lo 4 PcG in chromatin organisation

[?] How is PcG involved in chromatin compaction?

PcG is heavily involved in chromatin compaction. It was discovered in 2004 that PRC1 complexes were sufficient to compact nucleosomal arrays in vitro.

[?] What are Polycomb bodies?

Polycomb bodies are condensed nuclear speckles containing PcG complexes and many PcG repressed loci. They represent a higher-order organisation of PcG-mediated repression in the nucleus.

[?] What is the role of PHC1 and PHC2 in Polycomb body formation?

PHC1 and PHC2 (Polyhomeotic subunits of PRC1) are involved in maintaining long-range genome contacts through hetero-oligomerisation of PHC molecules at different sites in the genome. These long-range links contribute to the formation of Polycomb bodies.

[?] What happens to Polycomb bodies in PHC1 mutants?

Hi-C experiments show that PHC1 mutants lose Polycomb body formation at target loci (such as HOXA in the example given), demonstrating that PHC1 is essential for maintaining long-range contacts between PcG target sites.

[?] What are the levels of 3D genome organisation?

The levels of 3D genome organisation include: DNA double helix, nucleosomes, chromatin fibre, loops and topologically associating domains (TADs), and chromosome territories.

[?] How does PRC1 contribute to genome architecture?

PRC1 is essential to maintain contacts between PcG target sites. Contributions of PcG to genome architecture are still being unravelled, but PRC1-mediated compaction and long-range interactions are key aspects.

[?] What technique is used to study long-range genomic contacts?

Hi-C (High-throughput Chromosome Conformation Capture) is used to study long-range genomic contacts and has been instrumental in showing that PHC1 mutants lose Polycomb body formation at target lo