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. Author manuscript; available in PMC: 2010 May 3.
Published in final edited form as: Semin Reprod Med. 2009 Aug 26;27(5):358–368. doi: 10.1055/s-0029-1237424

Figure 2.

Figure 2

(A) Methylation reprogramming in the germ line. Primordial germ cells (PGCs) in the mouse become demethylated early in development. Remethylation begins in prospermatogonia on E16 in male germ cells and after birth in growing oocytes. Some stages of germ cell development are shown (modified from 73). (B) Methylation reprogramming in preimplantation embryos. The paternal genome (blue) is demethylated by an active mechanism immediately after fertilization. The maternal genome (red) is demethylated by a passive mechanism that depends on DNA replication. Both are remethylated around the time of implantation to different extents in embryonic (EM) and extraembryonic (EX) lineages. Methylated-imprinted genes and some repeat sequences (dashed line) do not become demethylated. Unmethylated imprinted genes (dashed line) do not become methylated. From Reik W, Dean W, Walter J. Epigenetic reprogramming in mammalian development. Science 2001;293(5532):1089–1093.