Meeting Abstract
Fibrillar collagens are a metazoan novelty that are a critical part of the extracellular matrix of muscle, skeleton, skin, and connective tissues. Comprised of three families of genes (Clade A, Clade B, Clade C), they underwent considerable duplication and neofunctionalization in jawed vertebrates (gnathostomes). Previous work has suggested that ancestral chordates possessed four fibrillar collagens (2 A’s, 1B, 1C) while most jawed vertebrates have eleven (5 A’s, 4 B’s, 2 C’s). We asked whether the expansion of this gene family coincides with gnathostome morphological novelties by investigating these genes in the sea lamprey Petromyzon marinus, an early diverging jawless vertebrate. To do this, we used phylogenetics and synteny to identify fibrillar collagen orthologs in the sea lamprey. We then performed in situ hybridizations on lamprey embryos for these genes across developmental stages, preparing plastic sections to identify tissue-specific expression. Overall, we have identified eight new fibrillar collagen genes in the sea lamprey and categorized their expression during head morphogenesis. We believe that Petromyzon marinus may have twelve fibrillar collagen genes (7 A’s, 4 B’s, 1 C), four being lineage-specific duplicates. Our phylogenetic and syntenic analyses have identified orthologs of Clade A / C genes in lamprey with strong certainty while Clade B remains uncertain, possibly due to more divergence. Our in situ hybridizations reveal expression of these genes that is less tissue-specific than their gnathostome orthologs. Lastly, we discuss how the the duplication and specialization of these collagens may have been involved in the diversification of musculoskeletal tissues during vertebrate evolution.
