Agr family includes three groups of genes, Ag1, Agr2 and Agr3, which encode the thioredoxin domain-containing secreted proteins and have been shown recently to participate in regeneration of the amputated body appendages in amphibians. By contrast, higher vertebrates have only Agr2 and Agr3, but lack Ag1, and have low ability to regenerate the body appendages. Thus, one may hypothesize that loss of Ag1 in evolution could be an important event that led to a decline of the regenerative capacity in higher vertebrates. To test this, we have studied now the expression and role of Ag1 in the regeneration of fins of a representative of another large group of lower vertebrates, the fish Danio rerio. As a result, we have demonstrated that amputation of the Danio fins, like amputation of the body appendages in amphibians, elicits an increase of Ag1 expression in cells of the stump. Furthermore, down-regulation of DAg1 by injections of Vivo-morpholino antisense oligonucleotides resulted in a retardation of the fin regeneration. These data are in a good agreement with the assumption that the loss of Ag1 in higher vertebrates ancestors could lead to the reduction of the regenerative capacity in their modern descendants.

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 cau dal 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 ver tebrates, 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.