FIG. 1.

Critical events during Xenopus oocyte maturation. Progesterone binds a putative cell surface receptor, which leads to a transient decrease in cyclic AMP (cAMP) levels and the activation of Eg2 kinase. Subsequently, dormant c-mos mRNA undergoes polyadenylation-induced translational activation. Newly synthesized Mos, a serine/threonine kinase, activates MAP kinase kinase (MAP kinase cascade), which culminates in the activation of MPF (a heterodimer composed of cyclin B and cdc2). Active MPF, which phosphorylates a number of substrates, is most directly responsible for the manifestations of oocyte maturation.