The analysis of chromatin remodeling and the staining for DNA methylation and histone acetylation do not provide definitive indicators of the developmental ability of inter-species cloned embryos

The restricted supply of oocytes in the domestic dog limits the development of reproductive biotechnologies in this species. Inter-species somatic cell nuclear transfer could be an alternative for cloning animals whose oocytes are difficult to obtain. In this study, the possibility of cloning dog embryos using pig oocytes was investigated by evaluating nuclear remodeling. Chromatin remodeling, assessed by premature chromosome condensation, pseudo-pronuclei formation, DNA methylation and histone acetylation, along with the developmental ability was compared between intra- and inter-species cloned embryos. The incidence of premature chromosome condensation was significantly higher in intra-species cloned embryos relative to inter-species cloned embryos (87.2% vs. 61.7%; P < 0.05), but comparable pseudo-pronuclei formation was observed in both (85.3% vs. 75.8%). None of the inter-species cloned embryos developed beyond the 8-cell stage while 18.3% of intra-species cloned embryos developed to the blastocyst stage. The relative level of both DNA methylation and histone acetylation was similar between intra- and inter-species cloned embryos at all times examined. These results suggest that although partial chromatin remodeling occurs, further investigation is needed to be able to use pig oocytes as recipient oocytes in dog cloning.