Fig. 3. XCds1 is inactivated at meiotic G2/M-phase transition. (A) XCds1 was immunoprecipitated with anti-XCds1 antibody from oocyte extracts prepared at different times during meiosis reinitiation after progesterone treatment. The immunoprecipitates were assayed for kinase activity using GST-XCdc25C(254-316)-WT as a substrate, whose phosphorylation was detected by autoradiography (top). Note that GST-XCdc25C(254-316)-S287A was not phosphorylated by XCds1 immunoprecipitated from immature oocyte extracts (S287A). Levels of XCds1 were confirmed by western blot with anti-XCds1 antibody (bottom). (B) Changes in XCds1 kinase activity shown in A were measured and compared with the occurrence of GVBD. (C) The same extracts as in A were subjected to total histone H1 kinase assay (top) and western blot analysis with anti-MAP kinase antibody (bottom). The decrease in H1 kinase activity at 3 hours may reflect the fact that a significant number of oocytes had already passed through metaphase-I, which is observed within 1 hour after GVBD (Ohsumi et al., 1994).