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Fig. 7 | BMC Biology

Fig. 7

From: Bivalent promoter hypermethylation in cancer is linked to the H327me3/H3K4me3 ratio in embryonic stem cells

Fig. 7

Model for cancer DNA hypermethylation. a Polycomb complexes target H3K27me3 to unmethylated CGI (green arrows) enriched for variable levels of H3K4me3. H3K27me3 is occluded from methylated interspersed CpG (black bar), e.g. repetitive elements/satellite DNA. Such normal Polycomb targets are transcriptionally silenced. b Ageing cells and cells undergoing the early events of transformation become globally hypomethylated at repetitive sequences. Polycomb H3K27me3 is redirected (most pronounced from hiBiv loci) to the high burden of unmethylated interspersed CpG. It is unclear during this phase if hiBiv promoters are expressed. c At later stages of cellular transformation and tumours, unprotected CGI are targets for retained de novo DNA methyltransferase activities—which is more prominent at hiBiv loci

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