Fig. 5. XCds1 inactivation depends on the activation of cyclin B-Cdc2 kinase but not MAP kinase. (A) Immature oocytes were incubated for 3 hours in the presence of U0126, a MEK inhibitor, and then added with progesterone. Oocytes were collected when GVBD occurred in progesterone-treated oocytes. (B) Immature oocytes were incubated overnight in the presence of olomoucine, a Cdk inhibitor, and then incubated with progesterone. Olomoucine and progesterone-treated oocytes with intact GV were collected when 100% of the control oocytes, which were treated with progesterone alone, had undergone GVBD. XCds1 was immunoprecipitated with anti-XCds1 antibody and assayed for its kinase activity using GST-XCdc25C(254-316)-WT as a substrate (top). Western blot analysis confirmed that equivalent amounts of XCds1 were recovered in the immunoprecipitates with anti-XCds1 antibody (A, middle upper; B, middle). The same extracts were subjected to total histone H1 kinase assay (A, middle lower; B, bottom) and western blot analysis with anti-MAP kinase antibody (A, bottom).