XIST Derepression in Active X Chromosome Hinders Pig Somatic Cell Nuclear Transfer

Summary Pig cloning by somatic cell nuclear transfer(SCNT) remains extremely inefficient, and many cloned embryosundergo 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 non-coding RNAgene, showed high ectopic expressionin abnormal embryos. We also proved that nullificationof the XISTgene in donor cells can normalize aberrant gene expression in cloned embryosand enhance long-term development capacity of the embryos. Furthermore, the increased quality of XIST-deficient embryoswas associated with the global H3K9me3 reduction. Injection of H3K9me demethylaseKdm4A into NT embryoscould improve the development of pre-implantation stage embryos. However, Kdm4A addition also induced XIST derepressionin the active X chromosome and thus was not able to enhance the in vivo long-term developmental capacity of porcine NT embryos.