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Yan X, Mischel P, Chang H. Extrachromosomal DNA in cancer. Nat Rev Cancer 2024; 24:261-273. [PMID: 38409389 DOI: 10.1038/s41568-024-00669-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 01/18/2024] [Indexed: 02/28/2024]
Abstract
Extrachromosomal DNA (ecDNA) has recently been recognized as a major contributor to cancer pathogenesis that is identified in most cancer types and is associated with poor outcomes. When it was discovered over 60 years ago, ecDNA was considered to be rare, and its impact on tumour biology was not well understood. The application of modern imaging and computational techniques has yielded powerful new insights into the importance of ecDNA in cancer. The non-chromosomal inheritance of ecDNA during cell division results in high oncogene copy number, intra-tumoural genetic heterogeneity and rapid tumour evolution that contributes to treatment resistance and shorter patient survival. In addition, the circular architecture of ecDNA results in altered patterns of gene regulation that drive elevated oncogene expression, potentially enabling the remodelling of tumour genomes. The generation of clusters of ecDNAs, termed ecDNA hubs, results in interactions between enhancers and promoters in trans, yielding a new paradigm in oncogenic transcription. In this Review, we highlight the rapid advancements in ecDNA research, providing new insights into ecDNA biogenesis, maintenance and transcription and its role in promoting tumour heterogeneity. To conclude, we delve into a set of unanswered questions whose answers will pave the way for the development of ecDNA targeted therapeutic approaches.
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Affiliation(s)
- Xiaowei Yan
- Department of Dermatology, Stanford University, Stanford, CA, USA
- Center for Personal Dynamic Regulomes, Stanford University, Stanford, CA, USA
| | - Paul Mischel
- Department of Pathology, Stanford University School of Medicine, Stanford, CA, USA.
- Sarafan ChEM-H, Stanford University, Stanford, CA, USA.
| | - Howard Chang
- Department of Dermatology, Stanford University, Stanford, CA, USA.
- Center for Personal Dynamic Regulomes, Stanford University, Stanford, CA, USA.
- Howard Hughes Medical Institute, Stanford University, Stanford, CA, USA.
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2
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Chen N, Buonomo SCB. Three-dimensional nuclear organisation and the DNA replication timing program. Curr Opin Struct Biol 2023; 83:102704. [PMID: 37741142 DOI: 10.1016/j.sbi.2023.102704] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2023] [Revised: 07/26/2023] [Accepted: 08/23/2023] [Indexed: 09/25/2023]
Abstract
In eukaryotic cells, genome duplication is temporally organised according to a program referred to as the replication-timing (RT) program. The RT of individual genomic domains strikingly parallels the three-dimensional architecture of their chromatin contacts and subnuclear distribution. However, it is unclear whether this correspondence is coincidental or whether it indicates a causal and regulatory relationship. In either case, the nature of the molecular mechanisms ensuring this spatio-temporal coordination is still unknown. Here, we review recent evidence that begins to uncover the existence of a shared molecular machinery at the core of the spatio-temporal co-regulation of DNA replication and genome architecture. Finally, we discuss the outstanding, key question of the biological role of their coordination.
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Affiliation(s)
- Naiming Chen
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Roger Land Building, Alexander Crum Brown Road, Edinburgh, EH9 3FF, UK
| | - Sara C B Buonomo
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Roger Land Building, Alexander Crum Brown Road, Edinburgh, EH9 3FF, UK.
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3
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Santos MM, Johnson MC, Fiedler L, Zegerman P. Global early replication disrupts gene expression and chromatin conformation in a single cell cycle. Genome Biol 2022; 23:217. [PMID: 36253803 PMCID: PMC9575230 DOI: 10.1186/s13059-022-02788-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2022] [Accepted: 10/10/2022] [Indexed: 12/03/2022] Open
Abstract
BACKGROUND The early embryonic divisions of many organisms, including fish, flies, and frogs, are characterized by a very rapid S-phase caused by high rates of replication initiation. In somatic cells, S-phase is much longer due to both a reduction in the total number of initiation events and the imposition of a temporal order of origin activation. The physiological importance of changes in the rate and timing of replication initiation in S-phase remains unclear. RESULTS Here we assess the importance of the temporal control of replication initiation using a conditional system in budding yeast to drive the early replication of the majority of origins in a single cell cycle. We show that global early replication disrupts the expression of over a quarter of all genes. By deleting individual origins, we show that delaying replication is sufficient to restore normal gene expression, directly implicating origin firing control in this regulation. Global early replication disrupts nucleosome positioning and transcription factor binding during S-phase, suggesting that the rate of S-phase is important to regulate the chromatin landscape. CONCLUSIONS Together, these data provide new insight into the role of the temporal control of origin firing during S-phase for coordinating replication, gene expression, and chromatin establishment as occurs in the early embryo.
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Affiliation(s)
- Miguel M Santos
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge, CB2 1GA, UK
- Wellcome Trust/Cancer Research UK Gurdon Institute, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QN, UK
| | - Mark C Johnson
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge, CB2 1GA, UK
- Wellcome Trust/Cancer Research UK Gurdon Institute, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QN, UK
| | - Lukáš Fiedler
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge, CB2 1GA, UK
- Wellcome Trust/Cancer Research UK Gurdon Institute, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QN, UK
| | - Philip Zegerman
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge, CB2 1GA, UK.
- Wellcome Trust/Cancer Research UK Gurdon Institute, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QN, UK.
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4
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Impact of Chromosomal Context on Origin Selection and the Replication Program. Genes (Basel) 2022; 13:genes13071244. [PMID: 35886027 PMCID: PMC9318681 DOI: 10.3390/genes13071244] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2022] [Revised: 06/28/2022] [Accepted: 07/08/2022] [Indexed: 02/01/2023] Open
Abstract
Eukaryotic DNA replication is regulated by conserved mechanisms that bring about a spatial and temporal organization in which distinct genomic domains are copied at characteristic times during S phase. Although this replication program has been closely linked with genome architecture, we still do not understand key aspects of how chromosomal context modulates the activity of replication origins. To address this question, we have exploited models that combine engineered genomic rearrangements with the unique replication programs of post-quiescence and pre-meiotic S phases. Our results demonstrate that large-scale inversions surprisingly do not affect cell proliferation and meiotic progression, despite inducing a restructuring of replication domains on each rearranged chromosome. Remarkably, these alterations in the organization of DNA replication are entirely due to changes in the positions of existing origins along the chromosome, as their efficiencies remain virtually unaffected genome wide. However, we identified striking alterations in origin firing proximal to the fusion points of each inversion, suggesting that the immediate chromosomal neighborhood of an origin is a crucial determinant of its activity. Interestingly, the impact of genome reorganization on replication initiation is highly comparable in the post-quiescent and pre-meiotic S phases, despite the differences in DNA metabolism in these two physiological states. Our findings therefore shed new light on how origin selection and the replication program are governed by chromosomal architecture.
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5
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Haws SA, Simandi Z, Barnett RJ, Phillips-Cremins JE. 3D genome, on repeat: Higher-order folding principles of the heterochromatinized repetitive genome. Cell 2022; 185:2690-2707. [PMID: 35868274 DOI: 10.1016/j.cell.2022.06.052] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2022] [Revised: 06/24/2022] [Accepted: 06/26/2022] [Indexed: 12/16/2022]
Abstract
Nearly half of the human genome is comprised of diverse repetitive sequences ranging from satellite repeats to retrotransposable elements. Such sequences are susceptible to stepwise expansions, duplications, inversions, and recombination events which can compromise genome function. In this review, we discuss the higher-order folding mechanisms of compartmentalization and loop extrusion and how they shape, and are shaped by, heterochromatin. Using primarily mammalian model systems, we contrast mechanisms governing H3K9me3-mediated heterochromatinization of the repetitive genome and highlight emerging links between repetitive elements and chromatin folding.
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Affiliation(s)
- Spencer A Haws
- Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, USA; Epigenetics Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA; Department of Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Zoltan Simandi
- Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, USA; Epigenetics Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA; Department of Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - R Jordan Barnett
- Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, USA; Epigenetics Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA; Department of Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Jennifer E Phillips-Cremins
- Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, USA; Epigenetics Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA; Department of Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
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6
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Hjelmen CE, Holmes VR, Burrus CG, Piron E, Mynes M, Garrett MA, Blackmon H, Johnston JS. Thoracic underreplication in Drosophila species estimates a minimum genome size and the dynamics of added DNA. Evolution 2020; 74:1423-1436. [PMID: 32438451 DOI: 10.1111/evo.14022] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2020] [Revised: 05/05/2020] [Accepted: 05/17/2020] [Indexed: 12/11/2022]
Abstract
Many cells in the thorax of Drosophila were found to stall during replication, a phenomenon known as underreplication. Unlike underreplication in nuclei of salivary and follicle cells, this stall occurs with less than one complete round of replication. This stall point allows precise estimations of early-replicating euchromatin and late-replicating heterochromatin regions, providing a powerful tool to investigate the dynamics of structural change across the genome. We measure underreplication in 132 species across the Drosophila genus and leverage these data to propose a model for estimating the rate at which additional DNA is accumulated as heterochromatin and euchromatin and also predict the minimum genome size for Drosophila. According to comparative phylogenetic approaches, the rates of change of heterochromatin differ strikingly between Drosophila subgenera. Although these subgenera differ in karyotype, there were no differences by chromosome number, suggesting other structural changes may influence accumulation of heterochromatin. Measurements were taken for both sexes, allowing the visualization of genome size and heterochromatin changes for the hypothetical path of XY sex chromosome differentiation. Additionally, the model presented here estimates a minimum genome size in Sophophora remarkably close to the smallest insect genome measured to date, in a species over 200 million years diverged from Drosophila.
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Affiliation(s)
- Carl E Hjelmen
- Department of Biology, Texas A&M University, College Station, Texas.,Department of Entomology, Texas A&M University, College Station, Texas
| | | | - Crystal G Burrus
- Department of Biology, Texas A&M University, College Station, Texas
| | - Elizabeth Piron
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas
| | - Melissa Mynes
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas
| | - Margaret A Garrett
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas
| | - Heath Blackmon
- Department of Biology, Texas A&M University, College Station, Texas
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7
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Lynch KL, Alvino GM, Kwan EX, Brewer BJ, Raghuraman MK. The effects of manipulating levels of replication initiation factors on origin firing efficiency in yeast. PLoS Genet 2019; 15:e1008430. [PMID: 31584938 PMCID: PMC6795477 DOI: 10.1371/journal.pgen.1008430] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Revised: 10/16/2019] [Accepted: 09/17/2019] [Indexed: 12/22/2022] Open
Abstract
Chromosome replication in Saccharomyces cerevisiae is initiated from ~300 origins that are regulated by DNA sequence and by the limited abundance of six trans-acting initiation proteins (Sld2, Sld3, Dpb11, Dbf4, Sld7 and Cdc45). We set out to determine how the levels of individual factors contribute to time of origin activation and/or origin efficiency using induced depletion of single factors and overexpression of sets of multiple factors. Depletion of Sld2 or Sld3 slows growth and S phase progression, decreases origin efficiency across the genome and impairs viability as a result of incomplete replication of the rDNA. We find that the most efficient early origins are relatively unaffected by depletion of either Sld2 or Sld3. However, Sld3 levels, and to a lesser extent Sld2 levels, are critical for firing of the less efficient early origins. Overexpression of Sld3 simultaneously with Sld2, Dpb11 and Dbf4 preserves the relative efficiency of origins. Only when Cdc45 and Sld7 are also overexpressed is origin efficiency equalized between early- and late-firing origins. Our data support a model in which Sld3 together with Cdc45 (and/or Sld7) is responsible for the differential efficiencies of origins across the yeast genome. Eukaryotic chromosome duplication begins at sites called origins of replication along the chromosomal DNA. A conserved property of eukaryotic origins is that they vary in efficiency—the proportion of cells in a population in which they “fire”—and in the average time of activation within S phase, but the molecular details underlying this variation are not well understood. Previous work has shown that limiting concentrations of a set of conserved replication initiation proteins referred to as “SSDDCS” (Sld2, Sld3, Dbf4, Dpb11, Cdc45, and Sld7) are rate limiting for origin activation in budding yeast and other eukaryotes; combined overexpression of these proteins increases and/or advances origin firing. However, it remained possible that different factors affect different aspects of origin activation (e.g., timing vs. efficiency). Here, by depleting individual factors or by overexpressing sets of factors in budding yeast, we demonstrate that it is levels of Sld3, Cdc45 and/or Sld7 levels are primarily responsible for modulating the differences in relative origin efficiency and timing. This work gives further insights into what shapes the landscape of genome duplication.
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Affiliation(s)
- Kelsey L. Lynch
- Molecular and Cellular Biology Program, University of Washington, Seattle, Washington, United States of America
- Department of Genome Sciences, University of Washington, Seattle, Washington, United States of America
| | - Gina M. Alvino
- Department of Genome Sciences, University of Washington, Seattle, Washington, United States of America
| | - Elizabeth X. Kwan
- Department of Genome Sciences, University of Washington, Seattle, Washington, United States of America
| | - Bonita J. Brewer
- Molecular and Cellular Biology Program, University of Washington, Seattle, Washington, United States of America
- Department of Genome Sciences, University of Washington, Seattle, Washington, United States of America
| | - M. K. Raghuraman
- Department of Genome Sciences, University of Washington, Seattle, Washington, United States of America
- * E-mail:
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8
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Abstract
Constitutive heterochromatin is a major component of the eukaryotic nucleus and is essential for the maintenance of genome stability. Highly concentrated at pericentromeric and telomeric domains, heterochromatin is riddled with repetitive sequences and has evolved specific ways to compartmentalize, silence, and repair repeats. The delicate balance between heterochromatin epigenetic maintenance and cellular processes such as mitosis and DNA repair and replication reveals a highly dynamic and plastic chromatin domain that can be perturbed by multiple mechanisms, with far-reaching consequences for genome integrity. Indeed, heterochromatin dysfunction provokes genetic turmoil by inducing aberrant repeat repair, chromosome segregation errors, transposon activation, and replication stress and is strongly implicated in aging and tumorigenesis. Here, we summarize the general principles of heterochromatin structure and function, discuss the importance of its maintenance for genome integrity, and propose that more comprehensive analyses of heterochromatin roles in tumorigenesis will be integral to future innovations in cancer treatment.
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Affiliation(s)
- Aniek Janssen
- Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, USA
| | - Serafin U. Colmenares
- Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, USA
| | - Gary H. Karpen
- Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, USA
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9
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Seller CA, O’Farrell PH. Rif1 prolongs the embryonic S phase at the Drosophila mid-blastula transition. PLoS Biol 2018; 16:e2005687. [PMID: 29746464 PMCID: PMC5963817 DOI: 10.1371/journal.pbio.2005687] [Citation(s) in RCA: 45] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2018] [Revised: 05/22/2018] [Accepted: 04/23/2018] [Indexed: 01/09/2023] Open
Abstract
In preparation for dramatic morphogenetic events of gastrulation, rapid embryonic cell cycles slow at the mid-blastula transition (MBT). In Drosophila melanogaster embryos, down-regulation of cyclin-dependent kinase 1 (Cdk1) activity initiates this slowing by delaying replication of heterochromatic satellite sequences and extending S phase. We found that Cdk1 activity inhibited the chromatin association of Rap1 interacting factor 1 (Rif1), a candidate repressor of replication. Furthermore, Rif1 bound selectively to satellite sequences following Cdk1 down-regulation at the MBT. In the next S phase, Rif1 dissociated from different satellites in an orderly schedule that anticipated their replication. Rif1 lacking potential phosphorylation sites failed to dissociate and dominantly prevented completion of replication. Loss of Rif1 in mutant embryos shortened the post-MBT S phase and rescued embryonic cell cycles disrupted by depletion of the S phase–promoting kinase, cell division cycle 7 (Cdc7). Our work shows that Rif1 and S phase kinases compose a replication timer controlling first the developmental onset of late replication and then the precise schedule of replication within S phase. In addition, we describe how onset of late replication fits into the progressive maturation of heterochromatin during development. Cells divide rapidly in the early embryos of most animals. However, during a conserved period of development known as the mid-blastula transition (MBT), the cell cycle slows down dramatically. In Drosophila embryos, genome duplication abruptly slows to initiate this cell cycle prolongation. This is achieved through the onset of late replication, a well-recognized phenomenon in which specific sequences of the genome await replication until long after other sequences have finished. Even though this temporal program of replication is a major determinant of the duration of S phase, the factors involved in this process remain unknown. Here, we use genetics and real-time microscopy to visualize replication in developing fly embryos and show that the protein Rap1 interacting factor 1 (Rif1) mediates the introduction of late replication at the MBT. We find that at this stage, Rif1 binds to and selectively delays the replication of large blocks of repetitive DNA known as satellite sequences. During the rapid cell cycles before the MBT, we show that the cyclin-dependent kinase 1 (Cdk1) prevents Rif1 from slowing down DNA replication by driving its removal from the chromatin. The developmental down-regulation of Cdk1 at the MBT allows Rif1 to associate with the satellite sequences and initiate cell cycle slowing. Our work provides new insights into the temporal programming of S phase and into the embryonic origin of late replication.
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Affiliation(s)
- Charles A. Seller
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, United States of America
| | - Patrick H. O’Farrell
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, United States of America
- * E-mail:
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10
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Abstract
Heterochromatin is a key architectural feature of eukaryotic chromosomes, which endows particular genomic domains with specific functional properties. The capacity of heterochromatin to restrain the activity of mobile elements, isolate DNA repair in repetitive regions and ensure accurate chromosome segregation is crucial for maintaining genomic stability. Nucleosomes at heterochromatin regions display histone post-translational modifications that contribute to developmental regulation by restricting lineage-specific gene expression. The mechanisms of heterochromatin establishment and of heterochromatin maintenance are separable and involve the ability of sequence-specific factors bound to nascent transcripts to recruit chromatin-modifying enzymes. Heterochromatin can spread along the chromatin from nucleation sites. The propensity of heterochromatin to promote its own spreading and inheritance is counteracted by inhibitory factors. Because of its importance for chromosome function, heterochromatin has key roles in the pathogenesis of various human diseases. In this Review, we discuss conserved principles of heterochromatin formation and function using selected examples from studies of a range of eukaryotes, from yeast to human, with an emphasis on insights obtained from unicellular model organisms.
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11
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Dvořáčková M, Raposo B, Matula P, Fuchs J, Schubert V, Peška V, Desvoyes B, Gutierrez C, Fajkus J. Replication of ribosomal DNA in Arabidopsis occurs both inside and outside the nucleolus during S phase progression. J Cell Sci 2018; 131:jcs.202416. [PMID: 28483825 DOI: 10.1242/jcs.202416] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2017] [Accepted: 04/06/2017] [Indexed: 12/14/2022] Open
Abstract
Ribosomal RNA genes (rDNA) have been used as valuable experimental systems in numerous studies. Here, we focus on elucidating the spatiotemporal organisation of rDNA replication in Arabidopsis thaliana To determine the subnuclear distribution of rDNA and the progression of its replication during the S phase, we apply 5-ethynyl-2'-deoxyuridine (EdU) labelling, fluorescence-activated cell sorting, fluorescence in situ hybridization and structured illumination microscopy. We show that rDNA is replicated inside and outside the nucleolus, where active transcription occurs at the same time. Nascent rDNA shows a maximum of nucleolar associations during early S phase. In addition to EdU patterns typical for early or late S phase, we describe two intermediate EdU profiles characteristic for mid S phase. Moreover, the use of lines containing mutations in the chromatin assembly factor-1 gene fas1 and wild-type progeny of fas1xfas2 crosses depleted of inactive copies allows for selective observation of the replication pattern of active rDNA. High-resolution data are presented, revealing the culmination of replication in the mid S phase in the nucleolus and its vicinity. Taken together, our results provide a detailed snapshot of replication of active and inactive rDNA during S phase progression.
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Affiliation(s)
- Martina Dvořáčková
- Laboratory of Molecular Complexes of Chromatin, Mendel Centre for Plant Genomics and Proteomics, CEITEC, Masaryk University, Kamenice 5, Brno 62500, Czech Republic
| | - Berta Raposo
- Department of Genome Dynamics and Function, Centro de Biología Molecular Severo Ochoa, CSIC-UAM, Nicolás Cabrera 1, Madrid 28049, Spain
| | - Petr Matula
- Department of Computer Graphics and Design, Faculty of Informatics, Masaryk University, Botanická 554/68a, Brno 60200, Czech Republic
| | - Joerg Fuchs
- Breeding Research Department, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK) Gatersleben, Corrensstrasse 3, Stadt Seeland D-06466, Germany
| | - Veit Schubert
- Breeding Research Department, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK) Gatersleben, Corrensstrasse 3, Stadt Seeland D-06466, Germany
| | - Vratislav Peška
- Laboratory of Molecular Complexes of Chromatin, Mendel Centre for Plant Genomics and Proteomics, CEITEC, Masaryk University, Kamenice 5, Brno 62500, Czech Republic.,Department of Cell Biology and Radiology, Institute of Biophysics ASCR, v.v.i., Královopolská 135, Brno 61265, Czech Republic
| | - Bénédicte Desvoyes
- Department of Genome Dynamics and Function, Centro de Biología Molecular Severo Ochoa, CSIC-UAM, Nicolás Cabrera 1, Madrid 28049, Spain
| | - Crisanto Gutierrez
- Department of Genome Dynamics and Function, Centro de Biología Molecular Severo Ochoa, CSIC-UAM, Nicolás Cabrera 1, Madrid 28049, Spain
| | - Jiří Fajkus
- Laboratory of Molecular Complexes of Chromatin, Mendel Centre for Plant Genomics and Proteomics, CEITEC, Masaryk University, Kamenice 5, Brno 62500, Czech Republic .,Department of Cell Biology and Radiology, Institute of Biophysics ASCR, v.v.i., Královopolská 135, Brno 61265, Czech Republic.,Laboratory of Functional Genomics and Proteomics, National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kotlářská 2, Brno 61137, Czech Republic
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12
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Kylie K, Romero J, Lindamulage IK, Knockleby J, Lee H. Dynamic regulation of histone H3K9 is linked to the switch between replication and transcription at the Dbf4 origin-promoter locus. Cell Cycle 2016; 15:2321-35. [PMID: 27341472 PMCID: PMC5004705 DOI: 10.1080/15384101.2016.1201254] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2016] [Revised: 05/20/2016] [Accepted: 06/08/2016] [Indexed: 02/07/2023] Open
Abstract
The co-regulation of DNA replication and gene transcription is still poorly understood. To gain a better understanding of this important control mechanism, we examined the DNA replication and transcription using the Dbf4 origin-promoter and Dbf4 pseudogene models. We found that origin firing and Dbf4 transcription activity were inversely regulated in a cell cycle-dependent manner. We also found that proteins critical for the regulation of replication (ORC, MCM), transcription (SP1, TFIIB), and cohesin (Smc1, Smc3) and Mediator functions (Med1, Med12) interact with specific sites within and the surrounding regions of the Dbf4 locus in a cell cycle-dependent manner. As expected, replication initiation occurred within a nucleosome-depleted region, and nucleosomes flanked the 2 replication initiation zones. Further, the histone H3 in this region was distinctly acetylated or trimethylated on lysine 9 in a cell cycle-dependent fluctuation pattern: H3K9ac was most prevalent when the Dbf4 transcription level was highest whereas the H3K9me3 level was greatest during and just after replication. The KDM4A histone demethylase, which is responsible for the H3K9me3 modification, was enriched at the Dbf4 origin in a manner coinciding with H3K9me3. Finally, HP1γ, a protein known to interact with H3K9me3 in the heterochromatin was also found enriched at the origin during DNA replication, indicating that H3K9me3 may be required for the regulation of replication at both heterochromatin and euchromatin regions. Taken together, our data show that mammalian cells employ an extremely sophisticated and multilayered co-regulation mechanism for replication and transcription in a highly coordinated manner.
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Affiliation(s)
- Kathleen Kylie
- Tumour Biology Group, Health Sciences North Research Institute, Sudbury, Ontario, Canada
| | - Julia Romero
- Tumour Biology Group, Health Sciences North Research Institute, Sudbury, Ontario, Canada
| | | | - James Knockleby
- Tumour Biology Group, Health Sciences North Research Institute, Sudbury, Ontario, Canada
| | - Hoyun Lee
- Tumour Biology Group, Health Sciences North Research Institute, Sudbury, Ontario, Canada
- Department of Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada
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13
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Chagin VO, Reinhart M, Cardoso MC. High-resolution analysis of Mammalian DNA replication units. Methods Mol Biol 2016; 1300:43-65. [PMID: 25916704 DOI: 10.1007/978-1-4939-2596-4_3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Genomic DNA of a eukaryotic cell is replicated once during the S-phase of the cell cycle to precisely maintain the complete genetic information. In the course of S-phase, semiconservative DNA synthesis is sequentially initiated and performed at thousands of discrete patches of the DNA helix termed replicons. At any given moment of S-phase, multiple replicons are active in parallel in different parts of the genome. In the last decades, tools and methods to visualize DNA synthesis inside cells have been developed. Pulse labeling with nucleotides as well as detecting components of the replication machinery yielded an overall picture of multiple discrete sites of active DNA synthesis termed replication foci (RFi) and forming spatiotemporal patterns within the cell nucleus. Recent advances in fluorescence microscopy and digital imaging in combination with computational image analysis allow a comprehensive quantitative analysis of RFi and provide valuable insights into the organization of the genomic DNA replication process and also of the genome itself. In this chapter, we describe in detail protocols for the visualization and quantification of RFi at different levels of optical and physical resolution.
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Affiliation(s)
- Vadim O Chagin
- Institute of Cytology, Russian Academy of Science, Saint Petersburg, Russia
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14
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Identification of chromatin marks at TERRA promoter and encoding region. Biochem Biophys Res Commun 2015; 467:1052-7. [PMID: 26449455 DOI: 10.1016/j.bbrc.2015.09.176] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2015] [Accepted: 09/30/2015] [Indexed: 12/27/2022]
Abstract
TERRA is a long non-coding RNA that is essential for telomere integrity. Although it is transcribed from subtelomeres and telomeres, how it is expressed in heterochromatic region is currently unknown. In this study, we focused our analysis on TERRA-encoding region TelBam3.4 and TelBam3.4-like sequences, and determined their transcription start sites, as well as enrichment of RNA polymerase II and histone modifications. We found that H3K4me3 and H3K9me3 are present at TERRA promoters, whereas H3K27ac and H3K9me3 are present at telomeric repeats. Consistently, we show that presence of active histone modifications H3K4me3 and H3K27ac are correlated to TERRA expression. These results mark an important step towards understanding telomere maintenance and transcription.
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15
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Liu J, Zimmer K, Rusch DB, Paranjape N, Podicheti R, Tang H, Calvi BR. DNA sequence templates adjacent nucleosome and ORC sites at gene amplification origins in Drosophila. Nucleic Acids Res 2015; 43:8746-61. [PMID: 26227968 PMCID: PMC4605296 DOI: 10.1093/nar/gkv766] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Accepted: 07/16/2015] [Indexed: 12/12/2022] Open
Abstract
Eukaryotic origins of DNA replication are bound by the origin recognition complex (ORC), which scaffolds assembly of a pre-replicative complex (pre-RC) that is then activated to initiate replication. Both pre-RC assembly and activation are strongly influenced by developmental changes to the epigenome, but molecular mechanisms remain incompletely defined. We have been examining the activation of origins responsible for developmental gene amplification in Drosophila. At a specific time in oogenesis, somatic follicle cells transition from genomic replication to a locus-specific replication from six amplicon origins. Previous evidence indicated that these amplicon origins are activated by nucleosome acetylation, but how this affects origin chromatin is unknown. Here, we examine nucleosome position in follicle cells using micrococcal nuclease digestion with Ilumina sequencing. The results indicate that ORC binding sites and other essential origin sequences are nucleosome-depleted regions (NDRs). Nucleosome position at the amplicons was highly similar among developmental stages during which ORC is or is not bound, indicating that being an NDR is not sufficient to specify ORC binding. Importantly, the data suggest that nucleosomes and ORC have opposite preferences for DNA sequence and structure. We propose that nucleosome hyperacetylation promotes pre-RC assembly onto adjacent DNA sequences that are disfavored by nucleosomes but favored by ORC.
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Affiliation(s)
- Jun Liu
- Department of Biology, Indiana University, Bloomington, IN 47405, USA
| | - Kurt Zimmer
- School of Informatics and Computing, Indiana University, Bloomington, IN 47405, USA
| | - Douglas B Rusch
- Center for Genomics and Bioinformatics, Indiana University, Bloomington, IN 47405, USA
| | - Neha Paranjape
- Department of Biology, Indiana University, Bloomington, IN 47405, USA
| | - Ram Podicheti
- School of Informatics and Computing, Indiana University, Bloomington, IN 47405, USA Center for Genomics and Bioinformatics, Indiana University, Bloomington, IN 47405, USA
| | - Haixu Tang
- School of Informatics and Computing, Indiana University, Bloomington, IN 47405, USA
| | - Brian R Calvi
- Department of Biology, Indiana University, Bloomington, IN 47405, USA
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16
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Li PC, Green MD, Forsburg SL. Mutations disrupting histone methylation have different effects on replication timing in S. pombe centromere. PLoS One 2013; 8:e61464. [PMID: 23658693 PMCID: PMC3641051 DOI: 10.1371/journal.pone.0061464] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2012] [Accepted: 03/11/2013] [Indexed: 11/19/2022] Open
Abstract
The fission yeast pericentromere comprises repetitive sequence elements packaged into heterchromatin marked by histone H3K9 methylation and Swi6 binding. Transient disruption of Swi6 during S phase allows a period of RNA synthesis which programs the RNAi machinery to maintain histone methylation. However, Swi6 is also required for early replication timing. We show that not only Swi6 but also the chromodomain protein Chp1 are delocalized during S phase. Different from loss of swi6, mutations that disrupt histone methylation in the centromere, chp1Δ and clr4Δ, undergo early DNA replication. However, timing is modestly delayed in RNAi mutants dcr1Δ or rdp1Δ, while hrr1Δ mutants resemble swi6Δ in their replication delay. Finally, we show that recruitment of RNA polymerase II in the centromere occurs independently of replication. These different effects indicate that replication timing is not simply linked to histone methylation.
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Affiliation(s)
- Pao-Chen Li
- Molecular & Computational Biology Program, University of Southern California, Los Angeles, California, United States of America
| | - Marc D. Green
- Molecular & Computational Biology Program, University of Southern California, Los Angeles, California, United States of America
| | - Susan L. Forsburg
- Molecular & Computational Biology Program, University of Southern California, Los Angeles, California, United States of America
- * E-mail:
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17
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Nishigaki M, Kawada Y, Misaki T, Murata K, Goshima T, Hirokawa T, Yamada C, Shimada M, Nakanishi M. Mitotic phosphorylation of MPP8 by cyclin-dependent kinases regulates chromatin dissociation. Biochem Biophys Res Commun 2013; 432:654-9. [DOI: 10.1016/j.bbrc.2013.02.027] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2013] [Accepted: 02/04/2013] [Indexed: 11/26/2022]
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18
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Whitehouse I, Smith DJ. Chromatin dynamics at the replication fork: there's more to life than histones. Curr Opin Genet Dev 2013; 23:140-6. [PMID: 23347596 DOI: 10.1016/j.gde.2012.12.007] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2012] [Revised: 12/12/2012] [Accepted: 12/20/2012] [Indexed: 12/31/2022]
Abstract
Before each division, eukaryotic cells face the daunting task of completely and accurately replicating a heterogeneous, chromatinized genome and repackaging both resulting daughters. Because replication requires strand separation, interactions between the DNA and its many associated proteins--including histones--must be transiently broken to allow the passage of the replication fork. Here, we will discuss the disruption and re-establishment of chromatin structure during replication, and the consequences of these processes for epigenetic inheritance.
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Affiliation(s)
- Iestyn Whitehouse
- Molecular Biology Program, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10065, USA.
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19
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Bechhoefer J, Rhind N. Replication timing and its emergence from stochastic processes. Trends Genet 2012; 28:374-81. [PMID: 22520729 DOI: 10.1016/j.tig.2012.03.011] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2012] [Revised: 03/21/2012] [Accepted: 03/22/2012] [Indexed: 01/28/2023]
Abstract
The temporal organization of DNA replication has puzzled cell biologists since before the mechanism of replication was understood. The realization that replication timing correlates with important features, such as transcription, chromatin structure and genome evolution, and is misregulated in cancer and aging has only deepened the fascination. Many ideas about replication timing have been proposed, but most have been short on mechanistic detail. However, recent work has begun to elucidate basic principles of replication timing. In particular, mathematical modeling of replication kinetics in several systems has shown that the reproducible replication timing patterns seen in population studies can be explained by stochastic origin firing at the single-cell level. This work suggests that replication timing need not be controlled by a hierarchical mechanism that imposes replication timing from a central regulator, but instead results from simple rules that affect individual origins.
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Affiliation(s)
- John Bechhoefer
- Department of Physics, Simon Fraser University, Burnaby, BC, V5A 1S6, Canada.
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20
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Structure, function and dynamics of nuclear subcompartments. Curr Opin Cell Biol 2012; 24:79-85. [DOI: 10.1016/j.ceb.2011.12.009] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2011] [Revised: 12/09/2011] [Accepted: 12/15/2011] [Indexed: 01/09/2023]
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21
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Liu J, McConnell K, Dixon M, Calvi BR. Analysis of model replication origins in Drosophila reveals new aspects of the chromatin landscape and its relationship to origin activity and the prereplicative complex. Mol Biol Cell 2011; 23:200-12. [PMID: 22049023 PMCID: PMC3248898 DOI: 10.1091/mbc.e11-05-0409] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
A study of model DNA replication origins in Drosophila reveals a codependence between histone acetylation and pre-RC assembly and leads to a chromatin switch model for the coordination of origin and promoter activity during development. Epigenetic regulation exerts a major influence on origins of DNA replication during development. The mechanisms for this regulation, however, are poorly defined. We showed previously that acetylation of nucleosomes regulates the origins that mediate developmental gene amplification during Drosophila oogenesis. Here we show that developmental activation of these origins is associated with acetylation of multiple histone lysines. Although these modifications are not unique to origin loci, we find that the level of acetylation is higher at the active origins and quantitatively correlated with the number of times these origins initiate replication. All of these acetylation marks were developmentally dynamic, rapidly increasing with origin activation and rapidly declining when the origins shut off and neighboring promoters turn on. Fine-scale analysis of the origins revealed that both hyperacetylation of nucleosomes and binding of the origin recognition complex (ORC) occur in a broad domain and that acetylation is highest on nucleosomes adjacent to one side of the major site of replication initiation. It was surprising to find that acetylation of some lysines depends on binding of ORC to the origin, suggesting that multiple histone acetyltransferases may be recruited during origin licensing. Our results reveal new insights into the origin epigenetic landscape and lead us to propose a chromatin switch model to explain the coordination of origin and promoter activity during development.
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Affiliation(s)
- Jun Liu
- Department of Biology, Indiana University, Bloomington, IN 47405, USA
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22
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Occurrence of 47,X,i(X)(q10),Y Klinefelter variant with hypogonadotropic hypogonadism. Fertil Steril 2011; 96:e115-7. [PMID: 21703612 DOI: 10.1016/j.fertnstert.2011.05.074] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2011] [Revised: 05/01/2011] [Accepted: 05/22/2011] [Indexed: 11/20/2022]
Abstract
OBJECTIVE To report a rare occurrence of 47,X,i(Xq),Y karyotype with hypogonadotropic hypogonadism in a man. DESIGN Case report. SETTING Infertility institute. PATIENT(S) Thirty-three-year-old man with primary infertility. INTERVENTION(S) Clinical evaluation, hormone assays, and assessment of X inactivation. MAIN OUTCOME MEASURE(S) Physical examination, semen analysis, and cytogenetic analysis. RESULT(S) The patient showed the classic phenotype of Klinefelter syndrome but with low levels of FSH and LH. The bromodeoxyuridine-33258 Hoechst technique showed faint staining of the long arm of the isochromosome. CONCLUSION(S) This is the first report of co-occurrence of hypogonadotropic hypogonadism with the 47,X,i(X)(q10),Y Klinefelter karyotype variant in a man.
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Lee TJ, Pascuzzi PE, Settlage SB, Shultz RW, Tanurdzic M, Rabinowicz PD, Menges M, Zheng P, Main D, Murray JAH, Sosinski B, Allen GC, Martienssen RA, Hanley-Bowdoin L, Vaughn MW, Thompson WF. Arabidopsis thaliana chromosome 4 replicates in two phases that correlate with chromatin state. PLoS Genet 2010; 6:e1000982. [PMID: 20548960 PMCID: PMC2883604 DOI: 10.1371/journal.pgen.1000982] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2010] [Accepted: 05/12/2010] [Indexed: 12/23/2022] Open
Abstract
DNA replication programs have been studied extensively in yeast and animal systems, where they have been shown to correlate with gene expression and certain epigenetic modifications. Despite the conservation of core DNA replication proteins, little is known about replication programs in plants. We used flow cytometry and tiling microarrays to profile DNA replication of Arabidopsis thaliana chromosome 4 (chr4) during early, mid, and late S phase. Replication profiles for early and mid S phase were similar and encompassed the majority of the euchromatin. Late S phase exhibited a distinctly different profile that includes the remaining euchromatin and essentially all of the heterochromatin. Termination zones were consistent between experiments, allowing us to define 163 putative replicons on chr4 that clustered into larger domains of predominately early or late replication. Early-replicating sequences, especially the initiation zones of early replicons, displayed a pattern of epigenetic modifications specifying an open chromatin conformation. Late replicons, and the termination zones of early replicons, showed an opposite pattern. Histone H3 acetylated on lysine 56 (H3K56ac) was enriched in early replicons, as well as the initiation zones of both early and late replicons. H3K56ac was also associated with expressed genes, but this effect was local whereas replication time correlated with H3K56ac over broad regions. The similarity of the replication profiles for early and mid S phase cells indicates that replication origin activation in euchromatin is stochastic. Replicon organization in Arabidopsis is strongly influenced by epigenetic modifications to histones and DNA. The domain organization of Arabidopsis is more similar to that in Drosophila than that in mammals, which may reflect genome size and complexity. The distinct patterns of association of H3K56ac with gene expression and early replication provide evidence that H3K56ac may be associated with initiation zones and replication origins. During growth and development, all plants and animals must replicate their DNA. This process is regulated to ensure that all sequences are completely and accurately replicated and is limited to S phase of the cell cycle. In the cell, DNA is packaged with histone proteins into chromatin, and both DNA and histones are subject to epigenetic modifications that affect chromatin state. Euchromatin and heterochromatin are chromatin states marked by epigenetic modifications specifying open and closed conformations, respectively. Using the model plant Arabidopsis thaliana, we show that the time at which a DNA sequence replicates is influenced by the epigenetic modifications to the surrounding chromatin. DNA replication occurs in two phases, with euchromatin replicating in early and mid S phase and heterochromatin replicating late. DNA replication time has been linked to gene expression in other organisms, and this is also true in Arabidopsis because more genes are active in euchromatin when compared to heterochromatin. The earliest replicating DNA sequences are associated with acetylation of histone H3 on lysine 56 (H3K56ac). H3K56ac is also abundant in active genes, but the patterns of association of H3K56ac with gene expression and DNA replication are distinct, suggesting that H3K56ac is independently linked to both processes.
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Affiliation(s)
- Tae-Jin Lee
- Department of Horticultural Science, North Carolina State University, Raleigh, North Carolina, United States of America
| | - Pete E. Pascuzzi
- Department of Molecular and Structural Biochemistry, North Carolina State University, Raleigh, North Carolina, United States of America
| | - Sharon B. Settlage
- Department of Molecular and Structural Biochemistry, North Carolina State University, Raleigh, North Carolina, United States of America
| | - Randall W. Shultz
- Department of Molecular and Structural Biochemistry, North Carolina State University, Raleigh, North Carolina, United States of America
| | - Milos Tanurdzic
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, United States of America
| | - Pablo D. Rabinowicz
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, United States of America
| | - Margit Menges
- School of Biosciences, Cardiff University, Cardiff, Wales, United Kingdom
| | - Ping Zheng
- Department of Horticulture and Landscape Architecture, Washington State University, Pullman, Washington, United States of America
| | - Dorrie Main
- Department of Horticulture and Landscape Architecture, Washington State University, Pullman, Washington, United States of America
| | - James A. H. Murray
- School of Biosciences, Cardiff University, Cardiff, Wales, United Kingdom
| | - Bryon Sosinski
- Department of Horticultural Science, North Carolina State University, Raleigh, North Carolina, United States of America
| | - George C. Allen
- Department of Horticultural Science, North Carolina State University, Raleigh, North Carolina, United States of America
| | - Robert A. Martienssen
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, United States of America
| | - Linda Hanley-Bowdoin
- Department of Molecular and Structural Biochemistry, North Carolina State University, Raleigh, North Carolina, United States of America
| | - Matthew W. Vaughn
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, United States of America
| | - William F. Thompson
- Departments of Plant Biology, Genetics, and Crop Science, North Carolina State University, Raleigh, North Carolina, United States of America
- * E-mail:
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25
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LIMA-DE-FARIA A, JAWORSKA HALINA. The relation between the chromosome size gradient and the sequence of DNA replication in rye. Hereditas 2009. [DOI: 10.1111/j.1601-5223.1972.tb00992.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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26
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Russo RE, Reali C, Radmilovich M, Fernández A, Trujillo-Cenóz O. Connexin 43 delimits functional domains of neurogenic precursors in the spinal cord. J Neurosci 2008; 28:3298-309. [PMID: 18367597 PMCID: PMC6670595 DOI: 10.1523/jneurosci.5736-07.2008] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2007] [Revised: 02/14/2008] [Accepted: 02/16/2008] [Indexed: 11/21/2022] Open
Abstract
The cells lining the central canal (CC) of the spinal cord derive from the ventral part of the neural tube and, in some vertebrates, are responsible for the functional recovery after spinal cord injury. The region that surrounds the CC in the turtle contains proliferating cells that seem to generate both glia and neurons. Understanding the biology of spinal progenitors with the potential to generate new neurons "in situ" is important for cell replacement therapies. Here, we aimed to identify and characterize precursor cells in the spinal cord of Trachemys dorbignyi. To evaluate the population of proliferating cells, 5-bromo-2'-deoxyuridine (BrdU) was injected every 4 h (50 microg/g, i.p.) during 24 h. We found BrdU(+) nuclei around the CC with a higher density in the lateral quadrants, in which whole-cell patch-clamp recordings showed extensive dye coupling of cells. Carbenoxolone (100 microM) increased the input resistance, suggesting strong gap junction coupling among precursors. The expression of brain lipid binding protein (a marker of a subtype of radial glia) and Pax6 matched the location of clusters, suggesting these cells belonged to a domain of neurogenic precursors. These domains were delimited by a high density of connexin 43 (Cx43) located on the endfeet of CC contacting cells. Our findings indicate that spinal precursors share basic properties with those in the embryo and neurogenic niches of the adult brain, and support a key role of functional clustering via Cx43 in spinal cord neurogenesis.
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Affiliation(s)
- Raúl E Russo
- Neurofisiología Celular y Molecular, Instituto de Investigaciones Biológicas Clemente Estable, CP 11600 Montevideo, Uruguay.
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27
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Takenaka Y, Nagahara H, Kitahata H, Yoshikawa K. Large-scale on-off switching of genetic activity mediated by the folding-unfolding transition in a giant DNA molecule: an hypothesis. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2008; 77:031905. [PMID: 18517420 DOI: 10.1103/physreve.77.031905] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2007] [Indexed: 05/26/2023]
Abstract
We present a model to describe the on-off switching of transcriptional activity in a genetic assembly by considering the intrinsic characteristics of a giant genomic DNA molecule which can undergo a discrete structural transition between coiled and compact states. We propose a model in which the transition in the higher-order structure of DNA plays an essential role in regulating stable on-off switching and/or the oscillation of a large number of genes under the fluctuations in a living cell, where such a structural transition is caused by environmental factors. This model explains the rapid and broad transcriptional response in a genetic assembly as well as its robustness against fluctuations.
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Affiliation(s)
- Yoshiko Takenaka
- Department of Physics, Graduate School of Science, Kyoto University, and Spatio-temporal Order Project, ICORP, JST, Kyoto 606-8502, Japan.
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28
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Schmidt M. Identification of putative neuroblasts at the base of adult neurogenesis in the olfactory midbrain of the spiny lobster, Panulirus argus. J Comp Neurol 2007; 503:64-84. [PMID: 17480012 DOI: 10.1002/cne.21366] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Continuous neurogenesis persists during adulthood in the olfactory midbrain of decapod crustaceans, including spiny lobsters, Panulirus argus. This encompasses generation of projection and local interneurons, whose somata are in the lateral soma cluster (LC) and medial soma cluster (MC), respectively. Both neuronal types originate from immediate precursors labeled by a single injection of BrdU and located in a small proliferation zone within each cluster. The aim of this study was to identify neuroblasts as a source of the dividing cells by multiple injections of BrdU over 2 days. All animals receiving multiple injections had one or a few 'extra' BrdU-positive nuclei near the proliferation zones, and these nuclei were significantly larger than nuclei of neurons or BrdU-positive cells in the proliferation zones. Since the defining morphological feature of neuroblasts in preadult neurogenesis in arthropods is being larger than their progeny, these large extra BrdU-positive nuclei represent "putative adult neuroblasts." Multiple BrdU-injections revealed a clump of small cells enclosing the putative adult neuroblasts in LC and MC, and these cells shared morphological characteristics with newly identified putative glial cells in the soma clusters and perivascular cells in the walls of arterioles. These results on P. argus suggest that adult neurogenesis is based on one adult neuroblast per soma cluster, adult neurogenesis appears to be a continuation of embryonic and larval neurogenesis, and the newly identified clumps of cells surrounding the putative adult neuroblasts might provide them with specific microenvironments necessary for their unusual lifelong proliferative and self-renewal capacity.
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Affiliation(s)
- Manfred Schmidt
- Department of Biology, Georgia State University, Atlanta, GA 30303, USA.
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29
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Regelson M, Eller CD, Horvath S, Marahrens Y. A link between repetitive sequences and gene replication time. Cytogenet Genome Res 2006; 112:184-93. [PMID: 16484771 DOI: 10.1159/000089869] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2005] [Accepted: 08/08/2005] [Indexed: 11/19/2022] Open
Abstract
Genes display a wide range of replication times in S phase. In general, late replication is associated with transcriptionally repressive states and early replication with transcriptional competence. Rare examples of early-replicating repressive states have also been identified that are consistent with molecular evidence that repressive states are not all uniform in nature. Here we show that the replication times of over 4000 Drosophila genes correlate with the abundance of repetitive sequences in approximately 200-kb regions flanking the genes. In particular, Satellite-Related sequences (SRs) and the simple sequence repeats (SSRs) (CA)n and (ACTG)n were increasingly abundant in the regions flanking progressively later replicating genes, while (CATA)n repeats were more abundant around earlier replicating genes. These four sequences comprise less than 0.5% of the 'euchromatic genome' in Drosophila, yet they account for 5% of the variation of gene replication timing. Although the effect is not strong, it is broad: 99% of the genome is within the region of correlation of at least one of the above repeats. The role of SSRs and non-centromeric SRs in the genome is not known. We propose that SSRs and SRs foster transcriptionally repressive states throughout the genome in order to minimize spurious transcription.
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Affiliation(s)
- M Regelson
- UCLA Department of Human Genetics, Gonda Center, David Geffen School of Medicine, Los Angeles, CA, USA
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30
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Dna replication in eukaryotes. Rev Physiol Biochem Pharmacol 2005. [DOI: 10.1007/bfb0030491] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/18/2023]
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31
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Belyakin SN, Christophides GK, Alekseyenko AA, Kriventseva EV, Belyaeva ES, Nanayev RA, Makunin IV, Kafatos FC, Zhimulev IF. Genomic analysis of Drosophila chromosome underreplication reveals a link between replication control and transcriptional territories. Proc Natl Acad Sci U S A 2005; 102:8269-74. [PMID: 15928082 PMCID: PMC1149430 DOI: 10.1073/pnas.0502702102] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
In Drosophila polytene chromosomes, most late-replicating regions remain underreplicated. A loss-of-function mutant of the suppressor of underreplication [Su(UR)] gene suppresses underreplication (UR), whereas extra copies of this gene enhance the level and number of regions showing UR. By combining DNA microarray analysis with manipulation of the number of Su(UR) gene copies, we achieved genomic-scale molecular identification of 1,036 genes that are arranged in clusters located in 52 UR chromosomal regions. These regions overlap extensively (96%) but are not completely identical with late-replicating regions of mitotically dividing Kc cells in culture. Reanalysis of published gene expression profiles revealed that genomic regions defined by replication properties include clusters of coordinately expressed genes. Genomic regions that are UR in polytene chromosomes and late replicated in Kc cell chromosomes show a particularly common association with transcriptional territories that are expressed in testis/males but not ovary/females or embryos. An attractive hypothesis for future testing is that factors involved in replication control, such as SU(UR), may interact physically with those involved in epigenetic silencing of transcription territories.
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Affiliation(s)
- Stepan N Belyakin
- Institute of Cytology and Genetics of Siberian Division, Russian Academy of Sciences, Novosibirsk 630090, Russia
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32
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Yompakdee C, Huberman JA. Enforcement of Late Replication Origin Firing by Clusters of Short G-rich DNA Sequences. J Biol Chem 2004; 279:42337-44. [PMID: 15294892 DOI: 10.1074/jbc.m407552200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Previous studies in budding yeast suggested that the default firing time of most DNA replication origins is early in S phase and that origins can be forced to fire later by proximity to certain cis-acting sequences. However, these cis-acting sequences were not well defined. We have attempted to characterize cis-acting sequences that affect replication timing in the fission yeast. We identified a stretch of 200 bp that was sufficient to compel nearby origins to fire late. The 200-bp stretch was able to force an origin to fire late whether adjacent to the origin or approximately 800 bp away in opposite orientation. The stretch contains a cluster of three close matches to a G-rich, 10-bp late consensus sequence (LCS). The three LCS elements cooperate with each other and with other sequences within the 200-bp stretch to enforce late replication. Although only a few origins that fire in very late S phase have been identified in fission yeast, all of them are located close to a cluster of LCS elements.
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Affiliation(s)
- Chulee Yompakdee
- Department of Cancer Genetics, Roswell Park Cancer Institute, Buffalo, New York 14263-0001, USA
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Kourmouli N, Jeppesen P, Mahadevhaiah S, Burgoyne P, Wu R, Gilbert DM, Bongiorni S, Prantera G, Fanti L, Pimpinelli S, Shi W, Fundele R, Singh PB. Heterochromatin and tri-methylated lysine 20 of histone H4 in animals. J Cell Sci 2004; 117:2491-501. [PMID: 15128874 DOI: 10.1242/jcs.01238] [Citation(s) in RCA: 201] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Tri-methylated lysine 20 on histone H4 (Me(3)K20H4) is a marker of constitutive heterochromatin in murine interphase and metaphase cells. Heterochromatin marked by Me(3)K20H4 replicates late during S phase of the cell cycle. Serum starvation increases the number of cells that exhibit high levels of Me(3)K20H4 at constitutive heterochromatin. Me(3)K20H4 is also present at the centromeric heterochromatin of most meiotic chromosomes during spermatogenesis and at the pseudoautosomal region, as well as at some telomeres. It is not present on the XY-body. During murine embryogenesis the maternal pronucleus contains Me(3)K20H4; Me(3)K20H4 is absent from the paternal pronucleus. On Drosophila polytene chromosomes Me(3)K20H4 is present in a 'punctate pattern' at many chromosomal bands, including the chromocenter. In coccids it is present on the facultatively heterochromatinised paternal chromosome set. We also present evidence that Me(3)K20H4 is dependent upon H3-specific Suv(3)9 histone methyltransferase activity, suggesting that there may be 'epigenetic cross-talk' between histones H3 and H4.
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Affiliation(s)
- Niki Kourmouli
- Nuclear Reprogramming Laboratory, Division of Gene Expression and Development, Roslin Institute, Edinburgh, EH25 9PS, UK
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34
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Abstract
We focus here on the intercalary heterochromatin (IH) of Drosophila melanogaster and, in particular, its molecular properties. In the polytene chromosomes of Drosophila, IH is represented by a reproducible set of dense bands scattered along the euchromatic arms. IH contains mainly unique DNA sequences, and shares certain features with other heterochromatin types such as pericentric, telomeric, and PEV-induced heterochromatin, the inactive mammalian X-chromosome and the heterochromatized male chromosome set in coccids. These features are transcriptional silencing, chromatin compactness, late DNA replication, underrreplication or elimination in somatic cells, and formation of the heterochromatin state in early embryogenesis. Post-translational modification of histones and the specific nonhistone protein complexes are shown to participate in the establishment and maintenance of silencing for all heterochromatin types. Many IH regions contain binding sites for HP1 and/or Pc-G proteins and all the regions are sites of heterochromatin-associated SuUR protein. Some IH regions are known to contain homeotic genes. Summarizing these data, we suggest that IH regions comprise stable inactivated genes, whose silencing is developmentally programmed.
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Affiliation(s)
- Igor F Zhimulev
- Institute of Cytology and Genetics, Siberian Division of Russian Academy of Sciences, Russia
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35
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Schawalder J, Paric E, Neff NF. Telomere and ribosomal DNA repeats are chromosomal targets of the bloom syndrome DNA helicase. BMC Cell Biol 2003; 4:15. [PMID: 14577841 PMCID: PMC270065 DOI: 10.1186/1471-2121-4-15] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2003] [Accepted: 10/27/2003] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Bloom syndrome is one of the most cancer-predisposing disorders and is characterized by genomic instability and a high frequency of sister chromatid exchange. The disorder is caused by loss of function of a 3' to 5' RecQ DNA helicase, BLM. The exact role of BLM in maintaining genomic integrity is not known but the helicase has been found to associate with several DNA repair complexes and some DNA replication foci. RESULTS Chromatin immunoprecipitation of BLM complexes recovered telomere and ribosomal DNA repeats. The N-terminus of BLM, required for NB localization, is the same as the telomere association domain of BLM. The C-terminus is required for ribosomal DNA localization. BLM localizes primarily to the non-transcribed spacer region of the ribosomal DNA repeat where replication forks initiate. Bloom syndrome cells expressing the deletion alleles lacking the ribosomal DNA and telomere association domains have altered cell cycle populations with increased S or G2/M cells relative to normal. CONCLUSION These results identify telomere and ribosomal DNA repeated sequence elements as chromosomal targets for the BLM DNA helicase during the S/G2 phase of the cell cycle. BLM is localized in nuclear bodies when it associates with telomeric repeats in both telomerase positive and negative cells. The BLM DNA helicase participates in genomic stability at ribosomal DNA repeats and telomeres.
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Affiliation(s)
- James Schawalder
- Laboratory of Molecular Genetics, New York Blood Center, New York, New York 10021, USA
- Helicon Therapeutics, Farmingdale, New York 11735, USA
| | - Enesa Paric
- Laboratory of Molecular Genetics, New York Blood Center, New York, New York 10021, USA
- Gene Therapy Vector Laboratory, North Shore University Hospital, Manhasset, New York 11030, USA
| | - Norma F Neff
- Laboratory of Molecular Genetics, New York Blood Center, New York, New York 10021, USA
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36
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Badugu R, Shareef MM, Kellum R. Novel Drosophila heterochromatin protein 1 (HP1)/origin recognition complex-associated protein (HOAP) repeat motif in HP1/HOAP interactions and chromocenter associations. J Biol Chem 2003; 278:34491-8. [PMID: 12826664 DOI: 10.1074/jbc.m305262200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Association of the highly conserved heterochromatin protein, HP1, with the specialized chromatin of centromeres and telomeres requires binding to a specific histone H3 modification of methylation on lysine 9. This modification is catalyzed by the Drosophila Su(var)3-9 gene product and its homologues. Specific DNA binding activities are also likely to be required for targeting this activity along with HP1 to specific chromosomal regions. The Drosophila HOAP protein is a DNA-binding protein that was identified as a component of a multiprotein complex of HP1 containing Drosophila origin recognition complex (ORC) subunits in the early Drosophila embryo. Here we show direct physical interactions between the HOAP protein and HP1 and specific ORC subunits. Two additional HP1-like proteins (HP1b and HP1c) were recently identified in Drosophila, and the unique chromosomal distribution of each isoform is determined by two independently acting HP1 domains (hinge and chromoshadow domain) (47). We find heterochromatin protein 1/origin recognition complex-associated protein (HOAP) to interact specifically with the originally described predominantly heterochromatic HP1a protein. Both the hinge and chromoshadow domains of HP1a are required for its interaction with HOAP, and a novel peptide repeat located in the carboxyl terminus of the HOAP protein is required for the interaction with the HP1 hinge domain. Peptides that interfere with HP1a/HOAP interactions in co-precipitation experiments also displace HP1 from the heterochromatic chromocenter of polytene chromosomes in larval salivary glands. A mutant for the HOAP protein also suppresses centric heterochromatin-induced silencing, supporting a role for HOAP in centric heterochromatin.
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Affiliation(s)
- RamaKrishna Badugu
- Department of Biology, University of Kentucky, Lexington, Kentucky 40506-0225, USA
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37
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Ouspenski II, Van Hooser AA, Brinkley BR. Relevance of histone acetylation and replication timing for deposition of centromeric histone CENP-A. Exp Cell Res 2003; 285:175-88. [PMID: 12706113 DOI: 10.1016/s0014-4827(03)00011-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A centromere-specific variant of histone H3, centromere protein A (CENP-A), is a critical determinant of centromeric chromatin, and its location on the chromosome may determine centromere identity. To search for factors that direct CENP-A deposition at a specific chromosomal locus, we took advantage of the observation that CENP-A, when expressed at elevated levels, can get incorporated at ectopic sites on the chromosome, in addition to the centromere. As core histone hypoacetylation and DNA replication timing have been implicated as epigenetic factors that may be important for centromere identity, we hypothesized that the sites of preferential CENP-A deposition will be distinguished by these parameters. We found that, on human dicentric chromosomes, ectopically expressed CENP-A preferentially incorporates at the active centromere only, despite the fact that the levels of histone acetylation and replication timing were indistinguishable at the two centromeres. In CHO cells, ectopically expressed CENP-A is preferentially targeted to some, but not all telomeric regions. Again, these regions could not be distinguished from other telomeres by their acetylation levels or replication timing. Thus histone acetylation and replication timing are not sufficient for specifying the sites of CENP-A deposition and likely for centromere identity.
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Affiliation(s)
- Ilia I Ouspenski
- Department of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
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38
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Abstract
Since its discovery almost two decades ago, heterochromatin protein 1 (HP1) has emerged as a major player in the transcriptional regulation of both heterochromatic and euchromatic genes as well as the mechanics of chromosome segregation and the functional and structural organization of the interphase nucleus. Recent years have brought the identification of a myriad of HP1-interacting proteins. Each of these is discussed in relationship to its role in heterochromatin assembly and HP1 function. The breadth of functions represented by HP1-interacting proteins testifies to its pivotal role in the daily operations of the nucleus.
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Affiliation(s)
- R Kellum
- School of Biological Sciences, 101 T. H. Morgan Building, University of Kentucky, Lexington, KY 40506-0225, USA.
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39
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Koryakov DE, Domanitskaya EV, Belyakin SN, Zhimulev IF. Abnormal tissue-dependent polytenization of a block of chromosome 3 pericentric heterochromatin in Drosophila melanogaster. J Cell Sci 2003; 116:1035-44. [PMID: 12584247 DOI: 10.1242/jcs.00283] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Heterochromatic DNA sequences in the polytene chromosomes of Drosophila melanogaster salivary glands are under-replicated in wild-type strains. In salivary glands of SuUR and in the nurse cells of otu mutants, under-replication is partly suppressed and a banded structure appears within the centric heterochromatin of chromosome 3. This novel banded structure in salivary gland chromosomes was called Plato Atlantis. In order to characterize the heterochromatic component of Plato Atlantis, we constructed a fine-scale cytogenetic map of deletions with break points within centric heterochromatin (Df(3L)1-16, Df(3L)2-66, Df(3R)10-65, Df(3R)4-75 and Df(3L)6B-29 + Df(3R)6B-29). Salivary gland chromosomes show that Df(3L)1-16 removes the complete Plato Atlantis, while Df(3L)2-66 deletes the most proximal 3L regions. These deletions therefore show a substantial cytological overlap. However, in the chromosomes of nurse cells, the same deficiencies remove distinct heterochromatic blocks, with the region of overlap being almost invisible. Satellite (AATAACATAG, AAGAG) and dodecasatellite DNAs mapped in a narrow interval in salivary glands but were found in three clearly distinguishable blocks in nurse cells. The 1.688 satellite was found at a single site in salivary glands but at two sites in nurse cells. We show that newly polytenized heterochromatic structures include blocks h47-h50d of mitotic heterochromatin in salivary glands, but the additional blocks h50p, h53 and h57 are also included in nurse cell chromosomes. Tissue specificity of the patterns of abnormal heterochromatic polytenization implies differential control of DNA replication in somatic and germline cells.
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Affiliation(s)
- Dmitry E Koryakov
- Department of Cytology and Genetics, Novosibirsk State University, Novosibirsk 630090, Russia
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40
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Abstract
Euchromatin, which has an open structure and is frequently transcribed, tends to replicate in early S phase. Heterochromatin, which is more condensed and rarely transcribed, usually replicates in late S phase. Here, we report significant deviation from this correlation in the fission yeast, Schizosaccharomyces pombe. We found that heterochromatic centromeres and silent mating-type cassettes replicate in early S phase. Only heterochromatic telomeres replicate in late S phase. Research in other laboratories has shown that occasionally other organisms also replicate some of their heterochromatin in early S phase. Thus, late replication is not an obligatory feature of heterochromatin.
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Affiliation(s)
- Soo-Mi Kim
- Department of Cancer Genetics, Roswell Park Cancer Institute, Buffalo, New York 14263, USA
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41
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Abstract
A long-standing hypothesis about eukaryotic DNA replication is that the late-replicating regions are transcriptionally inert and that repressing transcription delays replication initiation. But do contrasting results from yeast and a recent study in Drosophila imply that replication timing and transcriptional activity are differentially regulated in yeast and higher eukaryotes?
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Affiliation(s)
- Heather J McCune
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Anne D Donaldson
- Cancer Research UK Chromosome Replication Group, Division of Gene Regulation and Expression, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
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42
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Sporbert A, Gahl A, Ankerhold R, Leonhardt H, Cardoso MC. DNA polymerase clamp shows little turnover at established replication sites but sequential de novo assembly at adjacent origin clusters. Mol Cell 2002; 10:1355-65. [PMID: 12504011 DOI: 10.1016/s1097-2765(02)00729-3] [Citation(s) in RCA: 168] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The spatial and temporal organization of DNA replication was investigated in living cells with a green fluorescent protein fusion to the DNA polymerase clamp PCNA. In situ extractions and photobleaching experiments revealed that PCNA, unlike RPA34, shows little if any turnover at replication sites, suggesting that it remains associated with the replication machinery through multiple rounds of Okazaki fragment synthesis. Photobleaching analyses further showed that the transition from earlier to later replicons occurs by disassembly into a nucleoplasmic pool of rapidly diffusing subcomponents and reassembly at newly activated sites. The fact that these replication sites were de novo assembled in close proximity to earlier ones suggests that activation of neighboring origins may occur by a domino effect possibly involving local changes in chromatin structure and accessibility.
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Affiliation(s)
- Anje Sporbert
- Max Delbrück Center for Molecular Medicine, 13125 Berlin, Advanced Imaging Microscopy, 07745, Jena, Germany
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43
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Hultdin M, Grönlund E, Norrback KF, Just T, Taneja K, Roos G. Replication timing of human telomeric DNA and other repetitive sequences analyzed by fluorescence in situ hybridization and flow cytometry. Exp Cell Res 2001; 271:223-9. [PMID: 11716534 DOI: 10.1006/excr.2001.5391] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The replication timing of telomeres seems to differ between species. Yeast telomeres are late replicating, whereas limited data from very few human cell lines have indicated telomere replication throughout S phase. In the present study a series of permanent cell lines and patient samples was investigated using a flow cytometric approach for telomere length determination based on in situ hybridization using peptide nucleic acid probes and DNA staining. This method permits selective analysis of cells in specific phases of the cell cycle without perturbation of the cell cycle machinery. The timing of replication of telomeric C(3)TA(2) and T(2)AG(3) repeats was found to differ between individual samples and could precede or be concomitant with the replication of bulk DNA. Replication of the T(2)AG(3) strand seemed to occur somewhat later than that of the C(3)TA(2) strand in some samples. (GTG)(n) and other repetitive sequences generally showed a replication pattern similar to that of the bulk of DNA with slightly individual differences, whereas centromeric DNA repeats consistently replicated within a short time frame in late S phase. The apparent variability in replication timing seen for telomeric DNA might suggest individual differences in firing of replication origins.
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Affiliation(s)
- M Hultdin
- Department of Medical Biosciences, Pathology, Umeå University, Umeå, S-90187, Sweden
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44
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Kim SM, Huberman JA. Regulation of replication timing in fission yeast. EMBO J 2001; 20:6115-26. [PMID: 11689451 PMCID: PMC125695 DOI: 10.1093/emboj/20.21.6115] [Citation(s) in RCA: 109] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2001] [Revised: 09/06/2001] [Accepted: 09/06/2001] [Indexed: 11/12/2022] Open
Abstract
Here we report the first characterization of replication timing and its regulation in the fission yeast Schizosaccharomyces pombe. We used three different synchronization methods: centrifugal elutriation, cdc10 temperature-shift and release, and starvation for deoxyribonucleoside triphosphates (dNTPs) by treatment with hydroxyurea (HU) followed by removal of HU, to study the times when specific autonomously replicating sequence elements (ARS elements; potential replication origins) replicate during S phase. We found that individual ARS elements replicate at characteristic times, some early and some late, independently of synchronization method. In wild-type cells treated with HU, early ARS elements replicated but late ones did not. However, in HU-treated mutant cells lacking the Rad3 (similar to human ATR and ATM) or Cds1 (similar to human CHK2) checkpoint kinase, both early and late ARS elements were able to replicate. Thus under conditions of dNTP starvation the Rad3 and Cds1 kinases are needed to suppress the replication of normally late-replicating regions.
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Affiliation(s)
- Soo-Mi Kim
- Department of Cancer Genetics, Roswell Park Cancer Institute, Elm & Carlton Streets, Buffalo, NY 14263, USA Present address: Department of Biology, California Institute of Technology, Pasadena, CA 91125, USA Corresponding author e-mail:
| | - Joel A. Huberman
- Department of Cancer Genetics, Roswell Park Cancer Institute, Elm & Carlton Streets, Buffalo, NY 14263, USA Present address: Department of Biology, California Institute of Technology, Pasadena, CA 91125, USA Corresponding author e-mail:
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45
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Cameron HA, McKay RD. Adult neurogenesis produces a large pool of new granule cells in the dentate gyrus. J Comp Neurol 2001; 435:406-17. [PMID: 11406822 DOI: 10.1002/cne.1040] [Citation(s) in RCA: 1156] [Impact Index Per Article: 50.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Knowing the rate of addition of new granule cells to the adult dentate gyrus is critical to understanding the function of adult neurogenesis. Despite the large number of studies of neurogenesis in the adult dentate gyrus, basic questions about the magnitude of this phenomenon have never been addressed. The S-phase marker bromodeoxyuridine (BrdU) has been extensively used in recent studies of adult neurogenesis, but it has been carefully tested only in the embryonic brain. Here, we show that a high dose of BrdU (300 mg/kg) is a specific, quantitative, and nontoxic marker of dividing cells in the adult rat dentate gyrus, whereas lower doses label only a fraction of the S-phase cells. By using this high dose of BrdU along with a second S-phase marker, [(3)H]thymidine, we found that young adult rats have 9,400 dividing cells proliferating with a cell cycle time of 25 hours, which would generate 9,000 new cells each day, or more than 250,000 per month. Within 5-12 days of BrdU injection, a substantial pool of immature granule neurons, 50% of all BrdU-labeled cells in the dentate gyrus, could be identified with neuron-specific antibodies TuJ1 and TUC-4. This number of new granule neurons generated each month is 6% of the total size of the granule cell population and 30-60% of the size of the afferent and efferent populations (West et al. [1991] Anat Rec 231:482-497; Mulders et al. [1997] J Comp Neurol 385:83-94). The large number of the adult-generated granule cells supports the idea that these new neurons play an important role in hippocampal function.
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Affiliation(s)
- H A Cameron
- Laboratory of Molecular Biology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892 USA.
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46
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Abstract
The properties that define centromeres in complex eukaryotes are poorly understood because the underlying DNA is normally repetitive and indistinguishable from surrounding noncentromeric sequences. However, centromeric chromatin contains variant H3-like histones that may specify centromeric regions. Nucleosomes are normally assembled during DNA replication; therefore, we examined replication and chromatin assembly at centromeres in Drosophila cells. DNA in pericentric heterochromatin replicates late in S phase, and so centromeres are also thought to replicate late. In contrast to expectation, we show that centromeres replicate as isolated domains early in S phase. These domains do not appear to assemble conventional H3-containing nucleosomes, and deposition of the Cid centromeric H3-like variant proceeds by a replication-independent pathway. We suggest that late-replicating pericentric heterochromatin helps to maintain embedded centromeres by blocking conventional nucleosome assembly early in S phase, thereby allowing the deposition of centromeric histones.
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Affiliation(s)
- Kami Ahmad
- Howard Hughes Medical Institute, and Fred Hutchinson Cancer Research Center, Seattle, Washington 98109
| | - Steven Henikoff
- Howard Hughes Medical Institute, and Fred Hutchinson Cancer Research Center, Seattle, Washington 98109
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47
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Leach TJ, Chotkowski HL, Wotring MG, Dilwith RL, Glaser RL. Replication of heterochromatin and structure of polytene chromosomes. Mol Cell Biol 2000; 20:6308-16. [PMID: 10938107 PMCID: PMC86105 DOI: 10.1128/mcb.20.17.6308-6316.2000] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Heterochromatin is characteristically the last portion of the genome to be replicated. In polytene cells, heterochromatic sequences are underreplicated because S phase ends before replication of heterochromatin is completed. Truncated heterochromatic DNAs have been identified in polytene cells of Drosophila and may be the discontinuous molecules that form between fully replicated euchromatic and underreplicated heterochromatic regions of the chromosome. In this report, we characterize the temporal pattern of heterochromatic DNA truncation during development of polytene cells. Underreplication occurred during the first polytene S phase, yet DNA truncation, which was found within heterochromatic sequences of all four Drosophila chromosomes, did not occur until the second polytene S phase. DNA truncation was correlated with underreplication, since increasing the replication of satellite sequences with the cycE(1672) mutation caused decreased production of truncated DNAs. Finally, truncation of heterochromatic DNAs was neither quantitatively nor qualitatively affected by modifiers of position effect variegation including the Y chromosome, Su(var)205(2), parental origin, or temperature. We propose that heterochromatic satellite sequences present a barrier to DNA replication and that replication forks that transiently stall at such barriers in late S phase of diploid cells are left unresolved in the shortened S phase of polytene cells. DNA truncation then occurs in the second polytene S phase, when new replication forks extend to the position of forks left unresolved in the first polytene S phase.
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Affiliation(s)
- T J Leach
- Laboratory of Developmental Genetics, Wadsworth Center, New York State Department of Health, Albany, New York 12201, USA
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48
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Hara M, Igarashi J, Yamashita K, Iigo M, Yokosuka M, Ohtani-Kaneko R, Hirata K, Herbert DC. Proteins recognized by antibodies against isolated cytological heterochromatin from rat liver cells change their localization between cell species and between stages of mitosis (interphase vs metaphase). Tissue Cell 1999; 31:505-13. [PMID: 10612261 DOI: 10.1054/tice.1999.0056] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Heterochromatin in the cell nucleus seems to concentrate various proteins, such as Drosophila heterochromatin protein 1, which maintain the repressed state of gene expression. However, it still remains obscure how protein composition related to chromatin structure is different between heterochromatin and euchromatin in interphase nuclei. We isolated cytological heterochromatin from sonicated interphase nuclei obtained from rat liver cells and prepared antisera against it. The dense heterochromatic bodies seen in the preparation of intact nuclei were duplicated in a relatively pure form during the preparation of heterochromatin. In the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis, differences between the fractions of heterochromatin and euchromatin were noted by their protein composition. Isolated heterochromatin was then digested by DNase after partial digestion with trypsin and its dense structure changed to become highly sensitive to DNase. The prepared antibodies reacted with the heterochromatin region of rat liver cell nuclei and isolated cytological heterochromatin; however, they did not react with euchromatin. Using immunohistochemistry, the antibodies bound to each cell nucleus in all tissues observed; some cell types were distinguished by their differential stainability (e.g. staining in the cytoplasm). Staining of the mitotic cells showed that the proteins recognized by the antibodies were localized in the cytoplasm and, in part, on the chromosomes. Based on the results of molecular cloning from rat liver cDNA library using the antibodies as a probe, it seemed that the antibodies mainly recognized two proteins similar to arginase and general vesicular transport factor p115, respectively. The results obtained from these experiments reveal that some proteins located in the heterochromatin of interphase liver cell nuclei seem to play important roles in condensing a portion of the chromatin structure during interphase and suggest that proteins composing heterochromatin might be changed according to cell types or the stage of the cell cycle.
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Affiliation(s)
- M Hara
- Department of Anatomy, St Marianna University School of Medicine, Kawasaki, Japan.
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49
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Abstract
Mammalian artificial chromosomes (MACs) hold the promise of providing autonomous vectors for gene therapy in dividing cells. They would not require insertion into the genome and could include sufficient genomic sequences that surround the therapeutic gene to ensure proper tissue-specific and temporal regulation. Several groups have reported successful formation of MACs in human cells using transfection strategies that included alpha satellite DNA, the primary DNA found at normal human centromeres. These results, although extremely encouraging, have limitations such as unpredictable chromosome formation and success thus far in only one transformed human cell line. Examination of other cells where alpha satellite DNA has integrated into ectopic chromosomal locations, as well as naturally occurring dicentric and neocentromere-containing cell lines, suggests that alpha satellite DNA may not be necessary or sufficient for centromere formation. Overall, these results suggest that epigenetic modifications of centromeric DNA are required for efficient centromere formation. Models for this centromere-specific epigenetic modification include a specialized chromatin structure and differential replication timing of centromeric DNA. Thus, further investigation of these centromere-specific epigenetic modifications may suggest strategies for increasing the efficiency of generating human artificial chromosomes for use as gene therapy vectors.
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Affiliation(s)
- P E Warburton
- Department of Human Genetics, Mount Sinai School of Medicine, 1425 Madison Avenue, New York, New York, 10029, USA
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50
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Albagli O, Lantoine D, Quief S, Quignon F, Englert C, Kerckaert JP, Montarras D, Pinset C, Lindon C. Overexpressed BCL6 (LAZ3) oncoprotein triggers apoptosis, delays S phase progression and associates with replication foci. Oncogene 1999; 18:5063-75. [PMID: 10490843 DOI: 10.1038/sj.onc.1202892] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
One of the most frequent genetic abnormalities associated with non Hodgkin lymphoma is the structural alteration of the 5' non coding/regulatory region of the BCL6 (LAZ3) protooncogene. BCL6 encodes a POZ/Zn finger protein, a structure similar to that of many Drosophila developmental regulators and to another protein involved in a human hematopoietic malignancy, PLZF. BCL6 is a sequence specific transcriptional repressor controlling germinal center formation and T cell dependent immune response. Although the expression of BCL6 negatively correlates with cellular proliferation in different cell types, the influence of BCL6 on cell growth and survival is currently unknown so that the way its deregulation may contribute to cancer remains elusive. To directly address this issue, we used a tetracycline-regulated system in human U2OS osteosarcoma cells and thus found that BCL6 mediates growth suppression associated with impaired S phase progression and apoptosis. Interestingly, overexpressed BCL6 can colocalize with sites of ongoing DNA synthesis, suggesting that it may directly interfere with S phase initiation and/or progression. In contrast, the isolated Zn finger region of BCL6, which binds BCL6 target sequence but lacks transcriptional repression activity, slows, but does not suppress, U2OS cell growth, is less efficient at delaying S phase progression, and does not trigger apoptosis. Thus, for a large part, the effects of BCL6 overexpression on cell growth and survival depend on its ability to engage protein/protein interactions with itself and/or its transcriptional corepressors. That BCL6 restricts cell growth suggests that its deregulation upon structural alterations may alleviate negative controls on the cell cycle and cell survival.
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Affiliation(s)
- O Albagli
- INSERM U524, IRCL, Place de Verdun, 59045 Lille, France
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