title: Identification of duplicated fourth alpha2-adrenergic receptor subtype by cloning and mapping of five receptor genes in zebrafish.
abstract: The alpha(2)-adrenergic receptors (alpha(2)-ARs) belong to the large family of rhodopsinlike G-protein-coupled receptors that share a common structure of seven transmembrane (TM) alpha-helices. The aims of this study were (1) to determine the number of alpha(2)-AR genes in a teleost fish, the zebrafish (Danio rerio), (2) to study the gene duplication events that generated the alpha(2)-AR subtypes, and (3) to study changes in receptor structure that have occurred since the divergence of the mammalian and fish lineages. Here, we report the cloning and chromosomal mapping of fish orthologs for all three mammalian alpha(2)-ARs. In addition, we identified a fourth alpha(2)-AR subtype with two duplicates in zebrafish. Chromosomal mapping showed that the zebrafish alpha(2)-AR genes are located within conserved chromosomal segments, consistent with the origin of the four alpha(2)-AR subtypes by two rounds of chromosome or block duplication before the divergence of the ray fin fish and tetrapod lineages. Thus, the fourth subtype has apparently been present in the common ancestor of vertebrates but has been deleted or is yet to be identified in mammals. The overall percentage identity between the fish and mammalian orthologs is 53% to 67%, and in the TM regions 80% to 87%. These values are clearly lower than what is observed between mammalian orthologs. Still, all of the residues thought to be important for alpha(2)-adrenergic ligand binding are conserved across species and subtypes, and even the most divergent regions of the fish receptors show clear "molecular fingerprints" typical for orthologs of a given subtype.
authors.affiliation: Department of Pharmacology and Clinical Pharmacology, Turku Graduate School of Biomedical Sciences, University of Turku, Finland.
authors.forename: Jori O
authors.initials: JO
authors.lastname: Ruuskanen
authors.forename: Henri
authors.initials: H
authors.lastname: Xhaard
authors.forename: Anne
authors.initials: A
authors.lastname: Marjamäki
authors.forename: Erik
authors.initials: E
authors.lastname: Salaneck
authors.forename: Tiina
authors.initials: T
authors.lastname: Salminen
authors.forename: Yi-Lin
authors.initials: YL
authors.lastname: Yan
authors.forename: John H
authors.initials: JH
authors.lastname: Postlethwait
authors.forename: Mark S
authors.initials: MS
authors.lastname: Johnson
authors.forename: Dan
authors.initials: D
authors.lastname: Larhammar
authors.forename: Mika
authors.initials: M
authors.lastname: Scheinin
mesh_terms: D000818:Animals; D001483:Base Sequence; D015139:Blotting, Southern; D002874:Chromosome Mapping; D019143:Evolution, Molecular; D020440:Gene Duplication; D015723:Gene Library; D008969:Molecular Sequence Data; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D018341:Receptors, Adrenergic, alpha-2 / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D017385:Sequence Homology; D015027:Zebrafish / Q000235:genetics*
chemical_list: D018341:Receptors, Adrenergic, alpha-2