Requirement for Cdk2 in Cytostatic Factor Mediated Metaphase-Ii Arrest

The unfertilized eggs of vertebrates are arrested in metaphase of meiosis II because of the activity of cytostatic factor (CSF). Xenopus CSF is thought to contain the product of the Mos proto-oncogene, but other proteins synthesized during meiosis II are also required for arrest induced by CSF. In Xenopus oocytes, ablation of synthesis of cyclin-dependent kinase 2 (Cdk2) during meiosis resulted in absence of the metaphase II block, even though the Mos(xe) protein kinase was fully active at metaphase. Introduction of purified Cdk2 restored metaphase II arrest, and increasing the amount of Cdk2 during meiosis I (when Mos(xe) is present) led to metaphase arrest at meiosis I. These data indicate that metaphase arrest is a result of cooperation between a proto-oncogene kinase and a cyclin-dependent kinase and illustrate the interaction of a cell growth regulator with a cell cycle control element