MBE Advance Access published online on August 29, 2003
Molecular Biology and Evolution, doi:10.1093/molbev/msg224
Molecular Biology and Evolution © Society for Molecular Biology and Evolution 2003; all rights reserved
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1 Department of Pharmacology and Clinical Pharmacology, University of Turku, Turku, Finland; Turku Graduate School of Biomedical Sciences, University of Turku, Turku, Finland
* To whom correspondence should be addressed. E-mail: mschein{at}utu.fi.
The Key Words:
genome duplication, synteny, fish,
© 2003 Society for Molecular Biology and Evolution
Original Articles
Identification of Duplicated Fourth
2-Adrenergic Receptor Subtype by Cloning and Mapping of Five Receptor Genes in Zebrafish
2 Department of Biochemistry and Pharmacy, Åbo Akademi University, Turku, Finland
3 Department of Pharmacology and Clinical Pharmacology, University of Turku, Turku, Finland
4 Department of Neuroscience, Unit of Pharmacology, Uppsala University, Uppsala, Sweden
5 Institute of Neuroscience, University of Oregon, Eugene, Oregon, USA
Abstract 
2-adrenergic receptors (2-ARs) belong to the large family of rhodopsin-like G-protein coupled receptors that share a common structure of 7 transmembrane (TM) -helices. The aims of this study were (1) to determine the number of 2-AR genes in a teleost fish, the zebrafish (Danio rerio); (2) to study the gene duplication events that generated the 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 2-ARs. In addition, we identified a fourth 2-AR subtype with two duplicates in zebrafish. Chromosomal mapping showed that the zebrafish 2-AR genes are located within conserved chromosomal segments, consistent with the origin of the four 2-AR subtypes by two rounds of chromosome or block duplication prior to 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 53-67%, and in the TM regions 80-87%. These values are clearly lower than what is observed between mammalian orthologs. Still, all of the residues thought to be important for 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.2-adrenergic receptor
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