title: Seasonal variation of the three native gonadotropin-releasing hormone messenger ribonucleic acids levels in the brain of female red seabream.
abstract: We studied the seasonal variation of the expression of genes encoding the three native gonadotropin-releasing hormones (GnRHs), namely salmon(s) GnRH, chicken(c) GnRH-II, and seabream(sb) GnRH in red seabream, Pagrus (Chrysophrys) major, in order to better understand the regulatory mechanisms of GnRH gene expression by environmental and endocrine factors. Female red seabream, reared under natural conditions, were collected monthly or bimonthly from October to June, and the levels of the three distinct GnRH messenger ribonucleic acids (mRNAs) in the brains of those fish (n = 4-6) were determined by ribonuclease (RNase) protection analysis. The levels of sbGnRH mRNA correlated well with the observed ovarian histology; the levels of sbGnRH mRNA of immature fish in October and December were low, and increased in February and March in conjunction with active vitellogenesis. The sbGnRH mRNA levels reached a maximum level in April (spawning season), after which they rapidly decreased together with the observed ovarian regression in June. In contrast, the levels of sGnRH mRNA showed no variation, while those of cGnRH-II mRNA were elevated only slightly in March and April. The increase in sbGnRH mRNA levels correlates with the increase in day length, water temperature and serum steroids levels, suggesting that these factors are candidates for regulators of sbGnRH synthesis.
authors.affiliation: Inland Station, National Research Institute of Aquaculture, Fisheries Research Agency, Tamaki, Watarai, Mie 519-0423, Japan. kokuzawa@fra.affrc.go.jp
authors.forename: Koichi
authors.initials: K
authors.lastname: Okuzawa
authors.forename: Koichiro
authors.initials: K
authors.lastname: Gen
authors.forename: Martijn
authors.initials: M
authors.lastname: Bruysters
authors.forename: Jan
authors.initials: J
authors.lastname: Bogerd
authors.forename: Yoav
authors.initials: Y
authors.lastname: Gothilf
authors.forename: Yonathan
authors.initials: Y
authors.lastname: Zohar
authors.forename: Hirohiko
authors.initials: H
authors.lastname: Kagawa
mesh_terms: D000818:Animals; D001923:Brain Chemistry; D004958:Estradiol / Q000097:blood; D005260:Female; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000502:physiology; D007987:Gonadotropin-Releasing Hormone / Q000145:classification / Q000235:genetics*; D023282:Nuclease Protection Assays; D010053:Ovary / Q000033:anatomy & histology / Q000502:physiology; D010473:Perciformes / Q000235:genetics*; D012333:RNA, Messenger / Q000032:analysis*; D012621:Seasons; D013739:Testosterone / Q000097:blood
chemical_list: D012333:RNA, Messenger; D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; D004958:Estradiol