Typical demethylation events in cloned pig embryos - Clues on species-specific differences in epigenetic reprogramming of a cloned donor genome

We investigated whether a genomic demethylation process occurs in pig preim plantation embryos produced by either normal fertilization or somatic cell nuclear transfer. The methylation status of the centromeric satellite and t he PRE-1 short interspersed element (SINE) sequences was characterized usin g bisulfite-sequencing technology. Typical demethylation processes were ide ntified in these repetitive sequences of the cloned donor genome during cle avage, the patterns of which were similar to the ones detected in fertilize d counterparts. These findings are different from previous observations wit h cloned bovine embryos where various repeated regions of the donor genome exhibited aberrant methylation patterns. Our results indicate that species- specific differences exist in modifying the epigenetic status of cloned don or genomes.