Development In Vitro and Mitochondrial Fate of Interspecies Cloned Embryos

Contents Although the technique of interspecies somatic cell nuclear transfer can be used to increase the population size of endangered mammals, the mitochondrial heteroplasmy in cloned embryos and animals makes this idea doubtful. In present study, goat–sheep cloned embryos were constructed by fusing goat foetal fibroblasts (GFFs) into sheep oocytes and then cultured in vitro to investigate the capability of sheep oocyte dedifferentiating GFF nucleus. Moreover, at each stage of 1‐ (immediately after fused), 2‐, 4‐, 8‐, 16‐cell, morula and blastocyst, the copy number of mtDNA from GFF and sheep oocyte was examined using real‐time PCR. The results showed that: 7.4% of the fused cloned embryos can develop to the blastocyst stage; in the process of one cell to the morula stage, the copy number of two kinds of mtDNA was stable relatively; however, in the process of morula to the blastocyst stage, the decreasing in the copy number of GFF‐derived mtDNA, while the increasing in sheep oocyte‐derived, resulted in their ratio of decreasing sharply from 2.0 ± 1.0% to 0.012 ± 0.004%. This study demonstrates that: (i) the goat–sheep cloned embryos have the ability to develop to blastocyst in vitro; (ii) from the morula stage to the blastocyst stage of goat–sheep cloned embryos, goat derived mitochondria can be gradually replaced with those from sheep oocyte.