DNA and histone H3 methylation in mouse, bovine and rabbit zygotes at advanced pronuclear stages. Representative images (>20 zygotes for each case) of indirect fluorescent immunostaining using specific antibodies against: (A) methylated cytosine residues (5meC); (B) H3K9me2 and (C) H3K4me3. The asymmetry in 5meC and H3K9me2 signal intensities between paternal and maternal pronuclei of mouse, bovine and rabbit zygotes are clearly visible in lanes A and B respectively. H3K4me3-specific signal (lane C) is present in both pronuclei. Scale bar 20 μm.