To understand molecular mechanisms of retinal development, genes expressed selectively only in the early stage of retinal development were isolated by subtractive hybridization based on suppression polymerase chain reaction. The retina has no layered structure in 7-day chick embryos, in contrast with the fully developed multilayered structure of neurons in 15-day embryos. The subtraction between cDNA derived from retinal tissues at these different stages, followed by repeat rounds of 5'-RACE (rapid amplification of cDNA ends) and 3'-RACE, led to isolation of a novel gene with an open reading frame encoding a putative protein with 753 amino acids. Its specific expression in the 7-day embryonic retina was confirmed by Northern blot analysis. The gene, named "retinovin," would be used as a marker for identifying retinal stem cells present at the early stage of retinal development.