Background
SMCHD1 is an epigenetic repressor and plays critical role of gene repression on inactive X and autosomal locus e.g., D4Z4repeats and Hox gene cluster. It has also been implicated in human developmental disease muscular dystrophy Facioscapulohumeral muscular dystrophy (FSHD). Missense and nonsense mutations on SMCHD1 were found in FSHD patients and relevant with the onset of disease. These mutations spread the whole protein, and some impair SMCHD1’s function e.g., ATPase activity or nucleic acid binding ability.
Research methodologies and Major finding
We developed new mice strains which could inducible express GFP tagged WT SMCHD1 or R1867G mutant, which has been proved impairs the nucleic binding ability of SMCHD1. We derived MEFs and neural stem cell lines for imaging and genomics experiments respectively. We applied immunofluorescence and ChIP-seq experiments of SMCHD1 and found that impaired nucleic acid binding ability diminishes SMCHD1’s enrichment on the inactive X chromosome but doesn’t affect its binding at conserved binding sites. We also performed live cell imaging techniques, FRAP and Fluorescence Correlation Spectroscopy, and found that R1867G mutant shows faster recovery and unbind rate that WT, while nucleic acid interaction doesn’t contribute to the loading process of SMCHD1 to its binding sites. Lastly, using ChIP-seq and RNA-seq, we found R1867G is a loss of function mutation for SMCHD1’s roles on transcription regulation and interplay with other epigenetic events, especially H3K27me3, whose genome wide distribution was shuffled after interruption of SMCHD1.
Conclusion
By creating and using inducible mice strain harbors a patient mutation which impairs SMCHD1’s nucleic acid binding ability, we investigated its impact to SMCHD1’s target binding, protein dynamics, and epigenetic functions, and clarified the role of nucleic acid binding for epigenetic regulator SMCHD1.