Figure 1.

Neuronal plasticity involves three major mechanisms of chromatin regulation (histone posttranslational modifications, histone variant exchange, and nucleosomal remodeling) (left panel). Nucleosomes are subject to a diverse array of covalent modifications including, but not limited to, acetylation, phosphorylation, methylation, ubiquitylation, as well as direct methylation of DNA (right panel). Note that although a bona fide DNA demethylase has yet to be described, the growth arrest and DNA damage enzyme, Gadd45, as well as oxidation reactions of 5-methylcytosine to 5-hydroxymethylcytosine, have been implicated in DNA demethylase-like activities in cells.