GSE158341
Mammalian SWI/SNF continuously restores local accessibility to chromatin [MNase-Seq]
Open chromatin is a hallmark of regulatory regions and serves as a feature for their identification. Accessible genomic sites are mediated by the activity of transcription factors (TFs) that can engage with nucleosomes to enable stable gene expression changes that underlie development. While the variability of open chromatin between tissues has been studied in large detail, we have limited knowledge on the dynamics of accessible chromatin in any given cell. Answering this question is critical to better understand cellular memory but also to discern actual kinetics of TF binding and its consequence on local nucleosomal organization. Here we use small molecule inhibition of the catalytic subunit of the mouse SWI/SNF remodeler complex to show that accessibility at sites of TF binding critically relies on persistent activity of nucleosome remodelers. Within minutes of remodeler inhibition, accessibility decreases excluding that remodeler activity is only necessary in defined cell cycle transitions. Moreover, this surprisingly fast response is irrespective of TF function as it is similar for the pluripotency factor and activating TF Oct4 and the repressive TF Rest. Importantly, accessibility is rapidly restored upon inhibitor removal demonstrating that open chromatin is regenerated continuously and in a cell-autonomous fashion. Combined, this establishes a model where TF binding to chromatin and remodeler-mediated nucleosomal removal do not represent an initial opening event leading to a stable situation but instead open chromatin reflects an average of a highly dynamic situation that requires continued reestablishment. This argues against a model where open chromatin can persist in absence of continuous TF binding and remodeler activity. Overall design: MNase-Seq (2 replicates per condition) profiling of wildtype mouse embryonic stem cells treated with BRM014 compound, DMSO (control), or with BRM014 followed by wash-out of the compound.