Figure 1.  . Role of epigenetic changes in gene expression.

(A) Addition or removal of methyl groups by methyltransferases leads to hyper- or hypo-methylation of DNA, leading to gene repression or activation, respectively. (B) Chromosome segment composed of compact DNA wrapped around octamers of core histones (nucleosomes) in which the DNA material is inaccessible and gene functions can not be modified. (C) Epigenetic modifications in histone tails lead to loosening of DNA, rendering genes accessible for modifications of gene activity (i.e., activation and repression). (D) Common post-translational modifications occurring in the histone H3.3 tail that regulate gene transcription. (E) Acetylation at specific amino acid residues leads to transcription activation, whereas methylation leads to transcription inactivation.

Reproduced with permission from [26] © American Association for Cancer Research.