Explore the vast range of titles available.

Polycomb repressive complex 2 (PRC2) mediates gene silencing through chromatin reorganization by methylation of histone H3 lysine 27 (H3K27). Overexpression of the complex and point mutations in the individual subunits of PRC2 have been shown to contribute to tumorigenesis. Several inhibitors of the PRC2 activity have shown efficacy in EZH2-mutated lymphomas and are currently in clinical development, although the molecular basis of inhibitor recognition remains unknown. Here we report the crystal structures of the inhibitor-bound wild-type and Y641N PRC2. The structures illuminate an important role played by a stretch of 17 residues in the N-terminal region of EZH2, we call the activation loop, in the stimulation of the enzyme activity, inhibitor recognition and the potential development of the mutation-mediated drug resistance. The work presented here provides new avenues for the design and development of next-generation PRC2 inhibitors through establishment of a structure-based drug design platform. Polycomb repressive complex 2 (PRC2) mediates gene silencing through chromatin reorganization by methylation of histone H3 lysine 27 (H3K27). Here, the authors present crystal structures of the inhibitor-bound wild-type and a mutant form of PRC2.

The production of haematopoietic stem cells is repressed during early mammalian embryogenesis by an epigenetic mechanism that involves the action of the Polycomb protein EZH1. EZH1 controls multipotency of blood stem cells The first blood-cell progenitors that arise in mammalian embryos are lineage-restricted. Multipotent haematopoietic stem cells, which can differentiate into any type of blood cell, emerge only later during gestation. George Daley and colleagues show that this second-stage haematopoietic program, which is at the origin of all adult blood cells, is repressed during early embryogenesis through an epigenetic mechanism involving the action of the polycomb protein EZH1. Reducing EZH1 expression in human pluripotent stem cells in vitro unleashes their capacity to develop into multiple lymphoid lineages. In mouse embryos, reduced EZH1 expression promotes the precocious emergence of definitive haematopoietic stem cells. All haematopoietic cell lineages that circulate in the blood of adult mammals derive from multipotent haematopoietic stem cells (HSCs) 1 . By contrast, in the blood of mammalian embryos, lineage-restricted progenitors arise first, independently of HSCs, which only emerge later in gestation 2 , 3 . As best defined in the mouse, ‘primitive’ progenitors first appear in the yolk sac at 7.5 days post-coitum 2 , 3 . Subsequently, erythroid–myeloid progenitors that express fetal haemoglobin 4 , as well as fetal lymphoid progenitors 5 , develop in the yolk sac and the embryo proper, but these cells lack HSC potential. Ultimately, ‘definitive’ HSCs with long-term, multilineage potential and the ability to engraft irradiated adults emerge at 10.5 days post-coitum from arterial endothelium in the aorta-gonad-mesonephros and other haemogenic vasculature 3 . The molecular mechanisms of this reverse progression of haematopoietic ontogeny remain unexplained. We hypothesized that the definitive haematopoietic program might be actively repressed in early embryogenesis through epigenetic silencing 6 , and that alleviating this repression would elicit multipotency in otherwise lineage-restricted haematopoietic progenitors. Here we show that reduced expression of the Polycomb group protein EZH1 enhances multi-lymphoid output from human pluripotent stem cells. In addition, Ezh1 deficiency in mouse embryos results in precocious emergence of functional definitive HSCs in vivo . Thus, we identify EZH1 as a repressor of haematopoietic multipotency in the early mammalian embryo.

The enhancer-of-zeste homolog 2 (EZH2) gene product is an 87 kDa polycomb group (PcG) protein containing a C-terminal methyltransferase SET domain. EZH2, along with binding partners, i.e., EED and SUZ12, upon which it is dependent for activity forms the core of the polycomb repressive complex 2 (PRC2). PRC2 regulates gene silencing by catalyzing the methylation of histone H3 at lysine 27. Both overexpression and mutation of EZH2 are associated with the incidence and aggressiveness of various cancers. The novel crystal structure of the SET domain was determined in order to understand disease-associated EZH2 mutations and derive an explanation for its inactivity independent of complex formation. The 2.00 Å crystal structure reveals that, in its uncomplexed form, the EZH2 C-terminus folds back into the active site blocking engagement with substrate. Furthermore, the S-adenosyl-L-methionine (SAM) binding pocket observed in the crystal structure of homologous SET domains is notably absent. This suggests that a conformational change in the EZH2 SET domain, dependent upon complex formation, must take place for cofactor and substrate binding activities to be recapitulated. In addition, the data provide a structural context for clinically significant mutations found in the EZH2 SET domain.

Small cell lung cancer (SCLC) is a subtype of lung cancer with poor prognosis. Expression array analysis of 23 SCLC cases and 42 normal tissues revealed that EZH2 and other PRC2 members were highly expressed in SCLC. ChIP-seq for H3K27me3 suggested that genes with H3K27me3(+) in SCLC were extended not only to PRC2-target genes in ES cells but also to other target genes such as cellular adhesion-related genes. These H3K27me3(+) genes in SCLC were repressed significantly and introduction of the most repressed gene JUB into SCLC cell line lead to growth inhibition. Shorter overall survival of clinical SCLC cases correlated to repression of JUB alone, or a set of four genes including H3K27me3(+) genes. Treatment with EZH2 inhibitors, DZNep and GSK126, resulted in growth repression of SCLC cell lines. High PRC2 expression was suggested to contribute to gene repression in SCLC and may play a role in genesis of SCLC.

Parental epigenomes are established during gametogenesis. While they are largely reset after fertilization, broad domains of Polycomb repressive complex 2 (PRC2)-mediated formation of lysine 27–trimethylated histone H3 (H3K27me3) are inherited from oocytes in mice. How maternal H3K27me3 is established and inherited by embryos remains elusive. Here, we show that PRC1-mediated formation of lysine 119–monoubiquititinated histone H2A (H2AK119ub1) confers maternally heritable H3K27me3. Temporal profiling of H2AK119ub1 dynamics revealed that atypically broad H2AK119ub1 domains are established, along with H3K27me3, during oocyte growth. From the two-cell stage, H2AK119ub1 is progressively deposited at typical Polycomb targets and precedes H3K27me3. Reduction of H2AK119ub1 by depletion of Polycomb group ring finger 1 (PCGF1) and PCGF6—essential components of variant PRC1 (vPRC1)—leads to H3K27me3 loss at a subset of genes in oocytes. The gene-selective H3K27me3 deficiency is irreversibly inherited by embryos, causing loss of maternal H3K27me3-dependent imprinting, embryonic sublethality and placental enlargement at term. Collectively, our study unveils preceding dynamics of H2AK119ub1 over H3K27me3 at the maternal-to-zygotic transition, and identifies PCGF1/6–vPRC1 as an essential player in maternal epigenetic inheritance. In early mouse embryos, PRC1-mediated H2AK119ub1 deposition precedes H3K27me3. Deficiency in variant PRC1 reduces H2AK119ub1 and leads to gene-selective loss of H3K27me3 in oocytes, which is inherited by embryos.

Objective The Polycomb Repressive Complex 2 (PRC2) regulates neural stem cell behaviour during development of the cerebral cortex, yet how the loss of PRC2 developmentally influences cell identity in the mature brain is poorly defined. Using a mouse model in which the PRC2 gene Embryonic ectoderm development ( Eed) was conditionally deleted from the developing mouse dorsal telencephalon, we performed single nuclei RNA sequencing (snRNA-seq) on the cortical plate of an adult heterozygote Eed knockout mouse and an adult homozygote Eed knockout mouse compared to a littermate control. This work was part of a larger effort to understand consequences of mutations to PRC2 within the mature brain. Results Here we provide snRNA-seq data from the cortical plate of an adult heterozygous conditional Eed knockout, an adult homozygous conditional Eed knockout and an adult control mouse. This data provides insight on how loss of PRC2 function during development affects cell identity in the mature cortex.

Despite prolonged antiretroviral therapy, HIV-1 persists as transcriptionally inactive proviruses. The HIV-1 latency remains a principal obstacle in curing AIDS. It is important to understand mechanisms by which HIV-1 latency is established to make the latent reservoir smaller. We present a molecular characterization of distinct populations at an early phase of infection. We developed an original dual-color reporter virus to monitor LTR kinetics from establishment to maintenance stage. We found that there are two ways of latency establishment i.e., by immediate silencing and slow inactivation from active infection. Histone covalent modifications, particularly polycomb repressive complex 2 (PRC2)-mediated H3K27 trimethylation, appeared to dominate viral transcription at the early phase. PRC2 also contributes to time-dependent LTR dormancy in the chronic phase of the infection. Significant differences in sensitivity against several stimuli were observed between these two distinct populations. These results will expand our understanding of heterogeneous establishment of HIV-1 latency populations.

In female mammals, one of the two X chromosomes becomes inactivated during development by X-chromosome inactivation (XCI). Although Polycomb repressive complex (PRC) 1 and PRC2 have both been implicated in gene silencing, their exact roles in XCI during in vivo development have remained elusive. To this end, we have studied mouse embryos lacking either PRC1 or PRC2. Here we demonstrate that the loss of either PRC has a substantial impact on maintenance of gene silencing on the inactive X chromosome (Xi) in extra-embryonic tissues, with overlapping yet different genes affected, indicating potentially independent roles of the two complexes. Importantly, a lack of PRC1 does not affect PRC2/H3K27me3 accumulation and a lack of PRC2 does not impact PRC1/H2AK119ub1 accumulation on the Xi. Thus PRC1 and PRC2 contribute independently to the maintenance of XCI in early post-implantation extra-embryonic lineages, revealing that both Polycomb complexes can be directly involved and differently deployed in XCI. Polycomb repressive complexes 1 and 2 both regulate maintenance of X inactivation in extra-embryonic lineages of post-implantation embryos by affecting overlapping yet different genes, thus implying potentially independent roles for the two complexes.

Polycomb repressive complex 2 (PRC2) silences gene expression through trimethylation of K27 of histone H3 (H3K27me3) via its catalytic SET domain. A missense mutation in the substrate of PRC2, histone H3K27M, is associated with certain pediatric brain cancers and is linked to a global decrease of H3K27me3 in the affected cells thought to be mediated by inhibition of PRC2 activity. We present here the crystal structure of human PRC2 in complex with the inhibitory H3K27M peptide bound to the active site of the SET domain, with the methionine residue located in the pocket that normally accommodates the target lysine residue. The structure and binding studies suggest a mechanism for the oncogenic inhibition of H3K27M. The structure also reveals how binding of repressive marks, like H3K27me3, to the EED subunit of the complex leads to enhancement of the catalytic efficiency of the SET domain and thus the propagation of this repressive histone modification. Polycomb repressive complex 2 (PRC2) silences gene expression through trimethylation of K27 of histone H3 (H3K27Me). Here, the authors report the structure of the human PRC2 complex bound to the oncogenic H3K27M mutant, and suggest a mechanism for its potency in childhood brain cancers.

The formation of specialized cell types during development involves the silencing of genes not required in those cell types. An important player in this silencing process is the polycomb repressive complex 2 (PRC2), which methylates histone H3 on lysine residue 27 (H3K27me). Jiao and Liu determined the x-ray crystal structure of a functional PRC2 complex from a thermophilic yeast species (see the Perspective by Schapira). The intimate association of the three subunits confers stability to PRC2. The structure also reveals how the reaction product, H3K27me, stimulates PRC2 allosterically and how a cancer-associated histone mutation blocks the PRC2 active site. Science , this issue p. 10.1126/science.aac4383 ; see also p. 278 The structure of a gene silencing complex reveals how it self-activates and is inhibited by a cancer-associated chromatin mutation. [Also see Perspective by Schapira ] Polycomb repressive complex 2 (PRC2) catalyzes histone H3K27 trimethylation (H3K27me3), a hallmark of gene silencing. Here we report the crystal structures of an active PRC2 complex of 170 kilodaltons from the yeast Chaetomium thermophilum in both basal and stimulated states, which contain Ezh2, Eed, and the VEFS domain of Suz12 and are bound to a cancer-associated inhibiting H3K27M peptide and a S-adenosyl- l -homocysteine cofactor. The stimulated complex also contains an additional stimulating H3K27me3 peptide. Eed is engulfed by a belt-like structure of Ezh2, and Suz12(VEFS) contacts both of these two subunits to confer an unusual split active SET domain for catalysis. Comparison of PRC2 in the basal and stimulated states reveals a mobile Ezh2 motif that responds to stimulation to allosterically regulate the active site.