To provide a new VOPT [ventroptin (a BMP-4 neutralizing factor protein)] binding to BMP-4 belonging to a BMP (bone morphogenetic protein) and inhibiting actions of the BMP-4 and a gene DNA encoding the VOPT and to provide a method, etc., for screening BMP-4-neutralization activity promoters or inhibitors using the VOPT.

Molecules of an E8 chicken retina expressing specifically for the dorso-ventral axis are screened by an RLCS method (restriction landmark cDNA scanning method) and an mRNA is detected by a northern blot technique using a ventrally specifically expressing DNA fragment as a probe to screen a chicken retinal cDNA library. Thereby, a full-length VOPT cDNA encoding a signal sequence and three repetitive sequences rich in cysteine is obtained. A primer is designed on the basis of the chicken VOPT sequences to isolate a cDNA encoding a full-length murine VOPT from a murine ocular cDNA library according to the conventional methods.