Activation of mitogen-activated protein kinase during meiotic maturation in mouse oocytes.

Mitogen-activated protein kinase (MAP kinase) plays a role in the cascade of protein kinase activation in cultured cells. To investigate the involvement of MAP kinase in meiotic maturation, we measured MAP kinase activity, using myelin basic protein as a substrate, with histone H1 kinase activity, in mouse oocytes. MAP kinase activity was low 1 h after isolation from follicles (when oocytes lost their germinal vesicle), increased abruptly at 2 h, and remained high until the second metaphase (13 h after isolation from follicles). Histone H1 kinase activity increased gradually from 2 to 7 h after isolation. When immature oocytes were treated with puromycin, MAP kinase activity did not increase after isolation from follicles. In the presence of 3-isobutyl-1-methylxanthine, the treatment of immature oocytes with okadaic acid, a specific inhibitor of protein phosphatase 1 and 2A, induced germinal vesicle breakdown and activation of MAP kinase. These results suggest that MAP kinase is involved in the regulation of meiotic maturation, and that the activation of MAP kinase requires protein synthesis and is inhibited by the protein phosphatase during meiotic maturation in mouse oocytes.