Phylogenetic Analysis of Vertebrate Fibrillar Collagen Locates the Position of Zebrafish α3(I) and Suggests an Evolutionary Link Between Collagen α Chains and Hox Clusters

Type I collagen in tetrapods is usually a heterotrimeric molecule composed of two α1 and one α2 chains. In some teleosts, a third α chain has been identified by chromatography, suggesting that type I collagen should also exist as an α1(I)α2(I)α3(I) heterotrimer. We prepared, from zebrafish, three distinct cDNAs identified to be those of the collagen α1(I), α2(I), and α3(I) chains. In this study on the evolution of fibrillar collagen α chains and their relationships, an exhaustive phylogenetic analysis, using vertebrate fibrillar collagen sequences, showed that each α chain constitutes a monophyletic cluster. Results obtained with the newly isolated sequences of the zebrafish showed that the α3(I) chain is phylogenetically close to the α1(I) chain and support the hypothesis that the α3(I) chain arose from a duplication of the α1(I) gene. The duplication might occur during the duplication of the actinopterygian genome, soon after the divergence of actinopterygians and sarcopterygians, a hypothesis supported by the demonstration of a syntenic evolution between a set of fibrillar collagen genes and Hox clusters in mammals. An evolutionary scenario is proposed in which phylogenetic relationships of the α chains of fibrillar collagens of vertebrates could be related to Hox cluster history.