Figure 1.

Epigenetic mechanisms. Epigenetic mechanisms comprise (A) histone posttranslational modifications (HPTMs), (B) DNA methylation, and (C) microRNAs (miRNAs) regulation. Gene expression can be regulated before transcription initiation by HPTMs and DNA methylation. Both mechanisms induce a remodeling of the chromatin structure, thereby making genes either less or more accessible for transcription factors, according to the different epigenetic modifications. Unlike DNA methylation and HPTMs, miRNAs regulate the expression of genes at the post-transcriptional level. miRNAs negatively regulate genes through complementing their mRNAs, which results in mRNA degradation or translational repression.