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Somatic cell nuclear transfer in mammalian cloning suffers from a faulty epigenetic reprogramming, which is believed to cause developmental failures in cloned embryos. Regulating the epigenetic-modifying enzymes can rescue the chromatin of cloned embryos from aberrant epigenetic status, thereby potentially promoting cloning efficiency. In this study, we investigated the effect of two histone methyltransferase inhibitors, namely, DZNep and UNC0642, on the in vitro developmental competence of cloned pig embryos. We found that (1) treatment with 10 nM DZNep or 5 nM UNC0642 for 24 h after activation had the best promoting effect on the development of cloned embryos (blastocyst rate 10.32% vs 18.08% for DZNep, and 10.44% vs 18.14% for UNC0642); (2) 10 nM DZNep and 5 nM UNC0642 significantly decreased the levels of H3K27me3 and H3K9me2, respectively, at the 2-cell, 4-cell and blastocyst stages; (3) the apoptosis level was lower in the treatment groups than in untreated control; and (4) the transcriptional expression of epigenetic genes (EZH2, GLP, G9a, Setdb1, Setdb2, Suv39h1 and Suv39h2) was decreased and pluripotency genes (Nanog, Pou5f1, Sox2 and Bmp4) was increased in treatment groups compared with control. These results indicated that treatment with DZNep and UNC0642 improves the epigenetic reprogramming of cloned embryos, which could render beneficial effect on the embryo quality and aberrant gene expression, and finally improve the developmental competence of cloned pig embryos.

Cloned pigs generated by the somatic cell transfer nuclear (SCNT) technique are highly valuable for agriculture, biomedicine, and life sciences. However, the neonatal mortality rate of cloned pigs is very high. The reasons causing the massive loss of cloned pigs during their neonatal ages are unclear. In the present study, we found that the neonatal death of cloned pigs was associated with aberrant purine metabolism, impaired renal morphology and function, and decreased hepatic Hprt1 expression. The downregulation of Hprt1, a key purine metabolism regulation gene, in the liver was responsible for the elevation of an important purine metabolite, uric acid, in the serum, causing abnormalities in kidney morphology and function and leading to death of neonatal cloned pigs. This study provided insights into the pathophysiological mechanisms underlying the neonatal death of clone pigs, and results will help improve their survival rate.