Abstract
DNA methylation reprogramming plays important roles in mammalian embryogenesis. Mammalian somatic cell nuclear transfer (SCNT) embryos with reprogramming defects fail to develop. Thus, we compared DNA methylation reprogramming in preimplantation embryos from bovine SCNT and in vitro fertilization (IVF) and analyzed the influence of vitamin C (VC) on the reprogramming of DNA methylation. The results showed that global DNA methylation followed a typical pattern of demethylation and remethylation in IVF preimplantation embryos; however, the global genome remained hypermethylated in SCNT preimplantation embryos. Compared with the IVF group, locus DNA methylation reprogramming showed three patterns in the SCNT group. First, some pluripotency genes (POU5F1 and NANOG) and repeated elements (satellite I and α-satellite) showed insufficient demethylation and hypermethylation in the SCNT group. Second, a differentially methylated region (DMR) of an imprint control region (ICR) in H19 exhibited excessive demethylation and hypomethylation. Third, some pluripotency genes (CDX2 and SOX2) were hypomethylated in both the IVF and SCNT groups. Additionally, VC improved the DNA methylation reprogramming of satellite I, α-satellite and H19 but not that of POU5F1 and NANOG in SCNT preimplantation embryos. These results indicate that DNA methylation reprogramming was aberrant and that VC influenced DNA methylation reprogramming in SCNT embryos in a locus-specific manner.
Highlights
DNA methylation is an important epigenetic modification that occurs predominantly at CpG dinucleotides
To reveal the mechanisms of the abnormal development of Somatic cell nuclear transfer (SCNT) embryos, this study investigated the reprogramming of DNA methylation during bovine in vitro fertilization (IVF) and SCNT preimplantation embryonic development and examined the influence of Vitamin C (VC) on the development of and DNA methylation reprogramming in bovine SCNT preimplantation embryos
The 5-mC signal was stronger in each developmental stage of the SCNT embryos than it was in the corresponding developmental stage of the IVF embryos, and no obvious change in the 5-mC signal was found in any developmental stage of the SCNT embryos
Summary
DNA methylation is an important epigenetic modification that occurs predominantly at CpG dinucleotides. The other mechanism, called “passive” demethylation, occurs when DNA methylation is passively diluted by DNA replication following cell division due to the absence of the maintenance methyltransferase DNMT19. The above results suggest the importance of proper TET3-catalyzed DNA methylation reprogramming in normal mammalian early embryonic development. The anomalies associated with SCNT embryos may be caused by the incomplete reprogramming of epigenetic modifications in the somatic cell nucleus of an enucleated oocyte that involves the normal transcriptional reactivation of embryonically expressed genes[22,23]. It is important to investigate the reprogramming of DNA methylation in other species to expand our understanding of the mechanism responsible for the abnormal development of SCNT embryos
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