Figure 1.

Histone deacetylation involves the removal of acetyl groups from lysine on N‐termini of histones by histone deacetylase (HDAC) enzymes. The consequent inactive and silent chromatin blocks gene transcription by limiting contact with promoter regions. In the opposite direction, the tails of histones can be acetylated at different sites generating an accessible form of chromatin. The deacetylated histone tails connect tightly to shape a compressed, unattainable form of chromatin. In addition to histone deacetylation, methylation of DNA may also be considered relevant in the context of epigenetics in mood disorders and involves the covalent binding of a methyl group by enzymes called DNA methyltransferases; following promoter methylation, reduced gene transcription generally occurs.