The Collagens of the Ctenophore Pleurobrachia bachei

Abstract

The evolution of multicellular animals required the development of epithelial tissues that function in controlling the transport of molecules from one environment to another. Collagen proteins are crucial to the formation of epithelial tissues, and are therefore critical in understanding the origins of multicellularity and Metazoa. We looked for collagen proteins in the recently sequenced Ctenophore Pleurobrachia bachei genome, using collagen sequences from both Homo sapiens and basal organisms as templates. We discovered that P. bachei has 7 distinct type IV collagen sequences along three genomic scaffolds. Two of these were aligned in an in-line pattern along the genome, while another two were aligned in a head-to-head fashion, indicating both traditional and inverted gene duplication events. Furthermore, collagen IV intra-genic investigations showed that P. bachei has a more diverse set of α-chains than Homo sapiens. In addition, we found 4 conserved collagen domain proteins which we were unable to assign to specific collagen families. Given recent evidence suggesting that Ctenophores are the most basal phyla of the Metazoans, our findings suggest that the common ancestor to all Metazoa contained a much more developed collagen profile than previously appreciated.