HEB associates with PRC2 and SMAD2/3 to regulate developmental fates

Area of Science:

• Developmental Biology
• Stem Cell Biology
• Molecular Biology

Background:

• Embryonic stem cells (ESCs) require extracellular signals for lineage specification.
• Chromatin relaxation at developmental promoters is crucial for differentiation.
• Proteins connecting extrinsic cues to chromatin changes remain largely unknown.

Purpose of the Study:

• To identify proteins linking extracellular signals to chromatin relaxation in ESCs.
• To investigate the role of the helix-loop-helix (HLH) protein HEB in lineage specification.
• To elucidate the mechanism by which HEB influences developmental gene expression.

Main Methods:

• Chromatin immunoprecipitation to assess protein-DNA interactions.
• HEB depletion studies using RNA interference in mouse ESCs.
• Activin stimulation assays to induce differentiation.
• Analysis of HEB association with Polycomb repressive complex 2 (PRC2) and SMAD2/3 elements.

Main Results:

• HEB directly associates with PRC2 at developmental promoters, including genes for mesoderm/endoderm specification and Hox/Fox families.
• HEB depletion does not affect naive mouse ESCs but causes premature differentiation upon Activin exposure.
• HEB deposition at promoters depends on PRC2 but not Nodal signaling.
• HEB association with SMAD2/3 elements depends on Nodal but not PRC2.

Conclusions:

• HEB acts as a crucial link between Nodal signaling and the derepression of poised developmental promoters.
• HEB plays a fundamental role in lineage specification during mouse ESC differentiation.
• The findings reveal a novel mechanism for integrating extrinsic cues with chromatin regulation for developmental control.