ACTIVATION OF MITOGEN-ACTIVATED PROTEIN-KINASE DURING MEIOTIC MATURATION IN MOUSE OOCYTES

Mitogen-activated protein kinase (MAP kinase) plays a role in the casc ade of protein kinase activation in cultured cells. To investigate the involvement of MAP kinase in meiotic maturation, we measured MAP kina se activity, using myelin basic protein as a substrate, with histone H 1 kinase activity, in mouse oocytes. MAP kinase activity was low 1 h a fter isolation from follicles (when oocytes lost their germinal vesicl e), increased abruptly at 2 h, and remained high until the second meta phase (13 h after isolation from follicles). Histone H1 kinase activit y increased gradually from 2 to 7 h after isolation. When immature ooc ytes were treated with puromycin, MAP kinase activity did not increase after isolation from follicles. In the presence of 3-isobutyl-1-methy lxanthine, the treatment of immature oocytes with okadaic acid, a spec ific inhibitor of protein phosphatase 1 and 2A, induced germinal vesic le breakdown and activation of MAP kinase. These results suggest that MAP kinase is involved in the regulation of meiotic maturation, and th at the activation of MAP kinase requires protein synthesis and is inhi bited by the protein phosphatase during meiotic maturation in mouse oo cytes.