The core of the polycomb repressive complex is compositionally and functionally conserved in flies and humans

Area of Science:

• Developmental Biology
• Epigenetics
• Molecular Biology

Background:

• Polycomb group (PcG) genes are crucial for maintaining gene silencing during development in Drosophila and mammals.
• PcG proteins form distinct silencing complexes, and mutations are linked to developmental defects and human cancer.
• Human PcG proteins show divergence from fly counterparts, with multiple versions of each gene present.

Purpose of the Study:

• To investigate the impact of evolutionary changes on the composition and function of human Polycomb repressive complexes.
• To purify and characterize a human Polycomb repressive complex (hPRC-H) from HeLa cells.

Main Methods:

• Purification of a human Polycomb repressive complex (hPRC-H) from HeLa cells.
• Comparison of hPRC-H composition with Drosophila embryonic PRC1 (dPRC1).
• Functional assays to assess the nucleosome remodeling activity of hPRC-H.

Main Results:

• hPRC-H contains homologues of core PcG proteins found in dPRC1 but has fewer non-PcG components.
• hPRC-H preparations included multiple homologues for core PcG proteins, including a novel Ph homologue, HPH3.
• hPRC-H effectively inhibits nucleosomal array remodeling without blocking nuclease access.

Conclusions:

• Human Polycomb repressive complexes exhibit compositional differences compared to their Drosophila counterparts.
• Despite compositional variations, human and fly Polycomb complexes retain similar essential functions in gene silencing and chromatin regulation.
• hPRC-H's ability to block remodeling suggests a conserved mechanism for epigenetic gene repression.