XIST derepression in active X chromosome hinders pig somatic cell nuclear transfer

Pig cloning by somatic cell nuclear transfer (SCNT) remains extremely inefficient and many cloned embryos undergo abnormal development. Here by profiling transcriptome expression, we observed dysregulated chromosome-wide gene expression in every chromosome and identified a considerable number of genes that are aberrantly expressed in the abnormal cloned embryos. In particular, XIST, a long noncoding RNA gene, showed highly ectopic expression in abnormal embryos. We also proved that nullification of the XIST gene in donor cells can correct aberrant gene expression in cloned embryos and enhance long term development capacity of the embryos. Furthermore, the increased quality of XIST-deficient embryos was associated with the global H3K9me3 reduction. Injection of H3K9me demethylase Kdm4A into NT embryos could improve the development of preimplantation stage embryos. However, Kdm4A addition also induced XIST derepression in the active X chromosome, thus was not able to enhance the in vivo long term developmental capacity of porcine NT embryos. Overall design: Fetuses original tissue mRNA profiles of 30-day and 35-day cloned and naturally fertilized (NF) were generated by deep sequencing, in triplicate or two replicates. Embryos mRNA profiles of in vitro 6-day cloned and fertilized were generated by deep sequencing, in two replicates.