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Journal articles on the topic 'Chromatinas'
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1
Ishak, Muhiddin, Rashidah Baharudin, Isa Mohamed Rose, et al. "Genome-Wide Open Chromatin Methylome Profiles in Colorectal Cancer." Biomolecules 10, no. 5 (2020): 719. http://dx.doi.org/10.3390/biom10050719.
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The methylome of open chromatins was investigated in colorectal cancer (CRC) to explore cancer-specific methylation and potential biomarkers. Epigenome-wide methylome of open chromatins was studied in colorectal cancer tissues using the Infinium DNA MethylationEPIC assay. Differentially methylated regions were identified using the ChAMP Bioconductor. Our stringent analysis led to the discovery of 2187 significant differentially methylated open chromatins in CRCs. More hypomethylated probes were observed and the trend was similar across all chromosomes. The majority of hyper- and hypomethylated probes in open chromatin were in chromosome 1. Our unsupervised hierarchical clustering analysis showed that 40 significant differentially methylated open chromatins were able to segregate CRC from normal colonic tissues. Receiver operating characteristic analyses from the top 40 probes revealed several significant, highly discriminative, specific and sensitive probes such as OPLAH cg26256223, EYA4 cg01328892, and CCNA1 cg11513637, among others. OPLAH cg26256223 hypermethylation is associated with reduced gene expression in the CRC. This study reports many open chromatin loci with novel differential methylation statuses, some of which with the potential as candidate markers for diagnostic purposes.
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Fujii, Wataru, and Hiroaki Funahashi. "In vitro development of non-enucleated rat oocytes following microinjection of a cumulus nucleus and chemical activation." Zygote 16, no. 2 (2008): 117–25. http://dx.doi.org/10.1017/s0967199408004632.
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SummaryThe present study examined in vitro development and the cytological status of non-enucleated rat oocytes after microinjection of cumulus nuclei and chemical activation. Oocyte–cumulus complexes were collected from gonadotropin-treated prepubertal female Wistar rats 14 h after human chorionic gonadotropin (hCG) injection. Cumulus nuclei were injected into ovulated oocytes and then stimulated in the presence of 5 mM SrCl2 for 20 min at various time points (0–3.5 h) after injection. Some of the reconstituted eggs were cultured to observe the pronuclear formation, cleavage, and blastocyst formation. The incidences of eggs forming at least one pronucleus or containing two pronuclei were not significantly different among the periods (82.4–83.5% and 43.4–51.9%, respectively). Nor did the incidences of eggs cleaving (86.7–97.7%) and developing to the blastocyst stage (0–3.5%) differ depending on when, after injection, stimulation began. When some of the reconstituted eggs were observed for cytological morphology 1–1.5 h after injection, 71.7% of the eggs caused premature chromatin condensation, but only 46.2% of them formed two spindles around each of maternal and somatic chromatins. However, the morphology of the somatic spindles differed from that of the spindles, which formed around the oocyte chromatins. Only 7.5% of the eggs contained the normal chromosomal number. In many reconstituted oocytes, before activation, an abnormal spindle formation was observed in the somatic chromatins. In conclusion, these results show that non-enucleated rat oocytes injected with cumulus nuclei can form pronuclei and cleave following chemical activation, whereas blastocyst formation is very limited, probably caused by abnormalities in the spindle formation and distribution of somatic chromatids.
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Daban, Joan-Ramon. "The energy components of stacked chromatin layers explain the morphology, dimensions and mechanical properties of metaphase chromosomes." Journal of The Royal Society Interface 11, no. 92 (2014): 20131043. http://dx.doi.org/10.1098/rsif.2013.1043.
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The measurement of the dimensions of metaphase chromosomes in different animal and plant karyotypes prepared in different laboratories indicates that chromatids have a great variety of sizes which are dependent on the amount of DNA that they contain. However, all chromatids are elongated cylinders that have relatively similar shape proportions (length to diameter ratio approx. 13). To explain this geometry, it is considered that chromosomes are self-organizing structures formed by stacked layers of planar chromatin and that the energy of nucleosome–nucleosome interactions between chromatin layers inside the chromatid is approximately 3.6 × 10 −20 J per nucleosome, which is the value reported by other authors for internucleosome interactions in chromatin fibres. Nucleosomes in the periphery of the chromatid are in contact with the medium; they cannot fully interact with bulk chromatin within layers and this generates a surface potential that destabilizes the structure. Chromatids are smooth cylinders because this morphology has a lower surface energy than structures having irregular surfaces. The elongated shape of chromatids can be explained if the destabilizing surface potential is higher in the telomeres (approx. 0.16 mJ m −2 ) than in the lateral surface (approx. 0.012 mJ m −2 ). The results obtained by other authors in experimental studies of chromosome mechanics have been used to test the proposed supramolecular structure. It is demonstrated quantitatively that internucleosome interactions between chromatin layers can justify the work required for elastic chromosome stretching (approx. 0.1 pJ for large chromosomes). The high amount of work (up to approx. 10 pJ) required for large chromosome extensions is probably absorbed by chromatin layers through a mechanism involving nucleosome unwrapping.
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Chen, Yu-Fan, Chia-Ching Chou, and Marc R. Gartenberg. "Determinants of Sir2-Mediated, Silent Chromatin Cohesion." Molecular and Cellular Biology 36, no. 15 (2016): 2039–50. http://dx.doi.org/10.1128/mcb.00057-16.
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Cohesin associates with distinct sites on chromosomes to mediate sister chromatid cohesion. Single cohesin complexes are thought to bind by encircling both sister chromatids in a topological embrace. Transcriptionally repressed chromosomal domains in the yeastSaccharomyces cerevisiaerepresent specialized sites of cohesion where cohesin binds silent chromatin in a Sir2-dependent fashion. In this study, we investigated the molecular basis for Sir2-mediated cohesion. We identified a cluster of charged surface residues of Sir2, collectively termed the EKDK motif, that are required for cohesin function. In addition, we demonstrated that Esc8, a Sir2-interacting factor, is also required for silent chromatin cohesion. Esc8 was previously shown to associate with Isw1, the enzymatic core of ISW1 chromatin remodelers, to form a variant of the ISW1a chromatin remodeling complex. WhenESC8was deleted or the EKDK motif was mutated, cohesin binding at silenced chromatin domains persisted but cohesion of the domains was abolished. The data are not consistent with cohesin embracing both sister chromatids within silent chromatin domains. Transcriptional silencing remains largely intact in strains lackingESC8or bearing EKDK mutations, indicating that silencing and cohesion are separable functions of Sir2 and silent chromatin.
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Pinkaew, Aeggarut, Tulaya Limpiti, and Akraphon Trirat. "Chromatin Detection in Malaria Thick Blood Film Using Automated Image Processing." Applied Mechanics and Materials 781 (August 2015): 616–19. http://dx.doi.org/10.4028/www.scientific.net/amm.781.616.
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Malaria is a serious global health problem and rapid, accurate diagnosis is required to control the disease. An image processing algorithm to aid the diagnosis of malaria on thick blood films is developed. Morphological and automatic threshold selection techniques are applied on two color components from the HSI color model to identify chromatins of P. Falciparum and P. Vivax malaria species on the images. Chromatins are positively identified with good sensitivities for both species. After identifying the position of chromatins, the algorithm splits the image into small sub-images, each with a chromatin in the center. These small images can subsequently be used by technician to classify malaria species more conveniently.
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Oomen, Marlies E., Adam K. Hedger, Jonathan K. Watts, and Job Dekker. "Detecting chromatin interactions between and along sister chromatids with SisterC." Nature Methods 17, no. 10 (2020): 1002–9. http://dx.doi.org/10.1038/s41592-020-0930-9.
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Pelzer, J., B. Bohrmann, R. Johansen, et al. "Structure and function of nonorthodox chromatins: I. aggregation sensitivity of DNA is correlated to the Protein content of chromosomal material." Proceedings, annual meeting, Electron Microscopy Society of America 48, no. 3 (1990): 120–21. http://dx.doi.org/10.1017/s0424820100158145.
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Aggregation insensitive eukaryotic chromatin in which DNA is associated with histones can be crosslinked by all fixatives commonly used in electron microscopy. By crosslinking it becomes protected from aggregation during dehydration with organic solvents. This is not the case with most nonorthodox chromatins, where the ratio of protein to DNA is estimated to be 5 to 10 times lower and where the basic, acid-soluble proteins are rather different from the histones. The aggregation sensitivity of different chromatins is summarized in table 1.Nonorthodox aggregation sensitive chromatins were found in Eubacteria, bacteriophage- pools (fig. 1a,b), Cyanobacteria, mitochondria, and Dinoflagellates (fig. 2a,b). The latter organisms are of particular interest because of morphologic similarities to other flagellates like Euglena with its aggregation insensitive histone-containing chromosomes (fig. 3a,b). With respect to the distribution over the living world, nonorthodox chromatins might be more frequent than the histone-containing ones.
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Lawrimore, Josh, Ayush Doshi, Brandon Friedman, Elaine Yeh, and Kerry Bloom. "Geometric partitioning of cohesin and condensin is a consequence of chromatin loops." Molecular Biology of the Cell 29, no. 22 (2018): 2737–50. http://dx.doi.org/10.1091/mbc.e18-02-0131.
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SMC (structural maintenance of chromosomes) complexes condensin and cohesin are crucial for proper chromosome organization. Condensin has been reported to be a mechanochemical motor capable of forming chromatin loops, while cohesin passively diffuses along chromatin to tether sister chromatids. In budding yeast, the pericentric region is enriched in both condensin and cohesin. As in higher-eukaryotic chromosomes, condensin is localized to the axial chromatin of the pericentric region, while cohesin is enriched in the radial chromatin. Thus, the pericentric region serves as an ideal model for deducing the role of SMC complexes in chromosome organization. We find condensin-mediated chromatin loops establish a robust chromatin organization, while cohesin limits the area that chromatin loops can explore. Upon biorientation, extensional force from the mitotic spindle aggregates condensin-bound chromatin from its equilibrium position to the axial core of pericentric chromatin, resulting in amplified axial tension. The axial localization of condensin depends on condensin’s ability to bind to chromatin to form loops, while the radial localization of cohesin depends on cohesin’s ability to diffuse along chromatin. The different chromatin-tethering modalities of condensin and cohesin result in their geometric partitioning in the presence of an extensional force on chromatin.
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Matioli, G. T. "Repositioning of entangled chromatin during separation of sister chromatids by eversion." Medical Hypotheses 54, no. 1 (2000): 47–50. http://dx.doi.org/10.1054/mehy.1998.0826.
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Giménez-Abián, J. F., D. J. Clarke, A. M. Mullinger, C. S. Downes, and R. T. Johnson. "A postprophase topoisomerase II-dependent chromatid core separation step in the formation of metaphase chromosomes." Journal of Cell Biology 131, no. 1 (1995): 7–17. http://dx.doi.org/10.1083/jcb.131.1.7.
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Metaphase chromatids are believed to consist of loops of chromatin anchored to a central scaffold, of which a major component is the decatenatory enzyme DNA topoisomerase II. Silver impregnation selectively stains an axial element of metaphase and anaphase chromatids; but we find that in earlier stages of mitosis, silver staining reveals an initially single, folded midline structure, which separates at prometaphase to form two chromatid axes. Inhibition of topoisomerase II prevents this separation, and also prevents the contraction of chromatids that occurs when metaphase is arrested. Immunolocalization of topoisomerase II alpha reveals chromatid cores analogous to those seen with silver staining. We conclude that the chromatid cores in early mitosis form a single structure, constrained by DNA catenations, which must separate before metaphase chromatids can be resolved.
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Stephens, Andrew D., Rachel A. Haggerty, Paula A. Vasquez, et al. "Pericentric chromatin loops function as a nonlinear spring in mitotic force balance." Journal of Cell Biology 200, no. 6 (2013): 757–72. http://dx.doi.org/10.1083/jcb.201208163.
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The mechanisms by which sister chromatids maintain biorientation on the metaphase spindle are critical to the fidelity of chromosome segregation. Active force interplay exists between predominantly extensional microtubule-based spindle forces and restoring forces from chromatin. These forces regulate tension at the kinetochore that silences the spindle assembly checkpoint to ensure faithful chromosome segregation. Depletion of pericentric cohesin or condensin has been shown to increase the mean and variance of spindle length, which have been attributed to a softening of the linear chromatin spring. Models of the spindle apparatus with linear chromatin springs that match spindle dynamics fail to predict the behavior of pericentromeric chromatin in wild-type and mutant spindles. We demonstrate that a nonlinear spring with a threshold extension to switch between spring states predicts asymmetric chromatin stretching observed in vivo. The addition of cross-links between adjacent springs recapitulates coordination between pericentromeres of neighboring chromosomes.
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Soltanzadeh, Ramin, Hossein Rabbani, and Ardeshir Talebi. "Extraction of Nucleolus Candidate Zone in White Blood Cells of Peripheral Blood Smear Images Using Curvelet Transform." Computational and Mathematical Methods in Medicine 2012 (2012): 1–12. http://dx.doi.org/10.1155/2012/574184.
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The main part of each white blood cell (WBC) is its nucleus which contains chromosomes. Although white blood cells (WBCs) with giant nuclei are the main symptom of leukemia, they are not sufficient to prove this disease and other symptoms must be investigated. For example another important symptom of leukemia is the existence of nucleolus in nucleus. The nucleus contains chromatin and a structure called the nucleolus. Chromatin is DNA in its active form while nucleolus is composed of protein and RNA, which are usually inactive. In this paper, to diagnose this symptom and in order to discriminate between nucleoli and chromatins, we employ curvelet transform, which is a multiresolution transform for detecting 2D singularities in images. For this reason, at first nuclei are extracted by means ofK-means method, then curvelet transform is applied on extracted nuclei and the coefficients are modified, and finally reconstructed image is used to extract the candidate locations of chromatins and nucleoli. This method is applied on 100 microscopic images and succeeds with specificity of 80.2% and sensitivity of 84.3% to detect the nucleolus candidate zone. After nucleolus candidate zone detection, new features that can be used to classify atypical and blast cells such as gradient of saturation channel are extracted.
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Tate, Shin-ichi. "Establishing a model to demonstrate physical and mathematical properties of chromatin fibres in fission yeast cells - Research in the Molecular Biophysics Lab at Hiroshima University." Impact 2018, no. 3 (2018): 89–91. http://dx.doi.org/10.21820/23987073.2018.3.89.
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The field of molecular biology has provided great insights into the structure and function of key molecules. Thanks to this area of research, we can now grasp the biological details of DNA and have characterised an enormous number of molecules in massive data bases. These 'biological periodic tables' have allowed scientists to connect molecules to particular cellular events, furthering scientific understanding of biological processes. However, molecular biology has yet to answer questions regarding 'higher-order' molecular architecture, such as that of chromatin. Chromatin is the molecular material that serves as the building block for chromosomes, the structures that carry an organism's genetic information inside of the cell's nucleus. Understanding the physical properties of chromatin is crucial in developing a more thorough picture of how chromatin's structure relate to its key cellular functions. Moreover, by establishing a physical model of chromatin, scientists will be able to open the doors into the true inner workings of the cell nucleus. Professor Shin-ichi Tate and his team of researchers at Hiroshima University's Research Center for the Mathematics on Chromatin Live Dynamics (RcMcD), are attempting to do just that. Through a five-year grant funded by the Platform for Dynamic Approaches to Living Systems from the Ministry of Education, Culture, Sports, Science and Technology, Tate is aiming to gain a clearer understanding of the structure and dynamics of chromatin.
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Korfanty, Joanna, Tomasz Stokowy, Marek Chadalski, et al. "SPEN protein expression and interactions with chromatin in mouse testicular cells." Reproduction 156, no. 3 (2018): 195–206. http://dx.doi.org/10.1530/rep-18-0046.
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SPEN (spen family transcription repressor) is a nucleic acid-binding protein putatively involved in repression of gene expression. We hypothesized that SPEN could be involved in general downregulation of the transcription during the heat shock response in mouse spermatogenic cells through its interactions with chromatin. We documented predominant nuclear localization of the SPEN protein in spermatocytes and round spermatids, which was retained after heat shock. Moreover, the protein was excluded from the highly condensed chromatin. Chromatin immunoprecipitation experiments clearly indicated interactions of SPEN with chromatinin vivo. However, ChIP-Seq analyses did not reveal any strong specific peaks both in untreated and heat shocked cells, which might suggest dispersed localization of SPEN and/or its indirect binding to DNA. Usingin situproximity ligation assay we found closein vivoassociations of SPEN with MTA1 (metastasis-associated 1), a member of the nucleosome remodeling complex with histone deacetylase activity, which might contribute to interactions of SPEN with chromatin.
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Green, G. R., R. R. Ferlita, W. F. Walkenhorst, and D. L. Poccia. "Linker DNA destabilizes condensed chromatin." Biochemistry and Cell Biology 79, no. 3 (2001): 349–63. http://dx.doi.org/10.1139/o01-115.
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The contribution of the linker region to maintenance of condensed chromatin was examined in two model systems, namely sea urchin sperm nuclei and chicken red blood cell nuclei. Linkerless nuclei, prepared by extensive digestion with micrococcal nuclease, were compared with Native nuclei using several assays, including microscopic appearance, nuclear turbidity, salt stability, and trypsin resistance. Chromatin in the Linkerless nuclei was highly condensed, resembling pyknotic chromatin in apoptotic cells. Linkerless nuclei were more stable in low ionic strength buffers and more resistant to trypsin than Native nuclei. Analysis of histones from the trypsinized nuclei by polyacrylamide gel electrophoresis showed that specific histone H1, H2B, and H3 tail regions stabilized linker DNA in condensed nuclei. Thermal denaturation of soluble chromatin preparations from differentially trypsinized sperm nuclei demonstrated that the N-terminal regions of histones Sp H1, Sp H2B, and H3 bind tightly to linker DNA, causing it to denature at a high temperature. We conclude that linker DNA exerts a disruptive force on condensed chromatin structure which is counteracted by binding of specific histone tail regions to the linker DNA. The inherent instability of the linker region may be significant in all eukaryotic chromatins and may promote gene activation in living cells.Key words: chromatin condensation, sea urchin sperm, chicken red blood cell, nuclei, linker DNA, histone variants, micrococcal nuclease, nucleosome, trypsin, gel electrophoresis.
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Mishra, Prashant K., Sultan Ciftci-Yilmaz, David Reynolds, et al. "Polo kinase Cdc5 associates with centromeres to facilitate the removal of centromeric cohesin during mitosis." Molecular Biology of the Cell 27, no. 14 (2016): 2286–300. http://dx.doi.org/10.1091/mbc.e16-01-0004.
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Sister chromatid cohesion is essential for tension-sensing mechanisms that monitor bipolar attachment of replicated chromatids in metaphase. Cohesion is mediated by the association of cohesins along the length of sister chromatid arms. In contrast, centromeric cohesin generates intrastrand cohesion and sister centromeres, while highly cohesin enriched, are separated by >800 nm at metaphase in yeast. Removal of cohesin is necessary for sister chromatid separation during anaphase, and this is regulated by evolutionarily conserved polo-like kinase (Cdc5 in yeast, Plk1 in humans). Here we address how high levels of cohesins at centromeric chromatin are removed. Cdc5 associates with centromeric chromatin and cohesin-associated regions. Maximum enrichment of Cdc5 in centromeric chromatin occurs during the metaphase-to-anaphase transition and coincides with the removal of chromosome-associated cohesin. Cdc5 interacts with cohesin in vivo, and cohesin is required for association of Cdc5 at centromeric chromatin. Cohesin removal from centromeric chromatin requires Cdc5 but removal at distal chromosomal arm sites does not. Our results define a novel role for Cdc5 in regulating removal of centromeric cohesins and faithful chromosome segregation.
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Kireeva, Natashe, Margot Lakonishok, Igor Kireev, Tatsuya Hirano, and Andrew S. Belmont. "Visualization of early chromosome condensation." Journal of Cell Biology 166, no. 6 (2004): 775–85. http://dx.doi.org/10.1083/jcb.200406049.
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Current models of mitotic chromosome structure are based largely on the examination of maximally condensed metaphase chromosomes. Here, we test these models by correlating the distribution of two scaffold components with the appearance of prophase chromosome folding intermediates. We confirm an axial distribution of topoisomerase IIα and the condensin subunit, structural maintenance of chromosomes 2 (SMC2), in unextracted metaphase chromosomes, with SMC2 localizing to a 150–200-nm-diameter central core. In contrast to predictions of radial loop/scaffold models, this axial distribution does not appear until late prophase, after formation of uniformly condensed middle prophase chromosomes. Instead, SMC2 associates throughout early and middle prophase chromatids, frequently forming foci over the chromosome exterior. Early prophase condensation occurs through folding of large-scale chromatin fibers into condensed masses. These resolve into linear, 200–300-nm-diameter middle prophase chromatids that double in diameter by late prophase. We propose a unified model of chromosome structure in which hierarchical levels of chromatin folding are stabilized late in mitosis by an axial “glue.”
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Carmena, Mar. "Flies stretch their cells to avoid a chromatin trap." Journal of Cell Biology 199, no. 5 (2012): 719–21. http://dx.doi.org/10.1083/jcb.201210135.
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Before the final step of cytokinesis, termed abscission, dividing cells need to ensure that the cleavage plane is clear of chromatin. In this issue, Kotadia et al. (2012. J. Cell Biol. http://dx.doi.org/jcb.201208041) show that in Drosophila melanogaster, larval neuroblasts elongate to allow segregation of extra-long chromatids and clearance of the midzone, thereby avoiding cytokinesis failure and aneuploidy.
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Hendzel, Michael J., Michael J. Kruhlak, and David P. Bazett-Jones. "Organization of Highly Acetylated Chromatin around Sites of Heterogeneous Nuclear RNA Accumulation." Molecular Biology of the Cell 9, no. 9 (1998): 2491–507. http://dx.doi.org/10.1091/mbc.9.9.2491.
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Histones found within transcriptionally competent and active regions of the genome are highly acetylated. Moreover, these highly acetylated histones have very short half-lives. Thus, both histone acetyltransferases and histone deacetylases must enrich within or near these euchromatic regions of the interphase chromatids. Using an antibody specific for highly acetylated histone H3, we have investigated the organization of transcriptionally active and competent chromatin as well as nuclear histone acetyltransferase and deacetylase activities. We observe an exclusion of highly acetylated chromatin around the periphery of the nucleus and an enrichment near interchromatin granule clusters (IGCs). The highly acetylated chromatin is found in foci that may reflect the organization of highly acetylated chromatin into “chromonema” fibers. Transmission electron microscopy of Indian muntjac fibroblast cell nuclei indicates that the chromatin associated with the periphery of IGCs remains relatively condensed, most commonly found in domains containing chromatin folded beyond 30 nm. Using electron spectroscopic imaging, we demonstrate that IGCs are clusters of ribonucleoprotein particles. The individual granules comprise RNA-rich fibrils or globular regions that fold into individual granules. Quantitative analysis of individual granules indicates that they contain variable amounts of RNA estimated between 1.5 and >10 kb. We propose that interchromatin granules are heterogeneous nuclear RNA-containing particles, some of which may be pre-mRNA generated by nearby transcribed chromatin. An intermediary zone between the IGC and surrounding chromatin is described that contains factors with the potential to provide specificity to the localization of sequences near IGCs.
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Stanyte, Rugile, Johannes Nuebler, Claudia Blaukopf, et al. "Dynamics of sister chromatid resolution during cell cycle progression." Journal of Cell Biology 217, no. 6 (2018): 1985–2004. http://dx.doi.org/10.1083/jcb.201801157.
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Faithful genome transmission in dividing cells requires that the two copies of each chromosome’s DNA package into separate but physically linked sister chromatids. The linkage between sister chromatids is mediated by cohesin, yet where sister chromatids are linked and how they resolve during cell cycle progression has remained unclear. In this study, we investigated sister chromatid organization in live human cells using dCas9-mEGFP labeling of endogenous genomic loci. We detected substantial sister locus separation during G2 phase irrespective of the proximity to cohesin enrichment sites. Almost all sister loci separated within a few hours after their respective replication and then rapidly equilibrated their average distances within dynamic chromatin polymers. Our findings explain why the topology of sister chromatid resolution in G2 largely reflects the DNA replication program. Furthermore, these data suggest that cohesin enrichment sites are not persistent cohesive sites in human cells. Rather, cohesion might occur at variable genomic positions within the cell population.
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Stephens, Andrew D., Chloe E. Snider, Julian Haase, et al. "Individual pericentromeres display coordinated motion and stretching in the yeast spindle." Journal of Cell Biology 203, no. 3 (2013): 407–16. http://dx.doi.org/10.1083/jcb.201307104.
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The mitotic segregation apparatus composed of microtubules and chromatin functions to faithfully partition a duplicated genome into two daughter cells. Microtubules exert extensional pulling force on sister chromatids toward opposite poles, whereas pericentric chromatin resists with contractile springlike properties. Tension generated from these opposing forces silences the spindle checkpoint to ensure accurate chromosome segregation. It is unknown how the cell senses tension across multiple microtubule attachment sites, considering the stochastic dynamics of microtubule growth and shortening. In budding yeast, there is one microtubule attachment site per chromosome. By labeling several chromosomes, we find that pericentromeres display coordinated motion and stretching in metaphase. The pericentromeres of different chromosomes exhibit physical linkage dependent on centromere function and structural maintenance of chromosomes complexes. Coordinated motion is dependent on condensin and the kinesin motor Cin8, whereas coordinated stretching is dependent on pericentric cohesin and Cin8. Linking of pericentric chromatin through cohesin, condensin, and kinetochore microtubules functions to coordinate dynamics across multiple attachment sites.
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Moore, Susan C., Laure Jason, and Juan Ausió. "The elusive structural role of ubiquitinated histones." Biochemistry and Cell Biology 80, no. 3 (2002): 311–19. http://dx.doi.org/10.1139/o02-081.
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It is increasingly apparent that histone posttranslational modifications are important in chromatin structure and dynamics. However, histone ubiquitination has received little attention. Histones H1, H3, H2A, and H2B can be ubiquitinated in vivo, but the most prevalent are uH2A and uH2B. The size of this modification suggests some sort of structural impact. Physiological observations suggest that ubiquitinated histones may have multiple functions and structural effects. Ubiquitinated histones have been correlated with transcriptionally active DNA, implying that it may prevent chromatin folding or help maintain an open conformation. Also, in some organisms during spermiogenesis, a process involving extensive chromatin remodeling, uH2A levels increase just prior to histone replacement by protamines. Determination of chromatin's structural changes resulting from histone ubiquitination is therefore important. Recent work using reconstituted nucleosomes and chromatin fibers containing uH2A indicate that in the absence of linker histones, ubiquitination has little structural impact. DNase I digests and analytical ultracentrifugation of reconstituted ubiquitinated nucleosomes show no structural differences. Solubility assays using reconstituted chromatin fibers in the presence of divalent ions demonstrate that uH2A fibers are slightly more prone to aggregation than controls, and analytical ultracentrifugation results with different MgCl2 and NaCl concentrations determined that chromatin folding is not affected by this modification. Additional work to assess possible synergistic affects with histone acetylation also precludes any structural implications. Protamine displacement experiments concluded that the presence of uH2A does not significantly affect the ability of the protamines to displace histones. In addition, uH2A does not interfere with histone H1 binding to the nucleosome. While work with uH2B remains insufficient to come to any definitive conclusions about its structural impact, current work with uH2A indicates that, contrary to predictions, this histone modification does not affect either nucleosome or chromatin structure. Consequently, the search for a structural role for ubiquitinated histones continues and their effect on and importance in chromatin dynamics remains elusive.Key words: ubiquitinated histones, chromatin, nucleosome structure.
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Tremblay, Maxime, Martin Toussaint, Annie D’Amours, and Antonio Conconi. "Nucleotide excision repair and photolyase repair of UV photoproducts in nucleosomes: assessing the existence of nucleosome and non-nucleosome rDNA chromatin in vivoThis paper is one of a selection of papers published in this Special Issue, entitled 29th Annual International Asilomar Chromatin and Chromosomes Conference, and has undergone the Journal’s usual peer review process." Biochemistry and Cell Biology 87, no. 1 (2009): 337–46. http://dx.doi.org/10.1139/o08-128.
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The genome is organized into nuclear domains, which create microenvironments that favor distinct chromatin structures and functions (e.g., highly repetitive sequences, centromeres, telomeres, noncoding sequences, inactive genes, RNA polymerase II and III transcribed genes, and the nucleolus). Correlations have been drawn between gene silencing and proximity to a heterochromatic compartment. At the other end of the scale are ribosomal genes, which are transcribed at a very high rate by RNA polymerase I (~60% of total transcription), have a loose chromatin structure, and are clustered in the nucleolus. The rDNA sequences have 2 distinct structures: active rRNA genes, which have no nucleosomes; and inactive rRNA genes, which have nucleosomes. Like DNA transcription and replication, DNA repair is modulated by the structure of chromatin, and the kinetics of DNA repair vary among the nuclear domains. Although research on DNA repair in all chromosomal contexts is important to understand the mechanisms of genome maintenance, this review focuses on nucleotide excision repair and photolyase repair of UV photoproducts in the first-order packing of DNA in chromatin: the nucleosome. In addition, it summarizes the studies that have demonstrated the existence of the 2 rDNA chromatins, and the way this feature of the rDNA locus allows for direct comparison of DNA repair in 2 very different structures: nucleosome and non-nucleosome DNA.
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Daban, Joan-Ramon. "High concentration of DNA in condensed chromatin." Biochemistry and Cell Biology 81, no. 3 (2003): 91–99. http://dx.doi.org/10.1139/o03-037.
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The lengths of the DNA molecules of eukaryotic genomes are much greater than the dimensions of the metaphase chromosomes in which they are contained during mitosis. From this observation it has been generally assumed that the linear packing ratio of DNA is an adequate measure of the degree of DNA compaction. This review summarizes the evidence suggesting that the local concentration of DNA is more appropriate than the linear packing ratio for the study of chromatin condensation. The DNA concentrations corresponding to most of the models proposed for the 3040 nm chromatin fiber are not high enough for the construction of metaphase chromosomes. The interdigitated solenoid model has a higher density because of the stacking of nucleosomes in secondary helices and, after further folding into chromatids, it yields a final concentration of DNA that approaches the experimental value found for condensed chromosomes. Since recent results have shown that metaphase chromosomes contain high concentrations of the chromatin packing ions Mg2+ and Ca2+, it is discussed that dynamic rather than rigid models are required to explain the condensation of the extended fibers observed in the absence of these cations. Finally, considering the different lines of evidence demonstrating the stacking of nucleosomes in different chromatin complexes, it is suggested that the face-to-face interactions between nucleosomes may be the driving force for the formation of higher order structures with a high local concentration of DNA.Key words: chromosomes, metaphase chromosomes, chromatin, chromatin higher order structure, DNA.
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Lawrimore, Josh, Paula A. Vasquez, Michael R. Falvo, et al. "DNA loops generate intracentromere tension in mitosis." Journal of Cell Biology 210, no. 4 (2015): 553–64. http://dx.doi.org/10.1083/jcb.201502046.
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The centromere is the DNA locus that dictates kinetochore formation and is visibly apparent as heterochromatin that bridges sister kinetochores in metaphase. Sister centromeres are compacted and held together by cohesin, condensin, and topoisomerase-mediated entanglements until all sister chromosomes bi-orient along the spindle apparatus. The establishment of tension between sister chromatids is essential for quenching a checkpoint kinase signal generated from kinetochores lacking microtubule attachment or tension. How the centromere chromatin spring is organized and functions as a tensiometer is largely unexplored. We have discovered that centromere chromatin loops generate an extensional/poleward force sufficient to release nucleosomes proximal to the spindle axis. This study describes how the physical consequences of DNA looping directly underlie the biological mechanism for sister centromere separation and the spring-like properties of the centromere in mitosis.
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Hsu, Jing-mei, Jian Huang, Pamela B. Meluh, and Brehon C. Laurent. "The Yeast RSC Chromatin-Remodeling Complex Is Required for Kinetochore Function in Chromosome Segregation." Molecular and Cellular Biology 23, no. 9 (2003): 3202–15. http://dx.doi.org/10.1128/mcb.23.9.3202-3215.2003.
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ABSTRACT The accurate segregation of chromosomes requires the kinetochore, a complex protein machine that assembles onto centromeric DNA to mediate attachment of replicated sister chromatids to the mitotic spindle apparatus. This study reveals an important role for the yeast RSC ATP-dependent chromatin-remodeling complex at the kinetochore in chromosome transmission. Mutations in genes encoding two core subunits of RSC, the ATPase Sth1p and the Snf5p homolog Sfh1p, interact genetically with mutations in genes encoding kinetochore proteins and with a mutation in centromeric DNA. RSC also interacts genetically and physically with the histone and histone variant components of centromeric chromatin. Importantly, RSC is localized to centromeric and centromere-proximal chromosomal regions, and its association with these loci is dependent on Sth1p. Both sth1 and sfh1 mutants exhibit altered centromeric and centromere-proximal chromatin structure and increased missegregation of authentic chromosomes. Finally, RSC is not required for centromeric deposition of the histone H3 variant Cse4p, suggesting that RSC plays a role in reconfiguring centromeric and flanking nucleosomes following Cse4p recruitment for proper chromosome transmission.
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Willingale-Theune, J., M. Schweiger, M. Hirsch-Kauffmann, A. E. Meek, M. Paulin-Levasseur, and P. Traub. "Ultrastructure of Fanconi anemia fibroblasts." Journal of Cell Science 93, no. 4 (1989): 651–65. http://dx.doi.org/10.1242/jcs.93.4.651.
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Employing indirect immunofluorescence and conventional electron microscopy, gross nuclear aberrations were observed in cultured interphase fibroblasts derived from a patient suffering from Fanconi's anemia (FA). Such aberrations were predominantly expressed in cells at high passages between 28 and 34. The structure of the nuclei appeared compound in nature, often consisting of two to three nuclear fragments connected to each other by thin nuclear bridges containing chromatin and nuclear lamin material. In other cases, the nuclei appeared lobed or budded but the cells did not contain distinct nuclear fragments. Chromatin was conspicuously absent from some nuclear lobes, revealing empty, cage-like structures comprising nuclear lamin material. Micronuclei were often abundant in the perinuclear cytoplasm but in some instances they appeared to be composed of chromatin lacking a delineating nuclear lamin matrix. Residual cytoskeletons examined by whole-mount electron microscopy revealed a network of intermediate filaments (IFs) within FA fibroblasts forming a bridge between the plasma membrane and the nucleus or its major fragments. In addition, there were thinner, 3–4 nm filaments connecting individual IFs with the surface of the nucleus. Micronuclei that were not connected to the main nuclear body, but which were delineated by a distinct lamina and possessed nuclear pores, did not appear to be anchored to the IF network. Multinuclearity, nuclear fragmentation, irregular chromatin distribution and inter-nuclear chromatin/lamin bridges might result from a failure in the redistribution of chromatin to sister nuclei, incomplete cytokinesis and proliferation of nuclear envelope material. These phenomena point to precocious aging of FA fibroblasts and may occur as a consequence of spontaneous damage to the sister chromatids or through the action of DNA-toxic agents.
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Cuvier, Olivier, and Tatsuya Hirano. "A role of topoisomerase II in linking DNA replication to chromosome condensation." Journal of Cell Biology 160, no. 5 (2003): 645–55. http://dx.doi.org/10.1083/jcb.200209023.
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The condensin complex and topoisomerase II (topo II) have different biochemical activities in vitro, and both are required for mitotic chromosome condensation. We have used Xenopus egg extracts to investigate the functional interplay between condensin and topo II in chromosome condensation. When unreplicated chromatin is directly converted into chromosomes with single chromatids, the two proteins must function together, although they are independently targeted to chromosomes. In contrast, the requirement for topo II is temporarily separable from that of condensin when chromosome assembly is induced after DNA replication. This experimental setting allows us to find that, in the absence of condensin, topo II becomes enriched in an axial structure within uncondensed chromatin. Subsequent addition of condensin converts this structure into mitotic chromosomes in an ATP hydrolysis–dependent manner. Strikingly, preventing DNA replication by the addition of geminin or aphidicolin disturbs the formation of topo II–containing axes and alters the binding property of topo II with chromatin. Our results suggest that topo II plays an important role in an early stage of chromosome condensation, and that this function of topo II is tightly coupled with prior DNA replication.
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Jack, E. M., C. J. Harrison, G. R. White, C. H. Ockey, and T. D. Allen. "Fine-structural aspects of bromodeoxyuridine incorporation in sister chromatid differentiation and replication banding." Journal of Cell Science 94, no. 2 (1989): 287–97. http://dx.doi.org/10.1242/jcs.94.2.287.
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The structure of harlequin-stained chromosomes following substitution with low levels of 5-bromodeoxyuridine (BrdUrd) over two cell cycles and high levels over the last part of one cycle (replication banding) was studied in Chinese hamster ovary (CHO) cells. By using correlative light (LM) and scanning electron microscopy (SEM), it was shown that the effects of both the ultraviolet light (u.v.) and hot SSC treatment steps of the harlequin staining procedure were necessary to obtain sister-chromatid differentiation (SCD) or replication banding. u.v. treatment alone resulted in dark Giemsa staining of both chromatids with SEM morphology of short compact protuberances and an overall flattened smooth appearance in both the unsubstituted and BrdUrd-substituted chromatids, a morphology essentially similar to that of untreated chromosomes. SSC alone on the other hand resulted in dark-staining chromatids with an SEM morphology of raised, loosely packed loops of fibres in both types of chromatids. u.v. and SSC treatment together resulted in differentiation, with dark-staining unifilarly (TB) chromatids in the LM corresponding to raised loosely packed loops in the SEM and pale bifilarly (BB) chromatids corresponding to the smooth compact flattened SEM appearance. Where the BrdUrd-substituted strand became the template (BT), or when the nascent strand TB contained high levels of BrdUrd substitution in replication banding, the chromatid stained pale and showed the compact smooth appearance in the SEM. The Giemsa staining ability and ultrastructural morphology of harlequin staining is discussed with respect to putative DNA loss and also in terms of preferential protein-protein, protein-DNA cross-linkage in BrdUrd-containing DNA. These changes are also compared with the ultrastructural morphology observed after other banding methods, where deterioration of protein and DNA-protein interaction resulting in aggregation of chromatin fibres appears to be the major mechanism.
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Jin, Quan-Wen, Alison L. Pidoux, Corina Decker, Robin C. Allshire, and Ursula Fleig. "The Mal2p Protein Is an Essential Component of the Fission Yeast Centromere." Molecular and Cellular Biology 22, no. 20 (2002): 7168–83. http://dx.doi.org/10.1128/mcb.22.20.7168-7183.2002.
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ABSTRACT Precise segregation of chromosomes requires the activity of a specialized chromatin region, the centromere, that assembles the kinetochore complex to mediate the association with spindle microtubules. We show here that Mal2p, previously identified as a protein required for genome stability, is an essential component of the fission yeast centromere. Loss of functional Mal2p leads to extreme missegregation of chromosomes due to nondisjunction of sister chromatids and results in inviable cells. Mal2p associates specifically with the central region of the complex fission yeast centromere, where it is required for the specialized chromatin architecture as well as for transcriptional silencing of this region. Genetic evidence indicates that mal2 + interacts with mis12 +, encoding another component of the inner centromere core complex. In addition, Mal2p is required for correct metaphase spindle length. Our data imply that the Mal2p protein is required to build up a functional fission yeast centromere.
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Rizzoni, Marco, Enrico Cundari, Paolo Perticone, and Bianca Gustavino. "Chromatin Bridges between Sister Chromatids Induced in Late G2 Mitosis in CHO Cells by Trimethylpsoralen + UVA." Experimental Cell Research 209, no. 1 (1993): 149–55. http://dx.doi.org/10.1006/excr.1993.1295.
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Sapkota, Hem, Emilia Wasiak, John R. Daum, and Gary J. Gorbsky. "Multiple determinants and consequences of cohesion fatigue in mammalian cells." Molecular Biology of the Cell 29, no. 15 (2018): 1811–24. http://dx.doi.org/10.1091/mbc.e18-05-0315.
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Cells delayed in metaphase with intact mitotic spindles undergo cohesion fatigue, where sister chromatids separate asynchronously, while cells remain in mitosis. Cohesion fatigue requires release of sister chromatid cohesion. However, the pathways that breach sister chromatid cohesion during cohesion fatigue remain unknown. Using moderate-salt buffers to remove loosely bound chromatin cohesin, we show that “cohesive” cohesin is not released during chromatid separation during cohesion fatigue. Using a regulated protein heterodimerization system to lock different cohesin ring interfaces at specific times in mitosis, we show that the Wapl-mediated pathway of cohesin release is not required for cohesion fatigue. By manipulating microtubule stability and cohesin complex integrity in cell lines with varying sensitivity to cohesion fatigue, we show that rates of cohesion fatigue reflect a dynamic balance between spindle pulling forces and resistance to separation by interchromatid cohesion. Finally, while massive separation of chromatids in cohesion fatigue likely produces inviable cell progeny, we find that short metaphase delays, leading to partial chromatid separation, predispose cells to chromosome missegregation. Thus, complete separation of one or a few chromosomes and/or partial separation of sister chromatids may be an unrecognized but common source of chromosome instability that perpetuates the evolution of malignant cells in cancer.
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Gallego-Paez, Lina Marcela, Hiroshi Tanaka, Masashige Bando, et al. "Smc5/6-mediated regulation of replication progression contributes to chromosome assembly during mitosis in human cells." Molecular Biology of the Cell 25, no. 2 (2014): 302–17. http://dx.doi.org/10.1091/mbc.e13-01-0020.
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The structural maintenance of chromosomes (SMC) proteins constitute the core of critical complexes involved in structural organization of chromosomes. In yeast, the Smc5/6 complex is known to mediate repair of DNA breaks and replication of repetitive genomic regions, including ribosomal DNA loci and telomeres. In mammalian cells, which have diverse genome structure and scale from yeast, the Smc5/6 complex has also been implicated in DNA damage response, but its further function in unchallenged conditions remains elusive. In this study, we addressed the behavior and function of Smc5/6 during the cell cycle. Chromatin fractionation, immunofluorescence, and live-cell imaging analyses indicated that Smc5/6 associates with chromatin during interphase but largely dissociates from chromosomes when they condense in mitosis. Depletion of Smc5 and Smc6 resulted in aberrant mitotic chromosome phenotypes that were accompanied by the abnormal distribution of topoisomerase IIα (topo IIα) and condensins and by chromosome segregation errors. Importantly, interphase chromatin structure indicated by the premature chromosome condensation assay suggested that Smc5/6 is required for the on-time progression of DNA replication and subsequent binding of topo IIα on replicated chromatids. These results indicate an essential role of the Smc5/6 complex in processing DNA replication, which becomes indispensable for proper sister chromatid assembly in mitosis.
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Warsi, Tariq H., Michelle S. Navarro, and Jeff Bachant. "DNA Topoisomerase II Is a Determinant of the Tensile Properties of Yeast Centromeric Chromatin and the Tension Checkpoint." Molecular Biology of the Cell 19, no. 10 (2008): 4421–33. http://dx.doi.org/10.1091/mbc.e08-05-0547.
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Centromeric (CEN) chromatin is placed under mechanical tension and stretches as kinetochores biorient on the mitotic spindle. This deformation could conceivably provide a readout of biorientation to error correction mechanisms that monitor kinetochore–spindle interactions, but whether CEN chromatin acts in a tensiometer capacity is unresolved. Here, we report observations linking yeast Topoisomerase II (Top2) to both CEN mechanics and assessment of interkinetochore tension. First, in top2-4 and sumoylation-resistant top2-SNM mutants CEN chromatin stretches extensively during biorientation, resulting in increased sister kinetochore separation and preanaphase spindle extension. Our data indicate increased CEN stretching corresponds with alterations to CEN topology induced in response to tension. Second, Top2 potentiates aspects of the tension checkpoint. Mutations affecting the Mtw1 kinetochore protein activate Ipl1 kinase to detach kinetochores and induce spindle checkpoint arrest. In mtw1top2-4 and mtw1top2-SNM mutants, however, kinetochores are resistant to detachment and checkpoint arrest is attenuated. For top2-SNM cells, CEN stretching and checkpoint attenuation occur even in the absence of catenation linking sister chromatids. In sum, Top2 seems to play a novel role in CEN compaction that is distinct from decatenation. Perturbations to this function may allow weakened kinetochores to stretch CENs in a manner that mimics tension or evades Ipl1 surveillance.
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Afaq, Dr Sarah. "A Comparative Study Showing Systemic Lupus Erthematosus (SLE) Autoantibody Binding to Native Calf Thymus DNA, Native Chromatin and Nitric Oxide Modified Chromatin." International Journal of Scientific Research 2, no. 5 (2012): 456–59. http://dx.doi.org/10.15373/22778179/may2013/155.
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Yong-Gonzalez, Vladimir, Bi-Dar Wang, Pavel Butylin, Ilia Ouspenski, and Alexander Strunnikov. "Condensin function at centromere chromatin facilitates proper kinetochore tension and ensures correct mitotic segregation of sister chromatids." Genes to Cells 12, no. 9 (2007): 1075–90. http://dx.doi.org/10.1111/j.1365-2443.2007.01109.x.
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Jones, Keith T. "Mammalian egg activation: from Ca2+ spiking to cell cycle progression." Reproduction 130, no. 6 (2005): 813–23. http://dx.doi.org/10.1530/rep.1.00710.
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Mammalian eggs arrest at metaphase of the second meiotic division (MetII). Sperm break this arrest by inducing a series of Ca2+spikes that last for several hours. During this time cell cycle resumption is induced, sister chromatids undergo anaphase and the second polar body is extruded. This is followed by decondensation of the chromatin and the formation of pronuclei. Ca2+spiking is both the necessary and solely sufficient sperm signal to induce full egg activation. How MetII arrest is established, how the Ca2+spiking is induced and how the signal is transduced into cell cycle resumption are the topics of this review. Although the roles of most components of the signal transduction pathway remain to be fully investigated, here I present a model in which a sperm-specific phospholipase C (PLCζ) generates Ca2+spikes to activate calmodulin-dependent protein kinase II and so switch on the Anaphase-Promoting Complex/Cyclosome (APC/C). APC/C activation leads to securin and cyclin B1 degradation and in so doing allows sister chromatids to be segregated and to decondense.
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Luo, Jianjun, Xinjing Xu, Hana Hall, et al. "Histone H3 Exerts a Key Function in Mitotic Checkpoint Control." Molecular and Cellular Biology 30, no. 2 (2009): 537–49. http://dx.doi.org/10.1128/mcb.00980-09.
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ABSTRACT It has been firmly established that many interphase nuclear functions, including transcriptional regulation, are regulated by chromatin and histones. How mitotic progression and quality control might be influenced by histones is less well characterized. We show that histone H3 plays a crucial role in activating the spindle assembly checkpoint in response to a defect in mitosis. Prior to anaphase, all chromosomes must attach to spindles emanating from the opposite spindle pole bodies. The tension between sister chromatids generated by the poleward pulling force is an integral part of chromosome biorientation. Lack of tension due to erroneous attachment activates the spindle assembly checkpoint, which corrects the mistakes and ensures segregation fidelity. A histone H3 mutation impairs the ability of yeast cells to activate the checkpoint in a tensionless crisis, leading to missegregation and aneuploidy. The defects in tension sensing result directly from an attenuated H3-Sgo1p interaction essential for pericentric recruitment of Sgo1p. Reinstating the pericentric enrichment of Sgo1p alleviates the mitotic defects. Histone H3, and hence the chromatin, is thus a key factor transmitting the tension status to the spindle assembly checkpoint.
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SIMPSON, R. T. "Chromatin Research Surveyed: Chromatin." Science 243, no. 4895 (1989): 1220. http://dx.doi.org/10.1126/science.243.4895.1220.
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Messier, P. E., R. Drouin, and C. L. Richer. "Electron microscopy of gold-labeled human and equine chromosomes." Journal of Histochemistry & Cytochemistry 37, no. 9 (1989): 1443–47. http://dx.doi.org/10.1177/37.9.2768813.
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We present an immunochemical technique for the detection of 5-bromo-2'-deoxyuridine (BrdU) incorporated discontinuously into the chromosomal DNA. A monoclonal anti-BrdU antibody and a protein A-gold complex were used to produce chromosome banding of human and equine chromosomes, specific for electron microscopy (EM). Well-defined bands, symmetry of sister chromatids, concordance between homologues, and band patterns similar to those observed by light microscopy facilitate chromosome identification and karyotyping. From prophase to late metaphase, chromosomes condense and bands appear to fuse. The fusion appears to be owing to chromatin reorganization. Our results underline the value of using immunogold reagents, which are ideal probes for antigen localization on chromosomes.
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Eisenstein, Michael. "Finding chromatin's footprints." Nature Methods 2, no. 9 (2005): 718. http://dx.doi.org/10.1038/nmeth0905-718.
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Cain, Chris. "Chromatin's rising tide." Science-Business eXchange 7, no. 19 (2014): 545. http://dx.doi.org/10.1038/scibx.2014.545.
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Kumar, G., and S. Naseem. "EMS induced intercellular chromatin transmigration in Papaver somniferum L." Czech Journal of Genetics and Plant Breeding 49, No. 2 (2013): 86–89. http://dx.doi.org/10.17221/85/2012-cjgpb.
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The phenomenon of chromatin migration was observed during microsporogenesis in an ethyl methane sulphonate (EMS) treated population of poppy, which is an important medicinal plant. Cytomixis occurred through a cytoplasmic channel or by direct fusion of pollen mother cells (PMCs); the former was more recurring than the latter. The process was associated with irregular meiosis. PMCs with differing chromosome numbers from the normal diploid number (2n = 22) through cytomixis may lead to the production of aneuploid and polyploid gametes. An increase in the concentration of EMS had a positive effect on the percentage of PMCs showing cytomixis. In addition to cytomixis, other chromosomal abnormalities were also found. Cytomixis along with the related chromosomal abnormalities largely affected the post-meiotic products resulting in some pollen sterility.
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Tseng, Li-Chuan, and Rey-Huei Chen. "Temporal control of nuclear envelope assembly by phosphorylation of lamin B receptor." Molecular Biology of the Cell 22, no. 18 (2011): 3306–17. http://dx.doi.org/10.1091/mbc.e11-03-0199.
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The nuclear envelope of metazoans disassembles during mitosis and reforms in late anaphase after sister chromatids have well separated. The coordination of these mitotic events is important for genome stability, yet the temporal control of nuclear envelope reassembly is unknown. Although the steps of nuclear formation have been extensively studied in vitro using the reconstitution system from egg extracts, the temporal control can only be studied in vivo. Here, we use time-lapse microscopy to investigate this process in living HeLa cells. We demonstrate that Cdk1 activity prevents premature nuclear envelope assembly and that phosphorylation of the inner nuclear membrane protein lamin B receptor (LBR) by Cdk1 contributes to the temporal control. We further identify a region in the nucleoplasmic domain of LBR that inhibits premature chromatin binding of the protein. We propose that this inhibitory effect is partly mediated by Cdk1 phosphorylation. Furthermore, we show that the reduced chromatin-binding ability of LBR together with Aurora B activity contributes to nuclear envelope breakdown. Our studies reveal for the first time a mechanism that controls the timing of nuclear envelope reassembly through modification of an integral nuclear membrane protein.
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FELSENFELD, G., B. BURGESS-BEUSSE, C. FARRELL, et al. "Chromatin Boundaries and Chromatin Domains." Cold Spring Harbor Symposia on Quantitative Biology 69 (January 1, 2004): 245–50. http://dx.doi.org/10.1101/sqb.2004.69.245.
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Kim, Yea Woon, and AeRi Kim. "3C (Chromatin Conformation Capture): A Technique to Study Chromatin Organization." Journal of Life Science 22, no. 11 (2012): 1587–94. http://dx.doi.org/10.5352/jls.2012.22.11.1587.
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Dayal, Sangeeta, and Harshal Kumar. "Assessment of Genotoxic Effects of Nux Vomica as Homeopathic Drug on Mitotic Chromosomes of Vicia Faba." Biosciences, Biotechnology Research Asia 14, no. 4 (2017): 1497–502. http://dx.doi.org/10.13005/bbra/2597.
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ABSTRACT: Extract of Nux vomica is used as homeopathic drug to cure various nervous disorders like mental emotion epilepsy, prolepses of the rectum, hydrophobia etc. The given dose of this drug is very small because of its poisonous effect in higher dose. In the present investigation we want to assess toxic effects of Nux vomica on somatic chromosomes of Vicia faba. Four concentrations 5%, 10%, 20% and 30%, were used for the treatment of root tips of test plant. There were number of abnormalities observed like stickiness at orientation of chromosomes, un-organization of chromosomes, fragmentation during separation of chromatids, multiple chromatin bridges formation etc. These types of aberrations were increased with increased concentration and duration of treatment of this drug.
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Balicky, Eric M., Matthew W. Endres, Cary Lai, and Sharon E. Bickel. "Meiotic Cohesion Requires Accumulation of ORD on Chromosomes before Condensation." Molecular Biology of the Cell 13, no. 11 (2002): 3890–900. http://dx.doi.org/10.1091/mbc.e02-06-0332.
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Cohesion between sister chromatids is a prerequisite for accurate chromosome segregation during mitosis and meiosis. To allow chromosome condensation during prophase, the connections that hold sister chromatids together must be maintained but still permit extensive chromatin compaction. In Drosophila, null mutations in the orientation disruptor (ord) gene lead to meiotic nondisjunction in males and females because cohesion is absent by the time that sister kinetochores make stable microtubule attachments. We provide evidence that ORD is concentrated within the extrachromosomal domains of the nuclei ofDrosophila primary spermatocytes during early G2, but accumulates on the meiotic chromosomes by mid to late G2. Moreover, using fluorescence in situ hybridization to monitor cohesion directly, we show that cohesion defects first become detectable inord null spermatocytes shortly after the time when wild-type ORD associates with the chromosomes. After condensation, ORD remains bound at the centromeres of wild-type spermatocytes and persists there until centromeric cohesion is released during anaphase II. Our results suggest that association of ORD with meiotic chromosomes during mid to late G2 is required to maintain sister-chromatid cohesion during prophase condensation and that retention of ORD at the centromeres after condensation ensures the maintenance of centromeric cohesion until anaphase II.
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Langmore, John P. "Chromatin." Cell 59, no. 2 (1989): 243–44. http://dx.doi.org/10.1016/0092-8674(89)90284-5.
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Urnov, Fyodor, and Colyn Crane-Robinson. "Chromatin." European Journal of Biochemistry 269, no. 9 (2002): 2267. http://dx.doi.org/10.1046/j.1432-1033.2002.02884.x.
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