Reprogramming of Differentiated Somatic Cells by Nuclear Transplantation.

Abstract

Epigenetic reprogramming plays a central role in development of cloned embryos reconstituted by somatic cell nuclear transfer (SCNT) and aberrant reprogramming leads to inefficient development of cloned embryos. Here we provided evidence that trimethylation of H3K27 (H3K27me3) exhibited dramatic difference between normal fertilization produced blastocysts and SCNT cloned blastocysts. H3K27me3 specifically marked the inner cell mass (ICM) of normal blastocysts, whereas the ICM of somatic cloned blastocysts showed no H3K27me3 modification. Subsequently, we demonstrated that the differentiation related genes, which are marked by H3K27me3 in ES cells, were up-regulated significantly in cloned embryos compared to normal embryos. The Polycomb repressive complex PRC2 component genes (Eed, Ezh2, Suz12) responsible for H3K27me3 were down-regulated in cloned embryos. Our results indicate that down-regulation of PRC2 genes in cloned embryos leads to defective marking of H3K27me3 to the differentiation genes in the pluripotent ICM cells, which in turn drive the developmental genes expressing prematurely. Loss of somatic cloned embryos right after implantation might directly caused by defective chromatin modification. Meanwhile, derivation of customized NT-ES cells has been proposed as the most attractive approach to generate patient specific pluripotent stem cells for treatment of many degenerative and genetic diseases. However, safety concerns have been raised for potentially applying this technology in human because of the severely abnormal phenotypes seen in cloned animals. Here, we demonstrated that the ES cell lines derived from cloned and fertilized mouse blastocysts are indistinguishable based on their microRNA and protein expression profiles, consistent with their normal developmental potential and transcriptional profiles. Moreover, the NT-ES cells have been successfully differentiated into functional haematopoietic cells both in vitro and in vivo, which indicated that ES cell lines derived from somatic cloned or fertilized blastocysts have an identical therapeutic potential. (platform)