Influence of oocyte nuclei on demethylation of donor genome in cloned bovine embryos.

We recently demonstrated that satellite regions exhibit an aberrant DNA methylation in cloned bovine embryos. Here, we examined, using bisulfite-sequencing technology, whether the inefficient demethylation of cloned donor genomes could be rescued by the presence of oocytic nuclei. Both AciI digestion and sequencing analyses showed that satellite sequence was demethylated more efficiently in cloned tetraploid blastocysts than in diploid clones. When methyl-CpG density (the number of methyl-CpG sites per string) was scored, a significant decrease was observed in tetraploids (P<0.001). These results suggest that unknown mechanisms provided by oocytic nuclei could assist the demethylation of satellite sequences in tetraploid clones.