title: Stimulatory effects of insulin-like growth factor 1 on expression of gonadotropin subunit genes and release of follicle-stimulating hormone and luteinizing hormone in masu salmon pituitary cells early in gametogenesis.
abstract: Insulin-like growth factor-I (IGF-I) has been shown to be involved in pubertal activation of gonadotropin (GTH) secretion. The aim of this study was to determine if IGF-I directly stimulates synthesis and release of GTH at an early stage of gametogenesis. The effects of IGF-I on expression of genes encoding glycoprotein alpha (GPalpha), follicle-stimulating hormone (FSH) beta, and luteinizing hormone (LH) beta subunits and release of FSH and LH were examined using primary pituitary cells of masu salmon at three reproductive stages: early gametogenesis, maturing stage, and spawning. IGF-I alone or IGF-I + salmon GnRH (sGnRH) were added to the primary pituitary cell cultures. Amounts of GPalpha, FSHbeta, and LHbeta mRNAs were determined by real-time PCR. Plasma and medium levels of FSH and LH were determined by RIA. In males, IGF-I increased the amounts of all three subunit mRNAs early in gametogenesis in a dose-dependent manner, but not in the later stages. In females, IGF-I stimulated release of FSH and LH early in gametogenesis, whereas no stimulatory effects on the subunit mRNA levels were observed at any stage. IGF-I + sGnRH stimulated release of FSH and LH at all stages in both sexes, but had different effects on the subunit mRNA levels depending on subunit and stage. The present results suggest that IGF-I itself directly stimulates synthesis and release of GTH early in gametogenesis in masu salmon, possibly acting as a metabolic signal that triggers the onset of puberty.
authors.affiliation: Department of Animal and Marine Bioresource Science, Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, Fukuoka 812-8581, Japan.
authors.forename: Shunji
authors.initials: S
authors.lastname: Furukuma
authors.forename: Takeshi
authors.initials: T
authors.lastname: Onuma
authors.forename: Penny
authors.initials: P
authors.lastname: Swanson
authors.forename: Qiong
authors.initials: Q
authors.lastname: Luo
authors.forename: Nobuhisa
authors.initials: N
authors.lastname: Koide
authors.forename: Houji
authors.initials: H
authors.lastname: Okada
authors.forename: Akihisa
authors.initials: A
authors.lastname: Urano
authors.forename: Hironori
authors.initials: H
authors.lastname: Ando
mesh_terms: D000818:Animals; D005260:Female; D005640:Follicle Stimulating Hormone / Q000235:genetics / Q000378:metabolism; D005718:Gametogenesis / Q000502:physiology*; D005786:Gene Expression Regulation / Q000187:drug effects; D006062:Gonadotropins / Q000235:genetics / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000235:genetics / Q000378:metabolism; D008297:Male; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012098:Reproduction / Q000502:physiology; D012474:Salmon / Q000235:genetics / Q000378:metabolism*; D012621:Seasons; D012741:Sexual Maturation / Q000502:physiology
chemical_list: D006062:Gonadotropins; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone