RESUMO
Polycomb repressive complexes (PRCs) play a key role in gene repression and are indispensable for proper development. Canonical PRC1 forms condensates in vitro and in cells that are proposed to contribute to the maintenance of repression. However, how chromatin and the various subunits of PRC1 contribute to condensation is largely unexplored. Using a reconstitution approach and single-molecule imaging, we demonstrate that nucleosomal arrays and PRC1 act synergistically, reducing the critical concentration required for condensation by more than 20-fold. We find that the exact combination of PHC and CBX subunits determines condensate initiation, morphology, stability, and dynamics. Particularly, PHC2's polymerization activity influences condensate dynamics by promoting the formation of distinct domains that adhere to each other but do not coalesce. Live-cell imaging confirms CBX's role in condensate initiation and highlights PHC's importance for condensate stability. We propose that PRC1 composition can modulate condensate properties, providing crucial regulatory flexibility across developmental stages.
Assuntos
Proteínas de Ciclo Celular , Cromatina , Nucleossomos , Complexo Repressor Polycomb 1 , Complexo Repressor Polycomb 1/metabolismo , Complexo Repressor Polycomb 1/genética , Cromatina/metabolismo , Cromatina/genética , Humanos , Nucleossomos/metabolismo , Nucleossomos/genética , Animais , Imagem Individual de MoléculaRESUMO
Molecular mechanisms driving clonal aggressiveness in leukemia are not fully understood. We tracked and analyzed two mouse MLL-rearranged leukemic clones independently evolving towards higher aggressiveness. More aggressive subclones lost their growth differential ex vivo but restored it upon secondary transplantation, suggesting molecular memory of aggressiveness. Development of aggressiveness was associated with clone-specific gradual modulation of chromatin states and expression levels across the genome, with a surprising preferential trend of reversing the earlier changes between normal and leukemic progenitors. To focus on the core aggressiveness program, we identified genes with consistent changes of expression and chromatin marks that were maintained in vivo and ex vivo in both clones. Overexpressing selected core genes (Smad1 as aggressiveness driver, Irx5 and Plag1 as suppressors) affected leukemic progenitor growth in the predicted way and had convergent downstream effects on central transcription factors and repressive epigenetic modifiers, suggesting a broader regulatory network of leukemic aggressiveness.
RESUMO
Polycomb repressive complexes (PRC) play a key role in gene repression and are indispensable for proper development. Canonical PRC1 forms condensates in vitro and in cells and the ability of PRC1 to form condensates has been proposed to contribute to maintenance of repression. However, how chromatin and the various subunits of PRC1 contribute to condensation is largely unexplored. Using single-molecule imaging, we demonstrate that nucleosomal arrays and PRC1 act synergistically, reducing the critical concentration required for condensation by more than 20-fold. By reconstituting and imaging PRC1 with various subunit compositions, we find that the exact combination of PHC and CBX subunits determine the initiation, morphology, stability, and dynamics of condensates. In particular, the polymerization activity of PHC2 strongly influences condensate dynamics to promote formation of structures with distinct domains that adhere to each other but do not coalesce. Using live cell imaging, we confirmed that CBX properties are critical for condensate initiation and that PHC polymerization is important to maintain stable condensates. Together, we propose that PRC1 can fine-tune the degree and type of condensation by altering its composition which might offer important flexibility of regulatory function during different stages of development.
RESUMO
Polycomb group (PcG) proteins maintain the repressed state of lineage-inappropriate genes and are therefore essential for embryonic development and adult tissue homeostasis. One critical function of PcG complexes is modulating chromatin structure. Canonical Polycomb repressive complex 1 (cPRC1), particularly its component CBX2, can compact chromatin and phase-separate in vitro. These activities are hypothesized to be critical for forming a repressed physical environment in cells. While much has been learned by studying these PcG activities in cell culture models, it is largely unexplored how cPRC1 regulates adult stem cells and their subsequent differentiation in living animals. Here, we show in vivo evidence of a critical nonenzymatic repressive function of cPRC1 component CBX2 in the male germline. CBX2 is up-regulated as spermatogonial stem cells differentiate and is required to repress genes that were active in stem cells. CBX2 forms condensates (similar to previously described Polycomb bodies) that colocalize with target genes bound by CBX2 in differentiating spermatogonia. Single-cell analyses of mosaic Cbx2 mutant testes show that CBX2 is specifically required to produce differentiating A1 spermatogonia. Furthermore, the region of CBX2 responsible for compaction and phase separation is needed for the long-term maintenance of male germ cells in the animal. These results emphasize that the regulation of chromatin structure by CBX2 at a specific stage of spermatogenesis is critical, which distinguishes this from a mechanism that is reliant on histone modification.
Assuntos
Núcleo Celular , Cromatina , Animais , Masculino , Cromatina/metabolismo , Núcleo Celular/metabolismo , Complexo Repressor Polycomb 1/genética , Complexo Repressor Polycomb 1/metabolismo , Proteínas do Grupo Polycomb/genética , Proteínas do Grupo Polycomb/metabolismo , Espermatogênese/genéticaRESUMO
Prostaglandin E2 (PGE2) and 16,16-dimethyl-PGE2 (dmPGE2) are important regulators of hematopoietic stem and progenitor cell (HSPC) fate and offer potential to enhance stem cell therapies [C. Cutler et al. Blood 122, 3074-3081(2013); W. Goessling et al. Cell Stem Cell 8, 445-458 (2011); W. Goessling et al. Cell 136, 1136-1147 (2009)]. Here, we report that PGE2-induced changes in chromatin at enhancer regions through histone-variant H2A.Z permit acute inflammatory gene induction to promote HSPC fate. We found that dmPGE2-inducible enhancers retain MNase-accessible, H2A.Z-variant nucleosomes permissive of CREB transcription factor (TF) binding. CREB binding to enhancer nucleosomes following dmPGE2 stimulation is concomitant with deposition of histone acetyltransferases p300 and Tip60 on chromatin. Subsequent H2A.Z acetylation improves chromatin accessibility at stimuli-responsive enhancers. Our findings support a model where histone-variant nucleosomes retained within inducible enhancers facilitate TF binding. Histone-variant acetylation by TF-associated nucleosome remodelers creates the accessible nucleosome landscape required for immediate enhancer activation and gene induction. Our work provides a mechanism through which inflammatory mediators, such as dmPGE2, lead to acute transcriptional changes and modify HSPC behavior to improve stem cell transplantation.
Assuntos
Histonas , Nucleossomos , Histonas/metabolismo , Cromatina , Dinoprostona , Sequências Reguladoras de Ácido Nucleico , Montagem e Desmontagem da CromatinaRESUMO
Chromatin attains its three-dimensional (3D) conformation by establishing contacts between different noncontiguous regions. Sterile Alpha Motif (SAM)-mediated polymerization of the polyhomeotic (PH) protein regulates subnuclear clustering of Polycomb Repressive Complex 1 (PRC1) and chromatin topology. The mutations that perturb the ability of the PH to polymerize, disrupt long-range chromatin contacts, alter Hox gene expression, and lead to developmental defects. To understand the underlying mechanism, we combined the experiments and theory to investigate the effect of this SAM domain mutation on nucleosome occupancy and accessibility on a genome wide scale. Our data show that disruption of PH polymerization because of SAM domain mutation decreases nucleosome occupancy and alters accessibility. Polymer simulations investigating the interplay between distant chromatin contacts and nucleosome occupancy, both of which are regulated by PH polymerization, suggest that nucleosome density increases when contacts between different regions of chromatin are established. Taken together, it appears that SAM domain-mediated PH polymerization biomechanically regulates the organization of chromatin at multiple scales from nucleosomes to chromosomes and we suggest that higher order organization can have a top-down causation effect on nucleosome occupancy.
Assuntos
Proteínas de Drosophila , Nucleossomos , Nucleossomos/genética , Polimerização , Cromatina/genética , Mutação/genética , Núcleo CelularRESUMO
Polycomb group (PcG) proteins are crucial chromatin regulators that maintain repression of lineage-inappropriate genes and are therefore required for stable cell fate. Recent advances show that PcG proteins form distinct multi-protein complexes in various cellular environments, such as in early development, adult tissue maintenance and cancer. This surprising compositional diversity provides the basis for mechanistic diversity. Understanding this complexity deepens and refines the principles of PcG complex recruitment, target-gene repression and inheritance of memory. We review how the core molecular mechanism of Polycomb complexes operates in diverse developmental settings and propose that context-dependent changes in composition and mechanism are essential for proper epigenetic regulation in development.
Assuntos
Proteínas de Drosophila , Epigênese Genética , Diferenciação Celular/genética , Cromatina/genética , Proteínas de Drosophila/genética , Proteínas do Grupo Polycomb/genética , Proteínas do Grupo Polycomb/metabolismoRESUMO
Genetically encoded biosensors are powerful tools to monitor cellular behavior, but the difficulty in generating appropriate reporters for chromatin factors hampers our ability to dissect epigenetic pathways. Here, we present TRACE (transgene reporters across chromatin environments), a high-throughput, genome-wide technique to generate fluorescent human reporter cell lines responsive to manipulation of epigenetic factors. By profiling GFP expression from a large pool of individually barcoded lentiviral integrants in the presence and absence of a perturbation, we identify reporters responsive to pharmacological inhibition of the histone lysine demethylase LSD1 and genetic ablation of the PRC2 subunit SUZ12. Furthermore, by manipulating the HIV-1 host factor LEDGF through targeted deletion or fusion to chromatin reader domains, we alter lentiviral integration site preferences, thus broadening the types of chromatin examined by TRACE. The phenotypic reporters generated through TRACE will allow the genetic interrogation of a broad range of epigenetic pathways, furthering our mechanistic understanding of chromatin biology.
Assuntos
Técnicas Biossensoriais , Epigênese Genética , Genes Reporter , Vetores Genéticos , Proteínas de Fluorescência Verde/genética , Lentivirus/genética , Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Montagem e Desmontagem da Cromatina , Epigenoma , Proteínas de Fluorescência Verde/metabolismo , Células HEK293 , Células HeLa , Histona Desmetilases/genética , Histona Desmetilases/metabolismo , Humanos , Lentivirus/metabolismo , Proteínas de Neoplasias/genética , Proteínas de Neoplasias/metabolismo , Células THP-1 , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismoRESUMO
Chd7 encodes an ATP-dependent chromatin remodeler which has been shown to target specific genomic loci and alter local transcription potentially by remodeling chromatin structure. De novo mutations in CHD7 are the major cause of CHARGE syndrome which features multiple developmental defects. We examined whether nuclear RNAs might contribute to its targeting and function and identified a preferential interaction between CHD7 and lncRNAs derived from HERVH loci in pluripotent stem cells. Knockdown of HERVH family lncRNAs using LNAs or knockout of an individual copy of HERVH by CRISPR-Cas9 both resulted in increased binding of CHD7 and increased levels of H3K27ac at a subset of enhancers. Depletion of HERVH family RNAs led to the activation of multiple genes. CHD7 bound HERVH RNA with high affinity but low specificity and this interaction decreased the ability of CHD7 to bind and remodel nucleosomes. We present a model in which HERVH lncRNAs act as a decoy to modulate the dynamics of CHD7 binding to enhancers in pluripotent cells and the activation of numerous genes that might impact the differentiation process.
Assuntos
Montagem e Desmontagem da Cromatina , DNA Helicases/metabolismo , Proteínas de Ligação a DNA/metabolismo , Retrovirus Endógenos/genética , Regulação da Expressão Gênica , RNA Longo não Codificante , RNA Viral , Alelos , DNA Helicases/genética , Proteínas de Ligação a DNA/genética , Elementos Facilitadores Genéticos , Edição de Genes , Técnicas de Silenciamento de Genes , Histonas/metabolismo , Humanos , Modelos Biológicos , Mutação , Proteínas de Ligação a RNA/metabolismoRESUMO
As pluripotent human embryonic stem cells progress toward one germ layer fate, they lose the ability to adopt alternative fates. Using a low-dimensional reaction coordinate to monitor progression toward ectoderm, we show that a differentiating stem cell's probability of adopting a mesendodermal fate given appropriate signals falls sharply at a point along the ectoderm trajectory. We use this reaction coordinate to prospectively isolate and profile differentiating cells based on their mesendoderm competence and analyze their RNA sequencing (RNA-seq) and assay for transposase-accessible chromatin using sequencing (ATAC-seq) profiles to identify transcription factors that control the cell's mesendoderm competence. By modulating these key transcription factors, we can expand or contract the window of competence to adopt the mesendodermal fate along the ectodermal differentiation trajectory. The ability of the underlying gene regulatory network to modulate competence is essential for understanding human development and controlling the fate choices of stem cells in vitro.
Assuntos
Linhagem da Célula , Regulação da Expressão Gênica no Desenvolvimento , Camadas Germinativas/citologia , Células-Tronco Embrionárias Humanas/citologia , Mesoderma/citologia , Fator 3 de Transcrição de Octâmero/metabolismo , Fatores de Transcrição SOXB1/metabolismo , Diferenciação Celular , Perfilação da Expressão Gênica , Redes Reguladoras de Genes , Camadas Germinativas/metabolismo , Células-Tronco Embrionárias Humanas/metabolismo , Humanos , Mesoderma/metabolismo , Fator 3 de Transcrição de Octâmero/genética , RNA-Seq , Fatores de Transcrição SOXB1/genéticaRESUMO
The CBX family of proteins is central to proper mammalian development via key roles in Polycomb-mediated maintenance of repression. CBX proteins in differentiated lineages have chromatin compaction and phase separation activities that might contribute to maintaining repressed chromatin. The predominant CBX protein in pluripotent cells, CBX7, lacks the domain required for these activities. We inserted this functional domain into CBX7 in embryonic stem cells (ESCs) to test the hypothesis that it contributes a key epigenetic function. ESCs expressing this chimeric CBX7 were impaired in their ability to properly form embryoid bodies and neural progenitor cells and showed reduced activation of lineage-specific genes across differentiation. Neural progenitors exhibited a corresponding inappropriate maintenance of Polycomb binding at neural-specific loci over the course of differentiation. We propose that a switch in the ability to compact and phase separate is a central aspect of Polycomb group function during the transition from pluripotency to differentiated lineages.
Assuntos
Cromatina/química , Proteínas de Drosophila/metabolismo , Proteínas Associadas aos Microtúbulos/metabolismo , Proteínas do Grupo Polycomb/metabolismo , Animais , Diferenciação Celular , Linhagem da Célula , Drosophila/metabolismo , Corpos Embrioides , Células-Tronco Embrionárias/citologia , Epigênese Genética , Perfilação da Expressão Gênica , Genômica , Células HeLa , Humanos , Espectrometria de Massas , Camundongos , Microscopia Eletrônica , Neurônios/metabolismo , Peptídeos/química , Fenótipo , Células-Tronco Pluripotentes/citologia , Complexo Repressor Polycomb 1/metabolismo , Ligação Proteica , Domínios Proteicos , Proteínas Recombinantes de Fusão/química , Células-Tronco/citologiaRESUMO
Polycomb repressive complex 2 (PRC2) catalyzes methylation of histone H3 on lysine 27 and is required for normal development of complex eukaryotes. The nature of that requirement is not clear. H3K27me3 is associated with repressed genes, but the modification is not sufficient to induce repression and, in some instances, is not required. We blocked full methylation of H3K27 with both a small molecule inhibitor, GSK343, and by introducing a point mutation into EZH2, the catalytic subunit of PRC2, in the mouse CJ7 cell line. Cells with substantively decreased H3K27 methylation differentiate into embryoid bodies, which contrasts with EZH2 null cells. PRC2 targets had varied requirements for H3K27me3, with a subset that maintained normal levels of repression in the absence of methylation. The primary cellular phenotype of blocked H3K27 methylation was an inability of altered cells to maintain a differentiated state when challenged. This phenotype was determined by H3K27 methylation in embryonic stem cells through the first 4 days of differentiation. Full H3K27 methylation therefore was not necessary for formation of differentiated cell states during embryoid body formation but was required to maintain a stable differentiated state.
Assuntos
Diferenciação Celular/fisiologia , Corpos Embrioides/metabolismo , Histonas/metabolismo , Complexo Repressor Polycomb 2/metabolismo , Processamento de Proteína Pós-Traducional , Animais , Linhagem Celular , Células-Tronco Embrionárias/metabolismo , Proteína Potenciadora do Homólogo 2 de Zeste/genética , Indazóis/farmacologia , Lisina , Metilação/efeitos dos fármacos , Camundongos , Fenótipo , Complexo Repressor Polycomb 2/genética , Piridonas/farmacologia , TranscriptomaRESUMO
Elongin A (EloA) is an essential transcription factor that stimulates the rate of RNA polymerase II (Pol II) transcription elongation in vitro. However, its role as a transcription factor in vivo has remained underexplored. Here we show that in mouse embryonic stem cells, EloA localizes to both thousands of Pol II transcribed genes with preference for transcription start site and promoter regions and a large number of active enhancers across the genome. EloA deletion results in accumulation of transcripts from a subset of enhancers and their adjacent genes. Notably, EloA does not substantially enhance the elongation rate of Pol II in vivo. We also show that EloA localizes to the nucleoli and associates with RNA polymerase I transcribed ribosomal RNA gene, Rn45s. EloA is a highly disordered protein, which we demonstrate forms phase-separated condensates in vitro, and truncation mutations in the intrinsically disordered regions (IDR) of EloA interfere with its targeting and localization to the nucleoli. We conclude that EloA broadly associates with transcribed regions, tunes RNA Pol II transcription levels via impacts on enhancer RNA synthesis, and interacts with the rRNA producing/processing machinery in the nucleolus. Our work opens new avenues for further investigation of the role of this functionally multifaceted transcription factor in enhancer and ribosomal RNA biology.
Assuntos
Elonguina/metabolismo , Elementos Facilitadores Genéticos , Células-Tronco Embrionárias Murinas/metabolismo , RNA/genética , Ativação Transcricional , Animais , Linhagem Celular , Elonguina/genética , Deleção de Genes , Camundongos , RNA Polimerase II/genética , RNA Polimerase II/metabolismo , Sítio de Iniciação de TranscriçãoRESUMO
Elongin is an RNA polymerase II (RNAPII)-associated factor that has been shown to stimulate transcriptional elongation in vitro. The Elongin complex is thought to be required for transcriptional induction in response to cellular stimuli and to ubiquitinate RNAPII in response to DNA damage. Yet, the impact of the Elongin complex on transcription in vivo has not been well studied. Here, we performed comprehensive studies of the role of Elongin A, the largest subunit of the Elongin complex, on RNAPII transcription genome-wide. Our results suggest that Elongin A localizes to actively transcribed regions and potential enhancers, and the level of recruitment correlated with transcription levels. We also identified a large group of factors involved in transcription as Elongin A-associated factors. In addition, we found that loss of Elongin A leads to dramatically reduced levels of serine2-phosphorylated, but not total, RNAPII, and cells depleted of Elongin A show stronger promoter RNAPII pausing, suggesting that Elongin A may be involved in the release of paused RNAPII. Our RNA-seq studies suggest that loss of Elongin A did not alter global transcription, and unlike prior in vitro studies, we did not observe a dramatic impact on RNAPII elongation rates in our cell-based nascent RNA-seq experiments upon Elongin A depletion. Taken together, our studies provide the first comprehensive analysis of the role of Elongin A in regulating transcription in vivo. Our studies also revealed that unlike prior in vitro findings, depletion of Elongin A has little impact on global transcription profiles and transcription elongation in vivo.
Assuntos
Cromatina/metabolismo , Elonguina/genética , RNA Polimerase II/genética , RNA Mensageiro/genética , Elongação da Transcrição Genética , Linhagem Celular Tumoral , Cromatina/química , Biologia Computacional/métodos , Elonguina/antagonistas & inibidores , Elonguina/metabolismo , Elementos Facilitadores Genéticos , Células Epiteliais/citologia , Células Epiteliais/metabolismo , Regulação da Expressão Gênica , Humanos , Fosforilação , RNA Polimerase II/metabolismo , RNA Mensageiro/metabolismo , RNA Interferente Pequeno/genética , RNA Interferente Pequeno/metabolismo , Análise de Sequência de RNA , Serina/metabolismo , Transdução de SinaisRESUMO
Cooperation between DNA, RNA and protein regulates gene expression and controls differentiation through interactions that connect regions of nucleic acids and protein domains and through the assembly of biomolecular condensates. Here, we report that endoderm differentiation is regulated by the interaction between the long non-coding RNA (lncRNA) DIGIT and the bromodomain and extraterminal domain protein BRD3. BRD3 forms phase-separated condensates of which the formation is promoted by DIGIT, occupies enhancers of endoderm transcription factors and is required for endoderm differentiation. BRD3 binds to histone H3 acetylated at lysine 18 (H3K18ac) in vitro and co-occupies the genome with H3K18ac. DIGIT is also enriched in regions of H3K18ac, and the depletion of DIGIT results in decreased recruitment of BRD3 to these regions. Our findings show that cooperation between DIGIT and BRD3 at regions of H3K18ac regulates the transcription factors that drive endoderm differentiation and suggest that protein-lncRNA phase-separated condensates have a broader role as regulators of transcription.
Assuntos
Diferenciação Celular , Endoderma/citologia , Histonas/metabolismo , Células-Tronco Embrionárias Humanas/citologia , Transição de Fase , RNA Longo não Codificante/genética , Fatores de Transcrição/metabolismo , Acetilação , Endoderma/metabolismo , Genoma Humano , Histonas/genética , Células-Tronco Embrionárias Humanas/metabolismo , Humanos , Lisina/genética , Lisina/metabolismo , Domínios Proteicos , Processamento de Proteína Pós-Traducional , Fatores de Transcrição/genéticaRESUMO
MORC2 encodes an ATPase that plays a role in chromatin remodeling, DNA repair, and transcriptional regulation. Heterozygous variants in MORC2 have been reported in individuals with autosomal-dominant Charcot-Marie-Tooth disease type 2Z and spinal muscular atrophy, and the onset of symptoms ranges from infancy to the second decade of life. Here, we present a cohort of 20 individuals referred for exome sequencing who harbor pathogenic variants in the ATPase module of MORC2. Individuals presented with a similar phenotype consisting of developmental delay, intellectual disability, growth retardation, microcephaly, and variable craniofacial dysmorphism. Weakness, hyporeflexia, and electrophysiologic abnormalities suggestive of neuropathy were frequently observed but were not the predominant feature. Five of 18 individuals for whom brain imaging was available had lesions reminiscent of those observed in Leigh syndrome, and five of six individuals who had dilated eye exams had retinal pigmentary abnormalities. Functional assays revealed that these MORC2 variants result in hyperactivation of epigenetic silencing by the HUSH complex, supporting their pathogenicity. The described set of morphological, growth, developmental, and neurological findings and medical concerns expands the spectrum of genetic disorders resulting from pathogenic variants in MORC2.
Assuntos
Adenosina Trifosfatases/genética , Anormalidades Craniofaciais/genética , Transtornos do Crescimento/genética , Mutação/genética , Transtornos do Neurodesenvolvimento/genética , Fatores de Transcrição/genética , Adolescente , Adulto , Criança , Pré-Escolar , Feminino , Doenças Genéticas Inatas/genética , Heterozigoto , Humanos , Lactente , Deficiência Intelectual/genética , Masculino , Microcefalia/genética , Pessoa de Meia-Idade , Fenótipo , Adulto JovemRESUMO
Many proteins that are needed for progression through S-phase are produced from transcripts that peak in the S-phase, linking temporal expression of those proteins to the time that they are required in cell cycle. Here, we explore the potential roles of long non-coding RNAs in cell cycle progression. We use a sensitive click-chemistry approach to isolate nascent RNAs in a human cell line, and we identify more than 900 long non-coding RNAs (lncRNAs) whose synthesis peaks during the S-phase. More than 200 of these are long intergenic non-coding RNAs (lincRNAs) with S-phase-specific expression. We characterize three of these lincRNAs by knockdown and find that all three lincRNAs are required for appropriate S-phase progression. We infer that non-coding RNAs are key regulatory effectors during the cell cycle, acting on distinct regulatory networks, and herein, we provide a large catalog of candidate cell-cycle regulatory RNAs.
Assuntos
Ciclo Celular/genética , Perfilação da Expressão Gênica/métodos , RNA Longo não Codificante/genética , Fase S/genética , HumanosRESUMO
For mammals to develop properly, master regulatory genes must be repressed appropriately in a heritable manner. This review concerns the Polycomb Repressive Complex 1 (PRC1) family and the relationship between the establishment of repression and memory of the repressed state. The primary focus is on the CBX family of proteins in PRC1 complexes and their role in both chromatin compaction and phase separation. These two activities are linked and might contribute to both repression and memory.
Assuntos
Cromatina/genética , Proteínas Cromossômicas não Histona/genética , Epigênese Genética/genética , Complexo Repressor Polycomb 1/genética , Núcleo Celular/genética , Regulação da Expressão Gênica/genética , Humanos , Nucleossomos/genéticaRESUMO
During central nervous system development, spatiotemporal gene expression programs mediate specific lineage decisions to generate neuronal and glial cell types from neural stem cells (NSCs). However, little is known about the epigenetic landscape underlying these highly complex developmental events. Here, we perform ChIP-seq on distinct subtypes of Drosophila FACS-purified NSCs and their differentiated progeny to dissect the epigenetic changes accompanying the major lineage decisions in vivo By analyzing active and repressive histone modifications, we show that stem cell identity genes are silenced during differentiation by loss of their activating marks and not via repressive histone modifications. Our analysis also uncovers a new set of genes specifically required for altering lineage patterns in type II neuroblasts (NBs), one of the two main Drosophila NSC identities. Finally, we demonstrate that this subtype specification in NBs, unlike NSC differentiation, requires Polycomb-group-mediated repression.
Assuntos
Neoplasias Encefálicas/metabolismo , Proteínas de Drosophila/metabolismo , Histonas/metabolismo , Proteínas de Neoplasias/metabolismo , Células-Tronco Neoplásicas/metabolismo , Células-Tronco Neurais/metabolismo , Processamento de Proteína Pós-Traducional , Animais , Neoplasias Encefálicas/patologia , Drosophila melanogaster , Células-Tronco Neoplásicas/patologia , Células-Tronco Neurais/patologiaRESUMO
Mammalian development requires effective mechanisms to repress genes whose expression would generate inappropriately specified cells. The Polycomb-repressive complex 1 (PRC1) family complexes are central to maintaining this repression. These include a set of canonical PRC1 complexes, each of which contains four core proteins, including one from the CBX family. These complexes have been shown previously to reside in membraneless organelles called Polycomb bodies, leading to speculation that canonical PRC1 might be found in a separate phase from the rest of the nucleus. We show here that reconstituted PRC1 readily phase-separates into droplets in vitro at low concentrations and physiological salt conditions. This behavior is driven by the CBX2 subunit. Point mutations in an internal domain of Cbx2 eliminate phase separation. These same point mutations eliminate the formation of puncta in cells and have been shown previously to eliminate nucleosome compaction in vitro and generate axial patterning defects in mice. Thus, the domain of CBX2 that is important for phase separation is the same domain shown previously to be important for chromatin compaction and proper development, raising the possibility of a mechanistic or evolutionary link between these activities.