title: Four gonadotropin releasing hormone receptor genes in Atlantic cod are differentially expressed in the brain and pituitary during puberty.
abstract: Gonadotropin releasing hormones (GnRH) are an important part of the brain-pituitary-gonad axis in vertebrates. GnRH binding to its receptors (GnRH-R) stimulates synthesis and release of gonadotropins in the pituitary. GnRH-Rs also mediate other processes in the central nervous system such as reproductive behavior and neuromodulation. As many as five GnRH-R genes have been identified in two teleost fish species, but the function and phylogenetic relationship of these receptors is not fully understood. To gain a better understanding of the functional relationship between multiple GnRH-Rs in an important aquaculture species, the Atlantic cod (Gadus morhua), we identified four GnRH-Rs (gmGnRH-R) by RT-PCR, followed by full-length cloning and sequencing. The deduced amino acid sequences were used for phylogenetic analysis to identify conserved functional motifs and to clarify the relationship of gmGnRH-Rs with other vertebrate GnRH-Rs. The function of GnRH-R variants was investigated by quantitative PCR gene expression analysis in the brain and pituitary of female cod during a full reproductive cycle and in various peripheral tissues in sexually mature fish. Phylogenetic analysis revealed two types of teleost GnRH-Rs: Type I including gmGnRH-R1b and Type II including gmGnRH-R2a, gmGnRH-R2b and gmGnRH-R2c. All four gmGnRH-Rs are expressed in the brain, and gmGnRH-R1b, gmGnRH-R2a and gmGnRH-R2c are expressed in the pituitary. The only GnRH-R differentially expressed in the pituitary during the reproductive cycle is gmGnRH-R2a such that its expression is significantly increased during spawning. These data suggest that gmGnRH-R2a is the most likely candidate to mediate the hypophysiotropic function of GnRH in Atlantic cod.
authors.affiliation: Department of Basic Sciences and Aquatic Medicine, Norwegian School of Veterinary Science, PO Box 8146 Dep, 0033 Oslo, Norway. jon.hildahl@nvh.no
authors.forename: Jon
authors.initials: J
authors.lastname: Hildahl
authors.forename: Guro K
authors.initials: GK
authors.lastname: Sandvik
authors.forename: Rolf B
authors.initials: RB
authors.lastname: Edvardsen
authors.forename: Birgitta
authors.initials: B
authors.lastname: Norberg
authors.forename: Trude M
authors.initials: TM
authors.lastname: Haug
authors.forename: Finn-Arne
authors.initials: FA
authors.lastname: Weltzien
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001921:Brain / Q000378:metabolism*; D048389:Gadus morhua / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D010902:Pituitary Gland / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011966:Receptors, LHRH / Q000737:chemistry* / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment
chemical_list: D011966:Receptors, LHRH