title: Endocrine control of diurnal oocyte maturation in the kyusen wrasse, Halichoeres poecilopterus.
abstract: The present study examined diurnal cycles of oocyte development and maturation in the kyusen wrasse, Halichoeres poecilopterus, and investigated the sensitivity of oocytes to maturation-inducing hormone (MIH) and gonadotropic hormone (GTH). Female fish were sampled at fixed intervals throughout the day, revealing that final oocyte maturation and ovulation were completed by 6:00 hr, and that spawning occurred daily between 6:00 and 9:00 hr. In vitro experiments showed that the steroids 17,20beta-dihydroxy-4-pregnen-3-one (17,20beta-P) and 17,20beta,21-trihydroxy-4-pregnen-3-one (20beta-S) were equally potent and highly effective inducers of germinal vesicle breakdown (GVBD) in kyusen wrasse oocytes. Additionally, circulating levels of 17,20beta-P and 20beta-S increased around the time of GVBD and ovulation, suggesting that 17,20beta-P and 20beta-S act as MIHs in the kyusen wrasse. Moreover, in vitro experiments clearly showed that kyusen wrasse oocytes had a daily developmental cycle of GTH and MIH sensitivity, and that oocytes that completed vitellogenesis acquired GTH-induced maturational competence. An endogenous GTH surge likely occurs between 12:00 and 15:00 hr, and this daily pre-maturational GTH surge probably controls the diurnal maturation cycles of kyusen wrasse oocytes.
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D003350:Cortodoxone / Q000031:analogs & derivatives / Q000494:pharmacology; D005260:Female; D005399:Fishes / Q000502:physiology*; D006062:Gonadotropins / Q000494:pharmacology; D006728:Hormones / Q000494:pharmacology*; D006908:Hydroxyprogesterones / Q000494:pharmacology; D016200:Maturation-Promoting Factor / Q000494:pharmacology; D009865:Oocytes / Q000166:cytology / Q000187:drug effects* / Q000254:growth & development*; D010060:Ovulation / Q000187:drug effects
chemical_list: D006062:Gonadotropins; D006728:Hormones; D006908:Hydroxyprogesterones; C007433:17,20-dihydroxy-4-pregnen-3-one; C051954:17,20,21-trihydroxy-4-pregnen-3-one; D016200:Maturation-Promoting Factor; D003350:Cortodoxone