INSULIN AND INSULIN-LIKE GROWTH-FACTOR-I AND GROWTH-FACTOR-II INDUCE FINAL MATURATION OF OOCYTES OF RED SEABREAM, PAGRUS-MAJOR, IN-VITRO

The effects of various growth factors and peptides on in vitro germinal vesicle breakdown (GVBD) were examined in oocytes of the red seabream, Pagrus major, a daily spawning marine teleost. The oocytes used underwent GVBD in response to HCG but not to 17 alpha,20 beta-dihydroxy-4-pregnen-3- one (DHP), Insulin (1 mu M) and insulin-like growth factor-I (IGF-I, 10 nM) and IGF-II(13 nM) induced GVBD. Salmon gonadotropin-releasing hormone (GnRH), chicken GnRH (100 nM), angiotensin II and III(10 mu g/ml), inhibin A, activin A (200 ng/ml), and epidermal growth factor (1 nM) were ineffective. IGF-I was the most potent inducer of GVBD. In the presence of DHP, oocytes underwent GVBD in response to low doses of IGF-I or -II or insulin which alone were ineffective. GVBD occurred in response to DHP after oocytes were preincubated with IGF-I or with HCG. Actinomycin D inhibited GVBD induced by HCG alone or in combination with DHP, but actinomycin D did not block GVBD induced by IGF-I alone or in combination with DHP. Cycloheximide totally inhibited induction of GVBD by HCG or IGF-I, alone or in combination with DHP. These results suggest, for the first time in teleost, that growth factors, such as IGF-I, are involved in the induction of GVBD of oocytes. IGF-I appears to act directly on oocytes, and not via maturation-inducing hormone production, to induce GVBD. (C) 1994 Academic Press, Inc.