Optimizing treatment of DNA methyltransferase inhibitor RG108 on porcine fibroblasts for somatic cell nuclear transfer

Aberration in DNA methylation is believed to be one of the major causes of abnormal gene expression and inefficiency of somatic cell nuclear transfer (SCNT). RG108, a non-nucleoside DNA methyltransferase (DNMT) inhibitor, has been reported to facilitate somatic nuclear reprogramming and improved blastocyst formation. The aim of this study was to investigate interaction effect of RG108 treatment time (24-72 hr) and concentrations (0.05-50 µM) on donor cells, and further to optimize the treatment for porcine SCNT. Our results showed that RG108 treatment resulted in time-dependent decrease of genome-wide DNA methylation on foetal fibroblasts, which only happened after 72-hr treatment in our experiments, and no interaction effect between treatment time and concentration. Remarkable decrease of methylation in imprinted gene H19 and increased apoptosis was observed in 5 and 50 µM RG108-treated cells. Furthermore, the blastocyst rates of SCNT embryos were increased as the fibroblasts treated with RG108 at 5 and 50 µM, and additional treatment during cultivation of SCNT embryos would not provide any advantage for blastocyst formation. In conclusion, the RG108 treatment of 72 hr and 5 μM would be optimized time and concentration for porcine foetal fibroblasts to improve the SCNT embryonic development. In addition, combined treatment of RG108 on donor cells and SCNT embryos would not be beneficial for embryonic development.

Effects of DNMT1 and HDAC inhibitors on gene-specific methylation reprogramming during porcine somatic cell nuclear transfer

Somatic cell nuclear transfer (SCNT) in mammalian cloning currently remains inefficient. Incomplete or erroneous epigenetic reprogramming of specialized donor somatic nuclear and resulting aberrant gene expression during development of cloned embryos is commonly believed as the main reason that causes the low efficiency of SCNT. Use of small molecular reprogramming modifiers to assist the somatic nucleus to mimic naturally occurring DNA methylation and chromatin remodeling in nucleus of fertilization-derived zygotes, has been widely attempted to improve cloning efficiency. However, impacts of these small modifiers on gene-specific methylation dynamics and their potential effects on methylation of imprinted gene have rarely been traced. Here, we attempted two relatively novel DNMT1 inhibitor (DNMTi) and histone deacetylase inhibitor (HDACi), scriptaid and RG108, and demonstrated their effects on dynamics of gene-specific DNA methylation and transcription of porcine SCNT embryos. We found that scriptaid and RG108 had synergetic effects on rescuing the disrupted methylation imprint of H19 during SCNT at least partially by repression over-expressed MBD3 in eight-cell cloned embryos. Furthermore, we firstly identified a differential methylation regions (DMRs) at 5′ flanking regions of XIST gene and found that scriptaid alone and its combination with RG108 modify the dynamics of both transcription and DNA methylation levels in cloned embryos, by different manners. Additionally, we found that scriptaid alone and its combination with RG108 can significantly promote the transcription of NANOG in cloned embryos and enhance their pre-implantation developmental capacity. Our results would contribute to uncovering the epigenetic reprogramming mechanisms underlying the effects of assisted small molecules on improvement of mammalian cloning efficiency.