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

We recently demonstrated that satellite regions exhibit an aberrant DNA met hylation in cloned bu,;int: embryos. Here, we examined, using bisulfite-seq uencing technology, whether the inefficient demethylation of cloned donor g enomes could he rescued bg the presence of oocytic nuclei. Both AciI digest ion 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 sco red, a significant decrease was observed in tetraploids (P < 0.001). These results suggest that unknown mechanisms provided by oocytic nuclei could as sist the demethylation of satellite sequences in tetraploid clones. (C) 200 1 Federation of European Biochemical Societies. Published by Elsevier Scien ce B.V. All rights reserved.