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. Author manuscript; available in PMC: 2013 Apr 1.
Published in final edited form as: Curr Opin Genet Dev. 2011 Dec 21;22(2):72–78. doi: 10.1016/j.gde.2011.12.001

Figure 1. Timeline of epigenetic reprogramming.

Figure 1

The first wave of genome-wide DNA demethylation takes place shortly after fertilization, with the maternal genome passively demethylated and the methylcytosine of the paternal genome converted into hydroxymethylcytosine, which is passively eliminated. Imprinted DMRs are maintained despite this demethylation event. De novo DNA methylation occurs around implantation. In both male and female primordial germ cells another wave of DNA demethylation initiates as the cells migrate toward the genital ridge. All DMRs are also erased at this time. In male germ cells methylation imprints are acquired in prospermatogonia around E15.5–17.5. In the female germline methylation imprints are not acquired until after birth, in growing oocytes. Transcripts have been correlated with acquisition of DNA methylation in both the male and female germlines. Activities in male and female germ cells are represented in blue and red, respectively.