A Cbx8-Containing Polycomb Complex Facilitates the Transition to Gene Activation during ES Cell Differentiation

Abstract

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.

Barcelona conference on epigenetics and cancer 2016 – beyond cancer genomes

“…While during ESC mesodermal differentiation Mel18 contributes to the well-documented repression of genes encoding regulators of pluripotency and other cell lineages, they also discovered a function of Mel18-containing PRC1 to turn on transcription of mesodermal genes. 13 This is reminiscent of a previously reported function for Cbx8-containing PRC1 complexes in mediating the activation of regulatory genes during neuronal differentiation, 14 suggesting that contributions of PRC1 complexes during gene activation might be more widespread during cell fate transitions.…”

High-throughput analysis reveals novel maternal germline RNAs crucial for primordial germ cell preservation and proper migration

“…(Heasman, 2006). E2f1 also activates Cbx7, a member of the Polycomb repressor PRC1-like complex that plays a pivotal role in the transition from pluripotency to differentiation by regulating Cbx8 and Fzd1 (Klauke et al, 2013;Creppe et al, 2014;Mani et al, 2008;O'Loghlen et al, 2015). Thus, E2f1 in excess may tip the balance towards somatic differentiation in PGCs, causing their loss.…”

Downregulation of the Deiminase PADI2 Is an Early Event in Colorectal Carcinogenesis and Indicates Poor Prognosis

“…Cell lysis, Western blot, and RNA extraction were performed as previously described (22). For immunoblotting, we have used antibodies directed against PADI2 (Proteintech UK; 12110-1-AP) and C-terminal histone H3 (Abcam; ab204964).…”