Swapping the DNA binding domain of MeCP2 with that of MBD2 to abolish binding to non-CG methlyation results in RTT-like phenotypes in mice [ATAC-seq]

Mutations in the MECP2 gene cause the profound neurological disorder Rett syndrome. MeCP2 protein is an epigenetic reader that recruits the NCOR1/2 corepressor complexes to methylated cytosine in its canonical CG setting, but also to methylated CA motifs, which are abundant in neurons but rare in other cell types. In this study we set out to test the biological significance of this non-canonical mode of DNA binding. To achieve this, we replaced the endogenous MeCP2 DNA binding domain with that of MBD2, which only binds mCG. Knock-in mice expressing the hybrid “MM2” protein created by this domain-swap displayed severe Rett syndrome-like phenotypes. This indicates that binding to mCA, specifically the mCAC trinucleotide, is critical for normal brain function and it offers a plausible explanation for the delayed onset of Rett syndrome, due to the coincident late accumulation of mCAC and its cognate interpreter, MeCP2. We show that the small subset of genes aberrantly expressed in both Mecp2-null and MM2 mice is strikingly enriched for genes implicated in neurological disorders, highlighting targets with potential relevance to the Rett syndrome phenotype Overall design: Hypothalamus tissue taken at 6 week of age (same as whole genome bisulphite dataset from Lagger et al., 2017 PLoS Genetics, used for analysis). Mecp2 -/y (KO), Mecp2 MM2/y (MM2) and WT (MM2 littermates), n = 3 per genotype