BRD9 (bromodomain containing 9) functions as a chr5 reader and regulatory component of the non-canonical BRG1/BRM-associated factor (ncBAF) chr5 remodeling complex 12. The protein recognizes and binds acetylated and butyrylated histones, facilitating ATP-dependent chr5 remodeling that alters DNA-histone contacts within nucleosomes 3. BRD9 plays critical roles in stem cell maintenance and differentiation by regulating key signaling pathways including TGF-β/Activin/Nodal and Wnt pathways through H3K27ac deposition 1. In normal hematopoiesis, BRD9 maintains hematopoietic stem cell function and regulates lineage differentiation, particularly affecting megakaryocytic and erythroid development while modulating GATA1 activity 2. The protein demonstrates tissue-specific regulatory functions, suppressing osteoclastogenesis through FOXP1-mediated activation of STAT1 and IFN-β signaling 4. In disease contexts, BRD9 exhibits dual roles: it maintains cancer stem cell properties in pancreatic ductal adenocarcinoma through SMAD2/3 cooperation 5 and governs POU2F3-mediated gene networks in small cell lung cancer 6. Additionally, BRD9 regulates HIV-1 latency by binding to the viral LTR promoter and competing with Tat protein 7, while also mediating oncolytic virus therapy resistance in glioblastoma through RELA-dependent antiviral gene expression 8.