Inhibition of Aberrant DNA Re-methylation Improves Post-implantation Development of Somatic Cell Nuclear Transfer Embryos

Somatic cell nuclear transfer (SCNT) enables cloning of differentiated cells by reprogramming their nuclei to a totipotent state. However, successful full-term development of SCNT embryos is a low-efficiency process and arrested embryos frequently exhibit epigenetic abnormalities. Here, we generated genome-wide DNA methylation maps from mouse pre-implantation SCNT embryos. We identified widespread regions that were aberrantly re-methylated, leading to mis-expression of genes and retrotransposons important for zygotic genome activation. Inhibition of DNA methyltransferases (Dnmts) specifically rescued these re-methylation defects and improved the developmental capacity of cloned embryos. Moreover, combining inhibition of Dnmts with overexpression of histone demethylases led to stronger reductions in inappropriate DNA methylation and synergistic enhancement of full-term SCNT embryo development. These findings show that excessive DNA re-methylation is a potent barrier that limits full-term development of SCNT embryos and that removing multiple epigenetic barriers is a promising approach to achieve higher cloning efficiency.