Howard Hughes Medical Institute, WAB-149G, 200 Longwood Av., Boston, MA 02115, USA.
Cell Res. 2013 Mar;23(3):329-39. doi: 10.1038/cr.2013.22. Epub 2013 Feb 12.
Previous studies have revealed that mouse primordial germ cells (PGCs) undergo genome-wide DNA methylation reprogramming to reset the epigenome for totipotency. However, the precise 5-methylcytosine (5mC) dynamics and its relationship with the generation of 5-hydroxymethylcytosine (5hmC) are not clear. Here we analyzed the dynamics of 5mC and 5hmC during PGC reprograming and germ cell development. Unexpectedly, we found a specific period (E8.5-9.5) during which both 5mC and 5hmC levels are low. Subsequently, 5hmC levels increase reaching its peak at E11.5 and gradually decrease until E13.5 likely by replication-dependent dilution. Interestingly, 5hmC is enriched in chromocenters during this period. While this germ cell-specific 5hmC subnuclear localization pattern is maintained in female germ cells even in mature oocytes, such pattern is gradually lost in male germ cells as mitotic proliferation resumes during the neonatal stage. Pericentric 5hmC plays an important role in silencing major satellite repeat, especially in female PGCs. Global transcriptome analysis by RNA-seq revealed that the great majority of differentially expressed genes from E9.5 to 13.5 are upregulated in both male and female PGCs. Although only female PGCs enter meiosis during the prenatal stage, meiosis-related and a subset of imprinted genes are significantly upregulated in both male and female PGCs at E13.5. Thus, our study not only reveals the dynamics of 5mC and 5hmC during PGC reprogramming and germ cell development, but also their potential role in epigenetic reprogramming and transcriptional regulation of meiotic and imprinted genes.
先前的研究表明，小鼠原始生殖细胞（PGC）经历全基因组 DNA 甲基化重编程，以重置全能性的表观基因组。然而，5-甲基胞嘧啶（5mC）的精确动态及其与 5-羟甲基胞嘧啶（5hmC）生成的关系尚不清楚。在这里，我们分析了 PGC 重编程和生殖细胞发育过程中 5mC 和 5hmC 的动态。出乎意料的是，我们发现了一个特定的时期（E8.5-9.5），在此期间，5mC 和 5hmC 的水平都很低。随后，5hmC 水平增加，在 E11.5 达到峰值，然后逐渐下降，直到 E13.5，可能是通过复制依赖性稀释。有趣的是，在此期间，5hmC 在染色质中心富集。虽然这种生殖细胞特异性 5hmC 亚核定位模式在雌性生殖细胞中甚至在成熟卵母细胞中得以维持，但随着新生阶段有丝分裂增殖的恢复，这种模式在雄性生殖细胞中逐渐丢失。着丝粒周围的 5hmC 在沉默主要卫星重复序列中起着重要作用，特别是在雌性 PGC 中。通过 RNA-seq 进行的全基因组转录组分析表明，E9.5 到 13.5 之间差异表达基因的绝大多数在雌雄 PGC 中均上调。尽管只有雌性 PGC 在产前阶段进入减数分裂，但在 E13.5 时，减数分裂相关和一部分印记基因在雌雄 PGC 中均显著上调。因此，我们的研究不仅揭示了 PGC 重编程和生殖细胞发育过程中 5mC 和 5hmC 的动态，还揭示了它们在减数分裂和印记基因的表观遗传重编程和转录调控中的潜在作用。
