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Pcl-PRC2 is needed to generate high levels of H3-K27 trimethylation at Polycomb target genes

Maxim Nekrasov1, Tetyana Klymenko, Sven Fraterman

  • 1Gene Expression Programme, EMBL, Heidelberg, Germany.

The EMBO Journal
|September 1, 2007
PubMed

Insights

Polycomb Repressive Complex 2 (PRC2) with polycomblike (Pcl) generates high H3-K27 trimethylation for Polycomb target gene repression. This Pcl-PRC2 complex is crucial for maintaining gene silencing, unlike general PRC2 activity.

Area of Science:

  • Epigenetics
  • Chromatin Biology
  • Developmental Biology

Background:

  • Polycomb Repressive Complex 2 (PRC2) is a key epigenetic regulator.
  • PRC2 is implicated in H3-K27 trimethylation, a mark associated with gene silencing.
  • The precise role of PRC2 variants in regulating Polycomb target genes requires further elucidation.

Purpose of the Study:

  • To biochemically characterize a distinct Drosophila PRC2 complex containing polycomblike (Pcl).
  • To determine the specific HMTase activity of Pcl-PRC2 in vitro and in vivo.
  • To investigate the role of Pcl-PRC2 in regulating Polycomb target gene expression and H3-K27 methylation states.

Main Methods:

  • Biochemical purification of Drosophila PRC2 complexes.
  • In vitro HMTase assays using nucleosomes.
  • Analysis of Drosophila mutants lacking Pcl.
  • Assessment of gene expression and histone methylation states in mutant and wild-type flies.

Main Results:

  • A distinct Pcl-PRC2 complex was purified, exhibiting H3-K27 mono-, di-, and trimethylation activity.
  • Pcl-PRC2 is essential for high levels of H3-K27 trimethylation at Polycomb target genes.
  • Pcl-PRC2 is dispensable for genome-wide H3-K27 mono- and dimethylation.
  • Loss of Pcl leads to derepression of Polycomb target genes despite reduced, not abolished, H3-K27 trimethylation.

Conclusions:

  • Pcl-PRC2 is the specific HMTase responsible for high H3-K27 trimethylation at Polycomb target genes.
  • This high trimethylation level is critical for maintaining Polycomb-mediated gene repression.
  • Pcl-PRC2 activity is distinct from the general PRC2 complex's role in lower-level H3-K27 methylation.

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