Project description:Aebp2 encodes a zinc finger protein that is associated with the Polycomb Repressive Complex 2 (PRC2). The alternative promoters and protein isoforms of Aebp2 have been characterized in this study. Aebp2 is controlled through three alternative promoters, deriving three different transcripts which encode the embryonic (32 kDa) and somatic (52 kDa) forms. Chromatin ImmunoPrecipitation (ChIP) experiments revealed that AEBP2 binds to its own promoter as well as the promoters of Jarid2 and Snai2. While the embryonic form acts as a transcriptional repressor for Snai2, the somatic form functions as a transcriptional activator for Jarid2, Aebp2 and Snai2. Cell migration assays suggest that the Aebp2 somatic form can enhance cell migration. This is consistent with the functional association of Aebp2 with migratory neural crest cells. Overall, the two protein isoforms of AEBP2 may have opposite functions for the PcG target genes, and may play significant roles in cell migration during development.
Project description:The Polycomb repressive complexes PRC1 and PRC2 are key mediators of heritable gene silencing in multicellular organisms. Here we characterize AEBP2, a known PRC2 cofactor which, in vitro, has been shown to stimulate PRC2 activity. We show that AEBP2 localises specifically to PRC2 target loci, including the inactive X chromosome. Proteomic analysis confirms that AEBP2 associates exclusively with PRC2 complexes. However, analysis of embryos homozygous for a targeted mutation of Aebp2 unexpectedly revealed a Trithorax phenotype, normally linked to antagonism of Polycomb function. Consistent with this we observe elevated levels of PRC2 mediated histone H3K27 methylation at target loci in Aebp2 mutant embryonic stem cells. We further demonstrate that mutant ES cells assemble atypical hybrid PRC2 sub-complexes, potentially accounting for enhancement of Polycomb activity, and suggesting that AEBP2 normally plays a role in defining the mutually exclusive composition of PRC2 sub-complexes. H3K27me3, SUZ12, and AEBP2 ChIP-Seq in wild-type and AEBP2 KO mouse ESCs, biological replicates, pre-cleared chromatin as input, additionally FS2 ChIP-Seq in cells with FS2 tagged AEBP2, HiSeq2000
Project description:The Polycomb repressive complexes PRC1 and PRC2 are key mediators of heritable gene silencing in multicellular organisms. Here we characterize AEBP2, a known PRC2 cofactor which, in vitro, has been shown to stimulate PRC2 activity. We show that AEBP2 localises specifically to PRC2 target loci, including the inactive X chromosome. Proteomic analysis confirms that AEBP2 associates exclusively with PRC2 complexes. However, analysis of embryos homozygous for a targeted mutation of Aebp2 unexpectedly revealed a Trithorax phenotype, normally linked to antagonism of Polycomb function. Consistent with this we observe elevated levels of PRC2 mediated histone H3K27 methylation at target loci in Aebp2 mutant embryonic stem cells. We further demonstrate that mutant ES cells assemble atypical hybrid PRC2 sub-complexes, potentially accounting for enhancement of Polycomb activity, and suggesting that AEBP2 normally plays a role in defining the mutually exclusive composition of PRC2 sub-complexes.
Project description:Polycomb Repressive Complex 2 (PRC2) represses genes through catalyzing H3K27me3, a histone modification essential for maintenance of cellular identity. The complex’s catalytic activity, chromatin localization, and propagation along chromatin are modulated by accessory proteins such as AEBP2, MTF2, JARID2 and PALI, which is specifically required for mouse embryogenesis. AEBP2 exists in distinct isoforms: a short isoform that enhances PRC2 catalytic activity and promotes H3K27me3 spreading, facilitating robust gene repression, and a long isoform whose function has remained unclear. Here, we report that the N-terminal region of the long isoform contains a conserved DE-motif that inhibits PRC2 activity, both EZH2 automethylation and H3K27 methylation. Notably, re-expression of the long isoform in Mtf2/Jarid2/Aebp2 triple-knockout mouse embryonic stem cells failed to restore H3K27me3 and caused defective differentiation, unlike the short isoform. These findings uncover an isoform-specific regulatory mechanism by which AEBP2 controls PRC2 activity and contribute to a broader understanding of PRC2’s dynamic regulation during development
Project description:Loss-of-function mutations in BCOR, subunit of the non-canonical Polycomb Repressive Complex 1.1 (PRC1.1), are frequently observed in acute myeloid leukemia (AML) and associate with adverse risk, but underlying mechanisms driving leukemogenesis remain elusive. Here, we find that BCOR is a bridging factor tethering the catalytic and chromatin-binding moieties of the PRC1.1 complex. Degron-mediated depletion of BCOR or KDM2B induces a rapid but time-dependent transcriptional induction, whereby early-upregulated genes have a distinct epigenetic profile compared to late-upregulated genes that are more heavily decorated with H3K27me3. Combined KDM2B degradation and PRC2 inhibition further amplifies gene induction suggesting distinct yet collaborative control over target genes. Strikingly, both JARID2/AEBP2 and SUZ12 knockout cells, completely devoid of PRC2 functionality, retain PRC1.1-loss induced transcriptional activation, underscoring that PRC1.1 can repress target genes independent of a downstream PRC2.2-canonical PRC1 repressive axis. Finally, combined targeting of PRC1.1 and PRC2 induces differentiation of leukemic cells emphasizing that co-targeting PRC1.1 and PRC2 represents a promising strategy to improve treatment of AML patients
Project description:The Polycomb Repressive Complex 2 (PRC2) is composed of core subunits SUZ12, EED, RBBP4/7 and EZH1/2, which together are responsible for all di- and tri- methylation of lysine 27 on Histone H3 (H3K27me2/3) in higher eukaryotes. While two distinct forms, PRC2.1 (containing one Polycomb-like protein) and PRC2.2 (containing AEBP2 and JARID2) exist, little is known about their differential functions or interplay. Here we report the discovery of a new family of vertebrate specific PRC2.1 associated proteins; ‘PRC2 associated LCOR isoform 1’ (PALI1) and PALI2, encoded by the LCOR and LCORL gene loci, respectively. PALI1 promotes PRC2 methyltransferase activity in vitro and in vivo and is essential for mouse development. We uncover an antagonistic relationship between the PALI-PRC2.1 and AEBP2-PRC2.2 subtypes and establish that both are required for balanced regulation of Polycomb target genes during differentiation. This discovery links the Polycomb epigenetic system with co-repressors and nuclear receptors in the regulation of cellular identity.
Project description:The Polycomb Repressive Complex 2 (PRC2) is composed of core subunits SUZ12, EED, RBBP4/7 and EZH1/2, which together are responsible for all di- and tri- methylation of lysine 27 on Histone H3 (H3K27me2/3) in higher eukaryotes. While two distinct forms, PRC2.1 (containing one Polycomb-like protein) and PRC2.2 (containing AEBP2 and JARID2) exist, little is known about their differential functions or interplay. Here we report the discovery of a new family of vertebrate specific PRC2.1 associated proteins; ‘PRC2 associated LCOR isoform 1’ (PALI1) and PALI2, encoded by the LCOR and LCORL gene loci, respectively. PALI1 promotes PRC2 methyltransferase activity in vitro and in vivo and is essential for mouse development. We uncover an antagonistic relationship between the PALI-PRC2.1 and AEBP2-PRC2.2 subtypes and establish that both are required for balanced regulation of Polycomb target genes during differentiation. This discovery links the Polycomb epigenetic system with co-repressors and nuclear receptors in the regulation of cellular identity.
Project description:The Polycomb group proteins are repressive chromatin modifiers with essential roles in metazoan development, cellular differentiation and cell fate maintenance. How Polycomb proteins access active chromatin in order to confer transcriptional silencing during lineage transitions remains unclear. Here we show that the Polycomb Repressive Complex 2 (PRC2) component PHF19 binds the active chromatin mark H3K36me3 via its tudor domain. PHF19 associates with the H3K36me3 demethylase NO66, and is required to recruit the PRC2 complex and NO66 to stem cells genes during differentiation, leading to PRC2 mediated H3K27 tri-methylation, loss of H3K36me3 and transcriptional silencing. We propose a model whereby PHF19 functions during ES cell differentiation to transiently bind the H3K36me3 mark via its tudor domain, forming essential contact points that allow recruitment of PRC2 and H3K36me3 demethylase activity to active gene loci during their transition to a Polycomb-repressed state. Examination of PHF19 genome-wide binding in mouse embryonic stem cells