TY - JOUR. T1 - M32, a murine homologue of Drosophila heterochromatin protein 1 (HP1), localises to euchromatin within interphase nuclei and is largely excluded from constitutive heterochromatin. AU - Horsley, D. AU - Hutchings, A. AU - Butcher, G W. AU - Singh, P B. PY - 1996. Y1 - 1996. N2 - Mice possess two structural homologues of Drosophila HP1, termed M31 and M32 (Singh et al., 1991). We have previously shown that an M31-specific monoclonal antibody (MoAb), MAC 353, localises to constitutive heterochromatin (Wreggett et al., 1994). Here we report that a MoAb raised against the M32 protein (MAC 385) recognises a 22-kDa protein in murine nuclear extracts and that M32 is distributed in a fine-grain "speckled" pattern within interphase nuclei. M32 is also largely excluded from the large masses of constitutive heterochromatin that are labelled by MAC 353.. AB - Mice possess two structural homologues of Drosophila HP1, termed M31 and M32 (Singh et al., 1991). We have previously shown that an ...
Heterochromatin protein 1 is associated with centromeric heterochromatin in Drosophila, mice, and humans. Loss of function mutations in the gene encoding heterochromatin protein 1 in Drosophila, Suppressor of variegation2-5, decrease the mosaic repression observed for euchromatic genes that have been juxtaposed to centromeric heterochromatin. These heterochromatin protein 1 mutations not only suppress this position-effect variegation, but also cause recessive embryonic lethality. In this study, we analyze the latter phenotype in the hope of gaining insight into heterochromatin function. In our analyses of four alleles of Suppressor of variegation2-5, the lethality was found to be associated with defects in chromosome morphology and segregation. While some of these defects are seen throughout embryonic development, both the frequency and severity of the defects are greatest between cycles 10 and 14 when zygotic transcription of the Suppressor of variegation2-5 gene apparently begins. By this time ...
In eukaryotic cells, DNA is packaged in repeated units of nucleosomes, which are further organized into chromatin, a template for gene expression and genetic inheritance. Whereas euchromatin is less condensed and gene rich, heterochromatin is considered highly condensed, gene poor and less accessible to proteins such as transcription factors and the DNA repair machinery. Heterochromatin is also associated with a number of repressive covalent modifications of histone tails (Grewal and Elgin, 2007). At least two mechanisms are responsible for the highly compact state of heterochromatin: pericentric heterochromatin is dependent on heterochromatin protein 1 (HP1) (Eissenberg and Elgin, 2000) and intercalary heterochromatin is dependent on the polycomb group (PcG) of proteins (Belyaeva et al., 2008; Zhimulev and Belyaeva, 2003). HP1 and Pc recognize their respective target sites with discriminating specificities. Whereas HP1 prefers platforms with histone H3 bearing trimethylated Lys9, Pc targets ...
Constitutive heterochromatin, mainly formed at the gene-poor regions of pericentromeres, is believed to ensure a condensed and transcriptionally inert chromatin conformation. Pericentromeres consist of repetitive tandem satellite repeats and are crucial chromosomal elements that are responsible for accurate chromosome segregation in mitosis. The repeat sequences are not conserved and can greatly vary between different organisms, suggesting that pericentromeric functions might be controlled epigenetically. In this review, we will discuss how constitutive heterochromatin is formed and maintained at pericentromeres in order to ensure their integrity. We will describe the biogenesis and the function of main epigenetic pathways that are involved and how they are interconnected. Interestingly, recent findings suggest that alternative pathways could substitute for well-established pathways when disrupted, suggesting that constitutive heterochromatin harbors much more plasticity than previously assumed. In
Pericentric heterochromatin is a highly compacted structure required for accurate chromosome segregation in mitosis. In mammals, it relies on methylation of histone H3K9 by Suv39H enzymes, which provides a docking site for HP1 proteins, therefore mediating heterochromatin compaction. Here we show that, when this normal compaction pathway is defective, the histone acetyltransferase Tip60 is recruited to pericentric heterochromatin, where it mediates acetylation of histone H4K12. Furthermore, in such a context, depletion of Tip60 leads to derepression of satellite transcription, decompaction of pericentric heterochromatin, and defects in chromosome segregation in mitosis. Finally, we show that depletion of BRD2, a double bromodomain-containing protein that binds H4K12ac, phenocopies the Tip60 depletion with respect to heterochromatin decompaction and defects in chromosome segregation. Taking the results together, we identify a new compaction pathway of mammalian pericentric heterochromatin relying on
Boundaries between different chromatin states must be maintained for stable gene expression patterns [1], [2]. Although many different chromatin states have been described, the two most fundamental categories are active euchromatin and silent heterochromatin [3]. Constitutive heterochromatin is associated with H3K9me2/3, HP1, and low histone turnover [4], [5]. Although generally inactive, heterochromatin may be transcribed during defined periods of the cell cycle, but the resulting transcripts are degraded [6], [7], [8]. The fission yeast Schizosaccharomyces pombe uses several alternative heterochromatin formation pathways in different regions that may substitute for one another. The RNAi pathway, which involves the proteins Dcr1 and Ago1, is the predominant mechanism used to nucleate heterochromatin [9], [10]. RNAi‐independent heterochromatin formation depends on transcription and RNA surveillance by factors such as Mlo3‐TRAMP [11]. The constitutive heterochromatin regions in S. pombe are ...
In eukaryotes, Origin recognition complex (ORC) proteins establish the pre-replicative complex (pre-RC) at the origins and this is essential for the initiation of DNA replication. In human cells, ORC is a highly dynamic complex with many separate functions attributed to sub-complexes or individual subunits of ORC including heterochromatin organization, telomere and centromere function, centrosome duplication and cytokinesis. Heterochromatic domains are enriched with repressive histone marks, including histone H3 lysine 9 methylation, written by lysine methyltransferases (KMTs). ORC along with the pre-RC protein Origin Recognition Complex-Associated (ORCA/LRWD1), preferentially localizes to heterochromatic regions in post-replicated cells. The role of ORCA and ORC in heterochromatin organization remained elusive. In Chapter II, I describe my efforts to understand the significance of ORCA-ORCs association with heterochromatin. ORCA recognizes methylated H3K9 marks and interacts with repressive ...
The genome is organised into large scale structures in the interphase nucleus. Pericentromeric heterochromatin represents one such compartment characterised by histones H3 and H4 tri-methylated at K9 and K20 respectively and with a correspondingly low level of histone acetylation. HP1 proteins are concentrated in pericentric heterochromatin and histone deacetylase inhibitors such as trichostatin A (TSA) promote hyperacetylation of heterochromatic nucleosomes and the dispersal of HP1 proteins. We observed that in mouse cells, which contain prominent heterochromatin, DNA topoisomerase IIb (topoIIb) is also concentrated in heterochromatic regions. Similarly, a detergent-resistant fraction of topoIIb is associated with heterochromatin in human cell lines. Treatment with TSA displaced topoIIb from the heterochromatin with similar kinetics to the displacement of HP1b. Topoisomerase II is the cellular target for a number of clinically important cytotoxic anti-cancer agents known collectively as ...
Fig. 3. Chromocentres are located close to the nuclear periphery. (A) NucleusJ was used to compute the distance between the limit of the Hoechst DNA staining (blue) and the chromocentres (Cc, pink), boundary [d(Cc border)] or barycentre [d(Cc barycentre)]. The barycentre of the nucleus d(Nuc barycentre) (white cross) is also indicated. (B) Graphical representation of chromocentre distribution in respect to the limit of Hoechst DNA staining among the three cell types. The theoretical uniform distribution of chromocentres (top) is compared to observed distributions for d(Cc border) (middle) and d(Cc barycentre) (bottom). The uniform distribution of chromocentres is obtained by placing the same number of chromocentres as in the corresponding datasets between the periphery and the corresponding nuclear barycentres, for each nucleus of the dataset. Chromocenters and nuclei numbers are given at the bottom of the figure. The scales of the graphs were standardized by setting the maximum d(Nuc ...
Constitutive heterochromatin is important for maintaining chromosome stability but also delays the repair of DNA double strand breaks (DSB). DSB repair in complex mammalian genomes involves a fast phase (2-6 hrs) where most of the breaks are rapidly repaired, and a slow phase (up to 24 hrs) where the remaining damages in heterochromatin are repaired. We found that p53 deficiency delays the slow phase DNA repair after ionizing irradiation. P53 deficiency prevents down regulation of histone H3K9 trimethylation at pericentric heterochromatin after DNA damage. Moreover, p53 directly induces expression of the H3 K9 demethylase JMJD2b through promoter binding. P53 activation also indirectly down regulates expression of the H3 K9 methytransferase SUV39H1. Depletion of JMJD2b or sustained expression of SUV39H1 delays the repair of heterochromatin DNA and reduces clonogenic survival after ionizing irradiation. The results suggest that by regulating JMJD2b and SUV39H1 expression, p53 not only controls ...
CHROMATIN structure can influence transcriptional activity by mediating the accessibility of regulatory factors and polymerase to the gene and surrounding DNA. Active genes have a more open or euchromatic structure, while inactive loci have a more condensed nucleosome arrangement that shares many features with constitutively heterochromatic regions of the genome. Constitutive heterochromatin can modify the structure and activity of a euchromatic gene when repositioned next to it by a chromosomal-break event. This change, called position-effect variegation (PEV), was first observed in Drosophila upon isolation of chromosomal a rearrangement that moved the white gene close to the pericentric heterochromatin of the X chromosome and gave a mosaic eye phenotype. Subsequent studies of PEV and related phenomena in other organisms have led to the view that the silencing is due to the progression of heterochromatin along the chromosome to inactivate genes on the same DNA molecule (in cis) (reviewed in ...
Figure 3. NoRC regulates telomeric heterochromatin. (A) TIP5 localizes at telomeres. Left: Z‐projection of a deconvolved image of a representative U2OS cell stained with α‐TIP5 antibody (red) followed by Q‐FISH with a telomere‐specific PNA probe (green). The same nucleus depicting colocalization of TIP5 with telomeres (white spots) is shown below. Middle: a representative U2OS cell immunostained with α‐TIP5 (red) and α‐TRF2 (green) antibodies is shown. Colocalization of TIP5 and TRF2 is depicted in yellow. Right: quantification of telomeres colocalizing with TIP5 in a representative experiment (N=4), each dot on the plot represents one cell (unpaired t‐test, P‐value ***,0.001, n=45). Red bars indicate mean values. Scale bars, 5 μm. (B) TIP5 is associated with telomeres. ChIPs in U2OS cells monitoring TIP5, TRF2 and Pol I at telomeres. Telomere DNA was assayed by dot hybridization with a telomere‐specific riboprobe. Data are normalized to input values. Error bars represent ...
Nuclear topology, in particular, the 3D landscape of the genome within the nucleus, has come into focus as a regulator of genome activity [1] with heterochromatin as a key player [2-4]. First evidence that heterochromatin might be a silencing compartment was provided by Muellers position effect variegation (PEV) experiments in 1930 [5], demonstrating that rearrangement of genes near the heterochromatin in Drosophila causes gene silencing. Position effect variegation affects genes on the same chromosome (cis) as well as genes on different chromosomes (trans) [6]. Moreover, the effects of heterochromatin on gene activity were suggested in, e.g., mouse [7-9], Drosophila melanogaster [10], Caenorhabditis elegans [11], Saccharomyces cerevisiae [12] Schizosaccharomyces pombe [13] and in Plasmodium falciparum [14], and seem to be an evolutionarily conserved feature [15, 16].. Heterochromatin can be found in essentially all eukaryotes, but its distribution and composition differ from species to ...
BACKGROUND Heterochromatin has been reported to be a major silencing compartment during development and differentiation. Prominent heterochromatin compartments are located at the nuclear periphery and inside the nucleus (e.g., pericentric heterochromatin). Whether the position of a gene in relation to some or all heterochromatin compartments matters remains a matter of debate, which we have addressed in this study. Answering this question demanded solving the technical challenges of 3D measurements and the large-scale morphological changes accompanying cellular differentiation. RESULTS Here, we investigated the proximity effects of the nuclear periphery and pericentric heterochromatin on gene expression and additionally considered the effect of neighboring genomic features on a genes nuclear position. Using a well-established myogenic in vitro differentiation system and a differentiation-independent heterochromatin remodeling system dependent on ectopic MeCP2 expression, we first identified ...
THE establishment and maintenance of alternative chromatin states over the course of multiple cell divisions requires the complex integration of both genomic and nongenomic signals (reviewed in Straub and Becker 2008). Such signals work in concert throughout development to guide both cell specialization and adaptation to environmental changes in vivo (Blasco 2007; Feinberg 2007; Surani et al. 2007). Much of our current understanding of alternate patterns of gene expression comes from experiments performed in model organisms, including Drosophila melanogaster (reviewed in Pirrotta and Gross 2005; Girton and Johansen 2008), Saccharomyces cerevisiae (reviewed in Buhler and Gasser 2009), and Schizosaccharomyces pombe (reviewed in Grewal and Elgin 2002). These studies have demonstrated that repositioning of a euchromatic gene to a genomic location adjacent to transcriptionally silent heterochromatin results in variegated patterns of gene expression, a phenomenon called position-effect variegation. In ...
TY - JOUR. T1 - XMtr4-like protein coordinates nuclear RNA processing for heterochromatin assembly and for telomere maintenance. AU - Lee, Nathan N.. AU - Chalamcharla, Venkata R.. AU - Reyes-Turcu, Francisca. AU - Mehta, Sameet. AU - Zofall, Martin. AU - Balachandran, Vanivilasini. AU - Dhakshnamoorthy, Jothy. AU - Taneja, Nitika. AU - Yamanaka, Soichiro. AU - Zhou, Ming. AU - Grewal, Shiv I S. PY - 2013/11/21. Y1 - 2013/11/21. N2 - The regulation of protein-coding and noncoding RNAs is linked to nuclear processes, including chromatin modifications and gene silencing. However, the mechanisms that distinguish RNAs and mediate their functions are poorly understood. We describe a nuclear RNA-processing network in fission yeast with a core module comprising the Mtr4-like protein, Mtl1, and the zinc-finger protein, Red1. The Mtl1-Red1 core promotes degradation of mRNAs and noncoding RNAs and associates with different proteins to assemble heterochromatin via distinct mechanisms. Mtl1 also forms ...
One obstacle to a mechanistic understanding of CD4 versus CD8 lineage commitment is the lack of early markers for the lineage commitment process. Lineage commitment is associated with stable repression of CD4 or CD8 genes, an event that can be accompanied by positioning of loci near regions of heterochromatin. In this work we have examined the position of CD4 and CD8 loci relative to heterochromatin at different stages of thymic development to gain insight into the timing and mechanism of stable gene repression and lineage commitment. We found that CD4 and CD8 loci tended to be located near centromeric heterochromatin in early thymocytes that have not yet expressed CD4 or CD8, and in mature thymocytes and T cells that have repressed either CD4 or CD8. We also provided evidence that repositioning of CD4 or CD8 genes to heterochromatin can occur as an early response to positive selection, being detectable in CD4+ CD8+ thymocytes that are receiving positive selection signals. This implies that ...
A kinase better known for triggering DNA replication also helps create the sticky heterochromatin at centromeres of fission yeast, according to Julie Bailis, Susan Forsburg (Salk Institute, La Jolla, CA), and colleagues.. The dual action makes sense, as chromosomes must be stuck together as soon as they are replicated. The responsible kinase activity, Hsk1 (CDC7)-Dfp1, is restricted to S phase, when DNA replication takes place.. Dfp1 turned up in a two-hybrid screen with Swi6, the fission yeast equivalent of heterochromatin protein 1 (HP1). Cells with a mutant Dfp1 that no longer binds Swi6 can replicate their DNA but suffer segregation errors when their defective centromeres fall apart. Swi6 localization is normal in these cells but, based on in vitro results, Swi6 phosphorylation may be reduced. This is the first indication that Swi6 localization is not sufficient to define heterochromatin function.. An interesting parallel is known in budding yeast, where establishment of silent ...
This review focuses on the function of heterochromatin protein HP1 in response to DNA damage. We specifically outline the regulatory mechanisms in which HP1 and its interacting partners are involved. HP1 protein subtypes (HP1α, HP1β, and HP1γ) are the main components of constitutive heterochromatin, and HP1α and HP1β in particular are responsible for heterochromatin maintenance. The recruitment of these proteins to DNA lesions is also important from the perspective of proper DNA repair mechanisms. For example, HP1α is necessary for the binding of the main DNA damage-related protein 53BP1 at DNA repair foci, which are positive not only for the HP1α protein but also for the RAD51 protein, a component of DNA repair machinery ...
B138 Background: Treatment of breast cancer cells with histone deacetylase (HDAC) inhibitors results in chromatin decondensation and the sensitization of cancer cells to DNA damaging agents such as topoisomerase II inhibitors. We previously reported that the HDAC inhibitors induced chromatin decondensation through the down-regulation of heterochromatin maintenance proteins such as heterochromatin protein 1 (HP1), structural maintenance of chromatin proteins (SMC) 1-5 and DNA methyltransferase 1 (DNMT1). Here we report the role of HDAC2 in the expression of heterochromatin maintenance proteins, chromatin decondensation and DNA damage induced by topoisomerase inhibition. Methods: HDAC2 was selectively depleted using siRNA transfection. HDAC2 depleted cells were evaluated by microarray and Western blot analysis for changes in HP1, DNMT1 and SMC mRNA and protein expression. Chromatin decondensation was evaluated by electron microscopy. DNA damage and cell death induced by the topoisomerase ...
TY - JOUR. T1 - Modeling post-translational modifications and cancer-associated mutations that impact the heterochromatin protein 1α-importin α heterodimers. AU - Zimmermann, Michael T.. AU - Williams, Monique M.. AU - Klee, Eric W. AU - Lomberk, Gwen A.. AU - Urrutia, Raul. PY - 2019/1/1. Y1 - 2019/1/1. N2 - Heterochromatin protein 1α (HP1α) is a protein that mediates cancer-associated processes in the cell nucleus. Proteomic experiments, reported here, demonstrate that HP1α complexes with importin α (IMPα), a protein necessary for its nuclear transport. This data is congruent with Simple Linear Motif (SLiM) analyses that identify an IMPα-binding motif within the linker that joins the two globular domains of this protein. Using molecular modeling and dynamics simulations, we develop a model of the IMPα-HP1α complex and investigate the impact of phosphorylation and genomic variants on their interaction. We demonstrate that phosphorylation of the HP1α linker likely regulates its ...
The Wnt signaling pathway has key roles in development and generally promotes proliferation of stem cells and inhibits apoptosis. These effects are essentially opposite to the changes that occur in senescent stem cells. Thus, Ye et al. examined whether reduced Wnt signaling might have a role inhibitory in senescence. They monitored the formation of specialized domains of heterochromatin known as senescence-associated heterochromatin foci or SAHF, which are thought to repress transcription of genes that promote proliferation. In human WI38 fibroblasts, expression of Wnt2 mRNA was decreased as cells approached senescence. Formation of SAHF was inhibited when pharmacological inhibitors were used to decrease activity of glycogen synthase kinase 3β (a kinase activated downstream of Wnt). Furthermore, small hybrid RNAs were used to decrease expression of Wnt2 in young fibroblasts, and this promoted formation of SAHF, the authors marker of senescence. Accordingly, exposure of cells to a Wnt ligand ...
The initiation of DNA replication in S phase requires the prior assembly of an origin recognition complex (ORC)-dependent pre-replicative complex on chromatin during G1 phase of the cell division cycle. In human cells, the Orc2 subunit localized to the nucleus as expected, but it also localized to centrosomes throughout the entire cell cycle. Furthermore, Orc2 was tightly bound to heterochromatin and heterochromatin protein 1alpha (HP1alpha) and HP1beta in G1 and early S phase, but during late S, G2 and M phases tight chromatin association was restricted to centromeres. Depletion of Orc2 by siRNA caused multiple phenotypes. A population of cells showed an S-phase defect with little proliferating cell nuclear antigen (PCNA) on chromatin, although MCM proteins remained. Orc2 depletion also disrupted HP1 localization, but not histone-H3-lysine-9 methylation at prominent heterochromatic foci. Another subset of Orc2-depleted cells containing replicated DNA arrested with abnormally condensed ...
From BioPortfolio: Constitutive heterochromatin is an important component of eukaryotic genomes that has essential roles in nuclear architecture, DNA repair and genome stability, ...
A clue about what role this structure, called the PIN domain, might play in heterochromatin assembly came from scouring a protein database. The team found that other proteins that had similar structural features were associated with telomeres, the cap-like structures at the end of chromosomes. In fission yeast, telomeres are one of the locations where heterochromatin is found, another being the centromere -- the dense knob-like structure at the center of a chromosome. The team found that deleting the PIN domain from Chp1 prevented heterochromatin formation at the telomeres but didnt affect formation at the centromere. "This suggests different functions of RITS proteins at centromeres vs telomeres," says Joshua-Tor. "RITS might be exerting its effect at centromeres through Ago1 and the RNAi machinery, but might enforcing its function at the telomeres through Chp1 and its PIN domain." The team is now turning its focus to understanding how these various functions are regulated.. "The Chp1-Tas3 ...
Model for heterochromatin assembly and spreading at S. pombecentromeric outer repeats. Heterochromatic centromere sequences (yellow arrow) are transcribed by RNA Polymerase II. These centromere transcripts are targeted by RITS via siRNA loaded Ago1. Association of RITS with centromere heterochromatin is strengthened by binding of Chp1 to H3mK9. RITS activity can recruit both CLRC, via interactions with Stc1, and RDRC resulting in spreading of H3mK9 and amplification of siRNAs, respectively (see text for details). dsRNA generated either by bi-directional transcription from centromere promoters (black arrows) or by RDRC activity is recognized and processed by Dicer (Dcr1). The resulting centromere siRNAs are then loaded onto Ago1 first in the ARC complex and then in RITS ...
Kinetochores in multicellular eukaryotes are usually associated with heterochromatin. Whether this heterochromatin simply promotes the cohesion necessary for accurate chromosome segregation at cell division or whether it also has a role in kinetochore assembly is unclear. Schizosaccharomyces pombe is an important experimental system for investigating centromere function, but all of the previous work with this species has exploited a single strain or its derivatives. The laboratory strain and...
1. MillerD, BrinkworthM, IlesD (2010) Paternal DNA packaging in spermatozoa: more than the sum of its parts? DNA, histones, protamines and epigenetics. Reproduction 139: 287-301.. 2. Eirin-LopezJM, AusioJ (2009) Origin and evolution of chromosomal sperm proteins. Bioessays 31: 1062-1070.. 3. BraunRE (2001) Packaging paternal chromosomes with protamine. Nat Genet 28: 10-12.. 4. Sassone-CorsiP (2002) Unique chromatin remodeling and transcriptional regulation in spermatogenesis. Science 296: 2176-2178.. 5. BurtonA, Torres-PadillaME (2010) Epigenetic reprogramming and development: a unique heterochromatin organization in the preimplantation mouse embryo. Brief Funct Genomics 9: 444-454.. 6. RobertsonS, LinR (2012) The oocyte-to-embryo transition. Adv Exp Med Biol 757: 351-372.. 7. GovinJ, CaronC, LestratC, RousseauxS, KhochbinS (2004) The role of histones in chromatin remodelling during mammalian spermiogenesis. Eur J Biochem 271: 3459-3469.. 8. GoddeJS, UraK (2009) Dynamic alterations of linker ...
During mammalian development, chromatin dynamics and epigenetic marking are important for genome reprogramming. Recent data suggest an important role for the chromatin assembly machinery in this process. To analyze the role of chromatin assembly factor 1 (CAF-1) during pre-implantation development, we generated a mouse line carrying a targeted mutation in the gene encoding its large subunit, p150CAF-1. Loss of p150CAF-1 in homozygous mutants leads to developmental arrest at the 16-cell stage. Absence of p150CAF-1 in these embryos results in severe alterations in the nuclear organization of constitutive heterochromatin. We provide evidence that in wild-type embryos, heterochromatin domains are extensively reorganized between the two-cell and blastocyst stages. In p150CAF-1 mutant 16-cell stage embryos, the altered organization of heterochromatin displays similarities to the structure of heterochromatin in two- to four-cell stage wild-type embryos, suggesting that CAF-1 is required for the ...
Eukaryotic genomes are packaged into a complex structure known as chromatin. The basic unit of chromatin is the nucleosome, which consists of two copies each of the histone proteins H2A, H2B, H3, and H4. The flexible N‐termini of histone proteins are subject to various posttranslational modifications associated with different types of chromatin. Originally defined cytologically as chromosome regions that do not undergo post‐mitotic decondensation but remain condensed during interphase, a distinct type of chromatin referred to as heterochromatin is generally characterized by histone hypoacetylation and specific methylation of lysine 9 of the histone H3 tail (H3K9me). This mark is a binding site for proteins containing a so‐called chromodomain (CD), such as proteins of the heterochromatin protein 1 (HP1) family that recognize and bind methylated H3K9 via their CDs (Eissenberg & Elgin, 2000; Bannister et al, 2001; Lachner et al, 2001).. HP1 proteins have long been thought to play a central ...
Heterochromatic silencing is important for repressing gene expression, protecting cells against viral invasion, maintaining DNA integrity and for proper chromosome segregation. Recently, it has become apparent that expression of eukaryotic genomes is far more complex than had previously been anticipated. Strikingly, it has emerged that most of the genome is transcribed including intergenic regions and heterochromatin, calling for us to re-address the question of how gene silencing is regulated and re-evaluate the concept of heterochromatic regions of the genome being transcriptionally inactive. Although heterochromatic silencing can be regulated at the transcriptional level, RNA degrading activities supplied either by the exosome complex or RNAi also significantly contribute to this process. The exosome also regulates noncoding RNAs (ncRNAs) involved in the establishment of heterochromatin, further underscoring its role as the major cellular machinery involved in RNA processing and turn-over. This
TY - JOUR. T1 - Restricted heterochromatin formation links NFATc2 repressor activity with growth promotion in pancreatic cancer. AU - Baumgart, Sandra. AU - Glesel, Elisabeth. AU - Singh, Garima. AU - Chen, Naiming. AU - Reutlinger, Kristina. AU - Zhang, Jinsan. AU - Billadeau, Daniel D. AU - Fernandez-Zapico, Martin E. AU - Gress, Thomas M.. AU - Singh, Shiv K.. AU - Ellenrieder, Volker. PY - 2012/2. Y1 - 2012/2. N2 - Background & Aims: Transcriptional silencing of the p15 INK4b tumor suppressor pathway overcomes cellular protection against unrestrained proliferation in cancer. Here we show a novel pathway involving the oncogenic transcription factor nuclear factor of activated T cells (NFAT) c2 targeting a p15 INK4b-mediated failsafe mechanism to promote pancreatic cancer tumor growth. Methods: Immunohistochemistry, real-time polymerase chain reaction, immunoblotting, and immunofluorescence microscopy were used for expression studies. Cancer growth was assessed in vitro by [ 3H] thymidine ...
Heterochromatin is a type of tightly-coiled chromosomal material that carries genes. Although heterochromatin is largely inert...
The repair of DNA damage in highly compact, transcriptionally silent heterochromatin requires that repair and chromatin packaging machineries be tightly coupled and regulated. KAP1 is a heterochromatin protein and co-repressor which binds to HP1 during gene silencing, but is also robustly phosphorylated by ATM at serine 824 in response to DNA damage. The interplay between HP1-KAP1 binding/ATM phosphorylation during DNA repair is not known. We show that HP1α and unmodified KAP1 are enriched in endogenous heterochromatic loci and at a silent transgene prior to damage. Following damage, γH2AX and pKAP1-s824 rapidly increase and persist at these loci. Cells which lack HP1 fail to form discreet pKAP1-s824 foci after damage but levels are higher and more persistent. KAP1 is phosphorylated at Serine 473 in response to DNA damage and its levels are also modulated by HP1. Unlike pKAP1-s824, pKAP1-s473 does not accumulate at damage foci but is diffusely localized in the nucleus. While HP1 association ...
Figure 6. Suv39h1,2 knockout advances the replication timing of chromocenters. (a) The pulse-chase-pulse method to define the temporal order of spatial replication patterns. MEFs were labeled for 10 min with CldU, chased for various lengths of time, labeled for 10 min with IdU, and stained with fluorescent antibodies specific to CldU (green) and IdU (red). Exemplary confocal images of the dynamic changes in replication patterns observed with increasing chase times (from 0 min through 10 h) in D15, which were similar in all lines, are shown. (b) Displaying only the IdU stain within nuclei that display early CldU patterns reveals the temporal order in which each of the replication patterns take place, which were similar to other mouse cell lines (Wu et al., 2005). In brief, DNA synthesis begins at many small, discrete foci in the internal euchromatic region of the nucleus, excluding the nucleoli (and associated chromocenters) and nuclear periphery (pattern I). In pattern II, replication continues ...
Perez-Toledo, K., Rojas-Meza, A.P., Mancio-Silva, L., Hernandez-Cuevas, N.A., Delgadillo, D.M., Vargas, M., et al. (2009) Plasmodium falciparum heterochromatin protein 1 binds to tri-methylated histone 3 lysine 9 and is linked to mutually exclusive expression of var genes. Nucleic Acids Res 37: 2596-2606 ...
SUV39: The Su(var)3-9 gene was originally identified in a genetic screen as a suppressor of position effect variegation in Drosophila. This was the first hint that the Su(var)3-9 protein might be involved in regulating chromatin structure. In mice, there are two highly related homologues of the Drosophila Su(var)3-9, Suv39h1 and Suv39h2. Following the identification of Suv39h1 as a lysine methyltransferase capable of methylating Lys9 of histone H3 (H3K9), confirmation that this protein can modulate chromatin architecture came with the finding that it creates a specific binding site for the heterochromatin protein HP1. As Suv39h1 and HP1 interact, it is thought that Suv39h1 methylating H3 K9, and then HP1 binding to the methylated H3, forms a positive feedback loop allowing HP1 and H3 K9 methylation to spread along chromatin, generating repressive heterochromatin in the process. (1) Reference ...
PubMed comprises more than 30 million citations for biomedical literature from MEDLINE, life science journals, and online books. Citations may include links to full-text content from PubMed Central and publisher web sites.
PubMed comprises more than 30 million citations for biomedical literature from MEDLINE, life science journals, and online books. Citations may include links to full-text content from PubMed Central and publisher web sites.
ATRX is a centromeric heterochromatin binding protein belonging to the SNF2 family of helicase/ATPases with chromatin remodeling activity. Mutations in the human ATRX gene result in X-linked alpha-thalassaemia with mental retardation (ATRX) syndrome and correlate with changes in methylation of repetitive DNA sequences. We show here that ATRX also functions to regulate key stages of meiosis in mouse oocytes. At the germinal vesicle (GV) stage, ATRX was found associated with the perinucleolar heterochromatin rim in transcriptionally quiescent oocytes. Phosphorylation of ATRX during meiotic maturation is dependent upon calcium calmodulin kinase (CamKII) activity. Meiotic resumption also coincides with deacetylation of histone H4 at lysine 5 (H4K5 Ac) while ATRX and histone H3 methylated on lysine 9 (H3K9) remained bound to the centromeres and interstitial regions of condensing chromosomes, respectively. Inhibition of histone deacetylases (HDACs) with trichostatin A (TSA) disrupted ATRX binding to the
Lakisic G, Lebreton A, Pourpre R, Wendling O, Libertini E, Radford EJ, Le Guillou M, Champy MF, Wattenhofer-Donzé M, Soubigou G, Ait-Si-Ali S, Feunteun J, Sorg T, Coppée JY, Ferguson-Smith AC, Cossart P, Bierne H*. Role of the BAHD1 Chromatin-Repressive Complex in Placental Development and Regulation of Steroid Metabolism. PLoS Genetics. 2016 Mar 3;12(3):e1005898.. Libertini E, Lebreton A, Lakisic G, Dillies MA, Beck S, Coppée JY, Cossart P, Bierne H*. Overexpression of the Heterochromatinization Factor BAHD1 in HEK293 Cells Differentially Reshapes the DNA Methylome on Autosomes and X Chromosome. ...
The ability of cloned embryos to sustain full-term development depends on the ability of the recipient ooplasm to reprogram the donor cell genome. As the nuclear architecture has recently emerged as a key-factor in the regulation of gene expression, we questioned whether early embryos obtained from transfer of ES metaphasic chromosomes into mouse ooplasm would adopt the somatic or embryonic type of nuclear organization. We have particularly focused on the arrangement of chromosomal territories with respect to the nucleolar compartment, and the pericentric heterochromatin domains called chromocenters. We found that nuclear transfer triggers profound chromatin rearrangements including the dispersion of the donor cell chromocenters components. These rearrangements lead to a typical 1-cell pronuclear organization, namely a radial arrangement of the chromosome territories with centromeres attached to the nucleoli, which adopt the compact fibrillar structure of nucleolar precursor bodies (NPBs). Subsequently,
At the nuclear envelope, the nuclear lamina and heterochromatin are adjacent to the inner nuclear membrane. CBX3 binds DNA and is a component of…
The major satellite DNA of Mus musculus appears as a pericentromeric heterochromatin block in all chromosomes but the Y. While C-banding readily reveals the presence of this heterochromatin block, there is considerable polymorphism in C-band size among the chromosomes and among different subspecies. We have studied the distribution of C-band size differences in the chromosomes of 15 exotic inbred laboratory strains and substrains derived from wild populations of different subspecies of M. musculus. The variation in C-band size among these inbred strains can serve as a useful codominant cytological marker for estimating recombinational distances between the centromere and proximal genes in linkage crosses.
Their existence has persisted for one important reason: they protect the DNA found at ends of chromosomes from being lost by deterioration which accompanies cell division until the cells reach a "critical level" of genetic information loss. It is at this critical level that cells stop dividing and the process of aging is first seen at a cellular level. Without telomeres protecting DNA from damage and mutation, cancer can also become prevalent. Telomeres are a lot like plastic shoe lace tips that prevent the lace from fraying.. Heterochromatin is a way of describing chromatin: it is tightly coiled, and the opposite is euchromatin. Heterochromatin is usually found towards the "sides" of a cell, in the periphery. Examples of heterochromatin include the Barr body of the female X chromosome, centromeres, and more importantly to this study, telomeres. It is thought that the functionality of heterochromatin is to protect DNA from damage by not allowing it to be exposed to DNA machinery.. When a ...
The region of a chromosome that includes the centromeric DNA and associated proteins. In monocentric chromosomes, this region corresponds to a single area of the chromosome, whereas in holocentric chromosomes, it is evenly distributed along the chromosome…
Genome-wide profiling and functional analyses reveal a network of heterochromatin and small RNA factors that silences repetitive elements and prevents genotoxic stress to ensure fertility.
Unfolding heterochromatin for replication. ATP-dependent chromatin remodeling complex, that regulates spacing of nucleosomes using ATP to generate evenly spaced nucleosomes along the chromatin. The ATPase activity of the complex is regulated by the length of flanking DNA. Also involved in facilitating the DNA replication process. BAZ1A is the accessory, non-catalytic subunit of the complex which can enhance and direct the process provided by the ATPase subunit, SMARCA5, probably through targeting pericentromeric heterochromatin in late S phase. Moves end-positioned nucleosomes to a predominantly central position. May have a role in nuclear receptor-mediated transcription repression ...
Inside the nucleus is one or several nucleoli surrounded by a matrix called the nucleoplasm. The nucleoplasm is a liquid with a gel-like consistency (similar in this respect to the cytoplasm), in which many substances are dissolved. These substances include nucleotide triphospates, enzymes, proteins, and transcription factors. There also exists a network of fibers in the nucleoplasm known as the nuclear matrix. Genetic material (DNA) is also present in the nucleus, the DNA is present as a DNA-protein complex called chromatin. The DNA is present as a number of discrete units known as chromosomes. There are two types of chromatin: euchromatin and heterochromatin. Euchromatin is the least compact form of DNA, and the regions of DNA which constitute euchromatin contain genes which are frequently expressed by the cell. In heterochromatin, DNA is more tightly compacted. Regions of DNA which constitute heterochromatin generally contain genes which are not expressed by the cell (this type of ...
Temporal control of DNA replication has been implicated in epigenetic regulation of gene expression on the basis of observations that certain tissue-specific genes replicate earlier in expressing than non-expressing cells. Here, we show evidence that several leukocyte-specific genes replicate early in lymphocytes regardless of their transcription and also in fibroblasts, where these genes are never normally expressed. Instead, the heritable silencing of some genes (Rag-1, TdT, CD8alpha and lambda5) and their spatial recruitment to heterochromatin domains within the nucleus of lymphocytes resulted in a markedly delayed resolution of sister chromatids into doublet signals discernable by 3D fluorescence in situ hybridization (FISH). Integration of transgenes within heterochromatin (in cis) did, however, confer late replication and this was reversed after variegated transgene expression. These findings emphasise that chromosomal location is important for defining the replication timing of genes and show