H3K27me3 spreading organizes canonical PRC1 chromatin architecture to regulate developmental programs

Area of Science:

• Epigenetics and Gene Regulation
• Developmental Biology
• Cancer Biology

Background:

• Polycomb repressive complex 2 (PRC2) establishes heterochromatin via H3K27me3, recruiting canonical PRC1 (cPRC1).
• Polycomb-regulated genes exhibit long-range 3D interactions in early development that typically resolve during differentiation.
• Understanding the dynamics of Polycomb-anchored looping and its role in gene silencing is crucial for cell fate determination.

Purpose of the Study:

• To investigate how H3K27me3 spreading regulates Polycomb-anchored looping and gene silencing.
• To explore the impact of modulating H3K27me3 spreading on chromatin architecture and cell fate.
• To determine the therapeutic potential of targeting Polycomb looping in H3K27M-mutant glioma.

Main Methods:

• Utilized glioma-derived H3 Lys27-to-Met (H3K27M) mutations to restrict H3K27me3 spreading.
• Analyzed three-dimensional chromatin interactions and cPRC1 distribution.
• Assessed the effects of disrupting cPRC1 binding or aggregation on gene repression, differentiation, and tumor regression.

Main Results:

• H3K27me3 confinement concentrates cPRC1, leading to heightened 3D interactions resembling pluripotency chromatin.
• H3K27me3 spreading in pluripotent stem cells dilutes local cPRC1, weakening Polycomb loop contacts.
• Disrupting cPRC1 function in H3K27M-mutant glioma induces differentiation and tumor regression.

Conclusions:

• Polycomb-anchored looping is controlled by H3K27me3 spreading and is essential for regulating target gene silencing and cell fate.
• Histone modification-guided reader complex distribution is a key mechanism for nuclear organization.
• Targeting Polycomb looping offers a potential therapeutic strategy for H3K27M-mutant gliomas.