scholarly journals Functions of Polycomb Proteins on Active Targets

Epigenomes ◽  
2020 ◽  
Vol 4 (3) ◽  
pp. 17 ◽  
Author(s):  
Natalia Giner-Laguarda ◽  
Miguel Vidal
Keyword(s):  
Gene Expression ◽  
Cell Differentiation ◽  
Histone Modifications ◽  
Polycomb Group ◽  
Transcriptional Repressors ◽  
Regulatory Regions ◽  
Polycomb Proteins ◽  
Chromatin Regulators ◽  
Intergenic Regions ◽  
High Order Chromatin

Chromatin regulators of the Polycomb group of genes are well-known by their activities as transcriptional repressors. Characteristically, their presence at genomic sites occurs with specific histone modifications and sometimes high-order chromatin structures correlated with silencing of genes involved in cell differentiation. However, evidence gathered in recent years, on flies and mammals, shows that in addition to these sites, Polycomb products bind to a large number of active regulatory regions. Occupied sites include promoters and also intergenic regions, containing enhancers and super-enhancers. Contrasting with occupancies at repressed targets, characteristic histone modifications are low or undetectable. Functions on active targets are dual, restraining gene expression at some targets while promoting activity at others. Our aim here is to summarize the evidence available and discuss the convenience of broadening the scope of research to include Polycomb functions on active targets.

Polycomb group protein-mediated histone modifications during cell differentiation

Epigenomics ◽  
2015 ◽  
Vol 7 (1) ◽  
pp. 75-84 ◽  
Author(s):  
Abdul Aziz Khan ◽  
Andrew Jeoungun Lee ◽  
Tae-Young Roh
Keyword(s):  
Cell Differentiation ◽  
Histone Modifications ◽  
Polycomb Group ◽  
Polycomb Group Protein ◽  
Group Protein

scholarly journals BAP1 constrains pervasive H2AK119ub1 to control the transcriptional potential of the genome

2020 ◽  
Author(s):  
Nadezda A. Fursova ◽  
Anne H. Turberfield ◽  
Neil P. Blackledge ◽  
Emma L. Findlater ◽  
Anna Lastuvkova ◽  
...  
Keyword(s):  
Gene Expression ◽  
Histone Modifications ◽  
Transcription Initiation ◽  
Target Genes ◽  
Regulatory Elements ◽  
Polycomb Group ◽  
Gene Promoters ◽  
Histone H2a ◽  
Gene Regulatory Elements ◽  
Gene Regulatory

AbstractHistone-modifying systems play fundamental roles in gene regulation and the development of multicellular organisms. Histone modifications that are enriched at gene regulatory elements have been heavily studied, but the function of modifications that are found more broadly throughout the genome remains poorly understood. This is exemplified by histone H2A mono-ubiquitylation (H2AK119ub1) which is enriched at Polycomb-repressed gene promoters, but also covers the genome at lower levels. Here, using inducible genetic perturbations and quantitative genomics, we discover that the BAP1 deubiquitylase plays an essential role in constraining H2AK119ub1 throughout the genome. Removal of BAP1 leads to pervasive accumulation of H2AK119ub1, which causes widespread reductions in gene expression. We show that elevated H2AK119ub1 represses gene expression by counteracting transcription initiation from gene regulatory elements, causing reductions in transcription-associated histone modifications. Furthermore, failure to constrain pervasive H2AK119ub1 compromises Polycomb complex occupancy at a subset of Polycomb target genes leading to their derepression, therefore explaining the original genetic characterisation of BAP1 as a Polycomb group gene. Together, these observations reveal that the transcriptional potential of the genome can be modulated by regulating the levels of a pervasive histone modification, without the need for elaborate gene-specific targeting mechanisms.

scholarly journals Genome-wide Profiling of Histone Lysine Butyrylation Reveals its Role in the Positive Regulation of Gene Transcription in Rice

Rice ◽  
2019 ◽  
Vol 12 (1) ◽  
Author(s):  
Shuai Liu ◽  
Guanqing Liu ◽  
Peifeng Cheng ◽  
Chao Xue ◽  
Yong Zhou ◽  
...  
Keyword(s):  
Gene Expression ◽  
Histone Modifications ◽  
Rice Genome ◽  
Enrichment Analysis ◽  
Carbon Chain ◽  
Main Body ◽  
Rice Varieties ◽  
Genome Wide ◽  
Chromatin Immunoprecipitation Sequencing ◽  
Intergenic Regions

Abstract Background Histone modifications play important roles in growth and development of rice (Oryza sativa L.). Lysine butyrylation (Kbu) with a four-carbon chain is a newly-discovered histone acylation modification in rice. Main Body In this study, we performed chromatin immunoprecipitation sequencing (ChIP-seq) analyses, the result showed that major enrichment of histone Kbu located in genebody regions of rice genome, especially in exons. The enrichment level of Kbu histone modification is positively correlated with gene expression. Furthermore, we compared Kbu with DNase-seq and other histone modifications in rice. We found that 60.06% Kub enriched region co-located with DHSs in intergenic regions. The similar profiles were detected among Kbu and several acetylation modifications such as H3K4ac, H3K9ac, and H3K23ac, indicating that Kbu modification is an active signal of transcription. Genes with both histone Kbu and one other acetylation also had significantly increased expression compared with genes with only one acetylation. Gene Ontology (GO) enrichment analysis revealed that these genes with histone Kbu can regulate multiple metabolic process in different rice varieties. Conclusion Our study showed that the lysine butyrylation modificaiton may promote gene expression as histone acetylation and will provide resources for futher studies on histone Kbu and other epigenetic modifications in plants.

scholarly journals Circular ANRIL isoforms switch from repressors to activators of p15/CDKN2B expression during RAF1 oncogene-induced senescence

2020 ◽  
Author(s):  
Lisa Muniz ◽  
Sandra Lazorthes ◽  
Maxime Delmas ◽  
Julien Ouvrard ◽  
Marion Aguirrebengoa ◽  
...  
Keyword(s):  
Gene Expression ◽  
Cell Fate ◽  
Protein Localization ◽  
Polycomb Group ◽  
Circular Rnas ◽  
Polycomb Proteins ◽  
Cycle Arrest ◽  
Polycomb Protein ◽  
Stable Species ◽  
Non Coding Rnas

AbstractLong non-coding RNAs (ncRNAs) are major regulators of gene expression and cell fate. The INK4 locus encodes the tumour suppressor proteins p15INK4b, p16INK4a and p14ARF required for cell cycle arrest and whose expression increases during senescence. ANRIL is a ncRNA antisense to the p15 gene. In proliferative cells, ANRIL prevents senescence by repressing INK4 genes through the recruitment of Polycomb-group proteins. In models of replicative and RASval12 oncogene-induced senescence (OIS), the expression of ANRIL and Polycomb proteins decreases, thus allowing INK4 derepression. Here, we found in a model of RAF1 OIS that ANRIL expression rather increases, due in particular to an increased stability. This led us to search for circular ANRIL isoforms, as circular RNAs are rather stable species. We found that the expression of two circular ANRIL increases in several OIS models (RAF1, MEK1 and BRAF). In proliferative cells, they repress p15 expression, while in RAF1 OIS, they promote full induction of p15, p16 and p14ARF expression. Further analysis of one of these circular ANRIL shows that it interacts with Polycomb proteins and decreases EZH2 Polycomb protein localization and H3K27me3 at the p15 and p16 promoters, respectively. We propose that changes in the ratio between Polycomb proteins and circular ANRIL isoforms allow these isoforms to switch from repressors of p15 gene to activators of all INK4 genes in RAF1 OIS. Our data reveal that regulation of ANRIL expression depends on the senescence inducer and underline the importance of circular ANRIL in the regulation of INK4 gene expression and senescence.

scholarly journals Contribution of Polycomb Homologues Bmi-1 and Mel-18 to Medulloblastoma Pathogenesis

2007 ◽  
Vol 27 (13) ◽  
pp. 4968-4979 ◽  
Author(s):  
Dmitri Wiederschain ◽  
Lin Chen ◽  
Brett Johnson ◽  
Kimberly Bettano ◽  
Dowdy Jackson ◽  
...  
Keyword(s):  
Gene Expression ◽  
Cell Growth ◽  
Cancer Cell ◽  
Protein Complexes ◽  
Clonogenic Survival ◽  
Tumor Formation ◽  
Polycomb Group ◽  
Cancer Cell Growth ◽  
Inhibition Of Proliferation ◽  
Polycomb Proteins

ABSTRACT Bmi-1 and Mel-18 are structural homologues that belong to the Polycomb group of transcriptional regulators and are believed to stably maintain repression of gene expression by altering the state of chromatin at specific promoters. While a number of clinical and experimental observations have implicated Bmi-1 in human tumorigenesis, the role of Mel-18 in cancer cell growth has not been investigated. We report here that short hairpin RNA-mediated knockdown of either Bmi-1 or Mel-18 in human medulloblastoma DAOY cells results in the inhibition of proliferation, loss of clonogenic survival, anchorage-independent growth, and suppression of tumor formation in nude mice. Furthermore, overexpression of both Bmi-1 and Mel-18 significantly increases the clonogenic survival of Rat1 fibroblasts. In contrast, stable downregulation of Bmi-1 or Mel-18 alone does not affect the growth of normal human WI38 fibroblasts. Proteomics-based characterization of Bmi-1 and Mel-18 protein complexes isolated from cancer cells revealed substantial similarities in their respective compositions. Finally, gene expression analysis identified a number of cancer-relevant pathways that may be controlled by Bmi-1 and Mel-18 and also showed that these Polycomb proteins regulate a set of common gene targets. Taken together, these results suggest that Bmi-1 and Mel-18 may have overlapping functions in cancer cell growth.

scholarly journals Interplay of BAF and MLL4 promotes cell type-specific enhancer activation

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Young-Kwon Park ◽  
Ji-Eun Lee ◽  
Zhijiang Yan ◽  
Kaitlin McKernan ◽  
Tommy O’Haren ◽  
...  
Keyword(s):  
Cell Differentiation ◽  
Chromatin Remodeling ◽  
Direct Evidence ◽  
Cell Type ◽  
Chromatin Regulators ◽  
Chromatin Remodeling Complex ◽  
Histone H3k4 ◽  
Cell Type Specific ◽  
Pioneer Transcription Factor ◽  
Factor C

AbstractCell type-specific enhancers are activated by coordinated actions of lineage-determining transcription factors (LDTFs) and chromatin regulators. The SWI/SNF chromatin remodeling complex BAF and the histone H3K4 methyltransferase MLL4 (KMT2D) are both implicated in enhancer activation. However, the interplay between BAF and MLL4 in enhancer activation remains unclear. Using adipogenesis as a model system, we identify BAF as the major SWI/SNF complex that colocalizes with MLL4 and LDTFs on active enhancers and is required for cell differentiation. In contrast, the promoter enriched SWI/SNF complex PBAF is dispensable for adipogenesis. By depleting BAF subunits SMARCA4 (BRG1) and SMARCB1 (SNF5) as well as MLL4 in cells, we show that BAF and MLL4 reciprocally regulate each other’s binding on active enhancers before and during adipogenesis. By focusing on enhancer activation by the adipogenic pioneer transcription factor C/EBPβ without inducing cell differentiation, we provide direct evidence for an interdependent relationship between BAF and MLL4 in activating cell type-specific enhancers. Together, these findings reveal a positive feedback between BAF and MLL4 in promoting LDTF-dependent activation of cell type-specific enhancers.

scholarly journals Histone modifications form a cell-type-specific chromosomal bar code that persists through the cell cycle

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
John A. Halsall ◽  
Simon Andrews ◽  
Felix Krueger ◽  
Charlotte E. Rutledge ◽  
Gabriella Ficz ◽  
...  
Keyword(s):  
Gene Expression ◽  
Cell Cycle ◽  
Histone Modifications ◽  
Expression Patterns ◽  
Cell Types ◽  
Cell Type ◽  
Bar Code ◽  
Genes Encoding ◽  
Cell Type Specific ◽  
Rolling Windows

AbstractChromatin configuration influences gene expression in eukaryotes at multiple levels, from individual nucleosomes to chromatin domains several Mb long. Post-translational modifications (PTM) of core histones seem to be involved in chromatin structural transitions, but how remains unclear. To explore this, we used ChIP-seq and two cell types, HeLa and lymphoblastoid (LCL), to define how changes in chromatin packaging through the cell cycle influence the distributions of three transcription-associated histone modifications, H3K9ac, H3K4me3 and H3K27me3. We show that chromosome regions (bands) of 10–50 Mb, detectable by immunofluorescence microscopy of metaphase (M) chromosomes, are also present in G1 and G2. They comprise 1–5 Mb sub-bands that differ between HeLa and LCL but remain consistent through the cell cycle. The same sub-bands are defined by H3K9ac and H3K4me3, while H3K27me3 spreads more widely. We found little change between cell cycle phases, whether compared by 5 Kb rolling windows or when analysis was restricted to functional elements such as transcription start sites and topologically associating domains. Only a small number of genes showed cell-cycle related changes: at genes encoding proteins involved in mitosis, H3K9 became highly acetylated in G2M, possibly because of ongoing transcription. In conclusion, modified histone isoforms H3K9ac, H3K4me3 and H3K27me3 exhibit a characteristic genomic distribution at resolutions of 1 Mb and below that differs between HeLa and lymphoblastoid cells but remains remarkably consistent through the cell cycle. We suggest that this cell-type-specific chromosomal bar-code is part of a homeostatic mechanism by which cells retain their characteristic gene expression patterns, and hence their identity, through multiple mitoses.

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