cBAF generates subnucleosomes that expand OCT4 binding and function beyond DNA motifs at enhancers

Area of Science:

• Molecular Biology
• Chromatin Biology
• Epigenetics

Background:

• The canonical BRG/BRM-associated factor (cBAF) complex is crucial for opening chromatin at enhancers in mammalian cells.
• The precise structure and function of this open chromatin remain incompletely understood.

Purpose of the Study:

• To elucidate the nature of cBAF-mediated open chromatin.
• To investigate the role of cBAF-generated structures in transcription factor binding and function.

Main Methods:

• Genome-wide analysis of chromatin structure.
• Biochemical characterization of subnucleosomal particles.
• In vivo binding assays for transcription factor OCT4.

Main Results:

• cBAF complexes generate stable hemisome-like subnucleosomal particles containing histones and ~50-80 bp of DNA.
• These subnucleosomes are formed by targeting and splitting fragile nucleosomes.
• In mouse embryonic stem cells, subnucleosomes serve as binding substrates for OCT4, independent of DNA motifs.
• OCT4 interaction with subnucleosomes significantly enhances OCT4 occupancy and binding range at enhancers.

Conclusions:

• cBAF-dependent subnucleosomes represent a novel mechanism for chromatin modulation.
• These particles extend the functional reach of OCT4 beyond its canonical DNA binding sites.
• This mechanism provides a new perspective on how transcription factors orchestrate gene expression through chromatin opening.