We have identified a chick cDNA encoding the novel membrane protein, Protogenin. It has structural features of four immunoglobulin domains and five fibronectin type III domains and is closely related to the DCC/neogenin subclass of the Ig superfamily. protogenin gene is conserved among human, mouse and chick genome, and mapped on the same chromosome as other related members of the gene family such as neogenin, punc and nope. Expression of protogenin mRNA is most prominent in E1-E3 chick embryos and subsequently its expression level declines. The transcripts are found in early mesodermal cells, the neuroepithelial cell layer of the brain and the trunk neural tube, the neural layer of the retina and in the epithelial somite and dermomyotome.