A Cbx8-containing polycomb complex facilitates the transition to gene activation during ES cell differentiation

PLoS Genet. 2014 Dec 11;10(12):e1004851. doi: 10.1371/journal.pgen.1004851. eCollection 2014 Dec.


Polycomb proteins play an essential role in maintaining the repression of developmental genes in self-renewing embryonic stem cells. The exact mechanism allowing the derepression of polycomb target genes during cell differentiation remains unclear. Our project aimed to identify Cbx8 binding sites in differentiating mouse embryonic stem cells. Therefore, we used a genome-wide chromatin immunoprecipitation of endogenous Cbx8 coupled to direct massive parallel sequencing (ChIP-Seq). Our analysis identified 171 high confidence peaks. By crossing our data with previously published microarray analysis, we show that several differentiation genes transiently recruit Cbx8 during their early activation. Depletion of Cbx8 partially impairs the transcriptional activation of these genes. Both interaction analysis, as well as chromatin immunoprecipitation experiments support the idea that activating Cbx8 acts in the context of an intact PRC1 complex. Prolonged gene activation results in eviction of PRC1 despite persisting H3K27me3 and H2A ubiquitination. The composition of PRC1 is highly modular and changes when embryonic stem cells commit to differentiation. We further demonstrate that the exchange of Cbx7 for Cbx8 is required for the effective activation of differentiation genes. Taken together, our results establish a function for a Cbx8-containing complex in facilitating the transition from a Polycomb-repressed chromatin state to an active state. As this affects several key regulatory differentiation genes this mechanism is likely to contribute to the robust execution of differentiation programs.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Differentiation*
  • Cells, Cultured
  • Chromatin / genetics
  • Chromatin / metabolism
  • Chromatin Immunoprecipitation
  • Embryonic Stem Cells / cytology
  • Embryonic Stem Cells / metabolism*
  • Gene Deletion
  • Histones / genetics
  • Histones / metabolism
  • Mice
  • Mitochondrial Membrane Transport Proteins
  • Polycomb Repressive Complex 1 / genetics
  • Polycomb Repressive Complex 1 / metabolism
  • Polycomb-Group Proteins / genetics*
  • Polycomb-Group Proteins / metabolism
  • Protein Binding
  • Proteomics
  • Transcriptional Activation*
  • Ubiquitins / genetics
  • Ubiquitins / metabolism
  • Up-Regulation


  • Cbx7 protein, mouse
  • Chromatin
  • Histones
  • Mitochondrial Membrane Transport Proteins
  • Polycomb-Group Proteins
  • Ubiquitins
  • chromatin conjugate protein A24
  • Cbx8 protein, mouse
  • Polycomb Repressive Complex 1

Grant support

CC was supported by a postdoctoral FEBS long-term fellowship (http://www.febs.org/). MB is a Ramón y Cajal fellow (http://www.mineco.gob.es/). This work was supported by the MINECO grants SAF2012-39749 and RYC2010-07337 (http://www.mineco.gob.es/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.