Evolutionary genomics of odorant receptors: identification and characterization of orthologs in an echinoderm, a cephalochordate and a cnidarian.

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dc.contributor.author Churcher, Allison Mary
dc.date.accessioned 2011-08-17T20:51:06Z
dc.date.available 2012-07-29T11:22:03Z
dc.date.copyright 2011 en_US
dc.date.issued 2011-08-17
dc.identifier.uri http://hdl.handle.net/1828/3470
dc.description.abstract Animal chemosensation involves several families of G protein-coupled receptors (GPCRs) and, though some of these families are well characterized in vertebrates and nematode worms, receptors have not been identified for most metazoan lineages. In this dissertation, I use a combination of bioinformatics approaches to identify candidate chemosensory receptors in three invertebrates that occupy key positions in the metazoan phylogeny. In the sea urchin Strongylocentrotus purpuratus, I uncovered 192 candidate chemosensory receptors many of which are expressed in sensory structures including pedicellariae and tube feet. In the cephalochordate Branchiostoma floridae, my survey uncovered 50 full-length and 11 partial odorant receptors (OR). No ORs were identified in the urochordate Ciona intestinalis. By exposing conserved amino acid motifs and testing the ability of those motifs to discriminate between ORs and non-OR GPCRs, I identified three OR-specific amino acid motifs that are common in cephalochordate, fish and mammalian ORs and are found in less than 1% of non-ORs from the rhodopsin-like GPCR family. To further investigate the antiquity of vertebrate ORs, I used the OR-specific motifs as probes to search for orthologs among the protein predictions from 12 invertebrates. My search uncovered a novel group of genes in the cnidarian Nematostella vectensis. Phylogenetic analysis that included representatives from the major subgroups of rhodopsin-like GPCRs showed that the cnidarian genes, the cephalochordate and vertebrate ORs, and a subset of genes S. purpuratus from my initial survey, form a monophyletic clade. The taxonomic distribution of these genes indicates that the formation of this clade began at least 700 million years ago, prior to the divergence of cnidarians and bilaterians. Furthermore, my phylogenetic analyses show that three of the four major subgroups of rhodopsin-like GPCRs existed in the ancestor of cnidarians and bilaterians. The utility of the new genes I describe here is that they can be used to identify candidate olfactory cells and organs in cnidarians, echinoderms and cephalochordates that can be tested for function. These genes also provide the raw material for surveys of other metazoans as their genomes become available. My sequence level comparison between chordates, echinoderms and cnidarians exposed several conserved amino acid positions that may be useful for understanding receptor mediated signal transduction. ORs and other rhodopsin-like GPCRs have roles in cell migration, axon guidance and neurite growth; therefore duplication and divergence in the rhodopsin-like gene 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. en_US
dc.language English eng
dc.language.iso en en_US
dc.subject odorant receptor en_US
dc.subject G protein-coupled receptor en_US
dc.subject evolution en_US
dc.subject animal chemosensory systems en_US
dc.subject echinoderm en_US
dc.subject cephalochordate en_US
dc.subject evolution en_US
dc.subject cnidarian en_US
dc.title Evolutionary genomics of odorant receptors: identification and characterization of orthologs in an echinoderm, a cephalochordate and a cnidarian. en_US
dc.type Thesis en_US
dc.contributor.supervisor Taylor, John Stewart
dc.degree.department Dept. of Biology en_US
dc.degree.level Doctor of Philosophy Ph.D. en_US
dc.rights.temp Available to the World Wide Web en_US
dc.identifier.bibliographicCitation Burke RD, Angerer LM, Elphick MR, Humphrey GW, Yaguchi S, Kiyama T, Liang S, Mu X, Agca C, Klein WH, Brandhorst BP, Rowe M, Wilson K, Churcher AM, Taylor JS, Chen N, Murray G, Wang DY, Mellott D, Olinski R, Hallböök F, Thorndyke MC. 2006. A genomic view of the sea urchin nervous system. Developmental Biology. 300:434-460. en_US
dc.identifier.bibliographicCitation Churcher AM, Taylor JS. 2009. Amphioxus (Branchiostoma floridae) has orthologs of vertebrate odorant receptors. BMC Evolutionary Biology. 9:242. en_US
dc.identifier.bibliographicCitation Churcher AM , Taylor JS. 2011. The antiquity of chordate odorant receptors is revealed by the discovery of orthologs in the cnidarian Nematostella vectensis. Genome Biology and Evolution. 3:36-43. en_US
dc.description.scholarlevel Graduate en_US

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