title: Steroidogenesis in ovarian follicles of chub mackerel, Scomber japonicus.
abstract: We incubated different radiolabeled steroid precursors with intact chub mackerel ovarian follicles to clarify the synthetic pathways of steroid hormones during vitellogenesis and following final oocyte maturation (FOM). During vitellogenesis, estradiol-17beta (E2) was synthesized from pregnenolone via 17-hydroxypregnenolone, 17-hydroxyprogesterone, androstenedione, and testosterone. The physiological significance of the intermediate metabolites of E2 in the ovarian follicles was examined by comparing follicular steroidogenesis between gonochoric and hermaphroditic fish species. After vitellogenesis, the steroidogenic pathway shifted from E2 to maturation-inducing hormone (MIH) production owing to the inactivation of 17,20-lyase and the activation of 20 beta-hydroxysteroid dehydrogenase. Of the new steroids produced during FOM, 17,20beta-dihydroxy-4-pregnen-3-one (17,20beta-P) was most effective at inducing germinal vesicle breakdown in vitro. Circulating levels of 17,20beta-P increased specifically around the time of germinal vesicle migration, while another FOM-specific 20beta-hydroxylated progestin, 17,20beta,21-trihydroxy-4-pregnen-3-one, was present at consistently low levels during FOM. These results indicate that 17,20beta-P is the MIH of chub mackerel.
authors.affiliation: Laboratory of Marine Biology, Faculty of Bioresource and Bioenvironmental Sciences, Kyushu University, Hakozaki, Fukuoka 812-8584, Japan. rinya_m@agr.kyushu-u.ac.jp
authors.forename: Michiya
authors.initials: M
authors.lastname: Matsuyama
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Shiraishi
authors.forename: Jitendra K
authors.initials: JK
authors.lastname: Sundaray
authors.forename: Anisur
authors.initials: A
authors.lastname: Rahman
authors.forename: Kohei
authors.initials: K
authors.lastname: Ohta
authors.forename: Akihiko
authors.initials: A
authors.lastname: Yamaguchi
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001345:Autoradiography; D004958:Estradiol / Q000096:biosynthesis / Q000097:blood; D005260:Female; D012739:Gonadal Steroid Hormones / Q000096:biosynthesis* / Q000097:blood; D057850:Hermaphroditic Organisms; D006908:Hydroxyprogesterones / Q000097:blood; D006080:Ovarian Follicle / Q000378:metabolism*; D010473:Perciformes / Q000378:metabolism* / Q000502:physiology; D011284:Pregnenolone / Q000378:metabolism; D019849:Sex Determination Processes / Q000378:metabolism*; D014818:Vitellogenesis / Q000502:physiology
chemical_list: D012739:Gonadal Steroid Hormones; D006908:Hydroxyprogesterones; C007433:17,20-dihydroxy-4-pregnen-3-one; D004958:Estradiol; D011284:Pregnenolone