BRD3 is an epigenetic reader protein that recognizes and binds acetylated histones, particularly acetylated lysine residues on histones H2A, H2B, H3, and H4, thereby controlling gene expression and chr9 remodeling 1. As a member of the bromodomain and extra-terminal (BET) protein family, BRD3 recruits transcription factors and coactivators to target genes and activates RNA polymerase II for transcriptional elongation 2. BRD3 facilitates transcriptional initiation and elongation through its two tandem bromodomains, with the first bromodomain (BD1) primarily supporting steady-state gene expression 3. In endoderm differentiation, BRD3 undergoes liquid-liquid phase separation upon binding long non-coding RNA DIGIT, promoting recognition of histone H3 acetylated at lysine-18 (H3K18ac) to induce endoderm-specific gene expression. BRD3 also binds non-histone acetylated proteins such as GATA1 and GATA2 to regulate transcription. Clinically, BRD3 dysfunction is implicated in neurodevelopmental disorders, identified as a high-confidence candidate gene through large-scale variant analysis 4. Abnormal BET protein activation, including BRD3, correlates with various human diseases, particularly cancer 1. BET bromodomain inhibitors targeting BRD3 and related proteins have been developed and evaluated in cancer and inflammatory disease models, representing potential therapeutic approaches for BET-related pathologies.