Methylation of H3 at K9 and K27 in promoter regions is involved not only in silencing heterochromatin, but has also been shown to repress genes in transcriptionally active euchromatin (Kouzarides, 2007). It was, therefore, of interest to characterize this marker of gene repression in NAc after chronic cocaine. We focused on dimethyl-K9/K27, because preliminary ChIP experiments revealed that these modifications were the most dynamically regulated in the NAc by cocaine. A key advantage of this analysis is that it provides a highly novel look at genes that are largely repressed or silenced by cocaine, a relatively underexplored adaptation.
