Brd4 binds to active enhancers to control cell identity gene induction in adipogenesis and myogenesis

Area of Science:

• Epigenetics
• Molecular Biology
• Developmental Biology

Background:

• Brd4 (bromodomain-containing protein 4) is a key epigenetic regulator and cancer drug target.
• Its precise role in cell differentiation and animal development is not well understood.

Purpose of the Study:

• To elucidate the function of Brd4 in cell differentiation and animal development.
• To investigate the molecular mechanisms by which Brd4 regulates cell identity gene induction.

Main Methods:

• Utilized conditional knockout mouse models and derived cell lines.
• Performed co-localization studies of Brd4 with transcription factors and epigenetic modifiers.
• Analyzed the enrichment of transcription machinery and enhancer activity upon Brd4 deletion.

Main Results:

• Brd4 is essential for adipogenesis and myogenesis, controlling cell identity gene induction.
• Brd4 co-localizes with lineage-determining transcription factors (LDTFs) on active enhancers during differentiation.
• Brd4 recruitment to enhancers is mediated by LDTFs, H3K4 methyltransferases (MLL3/MLL4), and H3K27 acetyltransferases (CBP/p300).
• Brd4 deletion impairs Mediator and RNA polymerase II recruitment, preventing enhancer RNA production and cell differentiation.
• Brd4 is not required for maintaining cell identity in already differentiated cells.

Conclusions:

• Brd4 functions as an enhancer epigenomic reader, linking active enhancers to cell identity gene induction during differentiation.
• These findings highlight Brd4's critical role in developmental processes and identify potential therapeutic targets for differentiation-related disorders.