1
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da Costa-Nunes JA, Gierlinski M, Sasaki T, Haagensen EJ, Gilbert DM, Blow JJ. The location and development of Replicon Cluster Domains in early replicating DNA. Wellcome Open Res 2023; 8:158. [PMID: 37766844 PMCID: PMC10521077 DOI: 10.12688/wellcomeopenres.18742.2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/18/2023] [Indexed: 09/29/2023] Open
Abstract
Background: It has been known for many years that in metazoan cells, replication origins are organised into clusters where origins within each cluster fire near-synchronously. Despite clusters being a fundamental organising principle of metazoan DNA replication, the genomic location of origin clusters has not been documented. Methods: We synchronised human U2OS by thymidine block and release followed by L-mimosine block and release to create a population of cells progressing into S phase with a high degree of synchrony. At different times after release into S phase, cells were pulsed with EdU; the EdU-labelled DNA was then pulled down, sequenced and mapped onto the human genome. Results: The early replicating DNA showed features at a range of scales. Wavelet analysis showed that the major feature of the early replicating DNA was at a size of 500 kb, consistent with clusters of replication origins. Over the first two hours of S phase, these Replicon Cluster Domains broadened in width, consistent with their being enlarged by the progression of replication forks at their outer boundaries. The total replication signal associated with each Replicon Cluster Domain varied considerably, and this variation was reproducible and conserved over time. We provide evidence that this variability in replication signal was at least in part caused by Replicon Cluster Domains being activated at different times in different cells in the population. We also provide evidence that adjacent clusters had a statistical preference for being activated in sequence across a group, consistent with the 'domino' model of replication focus activation order observed by microscopy. Conclusions: We show that early replicating DNA is organised into Replicon Cluster Domains that behave as expected of replicon clusters observed by DNA fibre analysis. The coordinated activation of different Replicon Cluster Domains can generate the replication timing programme by which the genome is duplicated.
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Affiliation(s)
- José A. da Costa-Nunes
- Division of Molecular, Cell and Developmental Biology, School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
| | - Marek Gierlinski
- Data Analysis Group, School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
| | - Takayo Sasaki
- San Diego Biomedical Research Institute, San Diego, California, CA 92121, USA
| | - Emma J. Haagensen
- Division of Molecular, Cell and Developmental Biology, School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
- Present address: School of Medical Education, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
| | - David M. Gilbert
- San Diego Biomedical Research Institute, San Diego, California, CA 92121, USA
| | - J. Julian Blow
- Division of Molecular, Cell and Developmental Biology, School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
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2
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Abstract
The current model of replication-dependent (RD) histone biosynthesis posits that RD histone gene expression is coupled to DNA replication, occurring only in S phase of the cell cycle once DNA synthesis has begun. However, several key factors in the RD histone biosynthesis pathway are up-regulated by E2F or phosphorylated by CDK2, suggesting these processes may instead begin much earlier, at the point of cell-cycle commitment. In this study, we use both fixed- and live-cell imaging of human cells to address this question, revealing a hybrid model in which RD histone biosynthesis is first initiated in G1, followed by a strong increase in histone production in S phase of the cell cycle. This suggests a mechanism by which cells that have committed to the cell cycle build up an initial small pool of RD histones to be available for the start of DNA replication, before producing most of the necessary histones required in S phase. Thus, a clear distinction exists at completion of mitosis between cells that are born with the intention of proceeding through the cell cycle and replicating their DNA and cells that have chosen to exit the cell cycle and have no immediate need for histone synthesis.
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3
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Mamberti S, Cardoso MC. Are the processes of DNA replication and DNA repair reading a common structural chromatin unit? Nucleus 2020; 11:66-82. [PMID: 32275847 PMCID: PMC7289585 DOI: 10.1080/19491034.2020.1744415] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Decades of investigation on genomic DNA have brought us deeper insights into its organization within the nucleus and its metabolic mechanisms. This was fueled by the parallel development of experimental techniques and has stimulated model building to simulate genome conformation in agreement with the experimental data. Here, we will discuss our recent discoveries on the chromatin units of DNA replication and DNA damage response. We will highlight their remarkable structural similarities and how both revealed themselves as clusters of nanofocal structures each on the hundred thousand base pair size range corresponding well with chromatin loop sizes. We propose that the function of these two global genomic processes is determined by the loop level organization of chromatin structure with structure dictating function. Abbreviations: 3D-SIM: 3D-structured illumination microscopy; 3C: chromosome conformation capture; DDR: DNA damage response; FISH: fluorescent in situ hybridization; Hi-C: high conformation capture; HiP-HoP: highly predictive heteromorphic polymer model; IOD: inter-origin distance; LAD: lamina associated domain; STED: stimulated emission depletion microscopy; STORM: stochastic optical reconstruction microscopy; SBS: strings and binders switch model; TAD: topologically associated domain
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Affiliation(s)
- Stefania Mamberti
- Cell Biology and Epigenetics, Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
| | - M Cristina Cardoso
- Cell Biology and Epigenetics, Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
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4
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Chagin VO, Reinhart B, Becker A, Mortusewicz O, Jost KL, Rapp A, Leonhardt H, Cardoso MC. Processive DNA synthesis is associated with localized decompaction of constitutive heterochromatin at the sites of DNA replication and repair. Nucleus 2019; 10:231-253. [PMID: 31744372 PMCID: PMC6949026 DOI: 10.1080/19491034.2019.1688932] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2019] [Revised: 09/01/2019] [Accepted: 10/22/2019] [Indexed: 12/18/2022] Open
Abstract
Constitutive heterochromatin is considered as a functionally inert genome compartment, important for its architecture and stability. How such stable structure is maintained is not well understood. Here, we apply four different visualization schemes to label it and investigate its dynamics during DNA replication and repair. We show that replisomes assemble over the heterochromatin in a temporally ordered manner. Furthermore, heterochromatin undergoes transient decompaction locally at the active sites of DNA synthesis. Using selective laser microirradiation conditions that lead to damage repaired via processive DNA synthesis, we measured similarly local decompaction of heterochromatin. In both cases, we could not observe large-scale movement of heterochromatin to the domain surface. Instead, the processive DNA synthesis machinery assembled at the replication/repair sites. Altogether, our data are compatible with a progression of DNA replication/repair along the chromatin in a dynamic mode with localized and transient decompaction that does not globally remodels the whole heterochromatin compartment.
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Affiliation(s)
- Vadim O. Chagin
- Cell Biology & Epigenetics, Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
- Institute of Cytology, Russian Academy of Sciences, St. Petersburg, Russia
| | - Britta Reinhart
- Cell Biology & Epigenetics, Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
| | - Annette Becker
- Cell Biology & Epigenetics, Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
| | | | - K. Laurence Jost
- Cell Biology & Epigenetics, Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
| | - Alexander Rapp
- Cell Biology & Epigenetics, Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
| | | | - M. Cristina Cardoso
- Cell Biology & Epigenetics, Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
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5
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Affdal AO, Ravitsky V. Chapitre 9. Oncofertilité et jeunes filles prépubères : Un « droit à un avenir ouvert » ? ACTA ACUST UNITED AC 2019; Vol. 30:159-177. [PMID: 32372595 DOI: 10.3917/jibes.303.0159] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Chemotherapy and radiotherapy have increased the life expectancy of cancer patients but may cause premature ovarian failure and irreversible loss of fertility. In the context of childhood cancers, it is now acknowledged that possible negative effects of treatment on future reproductive autonomy are a major concern. While a few options are open to patients post-puberty, the only option currently open to prepubescent girls is cryopreservation of ovarian tissue and subsequent transplantation. Yet, this procedure raises ethical concerns related to its experimental nature and to risks involved in surgery and general anesthesia. In addition, the risk of malignant cells being reintroduced in the future following autologous transplantation of the ovarian tissue is still poorly evaluated. A number of ethical issues arise surrounding this procedure. While the girl's future reproductive autonomy is at stake, it is important to also consider risks associated with the procedure. Fertility preservation through cryopreservation of ovarian tissue thus raises a conflict between the principles of beneficence and non-maleficence. We argue that the ethical complexity surrounding fertility preservation for prepubescent girls should be resolved by applying the principle of "the child's right to an open future". We propose to consider 'beneficence' through the lens of the reproductive autonomy and her potentialin becoming a genetic parent.
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6
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Control of DNA replication timing in the 3D genome. Nat Rev Mol Cell Biol 2019; 20:721-737. [DOI: 10.1038/s41580-019-0162-y] [Citation(s) in RCA: 134] [Impact Index Per Article: 26.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/18/2019] [Indexed: 12/27/2022]
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7
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Dent MAR, Aranda-Anzaldo A. Lessons we can learn from neurons to make cancer cells quiescent. J Neurosci Res 2019; 97:1141-1152. [PMID: 30985022 DOI: 10.1002/jnr.24428] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2018] [Revised: 02/20/2019] [Accepted: 03/26/2019] [Indexed: 12/16/2022]
Abstract
Cancer is a major concern for contemporary societies. However, the incidence of cancer is unevenly distributed among tissues and cell types. In particular, the evidence indicates that neurons are absolutely resistant to cancer and this is commonly explained on the basis of the known postmitotic state of neurons. The dominant paradigm on cancer understands this problem as a disease caused by mutations in cellular genes that result in unrestrained cell proliferation and eventually in tissue invasion and metastasis. However, the evidence also shows that mutations and gross chromosomal anomalies are common in functional neurons that nevertheless do not become neoplastic. This fact suggests that in the real nonexperimental setting mutations per se are not enough for inducing carcinogenesis but also that the postmitotic state of neurons is not genetically controlled or determined, otherwise there should be reports of spontaneously transformed neurons. Here we discuss the evidence that the postmitotic state of neurons has a structural basis on the high stability of their nuclear higher order structure that performs like an absolute tumor suppressor. We also discuss evidence that it is possible to induce a similar structural postmitotic state in nonneural cell types as a practical strategy for stopping or reducing the progression of cancer.
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Affiliation(s)
- Myrna A R Dent
- Laboratorio de Biología Molecular y Neurociencias, Facultad de Medicina, Universidad Autónoma del Estado de México, Toluca, Mexico
| | - Armando Aranda-Anzaldo
- Laboratorio de Biología Molecular y Neurociencias, Facultad de Medicina, Universidad Autónoma del Estado de México, Toluca, Mexico
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8
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Origin Firing Regulations to Control Genome Replication Timing. Genes (Basel) 2019; 10:genes10030199. [PMID: 30845782 PMCID: PMC6470937 DOI: 10.3390/genes10030199] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Revised: 02/25/2019] [Accepted: 02/28/2019] [Indexed: 12/19/2022] Open
Abstract
Complete genome duplication is essential for genetic homeostasis over successive cell generations. Higher eukaryotes possess a complex genome replication program that involves replicating the genome in units of individual chromatin domains with a reproducible order or timing. Two types of replication origin firing regulations ensure complete and well-timed domain-wise genome replication: (1) the timing of origin firing within a domain must be determined and (2) enough origins must fire with appropriate positioning in a short time window to avoid inter-origin gaps too large to be fully copied. Fundamental principles of eukaryotic origin firing are known. We here discuss advances in understanding the regulation of origin firing to control firing time. Work with yeasts suggests that eukaryotes utilise distinct molecular pathways to determine firing time of distinct sets of origins, depending on the specific requirements of the genomic regions to be replicated. Although the exact nature of the timing control processes varies between eukaryotes, conserved aspects exist: (1) the first step of origin firing, pre-initiation complex (pre-IC formation), is the regulated step, (2) many regulation pathways control the firing kinase Dbf4-dependent kinase, (3) Rif1 is a conserved mediator of late origin firing and (4) competition between origins for limiting firing factors contributes to firing timing. Characterization of the molecular timing control pathways will enable us to manipulate them to address the biological role of replication timing, for example, in cell differentiation and genome instability.
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9
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Xiang W, Roberti MJ, Hériché JK, Huet S, Alexander S, Ellenberg J. Correlative live and super-resolution imaging reveals the dynamic structure of replication domains. J Cell Biol 2018; 217:1973-1984. [PMID: 29572382 PMCID: PMC5987722 DOI: 10.1083/jcb.201709074] [Citation(s) in RCA: 53] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2017] [Revised: 01/19/2018] [Accepted: 03/06/2018] [Indexed: 12/15/2022] Open
Abstract
Combining fluorescence labeling with live-cell confocal and correlative super-resolution microscopy, Xiang et al. characterize biophysical parameters defining the internal organization, spacing, and mechanical coupling of replication domains. Chromosome organization in higher eukaryotes controls gene expression, DNA replication, and DNA repair. Genome mapping has revealed the functional units of chromatin at the submegabase scale as self-interacting regions called topologically associating domains (TADs) and showed they correspond to replication domains (RDs). A quantitative structural and dynamic description of RD behavior in the nucleus is, however, missing because visualization of dynamic subdiffraction-sized RDs remains challenging. Using fluorescence labeling of RDs combined with correlative live and super-resolution microscopy in situ, we determined biophysical parameters to characterize the internal organization, spacing, and mechanical coupling of RDs. We found that RDs are typically 150 nm in size and contain four co-replicating regions spaced 60 nm apart. Spatially neighboring RDs are spaced 300 nm apart and connected by highly flexible linker regions that couple their motion only <550 nm. Our pipeline allows a robust quantitative characterization of chromosome structure in situ and provides important biophysical parameters to understand general principles of chromatin organization.
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Affiliation(s)
- Wanqing Xiang
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - M Julia Roberti
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Jean-Karim Hériché
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Sébastien Huet
- Université de Rennes 1, Structure fédérative de recherche Biosit, Rennes, France.,Centre National de la Recherche Scientifique, UMR 6290, Institut Génétique et Développement de Rennes, Rennes, France
| | - Stephanie Alexander
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Jan Ellenberg
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
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10
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Zhao PA, Rivera-Mulia JC, Gilbert DM. Replication Domains: Genome Compartmentalization into Functional Replication Units. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2018; 1042:229-257. [DOI: 10.1007/978-981-10-6955-0_11] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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11
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Maya‐Mendoza A, Jackson DA. Labeling DNA Replication Foci to Visualize Chromosome Territories In Vivo. ACTA ACUST UNITED AC 2017. [DOI: 10.1002/cpcb.19] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
| | - Dean A. Jackson
- Systems Microscopy Centre, Faculty of Life Sciences, The University of Manchester Manchester United Kingdom
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12
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Anatomy of Mammalian Replication Domains. Genes (Basel) 2017; 8:genes8040110. [PMID: 28350365 PMCID: PMC5406857 DOI: 10.3390/genes8040110] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2016] [Revised: 03/22/2017] [Accepted: 03/24/2017] [Indexed: 02/07/2023] Open
Abstract
Genetic information is faithfully copied by DNA replication through many rounds of cell division. In mammals, DNA is replicated in Mb-sized chromosomal units called “replication domains.” While genome-wide maps in multiple cell types and disease states have uncovered both dynamic and static properties of replication domains, we are still in the process of understanding the mechanisms that give rise to these properties. A better understanding of the molecular basis of replication domain regulation will bring new insights into chromosome structure and function.
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13
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Wilson KA, Elefanty AG, Stanley EG, Gilbert DM. Spatio-temporal re-organization of replication foci accompanies replication domain consolidation during human pluripotent stem cell lineage specification. Cell Cycle 2016; 15:2464-75. [PMID: 27433885 PMCID: PMC5026818 DOI: 10.1080/15384101.2016.1203492] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2016] [Revised: 06/08/2016] [Accepted: 06/13/2016] [Indexed: 10/21/2022] Open
Abstract
Lineage specification of both mouse and human pluripotent stem cells (PSCs) is accompanied by spatial consolidation of chromosome domains and temporal consolidation of their replication timing. Replication timing and chromatin organization are both established during G1 phase at the timing decision point (TDP). Here, we have developed live cell imaging tools to track spatio-temporal replication domain consolidation during differentiation. First, we demonstrate that the fluorescence ubiquitination cell cycle indicator (Fucci) system is incapable of demarcating G1/S or G2/M cell cycle transitions. Instead, we employ a combination of fluorescent PCNA to monitor S phase progression, cytokinesis to demarcate mitosis, and fluorescent nucleotides to label early and late replication foci and track their 3D organization into sub-nuclear chromatin compartments throughout all cell cycle transitions. We find that, as human PSCs differentiate, the length of S phase devoted to replication of spatially clustered replication foci increases, coincident with global compartmentalization of domains into temporally clustered blocks of chromatin. Importantly, re-localization and anchorage of domains was completed prior to the onset of S phase, even in the context of an abbreviated PSC G1 phase. This approach can also be employed to investigate cell fate transitions in single PSCs, which could be seen to differentiate preferentially from G1 phase. Together, our results establish real-time, live-cell imaging methods for tracking cell cycle transitions during human PSC differentiation that can be applied to study chromosome domain consolidation and other aspects of lineage specification.
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Affiliation(s)
- Korey A. Wilson
- Department of Biological Science, Florida State University, Tallahassee, FL, USA
| | - Andrew G. Elefanty
- Murdoch Childrens Research Institute, Parkville, Australia
- Department of Pediatrics, University of Melbourne, Parkville, Victoria, Australia
- Department of Anatomy and Developmental Biology, Monash University, Clayton, Victoria, Australia
| | - Edouard G. Stanley
- Murdoch Childrens Research Institute, Parkville, Australia
- Department of Pediatrics, University of Melbourne, Parkville, Victoria, Australia
- Department of Anatomy and Developmental Biology, Monash University, Clayton, Victoria, Australia
| | - David M. Gilbert
- Department of Biological Science, Florida State University, Tallahassee, FL, USA
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14
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4D Visualization of replication foci in mammalian cells corresponding to individual replicons. Nat Commun 2016; 7:11231. [PMID: 27052570 PMCID: PMC4829660 DOI: 10.1038/ncomms11231] [Citation(s) in RCA: 89] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2015] [Accepted: 03/03/2016] [Indexed: 01/05/2023] Open
Abstract
Since the pioneering proposal of the replicon model of DNA replication 50 years ago, the predicted replicons have not been identified and quantified at the cellular level. Here, we combine conventional and super-resolution microscopy of replication sites in live and fixed cells with computational image analysis. We complement these data with genome size measurements, comprehensive analysis of S-phase dynamics and quantification of replication fork speed and replicon size in human and mouse cells. These multidimensional analyses demonstrate that replication foci (RFi) in three-dimensional (3D) preserved somatic mammalian cells can be optically resolved down to single replicons throughout S-phase. This challenges the conventional interpretation of nuclear RFi as replication factories, that is, the complex entities that process multiple clustered replicons. Accordingly, 3D genome organization and duplication can be now followed within the chromatin context at the level of individual replicons.
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15
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Dileep V, Rivera-Mulia JC, Sima J, Gilbert DM. Large-Scale Chromatin Structure-Function Relationships during the Cell Cycle and Development: Insights from Replication Timing. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2015; 80:53-63. [PMID: 26590169 DOI: 10.1101/sqb.2015.80.027284] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Chromosome architecture has received a lot of attention since the recent development of genome-scale methods to measure chromatin interactions (Hi-C), enabling the first sequence-based models of chromosome tertiary structure. A view has emerged of chromosomes as a string of structural units (topologically associating domains; TADs) whose boundaries persist through the cell cycle and development. TADs with similar chromatin states tend to aggregate, forming spatially segregated chromatin compartments. However, high-resolution Hi-C has revealed substructure within TADs (subTADs) that poses a challenge for models that attribute significance to structural units at any given scale. More than 20 years ago, the DNA replication field independently identified stable structural (and functional) units of chromosomes (replication foci) as well as spatially segregated chromatin compartments (early and late foci), but lacked the means to link these units to genomic map units. Genome-wide studies of replication timing (RT) have now merged these two disciplines by identifying individual units of replication regulation (replication domains; RDs) that correspond to TADs and are arranged in 3D to form spatiotemporally segregated subnuclear compartments. Furthermore, classifying RDs/TADs by their constitutive versus developmentally regulated RT has revealed distinct classes of chromatin organization, providing unexpected insight into the relationship between large-scale chromosome structure and function.
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Affiliation(s)
- Vishnu Dileep
- Department of Biological Science, Florida State University, Tallahassee, Florida 32306-4295
| | | | - Jiao Sima
- Department of Biological Science, Florida State University, Tallahassee, Florida 32306-4295
| | - David M Gilbert
- Department of Biological Science, Florida State University, Tallahassee, Florida 32306-4295 Center for Genomics and Personalized Medicine, Florida State University, Tallahassee, Florida 32306-4295
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16
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Kuriya K, Higashiyama E, Avşar-Ban E, Tamaru Y, Ogata S, Takebayashi SI, Ogata M, Okumura K. Direct Visualization of DNA Replication Dynamics in Zebrafish Cells. Zebrafish 2015; 12:432-9. [PMID: 26540100 DOI: 10.1089/zeb.2015.1151] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Spatiotemporal regulation of DNA replication in the S-phase nucleus has been extensively studied in mammalian cells because it is tightly coupled with the regulation of other nuclear processes such as transcription. However, little is known about the replication dynamics in nonmammalian cells. Here, we analyzed the DNA replication processes of zebrafish (Danio rerio) cells through the direct visualization of replicating DNA in the nucleus and on DNA fiber molecules isolated from the nucleus. We found that zebrafish chromosomal DNA at the nuclear interior was replicated first, followed by replication of DNA at the nuclear periphery, which is reminiscent of the spatiotemporal regulation of mammalian DNA replication. However, the relative duration of interior DNA replication in zebrafish cells was longer compared to mammalian cells, possibly reflecting zebrafish-specific genomic organization. The rate of replication fork progression and ori-to-ori distance measured by the DNA combing technique were ∼ 1.4 kb/min and 100 kb, respectively, which are comparable to those in mammalian cells. To our knowledge, this is a first report that measures replication dynamics in zebrafish cells.
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Affiliation(s)
- Kenji Kuriya
- 1 Laboratory of Molecular and Cellular Biology, Department of Life Sciences, Graduate School of Bioresources, Mie University , Tsu, Japan
| | - Eriko Higashiyama
- 1 Laboratory of Molecular and Cellular Biology, Department of Life Sciences, Graduate School of Bioresources, Mie University , Tsu, Japan
| | - Eriko Avşar-Ban
- 2 Laboratory for the Utilization of Aquatic Bioresources, Department of Life Sciences, Graduate School of Bioresources, Mie University , Tsu, Japan
| | - Yutaka Tamaru
- 2 Laboratory for the Utilization of Aquatic Bioresources, Department of Life Sciences, Graduate School of Bioresources, Mie University , Tsu, Japan
| | - Shin Ogata
- 1 Laboratory of Molecular and Cellular Biology, Department of Life Sciences, Graduate School of Bioresources, Mie University , Tsu, Japan
| | - Shin-ichiro Takebayashi
- 3 Department of Biochemistry and Proteomics, Graduate School of Medicine, Mie University , Tsu, Japan
| | - Masato Ogata
- 3 Department of Biochemistry and Proteomics, Graduate School of Medicine, Mie University , Tsu, Japan
| | - Katsuzumi Okumura
- 1 Laboratory of Molecular and Cellular Biology, Department of Life Sciences, Graduate School of Bioresources, Mie University , Tsu, Japan
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17
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Abstract
DNA replication begins with the assembly of pre-replication complexes (pre-RCs) at thousands of DNA replication origins during the G1 phase of the cell cycle. At the G1-S-phase transition, pre-RCs are converted into pre-initiation complexes, in which the replicative helicase is activated, leading to DNA unwinding and initiation of DNA synthesis. However, only a subset of origins are activated during any S phase. Recent insights into the mechanisms underlying this choice reveal how flexibility in origin usage and temporal activation are linked to chromosome structure and organization, cell growth and differentiation, and replication stress.
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18
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Hyrien O, Rappailles A, Guilbaud G, Baker A, Chen CL, Goldar A, Petryk N, Kahli M, Ma E, d'Aubenton-Carafa Y, Audit B, Thermes C, Arneodo A. From simple bacterial and archaeal replicons to replication N/U-domains. J Mol Biol 2013; 425:4673-89. [PMID: 24095859 DOI: 10.1016/j.jmb.2013.09.021] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2013] [Revised: 09/15/2013] [Accepted: 09/19/2013] [Indexed: 10/26/2022]
Abstract
The Replicon Theory proposed 50 years ago has proven to apply for replicons of the three domains of life. Here, we review our knowledge of genome organization into single and multiple replicons in bacteria, archaea and eukarya. Bacterial and archaeal replicator/initiator systems are quite specific and efficient, whereas eukaryotic replicons show degenerate specificity and efficiency, allowing for complex regulation of origin firing time. We expand on recent evidence that ~50% of the human genome is organized as ~1,500 megabase-sized replication domains with a characteristic parabolic (U-shaped) replication timing profile and linear (N-shaped) gradient of replication fork polarity. These N/U-domains correspond to self-interacting segments of the chromatin fiber bordered by open chromatin zones and replicate by cascades of origin firing initiating at their borders and propagating to their center, possibly by fork-stimulated initiation. The conserved occurrence of this replication pattern in the germline of mammals has resulted over evolutionary times in the formation of megabase-sized domains with an N-shaped nucleotide compositional skew profile due to replication-associated mutational asymmetries. Overall, these results reveal an evolutionarily conserved but developmentally plastic organization of replication that is driving mammalian genome evolution.
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Affiliation(s)
- Olivier Hyrien
- Ecole Normale Supérieure, IBENS UMR8197 U1024, Paris 75005, France.
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Abstract
The onset of genomic DNA synthesis requires precise interactions of specialized initiator proteins with DNA at sites where the replication machinery can be loaded. These sites, defined as replication origins, are found at a few unique locations in all of the prokaryotic chromosomes examined so far. However, replication origins are dispersed among tens of thousands of loci in metazoan chromosomes, thereby raising questions regarding the role of specific nucleotide sequences and chromatin environment in origin selection and the mechanisms used by initiators to recognize replication origins. Close examination of bacterial and archaeal replication origins reveals an array of DNA sequence motifs that position individual initiator protein molecules and promote initiator oligomerization on origin DNA. Conversely, the need for specific recognition sequences in eukaryotic replication origins is relaxed. In fact, the primary rule for origin selection appears to be flexibility, a feature that is modulated either by structural elements or by epigenetic mechanisms at least partly linked to the organization of the genome for gene expression.
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Affiliation(s)
- Alan C Leonard
- Department of Biological Sciences, Florida Institute of Technology, Melbourne, Florida 32901
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20
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Efficient replication of Epstein-Barr virus-derived plasmids requires tethering by EBNA1 to host chromosomes. J Virol 2013; 87:13020-8. [PMID: 24067969 DOI: 10.1128/jvi.01606-13] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
The EBNA1 protein of Epstein-Barr virus enables plasmids carrying oriP both to duplicate and to segregate efficiently in proliferating cells. EBNA1 recruits the origin recognition complex (ORC) to establish a replication origin at one element of oriP, DS (dyad symmetry); at another element, FR (family of repeats), EBNA1 binds to an array of sites from which it tethers plasmids to host chromosomes for mitotic stability. We report experiments leading to the conclusion that tethering by EBNA1 to host chromosomes is also needed within interphase nuclei in order for plasmids to be replicated efficiently from oriP. The DNA-binding domain of EBNA1, which lacks chromosome-binding ability, was found to support weak, DS-specific replication in HEK293 cells after transient transfection, being 17% as active as wild-type EBNA1. The low efficiency of replication was not due to the failure of the DNA-binding domain to retain plasmids within nuclei, because plasmids were recovered in similar amounts and entirely from the nuclear fraction of these transiently transfected cells. A derivative of EBNA1 with its chromosome-tethering domains replaced by a 22-amino-acid nucleosome-binding domain was fully active in supporting oriP functions. The implication is that EBNA1's DNA-binding domain is able to recruit ORC to DS, but either this step or subsequent replication is only efficient if the plasmid is tethered to a host chromosome. Finally, with some cell lines, DS can hardly support even transient plasmid replication without FR. A loss of plasmids lacking FR from nuclei cannot account for this requirement, suggesting that the stronger tethering to chromosomes by FR is needed for plasmid replication within the nuclei of such cells.
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21
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Abstract
Patterns of replication within eukaryotic genomes correlate with gene expression, chromatin structure, and genome evolution. Recent advances in genome-scale mapping of replication kinetics have allowed these correlations to be explored in many species, cell types, and growth conditions, and these large data sets have allowed quantitative and computational analyses. One striking new correlation to emerge from these analyses is between replication timing and the three-dimensional structure of chromosomes. This correlation, which is significantly stronger than with any single histone modification or chromosome-binding protein, suggests that replication timing is controlled at the level of chromosomal domains. This conclusion dovetails with parallel work on the heterogeneity of origin firing and the competition between origins for limiting activators to suggest a model in which the stochastic probability of individual origin firing is modulated by chromosomal domain structure to produce patterns of replication. Whether these patterns have inherent biological functions or simply reflect higher-order genome structure is an open question.
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Affiliation(s)
- Nicholas Rhind
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA.
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22
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Abstract
Although distinct chromatin types have been long known to replicate at different timepoints of S phase, fine replication control has only recently become considered as an epigenetic phenomenon. It is now clear that in course of differentiation significant changes in genome replication timing occur, and these changes are intimately linked with the changes in transcriptional activity and nuclear architecture. Temporally coordinate replication is organized spatially into discrete units having specific chromosomal organization and function. Even though the functional aspects of such tight control of replication timing remain to be explored, one can confidently consider the replication program as yet another fundamental feature characteristic of the given differentiation state. The present review touches upon the molecular mechanisms of spatial and temporal control of replication timing, involving individual replication origins as well as large chromatin domains.
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EdU induces DNA damage response and cell death in mESC in culture. Chromosome Res 2013; 21:87-100. [PMID: 23463495 PMCID: PMC3601257 DOI: 10.1007/s10577-013-9340-5] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2012] [Revised: 02/08/2013] [Accepted: 02/09/2013] [Indexed: 11/29/2022]
Abstract
Recently, a novel DNA replication precursor analogue called 5-ethynyl-2′-deoxyuridine (EdU) has been widely used to monitor DNA synthesis as an alternative to bromodeoxyuridine. Use of EdU benefits from simplicity and reproducibility and the simple chemical detection systems allows excellent preservation of nuclear structure. However, the alkyne moiety is highly reactive, raising the possibility that incorporation might compromise genome stability. To assess the extent of possible DNA damage, we have analysed the effect of EdU incorporation into DNA during short- and long-term cell culture using a variety of cell lines. We show that EdU incorporation has no measurable impact on the rate of elongation of replication forks during synthesis. However, using different cell lines we find that during long-term cell culture variable responses to EdU incorporation are seen, which range from delayed cell cycle progression to complete cell cycle arrest. The most profound phenotypes were seen in mouse embryonic stem cells, which following incorporation of EdU accumulated in the G2/M-phase of the cell cycle before undergoing apoptosis. In long-term cell culture, EdU incorporation also triggered a DNA damage response in all cell types analysed. Our study shows that while EdU is extremely useful to tag sites of on-going replication, for long-term studies (i.e. beyond the cell cycle in which labelling is performed), a careful analysis of cell cycle perturbations must be performed in order to ensure that any conclusions made after EdU treatment are not a direct consequence of EdU-dependent activation of cell stress responses.
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24
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Pliss A, Malyavantham KS, Bhattacharya S, Berezney R. Chromatin dynamics in living cells: Identification of oscillatory motion. J Cell Physiol 2012; 228:609-16. [DOI: 10.1002/jcp.24169] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2012] [Accepted: 07/31/2012] [Indexed: 01/13/2023]
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25
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Systematic determination of replication activity type highlights interconnections between replication, chromatin structure and nuclear localization. PLoS One 2012; 7:e48986. [PMID: 23145042 PMCID: PMC3492150 DOI: 10.1371/journal.pone.0048986] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2012] [Accepted: 10/03/2012] [Indexed: 12/12/2022] Open
Abstract
DNA replication is a highly regulated process, with each genomic locus replicating at a distinct time of replication (ToR). Advances in ToR measurement technology enabled several genome-wide profiling studies that revealed tight associations between ToR and general genomic features and a remarkable ToR conservation in mammals. Genome wide studies further showed that at the hundreds kb-to-megabase scale the genome can be divided into constant ToR regions (CTRs) in which the replication process propagates at a faster pace due to the activation of multiple origins and temporal transition regions (TTRs) in which the replication process propagates at a slower pace. We developed a computational tool that assigns a ToR to every measured locus and determines its replication activity type (CTR versus TTR). Our algorithm, ARTO (Analysis of Replication Timing and Organization), uses signal processing methods to fit a constant piece-wise linear curve to the measured raw data. We tested our algorithm and provide performance and usability results. A Matlab implementation of ARTO is available at http://bioinfo.cs.technion.ac.il/people/zohar/ARTO/. Applying our algorithm to ToR data measured in multiple mouse and human samples allowed precise genome-wide ToR determination and replication activity type characterization. Analysis of the results highlighted the plasticity of the replication program. For example, we observed significant ToR differences in 10–25% of the genome when comparing different tissue types. Our analyses also provide evidence for activity type differences in up to 30% of the probes. Integration of the ToR data with multiple aspects of chromosome organization characteristics suggests that ToR plays a role in shaping the regional chromatin structure. Namely, repressive chromatin marks, are associated with late ToR both in TTRs and CTRs. Finally, characterization of the differences between TTRs and CTRs, with matching ToR, revealed that TTRs are associated with compact chromatin and are located significantly closer to the nuclear envelope. Supplementary material is available. Raw and processed data were deposited in Geo (GSE17236).
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Moindrot B, Audit B, Klous P, Baker A, Thermes C, de Laat W, Bouvet P, Mongelard F, Arneodo A. 3D chromatin conformation correlates with replication timing and is conserved in resting cells. Nucleic Acids Res 2012; 40:9470-81. [PMID: 22879376 PMCID: PMC3479194 DOI: 10.1093/nar/gks736] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Although chromatin folding is known to be of functional importance to control the gene expression program, less is known regarding its interplay with DNA replication. Here, using Circular Chromatin Conformation Capture combined with high-throughput sequencing, we identified megabase-sized self-interacting domains in the nucleus of a human lymphoblastoid cell line, as well as in cycling and resting peripheral blood mononuclear cells (PBMC). Strikingly, the boundaries of those domains coincide with early-initiation zones in every cell types. Preferential interactions have been observed between the consecutive early-initiation zones, but also between those separated by several tens of megabases. Thus, the 3D conformation of chromatin is strongly correlated with the replication timing along the whole chromosome. We furthermore provide direct clues that, in addition to the timing value per se, the shape of the timing profile at a given locus defines its set of genomic contacts. As this timing-related scheme of chromatin organization exists in lymphoblastoid cells, resting and cycling PBMC, this indicates that it is maintained several weeks or months after the previous S-phase. Lastly, our work highlights that the major chromatin changes accompanying PBMC entry into cell cycle occur while keeping largely unchanged the long-range chromatin contacts.
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Affiliation(s)
- Benoit Moindrot
- Laboratoire Joliot-Curie, Ecole Normale Supérieure de Lyon, CNRS, F-69007 Lyon, France
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27
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Jackson D, Wang X, Rudner DZ. Spatio-temporal organization of replication in bacteria and eukaryotes (nucleoids and nuclei). Cold Spring Harb Perspect Biol 2012; 4:a010389. [PMID: 22855726 DOI: 10.1101/cshperspect.a010389] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Here we discuss the spatio-temporal organization of replication in eubacteria and eukaryotes. Although there are significant differences in how replication is organized in cells that contain nuclei from those that do not, you will see that organization of replication in all organisms is principally dictated by the structured arrangement of the chromosome. We will begin with how replication is organized in eubacteria with particular emphasis on three well studied model organisms. We will then discuss spatial and temporal organization of replication in eukaryotes highlighting the similarities and differences between these two domains of life.
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Affiliation(s)
- Dean Jackson
- University of Manchester, Faculty of Life Sciences, Michael Smith Building, Oxford Road, Manchester M13 9PT, United Kingdom.
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28
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Maya-Mendoza A, Olivares-Chauvet P, Kohlmeier F, Jackson DA. Visualising chromosomal replication sites and replicons in mammalian cells. Methods 2012; 57:140-8. [PMID: 22683305 DOI: 10.1016/j.ymeth.2012.05.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2011] [Revised: 04/20/2012] [Accepted: 05/28/2012] [Indexed: 11/26/2022] Open
Abstract
The precise regulation of DNA replication is fundamental to the preservation of intact genomes during cell proliferation. Our understanding of this process has been based traditionally on a combination of techniques including biochemistry, molecular biology and cell biology. In this report we describe how the analysis of the S phase in mammalian cells using classical cell biology techniques has contributed to our understanding of the replication process. We describe traditional and state-of-the-art protocols for imaging sites of DNA synthesis in nuclei and the organisation of active replicons along DNA, as visualised on individual DNA fibres. We evaluate how the different approaches inform our understanding of the replication process, placing particular emphasis on ways in which the higher order chromatin structures and the spatial architecture of replication sites contribute to the orderly activation of defined regions of the genome at precise times of S phase.
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29
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The organization of a large transcriptional unit (Fyn) into structural DNA loops is cell-type specific and independent of transcription. Gene 2012; 493:1-8. [DOI: 10.1016/j.gene.2011.11.050] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2011] [Revised: 10/21/2011] [Accepted: 11/14/2011] [Indexed: 11/19/2022]
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30
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Sacco E, Hasan MM, Alberghina L, Vanoni M. Comparative analysis of the molecular mechanisms controlling the initiation of chromosomal DNA replication in yeast and in mammalian cells. Biotechnol Adv 2012; 30:73-98. [DOI: 10.1016/j.biotechadv.2011.09.009] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2011] [Accepted: 09/14/2011] [Indexed: 11/26/2022]
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31
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Evidence for sequential and increasing activation of replication origins along replication timing gradients in the human genome. PLoS Comput Biol 2011; 7:e1002322. [PMID: 22219720 PMCID: PMC3248390 DOI: 10.1371/journal.pcbi.1002322] [Citation(s) in RCA: 117] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2011] [Accepted: 11/07/2011] [Indexed: 12/28/2022] Open
Abstract
Genome-wide replication timing studies have suggested that mammalian chromosomes consist of megabase-scale domains of coordinated origin firing separated by large originless transition regions. Here, we report a quantitative genome-wide analysis of DNA replication kinetics in several human cell types that contradicts this view. DNA combing in HeLa cells sorted into four temporal compartments of S phase shows that replication origins are spaced at 40 kb intervals and fire as small clusters whose synchrony increases during S phase and that replication fork velocity (mean 0.7 kb/min, maximum 2.0 kb/min) remains constant and narrowly distributed through S phase. However, multi-scale analysis of a genome-wide replication timing profile shows a broad distribution of replication timing gradients with practically no regions larger than 100 kb replicating at less than 2 kb/min. Therefore, HeLa cells lack large regions of unidirectional fork progression. Temporal transition regions are replicated by sequential activation of origins at a rate that increases during S phase and replication timing gradients are set by the delay and the spacing between successive origin firings rather than by the velocity of single forks. Activation of internal origins in a specific temporal transition region is directly demonstrated by DNA combing of the IGH locus in HeLa cells. Analysis of published origin maps in HeLa cells and published replication timing and DNA combing data in several other cell types corroborate these findings, with the interesting exception of embryonic stem cells where regions of unidirectional fork progression seem more abundant. These results can be explained if origins fire independently of each other but under the control of long-range chromatin structure, or if replication forks progressing from early origins stimulate initiation in nearby unreplicated DNA. These findings shed a new light on the replication timing program of mammalian genomes and provide a general model for their replication kinetics. Eukaryotic chromosomes replicate from multiple replication origins that fire at different times in S phase. The mechanisms that specify origin position and firing time and coordinate origins to ensure complete genome duplication are unclear. Previous studies proposed either that origins are arranged in temporally coordinated groups or fire independently of each other in a stochastic manner. Here, we have performed a quantitative analysis of human genome replication kinetics using a combination of DNA combing, which reveals local patterns of origin firing and replication fork progression on single DNA molecules, and massive sequencing of newly replicated DNA, which reveals the population-averaged replication timing profile of the entire genome. We show that origins are activated synchronously in large regions of uniform replication timing but more gradually in temporal transition regions and that the rate of origin firing increases as replication progresses. Large regions of unidirectional fork progression are abundant in embryonic stem cells but rare in differentiated cells. We propose a model in which replication forks progressing from early origins stimulate initiation in nearby unreplicated DNA in a manner that explains the shape of the replication timing profile. These results provide a fundamental insight into the temporal regulation of mammalian genome replication.
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Innate structure of DNA foci restricts the mixing of DNA from different chromosome territories. PLoS One 2011; 6:e27527. [PMID: 22205925 PMCID: PMC3244381 DOI: 10.1371/journal.pone.0027527] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2010] [Accepted: 10/19/2011] [Indexed: 01/15/2023] Open
Abstract
The distribution of chromatin within the mammalian nucleus is constrained by its organization into chromosome territories (CTs). However, recent studies have suggested that promiscuous intra- and inter-chromosomal interactions play fundamental roles in regulating chromatin function and so might define the spatial integrity of CTs. In order to test the extent of DNA mixing between CTs, DNA foci of individual CTs were labeled in living cells following incorporation of Alexa-488 and Cy-3 conjugated replication precursor analogues during consecutive cell cycles. Uniquely labeled chromatin domains, resolved following random mitotic segregation, were visualized as discrete structures with defined borders. At the level of resolution analysed, evidence for mixing of chromatin from adjacent domains was only apparent within the surface volumes where neighboring CTs touched. However, while less than 1% of the nuclear volume represented domains of inter-chromosomal mixing, the dynamic plasticity of DNA foci within individual CTs allows continual transformation of CT structure so that different domains of chromatin mixing evolve over time. Notably, chromatin mixing at the boundaries of adjacent CTs had little impact on the innate structural properties of DNA foci. However, when TSA was used to alter the extent of histone acetylation changes in chromatin correlated with increased chromatin mixing. We propose that DNA foci maintain a structural integrity that restricts widespread mixing of DNA and discuss how the potential to dynamically remodel genome organization might alter during cell differentiation.
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Ma E, Hyrien O, Goldar A. Do replication forks control late origin firing in Saccharomyces cerevisiae? Nucleic Acids Res 2011; 40:2010-9. [PMID: 22086957 PMCID: PMC3300028 DOI: 10.1093/nar/gkr982] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Recent studies of eukaryotic DNA replication timing profiles suggest that the time-dependent rate of origin firing, I(t), has a universal shape, which ensures a reproducible replication completion time. However, measurements of I(t) are based on population averages, which may bias the shape of the I(t) because of imperfect cell synchrony and cell-to-cell variability. Here, we measure the population-averaged I(t) profile from synchronized Saccharomyces cerevisiae cells using DNA combing and we extract the single-cell I(t) profile using numerical deconvolution. The single cell I(t) and the population-averaged I(t) extracted from DNA combing and replication timing profiles are similar, indicating a genome scale invariance of the replication process, and excluding cell-to-cell variability in replication time as an explanation for the shape of I(t). The single cell I(t) correlates with fork density in wild-type cells, which is specifically loosened in late S phase in the clb5Δ mutant. A previously proposed numerical model that reproduces the wild-type I(t) profile, could also describe the clb5Δ mutant I(t) once modified to incorporate the decline in CDK activity and the looser dependency of initiation on fork density in the absence of Clb5p. Overall, these results suggest that the replication forks emanating from early fired origins facilitate origin firing in later-replicating regions.
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Affiliation(s)
- Emilie Ma
- Commissariat à l'Energie Atomique (CEA), iBiTec-S, 91191 Gif-sur-Yvette, France
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34
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Abstract
Mutation rates vary significantly within the genome and across species. Recent studies revealed a long suspected replication-timing effect on mutation rate, but the mechanisms that regulate the increase in mutation rate as the genome is replicated remain unclear. Evidence is emerging, however, that DNA repair systems, in general, are less efficient in late replicating heterochromatic regions compared to early replicating euchromatic regions of the genome. At the same time, mutation rates in both vertebrates and invertebrates have been shown to vary with generation time (GT). GT is correlated with genome size, which suggests a possible nucleotypic effect on species-specific mutation rates. These and other observations all converge on a role for DNA replication checkpoints in modulating generation times and mutation rates during the DNA synthetic phase (S phase) of the cell cycle. The following will examine the potential role of the intra-S checkpoint in regulating cell cycle times (GT) and mutation rates in eukaryotes. This article was published online on August 5, 2011. An error was subsequently identified. This notice is included in the online and print versions to indicate that both have been corrected October 4, 2011.
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Affiliation(s)
- John Herrick
- Department of Physics, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, Canada.
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35
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How dormant origins promote complete genome replication. Trends Biochem Sci 2011; 36:405-14. [PMID: 21641805 DOI: 10.1016/j.tibs.2011.05.002] [Citation(s) in RCA: 174] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2011] [Revised: 04/26/2011] [Accepted: 05/04/2011] [Indexed: 01/21/2023]
Abstract
Many replication origins that are licensed by loading MCM2-7 complexes in G1 are not normally used. Activation of these dormant origins during S phase provides a first line of defence for the genome if replication is inhibited. When replication forks fail, dormant origins are activated within regions of the genome currently engaged in replication. At the same time, DNA damage-response kinases activated by the stalled forks preferentially suppress the assembly of new replication factories, thereby ensuring that chromosomal regions experiencing replicative stress complete synthesis before new regions of the genome are replicated. Mice expressing reduced levels of MCM2-7 have fewer dormant origins, are cancer-prone and are genetically unstable, demonstrating the importance of dormant origins for preserving genome integrity. We review the function of dormant origins, the molecular mechanism of their regulation and their physiological implications.
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Trevilla-García C, Aranda-Anzaldo A. Cell-type-specific organization of nuclear DNA into structural looped domains. J Cell Biochem 2011; 112:531-40. [PMID: 21268074 DOI: 10.1002/jcb.22943] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
In the interphase nucleus of metazoan cells the DNA is organized in supercoiled loops anchored to a proteinaceous substructure known as the nuclear matrix (NM). The DNA is anchored to the NM by means of non-coding sequences of variable length known as matrix attachment regions or MARs operationally classified in structural-constitutive, resistant to high-salt extraction and transient-functional, non-resistant to high-salt extraction. The former are also known as true loop attachment regions or LARs that determine structural DNA loops. The DNA-NM interactions define a higher order structure within the cell nucleus (NHOS). We studied in a comparative fashion the NHOS in two primary cell types from the rat: hepatocytes and naive B lymphocytes, by analyzing the topological relationships between the NM and a set of eight short gene sequences located in six separate chromosomes and as such representing a coarse-grained, large-scale sample of the actual organization of nuclear DNA into structural loop domains. Our results indicate that such an organization is cell-type specific since most of the gene sequences studied showed significant differences in their relative position to the NM according to cell type. Such cell-type specific differences in the NHOS have no obvious correlation with the tissue-specific transcriptional activity of the corresponding genes, supporting the notion that permanent, structural DNA loops are different from transient, functional DNA loops that may be associated with transcription.
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