Figure 3

DNA methylation patterns in zygotes and the relationship with H3K9 modification. A. The zygotes were double stained for DNA methylation (5MeC, green) and H3K9 acetylation (ac-H3K9, red). In mouse zygote, no obvious signals of 5MeC could be seen in the whole paternal pronucleus except the perinucleolar regions (a, a'). In comparison, the paternal pronucleus in sheep zygote remained visible signals of 5MeC (b, b'). However, in some sheep zygotes, the paternal pronucleus showed very weak staining for 5MeC staining (c, c'). B. The zygotes were double stained for 5MeC (green) and H3K9 tri-methylation (m3-H3K9, red). In most cases, the paternal pronucleus remained some methylated regions (a), but m3-H3K9 was absent from the entire pronucleus area (a'). The boundary of paternal pronucleus is indicated by a white circle in the merged image. In b and b', both 5MeC and m3-H3K9 distributed equally in two parental pronuclei. This situation occurred in a few cases. All arrows in images were used to indicate the paternal pronucleus.