Regulation of Chromatin Remodeling by the Post-HSA Domain of BRG1, a Subunit the BAF ATP-Dependent Chromatin Remodeling Complex

Author

Min Sze Ewe, University of Nebraska Medical CenterFollow

Graduation Date

Fall 12-19-2025

Document Type

Thesis

Degree Name

Master of Science (MS)

Programs

Molecular Genetics & Cell Biology

First Advisor

Dr. Sandipan Brahma

Abstract

The ATP-dependent chromatin remodeler BAF complex regulates nucleosome positioning, chromatin accessibility, and tissue specific gene expression. Its catalytic subunit, BRG1, contains several regulatory domains including the post-HSA region, proposed to modulate ATPase activity. Multiple cancer-associated mutations map to these regulatory regions underscoring their importance, yet the precise role of the post-HSA region in chromatin remodeling remains poorly understood.

To investigate the function of the post-HSA domain, we ectopically expressed FLAG-tagged BRG1 with post-HSA deletion (Δpost-HSA BRG1) in mouse embryonic stem cells. Western blot analysis confirmed expression of the mutant protein. To determine the effects of mutant protein expression on chromatin structure over an induction time course, CUT&Tag mapping was performed targeting histone post translational modifications H3K27me3 and H2AK119ub, Ser5 phosphorylation of RNA polymerase II (RNAPII-S5P) representing paused RNAPII, and FLAG epitope to track mutant BRG1 occupancy. Spike-in calibration strategies were optimized using Drosophila S2 cells to ensure quantitative reproducibility.

Induction of Δpost-HSA BRG1 resulted in downregulation of transcriptionally repressive histone modifications genome wide. Interestingly, we observed a consistent but unexpected decrease in RNAPII-S5P occupancy at both active and repressive genes. These findings suggest that loss of the BRG1 post-HSA domain in BAF disrupts the regulation between chromatin structure and transcriptional machinery, potentially affecting the stability of promoter-proximally paused RNAPII. Experiments to directly measure effects on transcription initiation and elongations are underway.

Together, this study provides new insight into mechanisms regulating chromatin remodeling by the BAF complex and the roles of regulatory domains.

Comments

2025 Copyright, the authors

Recommended Citation

Ewe, Min Sze, "Regulation of Chromatin Remodeling by the Post-HSA Domain of BRG1, a Subunit the BAF ATP-Dependent Chromatin Remodeling Complex" (2025). Theses & Dissertations. 1025.
https://digitalcommons.unmc.edu/etd/1025