To provide a method for promoting nerve cell growth or myelination increase; to provide a pharmaceutical preparation for therapy of nerve or myelin drop diseases in nervous tissues; to provide a pharmaceutical preparation for treating central nervous system or peripheral nervous system neuron degenerative diseases; and to provide a pharmaceutical preparation for treating retinal nerve disorders.

Prosaposin and peptide derivatives derived therefrom promote neurite outgrowth in vitro. A peptide consensus sequence is determined by comparing the active neurite outgrowth-inducing saposin C peptide sequence with that of various hematopoietic and neuropoietic cytokines. These cytokine-derived peptides promote the same processes as their corresponding cytokines. In addition, prosaposin and saposin C promote increased nerve cell myelination ex vivo.

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