Abstract
Fibrillar collagens are involved in the formation of striated fibrils and are present from the first multicellular animals, sponges, to humans. Recently, a new evolutionary model for fibrillar collagens has been suggested (Boot-Handford, R. P., Tuckwell, D. S., Plumb, D. A., Farrington Rock, C., and Poulsom, R. (2003) J. Biol. Chem. 278, 31067-31077). In this model, a rare genomic event leads to the formation of the founder vertebrate fibrillar collagen gene prior to the early vertebrate genome duplications and the radiation of the vertebrate fibrillar collagen clades (A, B, and C). Here, we present the modular structure of the fibrillar collagen chains present in different invertebrates from the protostome Anopheles gambiae to the chordate Ciona intestinalis. From their modular structure and the use of a triple helix instead of C-propeptide sequences in phylogenetic analyses, we were able to show that the divergence of A and B clades arose early during evolution because alpha chains related to these clades are present in protostomes. Moreover, the event leading to the divergence of B and C clades from a founder gene arose before the appearance of vertebrates; altogether these data contradict the Boot-Handford model. Moreover, they indicate that all the key steps required for the formation of fibrils of variable structure and functionality arose step by step during invertebrate evolution.
Highlights
Fibrillar collagens are present from sponges to humans and are the primary component of striated fibrils [1, 2]
Blast searching of the S. purpuratus genome resources using a sequence encoding the 1␣ C-propeptide allowed us to identify two genomic sequences encoding the C-terminal part of the C-propeptides unrelated to those of the three known sea urchin fibrillar collagens
B Clade Fibrillar Collagen Is Present in Protostomes
Summary
Genomic Cloning and Reverse Transcriptase-PCR of Paracentrotus lividus Sequences Encoding Fibrillar Collagens—A search of sea urchin genes encoding fibrillar collagen ␣ chains was conducted at the Human Genome Sequencing Center Web site (Baylor College of Medicine, Houston, TX) using the C-propeptide sequence from the Strongylocentrotus purpuratus 1␣ chain [18]. From this analysis, we were able to discover two regions of the S. purpuratus genome encoding the C terminus of a classical C-propeptide distinct from the three previously characterized sea urchin fibrillar collagen chains [17,18,19]. Searches of S. purpuratus genomic sequences were conducted using the TSPN sequence from the human pro-␣1(V) chain This led to the identification of two contigs (Contig3949 and Contig50826) that might encode two TSPN modules related to fibrillar collagens of the B/C clade as suggested from Blast analysis. The coding regions of ci0100131606 and ci0100144916 that were not confirmed by ESTs were deduced by their similarity to comparable regions of fibrillar collagens characterized to date and from similarities to Ciona savignyi ortholog genes For this purpose, sequences from these two C. intestinalis genes were used to investigate the C. savignyi genome at NCBI. Ungapped alignments were computed to derive trees according to neighbor joining and maximum parsimony methods using the Phylo win program [23]; 1,000 replicates were generated for bootstrapping analysis
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