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  • Title: Endocrine control of diurnal oocyte maturation in the kyusen wrasse, Halichoeres poecilopterus.
    Author: Matsuyama M, Onozato S, Kashiwagi M.
    Journal: Zoolog Sci; 2002 Sep; 19(9):1045-53. PubMed ID: 12362059.
    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.
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