Project description:While the core members of the Polycomb family of proteins (PRC2, PRC1, PR-DUB) are well-characterized, little is known about the specific composition of and protein-protein interactions within these complexes in different cell types. We performed quantitative interaction proteomics and cross-linking mass spectrometry on core Polycomb complex members to identify novel interactors, the relative abundance (stoichiometry) of subunits, and the architecture of these complexes in mouse embryonic stem cells (mESCs) and neural progenitor cells (NPCs). Differentiation to NPCs resulted in dramatic binding changes for several substoichiometric interactors of PRC2 and PRC1. ChIP-seq of core PRC2 and PRC1 subunits in mESCs and NPCs also identified dynamic changes in the genomic localization of these complexes. We observed a loss of PRC2 from most H3K27me3 sites during differentiation, whereas PRC1 is retained at these sites. Additionally, we found PRC1 at enhancers and promoters of active genes independent of PRC2 binding. Overexpression studies using NPC-specific PRC1 interactors demonstrated that the subunit switching observed during differentiation can change PRC1 target site binding. Altogether, these findings extend our understanding of Polycomb family composition, architecture, and genome-wide localization. ChIP-seq samples for Suz12, Ezh2, Ring1b, Pcgf2, and inputs from mouse embryonic stems cells (mES) and neural progenitor cells (NPC) as well as NPC histone H3K4me1 ChIP-seq.
Project description:Polycomb Repressive Complex 2 (PRC2) plays crucial roles in transcriptional regulation and stem cell development. However, the context-specific functions associated with alternative subunits remain largely unexplored. Here we show that the related enzymatic subunits EZH1 and EZH2 undergo an expression switch during hematopoiesis. We examine the in vivo stoichiometry of the PRC2 complexes by quantitative proteomics and reveal the existence of an EZH1-SUZ12 sub-complex lacking EED. We provide evidence that EZH1 together with SUZ12 form a non-canonical PRC2 complex, occupy active chromatin domains in the absence of H3K27me3, and positively regulate gene expression. Loss of EZH2 expression leads to global repositioning of EZH1 chromatin occupancy to EZH2 targets. Moreover, we demonstrate that an erythroid-specific enhancer mediates transcriptional activation of EZH1, and a switch from GATA2 to GATA1 controls the developmental EZH1/2 switch by differential association with EZH1 enhancers during erythropoiesis. Thus, the lineage- and developmental stage-specific regulation of PRC2 expression and subunit composition leads to a switch from canonical silencing to non-canonical PRC2 functions during blood stem cell specification. Analysis of genomic occupancy of EZH1, EZH2, EED, SUZ12, various histone marks and transcription factors in primary human fetal liver proerythroblasts by ChIP-seq. Sample GSM970262 was used as the input DNA sample.
Project description:While the core subunits of Polycomb group (PcG) complexes are well characterized, little is known about the dynamics of these protein complexes during cellular differentiation. We used quantitative interaction proteomics to study PcG proteins in mouse embryonic stem cells (mESCs) and neural progenitor cells (NPCs). We found the stoichiometry of PRC1 and PRC2 to be highly dynamic during neural differentiation.
Project description:While the core members of the Polycomb family of proteins (PRC2, PRC1, PR-DUB) are well-characterized, little is known about the specific composition of and protein-protein interactions within these complexes in different cell types. We performed quantitative interaction proteomics and cross-linking mass spectrometry on core Polycomb complex members to identify novel interactors, the relative abundance (stoichiometry) of subunits, and the architecture of these complexes in mouse embryonic stem cells (mESCs) and neural progenitor cells (NPCs). Differentiation to NPCs resulted in dramatic binding changes for several substoichiometric interactors of PRC2 and PRC1. ChIP-seq of core PRC2 and PRC1 subunits in mESCs and NPCs also identified dynamic changes in the genomic localization of these complexes. We observed a loss of PRC2 from most H3K27me3 sites during differentiation, whereas PRC1 is retained at these sites. Additionally, we found PRC1 at enhancers and promoters of active genes independent of PRC2 binding. Overexpression studies using NPC-specific PRC1 interactors demonstrated that the subunit switching observed during differentiation can change PRC1 target site binding. Altogether, these findings extend our understanding of Polycomb family composition, architecture, and genome-wide localization.
Project description:Polycomb Repressive Complex 2 (PRC2) plays crucial roles in transcriptional regulation and stem cell development. However, the context-specific functions associated with alternative subunits remain largely unexplored. Here we show that the related enzymatic subunits EZH1 and EZH2 undergo an expression switch during hematopoiesis. We examine the in vivo stoichiometry of the PRC2 complexes by quantitative proteomics and reveal the existence of an EZH1-SUZ12 sub-complex lacking EED. We provide evidence that EZH1 together with SUZ12 form a non-canonical PRC2 complex, occupy active chromatin domains in the absence of H3K27me3, and positively regulate gene expression. Loss of EZH2 expression leads to global repositioning of EZH1 chromatin occupancy to EZH2 targets. Moreover, we demonstrate that an erythroid-specific enhancer mediates transcriptional activation of EZH1, and a switch from GATA2 to GATA1 controls the developmental EZH1/2 switch by differential association with EZH1 enhancers during erythropoiesis. Thus, the lineage- and developmental stage-specific regulation of PRC2 expression and subunit composition leads to a switch from canonical silencing to non-canonical PRC2 functions during blood stem cell specification. Transcriptional profiling in primary human fetal liver proerythroblasts upon lentiviral shRNA-mediated knockdown of EZH1, EZH2, EED, or SUZ12 by RNA-seq analysis.