Churcher AM and Taylor JS (2011), The antiquity of chordate odorant receptors is ...

ECB-ART-41846

Genome Biol Evol 2011 Jan 01;3:36-43. doi: 10.1093/gbe/evq079.

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The antiquity of chordate odorant receptors is revealed by the discovery of orthologs in the cnidarian Nematostella vectensis.

Churcher AM , Taylor JS .

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In vertebrates, olfaction is mediated by several families of G protein-coupled receptors (GPCRs) including odorant receptors (ORs). In this study, we investigated the antiquity of OR genes by searching for amino acid motifs found in chordate ORs among the protein predictions from 12 nonchordate species. Our search uncovered a novel group of genes in the cnidarian Nematostella vectensis. Phylogenetic analysis that included representatives from the other major lineages of rhodopsin-like GPCRs showed that the cnidarian genes, the cephalochordate and vertebrate ORs, and a family of genes from the echinoderm, Strongylocentrotus purpuratus, form a monophyletic clade. The taxonomic distribution of these genes indicates that the formation of this clade and therefore the diversification of the rhodopsin-like GPCR family began at least 700 million years ago, prior to the divergence of cnidarians and bilaterians. 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.

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Genes referenced: ago1b LOC100892350 LOC100892511 LOC115919910 opn5 rhol2

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FIG. 1.—. Phylogenetic analysis of Nematostella vectensis and Strongylocentrotus purpuratus OR-like genes, cephalochordate, and vertebrate ORs, and a diversity rhodopsin-like GPCRs that includes the TAARs and the FPRs. The unrooted NJ tree is based on approximately 200 amino acid positions and Poisson-corrected distances. The tree was constructed using the pairwise deletion option, and support for nodes was estimated using 1,000 bootstrap replicates. The bootstrap values for major clades are shown and the scale bar below indicates distance. Non-OR rhodopsin-like GPCRs were included based on the α, β, γ, and δ subgroup classification (Fredriksson et al. 2003). A list of these genes is included in supplementary table S2 (Supplementary Material online). Type I and II vertebrate OR designations are based on the classification in Niimura and Nei (2005). Motif-containing sequences are marked with “▪” and non-OR rhodopsin-like GPCRs from cnidarians are marked with “▴.”

FIG. 2.—. Conserved amino acid residues among Nematostella vectensis OR-like genes. The Weblogo (Crooks et al. 2004) is based on an alignment of 35 full-length N. vectensis OR-like genes from which the N and C termini have been removed. The seven TM-spanning domains (TM1-7) are labeled with blue bars and the intracellular (IL1-3) and extracellular (EL1-3) loops are also labeled. Amino acid positions that are common to fish ORs (Alioto and Ngai 2005) are indicated with “•.” Positions that are common to mouse ORs (Alioto and Ngai 2005) are shown with “-“ and those commonly found in cephalochordate ORs (Churcher and Taylor 2009) are shown by “*.” The region of the alignment that contains motifs 1 and 2 is highlighted in light gray.

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