Development of maturational competence of oocytes of red seabream, Pagrus major, after human chorionic gonadotropin treatment in vitro requires RNA and protein synthesis.

The effects of human chorionic gonadotropin (HCG) and 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (DHP) on in vitro germinal vesicle breakdown (GVBD) in oocytes obtained at different times of day from a daily spawning marine teleost, the red seabream Pagrus major, were investigated. Oocytes isolated at 0800 hr underwent GVBD in response to HCG (10 IU/ml) but not to DHP (10 ng/ml). GVBD could be induced in oocytes isolated at 1600 hr by either HCG or DHP. Oocytes underwent GVBD in response to DHP after DHP-insensitive oocytes were incubated with HCG for 30, 60, or 120 min. The effects of actinomycin D (a transcriptional inhibitor) and cycloheximide (a translational inhibitor) on HCG- and DHP-induced GVBD were also investigated. Actinomycin D (1 microgram/ml) totally inhibited HCG-induction of GVBD in oocytes isolated at 0600 and 0800 hr. Actinomycin D also significantly inhibited GVBD induced by HCG in combination with DHP in oocytes taken at 0600 and 0800 hr. Cycloheximide (1 microgram/ml) completely inhibited the inducation of GVBD by HCG or DHP, alone or in combination, in oocytes obtained at 0600, 1000, and 1400 hr. These results indicate that gonadotropin induces maturational competence (responsiveness to maturation-inducing steroid) in oocytes of red seabream. These results also suggest that gonadotropin-induced synthesis of new protein through a mechanism dependent on RNA is essential for the development of maturational competence in oocytes of red seabream.