Abstract
SummaryGenome-wide DNA methylation reprogramming occurs in mouse primordial germ cells (PGCs) and preimplantation embryos, but the precise dynamics and biological outcomes are largely unknown. We have carried out whole-genome bisulfite sequencing (BS-Seq) and RNA-Seq across key stages from E6.5 epiblast to E16.5 PGCs. Global loss of methylation takes place during PGC expansion and migration with evidence for passive demethylation, but sequences that carry long-term epigenetic memory (imprints, CpG islands on the X chromosome, germline-specific genes) only become demethylated upon entry of PGCs into the gonads. The transcriptional profile of PGCs is tightly controlled despite global hypomethylation, with transient expression of the pluripotency network, suggesting that reprogramming and pluripotency are inextricably linked. Our results provide a framework for the understanding of the epigenetic ground state of pluripotency in the germline.
Highlights
Epigenetic information in the mammalian genome is relatively stable in differentiated cells of the soma but is reprogrammed on a genome-wide scale in primordial germ cells (PGCs) and early embryos (Reik et al, 2001; Surani et al, 2007; Sasaki and Matsui, 2008; Smith et al, 2012)
Further optimization of the technique allowed us to include earlier stages of PGCs, and here we describe a systematic study of bisulfite sequencing (BS-Seq) and RNA-Seq of key stages of PCG development, which provides a framework for the understanding of epigenetic reprogramming, pluripotency, and transgenerational epigenetic inheritance
BS-Seq libraries were prepared from two independent samples of each time point, and two independent sequencing runs for a J1 embryonic stem cell (ESC) (129S4/SvJae) BS-Seq library were performed as well (Figure 1A)
Summary
Epigenetic information in the mammalian genome is relatively stable in differentiated cells of the soma but is reprogrammed on a genome-wide scale in primordial germ cells (PGCs) and early embryos (Reik et al, 2001; Surani et al, 2007; Sasaki and Matsui, 2008; Smith et al, 2012) This includes the erasure of DNA methylation and the large-scale reprogramming of histone modifications and histone variants (Hajkova et al, 2002, 2008; Lee et al, 2002; Lane et al, 2003; Yamazaki et al, 2003; Seki et al, 2005, 2007; Popp et al, 2010; Guibert et al, 2012). PGCs express Nanog, Oct, and Sox, and pluripotent stem cells (embryonic germ cells, EGCs) can be derived from them (Surani et al, 2007)
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