Phylogenetic Analysis of Vertebrate Fibrillar Collagen Locates the Position of Zebrafish alpha 3(I) and Suggests an Evolutionary Link Between Collagen alpha Chains and Hox Clusters

Type I collagen in tetrapods is usually a heterotrimeric molecule composed of two alpha 1 and one alpha 2 chains. In some teleosts, a third alpha chain has been identified by chromatography, suggesting that type I collagen should also exist as an alpha 1(I) alpha 2(I) alpha 3(I) heterotrimer. We prepared, from zebrafish, three distinct cDNAs identified to be those of the collagen alpha 1(I), alpha 2(I), and alpha 3(I) chains. In this study on the evolution of fibrillar collagen alpha chains and their relationships, an exhaustive phylogenetic analysis, using vertebrate fibrillar collagen sequences, showed that each alpha chain constitutes a monophyletic cluster. Results obtained with the newly isolated sequences of the zebrafish showed that the alpha 3(I) chain is phylogenetically close to the alpha 1(I) chain and support the hypothesis that the alpha 3(I) chain arose from a duplication of the alpha 1(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 alpha chains of fibrillar collagens of vertebrates could be related to Hox cluster history.