title: Opsins and clusters of sensory G-protein-coupled receptors in the sea urchin genome.
abstract: Rhodopsin-type G-protein-coupled receptors (GPCRs) contribute the majority of sensory receptors in vertebrates. With 979 members, they form the largest GPCR family in the sequenced sea urchin genome, constituting more than 3% of all predicted genes. The sea urchin genome encodes at least six Opsin proteins. Of these, one rhabdomeric, one ciliary and two G(o)-type Opsins can be assigned to ancient bilaterian Opsin subfamilies. Moreover, we identified four greatly expanded subfamilies of rhodopsin-type GPCRs that we call sea urchin specific rapidly expanded lineages of GPCRs (surreal-GPCRs). Our analysis of two of these groups revealed genomic clustering and single-exon gene structures similar to the most expanded group of vertebrate rhodopsin-type GPCRs, the olfactory receptors. We hypothesize that these genes arose by rapid duplication in the echinoid lineage and act as chemosensory receptors of the animal. In support of this, group B surreal-GPCRs are most prominently expressed in distinct classes of pedicellariae and tube feet of the adult sea urchin, structures that have previously been shown to react to chemical stimuli and to harbor sensory neurons in echinoderms. Notably, these structures also express different opsins, indicating that sea urchins possess an intricate molecular set-up to sense their environment.
authors.affiliation: Computational Unit, EMBL, 69117 Heidelberg, Germany. raible@embl.de
authors.forename: Florian
authors.initials: F
authors.lastname: Raible
authors.forename: Kristin
authors.initials: K
authors.lastname: Tessmar-Raible
authors.forename: Enrique
authors.initials: E
authors.lastname: Arboleda
authors.forename: Tobias
authors.initials: T
authors.lastname: Kaller
authors.forename: Peer
authors.initials: P
authors.lastname: Bork
authors.forename: Detlev
authors.initials: D
authors.lastname: Arendt
authors.forename: Maria I
authors.initials: MI
authors.lastname: Arnone
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016384:Consensus Sequence; D016678:Genome; D017403:In Situ Hybridization; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011487:Protein Conformation; D012313:RNA / Q000235:genetics / Q000302:isolation & purification; D011956:Receptors, Cell Surface / Q000235:genetics*; D043562:Receptors, G-Protein-Coupled / Q000737:chemistry / Q000235:genetics*; D017299:Rod Opsins / Q000235:genetics*; D012617:Sea Urchins / Q000235:genetics*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D017299:Rod Opsins; D012313:RNA