Figure 3.
Chromatin's epigenetic markers are involved in its restructuration and remodeling. Dynamic changes in the conformational structure of chromatin are mediated by DNA methylation, histone posttranslational modifications (HPTMs) and noncoding RNAs. DNA methyltransferases (DNMT1, DNMT3a, and DNMT3b) catalyze the addition of a methyl group (-CH3) at position C5 of deoxycytosine (5-mdC). DNA methylation marks can be removed by members of the TET (TET1, TET2, and TET3) protein family through the conversion of 5-mdC to 5-hydroxymethyl-cytosine (5-hmC). Methylation, acetylation, and ubiquitination are HPTMs that may be dynamically regulated by histone methyltransferases (HMTs) and histone demethylases (HDMs) or histone acetyltransferases (HATs) and histone deacetylases (HDACs). During transcriptional repression, messenger RNA (mRNA) can be repressed by noncoding RNAs, such as miRNAs. Precursors of miRNAs are exported to the cytoplasm, where they are processed by Dicer; then, the miRNA is loaded into the RISC complex and binds to the mRNA target. Depending on the base pairing between the miRNA and the mRNA target, the binding can be destabilized, degraded or inhibited.