MeCP2 links heterochromatin condensates and neurodevelopmental disease

MeCP2 (methyl CpG binding protein 2) is a key component of constitutive heterochromatin, which plays important roles in chromosome maintenance and transcriptional silencing. Mutations in MeCP2 cause Rett syndrome (RTT), a postnatal progressive neurodevelopmental disorder associated with severe mental disability and autism-like symptoms that manifests in girls during early childhood. Heterochromatin, long considered a dense and relatively static structure, is now understood to exhibit properties consistent with a liquid-like condensate. Here we report that MeCP2 is a dynamic component of heterochromatin condensates in cells, is stimulated by DNA to form liquid-like condensates, contains multiple domains that contribute to condensate formation, manifests physicochemical properties that selectively concentrate heterochromatin cofactors compared to components of transcriptionally active condensates, and when altered by RTT-causing mutations is disrupted in its ability to form condensates. We propose that MeCP2 enhances heterochromatin/euchromatin separation through its condensate partitioning properties and that condensate disruption may be a common consequence of RTT patient mutations.