title: Seasonal variation in the expression of five subtypes of gonadotropin-releasing hormone receptor genes in the brain of masu salmon from immaturity to spawning.
abstract: Seasonal variation in the expression of five subtypes of gonadotropin-releasing hormone receptor (GnRH-R) genes, designated as msGnRH-R1, -R2, -R3, -R4, and -R5, was examined in the brain of masu salmon (Oncorhynchus masou). In addition, responses of these genes to GnRH were examined in a GnRH analog (GnRHa) implantation experiment. Brain samples were collected one week after the implantation every month from immaturity through spawning. The absolute amount of GnRH-R mRNA in single forebrains was determined by real-time PCR assays. Among the five genes, R4 and R5 were dominantly expressed in both sexes. R1, R4, and R5 mRNAs showed similar changes throughout the experimental period in both sexes. Levels tended to be high in winter and low in the pre-spawning season, followed by elevations in the spawning period. The mRNA levels had weak to moderate negative correlations with the plasma level of estradiol-17beta (E2) in females. The effects of GnRHa on msGnRH-R mRNAs were not apparent for all the subtypes. These results indicate that the msGnRH-R1, -R4, and -R5 genes are synchronously expressed during sexual maturation. There was a trend toward decreased levels of their expression prior to the spawning period and then increased levels at spawning, possibly causing GnRH target neurons to sensitize to a GnRH stimulus. Furthermore, E2 may be involved in msGnRH-R gene expression in the brain of female masu salmon during sexual maturation.
authors.affiliation: Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan.
authors.forename: Aya
authors.initials: A
authors.lastname: Jodo
authors.forename: Takashi
authors.initials: T
authors.lastname: Kitahashi
authors.forename: Shinya
authors.initials: S
authors.lastname: Taniyama
authors.forename: Ramji Kumar
authors.initials: RK
authors.lastname: Bhandari
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ueda
authors.forename: Akihisa
authors.initials: A
authors.lastname: Urano
authors.forename: Hironori
authors.initials: H
authors.lastname: Ando
mesh_terms: D000375:Aging / Q000502:physiology; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D008297:Male; D017683:Oncorhynchus / Q000254:growth & development* / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D011966:Receptors, LHRH / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D012621:Seasons; D012741:Sexual Maturation / Q000502:physiology*; D013256:Steroids / Q000097:blood
chemical_list: D012333:RNA, Messenger; D011966:Receptors, LHRH; D013256:Steroids; D007987:Gonadotropin-Releasing Hormone