SEARCH · PubMed Health

Results for “Polycomb”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 505 records · Page 28Linked to original sources

PubMed1997

Self-association of chromo domain peptides.

The chromo domain is a sequence motif first recognised in the Drosophila polycomb protein and heterochromatin protein (HP1), two proteins associated with stable and heritable transcriptional silencing. Polycomb is one of a number of genes that are required to prevent ectopic homeotic gene expression in Drosophila, while HP1, the product of the Drosophila melanogaster Su(var)205 gene, is associated with the phenomenon of position effect variegation. These proteins are believed to be components of chromatin-associated multi-protein complexes that bring about stable transcriptional silencing and the chromo domain has been implicated in chromatin targeting, probably through protein-protein interaction. Recently, mammalian homologues of both polycomb and HP1 have been described. Here we demonstrate for the first time that oligopeptides containing a chromo domain derived from the mouse polycomb homologue M33 form multimeric complexes in solution, supporting the role of the chromo domain in multiprotein complex assembly.

Animals↗

PubMed2006

PHC3, a component of the hPRC-H complex, associates with E2F6 during G0 and is lost in osteosarcoma tumors.

Polyhomeotic-like 3 (PHC3) is a ubiquitously expressed member of the polycomb gene family and part of the human polycomb complex hPRC-H. We found that in normal cells PHC3 associated with both hPRC-H complex components and with the transcription factor E2F6. In differentiating and confluent cells, PHC3 and E2F6 showed nuclear colocalization in a punctate pattern that resembled the binding of polycomb bodies to heterochromatin. This punctate pattern was not seen in proliferating cells suggesting that PHC3 may be part of an E2F6-polycomb complex that has been shown to occupy and silence target promoters in G(0). Previous loss of heterozygosity (LoH) analyses had shown that the region containing PHC3 underwent frequent LoH in primary human osteosarcoma tumors. When we examined normal bone and human osteosarcoma tumors, we found loss of PHC3 expression in 36 of 56 osteosarcoma tumors. Sequence analysis revealed that PHC3 was mutated in nine of 15 primary osteosarcoma tumors. These findings suggest that loss of PHC3 may favor tumorigenesis by potentially disrupting the ability of cells to remain in G(0).

Base Sequence↗

PubMed1997

A silencer is required for maintenance of transcriptional repression throughout Drosophila development.

Transcriptional silencing by the Polycomb Group of genes maintains the position-specific repression of homeotic genes throughout Drosophila development. The Polycomb Group of genes characterized to date encode chromatin-associated proteins that have been suggested to form heterochromatin-like structures. By studying the expression of reporter genes, we have identified a 725 bp fragment, called MCP725, in the homeotic gene Abdominal-B, that accurately maintains position-specific silencing during proliferation of imaginal cells. Silencing by MCP725 requires the Polycomb and the Polycomblike genes, indicating that it contains a Polycomb response element To investigate the mechanisms of transcriptional silencing by MCP725, we have studied its temporal requirements by removing MCP725 from the transgene at various times during development. We have discovered that excision of MCP725 during larval stages leads to loss of silencing. Our findings indicate that the silencer is required for the maintenance of the repressed state throughout cell proliferation. They also suggest that propagation of the silenced state does not occur merely by templating of a heterochromatin structure by virtue of protein-protein interactions. Rather, they suggest that silencers play an active role in the maintenance of the position-specific repression throughout development.

Animals↗

PubMed1996

In vivo assay for protein-protein interactions using Drosophila chromosomes.

The ability of a chimeric HP1-Polycomb (Pc) protein to bind both to heterochromatin and to euchromatic sites of Pc protein binding was exploited to detect stable protein-protein interactions in vivo. Previously, we showed that endogenous Pc protein was recruited to ectopic heterochromatic binding sites by the chimeric protein. Here, we examine the association of other Pc group (Pc-G) proteins. We show that Posterior sex combs (Psc) protein also is recruited to heterochromatin by the chimeric protein, demonstrating that Psc protein participates in direct protein-protein interaction with Pc protein or Pc-associated protein. In flies carrying temperature-sensitive alleles of Enhancer of zeste[E(z)] the general decondensation of polytene chromosomes that occurs at the restrictive temperature is associated with loss of binding of endogenous Pc and chimeric HP1-Polycomb protein to euchromatin, but binding of HP1 and chimeric HP1-Polycomb protein to the heterochromatin is maintained. The E(z) mutation also results in the loss of chimera-dependent binding to heterochromatin by endogenous Pc and Psc proteins at the restrictive temperature, suggesting that interaction of these proteins is mediated by E(z) protein. A myc-tagged full-length Suppressor 2 of zeste [Su(z)2] protein interacts poorly or not at all with ectopic Pc-G complexes, but a truncated Su(z)2 protein is strongly recruited to all sites of chimeric protein binding. Trithorax protein is not recruited to the heterochromatin by the chimeric HP1-Polycomb protein, suggesting either that this protein does not interact directly with Pc-G complexes or that such interactions are regulated. Ectopic binding of chimeric chromosomal proteins provides a useful tool for distinguishing specific protein-protein interactions from specific protein-DNA interactions important for complex assembly in vivo.

Animals↗

PubMed1999

Molecular genetic analysis of the Drosophila trithorax-related gene which encodes a novel SET domain protein.

The products of the trithorax and Polycomb groups genes maintain the activity and silence, respectively, of many developmental genes including genes of the homeotic complexes. This transcriptional regulation is likely to involve modification of chromatin structure. Here, we report the cloning and characterization of a new gene, trithorax-related (trr), which shares sequence similarities with members of both the trithorax and Polycomb groups. The trr transcript is 9.6 kb in length and is present throughout development. The TRR protein, as predicted from the nucleotide sequence of the open reading frame, is 2431 amino acids in length and contains a PHD finger-like domain and a SET domain, two highly conserved protein motifs found in several trithorax and Polycomb group proteins, and in modifiers of position effect variegation. TRR is most similar in sequence to the human ALR protein, suggesting that trr is a Drosophila homologue of the ALR. TRR is also highly homologous to Drosophila TRITHORAX protein and to its human homologue, ALL-1/HRX. However, preliminary genetic analysis of a trr null allele suggests that TRR protein may not be involved in regulation of homeotic genes (i.e. not a member of the trithorax or Polycomb groups) or in position effect variegation.

Amino Acid Sequence↗

PubMed2006

Bmi1 cooperates with Dnmt1-associated protein 1 in gene silencing.

Polycomb group (PcG) proteins are involved in gene silencing through chromatin modifications. Among polycomb repressive complexes (PRCs), PRC1 exhibits H2A-K119 ubiquitin E3 ligase activity. However, the molecular mechanisms underlying PRC1-mediated gene silencing remain largely obscure. In this study, we found that Bmi1 directly interacts with Dnmt-associated protein 1 (Dmap1), which has been characterized to associate with the maintenance DNA methyltransferase, Dnmt1. Bmi1 was demonstrated to form a ternary complex with Dmap1 and Dnmt1 with Dmap1 in the central position. Chromatin immunoprecipitations confirmed the ternary complex formation within the context of the PRC1 at the Bmi1 target loci. Loss of Dmap1 binding to the Bmi1 target loci was tightly associated with derepressed gene expression in Bmi1-/- cells. Dmap1 knockdown exhibited the same impact as Bmi1 knockout did on the expression of Bmi1 targets, including Hox genes. Collectively, our findings suggest that Bmi1 incorporates Dmap1 in polycomb gene silencing.

Animals↗

PubMed1998

Male-to-female sex reversal in M33 mutant mice.

Polycomb genes in Drosophila maintain the repressed state of homeotic and other developmentally regulated genes by mediating changes in higher-order chromatin structure. M33, a mouse homologue of Polycomb, was isolated by means of the structural similarity of its chromodomain. The fifth exon of M33 contains a region of homology shared by Drosophila and Xenopus. In Drosophila, its deletion results in the loss of Polycomb function. Here we have disrupted M33 in mice by inserting a poly(A) capture-type neo(r) targeting vector into its fifth exon. More than half of the resultant M33cterm/M33cterm mutant mice died before weaning, and survivors showed male-to-female sex reversal. Formation of genital ridges was retarded in both XX and XY M33cterm/M33cterm embryos. Gonadal growth defects appeared near the time of expression of the Y-chromosome-specific Sry gene, suggesting that M33 deficiency may cause sex reversal by interfering with steps upstream of Sry. M33cterm/M33cterm mice may be a valuable model in which to test opposing views regarding sex determination.

Animals↗

PubMed2006

Argonaute-1 directs siRNA-mediated transcriptional gene silencing in human cells.

Argonaute proteins are the core components of effector complexes that facilitate RNA interference (RNAi). Small interfering RNAs (siRNAs) targeted to promoter regions mediate transcriptional gene silencing (TGS) in human cells through heterochromatin formation. RNAi effector complexes have yet to be implicated in the mechanism of mammalian TGS. Here we describe the role of the human Argonaute-1 homolog (AGO1) in directing TGS at the promoters for human immunodeficiency virus-1 coreceptor CCR5 and tumor suppressor RASSF1A. AGO1 associates with RNA polymerase II (RNAPII) and is required for histone H3 Lys9 dimethylation and TGS. AGO1, TAR RNA-binding protein-2 (7TRBP2) and Polycomb protein EZH2 colocalize to the siRNA-targeted RASSF1A promoter, implicating Polycomb silencing in the mechanism of mammalian TGS. These results establish a connection between RNAi components AGO1 and TRBP2, RNAPII transcription and Polycomb-regulated control of gene expression.

Argonaute Proteins↗

PubMed2004

Disruption of E2F signaling suppresses the INK4a-induced proliferative defect in M33-deficient mice.

Polycomb group (Pc-G) proteins associate to form large complexes that repress Hox genes, thereby imposing Hox gene expression pattern required for development. However, Pc-G proteins have a Hox-independent function in controlling cell proliferation. Here we show that embryonic fibroblasts derived from M33-deficient mice are impaired in the progression into the S phase of the cell cycle, as shown by a reduced rate of incorporation of bromodeoxyuridine. These cells have a senescent phenotype, associated to an abnormal accumulation of the cyclin-dependent kinase inhibitor p16INK4a protein. We demonstrate that this defect is bypassed in mutant embryonic fibroblasts expressing a transdominant negative form of the cell cycle controlling transcription factor E2F (E2F-DB). In addition, we show that the polycomb protein M33 controls critical expansion of B- and T-lymphocyte precursors. Together, our results emphasize M33-Polycomb protein function in cell cycle control.

Animals↗

PubMed2007

The N terminus of Drosophila ESC binds directly to histone H3 and is required for E(Z)-dependent trimethylation of H3 lysine 27.

Polycomb group proteins mediate heritable transcriptional silencing and function through multiprotein complexes that methylate and ubiquitinate histones. The 600-kDa E(Z)/ESC complex, also known as Polycomb repressive complex 2 (PRC2), specifically methylates histone H3 lysine 27 (H3 K27) through the intrinsic histone methyltransferase (HMTase) activity of the E(Z) SET domain. By itself, E(Z) exhibits no detectable HMTase activity and requires ESC for methylation of H3 K27. The molecular basis for this requirement is unknown. ESC binds directly, via its C-terminal WD repeats (beta-propeller domain), to E(Z). Here, we show that the N-terminal region of ESC that precedes its beta-propeller domain interacts directly with histone H3, thereby physically linking E(Z) to its substrate. We show that when expressed in stable S2 cell lines, an N-terminally truncated ESC (FLAG-ESC61-425), like full-length ESC, is incorporated into complexes with E(Z) and binds to a Ubx Polycomb response element in a chromatin immunoprecipitation assay. However, incorporation of this N-terminally truncated ESC into E(Z) complexes prevents trimethylation of histone H3 by E(Z). We also show that a closely related Drosophila melanogaster paralog of ESC, ESC-like (ESCL), and the mammalian homolog of ESC, EED, also interact with histone H3 via their N termini, indicating that the interaction of ESC with histone H3 is evolutionarily conserved, reflecting its functional importance. Our data suggest that one of the roles of ESC (and ESCL and EED) in PRC2 complexes is to enable E(Z) to utilize histone H3 as a substrate by physically linking enzyme and substrate.

Animals↗

PubMed2001

corto genetically interacts with Pc-G and trx-G genes and maintains the anterior boundary of Ultrabithorax expression in Drosophila larvae.

In Drosophila melanogaster, segment identity is determined by specific expression of homeotic genes (Hox). The Hox expression pattern is first initiated by gap and pair-rule genes and then maintained by genes of the Polycomb-group (Pc-G) and the trithorax-group (trx-G). The corto gene is a putative regulator of the Hox genes since mutants exhibit homeotic transformations. We show here that, in addition to previously reported genetic interactions with the Pc-G genes Enhancer of zeste, Polycomb and polyhomeotic, mutations in corto enhance the extra-sex-comb phenotype of multi sex combs, Polycomb-like and Sex combs on midleg. corto also genetically interacts with a number of trx-G genes (ash1, kismet, kohtalo, moira, osa, Trithorax-like and Vha55). The interactions with genes of the trx-G lead to phenotypes displayed in the wing, in the postpronotum or in the thoracic mechanosensory bristles. In addition, we analyzed the regulation of the Hox gene Ultrabithorax (Ubx) in corto mutants. Our results provide evidence that corto maintains the anterior border of Ubx expression in third-instar larvae. We suggest that this regulation is accomplished through an interaction with the products of the Pc-G and trx-G genes.

Animals↗

PubMed2025

Integrator promotes the association of TFIID and RNA polymerase II to maintain pluripotency during development.

The mechanisms by which the expression of pluripotency and Polycomb networks are harmonized to allow the transition from pluripotency to a differentiated state have not been fully elucidated. Integrator complex regulates transcription pause release and RNA processing in metazoans. We show that Integrator is required for stemness and plays a critical role as early as day 2 in embryonic development. While the catalytic endonuclease activity enhances cellular reprogramming, Integrator recruits RNA polymerase II (RNAPII) to promoters and super enhancers of pluripotency and Polycomb genes. Integrator coordinates expression of pluripotency and Polycomb networks by fostering the association of RNAPII and basal transcription factors. We pinpoint a critical role for TATA-binding protein-associated factors (TAFs) in Integrator entry into the preinitiation complex. Taken together, beyond its role in RNAPII pause release, Integrator recruitment of RNAPII ensures an orderly cellular differentiation during development.

RNA Polymerase II↗

PubMed2005

Double chromodomains cooperate to recognize the methylated histone H3 tail.

Chromodomains are modules implicated in the recognition of lysine-methylated histone tails and nucleic acids. CHD (for chromo-ATPase/helicase-DNA-binding) proteins regulate ATP-dependent nucleosome assembly and mobilization through their conserved double chromodomains and SWI2/SNF2 helicase/ATPase domain. The Drosophila CHD1 localizes to the interbands and puffs of the polytene chromosomes, which are classic sites of transcriptional activity. Other CHD isoforms (CHD3/4 or Mi-2) are important for nucleosome remodelling in histone deacetylase complexes. Deletion of chromodomains impairs nucleosome binding and remodelling by CHD proteins. Here we describe the structure of the tandem arrangement of the human CHD1 chromodomains, and its interactions with histone tails. Unlike HP1 and Polycomb proteins that use single chromodomains to bind to their respective methylated histone H3 tails, the two chromodomains of CHD1 cooperate to interact with one methylated H3 tail. We show that the human CHD1 double chromodomains target the lysine 4-methylated histone H3 tail (H3K4me), a hallmark of active chromatin. Methylammonium recognition involves two aromatic residues, not the three-residue aromatic cage used by chromodomains of HP1 and Polycomb proteins. Furthermore, unique inserts within chromodomain 1 of CHD1 block the expected site of H3 tail binding seen in HP1 and Polycomb, instead directing H3 binding to a groove at the inter-chromodomain junction.

Amino Acid Sequence↗

PubMed2003

Crystal structure of the malignant brain tumor (MBT) repeats in Sex Comb on Midleg-like 2 (SCML2).

Sex Comb on Midleg (SCM) belongs to the Polycomb group of proteins, which are involved in transcriptional regulation in Drosophila. It is one of the components of Polycomb repressive complex 1, a multiprotein complex of Polycomb group proteins involved in the maintenance of repression and the blocking of chromatin remodeling. SCM contains two approximately 100-residue malignant brain tumor (MBT) repeats at the N terminus. These repeats are also found in other proteins involved in transcriptional repression. Here, we report the 1.78-A crystal structure of the two MBT repeats of SCM-like 2 (SCML2), a human homologue of SCM. Each repeat consists of an extended arm and a beta-barrel core. There are significant structural similarities to the Tudor, PWWP, and chromo domains, suggesting probable evolutionary relationships and functional similarities between the MBT repeats and these domains.

Amino Acid Sequence↗

PubMed2001

Developmental dynamics of a polyhomeotic-EGFP fusion in vivo.

Polyhomeotic is a member of the Polycomb group of genes. The products of this group are chromatin-associated proteins that act together as multimeric complexes. These proteins are required for the maintenance of target gene repression in a permanent and heritable manner during development. In order to better understand the dynamics of their action during development, we generated transgenic flies expressing a polyhomeotic protein tagged with the enhanced green fluorescent protein. Here we show that this fusion protein (PH-EGFP) retains both the functional properties of the endogenous protein and its target specificity on polytene chromosomes. The distribution of the PH-EGFP protein is partly dependent on the presence of wildtype Polycomb protein, indicating that PH-EGFP behaves as does the wildtype PH protein. Therefore, the PH-EGFP chimera appears to be an appropriate reporter of PH protein distribution and a suitable tool for the study of Polycomb-group complex assembly in vivo. The subnuclear distribution of PH-EGFP is dynamic throughout development. In the interphase nucleus at the cellular blastoderm, a diffuse granular pattern is observed. From the early gastrula stage onward, a few brighter dots appear. As development progressed from germ band retraction through hatching of the larva, numerous discrete dots accumulate in the nucleus of epidermal cells. The increasing number of dots observed during development may indicate that PH-EGFP is recruited at different stages on different target sites, a result that is in good agreement with functional data previously reported.

Animals↗

PubMed2002

Homeotic transformations of the axial skeleton that accompany a targeted deletion of E2f6.

E2F transcription factors play an important role in regulating mammalian cell proliferation. E2F6, the most recently identified E2F family member, is a transcriptional repressor. In an effort to ascertain the in vivo biological function of E2F6, we have generated an E2f6 mutant mouse strain. Mice lacking E2F6 are viable and healthy. Surprisingly, E2f6-/- embryonic fibroblasts proliferate normally. However, E2f6-/- animals display overt homeotic transformations of the axial skeleton that are strikingly similar to the skeletal transformations observed in polycomb mutant mice. This observation is compatible with the recent finding that endogenous E2F6 and one or more mammalian polycomb proteins are components of the same multiprotein complex. The accumulated evidence suggests that, during development, E2F6 participates in the recruitment of polycomb proteins to specific target promoters.

Animals↗

PubMed1995

A screen for modifiers of Deformed function in Drosophila.

Proteins produced by the homeotic genes of the Hox family assign different identifies to cells on the anterior/posterior axis. Relatively little is known about the signalling pathways that modulate their activities or the factors with which they interact to assign specific segmental identifies. To identify genes that might encode such functions, we performed a screen for second site mutations that reduce the viability of animals carrying hypomorphic mutant alleles of the Drosophila homeotic locus, Deformed. Genes mapping to six complementation groups on the third chromosome were isolated as modifiers of Deformed function. Products of two of these genes, sallimus and moira, have been previously proposed as homeotic activators since they suppress the dominant adult phenotype of Polycomb mutants. Mutations in hedgehog, which encodes secreted signalling proteins, were also isolated as Deformed loss-of-function enhancers. Hedgehog mutant alleles also suppress the Polycomb phenotype. Mutations were also isolated in a few genes that interact with Deformed but not with Polycomb, indicating that the screen identified genes that are not general homeotic activators. Two of these genes, cap 'n' collar and defaced, have defects in embryonic head development that are similar to defects seen in loss of function Deformed mutants.

Animals↗

PubMed1998

P-Element insertion at the polyhomeotic gene leads to formation of a novel chimeric protein that negatively regulates yellow gene expression in P-element-induced alleles of Drosophila melanogaster.

Polyhomeotic is a member of the Polycomb group (Pc-G) of homeotic repressors. The proteins encoded by the Pc-G genes form repressive complexes on the polycomb group response element sites. The phP1 mutation was induced by insertion of a 1.2-kb P element into the 5' transcribed nontranslated region of the proximal polyhomeotic gene. The phP1 allele confers no mutant phenotype, but represses transcription of P-element-induced alleles at the yellow locus. The phP1 allele encodes a chimeric P-PH protein, consisting of the DNA-binding domain of the P element and the PH protein lacking 12 amino-terminal amino acids. The P-PH, Polycomb (PC), and Posterior sex combs (PSC) proteins were immunohistochemically detected on polytene chromosomes in the regions of P-element insertions.

Animals↗