Abstract
BackgroundMethyl-CpG-binding protein 2 (MeCP2), a protein with affinity for methylated cytosines, is crucial for neuronal development and function. MeCP2 regulates gene expression through activation, repression and chromatin remodeling. Mutations in MeCP2 cause Rett syndrome, and these patients display impaired nociception. We observed an increase in MeCP2 expression in mouse dorsal root ganglia (DRG) after peripheral nerve injury. The functional implication of increased MeCP2 is largely unknown. To identify regions of the genome bound by MeCP2 in the DRG and the changes induced by nerve injury, a chromatin immunoprecipitation of MeCP2 followed by sequencing (ChIP-seq) was performed 4 weeks after spared nerve injury (SNI).ResultsWhile the number of binding sites across the genome remained similar in the SNI model and sham control, SNI induced the redistribution of MeCP2 to transcriptionally relevant regions. To determine how differential binding of MeCP2 can affect gene expression in the DRG, we investigated mmu-miR-126, a microRNA locus that had enriched MeCP2 binding in the SNI model. Enriched MeCP2 binding to miR-126 locus after nerve injury repressed miR-126 expression, and this was not mediated by alterations in methylation pattern at the miR-126 locus. Downregulation of miR-126 resulted in the upregulation of its two target genes Dnmt1 and Vegfa in Neuro 2A cells and in SNI model compared to control. These target genes were significantly downregulated in Mecp2-null mice compared to wild-type littermates, indicating a regulatory role for MeCP2 in activating Dnmt1 and Vegfa expression. Intrathecal delivery of miR-126 was not sufficient to reverse nerve injury-induced mechanical and thermal hypersensitivity, but decreased Dnmt1 and Vegfa expression in the DRG.ConclusionsOur study shows a regulatory role for MeCP2 in that changes in global redistribution can result in direct and indirect modulation of gene expression in the DRG. Alterations in genome-wide binding of MeCP2 therefore provide a molecular basis for a better understanding of epigenetic regulation-induced molecular changes underlying nerve injury.Electronic supplementary materialThe online version of this article (doi:10.1186/s13072-016-0073-5) contains supplementary material, which is available to authorized users.
Highlights
Methyl-cytosine and guanine separated (CpG)-binding protein 2 (MeCP2), a protein with affinity for methylated cytosines, is crucial for neuronal development and function
gene ontology (GO) analysis of our Chromatin immunoprecipitation (ChIP)-seq results indicates that Methyl-CpG-binding protein 2 (MeCP2) binding occurs at the promoter of genes with neuronal function, ion channel activity and cellular membrane functions
Our ChIP-seq analysis to determine the functional implication of increased MeCP2 in the dorsal root ganglia (DRG) after nerve injury showed redistribution, and enrichment within transcribed regions in the spared nerve injury (SNI) model compared to sham control
Summary
Methyl-CpG-binding protein 2 (MeCP2), a protein with affinity for methylated cytosines, is crucial for neuronal development and function. MeCP2 regulates gene expression through activation, repression and chromatin remodeling. We observed an increase in MeCP2 expression in mouse dorsal root ganglia (DRG) after peripheral nerve injury. MeCP2 can decipher methylation patterns across the genome before binding to methylated DNA [1] and can mediate downstream transcriptional changes of a large number of genes [3]. Mutations in MECP2 result in Manners et al Epigenetics & Chromatin (2016) 9:23 the neurodevelopmental disorder Rett syndrome (RTT) [6]. Reduced sensitivity has been observed in mouse models with RTT and autism-associated mutations [8,9,10,11]. The observations from RTT patients and MeCP2-mutant mice indicate that MeCP2 contributes either directly or indirectly to reduced pain sensitivity
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