The covalent modification of DNA, on the other hand, induces long-term suppression of gene expression through direct interference with transcription

factor binding and recruitment of chromatin remodeling enzymes via the action of methyl-CpG binding proteins (MBDs), such as MeCP2. While an oversimplification of the process, cytosines located next to guanines (CpGs) are preferentially methylated. This is particularly true in CpG-rich regions known as CpG learn more islands. The authors began by measuring association between GDNF’s promoter region and the transcriptionally active mark of acetylation on histone H3 (H3Ac). Following stress, H3Ac-GDNF association was decreased in BALB mice but increased in B6 mice. This was consistent with the GDNF transcript levels measured in the previous experiment. Acetyl groups are actively removed from histones by histone deacetylase enzymes (HDACs). Covering all of the Angiogenesis inhibitor class I, II, and IV HDACs, the authors next examined HDACs 1–11 in the NAc and found that only HDAC2 was altered by stress. The HDAC2 increase was associated with GDNF’s promoter and specific to stressed BALB mice, further developing a model where GDNF is actively suppressed with stress by removal of H3Ac from GDNF’s promoter. Histone acetylation can be pharmacologically elevated by treatment with various HDAC inhibitors (HDACi).

The HDACi SAHA targets class I HDACs, including HDAC2 (Kilgore et al., 2010). The authors demonstrated that both systemic treatment with SAHA and local viral-mediated knockdown of HDAC2 in the NAc normalized GDNF levels, as well as the anxiety and depression-like behaviors in stressed BALB mice. Conversely, overexpression of HDAC2 further exacerbated the BALBs’ maladaptive behavioral and transcriptional responses to stress. Histone acetylation can work with DNA methylation to regulate gene transcription and behavior (Miller et al., 2008). Therefore, the authors used bisulfite mapping to detail the specific sites of cytosine methylation Plasmin within GDNF’s promoter and just downstream of the transcription start site. One promoter CpG site (CpG

2) was hypermethylated in the NAc of both strains of mice with stress, while another was specifically hypermethylated in stressed BALB mice (CpG 3). Stress also increased levels of DNMT 1 and 3a, isoforms of the enzymes responsible for methylating DNA. Continuous delivery of a DNMT inhibitor into the NAc via an osmotic pump reversed the GDNF hypermethylation, reduction in GDNF mRNA and malapdaptive behavioral stress responses in the BALB mice. MBDs, such as MeCP2, bind to methylated DNA and repress transcription. Unexpectedly, MeCP2 binding to the GDNF promoter was elevated in both strains of mice following stress. The authors have now observed two putative negative regulators of transcription in both strains with stress.