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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 ...
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 ...
International Human Genome Sequencing Consortium. Finishing the euchromatic sequence of the human genome. Nature. 2004 Oct 21;431(7011):931-45. PMID: [1] ...
The International Tomato Genome Sequencing Project was begun in 2004 by an international consortium including participants from Korea, China, the United Kingdom, India, the Netherlands, France, Japan, Spain, Italy and the United States. The initial approach was to sequence only the euchromatic sequence using a BAC-by-BAC approach, and in total more than 1,200 BACs have been sequenced. In 2009, a complementary whole-genome shotgun approach was initiated, which in conjunction with other data yielded high quality assemblies. The International Tomato Annotation Group (ITAG) annotates the genome builds generated by this combined sequencing approach. ...
Heterochromatin is a type of tightly-coiled chromosomal material that carries genes. Although heterochromatin is largely inert...
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
From BioPortfolio: Constitutive heterochromatin is an important component of eukaryotic genomes that has essential roles in nuclear architecture, DNA repair and genome stability, ...
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 ...
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
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 ...
The Berkeley Drosophila Genome Project (BDGP) is a consortium of the Drosophila Genome Center, whose goals are to finish the sequence of the euchromatic genome of Drosophila melanogaster to high quality and to generate and maintain biological annotations of this sequence. In addition to genomic sequencing, the BDGP is 1) producing gene disruptions using P element-mediated mutagenesis on a scale unprecedented in metazoans; 2) characterizing the sequence and expression of cDNAs; and 3) developing informatics tools that support the experimental process, identify features of DNA sequence, and allow us to present up-to-date information about the annotated sequence to the research community ...
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 ...
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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 ...
TY - JOUR. T1 - Achiasmatic meiosis and complex heterozygosity in female cyclopoid copepods (Copepoda, Crustacea). AU - Chinnappa, C. C.. AU - Victor, Reginald. PY - 1979/1. Y1 - 1979/1. N2 - In Mesocyclops edax S.A. Forbes, 2n=14, a North American copepod, the females are heterozygous for several interchanges leading to the formation of large rings of chromosomes (rings of 14, or of 12 plus 1 bivalent) at meiotic metaphase, comparable to those of the plant Oenothera, although no chiasmata are present. The chromosomes are more or less metacentric and have large terminal H-segments. In the rings homologous arms are held together by connecting fibers which insert close to the euchromatin-heterochromatin junctions. Coordinated orientation of the zigzag type seems to be the role.. AB - In Mesocyclops edax S.A. Forbes, 2n=14, a North American copepod, the females are heterozygous for several interchanges leading to the formation of large rings of chromosomes (rings of 14, or of 12 plus 1 bivalent) at ...
Here we present computational machinery to efficiently and accurately identify transposable element (TE) insertions in 146 next-generation sequenced inbred strains of Drosophila melanogaster. The panel of lines we use in our study is composed of strains from a pair of genetic mapping resources: the Drosophila Genetic Reference Panel (DGRP) and the Drosophila Synthetic Population Resource (DSPR). We identified 23,087 TE insertions in these lines, of which 83.3% are found in only one line. There are marked differences in the distribution of elements over the genome, with TEs found at higher densities on the X chromosome, and in regions of low recombination. We also identified many more TEs per base pair of intronic sequence and fewer TEs per base pair of exonic sequence than expected if TEs are located at random locations in the euchromatic genome. There was substantial variation in TE load across genes. For example, the paralogs derailed and derailed-2 show a significant difference in the number ...
The goals of the Drosophila Genome Center are to finish the sequence of the euchromatic genome of Drosophila melanogaster to high quality and to generate and maintain biological annotations of this sequence. In addition to genomic sequencing, the BDGP is 1) producing gene disruptions using P element-mediated mutagenesis on a scale unprecedented in metazoans; 2) characterizing the sequence and expression of cDNAs; and 3) developing informatics tools that support the experimental process, identify features of DNA sequence, and allow us to present up-to-date information about the annotated sequence to the research community. [Information of the supplier ...
Mr Kuntrapaka Srinivas, Consultant Orthopaedic Surgeon, MBBS, MS (Orth), MCh (Orth), FRCS, FRCS (Tr&Orth) at Spire Healthcare. Learn more about this consultant here.
MacroH2A is a histone H2A variant that is typically found in heterochromatic regions of the genome. A positively charged linker that connects the histone-fold with the macro-domain was suggested to have DNA-binding ...
MacroH2A is a histone H2A variant that is typically found in heterochromatic regions of the genome. A positively charged linker that connects the histone-fold with the macro-domain was suggested to have DNA-binding ...
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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 ...
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 ...
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,
Contingency genes are common in pathogenic microbes and enable, through pre-emptive mutational events, rapid, clonal switches in phenotype that are conducive to survival and proliferation in hosts. Antigenic variation, which is a highly successful survival strategy employed by eubacterial and eukaryotic pathogens, involves large repertoires of distinct contingency genes that are expressed differentially, enabling evasion of host acquired immunity. Most, but not all, antigenic variation systems make extensive use of subtelomeres. Study of model systems has shown that subtelomeres have unusual properties, including reversible silencing of genes mediated by proteins binding to the telomere, and engagement in ectopic recombination with other subtelomeres. There is a general theory that subtelomeric location confers a capacity for gene diversification through such recombination, although experimental evidence is that there is no increased mitotic recombination at such loci and that sequence ...
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 ...
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 ...
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 ...
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 ...
Werner syndrome (WS) is a premature aging disorder caused by WRN protein deficiency. Here, we report on the generation of a human WS model in human embryonic stem cells (ESCs). Differentiation of WRN-null ESCs to mesenchymal stem cells (MSCs) recapitulates features of premature cellular aging, a global loss of H3K9me3, and changes in heterochromatin architecture. We show that WRN associates with heterochromatin proteins SUV39H1 and HP1α and nuclear lamina-heterochromatin anchoring protein LAP2β. Targeted knock-in of catalytically inactive SUV39H1 in wild-type MSCs recapitulates accelerated cellular senescence, resembling WRN-deficient MSCs. Moreover, decrease in WRN and heterochromatin marks are detected in MSCs from older individuals. Our observations uncover a role for WRN in maintaining heterochromatin stability and highlight heterochromatin disorganization as a potential determinant of human aging. ...
We report here the molecular and cytological characterization of two proteins, ScoHET1 and ScoHET2 (for Sciara coprophila heterochromatin), which associate to constitutive heterochromatin in the dipteran S. coprophila. Both proteins, ScoHET1 of 37 kDa and ScoHET2 of 44 kDa, display two chromodomain motifs that contain the conserved residues essential for the recognition of methylated histone H3 at lysine 9. We raised antibodies to analyze the chromosomal location of ScoHET1 and ScoHET2 in somatic and germline cells. In S. coprophila polytene chromosomes, both proteins associate to the pericentromeric regions and to the heterochromatic subterminal bands of the chromosomes. In germinal nuclei, ScoHET1 and ScoHET2 proteins distribute to the heterochromatic regions of the regular chromosome complement and are abundantly present along the heterochromatic germline-limited
The rapid increase in levels of the various heterochromatin markers might be a stress response of the cells to the scratch. However, histone modifications that are induced by the stress response, such as phosphorylated Ser10 and Ser28 in histone H3 (H3S10p, H3S28p), are not associated with heterochromatin formation (Soloaga et al., 2003). Moreover, stress-response-associated histone modifications are usually increased for a relatively short period of time (1-2 hours) (Lim et al., 2004; Soloaga et al., 2003), whereas the heterochromatin-associated markers that were induced by migration signals lasted at their relatively high level for as long as 25 hours (Fig. 4). Therefore, our results suggest that the increase in the level of the heterochromatin markers is not a stress-related response, but rather a response to the migration signals.. The importance of increased heterochromatin formation and chromatin condensation for cell migration was verified by the experiments in which directed migration of ...
... , Zak Orth biography, cast member profile, filmography, and high-quality photo. Sasha Pieterse Talks About Health Struggles and Weight Loss on Dancing with. Cast Freddie Prinze Jr., Julia Stiles, Selma Blair, Shawn Hatosy, Zak Orth, Rosario. Stiles and Prinze are asked to carry a lot of weight in Down To You, which.
Production for the third, " Versace ", is slated to begin next month with an expected air date in 2018. The true-crime book was writtenby Vanity Fairs Maureen Orth , who was already covering other crimes Cunanan was suspected of committing before... More... ...
My journey started as a teenager. I was offered jaw surgery to correct an underbite. My parents turned it down as it was such a risky surgery. My orth
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
The recent completion of the Drosophila melanogaster genomic sequence to high quality and the availability of a greatly expanded set of Drosophila cDNA sequences, aligning to 78% of the predicted euchromatic gene... Authors: Sima Misra, Madeline A Crosby, Christopher J Mungall, Beverley B Matthews, Kathryn S Campbell, Pavel Hradecky, Yanmei Huang, Joshua S Kaminker, Gillian H Millburn, Simon E Prochnik, Christopher D Smith, Jonathan L Tupy, Eleanor J Whitfield, Leyla Bayraktaroglu, Benjamin P Berman, Brian R Bettencourt…. ...
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 ...
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
A characteristic of RdDM is CHH methylation, which is catalysed by DRM2. Therefore, we examined whether DRM2 is involved in the non‐CG hypermethylation in VN by using an equivalent bisulphite sequencing analysis with the sorted drm2 pollen nuclei. To evaluate the effect of mutation, we compared the number of hypermethylated non‐CG sites and percentage of mC between the wild‐type and mutant VN. We defined hypermethylated non‐CG sites in VN in pollen as the CHH or CHG sites that are methylated in more cloned DNA sequences from VN than from SN. We found a marked decrease in the number of hypermethylated non‐CG sites in both the 180CEN and Athila sequences analysed from drm2 VN (Fig 2B). Specifically, 12 CHH sites and 1 CHG site in the 180CEN sequences, and 7 CHH sites and 1 CHG site in the Athila sequences showed loss of hypermethylation in drm2 in comparison with wild‐type VN. In addition, many of the CHH sites that remained methylated in drm2 VN showed a lower percentage of mC than ...
Mr Maneesh Bhatia, Orthopaedic Surgeon, MBBS, MS (Orth), FRCSEd, FRCS (Tr & Orth) at Spire Healthcare. Learn more about this consultant here.
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
Heterochromatin, Drosophila, Drosophila Melanogaster, Chromatin, Gene, Chromosome, Genome, Histone, Proteins, Chromosomes, Maintenance, Methylation, Mutations, Position Effect Variegation, Egg, Lysine, Plays, Role, Chromosome 4, Euchromatin
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.
Professor Orth studies cancer therapies at the molecular and cellular level. During anti-cancer drug response there is often a disconnect in understanding molecular responses in cells and their fates. This is due to profound heterogeneity within the cancer cell population and tremendous variability in drug response that is difficult to study directly. These characteristics of cancer cells limits our ability to most effectively treat them, and could help explain drug resistance and treatment failure. Quantitative microscopy can add significantly to our understanding of therapeutic action. We relentlessly pursue how to apply advanced microscopy to the problem of cancer and develop single cell assays that allow us to study anti-cancer drug mechanism as it occurs. Through a direct and longitudinal approach, we develop a mechanistic model where we account for the response and fate of every single cell within a population. This powerful approach can be extended to in vivo tumor models ...
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 ...
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 ...
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 ...
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