Figure 8.

MPF is not synonymous with cyclin B-Cdk1 and instead consists of both cyclin B-Cdk1 and Gwl. (A) Nuclear material is required for MPF. In the starfish system, MPF is undetectable from enucleated donor oocytes, whereas cyclin B-Cdk1 is invariably activated after 1-MeAde treatment. MPF is restored when the nuclear material is added back to the donor enucleated oocytes. MPF (+) and (−), detectable and undetectable, respectively. (B) Greatwall kinase (Gwl) is essential for MPF. When Gwl activity is suppressed in the nuclei of donor oocytes by injection of its neutralizing antibodies, MPF is undetectable, even though cyclin B-Cdk1 is invariably activated. Conversely, injection of Gwl into enucleated oocytes restores MPF. (C) One order of magnitude excess levels of cyclin B-Cdk1 activity are required to induce GVBD in the microinjection assay, when purified cyclin B-Cdk1 is compared with cyclin B-Cdk1 found in cytoplasmic MPF. (D) For GVBD induction by microinjection, the addition of Gwl reduces the required activity of purified cyclin B-Cdk1 approximately to that contained in cytoplasmic MPF. rGwl, active recombinant Gwl; KD, kinase-dead form as a control. Reproduced from Fig. 2 in Ref. 13 with some modifications.