Abstract
Rett syndrome (RTT), a severe postnatal neurodevelopmental disorder, is caused by mutations in the X-linked gene encoding methyl-CpG-binding protein 2 (MeCP2). MeCP2 is a chromatin organizer regulating gene expression. RTT-causing mutations have been shown to affect this function. However, the mechanism by which MeCP2 organizes chromatin is unclear. In this study, we found that MeCP2 can induce compaction and liquid–liquid phase separation of nucleosomal arrays in vitro, and DNA methylation further enhances formation of chromatin condensates by MeCP2. Interestingly, RTT-causing mutations compromise MeCP2-mediated chromatin phase separation, while benign variants have little effect on this process. Moreover, MeCP2 competes with linker histone H1 to form mutually exclusive chromatin condensates in vitro and distinct heterochromatin foci in vivo. RTT-causing mutations reduce or even abolish the ability of MeCP2 to compete with histone H1 and to form chromatin condensates. Together, our results identify a novel mechanism by which phase separation underlies MeCP2-mediated heterochromatin formation and reveal the potential link between this process and the pathology of RTT.
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Acknowledgements
We thank Dr Xiaoqun Wang for helping us to get mouse brain slices, Dr Keping Hu for providing the MeCP2 plasmid as a gift, Master Ting Yao for her help in analytical ultracentrifugation experiments, and Dr Zhaolan Zhou for critical reading and discussion with our manuscript. This work was supported by grants from the Ministry of Science and Technology of China (2017YFA0504202 to G.L.; 2019YFA0508403 to P.L.; 2018YFE0203302 to P.C.), the National Natural Science Foundation of China (31525013, 31630041 and 31521002 to G.L.; 31871443 to P.L.; 31871290 to P.C.). The work was also supported by the Chinese Academy of Sciences (CAS) Strategic Priority Research Program (XDB19040202), the CAS Key Research Program on Frontier Science (QYZDY-SSW-SMC020) and an HHMI International Research Scholar grant (55008737) to G.L. We are particularly grateful to the SLSTU-Nikon Biological Imaging Center (Tsinghua university) for assistance with NIS-Elements AR Analysis, and Center for Bio-imaging & Core Facility for Protein Sciences (Institute of Biophysics, Chinese Academy of Sciences) for fluorescence and electron microscopy imaging data collection.
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L.W. carried out phase separation experiments and composed the figures. M.H. was responsible for AUC, EM images and cell fluorescence images. M.-Q.Z. performed CXMS experiments. J.Z. and L.H. generated the mice with the MeCP2 R106W mutation. D.W. helped with protein purification. Y.W. performed the statistical analysis of clinical data. Y.L. took part in the plasmid construction. P.C. helped with CXMS experiments and guided nucleosome assembly experiments. X.B. helped to discuss the project. M.-Q.D. guided CXMS experiments and data interpretation. G.L. and P.L. conceived and supervised the project, analyzed the data and wrote the manuscript with L.W. and M.H.
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Wang, L., Hu, M., Zuo, MQ. et al. Rett syndrome-causing mutations compromise MeCP2-mediated liquid–liquid phase separation of chromatin. Cell Res 30, 393–407 (2020). https://doi.org/10.1038/s41422-020-0288-7
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DOI: https://doi.org/10.1038/s41422-020-0288-7
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