, 2010). These results suggested that high levels of neuronal MeCP2 function to

affect global chromatin structure in a genome-wide manner. One plausible model then is that MeCP2 is bound across the neuronal genome and that activity-dependent phosphorylation of MeCP2 S421 occurs at specific regulatory elements of genes which modulate nervous system development. To address this issue, Cohen and collaborators performed MeCP2 ChIP-Seq GSK-3 inhibitor with a newly generated pan-MeCP2 antibody and confirmed the observations of Skene et al. that MeCP2 protein is broadly distributed across the neuronal genome with a binding pattern similar to that of histone H3. Next, the authors compared genome binding profiles of MeCP2 before and after neuronal stimulation in neuronal cultures and made the unexpected discovery that MeCP2 remains tightly associated with methylated DNA throughout the neuronal genome regardless of neuronal activation. They also confirmed a similarly widespread pattern of MeCP2 phosphorylation, closely tracking total bound MeCP2 in vivo. If MeCP2 remains constitutively bound to methylated DNA, does MeCP2 S421 phosphorylation effect activity-dependent transcriptional programs? To address this question, the authors employed ChIP-qPCR, ChIP-Seq, and oligonucleotide arrays and, contrary

FG-4592 to previous results from in vitro studies, found that induction of activity-dependent genes such as Bdnf and c-fos remained unchanged regardless of MeCP2 S421 phosphorylation. Furthermore they discovered that this phosphorylation event occurs broadly across

the genome in response to neuronal activation, arguing against a role for MeCP2 S421 phosphorylation as a regulator of activity-dependent gene transcription. These results suggest that MeCP2 functions not as a transcriptional repressor of a specific subset of genes but rather as a core component of chromatin whose activity-induced phosphorylation at a single serine residue controls distinct aspects of nervous system development and function. Aberrations in this process may contribute to the pathophysiology of RTT. Interpretation of the effects of MeCP2 phosphorylation are complicated, however, because phosphorylation occurs Mephenoxalone at multiple sites which could have different effects on MeCP2 binding and/or activity. A recent study generated a double phosphomutant at S421 and an additional nearby site (S424) and found very different phenotypes, reminiscent of some of the effects of MeCP2 overexpression ( Li et al., 2011). This study, like prior studies of MeCP2 phosphorylation, used ChIP at specific promoters and found enhanced occupancy. However Cohen et al. (2011) and Skene et al. (2010) have failed to find selective binding at promoters using ChIP-Seq, raising the possibility of differential sensitivity between these assays.