SCNT embryos are defective for H3K27me3 imprinting [ChIP-seq]

Animal cloning can be achieved through somatic cell nuclear transfer (SCNT), yet the success rate is very low. Recent studies have revealed H3K9me3 in donor cells and abnormal Xist activation as epigenetic barriers that impede SCNT reprogramming. Here we overcome both barriers by using Xist knockout donor cells combined with overexpressing Kdm4d and achieved the highest cloning efficiency in mice. However, post-implantation developmental defects and abnormal placenta were still observed, indicating presence of additional epigenetic barriers impedes SCNT cloning. Comparative DNA methylome analysis of IVF and SCNT blastocysts identified many abnormally methylated regions in SCNT embryos, despite successful global methylome reprogramming. Strikingly, allelic transcriptome and ChIP-seq analyses of preimplantation SCNT embryos revealed a complete loss of H3K27me3 imprinting, which likely accounts for postimplantation developmental defects of SCNT embryos. This study not only provides an efficient method for mouse cloning, but also paves the way for further improving SCNT cloning efficiency. ChIP-seq comparing H3K27me3 between mouse morula-stage embryos generated by in vitro fertilization (IVF) and somatic cell nuclear transfer (SCNT)