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 ...
ATRX is a member of the SNF2 family of helicase/ATPases that is thought to regulate gene expression via an effect on chromatin structure and/or function. Mutations in the hATRX gene cause severe syndromal mental retardation associated with alpha-thalassemia. Using indirect immunofluorescence and confocal microscopy we have shown that ATRX protein is associated with pericentromeric heterochromatin during interphase and mitosis. By coimmunofluorescence, ATRX localizes with a mouse homologue of the Drosophila heterochromatic protein HP1 in vivo, consistent with a previous two-hybrid screen identifying this interaction. From the analysis of a trap assay for nuclear proteins, we have shown that the localization of ATRX to heterochromatin is encoded by its N-terminal region, which contains a conserved plant homeodomain-like finger and a coiled-coil domain. In addition to its association with heterochromatin, at metaphase ATRX clearly binds to the short arms of human acrocentric chromosomes, where the arrays
One function of heterochromatin is the epigenetic silencing by sequestration of genes into transcriptionally repressed nuclear neighborhoods. Heterochromatin protein 1 (HP1) is a major component of heterochromatin and thus is a candidate for establishing and maintaining the transcriptionally repressive heterochromatin structure. Here we demonstrate that maintenance of stable heterochromatin domains in living cells involves the transient binding and dynamic exchange of HP1 from chromatin. HP1 exchange kinetics correlate with the condensation level of chromatin and are dependent on the histone methyltransferase Suv39h. The chromodomain and the chromoshadow domain of HP1 are both required for binding to native chromatin in vivo, but they contribute differentially to binding in euchromatin and heterochromatin. These data argue against HP1 repression of transcription by formation of static, higher order oligomeric networks but support a dynamic competition model, and they demonstrate that ...
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 ...
Packaging of DNA into chromatin is essential for the regulation of genome function in eukaryotes. Nucleosomes, the basic units of chromatin, are composed of ∼147 bp of DNA that is wrapped around an octomer built by four types of histones. Covalent modifications of histones, along with other factors, such as DNA methylation, chromatin-remodeling proteins, and small RNAs, contribute to the regulation of gene expression (Berger, 2007; Kouzarides, 2007; Berr et al., 2011). Heterochromatin is often used to refer to the parts of the genome that contain chromatin modifications associated with repression of gene expression. Constitutive heterochromatin describes regions of the genome that are stably maintained as heterochromatin throughout development and is often associated with 5-methylcytosine and H3K9me2 in plants (Bernatavichute et al., 2008). By contrast, facultative heterochromatin describes regions of the genome that exist as heterochromatin in some cell types and as euchromatin in other ...
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 two main forms of heterochromatin differ in structure slightly, which allows them to be better suited to the role they play. The material on this site can not be reproduced, distributed, transmitted, cached or otherwise used, except with prior written permission of Multiply. 6. When there is a DNA strand without heterochromatin, there is a possibility of endonucleases unnecessarily digesting that fragment. E) heterochromatin … Write. They also differ in their transcription and replication properties. It represents the major genes and isinvolved in transcription. chromatin. Nature News, Nature Publishing Group, Available here. Moreover, this is the main difference between heterochromatin and euchromatin as the latter has the characterization of light packing. Heterochromatin differs from euchromatin in that heterochromatin? Also, they both are associated with histone proteins. But, around 90% of the total human genome is euchromatin. All Rights Reserved. The chromatins are divided into ...
TY - JOUR. T1 - Detection of an altered heterochromatin structure in the absence of the nucleotide excision repair protein Rad4 in Saccharomtyces cerevisiae. AU - Zhang, Ling. AU - Chen, Hua. AU - Bi, Xin. AU - Gong, Feng. N1 - Funding Information: We thank Dr Charles Yanofsky, Dr Murray Deutscher and anonymous reviewers for critical reading of the manuscript and valuable comments. This work was supported by R01 ES017784 (To FG) and R01 GM62484 (To XB) from NIH.. PY - 2013/8/1. Y1 - 2013/8/1. N2 - Rad4p is a DNA damage recognition protein essential for global genomic nucleotide excision repair in Saccharomyces cerevisiae. Here, we show that Rad4p binds to the heterochromatic HML locus. In a yeast mutant lacking Rad4p, an increased level of SIR complex binding at the HML locus is accompanied by an altered, more compact heterochromatin structure, as revealed by a topological analysis of chromatin circles released from the locus. In addition, gene silencing at the HML locus is enhanced in the ...
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 ...
The transcriptional silencing of the cryptic mating-type loci in Saccharomyces cerevisiae is one of the best-studied models of repressive heterochromatin. However, this type of heterochromatin, which is mediated by the Sir proteins, has a distinct molecular composition compared to the more ubiquitous type of heterochromatin found in Schizosaccharomyces pombe, other fungi, animals, and plants and characterized by the presence of HP1 (heterochromatin protein 1). This review discusses how the loss of important heterochromatin proteins, including HP1, in the budding yeast lineage presented an evolutionary opportunity for the development and diversification of alternative varieties of heterochromatin, in which the conserved deacetylase Sir2 and the replication protein Orc1 play key roles. In addition, we highlight how this diversification has been facilitated by gene duplications and has contributed to adaptations in lifestyle. ...
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 ...
p,The PIWI-interacting RNA (piRNA) pathway protects genome integrity in part through establishing repressive heterochromatin at transposon loci. Silencing requires piRNA-guided targeting of nuclear PIWI proteins to nascent transposon transcripts, yet the subsequent molecular events are not understood. Here, we identify SFiNX (silencing factor interacting nuclear export variant), an interdependent protein complex required for Piwi-mediated cotranscriptional silencing in Drosophila. SFiNX consists of Nxf2-Nxt1, a gonad-specific variant of the heterodimeric messenger RNA export receptor Nxf1-Nxt1 and the Piwi-associated protein Panoramix. SFiNX mutant flies are sterile and exhibit transposon derepression because piRNA-loaded Piwi is unable to establish heterochromatin. Within SFiNX, Panoramix recruits heterochromatin effectors, while the RNA binding protein Nxf2 licenses cotranscriptional silencing. Our data reveal how Nxf2 might have evolved from an RNA transport receptor into a cotranscriptional ...
Regulation of gene transcription is central to developmental processes. By establishing and maintaining specific patterns of transcription, various pathways are co-ordinated for correct development of the organism. Primary control occurs through interactions between specific regulatory DNA sequences and a large variety of transcription factors. A higher order of control occurs through regulation of chromatin states. Position effect variegation in Drosophila is a well known example of how gene expression can be affected by chromatin organisation (Lu and Eissenberg, 1998). Heterochromatin-associated protein 1 (HP1) of Drosophila, is one of the key components in this phenomenon, and is involved in the generation and maintenance of an inactive heterochromatin structure that silences gene expression (Eissenberg and Elgin, 2000). Cell differentiation or developmental processes such as embryogenesis, also require chromatin modifications to maintain repression of homeotic genes mediated by ...
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 ...
Transposable elements (TEs) and DNA repeats are commonly targeted by DNA and histone methylation to achieve epigenetic gene silencing. We isolated mutations in two Arabidopsis genes, AtMORC1 and AtMORC6, which cause derepression of DNA-methylated genes and TEs but no losses of DNA or histone methylation. AtMORC1 and AtMORC6 are members of the conserved Microrchidia (MORC) adenosine triphosphatase (ATPase) family, which are predicted to catalyze alterations in chromosome superstructure. The atmorc1 and atmorc6 mutants show decondensation of pericentromeric heterochromatin, increased interaction of pericentromeric regions with the rest of the genome, and transcriptional defects that are largely restricted to loci residing in pericentromeric regions. Knockdown of the single MORC homolog in Caenorhabditis elegans also impairs transgene silencing. We propose that the MORC ATPases are conserved regulators of gene silencing in eukaryotes.. ...
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 ...
Heterochromatin protein 1 (HP1) of Drosophila and its homologs in vertebrates are key components of constitutive heterochromatin. Here we provide cytological evidence for the presence of heterochromatin within a euchromatic chromosome arm by immunolocalization of HP1 to the site of a silenced transg …
Conventional organization of a mammalian nucleus. Different landmarks contribute to genome segregation into functional compartments. The nuclear envelope defines the edge of the nucleus. The nuclear lamina is a meshwork of proteins that interact with heterochromatic genomic regions called lamina-associated domains (LADs), only interrupted by nuclear pore complexes (NPC). The two main other landmarks: the chromocenter, composed of clustered pericentromeric heterochromatin (PCH), and the nucleolus. (right) region of the nucleus with the histone marks associated with the different compartments. LADs at the periphery are enriched in H3K9me2/3 modifications and H3K27me3 at LAD borders. Heterochromatin regions show different levels of HP1 with higher concentration at PCH. The NPC interacts with euchromatin domains. Ac, acetylation; me2/3, di or tri-methylation; DNA 5mC, DNA methylation; HP1, Heterochromatin Protein 1; LBR, Lamin B Receptor; NET, Nuclear Envelope Transmembrane protein. After Canat , ...
The reason why we dont experience thousands of cancers every day in our body is because we have incredibly efficient molecular mechanisms that repair the frequent damages occurring in our DNA. But those that work in heterochromatin are quite extraordinary. said sciencedaily.com. Repeated sequences tend to recombine with each other during DNA repair, said Taehyun Ryu, USC graduate student and first author on this study. This would lead to chromosome aberrations as frequently observed in cancer cells. What prevents these outcomes in normal cells was unclear.. We knew that nuclear membrane dysfunctions are common in cancer cells, Chiolo said. Our studies now suggest how these dysfunctions can affect heterochromatin repair and have a causative role in cancer progression.. Working with the fruit fly Drosophila melanogaster, the team observed that breaks in heterochromatin are repaired after damaged sequences move away from the rest of the chromosome to the inner wall of the nuclear ...
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 ...
Distinct regions of the eukaryotic genome are packaged into different types of chromatin, with euchromatin representing gene rich, transcriptionally active regions and heterochromatin more condensed and gene poor. The assembly and maintenance of heterochromatin is important for many aspects of genom …
Analysis of cryosections of E7.5 embryos, and E11.5, E14.5 and E17.5 foetuses showed that despite the formation of the germ layers and increased structural complexity (Fig. 5, diagram) H4K20me3 and HP1α were not detected at E7.5, whereas H3K9me3 immunostaining was positive (Fig. 5, E7.5). In E11.5 foetuses, post mid-gestation (diagram), HP1α was detected as a weak and diffuse nuclear signal compared with that for H3K9me3, but H4K20me3 remains below detection levels (Fig. 5, E11.5). However, both HP1α and H4K20me3 were clearly present in E14.5 foetuses (Fig. 6A, E14.5) in derivatives of all three germ layers. At this stage, in brain tissue some cell nuclei contained weak dots whereas other cells stained in a diffuse pattern. At stage E17.5, both marks had adopted a strong heterochromatic pattern colocalising with DNA dense foci (Fig. 6A, E17.5 brain panels). A similar case was found in liver tissue, where the H4K20me3/HP1α heterochromatin foci seemed less abundant at E17.5 while diffuse ...
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 ...
Mammalian blood neutrophilic granulocytes are terminally differentiated cells, possessing extensive heterochromatin and lobulated (or ring-shaped) nuclei. Despite the extensive amount of heterochromatin, neutrophils are capable of increased gene expression, when activated by bacterial infection. Understanding the mechanisms of transcriptional repression and activation in neutrophils requires detailing the chromatin epigenetic markers, which are virtually undescribed in this cell type. Much is known about the heterochromatin epigenetic markers in other cell-types, permitting a basis for comparison with those of mature normal neutrophilic granulocytes. Immunostaining and immunoblotting procedures were employed to study the presence of repressive histone modifications and HP1 proteins in normal human and mouse blood neutrophils, and in vitro differentiated granulocytes of the mouse promyelocytic (MPRO) system. A variety of repressive histone methylation markers were detectable in these granulocytes (di-
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 ...
Mechanisms contributing to the maintenance of heterochromatin in proliferating cells are poorly understood. We demonstrate that chromatin assembly factor 1 (CAF-1) binds to mouse HP1 proteins via an N-terminal domain of its p150 subunit, a domain dispensable for nucleosome assembly during DNA replication. Mutations in p150 prevent association with HP1 in heterochromatin in cells that are not in S phase and the formation of CAF-1-HP1 complexes in nascent chromatin during DNA replication in vitro. We suggest that CAF-1 p150 has a heterochromatin-specific function distinct from its nucleosome assembly function during S phase. Just before mitosis, CAF-1 p150 and some HP1 progressively dissociate from heterochromatin concomitant with histone H3 phosphorylation. The HP1 proteins reassociate with chromatin at the end of mitosis, as histone H3 is dephosphorylated.. ...
Species in the subgenus Artibeus Leach, 1821 are widely distributed in Brazil. Conserved karyotypes characterize the group with identical diploid number and chromosome morphology. Recent studies suggested that the heterochromatin distribution and accumulation patterns can vary among species. In order to assess whether variation can also occur within species, we have analyzed the chromosomal distribution of constitutive heterochromatin in A. planirostris (Spix, 1823) and A. lituratus (Olfers, 1818) from Central Amazon (North Brazil) and contrasted our findings with those reported for other localities in Brazil. In addition, Ag-NOR staining and FISH with 18S rDNA, telomeric, and LINE-1 probes were performed to assess the potential role that these different repetitive markers had in shaping the current architecture of heterochromatic regions. Both species presented interindividual variation of constitutive heterochromatin. In addition, in A. planirostris the centromeres of most chromosomes are enriched
Normal cell division requires faithful DNA replication and proper DNA segregation in order to generate two identical daughter cells. Within cells DNA is always assembled with positively charged histones to form protein-DNA packaging structures called chromatin. The order of chromatin packaging regulates cellular functions including replication, gene expression and chromosome segregation. The compact chromatin region is called heterochromatin. The centromere is a rigid, gene-silent heterochromatin region and is essential for faithful chromosome segregation. To duplicate a cell, this region needs to be unpacked for replication and further be reassembled to maintain its function. I tackled how cells maintain faithful replication and reassembly at this region in S. pombe. ❧ I found that a replication protein Cdc18/Cdc6 associates with heterochromatin protein Swi6/HP1. A mutation cdc18-I43A that reduces Cdc18 association with Swi6 has no silencing defect at the centromere, but changes Swi6 ...
Structure wise, facultative heterochromatin is enriched with LINE sequences. and Georgatos, S.D. Despite being known for over 50 years, relatively few components of the Barr body have been identified. Calico or Tortoiseshell cat with mosaic fur (Photo Credit : Cheryl Toepfer/Shutterstock). XCI is facilitated by the upregulation of the long non-coding RNA gene, XIST, which coats its chromosome of origin, recruits heterochromatin factors, and silences gene expression. Females. The composition of the Barr body has been a matter of some conjecture for over 50 years. What are Mutations and what are the different types of Mutations? 5A). (, Kourmouli, N., Theodoropoulos, P.A., Dialynas, G., Bakou, A., Politou, A.S., Cowell, I.G., Singh, P.B. In addition, the lack of HP1 enrichment at the mouse Xi (21) may reflect the absence of a Barr body state in mouse cultured cells (4). How Big Is It and Does It Bite? To investigate the possibility that the Barr body in different cells is elevated for different ...
Because C. elegans chromosomes are holocentric and lack centromeric heterochromatin, HP1 proteins are dispensable for chromosome segregation and mitotic viability in this organism [23, 25]. We have exploited this fact to examine in detail the role of one of the C. elegans HP1 homologues, HPL-2, in regulating developmental pathways of gene expression, a second physiological function ascribed to heterochromatin. By comparing the effects of hpl-2 deletion at different stages of development, we have shed light on a novel role for this HP1 family member in dauer diapause, longevity and lipid metabolism. These three processes have in common an extremely tight response to environmental factors. Thus, our data link a response to environmental factors to the epigenetic regulator HPL-2. At least some of the genes identified in this study are shown by CHIP-on chip to be bound by HPL-2, and are therefore likely to represent direct targets.. We show that hpl-2 plays a role in the choice between dauer and ...
The SUMO protease SENP7 was recently proven to interact straight with Horsepower1 also to enable Horsepower1 retention and accumulation at pericentric heterochromatin without affecting H3K9me3 amounts (Maison et al, 2012; Romeo et al, 2015). bindings, SYCE2 interacts using the chromoshadow domains of Horsepower1 through its N-terminal hydrophobic series. SYCE2 reduces Horsepower1-H3K9me3 FN-1501 binding without impacting H3K9me3 amounts and potentiates ataxia telangiectasia mutatedCmediated double-strand break fix activity also in the lack of exogenous DNA harm. Such a somatic function of SYCE2 is noticed also if its expression levels are low ubiquitously. These findings claim that SYCE2 has a somatic function in the hyperlink between your nuclear microenvironment as well as the DNA harm response potentials being a scaffold of HP1 localization. Launch Meiosis is certainly a cell department procedure exclusive to germ cells and possesses some particular features distinctive from mitosis. The ...
The DNA in eukaryotes is arranged in fibres of chromatin. The chromatin may be more or less compacted and the degree of condensation of the chromatin affects the accessibility of the DNA. The accessibility of the DNA, in turn, affects transcription and gene regulation. Genes within inaccessible DNA are commonly repressed whereasgenes within accessible DNA are active and expressed. This thesis concerns the interplay between chromatin and transcription with focus on the function of the RNA polymerase II (pol II) subunit Rpb7. We have demonstrated that processing of centromeric transcripts by the ribonuclease III family protein Dcr1 is required for heterochromatin formation at the centromeres of Schizosaccharomyces pombe. A point mutation in the pol II subunit Rpb7 caused a specific defect in centromeric heterochromatin formation. We have shown i) that the centromeric transcripts that accumulate in dcr1delta cells are products of pol II, ii) the rpbG150D mutation is deficient in recognition and/or ...
In response to metabolic or environmental stress, cells activate powerful defense mechanisms to prevent the formation and accumulation of toxic protein aggregates. The main orchestrator of this cellular response is HSF1 (heat shock factor 1), a transcription factor involved in the up-regulation of protein-coding genes with protective roles. It has become very clear that HSF1 has a broader function than initially expected. Indeed, our previous work demonstrated that, upon stress, HSF1 activates the transcription of a non-coding RNA, named Satellite III, at pericentromeric heterochromatin. Here, we observe that the function of HSF1 extends to telomeres and identify subtelomeric DNA as a new genomic target of HSF1. We show that the binding of HSF1 to subtelomeric regions plays an essential role in the upregulation of non-coding TElomeric Repeat containing RNA (TERRA) transcription upon heat shock. Importantly, our data show that telomere integrity is impacted by heat shock and that telomeric DNA ...
Thus, Th17 differentiation requires active modulation of IL-2 expression both by cell-extrinsic and cell-intrinsic mechanisms.. The present paper from Kuchroos lab shows that, through STAT3 and AhR induction, Aiolos bounds to and silences the Il2 locus, suppressing the production of IL-2 and promoting Th17 differentiation in vitro and in vivo. The members of the Ikaros family are quite interesting since they directly promote transcription on some loci, but also have a strong impact on chromatin modification and can also actively silence genes by associating them to centromeric heterochromatin regions. And indeed, in Aiolos-deficient Th17 cells, the Il2 promoter was characterized by epigenetic modifications associated with active gene expression.. This is a formal demonstration of a role for an Ikaros family member in T cell differentiation ...
Core component of the CAF-1 complex, a complex thought to mediate chromatin assembly in DNA replication and DNA repair. Assembles histone octamers onto replicating DNA in vitro. CAF-1 performs the first step of the nucleosome assembly process, bringing newly synthesized histones H3 and H4 to replicating DNA; histones H2A/H2B can bind to this chromatin precursor subsequent to DNA replication to complete the histone octamer. CHAF1A binds to histones H3 and H4. It may play a role in heterochromatin maintenance in proliferating cells by bringing newly synthesized cbx proteins to heterochromatic DNA replication foci (By similarity).
To keep genome stability cells pack large portions of their genome into silent chromatin or heterochromatin. candida. The cryo-electron microscopy structure reveals the chromodomain of Chp1 binds the histone H3 lysine 9 methylated tail and the core of the nucleosome primarily histones H3 and H2B. Mutations in chromodomain of Chp1 loops which interact with the nucleosome core abolished this connection Moreover fission candida cells with Chp1 loop mutations have a defect in Chp1 recruitment and heterochromatin formation. This study reveals the structural basis for heterochromatic silencing and suggests that chromodomains could read histone code in the H3 tail and the nucleosome core which would provide an additional layer of rules. four chromodomain proteins are involved in heterochromatin formation and transcriptional gene silencing: Chp1 Chp2 Clr4 and Swi6. The chromodomain of Chp1 (Chp1CD) has the highest affinity for the H3K9me peptide and is essential for tethering the RITS complex to ...
Constitutive heterochromatin (HC) is important for maintaining chromosome stability, but also delays the repair of DNA double-strand breaks (DSBs). DSB repair in complex mammalian genomes involves a fast phase (2-6 h) in which most of the breaks are rapidly repaired, and a slow phase (up to 24 h) in which the remaining damages in HC are repaired. We found that p53 deficiency delays the slow-phase DNA repair after ionizing irradiation. p53 deficiency prevents downregulation of histone H3K9 trimethylation at the pericentric HC after DNA damage. Moreover, p53 directly induces expression of the H3K9 demethylase Jumonji domain 2 family demethylase (JMJD2b) through promoter binding. The p53 activation also indirectly downregulates expression of the H3K9 methyltransferase SUV39H1. Depletion of JMJD2b or sustained expression of SUV39H1 delays the repair of HC DNA and reduces clonogenic survival after ionizing irradiation. The results suggest that by regulating JMJD2b and SUV39H1 expression, p53 not only ...
Cells were treated with either UVA or TMP/UVA. a Sequential IP demonstrates association of early-replicating Alu sequences with DONSON and late-replicating Satellite 3 sequences with FANCM. LINE-1 elements replicate throughout the S phase and are found in all fractions. Representative blot (n = 3). b DONSON interaction with the H3K4me3 euchromatin mark is more frequent in early S phase cells than in late S phase, while there is little interaction with the H3K9me3 heterochromatin mark in either stage. Sorted early and late S phase cells were examined by PLA. Scored nuclei: PLA between GFP-D: H3K4me3 of early S phase = 67, late S phase = 64, PLA between GFP-D: H3K9me3 of early S phase = 70, late S phase = 85, from three biological replicates. Data are mean ± s.e.m. c FANCM interaction with H3K9me3 heterochromatin mark is biased toward late S phase, while there is low interaction frequency with H3K4me3 in either stage. Scored nuclei: PLA between FANCM: H3K4me3 of early S phase = 64, late S phase = ...
Mammalian telomeres are inherently heterochromatic. While enhanced telomere maintenance is evident in malignant cancers, some cancers appear to maintain telomeres by neither the common telomerase nor the alternative telomere repeat recombination mechanisms. Specifically, the roles of epigenetic modifications in telomere protection are largely unknown in human cancers. I have combined newly developed cellular and molecular approaches to show that in some cancer cell types, experimentally enhanced heterochromatinization localized specifically at telomeres reduced damage-induced foci at telomeres, suggesting augmentation of telomere stability. These results lead to the intriguing hypothesis that manipulating the epigenetic status at telomeres may be exploited to elicit damage at the telomeres of cancer cells as a novel approach to fight cancer. My current work in progress focuses on identifying novel chromatin modifiers that weaken telomere protection by modulating telomere compaction. It is ...
Sideridou M, Zakopoulou R, Evangelou K, Liontos M, Kotsinas A, Rampakakis E, Gagos S, Kahata K, Grabusic K, Gkouskou K, Trougakos IP, Kolettas E, Georgakilas AG, Volarevic S, Eliopoulos AG, Zannis-Hadjopoulos M, Moustakas A, Gorgoulis VG J. Cell Biol. 195 (7) 1123-1140 [2011-12-26; online 2011-12-28] E-cadherin (CDH1) loss occurs frequently in carcinogenesis, contributing to invasion and metastasis. We observed that mouse and human epithelial cell lines overexpressing the replication licensing factor Cdc6 underwent phenotypic changes with mesenchymal features and loss of E-cadherin. Analysis in various types of human cancer revealed a strong correlation between increased Cdc6 expression and reduced E-cadherin levels. Prompted by these findings, we discovered that Cdc6 repressed CDH1 transcription by binding to the E-boxes of its promoter, leading to dissociation of the chromosomal insulator CTCF, displacement of the histone variant H2A.Z, and promoter heterochromatinization. Mutational analysis ...
Autoimmune diseases are characterized by the presence of multiple autoantibodies that react with components of nuclear, cytoplasmic, or surface origin (for review see Nakamura and Tan, 1992; Fritzler, 1997). In clinical medicine, autoantibodies have been used to establish diagnosis, estimate prognosis, follow the progression of a specific autoimmune disease, and, finally, increase our knowledge of the pathophysiology of autoimmunity. In cell biology, autoantibodies have been extremely useful as probes for the identification of novel proteins and isolation of their corresponding genes. Human autoimmune sera have been particularly useful in the study of the eukaryotic nucleus where they have identified a wide range of nuclear antigens, including both single- and double-stranded DNA, RNA, histones, small nuclear RNA-binding proteins, transcription factors, nuclear lamins, heterochromatin-associated proteins, topoisomerase I and II, and centromere proteins (Tan, 1989, 1991; Earnshaw and Rattner, ...
Kishigami and colleagues [19] were the first to report that TSA treatment improves full term development of mouse embryos obtained by transfer of cumulus cell nuclei. This was confirmed the same year by Rybouchkin and colleagues who reported a remarkable and significant 5-fold increase in the efficiency of cloning from cumulus cells with a transient TSA treatment for 10 hours post activation [20]. In their initial work, Rybouchkin and colleagues suggested that increased acetylation of histones after TSA treatment was linked to the improved developmental rates [20]. In the present work, we confirm the reproducibility of the beneficial effects of TSA treatment on long term developmental potential using another mouse strain and different culture conditions, as reflected by a significantly higher birth rate of live pups. In our laboratory, 3.1% of the TSA-treated SCNT embryos developed to term, which is identical to the 3.1% of clones obtained from ES cells [26] and ten times higher than the ...
Publications related to biomolecular condensates, phase separation, llps and more. Developing strategies to activate tumor-cell-intrinsic immune response is critical for improving tumor immunotherapy by exploiting tumor vulnerability. KDM4A, as a histone H3 lysine 9 trimethylation (H3K9me3) demethylase, has been found to play a critical role in squamous cell carcinoma (SCC) growth and metastasis. Here we report that KDM4A inhibition promoted heterochromatin compaction and induced DNA replication stress, which elicited antitumor immunity in SCC. Mechanistically, KDM4A inhibition promoted the formation of liquid-like HP1γ puncta on heterochromatin and stall DNA replication, which activated tumor-cell-intrinsic cGAS-STING signaling through replication-stress-induced cytosolic DNA accumulation. Moreover, KDM4A inhibition collaborated with PD1 blockade to inhibit SCC growth and metastasis by recruiting and activating CD8+ T cells. In vivo lineage tracing demonstrated that KDM4A inhibition plus PD1 blockade
Fu et al. demonstrate a requirement for the heterochromatin factors CMT and DDM1 in RNA-directed DNA methylation in maize. Plant Cell https://doi.org/10.1105/
The constitutive heterochromatin of the centromere is marked by high levels of tri-methylated histone H3 Lysine 9 (H3K9) and binding of the heterochromatin protein 1 (HP1), which are thought to also have an important role in mitosis. Histone deacetylase inhibitors (HDACi) are a class of anticancer agents which affect many cellular processes, including mitosis. Here we examine the mechanism by which these drugs disrupt mitosis. We have used Drosophila embryos to demonstrate that treatment with the HDACi 100 μg/ml suberic bishydroxamic acid (SBHA, IC50 12 μg/ml), conditions that induce extensive H3K9 acetylation and aberrant mitosis in mammalian cells, induced aberrant mitosis in the absence of de novo transcription. We have examined the effect of the same treatment on the levels of H3K9 modification and HP1 binding in human cancer cells, and found only minor effects on H3K9 methylation and HP1 binding. Complete loss of tri-methylated H3K9 or depletion of HP1α and β had no effect on mitosis, ...
This chapter provides a general description of the types of genetic variation caused by transposable elements in animals and plants, and examines this variation within an evolutionary framework. It focuses on the variation induced by transposable elements in their host organisms. The host variation associated with transposable elements can result from several interconnected aspects of transposable element activity. Estimates of the frequencies of new transposable element-induced mutations have been made under laboratory conditions and varied over an enormous range. The partial or complete sterility associated with several systems of hybrid dysgenesis in Drosophila provides an interesting aspect of variation associated with transposable element activity. Heterochromatin proteins can recognize and silence transposable elements, some of which target heterochromatin for insertion. Thus, the evolution of heterochromatin could have led to a self-perpetuating expansion of domains rich in transposable elements.
Studencka, M.; Konzer, A.; Moneron, G.; Wenzel, D.; Opitz, L.; Salinas-Riester, G.; Bedet, C.; Krüger, M.; Hell, S. W.; Wisniewski, J. R. et al.; Schmidt, H.; Palladino, F.; Schulze, E.; Jedrusik-Bode, M. A.: Novel roles of Caenorhabditis elegans heterochromatin protein HP1 and linker histone in the regulation of innate immune gene expression. Molecular and Cellular Biology 32 (2), S. 251 - 265 (2012 ...
Studencka, M.; Konzer, A.; Moneron, G.; Wenzel, D.; Opitz, L.; Salinas-Riester, G.; Bedet, C.; Krüger, M.; Hell, S. W.; Wisniewski, J. R. et al.; Schmidt, H.; Palladino, F.; Schulze, E.; Jedrusik-Bode, M. A.: Novel roles of Caenorhabditis elegans heterochromatin protein HP1 and linker histone in the regulation of innate immune gene expression. Molecular and Cellular Biology 32 (2), pp. 251 - 265 (2012 ...
We also examined the H3-K9 methylation status of centromeric regions at the molecular level by native chromatin immunoprecipitation (NChIP). Compared with the classical formaldehyde cross-linked chromatin immunoprecipitation technique, this procedure has the advantage of avoiding the formaldehyde cross-linking step that can fix chromatin interactions that are transient or simply due to spatial proximity. For NChIP, native oligonucleosomes were prepared and purified after Mnase digestion of mouse cell nuclei (ONeill and Turner, 1995) to obtain a high enrichment in mononucleosome on bulk DNA visualized by EtBr (Fig. 4 C, Bulk DNA). Consistently, with the supposedly heterochromatic nature of centromeric regions, we find that these regions were more resistant to digestion, as attested by the detection of larger fragments when probing for major and to a lesser extent for minor satellite repeats when compared with bulk DNA (Fig. 4 C, compare minor and major to bulk). Detection of the larger ...
TY - JOUR. T1 - Precise centromere mapping using a combination of repeat junction markers and chromatin immunoprecipitation-polymerase chain reaction. AU - Luce, Amy C.. AU - Sharma, Anupma. AU - Mollere, Oliver S.B.. AU - Wolfgruber, Thomas K.. AU - Nagaki, Kiyotaka. AU - Jiang, Jiming. AU - Presting, Gernot G.. AU - Dawe, R. Kelly. PY - 2006/11/6. Y1 - 2006/11/6. N2 - Centromeres are difficult to map even in species where genetic resolution is excellent. Here we show that junctions between repeats provide reliable single-copy markers for recombinant inbred mapping within centromeres and pericentromeric heterochromatin. Repeat junction mapping was combined with anti-CENH3-mediated ChIP to provide a definitive map position for maize centromere 8.. AB - Centromeres are difficult to map even in species where genetic resolution is excellent. Here we show that junctions between repeats provide reliable single-copy markers for recombinant inbred mapping within centromeres and pericentromeric ...
The DEK oncoprotein is a chromatin architectural factor that has essential functions in the maintenance of heterochromatin integrity. It is an abundant and unique chromatin constituent showing no sequence homology to any other known protein, and is highly conserved among multicellular eukaryotes. DEK binds to DNA, RNA, and interacts with various chromatin components including histones. The affinity of DEK to its binding partners is determined by posttranslational modifications, predominantly by phosphorylation as well as poly(ADP-ribosyl)ation. When interacting with DNA, DEK preferentially binds to cruciform DNA structures which arise during perturbed DNA replication and the repair of DNA strand breaks.,br /,,br /,,br /,Several lines of evidence, among others the frequent overexpression in highly malignant tumors and the positive correlation between DEK expression levels and chemoresistance, have led to the definition of DEK as a bona fide oncogene. On the other hand, investigation of a ...
The sequencing of the human genome revealed that the C2H2-zinc finger proteins (ZFPs) are the largest family of human transcription factors. Around 300 members of this family contain, in addition to their zinc finger motifs, a KRAB domain that has been implicated in transcriptional repression. It is thought that KRAB-ZFPs mediate this effect through the recruitment of the corepressor KAP1, which induces facultative heterochromatin through the activity of several associated chromatin-modifying factors. Our studies focused on the elucidation of the molecular mechanisms of transcriptional repression induced by KRAB-ZFPs and KAP1. For this, we made use of the conditional binding activity of the KRAB-containing repressor tTRKRAB. This ectopic protein serves as a paradigm for endogenous KRAB-ZFP functions, as it depends on cellular KAP1 for transcriptional repression. tTRKRAB only binds to heterologous TetO sites in the absence of doxycycline, thus making repressor activity drug-regulated. When we targeted
Epigenetic modifications, such as acetylation, phosphorylation, methylation, ubiquitination, and ADP ribosylation, of the highly conserved core histones, H2A, H2B, H3, and H4, influence the genetic potential of DNA. The enormous regulatory potential of histone modification is illustrated in the vast array of epigenetic markers found throughout the genome. More than the other types of histone modification, acetylation and methylation of specific lysine residues on N-terminal histone tails are fundamental for the formation of chromatin domains, such as euchromatin, and facultative and constitutive heterochromatin. In addition, the modification of histories can cause a region of chromatin to undergo nuclear compartmentalization and, as such, specific epigenetic markers are non-randomly distributed within interphase nuclei. In this review, we summarize the principles behind epigenetic compartmentalization and the functional consequences of chromatin arrangement within interphase nuclei.. ...
Distinctive classes of small RNAs, 20 to 32 nucleotides long, play important regulatory roles for varied cellular processes. on small RNA cDNA library preparation and sequencing and ignited the finding of new users and families of small RNAs (15C24). Small RNAs, in association with their protein effector parts, mediate sequence-specific posttranscriptional and transcriptional gene rules. They control mRNA translation, stability and localization (examined in 87771-40-2 25, 26) and feed into processes that control 87771-40-2 transposons (examined in 27, 28) and heterochromatin structure (examined in 4, 29). This wide variety of functions activated great interest to recognize and characterize the tiny RNAs expressed in various organisms, cell and tissues types, in regular and disease state governments. Here we explain our protocols for the structure of little RNA libraries and their version for several high throughput sequencing strategies. The protocols result from strategies defined previously ...
Osteogenic lineage commitment is often evaluated by analyzing gene expression. However, many genes are transiently expressed during differentiation. The availability of genes for expression is influenced by epigenetic state, which affects the heterochromatin structure. DNA methylation, a form of epigenetic regulation, is stable and heritable. Therefore, analyzing methylation status may be less temporally dependent and more informative for evaluating lineage commitment. Here we analyzed the effect of mechanical stimulation on osteogenic differentiation by applying fluid shear stress for 24 hr to osteocytes and then applying the osteocyte-conditioned medium (CM) to progenitor cells. We analyzed gene expression and changes in DNA methylation after 24 hr of exposure to the CM using quantitative real-time polymerase chain reaction and bisulfite sequencing. With fluid shear stress stimulation, methylation decreased for both adipogenic and osteogenic markers, which typically increases availability of ...
Epigenetic mechanisms of gene regulation-chemical and conformational changes to DNA and the chromatin that bundles it-have had an important impact on genome organization and inheritance and on cell fate. These mechanisms are conserved in eukaryotes and provide an additional layer of information superimposed on the genetic code. Robert Martienssen, a pioneer in the study of epigenetics, investigates mechanisms involved in gene regulation and stem cell fate in yeast and model plants including Arabidopsis and maize. He and his colleagues have shed light on a phenomenon called position-effect variegation, caused by inactivation of a gene positioned near densely packed chromosomal material called heterochromatin. They have discovered that small RNA molecules arising from repeating genetic sequences program that heterochromatin. Martienssen and colleagues have described a remarkable process by which companion cells to sperm in plant pollen grains provide them with instructions that protect sperm DNA ...
Euchromatin is both transcriptionally and genetically active. Transitions between euchromatin and heterochromatin during DSB repair also impact transcription. Other DNA-containing material stains more lightly, diffusely across the interphase nucleus; it is called euchromatin. Histones are a family of proteins, described in Chapter 2.2, that form a complex with DNA called a nucleosome that is stabilized by the attraction of the negatively charged DNA to the positively charged histones. It is normal chromatin which possesses active genes. These findings help explain how TIP60 can be activated in transcriptionally active chromatin, which normally has low levels of H3K9me3. Pecinka et al. It is usually dispersed all around the nucleus and is replicated throughout the S phase. For example, in cancer cells tumor suppressor genes are hypermethylated resulting in unchecked cell growth (Baylin and Jones, 2011; Timp and Feinberg, 2013). Chromatin condensation is critical for maintaining transcriptional ...
Morphologically, there are two nuclear compartments: nuclear envelope and nucleoplasm. Nuclear envelope is the peripheral part of the nucleus that separates the interior of the nucleus, known as nucleoplasm, from the cytoplasm. Nucleoplasm-cytoplasm communication is regulated by nuclear pores, which are molecular complexes inserted in the nuclear envelope. In the nucleoplasm, DNA and associated proteins form the chromatin, which is referred as heterochromatin if it is highly condensed, or as euchromatin if it is loosely packaged. Heterochromatin and euchromatin are found in the same nucelus and the proportion of every of them depends on the type and physiological state of the cell. The nucleolus, a unique chromatin domain, is also found in the nucleoplasm, as well as other dense structures known as nuclear bodies, which are composed of chromatin and other proteins. Here, we could go into all the molecular processes involved in DNA transcription and replication, as well as gene regulation. In the ...
The X-IV translocation, [...], is shown to contain the wild-type allele, [...], at the white locus. This [...] has been replaced with a mutant gene, w, and a comparison of R([...])/w with R(w)/w[...] shows the former to give a variegated white phenotype while the latter is completely wild-type. It is concluded that the white variegation is due to an instability in the action of [...] when it is located in the rearranged chromosome ...
This year, our team attempted to engineer epigenetic control of gene expression. In eukaryotic cells, DNA is wound around nucleosomes, protein spools that consist of an octamer of histones. The DNA and protein together, termed chromatin, can be tightly packgaged (heterochromatin) or more loosely arranged (eucharomatin). The density of nucleosomal packaging is signaled by a host of histone modifying enzymes, and enforced by chromatin remodeling complexes. Euchromatin is accessible to the transcriptional machinery (active) while heterochromatin is inaccessible, and refractory to transcription (silenced).. In nature, the modulation of gene expression via the alteration of DNA structure is an incredibly powerful form of cellular memory. Indeed, epigenetic changes regulating genome-wide expression patterns can persist through multiple rounds of cell division and remain for the lifetime of the cell. This mechanism allows embryonic stem cells to differentiate into myriad cell types in higher ...
Heterochromatin, Drosophila, Drosophila Melanogaster, Chromatin, Gene, Chromosome, Genome, Histone, Proteins, Chromosomes, Maintenance, Methylation, Mutations, Position Effect Variegation, Egg, Lysine, Plays, Role, Chromosome 4, Euchromatin
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Uniprot: Component of heterochromatin that recognizes and binds histone H3 tails methylated at Lys-9 (H3K9me), leading to epigenetic repression. In contrast, it is excluded from chromatin when Tyr-41 of histone H3 is phosphorylated (H3Y41ph). Can interact with lamin-B receptor (LBR). This interaction can contribute to the association of the heterochromatin with the inner nuclear membrane. Involved in the formation of functional kinetochore through interaction with MIS12 complex proteins. more.. ...
In FSHD patient muscle, truncation of D4Z4 repeats does not significantly alter 4q35 localization to the heterochromatic rim. (A) Cytogenetic preparation of FSHD lymphoblastoid cells demonstrating different intensities of D4Z4 signals (green) at each 4q35 allele (red), permitting the mutant and wild-type alleles to be distinguished. (B) Both 4q35 alleles (green) in a mutant FSHD myoblast remain at the nuclear periphery depleted of hnRNA (red). (C) Localization of wild-type (arrow) and mutant (arrowhead) alleles in a FSHD myoblast using the same probes as in A. DAPI (blue) delineates the nucleus. (D) Quantitation of the localization of mutant (mut) versus wild-type (wt) allele in three FSHD myoblast cell lines (GM 17731, GM17899, and GM17869A) and in a normal myoblast line (50MB-1) before and after differentiation. 100 cells analyzed per sample. Localization of 4q35 (red) in a normal (E) and a FSHD myotube (F) with more intense D4Z4 signal (green) demarcating wild type versus weaker mutant 4q35 ...
This gene encodes an evolutionarily-conserved protein containing an N-terminal chromodomain and a C-terminal SET domain. The encoded protein is a histone methyltransferase that trimethylates lysine 9 of histone H3, which results in transcriptional gene silencing. Loss of function of this gene disrupts heterochromatin formation and may cause chromosome instability. Alternative splicing results in multiple transcript variants. [provided by RefSeq, Aug 2013 ...
Researchers have shown the fundamental role of the heterochromatin protein 1a (HP1a) in the reorganization of the 3D chromatin structure after fertilization. By combining powerful Drosophila genetics with 3D genome modeling, they discovered that HP1a is required to establish a proper chromatin 3D structure at multiple hierarchical levels during early embryonic development.
Heterochromatin - chromatin organisation, lines the nuclear membrane at the pores. Euchromatin - threadlike, delicate, abundant in active transcribed cells, regions of DNA to be transcribed or duplicated, must be coiled before genetic code can be read.. All the human bodys nucleated cells contain 46 chromosomes (23 pairs). Contain all the information that governs all cellular activitys. DNA molecules - form of genes. DNA molecule regulate specific functions. blueprint determines synthesis of an RNA molecule or polypeptide. Not visible in non dividing cells. ...
New study finds the chromatin structures (heterochromatin and euchromatin) may not be determinate of whether genes in a particular region of a chromosome get expressed. | Cell And Molecular Biology