Interspecies nuclear transfer reveals that demethylation of specific repetitive sequences is determined by recipient ooplasm but not by donor intrinsic property in cloned embryos.

DNA methylation/demethylation of donor genomes in recipient ooplasm after nuclear transfer occurs in a species-specific way. In cloned rabbit and bovine embryos, repetitive sequences maintain the donor-type methylation status, but typical demethylation of repetitive sequences takes place in cloned porcine embryos. To clarify whether the demethylation is controlled by donor nucleus intrinsic property or by recipient ooplasm, we used interspecies somatic cell nuclear transfer (iSCNT) model to examine the methylation status of repetitive sequences in pig-to-rabbit and rabbit-to-pig interspecies embryos. We found that no demethylation of pig repetitive sequences was observed in pig-to-rabbit iSCNT embryos, while the examined rabbit repetitive sequence Rsat IIE was demethylated in rabbit-to-pig iSCNT embryos. These results indicate that demethylation of donor repetitive sequences is determined by ooplasm but not by donor intrinsic property and that ooplasm from different species have different capabilities to demethylate genes. (c) 2005 Wiley-Liss, Inc.