MECP2 impairs neuronal structure by regulating KIBRA

The Role of MeCP2 in Regulating Synaptic Plasticity in the Context of Stress and Depression

Methyl-CpG-binding protein 2 (MeCP2) is a transcriptional regulator that is highly abundant in the brain. It binds to methylated genomic DNA to regulate a range of physiological functions implicated in neuronal development and adult synaptic plasticity. MeCP2 has mainly been studied for its role in neurodevelopmental disorders, but alterations in MeCP2 are also present in stress-related disorders such as major depression. Impairments in both stress regulation and synaptic plasticity are associated with depression, but the specific mechanisms underlying these changes have not been identified. Here, we review the interplay between stress, synaptic plasticity, and MeCP2. We focus our attention on the transcriptional regulation of important neuronal plasticity genes such as BDNF and reelin (RELN). Moreover, we provide evidence from recent studies showing a link between chronic stress-induced depressive symptoms and dysregulation of MeCP2 expression, underscoring the role of this protein in stress-related pathology. We conclude that MeCP2 is a promising target for the development of novel, more efficacious therapeutics for the treatment of stress-related disorders such as depression.

Neuronal activation modulates enhancer activity of genes for excitatory synaptogenesis through de novo DNA methylation

Post-mitotic neurons do exhibit DNA methylation changes, contrary to the longstanding belief that the epigenetic pattern in terminally differentiated cells is essentially unchanged. While the mechanism and physiological significance of DNA demethylation in neurons have been extensively elucidated, the occurrence of de novo DNA methylation and its impacts have been much less investigated. In the present study, we showed that neuronal activation induces de novo DNA methylation at enhancer regions, which can repress target genes in primary cultured hippocampal neurons. The functional significance of this de novo DNA methylation was underpinned by the demonstration that inhibition of DNA methyltransferase (DNMT) activity decreased neuronal activity-induced excitatory synaptogenesis. Overexpression of WW and C2 domain-containing 1 (Wwc1), a representative target gene of de novo DNA methylation, could phenocopy this DNMT inhibition-induced decrease in synaptogenesis. We found that both DNMT1 and DNMT3a were required for neuronal activity-induced de novo DNA methylation of the Wwc1 enhancer. Taken together, we concluded that neuronal activity-induced de novo DNA methylation that affects gene expression has an impact on neuronal physiology that is comparable to that of DNA demethylation. Since the different requirements of DNMTs for germ cell and embryonic development are known, our findings also have considerable implications for future studies on epigenomics in the field of reproductive biology.

Apoptotic Activity of MeCP2 Is Enhanced by C-Terminal Truncating Mutations

Methyl-CpG binding protein 2 (MeCP2) is a widely abundant, multifunctional protein most highly expressed in post-mitotic neurons. Mutations causing Rett syndrome and related neurodevelopmental disorders have been identified along the entire MECP2 locus, but symptoms vary depending on mutation type and location. C-terminal mutations are prevalent, but little is known about the function of the MeCP2 C-terminus. We employ the genetic efficiency of Drosophila to provide evidence that expression of p.Arg294* (more commonly identified as R294X), a human MECP2 E2 mutant allele causing truncation of the C-terminal domains, promotes apoptosis of identified neurons in vivo. We confirm this novel finding in HEK293T cells and then use Drosophila to map the region critical for neuronal apoptosis to a small sequence at the end of the C-terminal domain. In vitro studies in mammalian systems previously indicated a role of the MeCP2 E2 isoform in apoptosis, which is facilitated by phosphorylation at serine 80 (S80) and decreased by interactions with the forkhead protein FoxG1. We confirm the roles of S80 phosphorylation and forkhead domain transcription factors in affecting MeCP2-induced apoptosis in Drosophila in vivo, thus indicating mechanistic conservation between flies and mammalian cells. Our findings are consistent with a model in which C- and N-terminal interactions are required for healthy function of MeCP2.