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 preimplantation embryos produced by either normal fertilization or somatic cell nuclear transfer. The methylation status of the centromeric satellite and the PRE-1 short interspersed element (SINE) sequences was characterized using bisulfite-sequencing technology. Typical demethylation processes were identified in these repetitive sequences of the cloned donor genome during cleavage, the patterns of which were similar to the ones detected in fertilized counterparts. These findings are different from previous observations with 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 donor genomes.