4 weeks after the second injection for rod induction in adult Gnatl :Gnat2 ^cpf13 mice g-k, Effective generation of MG-derived rod photoreceptors in adult Gnatl ^/ :Gnat2 ^cpf13 mice, analyzed by scoring the number of Rhodopsin-tdTomato ⁺ MG-derived rods per mm ² (k) in the Dorsal (g), Nasal (h), Temporal (i), and Ventral (j) quadrants in retinal flat- mount preparations. Scale bar: 20 pm. Data in (k) are presented as mean ± SEM, n = 4 retinas. Figure 31. MG-derived rod photoreceptors integrate into the retinal circuitry and restore visual function in adult Gnatl ^/ :Gnat2 ^cpf13 mice. a. Evidence of calcium current in MG-derived rods. Figure shows averaged whole-cell current of 11 recordings from 6 MG-derived rods (3 retinas) subjected to a voltage ramp from -80 mV to +40 mV over 120 ms. b-d RGC spike responses to a green light stimulus (1.0- mm diameter) presented on a dark background. Intensity was either 1.3 (control cell) or -1.4 (treated cells) loglO nW mm ² . Spike rate in a response window (green, horizontal line) was measured relative to two baseline windows (gray, horizontal lines). RGCs from treated retinas showed either an ON response (c) or an OFF response (d). e, Average spike rate to a range of green light stimuli (-1.7 to -0.7 loglO nW mm ² ) for 17 control cells (n = 7 retinas, 4 animals) and 26 treated cells (n = 10 retinas, 6 animals). Treated cells showed significantly higher firing rates (* **, p < 0.001, t-test). RGCs with responses to the right of the dashed line were categorized as responding cells (n = 15). f, Average response (+SEM across cells) of control cells to a range of light intensities (n = 11/17 cells tested at a dim/bright range) g, Average response (+SEM across cells) of responding RGCs from treated retinas to a range of light intensities (n = 14/9 cells tested at a dim/bright range). Lines show fitted sigmoidal equations that share amplitude (A, 33.8 spikes s ¹ ) and exponent (q, 0.705) parameters but have unique semi-saturation constants (ofor green, -2.34 loglO nW mm ² ; ofor UV, -1.80 loglO nW mm ² ). Cells were ~3.4 times more sensitive to green than UV light, consistent with rod- mediated responses (Lyubarsky et ah, 1999; Ke et al, 2014). h, Post-stimulus time histogram (PSTH) showing ON-center RGC spike rate during a light flash in retinas from treated and wild-type (C57/B6; wt) animals. Firing rates are averaged across cells at either high (-1.7 to -0.7 loglO nW mm ² ) or low intensities (-3.8 to -3.4 loglO nW mm ² ). Shaded regions show +SEM across cells as a function of time i, Intensity-response curves for ON RGCs show spike rates (mean±SEM across cells) in treated and wt animals. Over a range of intensities, responses were significantly greater in wt animals (* *, p < 0.002). j, Same format as (h) for OFF-center RGCs. k, Same format as (i) for OFF-center RGCs (*, p < 0.05). 1, Example visually-evoked potentials (VEPs) to a light flash (~3.2 loglO nW mm ² 50 ms) in the primary visual cortex in Gnatl ^/ :Gnat2 ^cpf13 mice in the treatment group (treated), sham group (control) and wt group. For each group, responses from multiple trials in a single animal are superimposed. Responses were absent in the control animal and delayed in the treated animal relative to the wt animal m, Response amplitude (minimum value of VEP) for n = 2-3 animals in each of three groups. Each point represents a single trial, and each box plot shows median ± interquartile range; error bars indicate full range (minus outliers). All treated and wt animals showed significant responses (i.e., median response significantly different from zero; ***, p < 0.001, Wilcoxin signed-rank test), whereas control mice did not.

Figure 32. MGs may undergo only one cell division after b- catenin gene transfer a, A schematic illustration of EdU/BrdU double-labeling experiment. Wild- type retinas were injected with ShHlO-GFAP- -catenin (0 day), followed by an injection of EdU (10 days). BrdU was either co-injected with EdU (0 hour) or 24 hours later after EdU injection (24 hours). Retinas were harvested 14 days after b- catenin gene transfer b-g, Detection of EdU and BrdU labeled MGs. Scale bar: 20 pm. h, Statistical analysis of the percentage of MGs labeled by EdU (EdU ⁺ BrdU , green), BrdU (red), or both (EdU ⁺ BrdU ⁺ , yellow). Data are presented as mean ± SEM, n = 4 retinas.

Figure 33. MG-derived rod differentiation was observed across the whole retinal section. Wild-type retinas at 4 weeks of age were first injected with ShHlO- GFAP-GFP (label transduced MGs), and ShHlO-Rod-tdTomato (label MG-derived rods) in the absence (a-f) or presence (g-l) of ShHlO-GFAP^-catenin (stimulate MG proliferation), followed 2 weeks later by the second injection of ShHlO-GFAP- mediated gene transfer of Otx2, Crx and Nrl for rod induction. Retinal samples were analyzed by confocal microscopy at 10 days after the second injection. The boxed areas in c and i are enlarged in d-f and j-l, respectively. Arrowheads: MG-derived rods. Scale bars: 750 pm in a-c and g-i; 25 pm in d-f and j- 1.

Figure 34. Additional examples showing the progression of MG- derived rod differentiation. Wild-type retinas at 4 weeks of age were first injected with ShHlO- GFAP^-catenin, ShHlO-GFAP-GFP, and ShHlO-Rodopsin-tdTomato, followed 2 weeks later by the second injection of ShHlO-GFAP-mediated gene transfer of Otx2, Crx and Nrl for rod induction. MG-derived rod differentiation progressed through the initial (a-c), intermediate (d-f, g-i, j-l) and terminal (m-o, p-r) stages. Scale bar: 25 pm. Figure 35. ShHlO-rhodopsin-mediated gene transfer does not transduce photoreceptors even through the subretinal injection route. AAV2/5-CAG- GFP and ShHlO-Rhodopsion-tdTomato were co-injected into the subretinal space of the wild- type mouse retina at 4-weeks of age, and the expression of GFP and tdTomato was analyzed 4 weeks later by confocal microscopy in retinal sections a, Detection of AAV2/5-CAG-GFP. b, Detection of ShHlO-rhodopsin-tdTomato. Scale bar: 20 pm.

Figure 36. MG-derived rods eventually turned off the expression of GFAP- GFP over time. Wild-type retinas at 4 weeks of age were first injected with ShHlO- GFAP- -catenin, ShHlO-GFAP-GFP, and ShHlO-Rhodopsin-tdTomato, followed 2 weeks later by the second injection of ShHlO-GFAP-mediated gene transfer of Otx2, Crx and Nrl for rod induction a-c, Retinas were collected 12 weeks after the second injection and analyzed for the expression of GFAP-GFP in MG- derived rods labeled by Rhodopsin-tdTomato. Scale bar: 25 pm. d, Statistical analysis of the percentage of Rhodopsin-tdTomato ⁺ cells expressing GFAP-GFP. Data are presented as mean ± SEM, n = 7 retinas.

Figure 37. Treatment with Otx2, Crx, and Nrl individually or in pairs is not sufficient for rod induction. Wild-type retinas were injected with ShHlO-GFAP-b- catenin (MG proliferation), ShHlO-GFAP-GFP (label transduced MGs), and ShHlO- Rhodopsin-tdTomato (label MG-derived rods) at 4 weeks of age, followed 2 weeks later by the second injection of ShHlO-GFAP-mediated gene transfer of transcription factors for rod induction. Samples were analyzed by confocal microscopy in retinal sections at 4 weeks after the second injection a-c, Otx2 treatment d-f, Crx treatment g-i, Nrl treatment j-l, Otx2+Crx treatment m-o, Otx2+Nrl treatment p-r, Crx+Nrl treatment. Scale bar: 20 pm.

Figure 38. Time course analysis of MG-derived rod differentiation in wild- type retinas treated with Crx and Nrl. Wild-type retinas at 4 weeks of age were first injected with ShHlO-GFAP- -catenin, ShHlO-GFAP-GFP, and ShHlO-Rhodopsin- tdTomato, followed 2 weeks later by the second injection of ShHlO-GFAP-mediated gene transfer of Crx and Nrl. Rhodopsin-tdTomato ⁺ cells were only detected in the initial stage of rod differentiation at 1, 2 and 4 weeks after the second injection. Data are presented as mean ± SEM, n = 3 retinas at each time point. Figure 39. Fate mapping experiments indicate that the two-step

reprogramming method may occasionally produce cells with a horizontal cell morphology. The boxed area is enlarged to show an MG-derived tdTomato ⁺ cell with a horizontal cell morphology located in the upper inner nuclear layer. Arrowhead: cell soma. Arrows: cell processes. Scale bar: 5 pm.

Figure 40. MG-derived regeneration of rod photoreceptors decreases in aged mice a-d, Generation of Rhodopsin-tdTomato ⁺ MG-derived rod photoreceptors in 7- month-old mouse retinas in the Dorsal (a), Nasal (b), Temporal (c), and Ventral (d) quadrants in retinal flat-mount preparations. Scale bar: 20 pm. e, Quantification of Rhodopsin-tdTomato ⁺ MG-derived rods per mm ² in the four retinal quadrants. Data are presented as mean ± SEM, n = 4 retinas.

Figure 41. MG-derived rod photoreceptors express Rhodopsin and Peripherin- 2. Wild-type retinas were injected with ShHlO-GFAP- -catenin (MG proliferation) and ShHlO-Rhodopsin-tdTomato (label MG-derived rods) at 4 weeks of age, followed 2 weeks later by the second injection of ShHlO-GFAP-mediated gene transfer of

Otx2, Crx and Nrl for rod induction. Treated retinas were dissociated 4 weeks later after the second injection and analyzed for the expression of Rhodopsin (a-c) and Peripherin-2 (d-f) using immunohistochemistry and confocal microscopy.

Arrowheads: MG-derived rods were immunoreactive for Rhodopsin (c) and

Peripherin-2 (f). Scale bar: 20 pm.

Figure 42. Table of viral constructs, packaged viruses, and the virus titers after purification and concentration.

Figure 43. Stimulation of MG proliferation after AAV-ShHlO-GFAP-mediated gene transfer of Ascl 1 in the adult mouse retina. Miiller glia are labeled with tdTomato, Proliferative Miiller glia are labeled by EdU incorporation assay.

DETAILED DESCRIPTION

The disclosure is based, in part, on the finding that rod cells can be produced in vivo by carrying out a two-step method: first, an agent (e.g, a composition comprising a nucleic acid encoding beta-catenin, Lin28a, Lin28b, Notch, or Ascll) that proliferates MG cells is administered to the retina; second, after a period of time to allow proliferation of the MG cells, an agent that differentiates (e.g, into rod cells) the MG cells (e.g, a composition comprising a first nucleic acid encoding Otx2, a second nucleic acid encoding Crx, and a third nucleic acid encoding Nrl) is administered to the retina. To minimize potentially harmful off-target effects, the nucleic acids can be operably linked to a promoter that specifically expresses the nucleic acid in MG cells (e.g., expresses the nucleic acid in MG cells at least 5-fold, at least lO-fold, at least l5-fold, at least 20-fold, at least 25-fold, at least 50-fold, or more than 50-fold more than in non-retinal cells). To further minimize potentially harmful off-target effects, the nucleic acids operably linked to promoters for expression specifically in MG cells can expressed by one or more vectors (e.g., virus or virus-like particle vectors) that specifically target MG cells (e.g., expresses the vector in MG cells at least 5 -fold, at least lO-fold, at least 15 -fold, at least 20-fold, at least 25-fold, at least 50-fold, or more than 50-fold more than in non-retinal cells).

Thus, the present invention relates generally to compositions and methods of inducing proliferation of MG cells and compositions and methods for inducing differentiation of MG cells to photoreceptor cells or rods. In one embodiment, the method comprises a first step of stimulating MG proliferation and a second step of guiding rod differentiation in the proliferating MG cells. In a specific embodiment, the first step comprises administering to a subject a therapeutically effective amount of a MG cell proliferation agent and the second step comprises, a period of time after the first step, administering to the subject a therapeutically effective amount of a MG cell differentiation agent. In certain embodiments, this two-step method treats vision loss or impairment in a subject. In certain embodiments, this two-step method treats AMD, diabetic retinopathy, retrolental fibroplasia, Stargardt disease, RP, uveitis, Bardet-Biedl syndrome, or eye cancer. In certain embodiments, this two-step method generates new rodphotoreceptors in a retina.

In various embodiments, the method for increasing MG proliferation has the associated effect of increasing expression of amacrine cell markers in MG cells. Amacrine cell markers include, but are not limited to, Pax6, Syntaxinl, and NeuN. Therefore, in one embodiment, the invention relates to methods and compositions for inducing expression of one or more amacrine cell-specific proteins in MG cells.

In one embodiment, stimulation of MG proliferation is accomplished through treatment of MG cells with a WNT signaling effector. In one embodiment, the WNT signaling effector serves to increase b-catenin signaling. In one embodiment, the invention relates to compositions and methods for activating or increasing the level of B- catenin in MG cells. Accordingly, the invention provides activators (e.g., agonists) of b-catenin to increase the expression, activity, or both of b-catenin. In one embodiment, the activator of b-catenin includes but is not limited to a small molecule, a chemical compound, a protein, a peptide, a peptidomemetic, a nucleic acid, and the like. In an embodiment of the present invention, the composition increases the transcription of B- catenin or translation of b-catenin mRNA. In one embodiment of the present invention, the composition increases b-catenin activity.

In one embodiment, the present invention comprises a method for stimulating MG proliferation by increasing one or more of the level, production, and activity of b- catenin comprising administering to a subject an effective amount of a composition comprising an activator of b-catenin.

In one embodiment, the invention relates to compositions and methods for activating or increasing the expression, activity, or both of a downstream b-catenin signaling target. In one embodiment, a downstream b-catenin signaling target is one of Lin28a and Lin28b. Therefore, in one embodiment, the invention relates to methods and compositions for increasing the level of one or more of Lin28a and Lin28b in MG cells. Accordingly, the invention provides activators (e.g., agonists) of one or more of Lin28a and Lin28b. In one embodiment, the activator of one or more of Lin28a and Lin28b includes but is not limited to a small molecule, a chemical compound, a protein, a peptide, a peptidomemetic, a nucleic acid, and the like. In an embodiment of the present invention, the composition increases the transcription of one or more of Lin28a and Lin28b or translation of one or more of Lin28a and Lin28b mRNA. In another embodiment of the present invention, the composition increases one or more of Lin28a and Lin28b activity.

In one embodiment, the present invention comprises a method for stimulating MG proliferation by increasing one or more of the level, production, and activity of one or more of Lin28a and Lin28b comprising administering to a subject an effective amount of a composition comprising an activator of one or more of Lin28a and Lin28b.

In one embodiment, stimulation of MG proliferation is accomplished through inhibiting negative regulators of b-catenin or downstream b-catenin signaling targets. In one embodiment, a negative regulator of b-catenin is GSK3p. Therefore, in one embodiment the invention relates to methods and compositions for inhibiting GSK3 in MG cells. Accordingly, the invention provides inhibitors (e.g., antagonists) of GSK3 . In one embodiment, the inhibitor of GSK3 includes but is not limited to an antibody or a fragment thereof, a peptide, a nucleic acid, small molecule, a chemical compound, and the like. In an embodiment of the present invention, the composition decreases the transcription of GSK3 or translation of GSK3 mRNA. In another embodiment of the present invention, the composition inhibits GSK3 activity.

In one embodiment, the present invention comprises a method for stimulating MG proliferation by decreasing one or more of the level, production, and activity of GSK3 comprising administering to a subject an effective amount of a composition comprising an inhibitor of GSK3 .

In one embodiment, stimulating MG proliferation is accomplished through inhibiting one or more let-7 miRNA. In one embodiment, the inhibitor of one or more let- 7 miRNA includes but is not limited to an antibody or a fragment thereof, a peptide, a nucleic acid, small molecule, a chemical compound, and the like. In an embodiment of the present invention, the composition decreases the transcription or processing of one or more let-7 miRNA. In another embodiment of the present invention, the composition inhibits one or more let-7 miRNA activity. In one embodiment, the let-7 miRNA is one of let-7a, let-7b, and let-7f miRNA.

In one embodiment, the present invention comprises a method for stimulating MG proliferation by decreasing one or more of the level, production, and activity of one or more let-7 miRNA comprising administering to a subject an effective amount of a composition comprising an inhibitor of one or more let-7 miRNA.

In one embodiment, the present invention relates to compositions and methods for guiding differentiation of MG cells to photoreceptor cells. In one embodiment, a method of guiding MG differentiation comprises activating expression of cell-specific photoreceptor genes in MG cells. Accordingly, the invention provides activators (e.g., agonists) of one or more cell-specific photoreceptor genes. In one embodiment, the activator of one or more cell-specific photoreceptor genes includes but is not limited to a small molecule, a chemical compound, a protein, a peptide, a peptidomemetic, a nucleic acid, and the like. In an embodiment of the present invention, the composition increases the transcription of one or more cell-specific photoreceptor genes or translation of one or more cell-specific photoreceptor genes. In another embodiment of the present invention, the composition increases one or more cell-specific photoreceptor protein activity. Exemplary photoreceptor genes include, but are not limited to rhodopsin, rod a-transducin, rod arrestin, phosducin, ROM1, retinal cGMP, Guanylate Cyclase- Activating Protein Photoreceptor 2, Tubby Like Protein 1, Retinoschisin 1, G alpha 1, G gamma 1, cGMP PDE gamma, G beta 1, mUNCH9, rod PDE beta, Pleckstrin Homology Domain Retinal Protein 1, Peripherin 2, recoverin, ribeye, bassoon, and CtBP.

In one embodiment, the activator of one or more cell-specific photoreceptor genes is a transcription factor. Transcription factors that activate one or more one or more cell-specific photoreceptor genes include, but are not limited to Otx2, Crx, Nrl, Nr2e3 and NeuroD. In one embodiment, a composition that increases the transcription of one or more cell-specific photoreceptor genes comprises one of Otx2, Crx, Nrl, Nr2e3 and NeuroD. In one embodiment, a composition that increases the transcription of one or more cell-specific photoreceptor genes comprises Otx2, Crx, and Nrl. In one embodiment, the composition comprises two or more of Otx2, Crx, Nrl, Nr2e3 and NeuroD. In one embodiment, the composition comprises Otx2, Crx, and Nrl.

In one embodiment, the present invention comprises a method for guiding MG differentiation by increasing one or more of the level, production, and activity of one or more cell-specific photoreceptor genes or proteins comprising administering to a subject an effective amount of a composition comprising an activator of one or more cell- specific photoreceptor genes or proteins.

In various embodiments, the invention relates to compositions comprising activators of MG proliferation. In various embodiments, the invention relates to compositions for guiding MG cell differentiation to photoreceptors. In one embodiment, one or more of the compositions of the invention further comprise a MG-specific promoter. In one embodiment, a MG-specific promoter is GFAR In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO: 8.

In one embodiment, the invention provides methods of treatment of vision loss or impairment through administration of the compositions of the invention to a subject. In one embodiment, the method of treatment comprises administering to a subject a first composition (e.g., comprising a MG cell proliferation agent) to stimulate MG proliferation and a second composition (e.g., comprising a MG cell differentiation agent) to guide photoreceptor stimulation. In one embodiment, the compositions of the invention are administered concurrently. In one embodiment, the compositions of the invention are administered less than one day, less than two days, less than three days, less than four days, less than five days, less than six days, less than one week, less than two weeks, less than three weeks, less than four weeks, less than one month, or less than two months apart. In one embodiment, the compositions of the invention are administered more than one day, more than two days, more than three days, more than four days, more than five days, more than six days, more than one week, more than two weeks, more than three weeks, more than four weeks, more than one month, or more than two months apart.

In one embodiment, a subject has a condition associated with vision loss or impairment due to photoreceptor loss. Conditions associated with photoreceptor loss include, but are not limited to, age-related macular degeneration (AMD), diabetic retinopathy, retrolental fibroplasia, Stargardt disease, retinitis pigmentosa (RP), uveitis, Bardet-Biedl syndrome and eye cancers.

Definitions

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described.

As used herein, each of the following terms has the meaning associated with it in this section.

The articles“a” and“an” are used herein to refer to one or to more than one (i.e.. to at least one) of the grammatical object of the article. By way of example,“an element” means one element or more than one element.

“About” as used herein when referring to a measurable value such as an amount, a temporal duration, and the like, is meant to encompass variations of ±20% or ±10%, more preferably ±5%, even more preferably ±1%, and still more preferably ±0.1% from the specified value, as such variations are appropriate to perform the disclosed methods.

The term“abnormal” when used in the context of organisms, tissues, cells or components thereof, refers to those organisms, tissues, cells or components thereof that differ in at least one observable or detectable characteristic (e.g., age, treatment, time of day, etc.) from those organisms, tissues, cells or components thereof that display the“normal” (expected) respective characteristic. Characteristics which are normal or expected for one cell or tissue type, might be abnormal for a different cell or tissue type.

The term“activate,” as used herein, means to induce or increase a level, activity or function. Preferably, the activity is induced or increased by 50% compared to a comparator value, more preferably by 75%, and even more preferably by 95%.

“Activate,” as used herein, also means to increase a molecule, a reaction, an interaction, a gene, an mRNA, and/or a protein’s expression, stability, function or activity by a measurable amount or to increase entirely. Activators are compounds that, e.g., bind to, partially or totally induce stimulation, increase, promote, induce activation, activate, sensitize, or up regulate a protein, a gene, and an mRNA stability, expression, function and activity, e.g., agonists.

The term“antibody,” as used herein, refers to an immunoglobulin molecule which specifically binds with an antigen. Antibodies can be intact immunoglobulins derived from natural sources or from recombinant sources and can be immunoreactive portions of intact immunoglobulins. Antibodies are typically tetramers of

immunoglobulin molecules. The an antibody in the present invention may exist in a variety of forms where the antigen binding portion of the antibody is expressed as part of a contiguous polypeptide chain including, for example, a single domain antibody fragment (sdAb), a single chain antibody (scFv) and a humanized antibody (Harlow el al, 1999, In: Using Antibodies: A Laboratory Manual, Cold Spring Harbor

Laboratory Press, NY; Harlow et al, 1989, In: Antibodies: A Laboratory Manual,

Cold Spring Harbor, New York; Houston et al, 1988, Proc. Natl. Acad. Sci. USA 85:5879-5883; Bird et al, 1988, Science 242:423-426).

“Coding sequence” or“encoding nucleic acid” as used herein may refer to the nucleic acid (RNA or DNA molecule) that comprise a nucleotide sequence which encodes an antigen set forth herein. The coding sequence may further include initiation and termination signals operably linked to regulatory elements including a promoter and polyadenylation signal capable of directing expression in the cells of an individual or mammal to whom the nucleic acid is administered. The coding sequence may further include sequences that encode signal peptides.

A“disease” is a state of health of an animal wherein the animal cannot maintain homeostasis, and wherein if the disease is not ameliorated then the animal’s health continues to deteriorate.

In contrast, a“disorder” in an animal is a state of health in which the animal is able to maintain homeostasis, but in which the animal’s state of health is less favorable than it would be in the absence of the disorder. Left untreated, a disorder does not necessarily cause a further decrease in the animal’s state of health.

A disease or disorder is“alleviated” if the severity of at least one sign or symptom of the disease or disorder, the frequency with which such a sign or symptom is experienced by a patient, or both, is reduced.

“Encoding” refers to the inherent property of specific sequences of nucleotides in a polynucleotide, such as a gene, a cDNA, or an mRNA, to serve as templates for synthesis of other polymers and macromolecules in biological processes having either a defined sequence of nucleotides (i.e., rRNA, tRNA and mRNA) or a defined sequence of amino acids and the biological properties resulting therefrom. Thus, a gene encodes a protein if transcription and translation of mRNA corresponding to that gene produces the protein in a cell or other biological system. Both the coding strand, the nucleotide sequence of which is identical to the mRNA sequence and is usually provided in sequence listings, and the non-coding strand, used as the template for transcription of a gene or cDNA, can be referred to as encoding the protein or other product of that gene or cDNA.

As used herein, the terms“effective amount,”“pharmaceutically effective amount” and“therapeutically effective amount” refer to a nontoxic but sufficient amount of an agent to provide the desired biological result. That result can be reduction and/or alleviation of the frequency and/or severity of signs, symptoms, or causes of a disease, or any other desired alteration of a biological system. An appropriate therapeutic amount in any individual case may be determined by one of ordinary skill in the art using routine experimentation.

The term“expression” as used herein is defined as the transcription and/or translation of a particular nucleotide sequence driven by its promoter.

By“expression cassette” is meant a nucleic acid molecule comprising a coding sequence operably linked to promoter/regulatory sequences necessary for transcription and, optionally, translation of the coding sequence.

The term“expression vector” as used herein refers to a vector containing a nucleic acid sequence coding for at least part of a gene product capable of being transcribed. In some cases, RNA molecules are then translated into a protein, polypeptide, or peptide. In other cases, these sequences are not translated, for example, in the production of antisense molecules, siRNA, ribozymes, and the like. Expression vectors can contain a variety of control sequences, which refer to nucleic acid sequences necessary for the transcription and possibly translation of an operatively linked coding sequence in a particular host organism. In addition to control sequences that govern transcription and translation, vectors and expression vectors may contain nucleic acid sequences that serve other functions as well.

The terms“identical” or percent“identity” in the context of two or more nucleic acids or polypeptides, refer to two or more sequences or subsequences that are the same or have a specified percentage of nucleotides or amino acid residues that are the same, when compared and aligned (introducing gaps, if necessary) for maximum correspondence, not considering any conservative amino acid substitutions as part of the sequence identity. The percent identity may be measured using sequence comparison software or algorithms or by visual inspection. Various algorithms and software that may be used to obtain alignments of amino acid or nucleotide sequences are well-known in the art. These include, but are not limited to, BLAST, ALIGN, Megalign, BestFit, GCG Wisconsin Package, and variants thereof. In some embodiments, two nucleic acids or polypeptides of the disclosure are substantially identical, meaning they have at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, and in some embodiments at least 95%, 96%, 97%, 98%, 99% nucleotide or amino acid residue identity, when compared and aligned for maximum

correspondence, as measured using a sequence comparison algorithm or by visual inspection. In some embodiments, identity exists over a region of the sequences that is at least about 10, at least about 20, at least about 20-40, at least about 40-60 nucleotides or amino acid residues, at least about 60-80 nucleotides or amino acid residues in length or any integral value there between. In some embodiments, identity exists over a longer region than 60-80 nucleotides or amino acid residues, such as at least about 80-100 nucleotides or amino acid residues, and in some embodiments the sequences are substantially identical over the full length of the sequences being compared, for example, (i) the coding region of a nucleotide sequence or (ii) an amino acid sequence.

The term“inhibit,” as used herein, means to diminish, decrease, suppress or block an activity or function, for example, about ten percent relative to a control value. Preferably, the activity is suppressed or blocked by 50% compared to a control value, more preferably by 75%, and even more preferably by 95%.“Inhibit,” as used herein, also means to reduce a molecule, a reaction, an interaction, a gene, an mRNA, and/or a protein’s expression, stability, function or activity by a measurable amount or to prevent entirely. Inhibitors are compounds that, e.g., bind to, partially or totally block stimulation, decrease, prevent, delay activation, inactivate, desensitize, or down regulate a protein, a gene, and an mRNA stability, expression, function and activity, e.g., antagonists.

As used herein, an“instructional material” includes a publication, a recording, a diagram, or any other medium of expression which can be used to communicate the usefulness of a compound, composition, vector, or delivery system of the invention in the kit for effecting alleviation of the various diseases or disorders recited herein. Optionally, or alternately, the instructional material can describe one or more methods of alleviating the diseases or disorders in a cell or a tissue of a mammal. The instructional material of the kit of the invention can, for example, be affixed to a container which contains the identified compound, composition, vector, or delivery system of the invention or be shipped together with a container which contains the identified compound, composition, vector, or delivery system. Alternatively, the instructional material can be shipped separately from the container with the intention that the instructional material and the compound be used cooperatively by the recipient. “Isolated” means altered or removed from the natural state. For example, a nucleic acid or a peptide naturally present in a living animal is not“isolated,” but the same nucleic acid or peptide partially or completely separated from the coexisting materials of its natural state is“isolated.” An isolated nucleic acid or protein can exist in substantially purified form, or can exist in a non-native environment such as, for example, a host cell.

The term“microarray” refers broadly to both“DNA microarrays” and“DNA chip(s),” and encompasses all art-recognized solid supports, and all art-recognized methods for affixing nucleic acid molecules thereto or for synthesis of nucleic acids thereon.

By the term“modulating,” as used herein, is meant mediating a detectable increase or decrease in the activity and/or level of a mRNA, polypeptide, or a response in a subject compared with the activity and/or level of a mRNA, polypeptide or a response in the subject in the absence of a treatment or compound, and/or compared with the activity and/or level of a mRNA, polypeptide, or a response in an otherwise identical but untreated subject. The term encompasses perturbing and/or affecting a native signal or response thereby mediating a beneficial therapeutic response in a subject, preferably, a human.

The term“operably linked” as used herein refer to the linkage of nucleic acid sequences in such a manner that a nucleic acid molecule capable of directing the transcription of a given gene and/or the synthesis of a desired protein molecule is produced. The term also refers to the linkage of sequences encoding amino acids in such a manner that a functional (e.g., enzymatically active, capable of binding to a binding partner, capable of inhibiting, etc.) protein or polypeptide is produced. As used herein, the terms“operably linked” and“operationally linked” are used interchangeably.

The terms“patient,”“subject,”“individual,” and the like are used

interchangeably herein, and refer to any animal, or cells thereof whether in vitro or in situ, amenable to the methods described herein. In certain non-limiting embodiments, the patient, subject or individual is a human.

As used herein, the term“promoter/regulatory sequence” means a nucleic acid sequence which is required for expression of a gene product operably linked to the promoter/regulator sequence. In some instances, this sequence may be the core promoter sequence and in other instances, this sequence may also include an enhancer sequence and other regulatory elements which are required for expression of the gene product. The promoter/regulatory sequence may, for example, be one which expresses the gene product in an inducible manner.

An“inducible” promoter is a nucleotide sequence which, when operably linked with a polynucleotide which encodes or specifies a gene product, causes the gene product to be produced substantially only when an inducer which corresponds to the promoter is present.

A“constitutive” promoter is a nucleotide sequence which, when operably linked with a polynucleotide which encodes or specifies a gene product, causes the gene product to be produced in a cell under most or all physiological conditions of the cell.

“Polypeptide” refers to a polymer composed of amino acid residues, related naturally occurring structural variants, and synthetic non-naturally occurring analogs thereof linked via peptide bonds. Synthetic polypeptides can be synthesized, for example, using an automated polypeptide synthesizer.

The term“regulating” as used herein can mean any method of altering the level or activity of a substrate. Non-limiting examples of regulating with regard to a protein include affecting expression (including transcription and/or translation), affecting folding, affecting degradation or protein turnover, and affecting localization of a protein. Non-limiting examples of regulating with regard to a protein further include affecting the enzymatic activity.“Regulator” refers to a molecule whose activity includes affecting the level or activity of a substrate. A regulator can be direct or indirect. A regulator can function to activate or inhibit or otherwise modulate its substrate.

As used herein, a“recombinant cell” is a host cell that comprises a recombinant polynucleotide.

“Sample” or“biological sample” as used herein means a biological material from a subject, including but is not limited to organ, tissue, exosome, blood, plasma, saliva, urine and other body fluid. A sample can be any source of material obtained from a subject. A“therapeutic” treatment is a treatment administered to a subject who exhibits signs of pathology, for the purpose of diminishing or eliminating those signs.

As used herein,“treating a disease or disorder” means reducing the frequency with which a symptom of the disease or disorder is experienced by a patient.

A“vector” is a composition of matter which comprises an isolated nucleic acid and which can be used to deliver the isolated nucleic acid to the interior of a cell.

Numerous vectors are known in the art including, but not limited to, linear polynucleotides, polynucleotides associated with ionic or amphiphilic compounds, plasmids, and viruses. Thus, the term“vector” includes an autonomously replicating plasmid or a virus. The term should also be construed to include non-plasmid and non-viral compounds which facilitate transfer of nucleic acid into cells, such as, for example, polylysine compounds, liposomes, and the like. Examples of viral vectors include, but are not limited to, adenoviral vectors, adeno-associated virus vectors, retroviral vectors, and the like.

Ranges: throughout this disclosure, various aspects of the invention can be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 2.7, 3,

4, 5, 5.3, and 6. This applies regardless of the breadth of the range.

Description

The invention is based on the unexpected result that MG cells can be induced to re-enter the cell cycle and guided to differentiate into nascent rod- photoreceptors that have similar structure and characteristics (e.g., transducing signal from light) of native rods. Activation and Proliferation of MG Cells

In one embodiment, the invention relates to a method of inducing MG cell proliferation. Generally, the MG cells of the invention are induced to proliferate by contact with a composition (e.g., comprising a MG cell proliferation agent), e.g., a composition that stimulates WNT signaling. Non-limiting examples of MG cell proliferation agents include activators of one or more of b-catenin, Lin28a, Lin28b, Notch, or Ascll, and inhibitors of a negative regulator of MG cell proliferation (e.g., an inhibitor of GSK3 or let-7 miRNA). In exemplary embodiments, MG cell proliferation may be stimulated as described herein, by contact with an activator of one or more of b-catenin, Lin28a, Lin28b, Notch, and Ascll. In exemplary embodiments, MG cell proliferation may be stimulated as described herein, by contact with a nucleic acid encoding one or more of b-catenin, Lin28a, Lin28b, Notch, and Ascll. Alternatively, MG cell proliferation may be stimulated as described herein, by contact with an inhibitor of a negative regulator of MG cell proliferation. In exemplary embodiments, MG cell proliferation may be stimulated through inhibition of one or more of GSK2^ and let-7 miRNA. For example, a population of MG cells can be contacted with an anti-let-7 antibody under conditions appropriate for stimulating proliferation of the MG cells. Differentiation of MG Cells

In one embodiment, the invention relates to a method of inducing MG cells (e.g., proliferating MG cells) to differentiate into rod photoreceptors. In one embodiment, the method comprises contacting a proliferating cell with a composition (e.g., comprising a MG cell differentiation agent) that stimulates expression of rod- specific genes. Non-limiting examples of MG cell differentiation agents include a transcription factor selected from the group consisting of Otx2, Crx, Nrl, Nr2e3, and NeuroD, or a combination thereof, and a composition which activates one or more of rhodopsin, rod a-transducin, rod arrestin, phosducin, ROM1, retinal cGMP, Guanylate Cyclase-Activating Protein Photoreceptor 2, Tubby Like Protein 1, Retinoschisin 1, G alpha 1, G gamma 1, cGMP PDE gamma, G beta 1, mUNCH9, rod PDE beta, Pleckstrin Homology Domain Retinal Protein 1, Peripherin 2, recoverin, ribeye, bassoon, and CtBP, or a combination thereof. In one embodiment, a method of inducing MG cell differentiation comprises contacting a proliferating MG cell with a composition which activates one or more of rhodopsin, rod a-transducin, rod arrestin, phosducin, ROM1, retinal cGMP, Guanylate Cyclase- Activating Protein

Photoreceptor 2, Tubby Like Protein 1, Retinoschisin 1, G alpha 1, G gamma 1, cGMP PDE gamma, G beta 1, mUNCH9, rod PDE beta, Pleckstrin Homology

Domain Retinal Protein 1, Peripherin 2, recoverin, ribeye, bassoon, and CtBP In one embodiment, MG cell differentiation may be stimulated as described herein, by contacting a proliferating MG cell with Otx2, Crx, Nrl, Nr2e3 and NeuroD, or a combination thereof. In one embodiment, MG cell differentiation may be stimulated as described herein, by contacting a proliferating MG cell with Otx2, Crx, and Nrl. In a specific embodiment, MG cell differentiation may be stimulated as described herein, by administering to a subject Otx, Crx, and Nrl.

In a specific embodiment, MG cell differentiation may be stimulated as described herein by administering to a subject a first nucleic acid molecule encoding Otx2, a second nucleic acid molecule encoding Crx, and a third nucleic acid molecule encoding Nrl. In specific embodiments, the first nucleic acid molecule is operably linked to a promoter that specifically expresses the first nucleic acid in MG cells, the second nucleic acid molecule is operably linked to a promoter that specifically expresses the second nucleic acid in MG cells, and the third nucleic acid molecule is operably linked to a promoter that specifically expresses the third nucleic acid in MG cells.

In specific embodiments, MG cell differentiation may be stimulated as described herein, by administering to a subject: a first vector comprising a first nucleic acid operably linked to a promoter that specifically expresses the first nucleic acid in MG cells, a second vector comprising a second nucleic acid operably linked to a promoter that specifically expresses the second nucleic acid in MG cells, and a third vector comprising a third nucleic acid operably linked to a promoter that specifically expresses the third nucleic acid in MG cells. In specific embodiments, the promoter that specifically expresses the nucleic acid in MG cells is the GFAP promoter. In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO: 8.

In specific embodiments, the first vector is a virus or virus-like particle that specifically infects MG cells, the second vector is a virus or virus-like particle that specifically infects MG cells, and the third vector is a virus or virus-like particle that specifically infects MG cells. In specific embodiments, the first vector is AAV- ShHlO, the second vector is AAV-ShHlO, and the third vector is AAV-ShHlO. Two-Step Method

Provided herein is a two-step method for inducing new rod photoreceptor formation from MG cells. This two-step method can be used to treat vision loss or impairment in a subject, treat AMD, diabetic retinopathy, retrolental fibroplasia, Stargardt disease, RP, uveitis, Bardet-Biedl syndrome, or eye cancer in a subject, or generate new rod photoreceptors in a retina in a subject. Thus, in one embodiment, the invention provides a method to treat vision loss or impairment in a subject. The invention also provides a method to treat AMD, diabetic retinopathy, retrolental fibroplasia, Stargardt disease, RP, uveitis, Bardet-Biedl syndrome, or eye cancer in a subject. The invention also provides a method of inducing new rod-photoreceptor formation from MG cells.

In one embodiment, the method comprises a first step of inducing MG cell proliferation (see, e.g.. the section“Activation and Proliferation of MG Cells” above, and the working examples below) and a second step of guiding differentiation of the proliferating MG cells to rod photoreceptors (see, e.g., the section“Differentiation of MG Cells” above, and the working examples below). Therefore, in one embodiment, the method comprises contacting a MG cell with a first composition for inducing MG cell proliferation (e.g., a composition comprising a MG cell proliferation agent) and contacting the MG cell with a second composition that induces differentiation of the MG cells (e.g., proliferating MG cells) to rod photoreceptors (e.g., a composition comprising a MG cell differentiation agent). In one embodiment, a MG cell is contacted with a single composition comprising a first composition for inducing MG cell proliferation and a second composition that induces differentiation of the proliferating MG cells to rod photoreceptors. In an alternative embodiment, a MG cell is contacted with two or more compositions wherein the two or more compositions comprise at least a first composition for inducing MG cell proliferation and a second composition that induces differentiation of the proliferating MG cells to rod photoreceptors. In one embodiment, a MG cell is contacted with two or more compositions substantially concurrently. In certain embodiments, a MG cell is contacted concurrently with a MG cell proliferation agent and a MG cell

differentiation agent. In certain embodiments, a MG cell is contacted substantially concurrently (e.g., within 1 minute, within 5 minutes, within 10 minutes, within an hour, within two hours, or within three hours) with a MG cell proliferation agent and a MG cell differentiation agent. In certain embodiments in which the MG cell is contacted concurrently or substantially concurrently with a MG cell proliferation agent and a MG cell differentiation agent, the MG cell differentiation agent is a delayed release agent (e.g., is not released until 1 to 5 days, 5 to 10 days, 10 to 15 days, 15 to 20 days, or 20 to 30 days after the MG cell is contacted with the MG cell differentiation agent). In an alternative embodiment, contacting the MG cell with two or more compositions comprises contacting the MG cell with a first composition, allowing a sufficient amount of time for the MG cell to enter the cell cycle ( i.e . begin proliferating), and subsequently contacting the cell with at least a second composition to induce differentiation of the MG cell into a rod photoreceptor.

Activator Compositions

In various embodiments, the present invention includes compositions for use in methods of treating vision loss or impairment in a subject. The compositions of the present invention include compositions comprising a MG cell proliferation agent. In one embodiment, the composition activates WNT signaling in MG cells to induce MG cell proliferation. In one embodiment, the composition activates one or more of b- catenin, Lin28, Notch, and Ascll in MG cells to induce cell proliferation. The compositions of the present invention also include compositions comprising a MG cell differentiation agent. In one embodiment, the composition activates transcription of cell-specific genes to induce differentiation of cells to rod photoreceptors.

In one embodiment, the composition for treating vision loss or impairment comprises an activator of WNT signaling. In one embodiment, the composition for treating vision loss or impairment comprises an activator of one or more of b-catenin, Lin28a, Lin28b, Notch, and Ascll. In one embodiment, the composition for treating vision loss or impairment comprises an activator of one or more of rhodopsin, rod a- transducin, rod arrestin, phosducin, ROM1, retinal cGMP, Guanylate Cyclase- Activating Protein Photoreceptor 2, Tubby Like Protein 1, Retinoschisin 1, G alpha 1, G gamma 1, cGMP PDE gamma, G beta 1, mUNCH9, rod PDE beta, Pleckstrin Homology Domain Retinal Protein 1, Peripherin 2, recoverin, ribeye, bassoon, and CtBP

In one embodiment, the activator of the invention increases the amount of polypeptide, the amount of mRNA, the amount of activity, or a combination thereof of the target (e.g., b-catenin, Lin28a, Lin28b, Notch, or Ascll).

It will be understood by one skilled in the art, based upon the disclosure provided herein, that an increase in the level of protein encompasses the increase in expression, including transcription, translation, or both. The skilled artisan will also appreciate, once armed with the teachings of the present invention, that an increase in the level of protein includes an increase in protein activity. Thus, increasing the level or activity of a protein includes, but is not limited to, increasing the amount of the polypeptide, increasing transcription, translation, or both, of a nucleic acid encoding the protein, and it also includes increasing any activity of the polypeptide as well.

Thus, in one embodiment, the present invention relates to compositions for treatment of vision loss or impairment including a polypeptide, a recombinant polypeptide, an active polypeptide fragment, or an activator of expression or activity of a polypeptide, where the polypeptide or activator functions to increase, induce or otherwise activate proliferation of MG cells.

In another embodiment, the present invention relates to compositions for treatment of vision loss or impairment including a polypeptide, a recombinant polypeptide, an active polypeptide fragment, or an activator of expression or activity of a polypeptide, where the polypeptide or activator functions to increase, induce or otherwise activate one or more proteins to direct rod photoreceptor differentiation of proliferating MG cells.

It is understood by one skilled in the art, that an increase in the level of a protein encompasses the increase of protein expression. Thus, increasing the level or activity of a protein includes, but is not limited to, increasing transcription, translation, or both, of a nucleic acid encoding the protein; and it also includes increasing the stability of a nucleic acid encoding the protein. Additionally, the skilled artisan would appreciate, that an increase in the level of a protein includes an increase in one or more enzymatic activity of the protein.

An activator of the invention can include, but should not be construed as being limited to, a chemical compound, a protein, a peptidomemetic, an antibody, or a nucleic acid molecule. In one embodiment, an activator encompasses a chemical compound that increases the level, enzymatic activity, or the like of one or more of WNT signaling, b-catenin, Lin28a, Lin28b, Notch, and Ascll. In one embodiment, an activator encompasses a chemical compound that increases the level, enzymatic activity, or the like of one or more proteins to direct rod photoreceptor differentiation of proliferating MG cells. In one embodiment, an activator encompasses a chemical compound that increases the level, enzymatic activity, or the like of one or more of rhodopsin, rod a-transducin, rod arrestin, phosducin, ROM1, retinal cGMP, Guanylate Cyclase-Activating Protein Photoreceptor 2, Tubby Like Protein 1, Retinoschisin 1, G alpha 1, G gamma 1, cGMP PDE gamma, G beta 1, mUNCH9, rod PDE beta, Pleckstrin Homology Domain Retinal Protein 1, Peripherin 2, recoverin, ribeye, bassoon, and CtBP

It will be understood by one skilled in the art, based upon the disclosure provided herein, that an increase in the level, enzymatic activity, or the like of one or more proteins to direct rod photoreceptor differentiation of proliferating MG cells encompasses the increase in gene expression, including transcription, translation, or both of one or more proteins to direct rod photoreceptor differentiation of proliferating MG cells. Therefore, in one embodiment, an activator of the invention is a transcription factor. Transcription factors that increase the level of one or more proteins to direct rod photoreceptor differentiation of proliferating MG cells include, but are not limited to Otx2, Crx, Nrl, Nr2e3 and NeuroD. In a specific embodiment, an activator of the invention is the combination of transcription factors Otx2, Crx, and Nrl.

Further, one of skill in the art would, when equipped with this disclosure and the methods exemplified herein, appreciate that an activator includes such activators as discovered in the future, as can be identified by well-known criteria in the art of pharmacology, such as the physiological results of activation of MG proliferation and MG to rod photoreceptor differentiation as described in detail herein and/or as known in the art. Therefore, the present invention is not limited in any way to any particular activator as exemplified or disclosed herein; rather, the invention encompasses those activators that would be understood by the skilled artisan to be useful as are known in the art and as are discovered in the future.

Further methods of identifying and producing an activator are well known to those of ordinary skill in the art, including, but not limited, obtaining an activator from a naturally occurring source. Alternatively, an activator can be synthesized chemically. Further, the skilled artisan would appreciate, based upon the teachings provided herein, that an activator can be obtained from a recombinant organism. Compositions and methods for chemically synthesizing activators and for obtaining them from natural sources are well known in the art and are described in the art.

One of skill in the art will appreciate that an activator can be a small molecule chemical, a protein, a nucleic acid construct encoding a protein, or combinations thereof. In one embodiment, an activator comprises a nucleic acid operably linked to a promoter for MG cell-specific expression. In one embodiment, the promoter is the GFAP promoter. In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO: 8. Numerous vectors and other compositions and methods are well known for administering a protein or a nucleic acid construct encoding a protein to cells or tissues. In one embodiment, an activator comprising a nucleic acid construct is cloned into the ShHlO-GFAP vector for expression in MG cells.

Peptides

The present invention comprises a peptide comprising an activator of WNT signaling or a peptide that induces MG cell proliferation.

In one embodiment the peptide comprises b-catenin. An exemplary amino acid sequence of human b-catenin (GenBank Accession No. NR_001091679, encoded by GenBank Accession No. NM_001098209) is provided below:

1 matqadlmel dmamepdrka avshwqqqsy ldsgihsgat ttapslsgkg npeeedvdts

61 qvlyeweqgf sqsftqeqva didgqyamtr aqrvraamfp etldegmqip stqfdaahpt

121 nvqrlaepsq mlkhavvnli nyqddaelat raipeltkll ndedqvvvnk aavmvhqlsk

181 keasrhaimr spqmvsaivr tmqntndvet arctagtlhn lshhreglla ifksggipal

241 vkmlgspvds vlfyaittlh nlllhqegak mavrlagglq kmvallnktn vkflaittdc

301 lqilaygnqe skliilasgg pqalvnimrt ytyekllwtt srvlkvlsvc ssnkpaivea

361 ggmqalglhl tdpsqrlvqn clwtlrnlsd aatkqegmeg llgtlvqllg sddinvvtca 421 agilsnltcn nyknkmmvcq vggiealvrt vlragdredi tepaicalrh ltsrhqeaem

481 aqnavrlhyg lpvvvkllhp pshwplikat vglirnlalc panhaplreq gaiprlvqll

541 vrahqdtqrr tsmggtqqqf vegvrmeeiv egctgalhil ardvhnrivi rglntiplfv

601 qllyspieni qrvaagvlce laqdkeaaea ieaegatapl tellhsrneg vatyaaavlf

661 rmsedkpqdy kkrlsvelts slfrtepmaw netadlgldi gaqgeplgyr qddpsyrsfh

721 sggygqdalg mdpiranehemg ghhpgadypv dglpdlghaq dlmdglppgd snqlawfdtd

781 1 (SEQ ID NO: l).

In another embodiment, the peptide comprises Lin28a. An exemplary amino acid sequence of human Lin28a (GenBank Accession No. NP_078950, encoded by GenBank Accession No. NM_024674) is provided below:

1 mgsvsnqqfa ggcakaaeea peeapedaar aadepqllhg agickwfnvr mgfgflsmta

61 ragvaldppv dvfvhqsklh megfrslkeg eaveftfkks akglesirvt gpggvfcigs 121 errpkgksmq krrskgdrcy ncggldhhak ecklppqpkk chfcqsishm vascplkaqq 181 gpsaqgkpty freeeeeihs ptllpeaqn (SEQ ID NO:2).

In another embodiment, the peptide comprises Lin28b. An exemplary amino acid sequence of human Lin28b (GenBank Accession No. NR_001004317, encoded by GenBank Accession No. NM_001004317) is provided below:

1 maeggaskgg geepgklpep aeeesqvlrg tghckwfnvr mgfgfismin regspldipv

61 dvfvhqsklf megfrslkeg epveftfkks skglesirvt gpggspclgs errpkgktlq 121 krkpkgdrcy ncggldhhak ecslppqpkk chycqsimhm vancphknva qppassqgrq 181 eaesqpctst lprevggghg ctsppfpqea raeisersgr spqeasstks siapeeqskk 241 gpsvqkrkkt (SEQ ID NO:3).

In another embodiment, the peptide comprises Notch. An exemplary amino acid sequence of human Notch (GenBank Accession No. NP_060087, encoded by GenBank Accession No. NM_017617) is provided below:

1 mppllapllc lallpalaar gprcsqpget clnggkceaa ngteacvcgg afvgprcqdp

61 npclstpckn agtchvvdrr gvadyacsca lgfsgplclt pldnacltnp crnggtcdll

121 tlteykcrcp pgwsgkscqq adpcasnpca nggqclpfea syichcppsf hgptcrqdvn

181 ecgqkpglcr hggtchnevg syrcvcrath tgpncerpyv pcspspcqng gtcrptgdvt

241 hecaclpgft gqnceenidd cpgnnckngg acvdgvntyn crcppewtgq yctedvdecq

301 lmpnacqngg tchnthggyn cvcvngwtge dcseniddca saacfhgatc hdrvas fyce 361 cphgrtgllc hlndacisnp cnegsncdtn pvngkaictc psgytgpacs qdvdecslga

421 npcehagkci ntlgs fecqc lqgytgprce idvnecvsnp cqndatcldq igefqcicmp

481 gyegvhcevn tdecasspcl hngrcldkin efqcecptgf tghlcqydvd ecastpckng

541 akcldgpnty tcvctegytg thcevdidec dpdpchygsc kdgvatftcl crpgytghhc

601 etninecssq pcrhggtcqd rdnaylcfcl kgttgpncei nlddcasspc dsgtcldkid

661 gyecacepgy tgsmcninid ecagnpchng gtcedgingf tcrcpegyhd ptclsevnec

721 nsnpcvhgac rdslngykcd cdpgwsgtnc dinnnecesn pcvnggtckd mtsgyvctcr

781 egfsgpncqt ninecasnpc lnqgtciddv agykcncllp ytgatcevvl apcapspcrn

841 ggecrqsedy esfscvcptg wqgqtcevdi necvlspcrh gascqnthgg yrchcqagys

901 grncetdidd crpnpchngg sctdgintaf cdclpgfrgt fceedineca sdpcrnganc

961 tdcvdsytct cpagfsgihc enntpdctes scfnggtcvd gins ftclcp pgftgsycqh

1021 dvnecdsqpc lhggtcqdgc gsyrctcpqg ytgpncqnlv hwcdsspckn ggkcwqthtq

1081 yrcecpsgwt glycdvpsvs cevaaqrqgv dvarlcqhgg lcvdagnthh crcqagytgs

1141 ycedlvdecs pspcqngatc tdylggysck cvagyhgvnc seeideclsh pcqnggtcld

1201 lpntykcscp rgtqgvhcei nvddcnppvd pvsrspkcfn ngtcvdqvgg ys ctcppgfv

1261 gercegdvne clsnpcdarg tqncvqrvnd fhcecraght grrcesving ckgkpckngg

1321 tcavasntar gfickcpagf egatcendar tcgslrclng gtcisgprsp tclclgpftg

1381 pecqfpassp clggnpcynq gtceptsesp fyrclcpakf ngllchildy s fgggagrdi

1441 ppplieeace lpecqedagn kvcslqcnnh acgwdggdcs lnfndpwknc tqslqcwkyf

1501 sdghcdsqcn sagclfdgfd cqraegqcnp lydqyckdhf sdghcdqgcn saecewdgld 1561 caehvperla agtlvvvvlm ppeqlrnssf hflrelsrvl htnvvfkrda hgqqmifpyy

1621 greeelrkhp ikraaegwaa pdallgqvka sllpggsegg rrrreldpmd vrgsivylei

1681 dnrqcvqass qcfqsatdva aflgalaslg slnipykiea vqsetveppp paqlhfmyva

1741 aaafvllffv gcgvllsrkr rrqhgqlwfp egfkvseask kkrreplged svglkplkna

1801 sdgalmddnq newgdedlet kkfrfeepvv lpdlddqtdh rqwtqqhlda adlrmsamap

1861 tppqgevdad cmdvnvrgpd gftplmiasc sgggletgns eeeedapavi sdfiyqgasl

1921 hnqtdrtget alhlaarysr sdaakrllea sadaniqdnm grtplhaavs adaqgvfqil

1981 irnratdlda rmhdgttpli laarlavegm ledlinshad vnavddlgks alhwaaavnn

2041 vdaavvllkn gankdmqnnr eetplflaar egsyetakvl ldhfanrdit dhmdrlprdi

2101 aqermhhdiv rlldeynlvr spqlhgaplg gtptlspplc spngylgslk pgvqgkkvrk

2161 psskglacgs keakdlkarr kksqdgkgcl ldssgmlspv dslesphgyl sdvasppllp

2221 spfqqspsvp lnhlpgmpdt hlgighlnva akpemaalgg ggrlafetgp prlshlpvas

2281 gtstvlgsss ggalnftvgg stslngqcew lsrlqsgmvp nqynplrgsv apgplstqap

2341 slqhgmvgpl hsslaasals qmmsyqglps trlatqphlv qtqqvqpqnl qmqqqnlqpa

2401 niqqqqslqp pppppqphlg vssaasghlg rs flsgepsq advqplgpss lavhtilpqe

2461 spalptslps slvppvtaaq fltppsqhsy sspvdntpsh qlqvpehpfl tpspespdqw

2521 ssssphsnvs dwsegvsspp tsmqsqiari peafk (SEQ ID NO:4).

In some embodiments, the peptide comprises the intracellular domain of Notch. An exemplary amino acid sequence of human Notch intracellular domain is provided below:

1 gcgvllsrkr rrqhgqlwfp egfkvseask kkrreplged svglkplkna sdgalmddnq

61 newgdedlet kkfrfeepvv lpdlddqtdh rqwtqqhlda adlrmsamap tppqgevdad

121 cmdvnvrgpd gftplmiasc sgggletgns eeeedapavi sdfiyqgasl hnqtdrtget 181 alhlaarysr sdaakrllea sadaniqdnm grtplhaavs adaqgvfqil irnratdlda

241 rmhdgttpli laarlavegm ledlinshad vnavddlgks alhwaaavnn vdaavvllkn

301 gankdmqnnr eetplflaar egsyetakvl ldhfanrdit dhmdrlprdi aqermhhdiv

361 rlldeynlvr spqlhgaplg gtptlspplc spngylgslk pgvqgkkvrk psskglacgs

421 keakdlkarr kksqdgkgcl ldssgmlspv dslesphgyl sdvasppllp spfqqspsvp

481 lnhlpgmpdt hlgighlnva akpemaalgg ggrlafetgp prlshlpvas gtstvlgsss

541 ggalnftvgg stslngqcew lsrlqsgmvp nqynplrgsv apgplstqap slqhgmvgpl

601 hsslaasals qiransyqglps trlatqphlv qtqqvqpqnl qmqqqnlqpa niqqqqslqp

661 pppppqphlg vssaasghlg rsflsgepsq advqplgpss lavhtilpqe spalptslps

721 slvppvtaaq fltppsqhsy sspvdntpsh qlqvpehpfl tpspespdqw ssssphsnvs

781 dwsegvsspp tsmqsqiari peafk (SEQ ID NO:5).

In another embodiment, the peptide comprises Ascll. An exemplary amino acid sequence of human Ascll (GenBank Accession No. NP_004307, encoded by GenBank Accession No. NM_0043l6) is provided below:

1 messakmesg gagqqpqpqp qqpflppaac ffataaaaaa aaaaaaaqsa qqqqqqqqqq

61 qqapqlrpaa dgqpsggghk sapkqvkrqr ssspelmrck rrlnfsgfgy slpqqqpaav

121 arrnerernr vklvnlgfat lrehvpngaa nkkmskvetl rsaveyiral qqlldehdav

181 saafqagvls ptispnysnd lnsmagspvs syssdegsyd plspeeqell dftnwf

(SEQ ID NO:6).

The peptide of the present invention may be made using chemical methods. For example, peptides can be synthesized by solid phase techniques (Roberge J Y et al (1995) Science 269: 202-204), cleaved from the resin, and purified by preparative high performance liquid chromatography. Automated synthesis may be achieved, for example, using the ABI 431 A Peptide Synthesizer (Perkin Elmer) in accordance with the instructions provided by the manufacturer.

The peptide may alternatively be made by recombinant means or by cleavage from a longer polypeptide. The composition of a peptide may be confirmed by amino acid analysis or sequencing.

The variants of the polypeptides according to the present invention may be (i) one in which one or more of the amino acid residues are substituted with a conserved or non-conserved amino acid residue (preferably a conserved amino acid residue) and such substituted amino acid residue may or may not be one encoded by the genetic code, (ii) one in which there are one or more modified amino acid residues, e.g., residues that are modified by the attachment of substituent groups, (iii) one in which the polypeptide is an alternative splice variant of the polypeptide of the present invention, (iv) fragments of the polypeptides (e.g., the notch intracellular domain with respect to notch) and/or (v) one in which the polypeptide is fused with another polypeptide, such as a leader or secretory sequence or a sequence which is employed for purification (for example, His-tag) or for detection (for example, Sv5 epitope tag). The fragments include polypeptides generated via proteolytic cleavage (including multi-site proteolysis) of an original sequence. Variants may be post-translationally, or chemically modified. Such variants are deemed to be within the scope of those skilled in the art from the teaching herein.

The polypeptides of the invention can be post-translationally modified. For example, post-translational modifications that fall within the scope of the present invention include signal peptide cleavage, glycosylation, acetylation, isoprenylation, proteolysis, myristoylation, protein folding and proteolytic processing, etc. Some modifications or processing events require introduction of additional biological machinery.

The polypeptides of the invention may include unnatural amino acids formed by post-translational modification or by introducing unnatural amino acids during translation. A variety of approaches are available for introducing unnatural amino acids during protein translation. By way of example, special tRNAs, such as tRNAs which have suppressor properties, suppressor tRNAs, have been used in the process of site- directed non-native amino acid replacement (SNAAR). In SNAAR, a unique codon is required on the mRNA and the suppressor tRNA, acting to target a non native amino acid to a unique site during the protein synthesis (described in

W090/05785). However, the suppressor tRNA must not be recognizable by the aminoacyl tRNA synthetases present in the protein translation system. In certain cases, a non-native amino acid can be formed after the tRNA molecule is

aminoacylated using chemical reactions which specifically modify the native amino acid and do not significantly alter the functional activity of the aminoacylated tRNA. These reactions are referred to as post-aminoacylation modifications. For example, the epsilon-amino group of the lysine linked to its cognate tRNA (tRNALYS), could be modified with an amine specific photoaffmity label. Fusion and Chimeric Polypeptides

A protein of the invention may be conjugated with other molecules, such as proteins, to prepare fusion proteins. This may be accomplished, for example, by the synthesis of N-terminal or C-terminal fusion proteins provided that the resulting fusion protein retains the functionality of increasing WNT signaling.

A protein or fusion protein of the invention may be phosphorylated using conventional methods such as the method described in Reedijk et al. (The EMBO Journal 11(4): 1365, 1992).

Cyclic derivatives of the peptides or chimeric proteins of the invention are also part of the present invention. Cyclization may allow the peptide or chimeric protein to assume a more favorable conformation for association with other molecules.

Cyclization may be achieved using techniques known in the art. For example, disulfide bonds may be formed between two appropriately spaced components having free sulfhydryl groups, or an amide bond may be formed between an amino group of one component and a carboxyl group of another component. Cyclization may also be achieved using an azobenzene-containing amino acid as described by Ulysse, L., et al, J. Am. Chem. Soc. 1995, 117, 8466-8467. The components that form the bonds may be side chains of amino acids, non-amino acid components or a combination of the two. In an embodiment of the invention, cyclic peptides may comprise a beta-turn in the right position. Beta-turns may be introduced into the peptides of the invention by adding the amino acids Pro-Gly at the right position.

It may be desirable to produce a cyclic peptide which is more flexible than the cyclic peptides containing peptide bond linkages as described above. A more flexible peptide may be prepared by introducing cysteines at the right and left position of the peptide and forming a disulphide bridge between the two cysteines. The two cysteines are arranged so as not to deform the beta-sheet and turn. The peptide is more flexible as a result of the length of the disulfide linkage and the smaller number of hydrogen bonds in the beta-sheet portion. The relative flexibility of a cyclic peptide can be determined by molecular dynamics simulations.

(a) Tags

In a particular embodiment of the invention, a polypeptide of the invention further comprises a tag. The tag includes but is not limited to: polyhistidine tags (His- tags) (for example H6 and H10, etc.) or other tags for use in IMAC systems, for example, Ni ²⁺ affinity columns, etc., GST fusions, MBP fusions, streptavidine-tags, the BSP biotinylation target sequence of the bacterial enzyme BIRA and tag epitopes that are directed by antibodies (for example c-myc tags, FLAG-tags, among others). As will be observed by a person skilled in the art, the tag peptide can be used for purification, inspection, selection and/or visualization of the fusion protein of the invention. In a particular embodiment of the invention, the tag is a detection tag and/or a purification tag. It will be appreciated that the tag sequence will not interfere in the function of the protein of the invention.

(b) Leader and secretory sequences

Accordingly, the polypeptides of the invention can be fused to another polypeptide or tag, such as a leader or secretory sequence or a sequence which is employed for purification or for detection. In a particular embodiment, the polypeptide of the invention comprises the glutathione-S-transferase protein tag which provides the basis for rapid high-affinity purification of the polypeptide of the invention. Indeed, this GST- fusion protein can then be purified from cells via its high affinity for glutathione. Agarose beads can be coupled to glutathione, and such glutathione-agarose beads bind GST- proteins. Thus, in a particular embodiment of the invention, the polypeptide of the invention is bound to a solid support. In a preferred embodiment, if the polypeptide of the invention comprises a GST moiety, the polypeptide is coupled to a glutathione-modified support. In a particular case, the glutathione modified support is a glutathione-agarose bead. Additionally, a sequence encoding a protease cleavage site can be included between the affinity tag and the polypeptide sequence, thus permitting the removal of the binding tag after incubation with this specific enzyme and thus facilitating the purification of the corresponding protein of interest. Suitable protease cleavage sites for incorporation into the polypeptides of the invention include enterokinase, factor Xa, thrombin, TEV protease, PreScission protease, inteins and the like.

(c) Targeting sequences

The invention also relates to proteins or peptides of the invention fused to, or integrated into, a target protein, and/or a targeting domain capable of directing the chimeric protein to a desired cellular component or cell type or tissue. The chimeric proteins may also contain additional amino acid sequences or domains. The chimeric proteins are recombinant in the sense that the various components are from different sources, and as such are not found together in nature (i.e. are heterologous).

A target protein is a protein that is selected for degradation and for example may be a protein that is mutated or over expressed in a disease or condition. In another embodiment of the invention, a target protein is a protein that is abnormally degraded and for example may be a protein that is mutated or underexpressed in a disease or condition. The targeting domain can be a membrane spanning domain, a membrane binding domain, or a sequence directing the protein to associate with for example vesicles or with the nucleus. The targeting domain can target a protein of the invention to a particular cell type or tissue. For example, the targeting domain can be a cell surface ligand or an antibody against cell surface antigens of a target tissue. A targeting domain may target a protein to a MG cell. In one embodiment, an accessory peptide can be used to enhance interaction of the protein with the target MG cell.

(d) Intracellular targeting

Combined with certain formulations, peptides can be effective intracellular agents. In order to increase the efficacy of such peptides, the peptide can be provided as a fusion peptide along with a second peptide which promotes“transcytosis”, e.g., uptake of the peptide by epithelial cells. To illustrate, the peptide can be provided as a chimeric peptide which includes a heterologous peptide sequence (“internalizing peptide”) which drives the translocation of an extracellular form of a peptide across a cell membrane in order to facilitate intracellular localization of the peptide. In this regard, the peptide sequence is one which is active intracellularly. The internalizing peptide, by itself, is capable of crossing a cellular membrane by, e.g., transcytosis, at a relatively high rate. The internalizing peptide is conjugated, e.g., as a fusion protein, to the protein. The resulting chimeric peptide is transported into cells at a higher rate relative to the peptide alone to thereby provide a means for enhancing its introduction into cells to which it is applied.

In one embodiment, the internalizing peptide is derived from the Drosophila antennapedia protein, or homologs thereof. The 60 amino acid long homeodomain of the homeo-protein antennapedia has been demonstrated to translocate through biological membranes and can facilitate the translocation of heterologous polypeptides to which it is couples. See for example Derossi et al. (1994) J Biol Chem 269: 10444-10450; and Perez et al. (1992) J Cell Sci 102:717-722. Recently, it has been demonstrated that fragments as small as 16 amino acids long of this protein are sufficient to drive internalization. See Derossi et al. (1996) J Biol Chem 271: 18188- 18193.

The present invention contemplates a protein sequence for activation of WNT signaling, or a WNT signaling effector, as described herein, and at least a portion of the Antennapedia protein (or homolog thereof) sufficient to promote the

transmembrane transport of the chimeric protein.

Another example of an internalizing peptide is the HIV transactivator (TAT) protein. This protein appears to be divided into four domains (Kuppuswamy et al. (1989) Nucl. Acids Res. 17:3551-3561). Purified TAT protein is taken up by cells in tissue culture (Frankel and Pabo, (1989) Cell, 55: 1189-1193), and peptides, such as the fragment corresponding to residues 37-62 of TAT, are rapidly taken up by cell in vitro (Green and Loewenstein, (1989) Cell 55: 1179-1188). The highly basic region mediates internalization and targeting of the internalizing moiety to the nucleus (Ruben et al, (1989) J. Virol. 63: 1-8).

Another exemplary transcellular polypeptide can be generated to include a sufficient portion of mastoparan (T. Higashijima et al, (1990) J. Biol. Chem.

265: 14176) to increase the transmembrane transport of the chimeric protein.

While not wishing to be bound by any particular theory, it is noted that hydrophilic polypeptides may be also be physiologically transported across the membrane barriers by coupling or conjugating the polypeptide to a transportable peptide which is capable of crossing the membrane by receptor-mediated transcytosis, e.g. , a histone, insulin, transferrin, basic albumin, prolactin and insulin-like growth factor I (IGF-I), insulin-like growth factor II (IGF-II) or other growth factors.

Another class of translocating/intemalizing peptides exhibits pH- dependent membrane binding. For an internalizing peptide that assumes a helical conformation at an acidic pH, the internalizing peptide acquires the property of amphiphilicity, e.g., it has both hydrophobic and hydrophilic interfaces. More specifically, within a pH range of approximately 5.0-5.5, an internalizing peptide forms an alpha-helical, amphiphilic structure that facilitates insertion of the moiety into a target membrane. An alpha-helix-inducing acidic pH environment may be found, for example, in the low pH environment present within cellular endosomes. Such internalizing peptides can be used to facilitate transport of peptides, taken up by an endocytic mechanism, from endosomal compartments to the cytoplasm.

A preferred pH-dependent membrane-binding internalizing peptide includes a high percentage of helix-forming residues, such as glutamate, methionine, alanine and leucine. In addition, a preferred internalizing peptide sequence includes ionizable residues having pKa's within the range of pH 5-7, so that a sufficient uncharged membrane-binding domain will be present within the peptide at pH 5 to allow insertion into the target cell membrane.

In various embodiments, internalizing peptides include, but are not limited to, peptides of apo-lipoprotein A-l and B; peptide toxins, such as melittin, bombolittin, delta hemolysin and the pardaxins; antibiotic peptides, such as alamethicin; peptide hormones, such as calcitonin, corticotrophin releasing factor, beta endorphin, glucagon, parathyroid hormone, pancreatic polypeptide; and peptides corresponding to signal sequences of numerous secreted proteins. In addition, exemplary internalizing peptides may be modified through attachment of substituents that enhance the alpha-helical character of the internalizing peptide at acidic pH.

Yet another class of internalizing peptides suitable for use within the present invention include hydrophobic domains that are“hidden” at physiological pH, but are exposed in the low pH environment of the target cell endosome. Upon pH-induced unfolding and exposure of the hydrophobic domain, the moiety binds to lipid bilayers and effects translocation of the covalently linked polypeptide into the cell cytoplasm. Such internalizing peptides may be modeled after sequences identified in, e.g., Pseudomonas exotoxin A, clathrin, or Diphtheria toxin.

Pore-forming proteins or peptides may also serve as internalizing peptides herein. Pore-forming proteins or peptides may be obtained or derived from, for example, C9 complement protein, cytolytic T-cell molecules or NK-cell molecules. These moieties are capable of forming ring-like structures in membranes, thereby allowing transport of attached polypeptide through the membrane and into the cell interior. Mere membrane intercalation of an internalizing peptide may be sufficient for translocation of the proteins of the invention across cell membranes. However, translocation may be improved by attaching to the internalizing peptide a substrate for intracellular enzymes (i.e., an“accessory peptide”). It is preferred that an accessory peptide be attached to a portion(s) of the internalizing peptide that protrudes through the cell membrane to the cytoplasmic face. The accessory peptide may be

advantageously attached to one terminus of a translocating/intemalizing moiety or anchoring peptide. An accessory moiety of the present invention may contain one or more amino acid residues. In one embodiment, an accessory moiety may provide a substrate for cellular phosphorylation (for instance, the accessory peptide may contain a tyrosine residue).

Suitable accessory peptides include peptides that are kinase substrates, peptides that possess a single positive charge, and peptides that contain sequences which are glycosylated by membrane-bound gly cotransferases. Accessory peptides that are glycosylated by membrane-bound gly cotransferases may include the sequence x-NLT-x, where“x” may be another peptide, an amino acid, coupling agent or hydrophobic molecule, for example. When this hydrophobic tripeptide is incubated with microsomal vesicles, it crosses vesicular membranes, is glycosylated on the luminal side, and is entrapped within the vesicles due to its hydrophilicity (C.

Hirschberg et al, (1987) Ann. Rev. Biochem. 56:63-87). Accessory peptides that contain the sequence x-NLT-x thus will enhance target cell retention of corresponding polypeptide.

In certain instances, it may also be desirable to include a nuclear localization signal as part of the protein or fusion protein.

As described above, the internalizing and accessory peptides can each, independently, be added to the protein of the invention by either chemical cross- linking or in the form of a fusion protein. In the instance of fusion proteins, unstructured polypeptide linkers can be included between each of the peptide moieties.

In the generation of fusion proteins, it may be necessary to include unstructured linkers in order to ensure proper folding of the various peptide domains. Many synthetic and natural linkers are known in the art and can be adapted for use in the present invention.

(e) Expression system

Peptides of the invention may be developed using a biological expression system. The use of these systems allows the production of large libraries of random peptide sequences and the screening of these libraries for peptide sequences that bind to particular proteins. Libraries may be produced by cloning synthetic DNAthat encodes random peptide sequences into appropriate expression vectors (see Christian et al 1992, J. Mol. Biol. 227:711; Devlin et al, 1990 Science 249:404; Cwirla et al 1990, Proc. Natl. Acad, Sci. USA, 87:6378). Libraries may also be constructed by concurrent synthesis of overlapping peptides (see U.S. Pat. No. 4,708,871).

The peptides and chimeric proteins of the invention may be converted into pharmaceutical salts by reacting with inorganic acids such as hydrochloric acid, sulfuric acid, hydrobromic acid, phosphoric acid, etc., or organic acids such as formic acid, acetic acid, propionic acid, glycolic acid, lactic acid, pyruvic acid, oxalic acid, succinic acid, malic acid, tartaric acid, citric acid, benzoic acid, salicylic acid, benezenesulfonic acid, and toluenesulfonic acids.

Nucleic Acids

The invention also includes nucleic acids encoding the peptides described herein. In one embodiment, the invention includes an isolated nucleic acid comprising a coding sequence which encodes an activator of WNT signaling. In one embodiment the nucleotide sequence comprises a coding sequence which encodes b- catenin. In another embodiment, the nucleotide sequence comprises a coding sequence which encodes Lin28a. In another embodiment, the nucleotide sequence comprises a coding sequence which encodes Lin28b. In another embodiment, the nucleotide sequence comprises a coding sequence which encodes Notch. In another embodiment, the nucleotide sequence comprises a coding sequence which encodes Ascll.

The nucleotide sequences encoding b-catenin, Lin28a Lin28b, Notch, or Ascll can alternatively comprise sequence variations with respect to the original nucleotide sequences, for example, substitutions, insertions and/or deletions of one or more nucleotides, with the condition that the resulting polynucleotide encodes a polypeptide according to the invention which has the effect of increasing or activating WNT signaling.

In another embodiment, the invention includes a nucleic acid molecule encoding at least one transcription factor selected from the group consisting of Otx2, Crx, Nrl, Nr2e3, and NueroD. In specific embodiments, the nucleic acid molecule encodes Otx2. In specific embodiments, the nucleic acid molecule encodes Crx. In specific embodiments, the nucleic acid molecule encodes Nrl.

The nucleic acid molecules encoding Otx2, Crx, Nrl, Nr2e3, or NueroD can alternatively comprise sequence variations with respect to the original (e.g., wild type) nucleic acid molecules encoding Otx2, Crx, Nrl, Nr2e3, or NueroD, respectively, for example, substitutions, insertions and/or deletions of one or more nucleotides, with the condition that the resulting polynucleotide encodes a polypeptide according to the invention which has the effect of expressing Otx2, Crx, Nrl, Nr2e3, or NueroD capable of causing MG cell differentiation as described here.

In one embodiment, the invention relates to a construct, comprising a nucleotide sequence encoding Otx2, Crx, Nrl, Nr2e3, NueroD, or an activator of WNT signaling, or derivative thereof. In a particular embodiment, the construct is operatively bound to transcription (e.g., a promoter), and optionally translation, control elements. The construct can incorporate an operatively bound regulatory sequence of the expression of the nucleotide sequence of the invention, thus forming an expression cassette. In certain embodiments, the transcription control element (e.g., a promoter), is specific to particular cell type (e.g., MG cells). For example, nucleic acids described herein can be operably linked to a promoter for specific expression (i.e. , transcription) of the nucleic acid in MG cells. A nonlimiting example of a promoter for specific expression of a nucleic acid in MG cells is the GFAP promoter (see, e.g., Brenner et al, J Neurosci 14(3): 1070-7, 1994; Kuzmanovic et al, Retinal Cell Biology 44(8):3606-36l3, 2003). In certain embodiments, the GFAP promoter comprises the sequence:

agATctaACATATcCtggtGTgGAGTAGGGGACGCTGcTCTGACAGAGGcTCGGGGG CCtGAGCTGgcT

CTGTGAGCTGGGGAGGAGGCAGACAgCCAGGCCtTTGTcTGCAAGCAGACCTGGCAG CATTGGGCTGgC CGCCCCCCAGGgCCTCCTCTTCATGCCCAGTGAATGACTCACCTTGGCACAGACACAATG TTCGGGGTG GGCACAGTGCCTGCTTCCCGCCGCACCCCAGCCCCCCTCAAATGCCTTCCGAGAAGCCCA TTGAGCAGG GGGCTTGCATTGCACCCCAGCCTGACAGCCTGGCATCTTGGGATAAAAGCAGCACAGCCC CCTAGGGGC

TGCCCTTGCTGTGTGGCGCCACCGGCGGTGGAGAACAAGGCTCTATTCAGCCTGTGC CCAGGAAAGGGG ATCAGGGGATGCCCAGGCATGGACAGTGGGTGGCAGGGGGGGAGAGGAGGGCTGTCTGCT TCCCAGAAG TCCAAGGACACAAATGGGTGAGGGGAGAGCTCTCCCCATAGCTGGGCTGCGGCCCAACCC CACCCCCTC AGGCTATGCCAGGGGGT GTTGCCAGGGGCACCCGGGCATCGCCAGTCTAGCCCACTCCTTCATAAAGCC CTCGCATCCCAGGAGCGAGCAGAGCCAGAGCAGGTTGGAGAGGAGACGCATCACCTCCGC TGCTCGCGG

GGATCC (SEQ ID NO: 8).

A nucleic acid sequence of the invention may be prepared using recombinant DNA methods. Accordingly, a nucleic acid molecule which encodes an activator of WNT signaling, including, but not limited to b-catenin, Lin28a, and Lin28b, or which encodes Otx2, Crx, Nrl, Nr2e3, or NueroD, Notch, or Ascll, may be incorporated in a known manner into an appropriate expression vector which ensures good expression of the protein. In specific embodiments, the expression vector is specifically expressed in retinal cells (e.g., AAV-ShHlO (see, e.g.. Klimczak el al, PLoS One, 2009 and US Patent No. 8,663,624, each of which is incorporated by reference herein in its entirety)). In specific embodiments, the expression vector is a vector described in U.S. Patent No. 8,663,624, which is incorporated by reference herein in its entirety.

Therefore, in another aspect, the invention relates to a vector, comprising the nucleotide sequence of the invention or the construct of the invention. The choice of the vector will depend on the host cell in which it is to be subsequently introduced. In a particular embodiment, the vector of the invention is an expression vector. Suitable host cells include a wide variety of prokaryotic and eukaryotic host cells. In specific embodiments, the expression vector is selected from the group consisting of a viral vector, a bacterial vector and a mammalian cell vector. Prokaryote- and/or eukaryote- vector based systems can be employed for use with the present invention to produce polynucleotides, or their cognate polypeptides. Many such systems are commercially and widely available.

Further, the expression vector may be provided to a cell in the form of a viral vector. Viral vector technology is well known in the art and is described, for example, in Sambrook et al. (2001), and in Ausubel et al. (1997), and in other virology and molecular biology manuals. Viruses, which are useful as vectors include, but are not limited to, retroviruses, adenoviruses, adeno-associated viruses (e.g., ShHlO), herpes viruses, and lentiviruses. In general, a suitable vector contains an origin of replication functional in at least one organism, a promoter sequence, convenient restriction endonuclease sites, and one or more selectable markers. (See, e.g., WO 01/96584;

WO 01/29058; and U.S. Pat. No. 6,326,193).

In specific embodiments, the viral vector is a viral vector that specifically infects a retinal cell. In certain embodiments, a viral vector specifically infects a retinal cell if exhibits at least 5-fold, at least 10-fold, at least 15-fold, at least 20-fold, at least 25-fold, at least 50-fold, or more than 50-fold, increased infectivity of a retinal cell compared to the infectivity of a non-retinal cell. In specific embodiments, the viral vector that specifically infects a retinal cell is an AAV. In specific embodiments, the viral vector that specifically infects a retinal cell is an AAV described in U.S. Patent No. 8,663,624, which is incorporated by reference herein in its entirety. In specific embodiments in which the viral vector is an AAV, the capsid of the AAV viral vector comprises an amino acid sequence having at least about 85%, at least about 90%, at least about 95%, at least about 98%, at least about 99%, or 100%, amino acid sequence identity to the ShHlO amino acid sequence of SEQ ID NO:7:

1 MAADGYLPDW LEDNLSEGIR EWWDLKPGAP KPKANQQKQD DGRGLVLPGY KYLGPFNGLD

61 KGEPVNAADA AALEHDKAYD QQLKAGDNPY LRYNHADAEF QERLQEDTS F GGNLGRAVFQ

121 AKKRVLEPFG LVEEGAKTAP GKKRPVEQSP QEPDS SSGI G KTGQQPAKKR LNFGQTGDSE

181 SVPDPQPLGE PPATPAAVGP TTMASGGGAP MADNNEGADG VGNASGNWHC DSTWLGDRVI

241 TTSTRTWALP TYNNHLYKQI S SASTGASND NHYFGYSTPW GYFDFNRFHC HFSPRDWQRL

301 INNNWGFRPK RLNFKLFNVQ VKEVTTNDGV TTIANNLTST VQVFSDSEYQ LPYVLGSAHQ

361 GCLPPFPADV FMI PQYGYLT LNNGSQAVGR S SFYCLEYFP SQMLRTGNNF TFSYTFEDVP

421 FHS SYAHSQS LDRLMNPLID QYLYYLNRTQ DQSGSAQNKD LLFSRGS PAG MSVQPKNWLP

501 GPCYRQQRVS KTKTDNNNSN FTWTGASKYN LNGRESI INP GTAMASHKDD KNKFFPMSGV

561 MI FGKESAGA SNTALDNVMI TDEEEI KATN PVATERFGTV AVNLQSS STD PATGDVHVMG

621 ALPGMVWQDR DVYLQGPIWA KI PHTDGHFH PSPLMGGFGL KNPPPQI LI K NTPVPANPPA

701 EFSATKFAS F ITQYSTGQVS VEIEWELQKE NSKRWNPEVQ YTSNYAKSAN VD FTVDNNGL

7 61 YTEPRPI GTR YLTRPL (SEQ ID NO:7). In specific embodiments, the viral vector is AAV-ShHlO.

Vectors suitable for the insertion of the polynucleotides are vectors derived from expression vectors in prokaryotes such as pUCl8, pUCl9, Bluescript and the derivatives thereof, mpl8, mpl9, pBR322, pMB9, ColEl, pCRl, RP4, phages and

“shuttle” vectors such as pSA3 and pAT28, expression vectors in yeasts such as vectors of the type of 2 micron plasmids, integration plasmids, YEP vectors, centromere plasmids and the like, expression vectors in insect cells such as vectors of the pAC series and of the pVL, expression vectors in plants such as pIBI, pEarleyGate, pAVA, pCAMBIA, pGSA, pGWB, pMDC, pMY, pORE series and the like, and expression vectors in eukaryotic cells based on viral vectors (adenoviruses, viruses associated to adenoviruses such as retroviruses and, particularly, lentiviruses) as well as non- viral vectors such as pSilencer 4.1-CMV (Ambion), pcDNA3, pcDNA3. l/hyg, pHMCV/Zeo, pCR3. l, pEFI/His, pIND/GS, pRc/HCMV2, pSV40/Zeo2, pTRACER-HCMV, pUB6/V5-His, pVAXl, pZeoSV2, pCI, pSVL and PKSV-10, pBPV-l, pML2d and pTDTl. In a preferred embodiment, the vector is the MG cell specific ShHlO vector.

By way of illustration, the vector in which the nucleic acid sequence is introduced can be a plasmid which is or is not integrated in the genome of a host cell when it is introduced in the cell. Illustrative, non-limiting examples of vectors in which the nucleotide sequence of the invention or the gene construct of the invention can be inserted include a tet-on inducible vector for expression in eukaryote cells.

The vector may be obtained by conventional methods known by persons skilled in the art (Sambrook et al,“Molecular cloning, a Laboratory Manual”, 2nd ed., Cold Spring Harbor Laboratory Press, N.Y., 1989 Vol 1-3] In a particular embodiment, the vector is a vector useful for transforming animal cells.

The recombinant expression vectors may also contain nucleic acid molecules which encode a portion which provides increased expression of the recombinant protein; increased solubility of the protein; and/or aid in the purification of the protein by acting as a ligand in affinity purification. For example, a proteolytic cleavage site may be inserted in the recombinant peptide to allow separation of the recombinant protein from the fusion portion after purification of the fusion protein. Examples of fusion expression vectors include pGEX (Amrad Corp., Melbourne, Australia), pMAL (New England Biolabs, Beverly, Mass.) and pRIT5 (Pharmacia, Piscataway, N.J.) which fuse glutathione S-transferase (GST), maltose E binding protein, or protein A, respectively, to the recombinant protein.

Additional promoter elements, i.e., enhancers, regulate the frequency of transcriptional initiation. Typically, these are located in the region 30-110 bp upstream of the start site, although a number of promoters have recently been shown to contain functional elements downstream of the start site as well. The spacing between promoter elements frequently is flexible, so that promoter function is preserved when elements are inverted or moved relative to one another. In the thymidine kinase (tk) promoter, the spacing between promoter elements can be increased to 50 bp apart before activity begins to decline. Depending on the promoter, it appears that individual elements can function either co-operatively or independently to activate transcription.

A promoter may be one naturally associated with a gene or polynucleotide sequence, as may be obtained by isolating the 5' non-coding sequences located upstream of the coding segment and/or exon. Such a promoter can be referred to as “endogenous.” Similarly, an enhancer may be one naturally associated with a polynucleotide sequence, located either downstream or upstream of that sequence. Alternatively, certain advantages will be gained by positioning the coding polynucleotide segment under the control of a recombinant or heterologous promoter, which refers to a promoter that is not normally associated with a polynucleotide sequence in its natural environment. A recombinant or heterologous enhancer refers also to an enhancer not normally associated with a polynucleotide sequence in its natural environment. Such promoters or enhancers may include promoters or enhancers of other genes, and promoters or enhancers isolated from any other prokaryotic, viral, or eukaryotic cell, and promoters or enhancers not“naturally occurring,” /. e.. containing different elements of different transcriptional regulatory regions, and/or mutations that alter expression. In addition to producing nucleic acid sequences of promoters and enhancers synthetically, sequences may be produced using recombinant cloning and/or nucleic acid amplification technology, including PCR™, in connection with the compositions disclosed herein (U.S. Patent 4,683,202, U.S. Patent 5,928,906). Furthermore, it is contemplated the control sequences that direct transcription and/or expression of sequences within non-nuclear organelles such as mitochondria, chloroplasts, and the like, can be employed as well.

Naturally, it will be important to employ a promoter and/or enhancer that effectively directs the expression of the DNA segment in the cell type, organelle, and organism chosen for expression. Those of skill in the art of molecular biology generally know how to use promoters, enhancers, and cell type combinations for protein expression, for example, see Sambrook et al. (2001). The promoters employed may be constitutive, tissue-specific, inducible, and/or useful under the appropriate conditions to direct high level expression of the introduced DNA segment, such as is advantageous in the large-scale production of recombinant proteins and/or peptides. The promoter may be heterologous or endogenous.

A promoter sequence exemplified in the experimental examples presented herein is the GFAP (glial fibrillary acidic protein) promoter (e.g., SEQ ID NO: 8). This promoter sequence is capable of driving high levels of expression of any

polynucleotide sequence operatively linked thereto in MG cells. However, other constitutive promoter sequences may also be used, including, but not limited to the cytomegalovirus (CMV) promoter, simian virus 40 (SV40) early promoter, mouse mammary tumor virus (MMTV), human immunodeficiency virus (HIV) long terminal repeat (LTR) promoter, Moloney virus promoter, the avian leukemia virus promoter, Epstein-Barr virus immediate early promoter, Rous sarcoma virus promoter, as well as human gene promoters such as, but not limited to, the actin promoter, the myosin promoter, the hemoglobin promoter, and the muscle creatine promoter. Further, the invention should not be limited to the use of constitutive promoters. Inducible promoters are also contemplated as part of the invention. The use of an inducible promoter in the invention provides a molecular switch capable of turning on expression of the polynucleotide sequence which it is operatively linked when such expression is desired, or turning off the expression when expression is not desired. Examples of inducible promoters include, but are not limited to a metallothionine promoter, a glucocorticoid promoter, a progesterone promoter, and a tetracycline promoter. Further, the invention includes the use of a tissue specific promoter, which promoter is active only in a desired tissue. MG specific promoters include, but are not limited to, the RLBP 1 promoter, the CD44 promoter and the GFAP promoter sequences.

In one embodiment, the expression of the nucleic acid may be externally controlled. For example, the expression may be externally controlled using a doxycycline Tet-On system.

The recombinant expression vectors may also contain a selectable marker gene which facilitates the selection of transformed or transfected host cells. Suitable selectable marker genes are genes encoding proteins such as G418 and hygromycin which confer resistance to certain drugs, B-galactosidase, chloramphenicol acetyltransferase, firefly luciferase, or an immunoglobulin or portion thereof such as the Fc portion of an immunoglobulin preferably IgG. The selectable markers may be introduced on a separate vector from the nucleic acid of interest.

Reporter genes are used for identifying potentially transfected cells and for evaluating the functionality of regulatory sequences. Reporter genes that encode for easily assayable proteins are well known in the art. In general, a reporter gene is a gene that is not present in or expressed by the recipient organism or tissue and that encodes a protein whose expression is manifested by some easily detectable property, e.g., enzymatic activity. Expression of the reporter gene is assayed at a suitable time after the DNAhas been introduced into the recipient cells.

Suitable reporter genes may include genes encoding luciferase, beta- galactosidase, chloramphenicol acetyl transferase, secreted alkaline phosphatase, or the green fluorescent protein gene (see, e.g., Ui-Tei el al, 2000 FEBS Lett. 479:79- 82). Suitable expression systems are well known and may be prepared using well known techniques or obtained commercially. Internal deletion constructs may be generated using unique internal restriction sites or by partial digestion of non-unique restriction sites. Constructs may then be transfected into cells that display high levels of siRNA polynucleotide and/or polypeptide expression. In general, the construct with the minimal 5' flanking region showing the highest level of expression of reporter gene is identified as the promoter. Such promoter regions may be linked to a reporter gene and used to evaluate agents for the ability to modulate promoter-driven transcription.

Recombinant expression vectors may be introduced into host cells to produce a recombinant cell. The cells can be prokaryotic or eukaryotic. The vector of the invention can be used to transform eukaryotic cells such as yeast cells,

Saccharomyces cerevisiae, or mammal cells for example epithelial kidney 293 cells or U20S cells, or prokaryotic cells such as bacteria, Escherichia coli or Bacillus subtilis, for example. Nucleic acid can be introduced into a cell using conventional techniques such as calcium phosphate or calcium chloride co-precipitation, DEAE-dextran- mediated transfection, lipofectin, electroporation or microinjection. Suitable methods for transforming and transfecting host cells may be found in Sambrook el al. (Molecular Cloning: A Laboratory Manual, 2nd Edition, Cold Spring Harbor Laboratory press (1989)), and other laboratory textbooks.

For example, a protein of the invention may be expressed in bacterial cells such as E. coli, insect cells (using baculovirus), yeast cells or mammalian cells. Other suitable host cells can be found in Goeddel, Gene Expression Technology: Methods in Enzymology 185, Academic Press, San Diego, Calif. (1991).

Inhibitor Compositions

One of skill in the art will realize that diminishing the amount or activity of a molecule that itself diminishes the amount or activity of WNT signaling can serve to increase the amount or activity of WNT signaling. Therefore, in one embodiment, the invention provides an inhibitor of one or more negative regulators of WNT signaling or WNT signaling effectors. In various embodiments, the compositions of the invention decrease the amount of polypeptide, the amount of mRNA, the amount of enzymatic activity, or a combination thereof of one or more negative regulators of

WNT signaling. In one embodiments, the compositions of the invention decrease the amount of polypeptide, the amount of mRNA, the amount of enzymatic activity, or a combination thereof of GSK3 . In one embodiment, the composition inhibits one or more let-7 miRNA.

It will be understood by one skilled in the art, based upon the disclosure provided herein, that a decrease in the level of one or more negative regulators of WNT signaling encompasses the decrease in the expression, including transcription, translation, or both. The skilled artisan will also appreciate, once armed with the teachings of the present invention, that a decrease in the level of one or more negative regulators of WNT signaling includes a decrease in the activity of the protein. Thus, decrease in the level or activity of one or more negative regulators of WNT signaling includes, but is not limited to, decreasing the amount of polypeptide of one or more negative regulators of WNT signaling, and decreasing transcription, translation, or both, of a nucleic acid encoding one or more negative regulators of WNT signaling; and it also includes decreasing any activity of one or more negative regulators of WNT signaling. In one embodiment, the present invention provides a composition for inducing MG proliferation, wherein the composition inhibits a negative regulator of WNT signaling. In certain embodiments, the composition inhibits the expression, activity, or both of a WNT signaling regulator. In one embodiment, a negative regulator of WNT signaling is GSK3 . Therefore, in one embodiment an inhibitor of the invention inhibits GSK3 . In one embodiment, a negative regulator of Lin28, a protein in the WNT signaling pathway, is let-7 miRNA. Therefore, in various embodiments, the composition inhibits the expression, activity, or both of one or more let-7 miRNA. Human let-7 miRNA include, but are not limited to, hsa-let-7a-l, hsa-let-7a-2, hsa-let- 7a-3, hsa-let-7b, hsa-let-7c, hsa-let-7d, hsa-let-7e, hsa-let-7f-l, hsa-let-7f-2, hsa-let-7g and hsa-let-7i. In one embodiment, the composition inhibits hsa-let-7b.

An inhibitor may be one of, but is not limited to, a small interfering RNA (siRNA), a microRNA, an antisense nucleic acid, a ribozyme, an expression vector encoding a transdominant negative mutant, an intracellular antibody, a peptide and a small molecule. In one embodiment, one or more of a negative regulator of WNT signaling can be inhibited by way of inactivating and/or sequestering the protein. As such, inhibiting the effects of a negative regulator of WNT signaling can be accomplished by using a transdominant negative mutant. Alternatively an antibody specific for one or more negative regulator of WNT signaling, otherwise known as an inhibitor of one or more negative regulator of WNT signaling may be used. In another embodiment, the inhibitor is a protein and/or compound having the desirable property of interacting with one or more negative regulator of WNT signaling and thereby sequestering the protein. In one embodiment, the composition of the invention is used in combination with other therapeutic agents. siRNA

In one embodiment, siRNA is used to decrease the level of one or negative regulator of WNT signaling. RNA interference (RNAi) is a phenomenon in which the introduction of double-stranded RNA (dsRNA) into a diverse range of organisms and cell types causes degradation of the complementary mRNA. In the cell, long dsRNAs are cleaved into short 21-25 nucleotide small interfering RNAs, or siRNAs, by a ribonuclease known as Dicer. The siRNAs subsequently assemble with protein components into an RNA-induced silencing complex (RISC), unwinding in the process. Activated RISC then binds to complementary transcript by base pairing interactions between the siRNA antisense strand and the mRNA. The bound mRNA is cleaved and sequence specific degradation of mRNA results in gene silencing. See, for example, U.S. Patent No. 6,506,559; Fir e et al., 1998, Nature 39l(l9):306-3ll;

Timmons et al, 1998, Nature 395:854; Montgomery et al, 1998, TIG 14 (7):255-258; David R. Engelke, Ed., RNA Interference (RNAi) Nuts & Bolts of RNAi Technology, DNA Press, Eagleville, PA (2003); and Gregory J. Hannon, Ed., RNAi A Guide to Gene Silencing, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY (2003). Soutschek et al. (2004, Nature 432: 173-178) describe a chemical modification to siRNAs that aids in intravenous systemic delivery. Optimizing siRNAs involves consideration of overall G/C content, C/T content at the termini, Tm and the nucleotide content of the 3’ overhang. See, for instance, Schwartz et al, 2003, Cell, 115: 199-208 and Khvorova et al, 2003, Cell 15 115:209-216. Therefore, the present invention also includes methods of decreasing levels of one or more of a negative regulator of WNT signaling at the protein level using RNAi technology.

In other related aspects, the invention includes an isolated nucleic acid encoding an inhibitor, wherein an inhibitor such as an siRNA or antisense molecule, inhibits the desired negative regulator of WNT signaling, operably linked to a nucleic acid comprising a promoter/regulatory sequence such that the nucleic acid is preferably capable of directing expression of the protein encoded by the nucleic acid. Thus, the invention encompasses expression vectors and methods for the introduction of exogenous DNA into cells with concomitant expression of the exogenous DNA in the cells such as those described, for example, in Sambrook et al. (2001, Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory, New York), and in Ausubel et al. (1997, Current Protocols in Molecular Biology, John Wiley & Sons, New York) and as described elsewhere herein.

In another aspect, the invention includes a vector comprising an siRNA or antisense polynucleotide. Preferably, the siRNA or antisense polynucleotide is capable of inhibiting the expression of the desired negative regulator of WNT signaling. The incorporation of a desired polynucleotide into a vector and the choice of vectors is well- known in the art as described in, for example, Sambrook et ctl, supra, and Ausubel et al. , supra, and elsewhere herein.

The siRNA or antisense polynucleotide can be cloned into a number of types of vectors as described elsewhere herein. For expression of the siRNA or antisense polynucleotide, at least one module in each promoter functions to position the start site for RNA synthesis. In one embodiment, a promoter for expression in MG cells is the GFAP promoter. In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO: 8. In one embodiment, the siRNA or antisense

polynucleotide can be cloned into the ShHlO-GFAP vector for expression in MG cells.

In order to assess the expression of the siRNA or antisense polynucleotide, the expression vector to be introduced into a cell can also contain either a selectable marker gene or a reporter gene or both to facilitate identification and selection of expressing cells from the population of cells sought to be transfected or infected through viral vectors. In other embodiments, the selectable marker may be carried on a separate piece of DNA and used in a co-transfection procedure. Both selectable markers and reporter genes may be flanked with appropriate regulatory sequences to enable expression in the host cells. Useful selectable markers are known in the art and include, for example, antibiotic-resistance genes, such as neomycin resistance and the like.

In one embodiment, the invention encompasses methods for delivery of a siRNA or a combination of siRNAs of the invention to a cell in need thereof.

Antisense nucleic acids

In one embodiment of the invention, an antisense nucleic acid sequence which is expressed by a plasmid vector is used to inhibit one or more negative regulator of WNT signaling. The antisense expressing vector is used to transfect a mammalian cell or the mammal itself, thereby causing reduced endogenous expression of one or more negative regulator of WNT signaling.

Antisense molecules and their use for inhibiting gene expression are well known in the art (see, e.g.. Cohen, 1989, In: Oligodeoxyribonucleotides, Antisense Inhibitors of Gene Expression, CRC Press). Antisense nucleic acids are DNA or RNA molecules that are complementary, as that term is defined elsewhere herein, to at least a portion of a specific mRNA molecule (Weintraub, 1990, Scientific American 262:40). In the cell, antisense nucleic acids hybridize to the corresponding mRNA, forming a double- stranded molecule thereby inhibiting the translation of genes.

The use of antisense methods to inhibit the translation of genes is known in the art, and is described, for example, in Marcus-Sakura (1988, Anal. Biochem. 172:289). Such antisense molecules may be provided to the cell via genetic expression using DNA encoding the antisense molecule as taught by Inoue, 1993, U.S. Patent No. 5,190,931.

Alternatively, antisense molecules of the invention may be made synthetically and then provided to the cell. Antisense oligomers of between about 10 to about 30, and more preferably about 15 nucleotides, are preferred, since they are easily synthesized and introduced into a target cell. Synthetic antisense molecules contemplated by the invention include oligonucleotide derivatives known in the art which have improved biological activity compared to unmodified oligonucleotides (see U.S. Patent No. 5,023,243).

Ribozvmes

Ribozymes and their use for inhibiting gene expression are also well known in the art (see, e.g., Cech et a/., 1992, J. Biol. Chem. 267: 17479-17482; Hampel et a/., 1989, Biochemistry 28:4929-4933; Eckstein et a/., International Publication No. WO 92/07065; Altman et a/., U.S. Patent No. 5,168,053). Ribozymes are RNA molecules possessing the ability to specifically cleave other single-stranded RNA in a manner analogous to DNA restriction endonucleases. Through the modification of nucleotide sequences encoding these RNAs, molecules can be engineered to recognize specific nucleotide sequences in an RNA molecule and cleave it (Cech, 1988, J. Amer. Med. Assn. 260:3030). A major advantage of this approach is the fact that ribozymes are sequence-specific.

There are two basic types of ribozymes, namely, tetrahymena-type

(Hasselhoff, 1988, Nature 334:585) and hammerhead-type. Tetrahymena-type ribozymes recognize sequences which are four bases in length, while hammerhead- type ribozymes recognize base sequences 11-18 bases in length. The longer the sequence, the greater the likelihood that the sequence will occur exclusively in the target mRNA species. Consequently, hammerhead-type ribozymes are preferable to tetrahymena-type ribozymes for inactivating specific mRNA species, and 18-base recognition sequences are preferable to shorter recognition sequences which may occur randomly within various unrelated mRNA molecules.

In one embodiment of the invention, a ribozyme is used to inhibit a negative regulator of WNT signaling. Ribozymes useful for inhibiting the expression of a target molecule may be designed by incorporating target sequences into the basic ribozyme structure which are complementary, for example, to the mRNA sequence of the negative regulator of WNT signaling of the present invention. Ribozymes targeting a desired negative regulator of WNT signaling may be synthesized using commercially available reagents (Applied Biosystems, Inc., Foster City, CA) or they may be genetically expressed from DNA encoding them. Small Molecules

When the inhibitor of the invention is a small molecule, a small molecule inhibitor of one or more negative regulator of WNT signaling may be obtained using standard methods known to the skilled artisan. Such methods include chemical organic synthesis or biological means. Biological means include purification from a biological source, recombinant synthesis and in vitro translation systems, using methods well known in the art.

Combinatorial libraries of molecularly diverse chemical compounds potentially useful in treating a variety of diseases and conditions are well known in the art as are method of making the libraries. The method may use a variety of techniques well-known to the skilled artisan including solid phase synthesis, solution methods, parallel synthesis of single compounds, synthesis of chemical mixtures, rigid core structures, flexible linear sequences, deconvolution strategies, tagging techniques, and generating unbiased molecular landscapes for lead discovery vs. biased structures for lead development.

In a general method for small library synthesis, an activated core molecule is condensed with a number of building blocks, resulting in a combinatorial library of covalently linked, core-building block ensembles. The shape and rigidity of the core determines the orientation of the building blocks in shape space. The libraries can be biased by changing the core, linkage, or building blocks to target a characterized biological structure (“focused libraries”) or synthesized with less structural bias using flexible cores.

In one embodiment, the small molecule is able to inhibit one or more negative regulator of WNT signaling. In one embodiment, the small molecule is able to inhibit GSKSp. The inhibitor may also be a hybrid or fusion composition to facilitate, for instance, delivery to target cells or efficacy. In one embodiment, a hybrid composition may comprise a cell-specific targeting sequence. For example, in one embodiment, the inhibitor is targeted to MG cells.

Antibodies

As will be understood by one skilled in the art, any antibody that can recognize and bind to an antigen of interest is useful in the present invention. In one embodiment, an antigen of interest is a negative regulator of WNT signaling. In one embodiment, an antigen is GSK3 . In one embodiment, an antigen is let-7 miRNA, and an antibody that can recognize let-7 miRNA is an anti-miR.

Methods of making and using antibodies are well known in the art. For example, polyclonal antibodies useful in the present invention are generated by immunizing rabbits according to standard immunological techniques well-known in the art (see, e.g. , Harlow el al. , 1988, In: Antibodies, A Laboratory Manual, Cold Spring Harbor, NY).

The generation of polyclonal antibodies is accomplished by inoculating the desired animal with the antigen and isolating antibodies which specifically bind the antigen therefrom using standard antibody production methods such as those described in, for example, Harlow et al. (1988, In: Antibodies, A Laboratory Manual, Cold Spring Harbor, NY).

Monoclonal antibodies directed against full length or peptide fragments of a protein or peptide may be prepared using any well-known monoclonal antibody preparation procedures, such as those described, for example, in Harlow et al. (1988, In: Antibodies, A Laboratory Manual, Cold Spring Harbor, NY) and in Tuszynski et al. (1988, Blood, 72: 109-115). Quantities of the desired peptide may also be synthesized using chemical synthesis technology. Alternatively, DNA encoding the desired peptide may be cloned and expressed from an appropriate promoter sequence in cells suitable for the generation of large quantities of peptide. Monoclonal antibodies directed against the peptide are generated from mice immunized with the peptide using standard procedures as referenced herein.

Nucleic acid encoding the monoclonal antibody obtained using the procedures described herein may be cloned and sequenced using technology which is available in the art, and is described, for example, in Wright et al. (1992, Critical Rev. Immunol. 12: 125-168), and the references cited therein. Further, the antibody of the invention may be“humanized” using the technology described in, for example, Wright et al. , and in the references cited therein, and in Gu et al. (1997, Thrombosis and

Hematocyst 77:755-759), and other methods of humanizing antibodies well-known in the art or to be developed.

The present invention also includes the use of humanized antibodies specifically reactive with epitopes of an antigen of interest. The humanized antibodies of the invention have a human framework and have one or more complementarity determining regions (CDRs) from an antibody, typically a mouse antibody, specifically reactive with an antigen of interest. When the antibody used in the invention is humanized, the antibody may be generated as described in Queen, et al. (U.S. Patent No. 6, 180,370), Wright et al. , (supra) and in the references cited therein, or in Gu et al. (1997, Thrombosis and Hematocyst 77(4):755-759). The method disclosed in Queen et al. is directed in part toward designing humanized

immunoglobulins that are produced by expressing recombinant DNA segments encoding the heavy and light chain complementarity determining regions (CDRs) from a donor immunoglobulin capable of binding to a desired antigen, such as an epitope on an antigen of interest, attached to DNA segments encoding acceptor human framework regions. Generally speaking, the invention in the Queen patent has applicability toward the design of substantially any humanized immunoglobulin. Queen explains that the DNA segments will typically include an expression control DNA sequence operably linked to the humanized immunoglobulin coding sequences, including naturally-associated or heterologous promoter regions. The expression control sequences can be eukaryotic promoter systems in vectors capable of transforming or transfecting eukaryotic host cells or the expression control sequences can be prokaryotic promoter systems in vectors capable of transforming or transfecting prokaryotic host cells. Once the vector has been incorporated into the appropriate host, the host is maintained under conditions suitable for high level expression of the introduced nucleotide sequences and as desired the collection and purification of the humanized light chains, heavy chains, light/heavy chain dimers or intact antibodies, binding fragments or other immunoglobulin forms may follow (Beychok, Cells of Immunoglobulin Synthesis, Academic Press, New York, (1979), which is incorporated herein by reference).

The invention also includes functional equivalents of the antibodies described herein. Functional equivalents have binding characteristics comparable to those of the antibodies, and include, for example, hybridized and single chain antibodies, as well as fragments thereof. Methods of producing such functional equivalents are disclosed in PCT Application WO 93/21319 and PCT Application WO 89/09622.

Functional equivalents include polypeptides with amino acid sequences substantially the same as the amino acid sequence of the variable or hypervariable regions of the antibodies.“Substantially the same” amino acid sequence is defined herein as a sequence with at least 70%, preferably at least about 80%, more preferably at least about 90%, even more preferably at least about 95%, and most preferably at least 99% homology to another amino acid sequence (or any integer in between 70 and 99), as determined by the FASTA search method in accordance with Pearson and Lipman, 1988 Proc. Nat’l. Acad. Sci. USA 85: 2444-2448. Chimeric or other hybrid antibodies have constant regions derived substantially or exclusively from human antibody constant regions and variable regions derived substantially or exclusively from the sequence of the variable region of a monoclonal antibody from each stable hybridoma.

Single chain antibodies (scFv) or Fv fragments are polypeptides that consist of the variable region of the heavy chain of the antibody linked to the variable region of the light chain, with or without an interconnecting linker. Thus, the Fv comprises an antibody combining site.

Functional equivalents of the antibodies of the invention further include fragments of antibodies that have the same, or substantially the same, binding characteristics to those of the whole antibody. Such fragments may contain one or both Fab fragments or the F(ab')2 fragment. The antibody fragments contain all six complement determining regions of the whole antibody, although fragments containing fewer than all of such regions, such as three, four or five complement determining regions, are also functional. The functional equivalents are members of the IgG immunoglobulin class and subclasses thereof, but may be or may combine with any one of the following immunoglobulin classes: IgM, IgA, IgD, or IgE, and subclasses thereof. Heavy chains of various subclasses, such as the IgG subclasses, are responsible for different effector functions and thus, by choosing the desired heavy chain constant region, hybrid antibodies with desired effector function are produced. Exemplary constant regions are gamma 1 (IgGl), gamma 2 (IgG2), gamma 3 (IgG3), and gamma 4 (IgG4). The light chain constant region can be of the kappa or lambda type.

The immunoglobulins of the present invention can be monovalent, divalent or polyvalent. Monovalent immunoglobulins are dimers (HL) formed of a hybrid heavy chain associated through disulfide bridges with a hybrid light chain. Divalent immunoglobulins are tetramers (H2L2) formed of two dimers associated through at least one disulfide bridge. Inhibitors of miRNA

In an exemplary embodiment, a negative regulator of Lin28 is let-7 miRNA. Therefore, in this embodiment, the invention relates to methods of inhibiting let- 7 miRNA. However, the invention is not restricted to regulating a let-7 miRNA and therefore relates to methods of inhibiting any miRNA which functions to inhibit WNT signaling. Methods of inhibiting miRNA are generally known in the art. In one embodiment, a composition that inhibits miRNA is an anti-miR. Anti-miR antibodies appropriate for use in inhibiting miRNA are discussed elsewhere herein. In various alternative embodiments, a composition that inhibits a miRNA may be, but is not limited to, one of a miRNA sponge, a competing endogenous RNA (ceRNA), or circular RNA (circRNA) which serve to sequester the mature miRNA, disrupting endogenous miRNA: mRNA target binding. Treatment Methods

Vision loss or impairment is often due to loss or death of rod photoreceptors, and can be a concern associated with aging or a complication of disease such as diabetes. The current invention provides compositions and methods to induce formation of new rod photoreceptor cells and therefore any individual having vision loss or impairment associated with loss of rod photoreceptors can benefit from the method of the invention. Therefore, in one embodiment, the method of the invention relates to administering one or more activator and/or inhibitor compositions (e.g., a composition comprising a MG cell proliferation agent and/or a composition comprising a MG cell differentiation agent) of the invention to a subject identified as having vision loss or impairment. In one embodiment, a subject identified as having vision loss or impairment is a subject having an ophthalmic disease or degenerative eye condition. In one embodiment, an ophthalmic diseases or degenerative eye condition is one of macular degeneration, including age-related macular degeneration (AMD) and exudative or wet AMD, diabetic retinopathy, retrolental fibroplasia,

Stargardt disease, retinitis pigmentosa (RP), uveitis, Bardet-Biedl syndrome and eye cancers.

In one embodiment, the present invention provides methods of treating vision loss or impairment comprising administering an effective amount of a composition comprising an activator of WNT signaling to a subject. In one embodiment, the composition induces the proliferation of MG cells.

In one embodiment, the present invention provides methods of treating vision loss or impairment comprising administering an effective amount of a composition comprising an activator of rod photoreceptor genes to a subject. In one embodiment, the composition directs the differentiation of MG cells into rod photoreceptors.

In certain embodiments, the method comprises administering one or more compositions, where each composition comprises one or more activators or inhibitors. For example, in one embodiment, the method comprises administering a first composition comprising b-catenin and a second composition comprising one or more of Otx2, Crx, Nrl, Nr2e3 and NeuroD. In another embodiment, the method comprises administering a first composition comprising b-catenin and a second composition comprising Otx2, Crx, and Nrl. In an alternative embodiment, the method comprises administering a first composition comprising let-7 anti-miR and a second composition comprising one or more of Otx2, Crx, Nrl, Nr2e3 and NeuroD. In an alternative embodiment, the method comprises administering a first composition comprising let-7 anti-miR and a second composition comprising Otx2, Crx, and Nrl. In an alternative embodiment, the method comprises administering a first composition comprising Notch and a second composition comprising one or more of Otx2, Crx, Nrl, Nr2e3 and NeuroD. In an alternative embodiment, the method comprises administering a first composition comprising Notch and a second composition comprising Otx2, Crx, and Nrl. In an alternative embodiment, the method comprises administering a first composition comprising Ascll and a second composition comprising one or more of Otx2, Crx, Nrl, Nr2e3 and NeuroD. In an alternative embodiment, the method comprises administering a first composition comprising Ascll and a second composition comprising Otx2, Crx, and Nrl.

In certain embodiments, the method comprises administering one or more compositions, where each composition comprises one or more nucleic acid molecules encoding one or more activators or inhibitors. For example, in one embodiment, the method comprises administering a first composition comprising a nucleic acid molecule encoding b-catenin and a second composition comprising one or more nucleic acid molecules encoding one or more of Otx2, Crx, Nrl, Nr2e3 and NeuroD. In another embodiment, the method comprises administering a first composition comprising a nucleic acid molecule encoding b-catenin and a second composition comprising one or more nucleic acid molecules encoding Otx2, Crx, and Nrl. In another embodiment, the method comprises administering a first composition comprising a nucleic acid molecule encoding b-catenin and a second composition comprising a first nucleic acid molecule encoding Otx2, a second nucleic acid molecule encoding Crx, and a third nucleic acid molecule encoding Nrl. In certain embodiments, the second composition comprises a first vector comprising the first nucleic acid molecule, a second vector comprising the second nucleic acid molecule, and a third vector comprising the third nucleic acid molecule.

In an alternative embodiment, the method comprises administering a first composition comprising let-7 anti-miR and a second composition comprising one or more nucleic acid molecules encoding one or more of Otx2, Crx, Nrl, Nr2e3 and NeuroD. In an alternative embodiment, the method comprises administering a first composition comprising let-7 anti-miR and a second composition comprising one or more nucleic acid molecules encoding one or more of Otx2, Crx, and Nrl. In an alternative embodiment, the method comprises administering a first composition comprising let-7 anti-miR and a second composition comprising a first nucleic acid molecule encoding Otx2, a second nucleic acid molecule encoding Crx, and a third nucleic acid molecule encoding Nrl. In certain embodiments, the second composition comprises a first vector comprising the first nucleic acid molecule, a second vector comprising the second nucleic acid molecule, and a third vector comprising the third nucleic acid molecule.

In certain embodiments, the method comprises administering one or more compositions, where each composition comprises one or more nucleic acid molecules encoding one or more activators or inhibitors. For example, in one embodiment, the method comprises administering a first composition comprising a nucleic acid molecule encoding Notch and a second composition comprising one or more nucleic acid molecules encoding one or more of Otx2, Crx, Nrl, Nr2e3 and NeuroD. In another embodiment, the method comprises administering a first composition comprising a nucleic acid molecule encoding Notch and a second composition comprising one or more nucleic acid molecules encoding Otx2, Crx, and Nrl. In another embodiment, the method comprises administering a first composition comprising a nucleic acid molecule encoding Notch and a second composition comprising a first nucleic acid molecule encoding Otx2, a second nucleic acid molecule encoding Crx, and a third nucleic acid molecule encoding Nrl. In certain embodiments, the second composition comprises a first vector comprising the first nucleic acid molecule, a second vector comprising the second nucleic acid molecule, and a third vector comprising the third nucleic acid molecule.

The different compositions may be administered to the subject in any order and in any suitable interval. For example, in certain embodiments, the one or more compositions are administered simultaneously or near simultaneously. In certain embodiments, the method comprises a staggered administration of the one or more compositions, where a first composition is administered and a second composition administered at some later time point. Any suitable interval of administration which produces the desired therapeutic effect may be used.

Also provided herein is a method of treating vision loss or impairment in a subject, comprising: (a) administering to the subject a therapeutically effective amount of a Miiller glial (MG) cell proliferation agent; and (b) a period of time after the administering of step (a), administering to the subject a therapeutically effective amount of a MG cell differentiation agent.

In specific embodiments, the MG cell proliferation agent comprises a composition described herein that activates WNT signaling in MG cells to induce MG cell proliferation. In specific embodiments, the MG cell proliferation agent activates one or more of b-catenin and Lin28 in MG cells to induce cell proliferation. In specific embodiments, the MG cell proliferation agent comprises a protein selected from the group consisting of beta-catenin, Lin28a, and Lin28b. In specific embodiments, the MG cell proliferation agent comprises a beta-catenin protein. In specific embodiments, the MG cell proliferation agent comprises a nucleic acid encoding a protein selected from the group consisting of beta-catenin, Lin28a, and Lin28b. In specific embodiments, the MG cell proliferation agent comprises a nucleic acid encoding beta-catenin. In specific embodiments, the MG cell proliferation agent comprises a vector, wherein the vector comprises a nucleic acid encoding a protein selected from the group consisting of beta-catenin, Lin28a, and Lin28b. In specific embodiments, the MG cell the proliferation agent comprises a vector, wherein the vector comprises a nucleic acid encoding beta-catenin.

In specific embodiments, the MG cell proliferation agent activates Notch in MG cells to induce cell proliferation. In specific embodiments, the MG cell proliferation agent comprises a Notch protein. In specific embodiments, the MG cell proliferation agent comprises a nucleic acid encoding Notch. In specific

embodiments, the MG cell proliferation agent comprises a vector, wherein the vector comprises a nucleic acid encoding Notch.

In specific embodiments, the MG cell proliferation agent activates Ascll in MG cells to induce cell proliferation. In specific embodiments, the MG cell proliferation agent comprises an Ascll protein. In specific embodiments, the MG cell proliferation agent comprises a nucleic acid encoding Ascll. In specific embodiments, the MG cell proliferation agent comprises a vector, wherein the vector comprises a nucleic acid encoding Ascll.

In specific embodiments in which the MG cell proliferation agent comprises a nucleic acid, the nucleic acid is operably linked to a promoter, wherein the promoter specifically expresses the nucleic acid in MG cells. In specific embodiments, the promoter that specifically expresses the nucleic acid in MG cells comprises a glial fibrillary acidic protein (GFAP) promoter. In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO: 8.

In specific embodiments in which the MG cell proliferation agent comprises a vector, the vector is a virus or a virus-like particle. In specific embodiments in which the MG cell proliferation agent comprises a vector, the vector is an adeno-associated virus (AAV). In specific embodiments, the AAV is ShHlO.

In specific embodiments, the MG cell differentiation agent comprises a composition described herein that activates transcription of cell-specific genes to induce differentiation of cells to rod photoreceptors. In specific embodiments, the MG cell differentiation agent comprises one or more compositions that activates one or more of rhodopsin, rod a-transducin, rod arrestin, phosducin, ROM1, retinal cGMP, Guanylate Cyclase- Activating Protein Photoreceptor 2, Tubby Like Protein 1, Retinoschisin 1, G alpha 1, G gamma 1, cGMP PDE gamma, G beta 1, mUNCH9, rod PDE beta, Pleckstrin Homology Domain Retinal Protein 1, Peripherin 2, recoverin, ribeye, bassoon, and CtBP, or a combination thereof. In specific embodiments, the MG cell differentiation agent comprises one or more compositions that activates one or more transcription factors selected from the group consisting of Otx2, Crx, Nrl, Nr2e3, and NeuroD, or a combination thereof. In specific

embodiments, the MG cell differentiation agent comprises one or more compositions that activates Otx2, Crx, and Nrl.

In specific embodiments, the MG cell differentiation agent comprises at least one nucleic acid molecule encoding at least one transcription factor selected from the group consisting of Otx2, Crx, Nrl, Nr2e3, and NueroD. In specific embodiments, the differentiation agent comprises at least one nucleic acid molecule encoding Otx2, Crx, and Nrl. In specific embodiments, the MG cell differentiation agent comprises a first nucleic acid molecule, a second nucleic acid molecule, and a third nucleic acid molecule, wherein the first nucleic acid molecule encodes Otx2, wherein the second nucleic acid molecule encodes Crx, and wherein the third nucleic acid molecule encodes Nrl. In specific embodiments in which the MG cell differentiation agent comprises a nucleic acid molecule(s), the nucleic acid molecule is operably linked to a promoter, wherein the promoter specifically expresses the nucleic acid molecule in MG cells. In a specific embodiment, the promoter that specifically expresses the nucleic acid molecule in MG cells comprises a glial fibrillary acidic protein (GFAP) promoter. In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO:8.

In specific embodiments, the MG cell differentiation agent comprises a first vector, a second vector, and a third vector, wherein the first vector comprises a first nucleic acid molecule, the second vector comprises a second nucleic acid molecule, and the third vector comprises a third nucleic acid molecule, wherein the first nucleic acid m encodes a transcription factor selected from the group consisting of Otx2, Crx, Nrl, Nr2e3, and NueroD, the second nucleic acid molecule encodes a transcription factor selected from the group consisting of Otx2, Crx, Nrl, Nr2e3, and NueroD, and the third nucleic acid molecule encodes a transcription factor selected from the group consisting of Otx2, Crx, Nrl, Nr2e3, and NueroD, and wherein each of the first, second, and third nucleic acid molecules encode a different protein. For example, if the first nucleic acid molecule encodes Otx2, then neither the second nor the third nucleic acid molecule encodes Otx2. In another example if the first nucleic acid molecule encodes Otx2 and the second nucleic acid molecule encodes Crx, then the third nucleic acid molecule does not encode Otx2 or Crx. In specific embodiments, the differentiation agent comprises a first vector, a second vector, and a third vector, wherein the first vector comprises a first nucleic acid molecule, the second vector comprises a second nucleic acid molecule, and the third vector comprises a third nucleic acid molecule, wherein the first nucleic acid molecule encodes Otx2, the second nucleic acid molecule encodes Crx, and the third nucleic acid molecule encodes Nrl. In specific embodiments, the first nucleic acid molecule is operably linked to a first promoter, the second nucleic acid molecule is operably linked to a second promoter, and the third nucleic acid molecule is operably linked to a third promoter, and wherein the first, second, and third promoters express the nucleic acid molecule in MG cells. In specific embodiments, the first, second, and/or third promoters comprise a glial fibrillary acidic protein (GFAP) promoter. In certain embodiments, the GFAP promoter comprises the sequence of SEQ ID NO: 8. In specific embodiments, the first vector is a first virus or a first virus-like particle, the second vector is a second virus or a second virus-like particle, and the third vector is a third virus or a third virus-like particle. In specific embodiments, the first vector is a first adeno-associated virus (AAV), the second vector is a second AAV, and the third vector is a third AAV. In specific embodiments, the first, second, and/or third AAV is ShHlO.

In specific embodiments, the period of time of step (b) is at least one week, at least two weeks, at least three weeks, four weeks. In specific embodiments, the period of time of step (b) is two weeks.

In certain embodiments, the period of time of step (b) is less than 1 minute, less than 5 minutes, less than 10 minutes, less than one hour, less than two hours, or less than three hours. In certain embodiments in which the time of step (b) is less than three hours, the MG cell differentiation agent is formulated as a delayed release agent (e.g., the MG cell differentiation agent is not released until 1 to 5 days, 5 to 10 days,

10 to 15 days, 15 to 20 days, or 20 to 30 days after the subject is administered the MG cell differentiation agent).

In a specific embodiment, the subject is a subject identified as having vision loss or impairment. In a specific embodiment, the subject has a condition associated with vision loss or impairment due to photoreceptor loss. Non-limiting examples of conditions associated with vision loss or impairment due to photoreceptor loss include the condition is age-related macular degeneration (AMD), diabetic retinopathy, retrolental fibroplasia, Stargardt disease, retinitis pigmentosa (RP), uveitis, Bardet- Biedl syndrome and eye cancers. In a specific embodiment, the subject is a human.

Treatment Regimens

In one embodiment, the invention relates to a method of treating vision impairment or loss in a subject through administering to the individual a treatment regimen to induce MG cell differentiation into rod photoreceptor cells. In one embodiment, a composition to induce MG cell proliferation is administered to a subject prior to administration of one or more composition to induce differentiation of proliferating MG cells into rod photoreceptor cells. Thus, in specific embodiments, provided herein is a method of treating vision loss or impairment in a subject, comprising: (a) administering to the subject a therapeutically effective amount of a Miiller glial (MG) cell proliferation agent; and (b) a period of time after the administering of step (a), administering to the subject a therapeutically effective amount of a MG cell differentiation agent. In one embodiment, a treatment regimen comprises administering a composition to induce MG cell proliferation (e.g., a composition comprising a MG cell proliferation agent) at least one day, at least 2 days, at least 3 days, at least 4 days, at least 5 days, at least 6 days, at least 1 week, at least 2 weeks, at least 3 weeks, at least 4 weeks, at least one month, at least two months or more than two months prior to an administration of one or more composition to induce differentiation of MG cells (e.g., a composition comprising a MG cell differentiation agent). In one embodiment, a treatment regimen comprises administering a composition to induce MG cell proliferation (e.g., a composition comprising a MG cell proliferation agent) less than one day, less than 2 days, less than 3 days, less than 4 days, less than 5 days, less than 6 days, less than 1 week, less than 2 weeks, less than 3 weeks, less than 4 weeks, less than one month, less than two months or less than two months prior to administration of one or more composition to induce differentiation of MG cells (e.g., a composition comprising a MG cell differentiation agent). In one embodiment, a treatment regimen comprises administering a composition to induce MG cell proliferation (e.g., a composition comprising a MG cell proliferation agent) less than 1 minute, less than 5 minutes, less than 10 minutes, less than one hour, less than two hours, or less than three hours prior to administration of one or more composition to induce differentiation of MG cells (e.g., a composition comprising a MG cell differentiation agent). In certain embodiments in which the composition to induce MG cell proliferation is

administered less than 1 minute, less than 5 minutes, less than 10 minutes, less than one hour, less than two hours, or less than three hours prior to administration of one or more composition to induce differentiation of MG cells, the MG cell differentiation agent is formulated as a delayed release agent (e.g., the MG cell differentiation agent is not released until 1 to 5 days, 5 to 10 days, 10 to 15 days, 15 to 20 days, or 20 to 30 days after the subject is administered the MG cell differentiation agent).

In one embodiment, a treatment regimen comprises administering a composition to induce MG cell proliferation at least once prior to administration of one or more compositions to induce differentiation of MG cells. In one embodiment, a treatment regimen comprises administering a composition to induce MG cell proliferation at least once daily for at least 1 day, at least 7 days, at least 10 days, at least 1 month, at least 2 months, at least 3 months or more than 3 months prior to administration of one or more compositions to induce differentiation of MG cells.

In one embodiment, a treatment regimen comprises administering one or more compositions to induce differentiation of MG cells at least once following

administration of a composition to induce MG cell proliferation. In one embodiment, a treatment regimen comprises administering a composition to induce differentiation of MG cells at least once daily for at least 1 day, at least 7 days, at least 10 days, at least 1 month, at least 2 months, at least 3 months or more than 3 months following administration of a composition to induce MG cell proliferation.

In one embodiment, a treatment regimen includes multiple intravitreal injections of the compositions spaced over several days, weeks, months, a year, or even several years. Therefore, in one embodiment, a treatment regimen includes administering a composition to induce MG cell proliferation to the same subject multiple times spaced over several days, weeks, months, a year, or several years. In one embodiment, a treatment regimen includes administering a composition to induce MG cell proliferation to the same eye multiple times spaced over several days, weeks, months, a year, or several years.

In one embodiment, a treatment regimen includes administering a composition to induce differentiation of MG cells to the same subject multiple times spaced over several days, weeks, months, a year, or several years. In one embodiment, a treatment regimen includes administering a composition to induce differentiation of MG cells to the same eye multiple times spaced over several days, weeks, months, a year, or several years.

In one embodiment, a treatment regimen may include a single administration of a composition to induce MG cell proliferation and multiple administrations of a composition to induce differentiation of MG cells. In one embodiment, a treatment regimen may include multiple administrations of a composition to induce MG cell proliferation and a single administration of a composition to induce differentiation of MG cells. In one embodiment, a treatment regimen may include multiple

administrations of a composition to induce MG cell proliferation and multiple administrations of a composition to induce differentiation of MG cells.

In some embodiments, a therapeutically effective amount of a MG cell proliferation is an amount that, when administered to a subject (e.g., administered via intravitreal injection into an eye) in one or more doses, is effective to proliferate MG cells such that, subsequent administration of a therapeutically effective amount of a MG cell differentiation agent slows the progression of retinal degeneration in the subject. In some cases, a therapeutically effective amount of a MG cell differentiation agent is an amount that, when administered to a subject (e.g., administered via intravitreal injection into an eye) in one or more doses, is effective to slow the progression of retinal degeneration in the subject. For example, a therapeutically effective amount of a MG cell proliferation agent can be an amount, when administered to a subject (e.g., administered via intravitreal injection to a subject) in one or more doses, in combination with subsequent administration of a therapeutically effective amount of a MG cell differentiation agent, is effective to slow the progression of retinal degeneration by at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, or more than 80%, compared to the progression of retinal degeneration in the absence of treatment with the MG cell proliferation agent and the MG cell differentiation agent.

In some embodiments, a therapeutically effective amount of a MG cell proliferation is an amount that, when administered to a subject (e.g., administered via intravitreal injection into an eye) in one or more doses, is effective to proliferate MG cells such that, subsequent administration of a therapeutically effective amount of a MG cell differentiation agent is effective to improve vision in the subject. In some cases, a therapeutically effective amount of a MG cell differentiation agent is an amount that, when administered to a subject (e.g., administered via intravitreal injection into an eye) in one or more doses, is effective to improve vision in the subject. For example, a therapeutically effective amount of a MG cell proliferation agent can be an amount, when administered to a subject (e.g., administered via intravitreal injection to a subject) in one or more doses, in combination with subsequent administration of a therapeutically effective amount of a MG cell differentiation agent, is effective to improve vision by at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, or more than 80%, compared to the subject's vision in the absence of treatment with the MG cell proliferation agent and the MG cell differentiation agent.

In some embodiments, a therapeutically effective amount of a MG cell proliferation is an amount that, when administered to a subject (e.g., administered via intravitreal injection into an eye) in one or more doses, is effective to proliferate MG cells such that, subsequent administration of a therapeutically effective amount of a MG cell differentiation agent is effective to increase the number of rod cells in the subject. In some cases, a therapeutically effective amount of a MG cell differentiation agent is an amount that, when administered to a subject (e.g., administered via intravitreal injection into an eye) in one or more doses, is effective to increase the number of rod cells in the subject. An increase in the number of rod cells can be evaluated by looking at improvement of one or more clinical symptoms known in the art, such as, e.g., tests of functional vision, such as visual acuity, visual field, contrast sensitivity, color vision, mobility, and light sensitivity.

In some embodiments, a therapeutically effective amount of a MG cell proliferation is an amount that, when administered to a subject (e.g., administered via intravitreal injection into an eye) in one or more doses, is effective to decrease the rate of vision loss in an eye with impaired vision. In some cases, a therapeutically effective amount of a MG cell differentiation agent is an amount that, when administered to a subject (e.g., administered via intravitreal injection into an eye) in one or more doses, is effective to decrease the rate of vision loss in an eye with impaired vision.

Improvement of clinical symptoms are monitored by one or more methods known to the art, for example, tests of functional vision, such as visual acuity, visual field, contrast sensitivity, mobility, and light sensitivity. Clinical symptoms may also be monitored by anatomical or physiological means, such as indirect ophthalmoscopy, fundus photography, fluorescein angiopathy, optical coherence tomography, electroretinography (full-field, multifocal, or other), external eye examination, slit lamp biomicroscopy, applanation tonometry, pachymetry, autorefaction, or other measures of functional vision.

Pharmaceutical Formulations and Administration

Administration of the compositions of the present invention to a subject, preferably a mammal, more preferably a human, may be carried out using known procedures, at dosages and for periods of time effective to prevent or treat vision loss or impairment in the subject. An effective amount of the therapeutic compositions necessary to achieve a therapeutic effect may vary according to factors such as the state of the disease or disorder in the subject; the age, sex, and weight of the subject; and the ability of the therapeutic compound to cross the blood-brain barrier and the blood-retina barrier

The regimen of administration may affect what constitutes an effective amount. In one embodiment, two or more compositions may be administered to the subject concurrently. In another embodiment, two or more compositions may be administered to the subject at different times to constitute a course of treatment.

Further, the dosages of the compositions may be proportionally increased or decreased as indicated by the exigencies of the therapeutic situation. One of ordinary skill in the art would be able to study the relevant factors and make the determination regarding the effective amount of the therapeutic compound without undue experimentation.

Actual dosage levels of the active ingredients in the pharmaceutical compositions of this invention may be varied so as to obtain an amount of the active ingredient that is effective to achieve the desired therapeutic response for a particular subject, composition, and mode of administration, without being toxic to the subject.

In particular, the selected dosage level will depend upon a variety of factors including the activity of the particular composition employed, the time of

administration, the rate of excretion of the composition, the duration of the treatment, other drugs, compounds or materials used in combination with the composition, the age, sex, weight, condition, general health and prior medical history of the subject being treated, and like factors well known in the medical arts.

A medical doctor, e.g., physician or veterinarian, having ordinary skill in the art may readily determine and prescribe the effective amount of the pharmaceutical composition required. For example, the physician or veterinarian could start doses of the compounds of the invention employed in the pharmaceutical composition at levels lower than that required in order to achieve the desired therapeutic effect and gradually increase the dosage until the desired effect is achieved.

Typically, dosages which may be administered in a method of the invention to a mammal, preferably a human, range in amount from 0.5 ng to about 50 mg per kilogram of body weight of the mammal, while the precise dosage administered will vary depending upon any number of factors, including but not limited to, the type of mammal and type of disease state being treated, the age of the mammal and the route of administration. Preferably, the dosage of the compound will vary from about 1 ng to about 10 mg per kilogram of body weight of the mammal. More preferably, the dosage will vary from about 3 ng to about 1 mg per kilogram of body weight of the mammal.

Eye drops and intravitreal or periocular (Sub-Tenon or subconjunctival) injections are the conventional dosage forms that account for greater than ninety percent of the currently available ophthalmic formulations. To improve bioavailability and reduce the complications associated with repeated injections, the present invention contemplates sustained delivery of the compositions of the invention alone or in combination with other medications. The sustained delivery in the present invention can be achieved through a number of different delivery systems, including but not limited to polymeric gels, colloidal systems including liposomes and nanoparticles, cyclodextrins, collagen shields, diffusion chambers, flexible carrier strips, and intravitreal implants.

In the present invention, ocular and intraocular drug delivery systems deliver the compositions to the back of the eye. These drug delivery systems include: using the sclera itself as a drug delivery reservoir,“prodrug” formulations that pass through the tissue, tiny biodegradable pellets that release the combinations over time, intravitreal implants, intravitreal silicone inserts, intravitreal and transscleral poly(lactic- co-glycolic acid) microspheres, calcium-alginate inserts, encapsulated cells, transscleral iontophoresis, nanoparticles (e.g., calcium phosphate), and genetically modified viruses that can deliver therapeutic proteins into therapy.

In one embodiment, one or more composition of the invention is administered using intraocular or intravitreal injection. For administration of a composition using intraocular injection, anesthesia may be administered via methods known to those of skill in the art including, but not limited to, topical administration of proparacaine or tetracaine drops, 2% lidocaine gel or subconjunctival injection of 2% lidocaine solution. In general, intravitreal injections are administered under controlled aseptic conditions, using mask, sterile gloves, a sterile drape, and a sterile lid speculum. Prior to injection the periocular area is cleaned. Solutions for use in cleaning the periocular area are known to those of skill in the art and may include a povidone-iodine preparation. Following intravitreal injection, irrigation of the eyes may be performed with an appropriate solution. In one embodiment, a solution appropriate for use is a balanced salt solution.

The compositions of the present invention can be in the form of solutions. Solutions can be administered topically by applying them to the cul-de-sac of the eye from a dropper controlled bottle or dispenser. A typical dose regimen for an adult human may range from about 2 to about 8 drops per day, applied at bed-time or throughout the day. Dosages for adult humans may, however, be higher, in which case the drops are administered by“bunching”, e.g., 5 doses administered over a 5 minute period, repeated about 4 times daily. A topical solution in accordance with one embodiment of the invention comprises a therapeutic dose of a composition of the invention in an artificial tear formulation. Such artificial tear formulations are used for restoring the normal barrier function of damaged comeal epithelium following surgery. Typically, artificial tear compositions contain ionic components found in normal human tear film, as well as various combinations of one or more of tonicity agents (e.g., soluble salts, such as Na, Ca, K, and Mg chlorides, and dextrose and sorbitol), buffers (e.g., alkali metal phosphate buffers), viscosity /lubricating agents (e.g., alkyl and hydroxyalkyl celluloses, dextrans, polyacrylamides), nonionic surfactants, sequestering agents (e.g., disodium edetate, citric acid, and sodium citrate), and preservatives (e.g., benzalkonium chloride, and thimerosal). In one embodiment, artificial tear compositions are preservative free. The quantities and relative proportions of each of these components incorporated into an artificial tear composition are readily determinable by the skilled formulation chemist. The ionic species bicarbonate is used in artificial tear compositions, e.g., U.S. Pat. No.

5,403,598 and Ubels, J L, et al, Arch. Ophthalmol. 1995, 113: 371-8.

Alternatively, compositions of the present invention can be in the form of ophthalmic ointments. Ophthalmic ointments have the benefit of providing prolonged drug contact time with the eye surface. Ophthalmic ointments will generally include a base comprised of, for example, white petrolatum and mineral oil, often with anhydrous lanolin, polyethylene-mineral oil gel, and other substances recognized by the formulation chemist as being non-irritating to the eye, which permit diffusion of the drug into the ocular fluid, and which retain activity of the medicament for a reasonable period of time under storage conditions.

Therapeutic amounts of a composition of the invention can be administered orally. For these oral dosage forms, the composition may be formulated with a pharmaceutically acceptable solid or liquid carrier. Solid form preparations include powders, tablets, pills, capsules, cachets, and dispersible granules. The concentration or effective amount of the composition to be administered per dosage is widely dependent on the actual composition. However, a total oral daily dosage normally ranges from about 50 mg to 30 g, and more preferably from about 250 mg to 25 g. A solid carrier can be one or more substances which may also function as a diluent, a flavoring agent, a solubilizer, a lubricant, a suspending agent, a binder, a preservative, a tablet disintegrating aid, or an encapsulating material. Suitable carriers include magnesium carbonate, magnesium stearate, talc, sugar, lactose, pectin, dextrin, starch gelatin, tragacanth, methylcellulose, sodium carboxymethylcellulose, microcrystalline cellulose, a low melting wax, cocoa butter, and the like. The term“preparation” is intended to include the formulation of the active compound with encapsulating material as a carrier providing a capsule in which the active component, with or without other carriers, is surrounded by a carrier, which is thus in association with it. Similarly, cachets and lozenges are included. Tablets, powders, capsules, pills cachets, and lozenges can be used as solid dosage forms suitable for oral administration. A composition may also be administered surgically as an ocular implant. As one example, a reservoir container having a diffusible wall of polyvinyl alcohol or polyvinyl acetate and containing milligram quantities of a composition may be implanted in the sclera. As another example, a composition in milligram quantities may be incorporated into a polymeric matrix having dimensions of about 2 mm by 4 mm, and made of a polymer such as polycaprolactone, poly(gly colic) acid, poly(lactic) acid, or a polyanhydride, or a lipid such as sebacic acid, and may be implanted on the sclera or in the eye. This is usually accomplished with the subject receiving either a topical or local anesthetic and using a small (3-4 mm incision) made behind the cornea. The matrix, containing a composition, is then inserted through the incision and sutured to the sclera using 9-0 nylon.

A composition may also be contained within an inert matrix for either topical application or injection into the eye. As one example of an inert matrix, liposomes may be prepared from dipalmitoyl phosphatidylcholine (DPPC), preferably prepared from egg phosphatidylcholine (PC) since this lipid has a low heat transition.

Liposomes are made using standard procedures as known to one skilled in the art. A composition, in amounts ranging from nanogram to microgram quantities, is added to a solution of egg PC, and the lipophilic drug binds to the liposome.

A time-release drug delivery system may be implanted intraocularly to result in sustained release of the active agent over a period of time. The implantable formation may be in the form of a capsule of a polymer (e.g, polycaprolactone, poly(gly colic) acid, poly(lactic) acid, polyanhydride) or lipids that may be formulation as microspheres. As an illustrative example, a composition may be mixed with polyvinyl alcohol (PVA), the mixture then dried and coated with ethylene vinyl acetate, then cooled again with PVA. The composition bound with liposomes may be applied topically, either in the form of drops or as an aqueous based cream, or may be injected intraocularly. In a formulation for topical application, the drug is slowly released overtime as the liposome capsule degrades due to wear and tear from the eye surface. In a formulation for intraocular injection, the liposome capsule degrades due to cellular digestion. Both of these formulations provide advantages of a slow release drug delivery system, allowing the subject a constant exposure to the drug over time. In a time-release formulation, the microsphere, capsule, liposome, etc. may contain a concentration of a composition that could be toxic if administered as a bolus dose. The time-release administration, however, is formulated so that the

concentration released at any period of time does not exceed a toxic amount. This is accomplished, for example, through various formulations of the vehicle (coated or uncoated microsphere, coated or uncoated capsule, lipid or polymer components, unilamellar or multilamellar structure, and combinations of the above, etc.). Other variables may include the subject's pharmacokinetic-pharmacodynamic parameters (e.g., body mass, gender, plasma clearance rate, hepatic function, etc.). The formation and loading of microspheres, microcapsules, liposomes, etc. and their ocular implantation are standard techniques known by one skilled in the art, for example, the use a ganciclovir sustained-release implant to treat cytomegalovirus retinitis, disclosed in Vitreoretinal Surgical Techniques, Peyman el al, Eds. (Martin Dunitz. London 2001, chapter 45); Handbook of Pharmaceutical Controlled Release

Technology, Wise, Ed. (Marcel Dekker, New York 2000), the relevant sections of which are incorporated by reference herein in their entirety.

Multiple compositions of the invention may be administered simultaneously, separately or spaced out over a period of time so as to obtain the maximum efficacy of the combination; it being possible for each administration to vary in its duration from a rapid administration to a continuous perfusion. As a result, for the purposes of the present invention, the combinations are not exclusively limited to those which are obtained by physical association of the constituents, but also to those which permit a separate administration, which can be simultaneous or spaced out over a period of time.

The administration of a nucleic acid or peptide inhibitor of the invention to the subject may be accomplished using gene therapy. Gene therapy is based on inserting a therapeutic gene into a cell by means of an ex vivo or an in vivo technique. Suitable vectors and methods have been described for genetic therapy in vitro or in vivo, and are known as expert on the matter; see, for example, Giordano, Nature Medicine 2 (1996), 534-539; Schaper, Circ. Res 79 (1996), 911-919; Anderson, Science 256

(1992), 808-813; Isner, Lancet 348 (1996), 370-374; Muhlhauser, Circ. Res 77 (1995), 1077-1086; Wang, Nature Medicine 2 (1996), 714-716; W094/29469; W097/00957 or Schaper, Current Opinion in Biotechnology 7 (1996), 635-640 and the references quoted therein. A polynucleotide, or a polynucleotide encoding a peptide of the invention, can be designed for direct insertion or by insertion through liposomes or viral vectors (for example, adenoviral or retroviral vectors) in the cell. Suitable gene distribution systems that can be used according to the invention may include liposomes, distribution systems mediated by receptor, naked DNA and viral vectors such as the herpes virus, the retrovirus, the adenovirus and adeno-associated viruses, among others. The distribution of nucleic acids to a specific site in the body for genetic therapy can also be achieved by using a biolistic distribution system, such as that described by Williams (Proc. Natl. Acad. Sci. USA, 88 (1991), 2726-2729). The standard methods for transfecting cells with recombining DNA are well known by an expert on the subject of molecular biology, see, for example, W094/29469. Genetic therapy can be carried out by directly administering the recombining DNA molecule or the vector of the invention to a patient. In one embodiment, a DNA molecule is administered to the patient through intravitreal inj ection.

EXAMPLES

The invention is further described in detail by reference to the following experimental examples. These examples are provided for purposes of illustration only, and are not intended to be limiting unless otherwise specified. Thus, the invention should in no way be construed as being limited to the following examples, but rather, should be construed to encompass any and all variations which become evident as a result of the teaching provided herein.

Without further description, it is believed that one of ordinary skill in the art can, using the preceding description and the following illustrative examples, make and utilize the compositions of the present invention and practice the claimed methods. The following working examples therefore, specifically point out the preferred embodiments of the present invention, and are not to be construed as limiting in any way the remainder of the disclosure. Example 1

Wnt regulates proliferation and neurogenic potential of Miiller glial cells through a Lin28/let-7 miRNA-dependent pathway in adult mammalian retina

The experiments presented herein examined whether retinal injury may induce signaling events, which in turn stimulate MG proliferation, and that by directly activating these signals, MGs can be stimulated to re-enter the cell cycle without the need to introduce retinal injury. Wnt signaling regulates proliferation of adult hippocampal stem cells (Lie et al., Nature, 2005, 437: 1370-1375). In the adult mammalian retina, injury enhances Wnt signaling and Wnt activation promotes injury -induced MG proliferation (Das et al, Dev Biol. 2006, 299:283-302; Liu et al,

Invest Opthalmol Vis Sci. 2013, 54:444-453). The canonical Wnt signaling pathway involves the binding of Wnt proteins to cell surface receptors of the Frizzled family, causing the receptors to activate Dishevelled family proteins and ultimately resulting in stabilization and nuclear accumulation of b-catenin, a key effector of Wnt signaling that regulates gene transcription (Logan and Nusse, Annu Rev Cell Dev Biol. 2004, 20:781-810).

Experimental data presented herein demonstrate that retinal injury elicited an early and transient activation of Wnt signaling, prior to eliciting a proliferative response of MGs. Activation of Wnt signaling was manifested by an upregulation of multiple Wnt genes, downregulation of the Wnt antagonist Dkkl and WIF-l, and transcriptional activation of Wnt target genes (Ccndl, Lefl, and Axin2). Furthermore, pharmacological Inhibition of Wnt signaling by XAV939 significantly reduced injury- induced MG proliferation. Consistent with studies in zebrafish that demonstrate that Wnt signaling plays an indispensable role in injury -induced proliferation of MG- derived retinal progenitors (Ramachandran et al. , Proc Natl Acad Sci U S A, 2011,

108: 15858- 15863; Wan et al, Cell Rep. 2014, 9:285-297), these results indicate that Wnt signaling is a conserved pathway that is a critical determinant for the proliferative response of MGs in mammals.

Furthermore, a MG-specific gene transfer tool (ShHlO-GFAP) has been developed to deliver wild-type b-catenin and observed a robust proliferative response of MGs that was equivalent to retinal injury in combination with mitogenic growth factor treatment (Karl et al, Proc Natl Acad Sci U S A, 2008). In addition to the high efficiency in inducing MG proliferation, targeting the intracellular signaling pathway (s) of MGs also eliminates the need for a global treatment of the entire retina with growth factors, which could cause undesirable side effects from untargeted cells.

GSK3 regulates Wnt signaling by promoting b-catenin degradation. GSK3 plays an important role in the maintenance and self-renewal of human and mouse embryonic stem cells (Bone et al, Chem Biol. 2009, 16: 15-27; Sato et al, Nat Med. 2004, 10:55-63; Ying et al, Nature, 2008, 453:519-523). Genetic deletion of GSK3 in mice leads to expanded proliferation of neural progenitors in the brain (Kim et al, Nat Neurosci. 2009, 12: 1390-1397). Genetic evidence is required to determine whether GSK3 participates in regulating the progenitor/stem cell status of MGs in mammals. The experimental results presented herein show that deletion of GSK3 resulted in b- catenin stabilization, transcriptional activation of the Wnt reporter, and as a result,

MG proliferation in uninjured adult mouse retina. Controlling GSK2^ kinase activity therefore appears to be an additional regulatory mechanism that tunes the proliferative response of MGs in adult mammalian retina.

Upon re-entering the cell cycle after Wnt activation, proliferating MGs migrate along their radial processes with a majority of them moving to the ONL where photoreceptors are located. Photoreceptors (rods and cones) are the primary sensory neurons mediating the first step in vision. They are also most vulnerable cells in retinal degenerative diseases, such as retinitis pigmentosa and age-related macular degeneration. However, expression of photoreceptor genes was not detected in the EdU ⁺ cells. Without being bound by a particular theory, it is likely that further re programming is needed to guide the differentiation of cycling MGs to photoreceptors. During early retinal development, the differentiation of retinal progenitor cells is regulated by both extrinsic cues and the intrinsic properties of progenitor cells (Cepko et al, Proc Natl Acad Sci U S A, 1996, 93:589-595; Harris, Curr Opin Genet Dev. 1997, 7:651-658; Livesey and Cepko, Nat Rev Neurosci. 2001, 2: 109-118), that impinge on the transcription network of progenitors for determining their cell fates (Swaroop et al, Nat Rev Neurosci. 2010, 11 :563-576). ShHlO-GFAP-mediated gene transfer provides a practical tool for MG- specific delivery of transcription factors that may guide the differentiation of cycling MGs to specific cell fates. This approach may prove useful in replenishing photoreceptors that typically die in retinal degenerative diseases.

Lin28 has emerged as a master control gene that defines“sternness” in multiple tissue lineages (Shyh-Chang and Daley, Cell Stem Cell, 2013, 12:395-406). As an RNA-binding protein, Lin28 represses let-7 miRNA biogenesis, and thus regulates the self-renewal of mammalian embryonic stem cells. Upstream factors regulating Lin28 remain largely unexplored relative to the effectors and targets downstream of Lin28/let-7 miRNAs. In breast cancer cells, Wnt^-catenin activates the expression of Lin28a, but not Lin28b, through direct binding to the Lin28a promoter and activating its transcription (Cai et al, J Cell Sci. 2013, 126:2877-2889). Experimental results presented herein demonstrate that gene transfer of b-catenin in MGs induced the expression of both Lin28a and Lin28b. Using ChIP assays, distinct b-catenin binding sites were identified in the proximal region of Lin28a and Lin28b promoters that are critical for transcriptional activation. Mutation of these binding sites abolished b-catenin-induced Lin28a/Lin28b- GFP reporter activity. The two b- catenin binding sites in the Lin28a promoter identified are different from the one reported for augmenting cancer cell expansion (Cai et al, J Cell Sci. 2013, 126:2877- 2889), suggesting that distinct b-catenin binding sites may be used to drive Lin28a transcription in progenitor/stem cells. Further, it is demonstrated that Lin28a and Lin28b are essential factors in regulating MG proliferation in vivo, as gene transfer of Lin28a or Lin28b was sufficient to stimulate MG proliferation; and co- deletion of Lin28a and Lin28b abolished b-catenin-induced MG proliferation. Navigating further downstream, both b-catenin and Lin28 suppressed let-7 miRNA expression, and co deletion of Lin28a and Lin28b neutralized b-catenin-mediated effects on let-7 miRNA expression, indicating that Wnt^-catenin acts through Lin28 to suppress let-7 miRNA biogenesis. Importantly, let-7 miRNA regulation is functionally relevant for Wnt- activated MG proliferation as b-catenin-mediated proliferation effects were nearly completely suppressed by let-7b miRNA overexpression.

Previous studies in mice used retinal injury, in combination with growth factor treatment (Karl et al, Proc Natl Acad Sci U S A, 2008, 105: 19508-19513) or transgenic expression of the proneural transcription factor Ascll (Ueki et al, Proc Natl Acad Sci U S A, 2015, 112: 13717-13722), to stimulate the proliferation of MGs, reprogramming these cells to a neurogenic competent state. The neurogenic competence of cell cycle reactivated MGs after injury decreases in an age-dependent manner (Loffler et al, Glia, 2015, 63: 1809-1824). Intriguingly, without retinal injury, after gene transfer of b-catenin, Lin28a, or Lin28b, a subset of MGs migrated to the lower part of the inner nuclear layer and expressed markers for amacrine cells: Pax6, Syntaxinl, and NeuN, indicating that the cell cycle reactivated MGs possess neurogenic potential in an uninjured retina. Taken together, these results provide evidence that GSK3-Wnt-Lin28-let-7miRNA constitutes a central signaling pathway in regulating the proliferative response and neurogenic potential of MGs in adult mammalian retina.

The materials and methods employed in these experiments are now described.

Materials and Methods

Cell culture and transfection

HEK293T cells were cultured in Dulbecco’s Modified Eagle Medium (DMEM, Invitrogen, Grand Island, NY), supplemented with 10% (v/v) fetal bovine serum (FBS, Sigma, St. Louis, MO) and antibiotics (100 unit/ml penicillin and 100 mg/ml streptomycin) in a 37°C incubator with 5% CO2. Cells were transfected 24 hours after seeding in a 24-well plate. For Lin28 promoter analysis, cells were transfected with pLin28-GFP and pCAG- -catenin or pCAGEN, together with a pCAG-tdTomato for normalization. Cells were collected 48 hours after transfection.

Animals

Wild-type mice (strain C57BL/6J), Rosa26-tdTomato reporter mice and

Lin28a ^loxp/loxp ; Lin28b ^loxp/loxp mice were obtained from The Jackson Laboratory (Bar Harbor, ME). GSK3 ^loxp/loxp mice obtained.

Intravitreal injection

Adult mice at 4 weeks of age were anesthetized with an intraperitoneal injection of ketamine (50 mg/kg mouse body weight) and xylazine (5 mg/kg mouse body weight). Intravitreal injection was performed using a microsyringe equipped with a 33 gauge needle. The tip of the needle was passed through the sclera, at the equator and next to the dorsal limbus of the eye, into the vitreous cavity. Injection volume is 1 pl per eye for AAVs or other chemicals including NMDA (Acros

Organics, 100 mM) and XAV939 (Sigma, 10 mM).

AAV production

Adeno-associated virus (AAV) was produced by the plasmid co- transfection method, and the cell lysates were purified via iodixanol gradient ultracentrifugation as previously reported (Grieger et al, Nat Protoc. 2006, 1 : 1412-1428). Purified AAVs were concentrated with Amicon Ultra-l5 Centrifugal Filter Units (Millipore, Bedford, MA) to a final titer of 1.0-5.0 X 1013 genome copies/mL, determined by real-time PCR.

Retinal cell dissociation and Fluorescence-activated cell sorting (FACS) Retinal dissection was performed in HBSS. Dissected retinas were incubated at 37°C for 20 minutes in the activated Papain mix composed of 40 pl Papain

(Worthington, 500 U/mL), 40 mΐ Cysteine/EDTA mix (25m M cysteine + 5 mM EDTA, pH 6~7) and 320 mΐ HBSS/HEPES (normal HBSS + 10 mM HEPES). Cell pellet was collected after centrifugation for 3 minutes at 3000 rpm, and treated with 10 mΐ DNase I (Roche, 10 U/ mΐ) in 400 mΐ HBSS at room temperature for 3 minutes with gentle trituration. Dissociated cells were collected after another centrifugation and resuspended in an appropriate volume of HBSS for further experiments. To purify tdTomato ⁺ MGs, retinas were isolated from MG-specific reporter mice with vehicle or NMDA treatment. After retinal dissociation, single-cell resuspension was washed in DPBS before cell sorting using a BD FACS Aria cell sorter. After cell sorting, both tdTomato ⁺ MGs and non-MGs were subject to RNA isolation and reverse

transcription.

Immunohistochemistry and Imaging

Retinas were fixed with 4% paraformaldehyde in PBS for 30 minutes at room temperature, followed by overnight incubation at 4°C in PBS containing 30% sucrose. Retinas were placed in Tissue-Tek OCT Compound (Sakura Fintek, Torrance, CA) and sectioned using a Leica CM1850 cryostat at the thickness of 20 mih. Sample slides were washed with PBS before incubation with a blocking buffer containing 5% normal donkey serum, 0.1% Triton X-100, and 0.1% NaN3 in PBS for 2 hours at room temperature. Primary antibodies were added for overnight incubation at 4°C. Primary antibodies used: mouse anti-CyclinD3 (1 :300 dilution; Thermo Scientific), mouse anti- rhodopsin (1 :200 dilution; Thermo Scientific), mouse anti-NeuN (1: 100 dilution; Millipore), mouse 3hίί-r27 ^Mr1 (1: 100 dilution; BD Transduction

Laboratories), mouse anti-GS (1:500 dilution; Millipore), rabbit anti-Ki67 (1:200 dilution; Thermo Scientific), rabbit anti-phospho-histone H3 (PH3) (1: 100;

Millipore), mouse anti-HuC/D (1:500 dilution; Thermo Scientific), rabbit anti-Pax6 (1:500 dilution; BioLegend), and mouse anti-Syntaxinl (1 :400 dilution; Santa Cruz). Sections were washed with PBS and incubated with secondary antibodies (1:500 dilution; Jackson ImmunoResearch) for 2 hours at room temperature. Cell nuclei were counterstained with DAPI (Sigma, St. Louis, MO). Confocal Images were acquired using a Zeiss LSM 510 EXCITER microscope.

RNA isolation, RT-PCR, and Real-Time qPCR

Total RNA was extracted from retinas using TRIzol (Invitrogen, Grand Island, NY) according to the manufacture’s protocol. Reverse transcription (RT) was then performed at 42°C for 2 hours in a volume of 20 mΐ containing 0.5 pg of oligo(dT),

1 RT buffer, 0.5 mM each deoxyribonucleotide triphosphate, 0.1 mM dithiothreitol, and 200 U of Superscript II reverse transcriptase (Invitrogen, Grand Island, NY). Real-Time quantitative PCR (qPCR) was performed in triplicate with SsoFast™ EvaGreen supermix (Bio-Rad, Hercules, CA) using an iCycler real-time PCR detection system (Bio-Rad, Hercules, CA). The amplification protocol was 30 seconds at 94°C, 30 seconds at 56°C, and 30 seconds at 72°C, with a signal detection period of 7 seconds at 80°C. A melt curve analysis was performed at the end of the reaction to check the reaction specificity. Results were obtained after normalization to the expression level of the housekeeping gene, B-actin. All experiments were performed at least twice to ensure repeatable results. EdU injection and incorporation assay

EdU solution (lul) was intravitreally injected into the vitreous chamber at the concentration of 1 mg/ml. Analysis of EdU incorporation was performed using Click- iT EdU Kit (Invitrogen, Grand Island, NY). In brief, retinal cryostat sections or flatmount preparations were washed in PBS first for lOmin and then washed twice in PBS containing 3% BSA, followed by permeabilization in PBS containing 0.5% Triton X-100 for 20 min. After washing twice in PBS containing 3% BSA, EdU detection components were resuspended according to manufacturer’s instructions and applied directly to retinal samples. The solution for each EdU reaction has a total volume of 250 pl composed of 215 mΐ IX Click-iT reaction buffer, 10 mΐ CuS04, 0.6 mΐ Alexa Fluor azide, and 25 mΐ IX Reaction buffer additive. After incubation in the reaction solution for 30 minutes at room temperature, samples were washed with PBS and mounted with Fluoromount-G for detection. miRNA analysis

Small RNAs were extracted with the mirVana™ miRNA Isolation Kit and reverse transcribed using TaqMan MicroRNA Reverse Transcription Kit (Invitrogen, Grand Island, NY) according to the manufacturer’s instructions. Quantitative RT-PCR was performed using specific primers and probes for snoRNA-202, has-let-7a, 7b, and 7f supplied in Taqman MicroRNA Assay Kits (Invitrogen, Grand Island, NY). Fold changes were determined using the A(ACT) method after normalization to mouse snoRNA-202 endogenous controls.

Chromatin immunoprecipitation assays

HEK293T cells were transfected with the corresponding promoter and expression constructs using PEI (Poly sciences, Inc., Warrington, PA). After incubation for 48 hours, cells were fixed using 1% formaldehyde for 10 minutes at room temperature. Cross-linking reactions were terminated by adding glycine to a final concentration of 0.125 M. After washing with PBS, cells were resuspended in 6 ml Lysis Buffer (Santa Cruz Biotechnology, Dallas, TX). Crude nuclear extract was collected after centrifugation and resuspended in 1.9 ml Lysis Buffer High Salt (Santa Cruz Biotechnology, Dallas, TX). Chromatin resuspension was sonicated on ice using Branson Sonifier (power output setting=5, 4 times at an interval of 30 seconds, continuous mode). The Supernatant, collected after centrifugation at 10,000 rpm for 15 minutes at 4 °C, was pre-cleared by protein A/G PLUS-Agrose beads (Santa Cruz Biotechnology, Dallas, TX) and then incubated with the primary antibody overnight at 4 °C. After incubation with beads for 2 hours at 4 °C, beads were washed twice with 1 ml Lysis Buffer High Salt and Wash Buffer (Santa Cruz Biotechnology, Dallas, TX) and resuspended in 400 pl Elution Buffer (Santa Cruz Biotechnology, Dallas, TX).

The resuspension was incubated overnight at 65 °C for reverse crosslinking. DNA was isolated using Qiagen Qiaquick PCR purification Kit (Qiagen, Valencia, CA) and analyzed by PCR.

Statistical Analysis

Statistical differences between different experimental groups were analyzed by a Student’s t-test or one-way ANOVAtest using Prism 6 (GraphPad Software, San Diego, CA). Data are presented as mean ± SEM. A value of p < 0.05 is considered significant.

The results of the experiments are now described. Results

Neurotoxic injury leads to transient proliferation ofMGs in adult mouse retina

To examine MG proliferation induced by neurotoxic injury in the adult mammalian retina, 200 nmol was injected NMDA into the vitreous chamber of the mouse retina at 4 weeks of age. The same dosage of NMDA was previously used to introduce retinal injury leading to MG proliferation in adult rat and mouse retina (Karl et al., Proc Natl Acad Sci U S A, 2008, 105: 19508-19513; Ooto et al., Proc Natl Acad Sci U S A, 2004, 101 : 13654-13659). Anti-HuC/D immunohistochemistry was used to assay the time course of NMDA-induced cell death in the ganglion cell layer (GCL).

A progressive loss of retinal ganglion cells and amacrine cells was observed with only -45% of HuC/D ⁺ cells remaining 36 hours post-NMD A injection (Figure 1). To assay cell proliferation, lpl of 1 mg/ml of EdU, a nucleoside analog of thymidine that is incorporated into DNA during active DNA synthesis, was injected into the vitreous chamber 5 hours before tissue collection at 24, 36, 48, 60, 72, and 96 hours post- NMD A injection. NMDA-induced cell proliferation was quantified by scoring the number of EdU ⁺ cells/mm ² in retinal flatmount preparations. A small number (4.7 ± 0.8) of EdU ⁺ cells appeared 36 hours post-NMD A injection. The number of EdU ⁺ cells continued to increase, reaching 223.3 ± 8.3 and 264.5 ± 8.4 at 48 and 60 hours, respectively, before it was reduced to 5.8± 1.1 at 72 hours post-NMDA injection (Figure 2A). The EdU ⁺ cells were also immunoreactive for CyclinD3 and p27 ^kipl (Figure 2B), MG-specific nuclear antigens (Dyer and Cepko, Nat Neurosci. 2000, 3:873-880). These results indicate that NMDA-induced neurotoxic injury transiently stimulated MG proliferation within a time window of 36-72 hours after NMDA- induced neurotoxic injury.

Wnt signaling is a molecular determinant for MG proliferation induced by neurotoxic injury

To examine whether Wnt signaling is activated by NMDA-induced neurotoxic injury, quantitative PCR was performed to assay the RNA levels of Wnt genes at 3, 6, 12, 18, 24, 36, and 48 hours post-NMDA inj ecti on, relative to the PBS injected retina as a control. Significantly, the RNA levels for several Wnt genes, including Wnt2b, Wnt8a, Wnt8b, Wnt9a, and WntlOa, were upregulated at least 3-fold between 6-24 hours post-NMDA injection (Figure 2C), a time frame before MGs re-entered the cell cycle at 36-72 hours post-NMDA inj ecti on (Figure 2A). Whereas the RNA levels for Dkkl, a Wnt signaling antagonist, were downregulated to 13.2 ± 0.6% of the control 24 hours post-NMDA injection (Figure 2C). Interestingly, the RNA levels for WIF-l, a secreted protein that binds to Wnt proteins and inhibits their activities (Hsieh et al. , Nature, 1999, 398:431-436), were also reduced to 1.6 ± 0.2% of the control 12 hours post-NMDA inj ecti on (Figure 2C). The upregulation of Wnt genes and a concomitant downregulation of WIF-l and Dkkl would predict activation of the canonical Wnt/b- catenin signaling pathway. Indeed, 24 hours post-NMDA injection, a 3.4-fold upregulation of CyclinDl (Ccndl, Figure 2D), a target gene of the Wnt signaling pathway (Shtutman et al. , Proc Natl Acad Sci U S A, 1999, 96:5522-5527; Tetsu and McCormick, Nature, 1999, 398:422-426) and key regulator of the cell cycle progression from the Gl to S phase (Resnitzky et al, Mol Cell Biol. 1994, 14: 1669- 1679), was detected. There was also significant upregulation of Left and Axin2 (Figure 2D), two other target genes activated by Wnt signaling (Filali el al, J Biol Chem. 2002, 277:33398-33410; Hovanes et al, Nat Genet. 2001, 28:53-57). These results indicate that NMDA-induced neurotoxic injury led to activation of the Wnt signaling pathway, which preceded the proliferative response of MGs.

To examine whether NMDA-induced activation of Wnt is a cell -autonomous response of MGs or an indirect effect mediated through non-MGs, a MG- specific reporter mouse line was generated by crossing the GFAP-Cre line to the Rosa26- tdTomato reporter line (Kuzmanovic el al, Invest Ophthalmol Vis Sci. 2003, 44:3606- 3613; Madisen et al, Nat Neurosci. 2010, 13: 133-140), resulting in cell-type-specific labeling of MGs with tdTomato (Figure 2E), and used fluorescence-activated cell sorting (FACS) to isolate tdTomato ⁺ MGs after NMDA treatment. The RNA levels for Wnt genes and Wnt antagonists were assayed in tdTomato ⁺ MGs and the non-MG population at 18 hours post-NMD A injection, when significant fold changes were observed for Wnt genes using total retinal RNA (Figure 2C). While the RNAs levels for Wnt genes (Wnt2b, Wnt8a, Wnt8b, Wnt9a, and WntlOa) and Wnt antagonists (Dkkl and WIF-l) remained largely unchanged in the non-MG group, even greater fold changes were detected for these genes in MGs (Figure 2F). Consistently, robust activation of Wnt target genes (CyclinDl, Lefl, and Axin2) was also detected in MGs (Figure 2G).

To examine the ability of inhibition of Wnt signaling to suppress NMDA- induced MG proliferation, NMDA was co-injected with XAV939, a selective Wnt signaling antagonist (Huang et al. , Nature, 2009, 461:614-620), and the number of EdU ⁺ cells per mm ² in retinal flatmount preparations was quantified 60 hours post- injection, when the maximum number of EdU ⁺ cells were detected (Figure 2A). The number of EdU ⁺ cells was significantly reduced when Wnt signaling was inhibited by XAV939, in comparison to NMDA injection alone (Figures 2H-2J). To assay whether XAV939 treatment affects NMDA-induced retinal damage, the number of HuC/D+ cells was quantified in the GCL at 60 hours post-injection. A similar level of cell death was observed in retinas co-injected with XAV939, in comparison to NMDA injection alone. Taken together, these results indicate that Wnt signaling is a critical molecular determinant for MG proliferation induced by neurotoxic injury. MG-specific gene transfer in adult mouse retina

To develop a gene transfer method specifically for MGs in the adult mouse retina, an adeno-associated virus (AAV) variant, known as ShHlO (Klimczak el ah, PLoS One, 2009, 4:e7467; Koerber et al, Mol Ther. 2009, 17:2088-2095) was modified by replacing the ubiquitous CAG promoter with the MG-specific promoter GFAP (Kuzmanovic et al, Invest Ophthalmol Vis Sci. 2003, 44:3606-3613). ShHlO- CAG-mediated gene transfer of the green fluorescence protein (GFP), via intravitreal injections in the adult mouse eye, resulted in transgene expression predominantly in MGs as well as a subset of retinal ganglion cells and amacrine cells labeled by NeuN immunoreactivity (Figures 3A-3C), a transduction pattern similar to that observed in the adult rat retina (Klimczak et al, PLoS One, 2009, 4:e7467). By contrast, ShHlO- GFAP-mediated gene transfer was highly specific for MGs as GFP expression was not detected in retinal ganglion cells or amacrine cells (Figures 3D-3F). Neither ShHlO- CAG nor ShHl 0-GFAP led to photoreceptor transduction. In addition, ShHl 0-GFAP- mediated gene transfer was also highly efficient to transduce MGs as assessed by immunohistochemistry to detect MG-specific antigens in the cytoplasm, such as glutamine synthetase (Figures 3G-3I), or in the nucleus such as p27 ^kipl (Figures 3J- 3L) and CyclinD3 (Figures 3M-30). Most MGs were transduced in the infection area as GFP expression was detected in both MG processes labeled by glutamine synthetase immunoreactivity (arrows in Figure 31), as well as in MG nuclei labeled by p27 ^kipi ( _arr ows in Figure 3L) or CyclinD3 (arrows in Figure 30) immunoreactivity.

To further assess the specificity of ShHlO-GFAP-mediated gene transfer, ShHlO- GFAP-GFP infected retinas were dissociated into single cells and analyze the percentage of GFP ⁺ cells that express MG-specific nuclear antigens CyclinD3 and p27 ^kipi Out of 524 GFP ⁺ cells analyzed from 6 retinas, all of them (100%) were immunoreactive for CyclinD3 or p27 ^{ki l} . indicating that ShHlO-GFAP may only transduce MGs. Gene transfer of b-catenin activates Wnt signaling and stimulates MG proliferation without retinal injury Previous reports indicate that retinal injury is a prerequisite to stimulate the proliferative response of MGs in adult mammalian retina. Therefore, the ability of direct activation of Wnt signaling, without retinal injury, to stimulate MG

proliferation using ShHlO-GFAP-mediated gene transfer of wild-type b-catenin was examined. To assess the activation of the canonical Wnt pathway, a ShHlO-Wnt reporter in which the GFP reporter gene is driven by Tcf/Lef-mediated transcriptional activation was developed. Two weeks after viral infection in the adult mouse retina, significant activation of the reporter gene was observed in MGs co-infected with ShHlO-GFAP-B- catenin, in comparison to those infected with the ShHlO-Wnt reporter alone (Figures 4A and 4B). Using quantitative PCR, a time course study of Wnt target gene activation was performed, following gene transfer of b-catenin in MGs, in comparison to ShHlO-GFAP- GFP infected retinas as a control (Figure 4C). One week post-viral infection, a significant increase in the RNA level was readily detectable for Ccndl (121.8 ± 2.9%), Lefl (134.8 ± 3.0%), and Axin2 (169.5 ± 2.6%). The expression of Wnt target genes continued to increase two weeks post- viral infection, reaching the peak level for Lefl (167.7 ± 7.0%) and Axin2 (198.8 ± 3.7%) except for Ccndl (147.7 ± 2.4%) whose expression increased further (171.5 ± 3.4%) at four weeks post- viral infection.

To examine whether Wnt activation leads to MG proliferation, EdU incorporation was analyzed following ShHlO-GFAP-mediated gene transfer of wild- type b-catenin in adult mouse retina at 4 weeks of age. Intravitreal injection of EdU was performed 10 days post- viral infection, and the treated retinas were collected 4 days later for the analysis of EdU incorporation. EdU ⁺ cells were detected in retinal sections co- labeled by immunohistochemistry for MG-specific antigens including glutamine synthetase (Figures 5A-5F), CyclinD3 (Figures 5G-5L), and p27 ^{kl| l}

(Figures 5M-5R). Many EdU ⁺ cells were detected following b-catenin gene transfer, indicating that these cells re-entered the cell cycle. The nuclear-localizing EdU signals were surrounded by the MG cytoplasm labeled by glutamine synthetase

immunoreactivity (Figure 5F), and were co-localized with MG nuclear antigens CyclinD3 (Figure 5L) or p27 ^kipl (Figure 5R). In these co-labeling experiments, all EdU ⁺ cells were positive for MG-specific antigens, indicating that the proliferating cells were MGs. Noticeably, when MGs re-entered the cell cycle, their somas migrated along their radial processes instead of being localized in the middle of the inner nuclear layer (INL) as they normally do. A quantitative analysis (Figure 5Y) showed that the EdU ⁺ cells were unevenly distributed in retinal layers, with a majority of them (66.2±2.1%) migrating to the outer nuclear layer (ONL) where

photoreceptors are localized. The migration of cell cycle reactivated MGs to the ONL was further confirmed by ShHlO-GFAP- -catenin infection in the MG-specific reporter mice (Figure 1E), where EdU signals were detected in the tdTomato ⁺ MGs in the ONL (Figures 5S-5X). About 25.9±l.l% of the EdU ⁺ cells were in the INL, and l2.5±0.6% of them in the outer plexiform layer (OPL), possibly in the course of migrating to the ONL. Many fewer EdU ⁺ cells migrated to the inner plexiform layer (IPL) and ganglion cell layer (GCL). As a result of Wnt-induced cell proliferation, more CyclinD3 ⁺ MGs were present relative to the untreated retina (Figure 5Z).

Characterization of cell cycle progression, distribution and efficiency of MG proliferation following b-catenin gene transfer

EdU is incorporated into the newly synthesized DNA during the S phase of the cell cycle. To examine the progression of EdU-labeled MGs through other active phases of the cell cycle, co-labeling experiments were performed (Figure 6) for EdU detection and immunohistochemical analysis of cell proliferation antigens: Ki67 (Figures 6A-6D) and phospho-histone H3 (PH3) (Figures 6E-6H), expressed in the nucleus of cells in the active phases (Gl, S, G2, and Mitosis) of the cell cycle for Ki67 (Scholzen and Gerdes, J Cell Physiol. 2000, 182:311-322), and late G2 and the actual phases of Mitosis for PH3 (Hendzel et al., Chromosoma, 1997, 106:348-360). The percentages of Ki67 or PH3 positive cells that were also EdU positive, and vice versa (Figure 61) were quantified. The vast majority of Ki67 or PH3 positive cells were EdU positive, 92.8 ± 3.4% and 94.7 ± 2.3%, respectively. On the other hand, only a small portion of EdU positive cells were labeled positive for Ki67 or PH3, 14.5 ± 0.7% and 15.6 ± 0.9%, respectively, indicating that most EdU ⁺ MGs hadn’t proceeded to the later phases of the cell cycle in the 4-day time frame between EdU injection and tissue collection.

To further analyze the efficiency and distribution pattern of MG proliferation following b-catenin gene transfer, EdU-labeled cells were examined in retinal flatmount preparations. In the ShHlO-GFAP-GFP infected retina as a control, neither the viral infection nor the injection procedure itself led to cell proliferation (Figures 7A and 7B). By contrast, many MGs re-entered the cell cycle in the b-catenin treated retina, labeled by ShHlO-GFAP-GFP co-infection (Figures 7C and 7D). The numbers of EdU ⁺ cells/mm ² were quantified in four retinal quadrants (dorsal, ventral, temporal, and nasal) at three distances (700, 1400, and 2l00pm) from the center of the retina (Figure 7E). Although the number of EdU ⁺ cells in each of the four quadrants was not significantly different from one another as long as their distance from the center remained the same, it appeared that there was a slight gradient of an increasing number of EdU ⁺ cells from the center to the periphery (Figure 7F), with 695.2 ± 18.7 EdU ⁺ cells at 700 urn, 935.8 ± 24.2 EdU ⁺ cells at 1400 urn, and 1019.5 ± 28.3 EdU ⁺ cells at 2100 um to the center. The results show that Wnt activation was highly efficient to stimulate MG proliferation in an uninjured retina as the number of EdU ⁺ was comparable to that obtained by retinal injury in combination with mitogenic growth factor treatment (Karl et al, Proc Natl Acad Sci U S A, 2008, 105: 19508- 19513).

EdU incorporation assay can only label a small fraction of cell cycle reactivated MGs when they are proceeding through the S phase of the cell cycle at the time of EdU injection. The number of EdU ⁺ cells was quantified as a percentage of all Wnt-activated MGs labeled by ShHlO-GFAP-GFP co-infection after retinal dissociation (Figures 7G-7I). All EdU ⁺ cells were GFP ⁺ , however, only ~8% of GFP ⁺ cells were labeled by EdU, indicating that the majority of Wnt-activated MGs were not at the S phase of the cell cycle at the time of EdU injection. Interestingly, gene transfer of a dominant active form of b-catenin did not result in a significant increase in MG proliferation relative to wild-type b-catenin.

08K3b deletion stabilizes b-catenin and activates Wnt signaling

GSK2^ regulates Wnt signaling by phosphorylation of b-catenin, resulting in its degradation by the ubiquitin-proteasome system (Logan and Nusse, 2004). To investigate whether GSK2^ plays a role in regulating Wnt signaling and MG proliferation in adult mammalian retina, GSK2^ was deleted by infecting

GSK2^ ^loxp/lox P mice at 4 weeks of age with ShHlO-GFAP-Cre, resulting in Cre- recombinase expression specifically in MGs as indicated in the Rosa26 reporter mouse line. In comparison to GSK3 ^loxp/loxp mice infected with ShHlO-GFAP- tdTomato alone as a control (Figures 8A-8F), deletion of GSK3 resulted in stabilization and nuclear accumulation of b-catenin in MGs, labeled by ShHlO-GFAP- tdTomato co-infection (Figures 8G-8L). To further assess whether GSK3 deletion activates Wnt signaling, GSK3 ^loxp/loxp mouse retina were infected with ShHlO- GFAP-Cre and the ShHlO-Wnt reporter. In comparison to GSK3 ^loxp/loxp mice infected with the ShHlO-Wnt reporter alone (Figure 8M), significant activation of the reporter gene was observed 2 weeks after ShHlO-GFAP-Cre co-injection (Figure 8N). These results indicate that GSK3 deletion resulted in the activation of the canonical Wnt signaling pathway in MGs.

GSK3f deletion stimulates MG proliferation without retinal injury

In zebrafish, pharmacological inhibition of GSK3 leads to b-catenin stabilization and MG proliferation (Ramachandran et al, 2011). In cultured mouse retinal explants, GSK3 inhibitor treatment enhances MG proliferation in SvJl29 mice (Suga et al, PLoS One, 2014, 9:e94556). To investigate whether OdK3b deletion is sufficient to stimulate MG proliferation without retinal injury, EdU incorporation was assayed in the OdK3b ^1ocr/1ocr mouse retina infected with ShHlO-GFAP-Cre at 4 weeks of age. While no EdU signal was detected in the OdK3b ^1ocr/1ocr mouse retina with sham injection (Figures 9A-9C and 9G-9I), 374.3±27.3/mm ² EdU ⁺ cells were scored two weeks after ShHlO- GFAP-Cre injection, co-labeled by immunohistochemistry for MG-specific nuclear antigens CyclinD3 (Figures 9D-9F) and p27 ^{ki l} (Figures 9J- 9L). The results demonstrate that GSK2^ deletion, and thus stabilization of endogenous b-catenin, is sufficient to stimulate the proliferative response of MGs without retinal injury.

Wnt activation induces Lin28 expression in adult MGs

The pluripotency factor Lin28 is highly expressed in mammalian embryonic stem cells and cancer cells (Moss and Tang, Dev Biol. 2003, 258:432-442). Lin28 was used together with Oct4, Sox2, and Nanog to reprogram human somatic fibroblasts to pluripotent stem cells (Yu et al, Science, 2007, 318: 1917-1920). In zebrafish, Lin28 regulates MG proliferation in response to retinal injury (Ramachandran et ctl, Nat Cell Biol. 2010, 12: 1101-1107). To determine the role of Lin28 in MG proliferation in mammals, the ability of Wnt signaling to regulate Lin28 expression was examined by analyzing Lin28 RNA levels following gene transfer of b-catenin in adult mouse retina. In comparison to ShHlO-GFAP-GFP infection as a control, the RNA levels for both Lin28a and Lin28b were significantly upregulated at two weeks after ShHlO- GFAP- -catenin infection (Figure 10A). Lin28 protein levels were assessed using immunohistochemistry in retinal sections. In the ShHlO-GFAP-GFP infected retina as a control, Lin28a (Figures 10B-10D) or Lin28b (Figures 10H-10J) was not detected. By contrast, ShHlO-GFAP-mediated gene transfer of b-catenin resulted in detection of Lin28a (Figures 10E-10G) and Lin28b (Figures 10K-10M) immunoreactivity in MGs, labeled by ShHlO-GFAP-GFP co-infection. The detection of Lin28a and Lin28b immunoreactivity was specific as co-deletion of Lin28a and Lin28b by ShHlO-GFAP- Cre infection in Lin28a ^loxp/loxp ; Lin28b ^loxp/loxp double floxed mice completely abolished B- catenin-induced Lin28a or Lin28b expression. The results indicate that activation of Wnt signaling induces the expression of both Lin28a and Lin28b in adult mouse MGs.

Yhί/b-oaίbhίh directly regulates Lin28 transcription

To determine whether Lin28 is a direct transcriptional target of Wnt/B- catenin signaling, 3kb promoter sequence of the mouse Lin28 was cloned to drive the expression of a GFP reporter, namely Lin28a-GFP and Lin28b-GFP. The promoter activity was tested in HEK293T cells transfected with Lin28a-GFP or Lin28b-GFP and CAG-tdTomato (a transfection marker), with or without a Flag-tagged b-catenin. In the absence of b-catenin, the reporter gene expression was barely detectable for either Lin28a-GFP (Figures 11A-11C) or Lin28b-GFP (Figures 11J-11L). In the presence of b-catenin, however, the reporter gene expression markedly increased for both Lin28a (Figures 11D-11F) and Lin28b (Figures 11M-110). To further examine whether B- Catenin activates Lin28a and Lin28b transcription by direct binding to their promoters as a co-activator of LEF/TCF in the canonical Wnt^-catenin pathway, chromatin immunoprecipitation (ChIP) assays were performed in HEK293T cells transfected with an expression vector encoding a Flag-tagged b-catenin or a Flag- tagged GFP as a control, together with the Lin28 promoter construct. Analysis of multiple independent clones from the ChIP assay using an anti-Flag antibody revealed b-catenin-specific binding to both Lin28a and Lin28b promoters, proximally located within 500 bp upstream of the ATG start codon. Examination of the proximal promoter sequences using Matlnspector (Cartharius el al, Bioinformatics, 2005, 21:2933-2942) led to the identification of two putative b-catenin binding sites for Lin28a (Figure 11S) and Lin28b (Figure 11T), which were confirmed by additional ChIP assay experiments using primers flanking the putative binding sites for Lin28a (Figure 11U) and Lin28b (Figure 11V). To further validate these binding sites, Lin28- GFP reporter constructs were generated with the binding sites mutated (Figures 11 S and 11T), dubbed Lin28amut-GFP and Lin28bmut-GFP. Mutation of these binding sites abolished b-catenin-activated reporter gene expression for Lin28a (Figures 11G- 111 and 11W) and Lin28b (Figures 11P-11R and 11X). Taken together, these results demonstrate that b-catenin activates the transcription of Lin28a and Lin28b through direct binding to the cis-regulatory elements of their promoters.

To further test whether b-catenin activates the promoters of Lin28a and Lin28b in MGs, adult mouse retinas were infected at 4 weeks of age with ShHlO- Lin28a- GFP or ShHlO-Lin28b-GFP, in the presence or absence of ShHlO-GFAP-b- catenin co- infection. Two weeks after viral infection, the reporter gene expression was detected only in the presence of b-catenin for Lin28a (Figures 12A-12F) and Lin28b (Figures 12J- 120). Mutation of the binding sites abolished b-catenin- activated reporter gene expression for Lin28a (Figures 12G-12I) and Lin28b (Figures 12P-12R). The binding of b-catenin to the Lin28 promoters was further confirmed by ChIP assays using viral infected retinal tissues for Lin28a (Figure 12S) and Lin28b (Figure 12T).

Lin28 plays an essential role in controlling MG proliferation via let-7 miRNAs

Lin28 is a direct transcriptional target of Wnt^-catenin signaling. To determine whether gene transfer of Lin28 is sufficient to stimulate MG proliferation without retinal injury, EdU incorporation analysis was performed on adult mouse retinas infected with ShHlO-GFAP-Lin28a (Figure 13A) or ShHlO-GFAP-Lin28b (Figure 13B). Two weeks after viral infection, many MGs re-entered the cell cycle with greater than 1000 EdU ⁺ cells per mm ² at 1400 pm from the retinal center in Lin28a or Lin28b infected retinas, a robust proliferation effect relative to b-catenin gene transfer or GSK3 deletion (Figure 13C). To determine whether Lin28 was required for b-catenin-induced MG proliferation, co-deletion of Lin28a and Lin28b in Lin28a ^loxp/loxp ; Lin28b ^loxp/loxp double floxed mice was performed. MG proliferation induced by gene transfer of b-catenin was largely neutralized in ShHlO-GFAP-Cre infected retinas (Figures 13D-13F). To determine if Lin28 plays a role in NMDA- induced MG proliferation, ShHlO-GFAP-Cre was injected intravitreally into the retinas of Lin28a ^loxp/loxp ; Lin28b ^loxp/loxp double floxed mice two weeks before NMDA injection. EdU injection was performed 5 hours before tissue collection at 60 hours post-NMDA injection. The number of EdU ⁺ MGs induced by NMDA damage was largely reduced when Lin28a and Lin28b were co-deleted (Figure 13G- 131). These results demonstrate that Lin28 serves as a key molecular switch downstream of the canonical Wnt signaling pathway to regulate MG proliferation in both injured and uninj ured retinas .

Lin28 plays a central role in regulating proliferative growth of cancer cells and embryonic stem cells through inhibition of posttranscriptional maturation of let-7 miRNAs (Heo et al., Mol Cell, 2008, 32:276-284; Newman et al., RNA, 2008, 14;1539- 1549; Rybak et al., Nat Cell Biol. 2008, 10:987-993; Viswanathan et al, Science, 2008, 320:97-100). let-7 miRNAs suppress cell proliferation pathways through mRNA degradation or translation inhibition of a network of cell-cycle regulators (Shyh-Chang and Daley, Cell Stem Cell, 2013, 12:395-406). Therefore, Lin28 promotes cell proliferation through let-7 repression (Viswanathan et al, Nat Genet. 2009, 41:843-848). As a further downstream effector of Wnt signaling, let-7 miRNA levels were examined using quantitative PCR assays. ShHlO-GFAP-mediated gene transfer of Lin28a or Lin28b in the adult mouse retina, compared to ShHlO- GFAP-GFP infection as a control, led to a significant reduction in let-7a, 7b, and 7f miRNA levels two weeks after viral infection (Figure 14A). Significantly, a marked decrease in let-7a, 7b, and 7f miRNA levels was also observed in retinas infected by ShHlO-GFAP^-catenin (Figure 14A). To determine whether b-catenin-induced downregulation of let-7 miRNAs is mediated by Lin28, Lin28a and Lin28b were co deleted by injection of ShHlO-GFAP-Cre together with ShHlO-GFAP^-catenin in Lin28a ^loxp/loxp ; Lin28b ^loxp/loxp double floxed mice. Co-deletion of Lin28a and Lin28b largely neutralized b-catenin-mediated effects on let-7 miRNA downregulation (Figure 14B), indicating that Wnt^-catenin acts through Lin28 to regulate let-7 miRNA expression. To determine whether Wnt/Lin28-regulated let-7 miRNA expression occurs in MGs, a let-7 miRNA-responsive GFP sensor was constructed, with 3 perfectly complementary let-7 binding sites inserted in the 3’-UTR of the GFP sensor (Cimadamore et al, Proc Natl Acad Sci U S A, 2013, 110:E3017-3026; Rybak et al, Nat Cell Biol. 2008, 10:987-993), and packaged into ShHlO-GFAP for MG- specific delivery. In the viral transduction area labeled by ShHlO-GFAP-tdTomato co- infection, the GFP sensor expression was barely detectable, indicating a high level of let- 7 miRNAs present in MGs to suppress proliferation under normal conditions (Figures 15A-15C). Co-infection with ShHlO-GFAP-Lin28a (Figures 15D-25F) or ShHlO-GFAP- Lin28b (Figures 15G-15I) activated the GFP sensor expression in MGs. Significantly, ShHlO-GFAP-mediated gene transfer of b-catenin also activated the GFP senor expression in MGs (Figures 15J-15L), indicating that Wnt/Lin28- mediated regulation of let-7 miRNAs takes place in MGs.

To examine whether let-7 miRNA is critically involved in Wnt/ b-catenin- mediated effects on MG proliferation, let-7b miRNA was co-expressed with b-catenin in MGs using ShHlO-GFAP-mediated gene transfer in the adult mouse retina at 4 weeks of age. b-catenin-induced MG proliferation was largely suppressed (Figures 14C-14E). Taken together, these results delineate a key role of the Wnt/Lin28/let-7 signaling module in regulating the proliferative response of MGs in adult mouse retina. Neurogenic potential ofWnt/Lin28-activatedMGs

To analyze the fates of cell cycle reactivated MGs, EdU was injected at 10 days after ShHlO-GFAP-mediated gene transfer of b-catenin, Lin28a, or Lin28b in the 4- week-old adult mouse retina, and the number of EdU ⁺ cells was quantified at 4, 7, and 10 days after EdU injection. Although many EdU ⁺ cells were scored per mm ² in retinas treated with b-catenin (970.3±40), Lin28a (l325.3±64.4), or Lin28b

(ll77.3±94.2) at 4 days after EdU injection, the number of EdU ⁺ cells declined over time for all three treatment groups with only a very small number of EdU ⁺ cells remaining at 10 days after EdU injection (Figure 16). These results are consistent with the previous report on injury -induced MG proliferation (Ooto et al, Proc Natl Acad Sci U S A, 2004, 101 : 13654- 13659) that the majority of cell cycle reactivated MGs die, resulting in a time-dependent decrease in the number of BrdU labeled cells. To examine neurogenic potential of the cell cycle reactivated MGs, the expression of cell-type-specific markers by EdU ⁺ cells after retinal dissociation was evaluated at 4 days after EdU injection in retinas infected with ShHlO-GFAP- -catenin, Lin28a, or Lin28b. Expression of markers for rods (rhodopsin), cones (red/green or blue cone opsins), bipolar cells (PKCa), and ganglion cells (Tuj 1 or Bm3) was not detected in EdU ⁺ cells for all three treatment groups. Intriguingly, a small number of EdU ⁺ cells were immunoreactive for amacrine cell markers (Figure 17). In B- catenin-treated retinas (Figures 17A - 17C and 17J), 33.l±4.3% of EdU ⁺ cells were positive for Pax6 (progenitors and amacrine cells), 6.5±l.5% were positive for Syntaxinl (amacrine cells), and 6.0±0.9% were positive for NeuN (amacrine and ganglion cells). In Lin28a-treated retinas (Figures 17D-17F and 17J), 5l.0±4.0% of EdU ⁺ cells were positive for Pax6, 6. l±l. l% were positive for Syntaxinl, and 5.l±l.0% were positive for NeuN. In Lin28b-treated retinas (Figures, 17G-17I and 17J), 49.5±2.6% of EdU ⁺ cells were positive for Pax6, 5.5±0.9% were positive for Syntaxinl, and 5.9±2.0% were positive for NeuN. Using confocal microscopy in intact retina, the expression of amacrine cell markers was confirmed in a small subset of the cell cycle reactivated MGs located in the lower part of the inner nuclear layer where the amacrine cell somas are located, following ShHlO-GFAP-mediated gene transfer of b-catenin, Lin28a, or Lin28b (Figure S18). These results signify neurogenic potential of Wnt/Lin28-activated MGs in adult mammalian retina. Example 2

Gene transfer of b-catenin activates MG proliferation without retinal injury in a mouse model of retinal degeneration

Photoreceptors (rods and cones) are particularly vulnerable to various degenerative conditions. Retinitis pigmentosa (RP) refers to a major group of hereditary retinal degenerative diseases commonly caused by mutations in rod- specific genes. These genetic defects cause rods to die followed by gradual degeneration of cones (Ferrari et al., Curr Genomics, 2011, 12:238-249). A major challenge to restoring vision in RP is the heterogeneous nature of the disease, as it is caused by many mutations; thus, each mutation may require a unique therapy. MG- derived retinal regeneration may represent a general therapeutic strategy regardless of disease-causing mutation(s). Rdl mice, a widely used mouse model of RP, carry a recessive mutation in the rod-specific gene phosphodiesterase-6B, which is mutated in about 4-5% of human RP patients in the US (Hartong el al, Lancet, 2006, 368: 1795- 1809). In rdl mice, rods die rapidly followed by a slower phase of cone degeneration. Previous studies have attempted to protect photoreceptors in rdl mice, with treatments including neurotrophic factors (LaVail et al. , Invest Ophthalmol Vis Sci. 1998,

39:592-602), calcium channel blockers (Frasson et al, Nat Med. 1999, 5: 1183-1187), or anti-apoptosis gene transfer (Bennett et al, Gene Ther. 1998, 5: 1156-1164).

Neuroprotection-based therapeutic intervention would benefit RP patients at an early/intermediate stage of the disease when most photoreceptors are alive.

Generation of new photoreceptors from reprogrammed MGs will provide an alternative therapeutic strategy to repopulate photoreceptors even at advanced stages of disease when most photoreceptors have died.

Experiments have been designed to investigate ShHlO-GFAP -mediated gene transfer of b-catenin activation of MG proliferation in rdl mice. ShHlO-GFAP- mediated gene transfer of b-catenin is performed in rdl mice by intravitreal injection at postnatal day 14, 21, or 35, representing early, intermediate, and late stage of photoreceptor degeneration respectively. Activation of Wnt target genes (CyclinDl, Lefl, and Axin2) are examined at 1, 2 and 4 weeks after viral injection. EdU administration and proliferation analysis are performed as described elsewhere herein for the wild-type retina.

Example 3

Regeneration of rod photoreceptors from Miiller glial cells in adult mouse retina

Activation of MGs has potential for ultimately restoring the regenerative capability in humans in order to treat blinding diseases. Elsewhere herein, the injury- induced signaling pathway(s) that are responsible for activating the proliferative response of MGs are identified and it was demonstrated that MG proliferation can be activated to generate retinal progenitor/stem cells, without retinal injury (see Example 1). Differentiation of MG-derived progenitor/stem cells to rod photoreceptors (Figure 19) can be guided by gene transfer of pro-rod transcription factors to generate MG- derived new rods with the molecular, structural, and functional properties of native rods.

The experiments are now described.

Guide the differentiation of MG-derived retinal progenitor /stem cells to rod photoreceptors.

Upon injury and growth factor treatment, a subset of mammalian MGs re enter the cell cycle, but only a very small number of MG-derived retinal progenitors differentiate into retinal neurons, including rods (Ooto et al, Proc Natl Acad Sci U S A, 2004, 101 : 13654-13659; Del Debbio et al, PLoS One, 2010, 5:el2425) and amacrine cells (Karl et al, Proc Natl Acad Sci U S A, 2008, 105: 19508-19513). Efficient production of MG-derived photoreceptors represents a major challenge to restoring the regenerative capability in the mammalian retina. To achieve high efficiency in regeneration of rod photoreceptors, the differentiation of MG-derived retinal progenitors is guided by delivering a set of pro-rod transcription factors that play an essential role in rod photoreceptor differentiation during retinal development, involving the proliferation and terminal differentiation of retinal progenitor cells into specific cell types. Differentiation of retinal progenitors is regulated by both extrinsic cues and the intrinsic properties of progenitor cells (Cepko et al, Proc Natl Acad Sci U S A, 1996, 93:589-595; Harris, Curr Opin Genet Dev. 1997, 7:651-658; Livesey and Cepko, Nat Rev Neurosci. 2001, 2: 109-118; Yang, Semin Cell Dev Biol. 2004, 15:91-103), that impinge on the transcription network of retinal progenitor cells for their cell fate determination (Swaroop et al, Nat Rev Neurosci. 2010, 11 :563-576). Retinal progenitor cells go through a progression of competency states, each controlled by a distinct network of transcription factors to make particular cell types in a specific time window. For example, a specific set of transcription factors may allow a retinal progenitor cell to produce a rod instead of a bipolar cell or an amacrine cell. Transcription factors, which are known to play an important role in the specification and differentiation of rod photoreceptors during retinal development, h tested and used to guide the differentiation of MG-derived progenitor cells. ShHlO- GFAP-mediated gene transfer provides a practical tool for MG-specific delivery of these transcription factors. This approach may prove useful in replenishing photoreceptors that typically die in retinal degenerative diseases.

Construction of a reporter to track the differentiation of MG-derived retinal progenitors to rod photoreceptors.

Attempts to stimulate mammalian MGs for photoreceptor regeneration have met with little success. Very few rods were generated when the mammalian retina was first injured and subsequently treated with growth factors. Not only were these newly generated rods limited in number, they were imbedded in an overwhelming majority of native rods, generated from retinal progenitor cells during retinal development. Anti-rhodopsin immunohistochemistry was used to identify these MG-derived new rods (Ooto et al., Proc Natl Acad Sci U S A, 2004, 101: 13654-13659). However, it was not clear whether the EdU ⁺ MGs had rhodopsin expression, because the sparsely scattered EdU ⁺ cells were surrounded by native rods that all express rhodopsin protein (Figure 20 from Ooto et al, Proc Natl Acad Sci U S A, 2004, 101: 13654-13659).

To overcome the above limitation, MG-derived new rods are exclusively labeled using a method that does not detect the native rods. Importantly, this approach allows tracking and characterization of the differentiation of MG-derived retinal progenitors to rods at progressive stages. A reporter for cell-type-specific delivery to MGs is turned on when MG-derived retinal progenitors undergo rod differentiation. The reporter construct contains a 2.1 kb rhodopsin promoter driving the expression of tdTomato specifically in rods (Matsuda and Cepko, Proc Natl Acad Sci U S A, 2004, 101 : 16-22). The reporter construct was tested by in vivo electroporation to co transfect a ubiquitous pCAG-GFP plasmid and the rhodopsin-tdTomato reporter plasmid in the newborn mouse retina. The results show that the rhodopsin-tdTomato reporter exclusively labels rods while GFP expression driven by the ubiquitous CAG promoter labels multiple retinal cell types including rods, bipolar cells, amacrine cells, and MGs (Figure 21). The rhodopsin-tdTomato cassette cloned into the ShHlO vector is used for delivery to MGs. This reporter is referred to as ShHlO-rhodopsin-tdTomato hereafter.

Guide the differentiation ofMG-derived retinal progenitors to rod

photoreceptors.

To guide the differentiation of MG-derived retinal progenitors to rod photoreceptors, the major consideration was the choice of pro-rod transcription factors. Three transcription factors (Otx2, Crx, and Nrl) are essential for determining the rod cell fate of retinal progenitor cells during early retinal development. Otx2 is an early transcription factor for photoreceptor cell fate determination. Otx2 deficiency leads to overproduction of amacrine-like cells at the expense of both rod and cone photoreceptors (Nishida e/ a/., Nat Neurosci. 2003, 6: 1255-1263). Crx is another transcription factor required for terminal differentiation and maintenance of photoreceptors (Chen et al, Neuron, 1997, 19: 1017-1030; Furukawa el a/.. Cell, 1997, 91 :531-541). Nrl is a basic motif-leucine zipper transcription factor that promotes rod cell fate by transcriptional activation of important rod genes including rhodopsin (Rehemtulla et al, Proc Natl Acad Sci U S A, 1996, 93: 191-195). Nrl also suppresses cone photoreceptor cell fate by transcriptional activation of Nr2e3 (Mears et al, Nat Genet. 2001, 29:447-452, Mitton et al, J Biol Chem. 2000, 275:29794- 29799).

cDNAs encoding Otx2, Crx, and Nrl were cloned into ShHlO-GFAP for MG- specific gene transfer. A two-step protocol for rod induction was used to guide the differentiation of MG-derived retinal progenitors to rod photoreceptors (Figure 22). First, MG proliferation was stimulated by injection of ShHlO-GFAP- -catenin in adult mouse retina at 4-5 weeks of age, followed by the second injection of ShHlO- GFAP-Otx2, ShHlO-GFAP-Crx, and ShHlO-GFAP -Nrl to guide rod differentiation with a two-week time interval between the two injections. Also included in the first injection were ShHlO-GFAP-GFP (as a viral infection marker to label all transduced MGs) and the ShHlO- rhodopsin-tdTomato reporter to monitor the differentiation of MGs to rod photoreceptors. Recombinant viruses were purified and concentrated to the titer of 1.0X10 ¹³ cfu/ml and mixed at the ratio of 1 : 1 : 1 for a total volume of 1 pl intravitreal injection. Greater than 90% of co-transduction efficiency was achieved by injection of a mix of multiple high titer adeno-associated viruses to restore color vision in red-green color blind primates (Mancuso et al. , Nature, 2009, 461 :784-787).

One week after ShHlO-GFAP-mediated gene transfer of Otx2, Crx, and Nrl, the ShHlO-rhodopsin-tdTomato reporter was turned on in a subset of MGs, and all of rhodopsin-tdTomato positive cells were labeled by co-injected ShHlO-GFAP-GFP, indicating that the MG-derived retinal progenitors were undergoing rod

differentiation. Based on the morphological changes, the differentiation of MGs was categorized according to three stages: the initial, intermediate, and terminal stage. Initial stage: A majority (close to 75%) of the rhodopsin-tdTomato ⁺ cells appeared morphologically similar to MGs with the upper processes ending at the outer limiting membrane, and the lower processes (MG end feet) extending to the fiber layer of retinal ganglion cells (Figure 23A - 23C). Intermediate stage: A number of (about 20%) of the rhodopsin-tdTomato ⁺ cells were undergoing morphological changes after the last cell division, one daughter cell was differentiating to the rod as evidenced by the soma migration to the outer nuclear layer while the other daughter cell maintained the MG morphology; and most intriguingly, the MG-derived rod cell developed photoreceptor outer/inner segments (Figure 23D - 23F), a specialized structure for rod phototransduction. Terminal stage: A small portion (about 5%) of the rhodopsin- tdTomato positive cells appeared to have differentiated to mature rods,

morphologically identical to the native rods (Figure 23G - 231). Two weeks after the second injection for rod induction, the majority (about 75%) of the rhodopsin- tdTomato ⁺ cells differentiated to mature rods at the terminal stage. About 25% of the rhodopsin-tdTomato ⁺ cells at the intermediate stage, and very few (<l%) of them were MG-like at the initial stage. The differentiation process of MGs through progressive stages to rod photoreceptors mimicked the developmental stages of rod photoreceptor differentiation from retinal progenitor cells.

ShHIO-rhodopsin-mediated gene transfer does not transduce native photoreceptors.

All rhodopsin-tdTomato ⁺ cells were also positive for GFAP-GFP, indicating that no native rods were transduced by ShHlO-rhodopsin-tdTomato. To further examine whether ShHlO-rhodopsin-mediated gene transfer could transduce native rods, ShHlO-rhodopsin-tdTomato was injected into the subretinal space to give the virus maximum chance to infect photoreceptors. While the co-injected AAV2/5-CAG- GFP showed transduction of photoreceptors in the ONL, no tdTomato signal was detected (Figure 24). These results confirm that ShHlO-rhodopsin-mediated gene transfer does not transduce native photoreceptors.

Experiments have been designed to determine whether newly generated rods incorporate EdU by intravitreal injection of EdU 10 days after b-catenin gene transfer, and to analyze EdU incorporation 2 weeks after the second injection.

Experiments have been designed to characterize and quantify the percentage of MG-derived rods at different differentiation stages over time, specifically, 1 or 2 weeks after the second injection.

Experiments have been designed to induce rod differentiation by ShHlO- GFAP-mediated gene transfer of Otx2, Crx, and Nrl individually or Otx2+Crx, Otx2+Nrl, and Crx+Nrl combinations for the second injection. Gene transfer of fewer number of transcription factors may lead to higher rod differentiation efficiency.

Fate mapping for tracing the cell lineage of MG-derived rod photoreceptors.

As an alternative approach to demonstrate that the new rods are generated from MGs, fate mapping studies were used to trace the cell fate of MGs following the two- step rod induction protocol (Figure 22). To this end, a MG fate mapping mouse line was generated by crossing the GFAP-Cre line to the Rosa26-tdTomato reporter line (Kuzmanovic et al., Invest Ophthalmol Vis Sci. 2003, 44:3606-3613; Madisen et al, Nat Neurosci. 2010, 13: 133-140), resulting in permanently labeling MGs with tdTomato (Figure 25A). MG-derived cells were traced with tdTomato labeling. The results show that new rods were generated from MGs after the treatment with the first injection of B- catenin followed by the second injection of Otx2, Crx, and Nrl (Figure 25B).

Characterize the cellular structure and molecular features of MG-derived new rods.

The rod is a primary sensory neuron consisting of the outer and inner segments, soma, axon and axon terminal. With these specialized structures, rods are highly efficient photon detectors that transmit signals to second-order retinal neurons. Expression of a cohort of rod-specific genes is required for the formation and maintenance of these structures as well as serving as signaling molecules for rod phototransduction, which is initiated by rhodopsin, a G protein-coupled receptor enriched in the rod outer segment. Upon photon absorption, rhodopsin changes conformation from a resting state to an enzymatically active state to catalyze the activation of the rod a-transducin, which in turn, activates cGMP phosphodiesterase, resulting in a decrease in free cGMP and closure of CNG cation channels. The resultant hyperpolarization decreases the open probability of Ca ⁺⁺ channels near rod synaptic ribbons, decreasing glutamate release. To shut off the rod phototransduction cascade, photoactivated rhodopsin is silenced by its binding to rod arrestin (Krupnick et al, J Biol Chem. 1997, 272: 18125-18131), which regulates rhodopsin

photochemistry (Sommer and Farrens, Vision Res. 2006, 46:4532-4546). A variety of techniques are used to characterize the regenerated rods and demonstrate that the cellular structure and molecular features of the MG-derived new rods are similar to native rods.

Using immunohistochemistry and confocal microscopy, MG-derived new rods were investigated for the expression of a cohort of rod-specific genes, such as rhodopsin, rod a-transducin, rod arrestin, and recoverin critical for rod

phototransduction, as well as genes critical for the maintenance of the rod synaptic terminal structure (such as ribeye, bassoon, and CtBP) in close apposition to the post- synaptic specialization of rod bipolar cells (PKCa and mGluR6). The results showed that MG-derived new rods, labeled by rhodopsin-tdTomato, were appropriately located in the outer nuclear layer and morphologically similar to native rods (Figure 26A). These regenerated rods not only developed outer and inner segments, the axon terminal was also enlarged to form a synaptic bouton (Figure 26B), inside of which the rod ribbon synapse protein CtBP was expressed (Figure 26C, 26D).

Ultrastructural analysis of MG-derived rod photoreceptors.

Using electron microscopy (EM), ultrastructural analysis is performed on MG- derived new rods, including the outer segment, synaptic ribbon, and rod-triad synapse. The rod makes postsynaptic contacts with horizontal cells and rod bipolar cells to form the classic triad synapse. The rod synaptic ribbon is an electron-dense specialization where several rows of glutamate-packed vesicles are tethered for release. MG-derived new rods are identified by immunogold labeling with an anti- tdTomato antibody for scanning EM.

Investigate whether MG-derived rods integrate into the existing neural circuits in the retina

Vision is initiated by light-responsive photoreceptors, propagated through synaptic transmission to second-order neurons (bipolar and amacrine cells). The information is integrated by retinal ganglion cells (RGCs), the output neurons in the retina, and transmitted to the brain. Regenerative therapy is of great interest because of its potential to replenish lost photoreceptors and restore vision. Recent advances in photoreceptor transplantation suggest that new photoreceptors can respond to light, integrate into the existing retinal circuitry (MacLaren el al, Nature, 2006, 444:203- 207; Pearson et al., Nature, 2012, 485:99-103). MG-derived rods integrate into retinal circuits and have potential to restore visual function. Without introduction of retinal injury, the results demonstrate that MG-derived rods appear morphologically similar to wild-type rods, and form cellular specializations for phototransduction, and further, MG-derived rods activate photoreceptor-mediated light response in RGCs.

A mouse model was utilized in which newly gained rod function can be assessed unambiguously. Gnat 1 ^_/ have no rod function due to the absence of rod a- transducin, an essential component for rod phototransduction (Calvert el al. , Proc Natl Acad Sci U S A, 2000, 97: 13913-13918). Gnat2 ^cpf13 homozygotes have poor cone- mediated responses evident by 3 weeks of age and completely lack cone-mediated responses at 9 weeks of age (Chang et al. , Invest Ophthalmol Vis Sci. 2006, 47:5017- 5021). Gnatl ^/ :Gnat2 ^cpf13 double mutant mice lack photoreceptor-mediated light response and were used for functional assessment of MG-derived new rods.

Phototransduction occurs in the outer segment of photoreceptors. Light-dependent translocation of rod photoreceptor-specific G protein, Gnatl (rod a-transducin), between the outer segment and the other functional compartments of photoreceptors allows these cells to adapt to a wide range of light intensities (Sokolov et al. , Neuron, 2002, 34:95-106). Recent studies show that transducin translocation also contributes to rod survival and synaptic transmission to rod bipolar cells (Majumder et al, Proc Natl Acad Sci U S A, 2013, 110: 12468-12473). To reconstitute rod phototransduction in MG-derived rods in Gnatl ^/ :Gnat2 ^cpf13 mice, ShHlO-rhodopsin-mediated gene transfer of wild-type rod a- transducin in MGs, which does not transduce native rods (Figure 24) was utilized. The results (Figure 27) indicate that Gnatl (rod a- transducin) was localized in the rod outer segments in the dark (Figure 27A); upon light stimulation (10,000 lux for 2 hours) it translocated to other cellular

compartments including the inner segments and synaptic terminals (Figure 27D), while the localization of co-expressed ShHlO-rhodopsin- tdTomato (Figure 27B, 27E) was not affected by the light stimulation.

Retinal ganglion cells were recorded from the ventral retina of Gnatl

:Gnat2 ^cpf13 mice, using an in vitro preparation described previously (Wang et al, J Neurosci. 2011, 31:7670-7681; Ke et al, Neuron, 2014, 81 :388-401). In the ventral mouse retina, cones express primarily UV-sensitive opsin, with peak sensitivity at 360 nm, whereas rods express the typical green-sensitivity with peak at 500 nm (Wang et al, J Neurosci. 2011, 31 :7670-7681; Applebury et al, Neuron, 2000, 27:513-523; Nikonov et al, J Gen Physiol. 2006, 127:359-374; Baden et al, Neuron, 2013, 80: 1206-1217). Large somas (diameter, >20 pm) in the ganglion cell layer were targeted for loose-patch recordings of action potentials using IR imaging to minimize photobleaching. Control retinas, receiving either no b-catenin or three pro-rod differentiation factors, lacked any light responses; whereas treated retinas with rescued rod function show responses to dim light with green > UV sensitivity. Whole cell voltage-clamp recordings of membrane currents were used to assay the integrity of synaptic inputs in these ganglion cells, as described in wild-type retinas (Ke et al, Neuron, 2014, 81 :388-401; Murphy and Rieke, Neuron, 2006, 52:511-524).

Example 4

Restoration of vision after de novo genesis of rod photoreceptors in mammalian retinas

Summary

In zebrafish, Miiller glial cells (MGs) are a source of retinal stem cells that can replenish damaged retinal neurons and restore vision ¹ . In mammals, however, MGs lack regenerative capability as they do not spontaneously re-enter the cell cycle to generate a population of stem/progenitor cells that differentiate into retinal neurons. The regenerative machinery may exist in the mammalian retina, however, as retinal injury can stimulate MG proliferation followed by limited neurogenesis ^{2 7} . The fundamental question remains whether MG-derived regeneration can be exploited to restore vision in mammalian retinas. Previously, we showed that gene transfer of b- catenin stimulates MG proliferation in the absence of injury in mouse retinas ⁸ . Here, we report that following gene transfer of b-catenin, cell-cycle-reactivated MGs can be reprogrammed into rod photoreceptors via a subsequent gene transfer of transcription factors that are essential for rod cell fate specification and determination. MG-derived rods restored visual responses in Gnatl ^/ :Gnat2 ^cpf13 double mutant mice, a model of congenital blindness ^{9 10} , throughout the visual pathway from the retina to the primary visual cortex in the brain. Together, our results provide evidence of vision restoration after de novo MG-derived genesis of rod photoreceptors in mammalian retinas.

Results and Discussion

In cold-blooded vertebrates such as zebrafish, Miiller glial cells (MGs) are retinal stem cells as they readily proliferate to replenish damaged retinal neurons, establishing a powerful self-repair mechanism ^{11 17} . In mammals, however, MGs lack regenerative capability as they do not spontaneously re-enter the cell cycle ¹⁸ . Injuring the mammalian retina does activate the proliferation of MGs, but with limited neurogenesis ^{2 7} . The necessity for retinal injury to activate MG proliferation is obviously counterproductive for regeneration as it massively kills retinal neurons.

Furthermore, there has been no convincing evidence that MG-derived regeneration restores vision in the mammalian retina. To test whether MG-derived neurogenesis improves vision without the necessity for retinal injury, we reprogrammed MGs in vivo to generate new rod photoreceptors in mature mouse retinas. We previously reported that ShHlO-GFAP-mediated gene transfer of b-catenin in MGs stimulates these cells to re-enter the cell cycle in the uninjured mouse retina ⁸ . To reprogram the cell-cycle-reactivated MGs into rod photoreceptors, we tested a combination of three transcription factors (Otx2, Crx, and Nrl) that are essential for determining rod cell fate during retinal development. Otx2 is an early expressed homeodomain

transcription factor, deficiency of which leads to overproduction of amacrine-like cells at the expense of both rod and cone photoreceptors ¹⁹ . Crx is another

homeodomain transcription factor required for terminal differentiation and maintenance of both rod and cone photoreceptors ²⁰ · ²¹ . Nrl is a basic motif leucine zipper transcription factor that promotes rod cell fate by transcriptional activation of rod-specific genes while repressing expression of cone-specific genes ²² .

In the developing mouse retina, generation of retinal cell types is completed by the first two weeks after birth ²³ . To examine whether new rod photoreceptors could be generated from MGs in the mature mouse retina, we used a two-step

reprogramming method to first stimulate MG proliferation by intravitreal injection of ShHlO-GFAP-b- catenin in the mouse retina at 4 weeks of age. This was followed two weeks later by a second injection of ShHlO-GFAP-mediated gene transfer of Otx2, Crx, and Nrl. We first examined whether MGs could undergo successive rounds of cell division after the initial gene transfer of b-catenin. Following an EdU/BrdU double-labeling procedure previously used to analyze the clonal expansion of horizontal cells ²⁴ , proliferating MGs were labeled with EdU at 10 days after the injection of ShHlO-GFAP^-catenin, and 24 hours later the S phase cells were labeled with BrdU. Retinas were harvested 4 days later and were assayed to determine whether the EdU ⁺ cells progressed through another cell division into a second round of S phase. Very few cells were co-labeled by EdU and BrdU (Fig. 32), indicating that the vast majority of MGs may undergo only one cell division after b-catenin gene transfer.

To identify MGs that may undergo rod photoreceptor differentiation after the second injection of ShHlO-GFAP-mediated gene transfer of Otx2, Crx, and Nrl, we included in the first injection ShHlO-Rhodopsin-tdTomato, a 2.1 kb rhodopsin promoter ^{25 28} driving the expression of tdTomato, together with ShHlO-GFAP-GFP to label all transduced MGs (Fig. 28a). Based on the morphological changes observed from different retinal samples after the second injection for rod induction, the progression of MG-derived rod differentiation was categorized into initial, intermediate, and terminal stages. At the initial stage, MGs turned on the expression of Rhodopsin-tdTomato, and the Rhodopsin- tdTomato ⁺ cells appeared

morphologically similar to MGs with the upper processes ending at the outer limiting membrane, and the lower processes (MG end feet) extending to the fiber layer of retinal ganglion cells (Fig. 28b-d). At the intermediate stage, there was an asymmetric cell division whereby the Rhodopsin-tdTomato ⁺ cell produced two daughter cells with different cell fates (Fig. 28e-g). One daughter cell apparently differentiated to a rod photoreceptor with its soma localized in the outer nuclear layer (ONL), and intriguingly, the MG-derived rod cell generated outer/inner segments, a specialized cellular structure essential for rod phototransduction. The second daughter cell remained in the inner nuclear layer (INL) with a typical MG morphology. At the terminal stage, the Rhodopsin-tdTomato ⁺ cell appeared to have differentiated to a mature rod cell, morphologically very similar to native rods with outer/inner segments and an enlarged synaptic bouton-like terminal (Fig. 28h-j). The MG-derived rod differentiation was observed from the center to periphery in the whole retinal section, whereas no Rhodopsin-tdTomato ⁺ cells were observed in control retinas receiving the same treatments except ShHlO-GFAP- -catenin was omitted from the first injection (Fig. 33).

We quantified the progression of rod differentiation over time (1,000-1,200 Rhodopsin-tdTomato ⁺ cells, 6-8 retinas for each time point, additional examples of MG- derived rod differentiation are shown in Fig. 34). One week after the second injection (Fig. 28k), the majority of Rhodopsin-tdTomato ⁺ cells (73.5%) were in the initial stage, with a smaller number in the intermediate (20.6%) and terminal stages (5.9%). Two weeks after the second injection (Fig. 281), there were almost no Rhodopsin-tdTomato ⁺ cells in the initial stage (0.4%), a small number in the intermediate stage (24.8%) and a majority (74.8%) that had differentiated to mature rods in the terminal stage. Four weeks after the second injection (Fig. 28m), nearly all Rhodopsin-tdTomato ⁺ cells differentiated to mature rods in the terminal stage

(97.4%). The Rhodopsin-tdTomato ⁺ cells were also positive for GFAP-GFP (Fig. 28e, h), indicating that they were indeed derived from MGs, as gene transfer using the ShHlO AAV serotype and GFAP gene promoter should selectively transduce MGs but not photoreceptors ⁸ . To examine further if native rods could be transduced by the ShHlO serotype, ShHlO-rhodopsin-tdTomato was injected together with AAV2/5- CAG-GFP in the subretinal space to maximize the chance for photoreceptor infection. AAV2/5-CAG-GFP acted as a positive control that should transduce photoreceptors and drive GFP expression. While the co-injected AAV2/5- CAG-GFP transduced many photoreceptors in the ONL, no tdTomato signal was detected in the same retinal region (Fig. 35), demonstrating that the ShHlO-rhodopsin- mediated gene transfer does not transduce photoreceptors effectively. The expression of GFAP-GFP was eventually turned off in MG-derived rods over time, and no GFP signal was detected in Rhodopsin-tdTomato ⁺ cells 12 weeks after the second injection (Fig. 36). We also tested whether treatment with Otx2, Crx, and Nrl individually or in pairs was sufficient for rod induction (Fig. 37). Four weeks after the second injection, no Rhodopsin-tdTomato ⁺ cells were detected with these treatments except for the combination of Crx and Nrl, which resulted in a few Rhodopsin-tdTomato ⁺ cells detected in the initial stage of rod differentiation at 1, 2, and 4 weeks after the second injection (Fig. 38); however, the level of differentiation in the Crx+Nrl test group was not clinically significant.

To trace the lineages of MGs following our two-step reprogramming method, we generated a MG fate mapping mouse line by crossing the GFAP-Cre line to the Rosa26-tdTomato reporter line ²⁹ · ³⁰ , resulting in permanent labeling of MGs with tdTomato (Fig. 28n) ⁸ . MG fate mapping mice at 4 weeks of age were first injected with ShHlO-GFAP- -catenin to stimulate MG proliferation, followed two weeks later by ShHlO-GFAP-mediated gene transfer of Otx2, Crx, and Nrl for rod induction. Four weeks after the second injection, tdTomato ⁺ cells were observed in the ONL and appeared to have differentiated into mature rods with the formation of outer/inner segments (Fig. 28o), further demonstrating that the rod cells were derived from MGs in the treated mouse retina. We occasionally observed MG-derived tdTomato ⁺ cells with a horizontal cell morphology located in the upper inner nuclear layer (Fig. 39). This observation was consistent with a role for Otx2 to promote the fate of photoreceptors and horizontal cells ³¹ . To assess the efficiency of rod induction, we quantified the number of Rhodopsin- tdTomato ⁺ cells in retinal flatmount preparations at 4 weeks after the second injection, when nearly all Rhodopsin-tdTomato ⁺ cells were at the terminal stage of rod differentiation (Fig. 28m). The Rhodopsin-tdTomato ⁺ cells were evenly distributed across the retina, with over 800 Rhodopsin-tdTomato ⁺ cells per mm ² scored in the dorsal, nasal, temporal, and ventral retina (Fig. 28p-t). By contrast, no MG-derived rods were observed in control retinas (ShHlO-GFAP- -catenin omitted from the first injection) from wild-type mice (Fig. 28t). We also examined regenerative capability of MGs in 7-month-old mouse retinas. The production of Rhodopsin-tdTomato ⁺ cells was reduced to -200 per mm ² scored in the dorsal, nasal, temporal, and ventral retina (Fig. 40).

The rod is a primary sensory neuron consisting of specialized cellular structures for detection of photons and communication with downstream neurons, including the outer/inner segments and the synaptic terminal. Using confocal microscopy and immunohistochemistry, we examined whether MG-derived rod cells expressed a set of rod genes (Rhodopsin, Gnatl/rod a-transducin, Peripherin-2, Recoverin, and Ribeye) that play important roles in the formation/maintenance of rod cellular structures and are essential for phototransduction. Wild-type mice at 4 weeks of age were first injected with ShHlO-GFAP- -catenin (stimulate MG proliferation) and ShHlO-Rhodopsin-tdTomato (label MG-derived rods). Four weeks after the second injection for ShHlO-GFAP- mediated gene transfer of Otx2, Crx, and Nrl, we observed that the Rhodopsin-tdTomato ⁺ cells expressed Rhodopsin and Peripherin-2 in the rod outer segment (Fig. 29a-d, 29e-h), Gnat-l and Recoverin in the rod soma and processes (Fig. 29i-l, 29m-p), and Ribeye in the rod synaptic terminal (Fig. 29q- t), which was enlarged to form a synaptic bouton in close apposition to the post- synaptic specialties of PKCa ⁺ rod bipolar cell dendrites (Fig. 29u-x). As the immunoreactivity for Rhodopsin and Peripherin-2 were present at high density and in close proximity to native rods, we also dissociated retinal cells and detected the expression of Rhodopsin and Peripherin-2 in Rhodopsin- tdTomato ⁺ cells (Fig. 41). The rod outer segment (ROS) consists of densely packed membrane discs housing the visual pigment and essential proteins for rod phototransduction. The rod inner segment (RIS) is filled with long thin mitochondria providing a main energy source to meet the high metabolic needs of rod photoreceptors. Synthesized proteins and membranes are trafficked from the RIS to ROS via the connecting cilium (CC), a microtubule-based structure crucial for the function and survival of rod

photoreceptors. Rods communicate with second-order neurons, bipolar and horizontal cells, through a highly specialized triad synaptic structure. Ultrastructural analysis using transmission electron microscopy showed that the MG-derived rods correctly formed the ROS (Fig. 29y), RIS (Fig. 29z), CC (Fig. 29z' and 29z"), and classic triad synapse (Fig. 29z"'), which were morphologically similar to native rods.

To unambiguously assess the functionality of newly generated rod

photoreceptors, we reprogrammed MGs in Gnatl :Gnat2 ^cpf13 double mutant mice, which lack photoreceptor-mediated light responses. Gnatl ⁷ mice lack rod function due to the absence of rod a-transducin, an essential component for rod

phototransduction, and are a model of congenital stationary night blindness ⁹ .

Gnat2 ^cpfB homozygotes have mutated cone a-transducin, with poor cone-mediated responses evident by 3 weeks of age and complete lack of cone-mediated responses at 9 weeks of age ¹⁰ . Phototransduction occurs in the outer segment of photoreceptors. Light-driven translocation of Gnatl allows rods to adapt over a wide range of light intensities ³² , and also contributes to rod survival and synaptic transmission to rod bipolar cells ³³ . To reconstitute phototransduction in MG-derived rods in Gnatl ⁷ :Gnat2 ^cpf13 mice, we used ShHlO- Rhodopsin-mediated gene transfer of the wild-type Gnatl in MGs, a virus serotype that should not transduce native rods (Fig. 35). Gnatl :Gnat2 ^cpf13 mice at 4 weeks of age were first injected with ShHlO-GFAP- -catenin (to stimulate MG proliferation), ShHlO-Rhodopsin-tdTomato (to label MG-derived rods), and ShHlO-Rhodopsin-Gnatl (to correct the Gnat mutation in MG-derived rods). Four weeks after the second injection for ShHlO-GFAP-mediated gene transfer of Otx2, Crx, and Nrl, we observed that Gnatl was localized to the ROS in the Rhodopsin-tdTomato ⁺ MG-derived rods in the dark- adapted retina (Fig. 30a). After light stimulation (10,000 lux for 2 hours), Gnatl translocated towards the inner retina to other cellular compartments including the RIS, rod soma, and synaptic terminal (Fig. 30d). However, the co-expressed Rhodopsin-tdTomato, which served as an internal control, was distributed in all cellular compartments regardless of light stimulation (Fig. 30b, e). Furthermore, MG-derived rods were generated as effectively in Gnatl ^/ :Gnat2 ^cpf13 mice as those in wild-type mice, assessed by scoring the number of Rhodopsin-tdTomato ⁺ cells in the four quadrants in retinal flatmount preparations (Fig. 30g-k). By contrast, no MG-derived rods were observed in control retinas (ShHlO-GFAP- -catenin omitted from the first injection) from Gnatl ^/ :Gnat2 ^cpf13 mice (Fig. 30k).

Vision is initiated by light-responsive photoreceptors and propagated through synaptic transmission to bipolar cells. Synaptic release from rod photoreceptors requires the calcium current ³⁴ · ³⁵ . We first examined the calcium current of MG- derived rods in a retinal slice preparation from Gnatl ^/ :Gnat2 ^cpf13 mice at 4 weeks after the second injection for rod induction. We targeted MG-derived rods (GFAP- GFP ⁺ cells) for whole cell voltage clamp using a Cs-based internal solution to reveal voltage-gated calcium currents. Prominent inward currents were recorded with a peak near 0 mV from treated retinas (an average of 11 recordings taken from 6 cells of 3 retinas; Fig. 3 la), consistent with L-type calcium currents expected in rods ³⁶ .

Visual information is integrated by retinal ganglion cells (RGCs), the output neurons of the retina. To examine whether MG-derived rod photoreceptors integrate into retinal circuits, we recorded photoreceptor-mediated light responses from RGCs of Gnatl ^/ :Gnat2 ^cpf13 mice at 4 weeks after the second injection for rod induction, using an in vitro preparation described previously ³⁷ · ³⁸ . To distinguish rod- from cone- mediated light responses, we targeted RGCs in the ventral retina, where cones primarily express UV- sensitive cone opsin, with peak sensitivity at 360 nm, whereas rods express the typical green-sensitive rhodopsin with peak at 500 nm ³⁷ · ^{39 41} . Large somas (diameter, >20 pm) in the ganglion cell layer were targeted for loose-patch recordings of action potentials using IR imaging to minimize photobleaching, and subsequently the tissue was exposed to various levels of green and UV light presented within a circular region (l-mm diameter) relative to a dark background. In control retinas (ShHlO-GFAP- -catenin omitted from the first injection), RGCs (n = 19 cells from 7 retinas, 4 animals) lacked light responses (Fig. 3 lb, e, f); whereas about half of RGCs from treated retinas (n = 15 of 27 cells from 10 retinas, 6 animals) showed clear responses following either light onset (ON cells, n = 6; Fig. 3lc) or light offset (OFF cells, n = 9; Fig. 3ld, e, g). For the entire sample, RGCs from the treated retina showed stronger responses (18.0 +/- 3.6 spikes s ¹ ; mean +/- sem) to green light at an intermediate intensity compared to RGCs from the control retina (-0.03 +/- 0.76 spikes s ¹ ; p = 2.7x 10 ⁴ ; Fig. 3le). For the responding RGCs from the treated retina (n = 15; Fig. 3le), the firing rate was ~3.4 times more sensitive to green light as compared to UV light (Fig. 3lg), consistent with a rod- mediated response ³⁷ · ³⁸ · ⁴² . By comparison, the control cells lacked responses to either green or UV light (Fig. 3lf). The responding RGCs from treated retinas showed lower sensitivity than RGCs from wild-type (wt; C57/B6 strain) retinas (Fig. 3lh-k); this was especially evident for ON RGCs (Fig. 3 li). For both ON and OFF RGCs, responses to a high light level in the treated retina resembled RGC responses to a low light level in the wt retina (Fig. 3lh, j), which is likely explained by the relatively smaller number of responsive rods in the treated retina.

Given the significant photoreceptor-mediated light responses recorded from RGCs of the treated Gnatl ^/ :Gnat2 ^cpf13 mice in vitro, we reasoned that photoresponses could be transmitted from the retina to the primary visual cortex in the brain in vivo. Visually- evoked potentials (VEPs) were recorded in the primary visual cortices of lightly -anesthetized Gnatl ^/ :Gnat2 ^cpf13 mice at 4 weeks after the second injection for rod induction from the treated and control (ShHlO-GFAP- -catenin omitted from the first injection) groups. Stimuli were first delivered at low intensity, and the intensity was gradually increased in each session (1.2, 2.8 and 3.2 loglO nW mm ² at the retina; see Methods). VEPs were identified as negative deflections in the cortical local field potentials (LFPs) following stimulus onset. No response was observed at the dimmest intensity, but gradually stronger responses were observed for the two brighter intensities. At the highest intensity (3.2 loglO nW mm ² ), the light stimulus drove a distinctive cortical response in the LFP of the treated group, while no response was recorded in the control group (Fig. 311, m). The responses of the treated group were delayed and smaller relative to responses of C57/B6 wt controls (Fig. 311), perhaps explained by the cortical integration of relatively lower outputs from RGCs in the treated animals. Nevertheless, the significant post-stimulus LFP amplitudes from the treated mice confirmed rescued light response in the primary visual cortices in comparison to the control group (Fig. 3lm). Our results demonstrate that MGs, without retinal injury, can be

reprogrammed in vivo to generate new rod photoreceptors that integrate into retinal circuits, and restore vision in mammals.

Example 5

Gene transfer of Ascii stimulates MG proliferation

To examine whether Ascll expression leads to MG proliferation, EdU incorporation was analyzed following ShHlO-GFAP-mediated gene transfer of wild- type Ascll in adult mouse retina at 4 weeks of age and MG cell proliferation was performed as described in Example 1. As shown in Figure 43, ShHlO-GFAP-mediate gene transfer of wild-type Ascll in adult mouse retina stimulated MG proliferation, as observed by colocalization of MG labeled cells with EdU488.

Methods

Animals

All procedures involving the use of animals in this study were performed in accordance with National Institutes of Health guidelines. Wild-type mice (strain C57BL/6J) and Rosa26-tdTomato reporter mice (strain B6.Cg- Gt(ROSA)26Sor ^{tml4(CAG tdTomato)Hze} /J) were obtained from the Jackson Laboratory (Bar Harbor, ME). Gnatl ^/ :Gnat2 ^cpf13 double mutant mice were kindly provided by Dr. Bo Chang (The Jackson Laboratory, Bar Harbor, ME). For light adaptation, the mice were placed in the dark for at least 12 hours and the pupils were dilated with 1% tropicamide and 1% atropine before exposure to 10,000 lux white light for 2 hours. For dark adaptation, the mice were maintained in the dark for more than 12 hours and all procedures were performed under infrared illumination.

AAV production and intravitreal injection

cDNAs encoding GFP, tdTomato, b-Catenin, Otx2, Crx and Nrl were subcloned and inserted into a AAV vector backbone where the expression was driven by the GFAP promoter (a gift from Dr. Lin Tian at UC Davis), or the Rhodopsin promoter (subcloned from pRho-DsRed (Addgene #11156). The Gnatl cDNA, reversely transcribed and amplified from mouse retinal RNAs, was used to replace tdTomato in pAAV-Rho-tdTomato to build the pAAV-Rho-Gnatl vector. Individual Adeno-associated virus (AAV) was produced by plasmid co-transfection and iodixanol gradient ultracentrifugation. Purified AAVs were concentrated with Amicon Ultra-l5 Filter Units (Millipore, Bedford, MA) to a final titer of 1.0-5.0 X 10 ¹³ genome copies/mL (Fig. 42). Intravitreal injection was performed using a

microsyringe equipped with a 33-gauge needle. The tip of the needle was passed through the sclera, at the equator and next to the dorsal limbus of the eye, into the vitreous cavity. Injection volume was 1 pl per eye for AAVs.

EdU and BrdU co-labeling and detection

EdU or BrdU solution (1 pL, 1 mg/mL) was intravitreally injected into the vitreous chamber. For BrdU detection, the retinas were rinsed with PBS after fixation with 4% paraformaldehyde and incubated with 2 M HC1 for 30 min at room temperature. Rinse the retinas with PBS and incubate with a blocking buffer containing 5% normal donkey serum, 0.1% Triton X-100, and 0.1% NaN3 in PBS for 2 hours at room temperature. Primary antibody for BrdU (Thermo Scientific) was added for overnight incubation at 4°C. Retinas were washed with PBS and incubated with secondary antibody (DyLight™594- conjugated AffmiPure Donkey Anti-Mouse IgG, Jackson ImmunoResearch) for 2 hours at room temperature. Analysis of EdU incorporation was performed using Click-iT EdU Kit (Thermo Scientific). EdU detection components were re-suspended according to manufacturer’s instructions and applied directly to retinal samples. In brief, the solution for each EdU reaction has a total volume of 250 pl composed of 215 pl IX Click-iT reaction buffer, 10 pl CuS04, 0.6 pl Alexa Fluor azide, and 25 pl IX Reaction buffer additive. After incubation in the reaction solution for 30 min at room temperature, samples were washed with PBS and mounted with Fluoromount-G for detection. Immunohistochemistry and Imaging

Retinas were fixed with 4% paraformaldehyde in PBS for 30 min at room temperature, and sectioned at 20-pm thickness. Sample slides were washed with PBS before incubation with a blocking buffer containing 5% normal donkey serum, 0.1% Triton X-100, and 0.1% NaN3 in PBS for 2 hours at room temperature. Primary antibodies were added for overnight incubation at 4°C. Primary antibodies used: Rhodopsin (1 :250, Thermo Scientific, MS-1233-P1), Peripherin-2 (1 :500, Millipore, MABN293), Recoverin (1:500, Millipore, AB5585), Gnatl (1: 1000, Santa Cruz, sc-

389), PKCa (1: 100, Santa Cruz, sc- 8393), and Ribeye (1 :500, Synaptic Systems, 192103). Sections were washed with PBS and incubated with secondary antibodies (Jackson ImmunoResearch) for 2 hours at room temperature. Cell nuclei were counterstained with DAPI (Sigma). Confocal Images were acquired using a Zeiss LSM 510 EXCITER microscope.

Transmission electron microscopy

The whole eye was fixed in 2.5% gluteraldehyde and 2% paraformaldehyde in 0.1M sodium cacodylate buffer pH7.4 with for 1 hour at room temperature. After the cornea was removed, samples were postfixed in 1% osmium tetroxide for 1 hour, en bloc stained in 2% aqueous uranyl acetate for a further hour then rinsed, dehydrated in ethanol and propylene oxide and infiltrated with Embed 812 (Electron Microscopy Science). The blocks were hardened overnight at 60°C. 60-nm sections were cut with a Leica ultramicrotome and collected on formvar/carbon coated nickel grids. Grids were placed section side down on drops of 1% hydrogen peroxide for 5 minutes, blocked for nonspecific binding on 3% bovine serum albumin in PBS containing 1% Triton-X for 30 minutes. Grids were incubated overnight as a primary antibody with either a rabbit anti-GFP (T. Siidhof lab, Stanford University) at 1:200 or rabbit anti- TdTomato at 1: 100 (Clontech, 632496), rinsed in buffer and then incubated with the secondary antibody 10 nm protein A gold (Utrecht UMC) for 30 mins. The grids were well rinsed in PBS, fixed in 1% gluteraldehyde for 5 mins, rinsed again, dried and stained using 2% aqueous uranyl acetate and lead citrate. Sample grids were viewed using FEI Tencai Biotwin TEM at 80 kV of accelating voltage. Images were acquired with a Morada CCD camera and iTEM (Olympus) software. Mouse retinal slice preparation and calcium current recordings

Gnatr ^/ :Gnat2 ^cpfB mice were anaesthetized with isoflurane (Sigma), sacrificed by cervical dislocation, and their eyes enucleated. Whole retinas were isolated and placed on a 0.45-mih cellulose acetate/nitrate membrane filter (Millipore), which was secured with vacuum grease to a glass slide adjacent to the recording chamber. Slices were cut to a thickness of 150 pm using a tissue sheer, and transferred to the recording chamber while remaining submerged. The recording chamber was immediately attached to a perfusion system, and the slices were perfused at a rate of 5 mL min-l with Ames media bubbled with 95% Ch and 5% CC . All stages of retinal preparation were carried out at room temperature in a dark room. The standard recording solution for regenerated rods was composed of (in mM): 108 gluconic acid, 5 EGTA, 10 CsCl, 10 TEA, 4 MgATP, lLiGTP. The pH was adjusted to 7.4 with CsOH. The osmolarity of both extracellular and intracellular solutions was 289-293, with a pH of 7.35-7.40.

Patch pipettes (tip resistance, 10 - 12 MW ) were fabricated from borosilicate glass (TWF150-4, WPI) using a two-stage vertical puller (Narishige). Pipettes were coated with Sticky Wax, (Kerr Corp). Whole-cell recordings were obtained using a dual EPC10/2 amplifier (HEKA Instruments). Slices were viewed with a Zeiss Axioskop 2FS plus equipped with a water-immersion 40X DIC objective and using an infrared filter for illumination. Regenerated rods were identified by their shape, GFP fluorescence and position in the slice. Illumination for epifluorescence was performed using an X-Cite 120Q lamp (EXFO) with a 488 nm bandpass excitation filter set for imaging GFP fluorescence or 590 bandpass filter set for imaging RFP Images were acquired before whole cell recording with Andor iXon camera controlled by a Shutter driver VCM-D1. Data were acquired using PatchMaster (HEKA Instruments), and analysis performed using Igor Pro (WaveMetrics) and Origin 7.5 (Microcal). Currents were elicited at 60-second intervals, collected at 20 kHz, and low-pass filtered at 1 kHz. RGC recordings

Retinas from Gnatl ^/ :Gnat2 ^cpfB double mutant mice were prepared as described previously (Wang et al, 2011; Ke el al, 2014). After dissecting the retina under infrared light, the tissue was superfused with Ames’ medium bubbled with 95% C and 5% CC in a chamber on a microscope (Olympus BX51WI) stage at ~34 deg C. A patch pipette (tip resistance, ~3-5 MW) filled with Ames’ medium was used to form a loose seal (-50-200 MW) on a large soma (>20-pm diameter) to record action potentials. Cells were targeted under microscopic control using infrared light, a 60X water objective lens (NA, 0.9) and an infrared-sensitive camera (Retiga 1300, Qcapture software; Qimaging Corporation). Data were sampled at 10 kHz and recorded on a computer using a MultiClamp 700B amplifier and pClamp9 software (Molecular Devices).

A total of 12 animals were studied, six treated animals, four controls (i.e.. beta-catenin delivery omitted from first virus injection) and two C57/B6 wildtype. Of these, six animals (three treated, three controls) were studied in a double blind fashion; the person performing the virus injection was not aware of the identity of the virus condition, and the person performing the recording did not know the treatment group of the animal until the conclusion of all experiments.

Light stimuli were 1 -mm-diameter spots generated by green (peak, 530 nm) or ultraviolet (UV; peak, 370 nm) LEDs that were diffused and windowed by the aperture in the microscope’s fluorescence port and projected through a 4X objective lens (NA, 0.13) onto the photoreceptor layer. In some experiments, light was attenuated with a 2.0 neutral density filter (NDF; Kodak Wratten, Edmund Optics) that attenuated green and UV light by 130- and 880-fold, respectively. Light was presented as 200-ms flashes on darkness every 10 secs. In one block of trials, green and UV light flashes were alternated for 10 levels, with increasing intensity over time. For some cells, the entire block was repeated both with and without the NDF in place. For some cells with weak or absent responses, light flashes were presented in the brighter range only. For cells with sensitive responses, flashes were presented either in the dimmer range only or in both ranges. Firing rate (spikes s ¹ ) was recorded during a response window (300-500 ms) and normalized by subtracting the average firing rate measured during baseline periods before (500 ms) and after the flash (500 ms, Fig. 3 lb-d). If there was an obvious response to either light onset or offset, the response window was adjusted accordingly (Fig. 3lc, d). If there was not an obvious response, the window for light onset was used by default (Fig. 3 lb). RGC responses were quantified by averaging firing rates for green flashes in the intensity range of -1.7 to -0.7 loglO nW/mm ² (Fig. 3le), which included four flash levels for blocks with or without the NDF in place. From these averaged responses, we selected responding cells from the treated group that exceeded the largest response measured in the control group. For responding RGCs in the treated group, we averaged the response across cells and combined data over the dimmer and brighter stimulus ranges (Fig. 3lg). We fit the flash intensity -response function using the equation:

R(I) = AF (F + o' ¹ ) ¹ ,

where I is intensity (nW mm ^-2 ), A is the maximum response amplitude (spikes s ¹ ), s is the intensity that drives a half-saturating response, and q determines the slope. The fitted curves shared A and q parameters with unique s parameters for green and UV stimuli. Fitting was performed using least- squares routines in Matlab (Mathworks). Visually-evoked potentials (VEPs) and multi-unit activity (MUA) recordings

Under isoflurane anesthesia (2%; Baxter, Deerfield IL), an injection of xylocaine/epinephrine (1.0%; AstraZeneca, Wilmington, DE) was delivered beneath the skin overlying the skull. The skull was then exposed, cleaned of tissue, and coated with a thin layer of cyanoacrylate adhesive (VetBond, 3M, St. Paul MN). A second layer of cyanoacrylate adhesive (Maxi-Cure, BSI, Atascadero CA) was used to attach 2 metal bars to the pretreated skull; these bars were then used to secure the head into a custom-built stereotaxic apparatus. A craniotomy was made over primary visual cortex, leaving the dura mater intact. Body temperature was maintained at 36°C during surgery and experiments via a heating pad placed below the subject. Pupils were dilated with 1% tropicamide and 1% atropine, and the eyes were then coated with a thin layer of silicone oil (Sigma, St. Louis MO) to prevent dehydration.

Neurophysiological signals were collected using a 16-site silicon probe with 4 recording sites on each of 4 shanks (l00-pm vertical separation between recording sites; 125 -pm horizontal spacing between shanks; 1-2-MW impedance; NeuroNexus Technologies, Ann Arbor MI). After the probe was lowered through the dura mater and into the cortex, a layer of agarose (1.5% in ACSF; Sigma) was applied to cover the craniotomy. An insulated silver wire (0.25-mm diameter; Medwire, Mt. Vernon NY) inserted above the cerebellum served as a reference electrode. Signals were preamplified IOc (MPA8I preamplifiers; Multi Channel Systems MCS GmbH, Reutlingen, Germany) before being amplified 200x and band-pass filtered at 0.3-5000 Hz (Model 3500; A-M Systems, Inc., Carlsborg, WA). The amplified and filtered signals were sampled at 25 kHz using a digital interface (Power 1401 mk 2;

Cambridge Electronic Design, Cambridge, UK).

After the recording probe was implanted, isoflurane was lowered to 1.0-1.5% and mice were given 30 minutes to adapt to the dimly-lit testing area before visual stimuli were delivered. Stimuli were 50-ms flashes of white light from a light- emitting diode (LED) that was placed 1 cm from the eye. The LED had two peaks, at -460 and -550 nm, with an integrated intensity of -20 pW mm ² ; taking into account the spectral tuning of Rhodopsin, this corresponded to an equivalent intensity at 500 nm (i.e., the peak sensitivity of Rhodopsin) of -7.55 pW mm ² at the cornea and -1.42 pW mm ² (or -3.2 loglO nW mm ² ) on the retina (assuming a 4-mm ² dilated pupil area and evenly-spread light over the -21.2 mm ² retinal area). Visually-evoked potentials were identified as negative deflections in the cortical local field potentials (LFPs) following stimulus onset, with greater negative amplitudes in deeper cortical layers than in superficial layers. For LFP analyses, the recording channel with the greatest negative amplitude in response to visual stimulation was used. Maximum negative deflections in the LFP during the 0.5 s following stimulus onset were measured, and, for each animal, we tested whether the median of the response distribution differed from zero (Wilcoxin signed-rank test). Analyses were performed using MATLAB (The MathWorks, Inc., Natick, MA), Spike2 (Cambridge Electronic Design) and GraphPad Prism 6 (GraphPad Software, San Diego, CA).

Statistical analysis

Statistical differences between different experimental groups were typically analyzed by a Student’s t-test or one-way ANOVA test except in cases where the data were not normally distributed ( e.g ., LFP amplitudes), in which case a non-parametric test was used, as described above. Data are presented as mean ± SEM, except where data were skewed (e.g., LFP amplitudes), in which case a box plot indicates median ± inter-quartile range. A value of p < 0.05 is considered significant. References

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The disclosures of each and every patent, patent application, and publication cited herein are hereby incorporated herein by reference in their entirety. In case of conflict, the present disclosure controls.

While this invention has been disclosed with reference to specific

embodiments, it is apparent that other embodiments and variations of this invention may be devised by others skilled in the art without departing from the true spirit and scope of the invention. The appended claims are intended to be construed to include all such embodiments and equivalent variations.