MeCP2 binds to non-CG methylated DNA as neurons mature, influencing transcription and the timing of onset for Rett syndrome

MeCP2 binds to non-CG methylated DNA as neurons mature, influencing transcription and the timing of onset for Rett syndrome

Epigenetic mechanisms, such as DNA methylation, regulate transcriptional programs to afford the genome flexibility in responding to developmental and environmental cues in health and disease.

A prime example involving epigenetic dysfunction is the postnatal neurodevelopmental disorder Rett syndrome (RTT), which is caused by mutations in the gene encoding methyl-CpG binding protein 2 (MeCP2). Despite decades of research, it remains unclear how MeCP2 regulates transcription or why RTT features appear 6-18 months after birth. Here we report integrated analyses of genomic binding of MeCP2, gene-expression data, and patterns of DNA methylation.

In addition to the expected high-affinity binding to methylated cytosine in the CG context (mCG), we find a distinct epigenetic pattern of substantial MeCP2 binding to methylated cytosine in the non-CG context (mCH, where H = A, C, or T) in the adult brain. Unexpectedly, we discovered that genes that acquire elevated mCH after birth become preferentially misregulated in mouse models of MeCP2 disorders, suggesting that MeCP2 binding at mCH loci is key for regulating neuronal gene expression in vivo.

MeCP2 binds to non-CG methylated DNA as neurons mature, influencing transcription and the timing of onset for Rett syndrome
MeCP2 binds to non-CG methylated DNA as neurons mature, influencing transcription and the timing of onset for Rett syndrome

This pattern is unique to the maturing and adult nervous system, as it requires the increase in mCH after birth to guide differential MeCP2 binding among mCG, mCH, and nonmethylated DNA elements. Notably, MeCP2 binds mCH with higher affinity than nonmethylated identical DNA sequences to influence the level of Bdnf, a gene implicated in the pathophysiology of RTT.

This study thus provides insight into the molecular mechanism governing MeCP2 targeting and sheds light on the delayed onset of RTT symptoms.

the National Institute of Neurological Disorders and Stroke (NINDS), the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), the International Rett Syndrome Foundation (IRSF) and the Rett Syndrome Research Trust (RSRT) convened a workshop involving a broad cross-section of basic scientists, clinicians and representatives from the

Preclinical research in Rett syndrome: setting the foundation for translational success

National Institutes of Health (NIH), the US Food and Drug Administration (FDA), the pharmaceutical industry and private foundations to assess the state of the art in animal studies of Rett syndrome (RTT). The aim of the workshop was to identify crucial knowledge gaps and to suggest scientific priorities and best practices for the use of animal models in preclinical evaluation of potential new RTT therapeutics.

This review summarizes outcomes from the workshop and extensive follow-up discussions among participants, and includes: (1) a comprehensive summary of the physiological and behavioral phenotypes of RTT mouse models to date, and areas in which further phenotypic analyses are required to enhance the utility of these models for translational studies; (2) discussion of the impact of genetic differences among mouse models, and methodological differences among laboratories, on the expression and analysis, respectively, of phenotypic traits; and

(3) definitions of the standards that the community of RTT researchers can implement for rigorous preclinical study design and transparent reporting to ensure that decisions to initiate costly clinical trials are grounded in reliable preclinical data.

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