Fig. 1

Summary of epigenetic mechanisms. There are multiple epigenetic processes that interact to determine whether DNA (Ia) open and accessible to transcription or (IIb) closed and inaccessible to transcription. Epigenetic processes include (II) DNA methylation, which is the methylation of cytosine residues in CpG dinucleotides, (IIIa) histone tail modifications which can facilitate accessible DNA (histone acetylation and methylation) or (IIIb) histone tail modifications which are associated with inaccessible DNA (histone deacetylation and demethylation), (IV) non-coding RNA which interact with DNA and/or other epigenetic processes, and (V) higher-order chromatin structure (image modified from [9])