The GDF9-Ccnb1^−/− oocytes resumed meiosis normally but failed to arrest at the MII after PBE. (A) Entry into interphase after PBE in ovulated GDF9-Ccnb1^−/− oocytes. Control oocytes formed metaphase II spindles with condensed chromosomes after extrusion of PB1 (a and c). The GDF9-Ccnb1^−/− oocytes formed new nuclei with decondensed chromatin after extrusion of PB1 (b and d). BF, brightfield; S, spindle; N, nucleus. Bar, 20 µm. (B) The percentages of oocytes with nucleus formation after PBE. All the GDF9-Ccnb1^−/− oocytes formed nuclei after PBE, and no control oocytes formed nuclei. (C) Detection of DNA damage with phospho-histone H2A.X (γH2AX) staining in the GDF9-Ccnb1^−/− oocytes. (D) Characterization of chromatin compaction with H3K9me3 staining in the GDF9-Ccnb1^−/− oocytes. (E) Characterization of chromatin compaction with H3K27me3 staining in the GDF9-Ccnb1^−/− oocytes. In C–E, WT GV oocytes were used as the control, and 10 oocytes were used for staining in each group. Bars, 20 µm. (F) The GVBD rate of the GDF9-Ccnb1^−/− and control oocytes. The GVBD rate of GDF9-Ccnb1^−/− oocytes (89.39 ± 1.4%) was comparable with that of control oocytes (88.89 ± 1.0%). (G) The PBE rate of the GDF9-Ccnb1^−/− and control oocytes. The PBE rate of GDF9-Ccnb1^−/− oocytes (82.95 ± 0.7%) was also comparable with that of control oocytes (82.32 ± 2.2%). The GVBD and PBE rates were scored after 3-h and 14-h incubation periods, respectively. The numbers of oocytes used (n) are shown. Data are presented as mean ± SEM.