EPOP Restricts PRC2.1 Targeting to Chromatin by Directly Modulating Enzyme Complex Dimerization.

Area of Science:

• Epigenetics
• Molecular Biology
• Developmental Biology

Background:

• Polycomb repressive complex 2 (PRC2) is crucial for developmental gene repression, existing as PRC2.1 and PRC2.2 holocomplexes.
• EPOP, a PRC2.1-specific subunit, has an enigmatic inhibitory role, interacting with Elongin BC.

Purpose of the Study:

• To elucidate the molecular mechanism by which EPOP regulates PRC2.1 activity.
• To investigate EPOP's role in modulating PRC2.1 oligomerization and chromatin association.

Main Methods:

• Investigated EPOP's effect on PRC2.1 oligomerization state.
• Assessed PRC2.1 chromatin association and genome-wide H3K27me3 enrichment using an EPOP mutant.
• Examined the role of Elongin BC in EPOP-mediated PRC2.1 inhibition.

Main Results:

• EPOP directly modulates PRC2.1 oligomerization, disrupting the dimer.
• EPOP weakens PRC2.1 chromatin association by disabling the dimeric avidity effect.
• An EPOP mutant defective in PRC2 binding increased MTF2 and H3K27me3 enrichment in mouse cells.
• Elongin BC is largely dispensable for EPOP's inhibitory function on PRC2.1.

Conclusions:

• EPOP defines a unique PRC2.1 subclass that prevents over-repression of key developmental regulators.
• This mechanism is vital for maintaining epigenetic programs during early differentiation.
• EPOP's function is primarily mediated through direct modulation of PRC2.1 oligomerization, not solely through Elongin BC interaction.