Meeting Abstract

P3.93  Thursday, Jan. 6  The discovery of orthologs of chordate odorant receptors in the cnidarian Nematostella vectensis reveals this lineage of genes has ancient roots CHURCHER, A.M.*; TAYLOR, J.S.; Univ. of Victoria, Victoria BC; Univ. of Victoria, Victoria BC amchurch@uvic.ca

Vertebrate odorant receptors (ORs) are one of several families of G protein-coupled receptors (GPCRs) that function in olfaction. The repertoires of OR genes in vertebrates range from 44 genes in pufferfish to over 1000 in some mammals. These genes however, do not appear to be related to the chemosensory genes found in insects and nematode worms. The recent discovery of OR genes in cephalochordates is evidence that ORs evolved earlier on in metazoan evolution than previously believed. Here, we investigated the antiquity of OR genes by using amino acid motif that are commonly found in cephalochordate and vertebrate ORs to search for orthologs in the protein predictions from 12 non-chordate species. Using this approach followed by iterative Blastp searches for paralogs, we found a novel group of genes in the cnidarian Nematostella vectensis. Our phylogenetic analysis that included representatives from the other major lineages of rhodopsin-like GPCRs showed that the N. vectensis genes, the cephalochordate and vertebrate ORs, and a family of genes from the echinoderm, Strongylocentrotus purpuratus, form a monophyletic clade. Our phylogenetic analysis also reveals that the diversification of the rhodopsin-like GPCR family began at least 700 million years ago, prior to the divergence of cnidarians and bilatarians. ORs and other rhodopsin-like GPCRs have roles in cell migration, axon guidance and neurite growth; therefore duplication and divergence in this family may have played a key role in the evolution of cell type diversity (including the emergence of complex nervous systems) and in the evolution of metazoan body plan diversity.