BPS2026 – Imaging, quantifying, and mapping SWI/SNF chromatin remodeler dynamics in live human cells: From single-molecule binding landscape to condensation-mediated intranuclear organization

SWI/SNF chromatin remodelers are a key family of multi-subunit complexes that regulate genome access via nucleosome translocation/ejection. Despite their prevalent implications in human cancers, their intranuclear organization and dynamics in vivo remain poorly understood. Using single-molecule tracking (SMT), we systematically quantified the live-cell diffusion and chromatin-binding dynamics of the fully assembled SWI/SNF remodeler complexes. Leveraging a novel super-resolved density mapping strategy, STAR, we further unveiled heterogenous, nanoscale remodeler binding “hotspots” across the nucleoplasm, pointing to a model where successive longer lived binding events preferentially clustered within the “hotspots” lead to sustained productive remodeling. To further elucidate the mechanistic driving force for such intranuclear organization, we showed that BRG1, the core ATPase/translocase subunit common to all major subtypes of the SWI/SNF family, undergoes phase separation in live cells, mediated by its IDR-rich C terminus (BRG1 C ). Condensates of BRG1 C form across a wide range of expression levels, are highly dynamic, and spatially colocalize with the nucleolus, with their formation, localization and liquid-like properties governed by a specific molecular grammar. Moreover, live-cell SMT revealed differential diffusional and chromatin-binding dynamics of BRG1 C in a condensate-specific and chromatin-hyperacetylation-dependent manner, modulable by nucleolar RNAs. These findings shed critical insights into a multi-modal, condensation-mediated landscape for organizing remodeler dynamics in space and time to regulate remodeling activity and genome access.