Figure 1.
Epigenetic regulation of gene expression. Gene expression is controlled in the promoter regions by a combination of DNA methylation and chromatin configuration. In normal cells, gene expression is silenced by condensing chromatin, methylating (at cytosine) DNA and deactylating histones. By contrast, active genes are those with open nucleosome spacing around the transcription start site, are unmethylated and associated with acetylated histones. CpG islands that are rich in cytosine and guanine—and are typically unmethylated to promote gene expression—can be epigenetically silenced by hypermethylation in cancer. Adapted from Figueiredo, L. M. et al. Nat. Rev. Microbiol. 7, 504–513 (2009).