Five Different Types of Putative GnRH Receptor Gene are Expressed in the Brain of Masu Salmon (Oncorhynchus masou)

Abstract

-Recent studies have shown that there are multiple genes encoding gonadotropin-releasing hormone receptor (GnRH-R) in single species. In salmonids, however, only a single gene has been identified in the rainbow trout. We therefore isolated partial cDNAs from the brain and the pituitary of masu salmon Oncorhynchus masou by reverse transcription-polymerase chain reaction and 5'-rapid amplification of cDNA ends, using primers corresponding to conserved transmembrane domains (TMs). Five different partial cDNAs were isolated from an individual and termed as msGnRH-R1, R2, R3, R4 and R5. They are divided into two groups, msGnRH-R1, R2, R3 and msGnRH-R4, R5. Two groups share 59-71% nucleotide sequence identities. Phylogenetic analysis showed that the former group is closely related to the goldfish GnRH-R GfA, and the latter to GfB. All five msGnRH-R genes were expressed in the brain and msGnRH-R1, R3 and R5 were expressed in the pituitary. In addition, we found mRNA for msGnRH-R1 in the kidney and ovary, and R2 in the ovary, whereas msGnRH-R5 gene was widely expressed in the muscle, heart, kidney and testis. Differences in the expression of msGnRH-R genes between maturing and spawning fish were observed in the brain and pituitary, except for the constantly expressed msGnRH-R5. A splicing variant of msGnRH-R1 mRNA that is capable of generating a truncated GnRH-R that consists of 5TMs was also expressed in the brain, pituitary and kidney. These results indicate that five different types of putative GnRH-R gene are present and expressed in the brain of masu salmon.

Evolution of gonadotropin-releasing hormone (GnRH) structure and its receptor

“…Homologs of many mammalian GnRH receptors were cloned from a marsupial (possum) (King et al, 2000;Cheung and Hearn, 2002), two forms from the goldfish , bullfrog, brown frog and clawed toad (Troskie et al, 2000;Wang et al, 2001;Seong et al, 2003), chicken (Sun et al, 2000), medaka (Okubo et al, 2001), striped bass (Alok et al, 2000), trout and salmon (Madigou et al, 2000;Jodo et al, 2003), cichlid (Robinson et al, 2001), Japanesse eel (Okubo et al, 2000), amberjack, rubber eel, and sea squirt (Millar et al, 2004). The non-mammalian receptors with the greatest homology to the mammalian pituitary receptors have 42-47% amino acid identity with them, but 58-67% identity among each other.…”

Gonadotropin-Releasing Hormone and Receptor Distributions in the Visual Processing Regions of Four Coral Reef Fishes

“…Studies in fishes indicate that up to five different types of GnRH receptor genes are expressed in the brain of a single species [Jodo et al, 2003;Lethimonier et al, 2004]. Further, variation in spatiotemporal patterns of multiple GnRH receptors indicates different roles in GnRH action [Illing et al, 1999;Parhar et al, 2002;Peter et al, 2003;Jodo et al, 2003;Soga et al, 2005;Chen and Fernald, 2006].…”

“…The GnRH-RIII examined in this study is only identified and cloned in perciform fishes [Jodo et al, 2003;Lethimonier et al, 2004;Soga et al, 2005], but is related to the type I class of GnRH receptors in other vertebrates. Even though GnRH receptor staining within visual regions of the reef species examined here is similar to other fish studies that used multiple labeling techniques [Peter et al, 2003;Soga et al, 2005;Chen and Fernald, 2006], our current examination of a single GnRH receptor likely does not reveal the entire GnRH receptor distribution in these perciform species and we cannot rule out differential binding properties of the antibody as a cause for the variations observed among species.…”

Hormonal regulation of follicular atresia in teleost fish

“…Recently, three molecular forms of GnRH-R have been demonstrated in various cell types of the pituitary gland of tilapia (Parhar et al, 2005), and there is a report on identification of a third novel form of GnRH-R in medaka (Okubo et al, 2003). Furthermore, five different forms of GnRH-R cDNA have been described in masu salmon (Jodo et al, 2003). However, there is little information on their ligand selectivity and functional significance at the present time.…”