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Gonadotropin-stimulated fish follicle layers play a major role in inducing oocyte maturation via the stimulated secretion of steroids. In order to determine the molecular mechanism of the action of gonadotropin on fish ovarian follicles, we investigated the effect of pregnant mare serum gonadotropin (PMSG) on the accumulation of cAMP and on the protein phosphorylation in isolated ovarian follicle layers of the teleost, Oryzias latipes. Incubation of isolated follicle layers with PMSG resulted in a rapid increase in the production of cAMP. The response could be detected within 5min after the addition of PMSG. When the homogenate of the follicle layers was incubated with [y-32P]ATP, four endogenous proteins with M, of 250 K (Pl), 120 K (P2), 94 K (P3) and 75 K (P4) were phosphorylated. The phosphorylation of 94 K protein (P3) was not affected by cAMP, while that of Pl, P2 and P4 was stimulated by the addition of cAMP. The enhancement of the phosphorylation by cAMP was low, but was inhibited by the protein kinase inhibitor protein from rabbit skeletal muscle and H8 (N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride), an inhibitor of cyclic nucleotide-dependent protein kinases. Phosphorylation of the 94 K protein (P3) was markedly enhanced by Ca“ and calmodulin, indicating that ovarian follicle layers of the teleost contain an intrinsic calmodulin-dependent protein kinase and that P3 is an endogenous protein substrate for the kinase. The phosphorylation of Pl, P2 and P4 was also enhanced by PMSG or forskolin in isolated intact follicle layers which had been prelabeled with [32P]phosphoric acid. In addition, the phosphorylation of Pl, P2 and P4 in the [32P]labeled isolated follicle layers was markedly reduced by prior exposure to PMSG or forskolin, indicating that the phosphorylation of the three proteins is under regulation of PMSG via cAMP. These results altogether strongly indicate that cAMP-dependent phosphorylation of the three proteins (Pl, P2 and P4) is involved in the early action of PMSG on ovarian follicles of the fish. induced maturation of oocytes in response to GTH, but the GTH-induced maturation of oocytes Maturation of fish and amphibian oocytes surrounded by follicle cells can be induced in virro by a pituitary extract or gonadotropin (GTH), or by steroids such as progestins, androgens, and corticosteroids. In amphibia, the pituitary GTH acts on the ovarian follicular tissues, causing them to mature (13, 24, 28, 32, 33, 35). In the freshwater teleost, Oiyzias /aripes, removal of all follicular constituents resulted in a failure of was not affected by removal of thecal cells and basal lamina from the follicle. Moreover, denuded oocytes were able to mature in the presence of GTH, when cocultured either with thecal cells previously separated from large preovulatory follicles or with post-ovulatory follicles. The results thus indicate that granulosa cells of large preand post-

biomedical research

&lt;b&gt;PHOSPHORYLATION OF FOLLICLE PROTEINS FROM THE TELEOST, &lt;i&gt;ORYZIAS LATIPES&lt;/i&gt;, IN THE ACTION OF GONADOTROPIN AND &lt;/b&gt;&lt;b&gt;FORSKOLIN &lt;/b&gt;