Resolving multiple epigenetic barriers to pig SCNT-mediated reprogramming during embryonic genome activation [RNA-Seq]

Pig cloning by somatic cell nuclear transfer (SCNT) frequently undergoes incomplete epigenetic remodeling during the maternal-to-zygotic transition, which leads to a significant embryonic loss before implantation. Here, we generated the first genome-wide landscapes of histone methylation in pig SCNT embryos. Excessive H3K9me3 and H3K27me3, but not H3K4me3, were observed in the genomic regions with unfaithful embryonic genome activation and donor cell-specific gene silencing. A combination of H3K9 demethylase KDM4A and GSK126, an inhibitor of H3K27me3 writer, could remove these epigenetic barriers and restore the global transcriptome in SCNT embryos. More importantly, TDG was defined as a pig-specific epigenetic regulator for nuclear reprogramming, which was not reactivated by H3K9me3 and H3K27me3 removal. Both combined treatment and transient TDG overexpression could promote DNA demethylation and enhance the blastocyst forming rates of SCNT embryos, which offers valuable methods to increase the cloning efficiency of genome-edited pigs for agricultural and biomedical purposes.