Abstract - We have recently demonstrated that the Ag1 protein is necessary for the fin regeneration in Danio rerio fish. Robust activation of the ag1 gene expression in cells of the wound epithelium is observed after caudal fin amputation. Moreover, the inhibition of translation of ag1 mRNA leads to the retardation of the caudal fin regeneration. The results of our research are important because the ag1 gene is contained only in lower vertebrates (fish and amphibians) with good regenerative capacity, whereas this gene is missing in higher vertebrates, which are not capable of the efficient limb regeneration. Our data indicate that the reduction of the potential regenerative ability in higher vertebrates including humans can be explained by the extinction of some genes, particularly the ag1 gene, essential for regeneration.