Distribution patterns of global DNA methylation (A) and methylation at histone H3K9 (B) in pronucleus-stage mouse zygotes. The zygotes were stained with 5mC-specific antibody (green) and counterstained with DAPI (red), or stained for H3K9 dimethylation (green) and counterstained with Hoechst 33342 (blue). MP-/FP + indicates absence of a signal in male pronuclei and presence of a signal in female pronuclei; MP-/FP- indicates that both pronuclei had a very weak signal or lacked a signal; and MP+/FP + indicates both pronuclei had a signal. The polar body (Pb) was always positively stained. MP: male pronucleus; FP: female pronucleus; (+) positive signal; (−) negative or weak signal.