1
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Gordon R. The chromolinker hypothesis: Are eukaryotic genomes also circular? Biosystems 2024; 244:105280. [PMID: 39097218 DOI: 10.1016/j.biosystems.2024.105280] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2024] [Revised: 07/29/2024] [Accepted: 07/31/2024] [Indexed: 08/05/2024]
Abstract
Over more than the past century, reports that chromosomes in Eukaryotes are linked have been published. Recently this has been confirmed by micromanipulation. The chromolinkers are DNAse sensitive, as has been previously reported. The arguments for and against chromolinkers have been reviewed, and a call for definitive research made, because if chromolinkers do exist, the whole basis for genetics may require revision.
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Affiliation(s)
- Richard Gordon
- Gulf Specimen Marine Laboratory & Aquarium, 222 Clark Drive, Panacea, FL, 32346, USA.
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2
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Chua GNL, Liu S. When Force Met Fluorescence: Single-Molecule Manipulation and Visualization of Protein-DNA Interactions. Annu Rev Biophys 2024; 53:169-191. [PMID: 38237015 DOI: 10.1146/annurev-biophys-030822-032904] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/26/2024]
Abstract
Myriad DNA-binding proteins undergo dynamic assembly, translocation, and conformational changes while on DNA or alter the physical configuration of the DNA substrate to control its metabolism. It is now possible to directly observe these activities-often central to the protein function-thanks to the advent of single-molecule fluorescence- and force-based techniques. In particular, the integration of fluorescence detection and force manipulation has unlocked multidimensional measurements of protein-DNA interactions and yielded unprecedented mechanistic insights into the biomolecular processes that orchestrate cellular life. In this review, we first introduce the different experimental geometries developed for single-molecule correlative force and fluorescence microscopy, with a focus on optical tweezers as the manipulation technique. We then describe the utility of these integrative platforms for imaging protein dynamics on DNA and chromatin, as well as their unique capabilities in generating complex DNA configurations and uncovering force-dependent protein behaviors. Finally, we give a perspective on the future directions of this emerging research field.
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Affiliation(s)
- Gabriella N L Chua
- Laboratory of Nanoscale Biophysics and Biochemistry, The Rockefeller University, New York, New York, USA;
- Tri-Institutional PhD Program in Chemical Biology, New York, New York, USA
| | - Shixin Liu
- Laboratory of Nanoscale Biophysics and Biochemistry, The Rockefeller University, New York, New York, USA;
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3
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Cai P, Casas CJ, Plancarte GQ, Mikawa T, Hua LL. Ipsilateral restriction of chromosome movement along a centrosome, and apical-basal axis during the cell cycle. RESEARCH SQUARE 2024:rs.3.rs-4283973. [PMID: 38746098 PMCID: PMC11092853 DOI: 10.21203/rs.3.rs-4283973/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2024]
Abstract
Little is known about how distance between homologous chromosomes are controlled during the cell cycle. Here, we show that the distribution of centromere components display two discrete clusters placed to either side of the centrosome and apical/basal axis from prophase to G1 interphase. 4-Dimensional live cell imaging analysis of centromere and centrosome tracking reveals that centromeres oscillate largely within one cluster, but do not cross over to the other cluster. We propose a model of an axis-dependent ipsilateral restriction of chromosome oscillations throughout mitosis.
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4
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Cai P, Casas CJ, Plancarte GQ, Hua LL, Mikawa T. Ipsilateral restriction of chromosome movement along a centrosome, and apical-basal axis during the cell cycle. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.03.27.534352. [PMID: 37034601 PMCID: PMC10081237 DOI: 10.1101/2023.03.27.534352] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
Little is known about how distance between homologous chromosomes are controlled during the cell cycle. Here, we show that the distribution of centromere components display two discrete clusters placed to either side of the centrosome and apical/basal axis from prophase to G 1 interphase. 4-Dimensional live cell imaging analysis of centromere and centrosome tracking reveals that centromeres oscillate largely within one cluster, but do not cross over to the other cluster. We propose a model of an axis-dependent ipsilateral restriction of chromosome oscillations throughout mitosis.
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5
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Forte G, Boteva L, Conforto F, Gilbert N, Cook PR, Marenduzzo D. Bridging condensins mediate compaction of mitotic chromosomes. J Cell Biol 2024; 223:e202209113. [PMID: 37976091 PMCID: PMC10655892 DOI: 10.1083/jcb.202209113] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2022] [Revised: 07/08/2023] [Accepted: 11/01/2023] [Indexed: 11/19/2023] Open
Abstract
Eukaryotic chromosomes compact during mitosis into elongated cylinders-and not the spherical globules expected of self-attracting long flexible polymers. This process is mainly driven by condensin-like proteins. Here, we present Brownian-dynamic simulations involving two types of such proteins with different activities. One, which we refer to as looping condensins, anchors long-lived chromatin loops to create bottlebrush structures. The second, referred to as bridging condensins, forms multivalent bridges between distant parts of these loops. We show that binding of bridging condensins leads to the formation of shorter and stiffer mitotic-like cylinders without requiring any additional energy input. These cylinders have several features matching experimental observations. For instance, the axial condensin backbone breaks up into clusters as found by microscopy, and cylinder elasticity qualitatively matches that seen in chromosome pulling experiments. Additionally, simulating global condensin depletion or local faulty condensin loading gives phenotypes seen experimentally and points to a mechanistic basis for the structure of common fragile sites in mitotic chromosomes.
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Affiliation(s)
- Giada Forte
- School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK
| | - Lora Boteva
- MRC Human Genetics Unit, Western General Hospital, Institute of Genetics and Cancer, University of Edinburgh, Edinburgh, UK
| | - Filippo Conforto
- School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK
| | - Nick Gilbert
- MRC Human Genetics Unit, Western General Hospital, Institute of Genetics and Cancer, University of Edinburgh, Edinburgh, UK
| | - Peter R. Cook
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK
| | - Davide Marenduzzo
- School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK
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6
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Chauhan K, Mishra G, Kishore V, Kumar S. Appearance of de Gennes length in force-induced transitions. Phys Rev E 2023; 108:L042501. [PMID: 37978702 DOI: 10.1103/physreve.108.l042501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2022] [Accepted: 06/12/2023] [Indexed: 11/19/2023]
Abstract
Using Langevin dynamic simulations, a simple coarse-grained model of a DNA protein construct is used to study the DNA rupture and the protein unfolding. We identify three distinct states: (i) zipped DNA and collapsed protein, (ii) unzipped DNA and stretched protein, and (iii) unzipped DNA and collapsed protein. Here, we find a phase diagram that shows these states depending on the size of the DNA handle and the protein. For a less stable protein, unfolding is solely governed by the size of the linker DNA, whereas if the protein's stability increases, complete unfolding becomes impossible because the rupture force for DNA has reached a saturation regime influenced by the de Gennes length. We show that unfolding occurs via a few intermediate states by monitoring the force-extension curve of the entire protein. We extend our study to a heterogeneous protein system, where similar intermediate states in two systems can lead to different protein unfolding paths.
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Affiliation(s)
- Keerti Chauhan
- Department of Physics, Banaras Hindu University, Varanasi 221 005, India
| | - Garima Mishra
- Department of Physics, Ashoka University, Sonipat 131 029, India
| | - Vimal Kishore
- Department of Physics, Banaras Hindu University, Varanasi 221 005, India
| | - Sanjay Kumar
- Department of Physics, Banaras Hindu University, Varanasi 221 005, India
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7
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Polovnikov KE, Slavov B, Belan S, Imakaev M, Brandão HB, Mirny LA. Crumpled polymer with loops recapitulates key features of chromosome organization. PHYSICAL REVIEW. X 2023; 13:041029. [PMID: 38774252 PMCID: PMC11108028 DOI: 10.1103/physrevx.13.041029] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 05/24/2024]
Abstract
Chromosomes are exceedingly long topologically-constrained polymers compacted in a cell nucleus. We recently suggested that chromosomes are organized into loops by an active process of loop extrusion. Yet loops remain elusive to direct observations in living cells; detection and characterization of myriads of such loops is a major challenge. The lack of a tractable physical model of a polymer folded into loops limits our ability to interpret experimental data and detect loops. Here, we introduce a new physical model - a polymer folded into a sequence of loops, and solve it analytically. Our model and a simple geometrical argument show how loops affect statistics of contacts in a polymer across different scales, explaining universally observed shapes of the contact probability. Moreover, we reveal that folding into loops reduces the density of topological entanglements, a novel phenomenon we refer as "the dilution of entanglements". Supported by simulations this finding suggests that up to ~ 1 - 2Mb chromosomes with loops are not topologically constrained, yet become crumpled at larger scales. Our theoretical framework allows inference of loop characteristics, draws a new picture of chromosome organization, and shows how folding into loops affects topological properties of crumpled polymers.
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Affiliation(s)
- Kirill E. Polovnikov
- Current address: Institut Curie, PSL Research University, Sorbonne Université, CNRS UMR3664, Paris, France
- Institute of Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, MA 02139
| | | | - Sergey Belan
- Landau Institute for Theoretical Physics, Russian Academy of Sciences, Chernogolovka, Russia
- National Research University Higher School of Economics, Faculty of Physics, Moscow, Russia
| | - Maxim Imakaev
- Institute of Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Hugo B. Brandão
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02142
| | - Leonid A. Mirny
- Institute of Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, MA 02139
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139
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8
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Ruben BS, Brahmachari S, Contessoto VG, Cheng RR, Oliveira Junior AB, Di Pierro M, Onuchic JN. Structural reorganization and relaxation dynamics of axially stressed chromosomes. Biophys J 2023; 122:1633-1645. [PMID: 36960531 PMCID: PMC10183323 DOI: 10.1016/j.bpj.2023.03.029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2022] [Revised: 02/06/2023] [Accepted: 03/17/2023] [Indexed: 03/25/2023] Open
Abstract
Chromosomes endure mechanical stresses throughout the cell cycle; for example, resulting from the pulling of chromosomes by spindle fibers during mitosis or deformation of the nucleus during cell migration. The response to physical stress is closely related to chromosome structure and function. Micromechanical studies of mitotic chromosomes have revealed them to be remarkably extensible objects and informed early models of mitotic chromosome organization. We use a data-driven, coarse-grained polymer modeling approach to explore the relationship between the spatial organization of individual chromosomes and their emergent mechanical properties. In particular, we investigate the mechanical properties of our model chromosomes by axially stretching them. Simulated stretching led to a linear force-extension curve for small strain, with mitotic chromosomes behaving about 10-fold stiffer than interphase chromosomes. Studying their relaxation dynamics, we found that chromosomes are viscoelastic solids with a highly liquid-like, viscous behavior in interphase that becomes solid-like in mitosis. This emergent mechanical stiffness originates from lengthwise compaction, an effective potential capturing the activity of loop-extruding SMC complexes. Chromosomes denature under large strains via unraveling, which is characterized by opening of large-scale folding patterns. By quantifying the effect of mechanical perturbations on the chromosome's structural features, our model provides a nuanced understanding of in vivo mechanics of chromosomes.
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Affiliation(s)
- Benjamin S Ruben
- Center for Theoretical Biological Physics, Rice University, Houston, Texas; Biophysics PhD Program, Harvard University, Cambridge, Massachusetts.
| | | | | | - Ryan R Cheng
- Center for Theoretical Biological Physics, Rice University, Houston, Texas; Department of Chemistry, University of Kentucky, Lexington, Kentucky
| | | | - Michele Di Pierro
- Department of Physics, Northeastern University, Boston, Massachusetts; Center for Theoretical Biological Physics, Northeastern University, Boston, Massachusetts
| | - José N Onuchic
- Center for Theoretical Biological Physics, Rice University, Houston, Texas; Department of Physics and Astronomy, Department of Chemistry, Department of BioSciences, Rice University, Houston, Texas
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9
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Dey A, Shi G, Takaki R, Thirumalai D. Structural changes in chromosomes driven by multiple condensin motors during mitosis. Cell Rep 2023; 42:112348. [PMID: 37027299 DOI: 10.1016/j.celrep.2023.112348] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2022] [Revised: 11/10/2022] [Accepted: 03/21/2023] [Indexed: 04/08/2023] Open
Abstract
We create a computational framework that utilizes loop extrusion (LE) by multiple condensin I/II motors to predict changes in chromosome organization during mitosis. The theory accurately reproduces the experimental contact probability profiles for the mitotic chromosomes in HeLa and DT40 cells. The LE rate is smaller at the start of mitosis and increases as the cells approach metaphase. Condensin II-mediated mean loop size is about six times larger than loops because of condensin I. The loops, which overlap each other, are stapled to a central dynamically changing helical scaffold formed by the motors during the LE process. A polymer physics-based data-driven method that uses the Hi-C contact map as the only input shows that the helix is characterized as random helix perversions (RHPs) in which the handedness changes randomly along the scaffold. The theoretical predictions, which are testable using imaging experiments, do not contain any parameters.
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Affiliation(s)
- Atreya Dey
- Department of Chemistry, The University of Texas at Austin, Austin, TX 78712, USA
| | - Guang Shi
- Department of Materials Science, University of Illinois, Urbana, IL 61801, USA
| | - Ryota Takaki
- Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Str.38, 01187 Dresden, Saxony, Germany
| | - D Thirumalai
- Department of Chemistry, The University of Texas at Austin, Austin, TX 78712, USA; Department of Physics, The University of Texas at Austin, Austin, TX 78712, USA.
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10
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Abstract
Cells generate and sense mechanical forces that trigger biochemical signals to elicit cellular responses that control cell fate changes. Mechanical forces also physically distort neighboring cells and the surrounding connective tissue, which propagate mechanochemical signals over long distances to guide tissue patterning, organogenesis, and adult tissue homeostasis. As the largest and stiffest organelle, the nucleus is particularly sensitive to mechanical force and deformation. Nuclear responses to mechanical force include adaptations in chromatin architecture and transcriptional activity that trigger changes in cell state. These force-driven changes also influence the mechanical properties of chromatin and nuclei themselves to prevent aberrant alterations in nuclear shape and help maintain genome integrity. This review will discuss principles of nuclear mechanotransduction and chromatin mechanics and their role in DNA damage and cell fate regulation.
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Affiliation(s)
- Yekaterina A Miroshnikova
- Helsinki Institute of Life Science, Biomedicum Helsinki, University of Helsinki, Helsinki 00014, Finland
- Wihuri Research Institute, Biomedicum Helsinki, University of Helsinki, Helsinki 00290, Finland
- Stem Cells and Metabolism Research Program, Faculty of Medicine, University of Helsinki, Helsinki 00014, Finland
- Max Planck Institute for Biology of Ageing, Cologne 50931, Germany
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Sara A Wickström
- Helsinki Institute of Life Science, Biomedicum Helsinki, University of Helsinki, Helsinki 00014, Finland
- Wihuri Research Institute, Biomedicum Helsinki, University of Helsinki, Helsinki 00290, Finland
- Stem Cells and Metabolism Research Program, Faculty of Medicine, University of Helsinki, Helsinki 00014, Finland
- Max Planck Institute for Biology of Ageing, Cologne 50931, Germany
- Cluster of Excellence Cellular Stress Responses in Aging-Associated Diseases (CECAD), University of Cologne, Cologne 50931, Germany
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11
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Choppakatla P, Dekker B, Cutts EE, Vannini A, Dekker J, Funabiki H. Linker histone H1.8 inhibits chromatin binding of condensins and DNA topoisomerase II to tune chromosome length and individualization. eLife 2021; 10:e68918. [PMID: 34406118 PMCID: PMC8416026 DOI: 10.7554/elife.68918] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Accepted: 08/13/2021] [Indexed: 12/14/2022] Open
Abstract
DNA loop extrusion by condensins and decatenation by DNA topoisomerase II (topo II) are thought to drive mitotic chromosome compaction and individualization. Here, we reveal that the linker histone H1.8 antagonizes condensins and topo II to shape mitotic chromosome organization. In vitro chromatin reconstitution experiments demonstrate that H1.8 inhibits binding of condensins and topo II to nucleosome arrays. Accordingly, H1.8 depletion in Xenopus egg extracts increased condensins and topo II levels on mitotic chromatin. Chromosome morphology and Hi-C analyses suggest that H1.8 depletion makes chromosomes thinner and longer through shortening the average loop size and reducing the DNA amount in each layer of mitotic loops. Furthermore, excess loading of condensins and topo II to chromosomes by H1.8 depletion causes hyper-chromosome individualization and dispersion. We propose that condensins and topo II are essential for chromosome individualization, but their functions are tuned by the linker histone to keep chromosomes together until anaphase.
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Affiliation(s)
- Pavan Choppakatla
- Laboratory of Chromosome and Cell Biology, The Rockefeller UniversityNew YorkUnited States
| | - Bastiaan Dekker
- Program in Systems Biology, Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical SchoolWorcesterUnited States
| | - Erin E Cutts
- Division of Structural Biology, The Institute of Cancer ResearchLondonUnited Kingdom
| | - Alessandro Vannini
- Division of Structural Biology, The Institute of Cancer ResearchLondonUnited Kingdom
- Fondazione Human Technopole, Structural Biology Research Centre, 20157MilanItaly
| | - Job Dekker
- Program in Systems Biology, Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical SchoolWorcesterUnited States
- Howard Hughes Medical InstituteChevy ChaseUnited States
| | - Hironori Funabiki
- Laboratory of Chromosome and Cell Biology, The Rockefeller UniversityNew YorkUnited States
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12
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Shintomi K, Hirano T. Guiding functions of the C-terminal domain of topoisomerase IIα advance mitotic chromosome assembly. Nat Commun 2021; 12:2917. [PMID: 34006877 PMCID: PMC8131626 DOI: 10.1038/s41467-021-23205-w] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2020] [Accepted: 04/20/2021] [Indexed: 12/21/2022] Open
Abstract
Topoisomerase II (topo II) is one of the six proteins essential for mitotic chromatid reconstitution in vitro. It is not fully understood, however, mechanistically how this enzyme regulates this process. In an attempt to further refine the reconstitution assay, we have found that chromosomal binding of Xenopus laevis topo IIα is sensitive to buffer conditions and depends on its C-terminal domain (CTD). Enzymological assays using circular DNA substrates supports the idea that topo IIα first resolves inter-chromatid entanglements to drive individualization and then generates intra-chromatid entanglements to promote thickening. Importantly, only the latter process requires the CTD. By using frog egg extracts, we also show that the CTD contributes to proper formation of nucleosome-depleted chromatids by competing with a linker histone for non-nucleosomal DNA. Our results demonstrate that topo IIα utilizes its CTD to deliver the enzymatic core to crowded environments created during mitotic chromatid assembly, thereby fine-tuning this process. Topoisomerase IIα (topo IIα) is critical for mitotic chromatid assembly. Here the authors report a refinement of the mitotic chromatid reconstitution assay and provide novel insights into the C-terminal domain (CTD) of topo IIα.
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Affiliation(s)
| | - Tatsuya Hirano
- Chromosome Dynamics Laboratory, RIKEN, Wako, Saitama, Japan.
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13
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Paulson JR, Hudson DF, Cisneros-Soberanis F, Earnshaw WC. Mitotic chromosomes. Semin Cell Dev Biol 2021; 117:7-29. [PMID: 33836947 PMCID: PMC8406421 DOI: 10.1016/j.semcdb.2021.03.014] [Citation(s) in RCA: 38] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2021] [Revised: 03/23/2021] [Accepted: 03/23/2021] [Indexed: 01/25/2023]
Abstract
Our understanding of the structure and function of mitotic chromosomes has come a long way since these iconic objects were first recognized more than 140 years ago, though many details remain to be elucidated. In this chapter, we start with the early history of chromosome studies and then describe the path that led to our current understanding of the formation and structure of mitotic chromosomes. We also discuss some of the remaining questions. It is now well established that each mitotic chromatid consists of a central organizing region containing a so-called "chromosome scaffold" from which loops of DNA project radially. Only a few key non-histone proteins and protein complexes are required to form the chromosome: topoisomerase IIα, cohesin, condensin I and condensin II, and the chromokinesin KIF4A. These proteins are concentrated along the axis of the chromatid. Condensins I and II are primarily responsible for shaping the chromosome and the scaffold, and they produce the loops of DNA by an ATP-dependent process known as loop extrusion. Modelling of Hi-C data suggests that condensin II adopts a spiral staircase arrangement with an extruded loop extending out from each step in a roughly helical pattern. Condensin I then forms loops nested within these larger condensin II loops, thereby giving rise to the final compaction of the mitotic chromosome in a process that requires Topo IIα.
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Affiliation(s)
- James R Paulson
- Department of Chemistry, University of Wisconsin Oshkosh, 800 Algoma Boulevard, Oshkosh, WI 54901, USA.
| | - Damien F Hudson
- Murdoch Children's Research Institute, Royal Children's Hospital, Parkville, VIC 3052, Australia
| | - Fernanda Cisneros-Soberanis
- Wellcome Trust Centre for Cell Biology, ICB, University of Edinburgh, Michael Swann Building, King's Buildings, Max Born Crescent, Edinburgh EH9 3BF, Scotland, UK
| | - William C Earnshaw
- Wellcome Trust Centre for Cell Biology, ICB, University of Edinburgh, Michael Swann Building, King's Buildings, Max Born Crescent, Edinburgh EH9 3BF, Scotland, UK.
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14
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Mechanical Mechanisms of Chromosome Segregation. Cells 2021; 10:cells10020465. [PMID: 33671543 PMCID: PMC7926803 DOI: 10.3390/cells10020465] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Revised: 02/17/2021] [Accepted: 02/19/2021] [Indexed: 12/11/2022] Open
Abstract
Chromosome segregation—the partitioning of genetic material into two daughter cells—is one of the most crucial processes in cell division. In all Eukaryotes, chromosome segregation is driven by the spindle, a microtubule-based, self-organizing subcellular structure. Extensive research performed over the past 150 years has identified numerous commonalities and contrasts between spindles in different systems. In this review, we use simple coarse-grained models to organize and integrate previous studies of chromosome segregation. We discuss sites of force generation in spindles and fundamental mechanical principles that any understanding of chromosome segregation must be based upon. We argue that conserved sites of force generation may interact differently in different spindles, leading to distinct mechanical mechanisms of chromosome segregation. We suggest experiments to determine which mechanical mechanism is operative in a particular spindle under study. Finally, we propose that combining biophysical experiments, coarse-grained theories, and evolutionary genetics will be a productive approach to enhance our understanding of chromosome segregation in the future.
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15
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Pitman M, Dalal Y, Papoian GA. Minimal Cylinder Analysis Reveals the Mechanical Properties of Oncogenic Nucleosomes. Biophys J 2020; 118:2309-2318. [PMID: 32097625 PMCID: PMC7203005 DOI: 10.1016/j.bpj.2020.01.042] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2019] [Revised: 01/11/2020] [Accepted: 01/27/2020] [Indexed: 12/20/2022] Open
Abstract
Histone variants regulate replication, transcription, DNA damage repair, and chromosome segregation. Though widely accepted as a paradigm, it has not been rigorously demonstrated that histone variants encode unique mechanical properties. Here, we present a new theoretical approach called minimal cylinder analysis that uses strain fluctuations to determine the Young's modulus of nucleosomes from all-atom molecular dynamics simulations. Recently, we validated this computational tool against in vitro single-molecule nanoindentation of histone variant nucleosomes. In this report, we further extend minimal cylinder analysis to study the biophysical properties of hybrid nucleosomes that are known to exist in human cancer cells and contain H3 histone variants CENP-A and H3.3. Here, we report that the heterotypic nucleosome has an intermediate elasticity (8.5 ± 0.5 MPa) compared to CENP-A (6.2 ± 0.4 MPa) and H3 (9.8 ± 0.7 MPa) and that the dynamics of both canonical and CENP-A nucleosomes are preserved and partitioned across the nucleosome pseudodyad. Furthermore, we investigate the mechanism by which the elasticity of these heterotypic nucleosomes augments cryptic binding surfaces. From these analyses, we predict that the heterotypic nucleosome is permissive to the binding of one copy of the kinetochore protein CENP-C while still retaining a closed DNA end configuration required for linker histone H1 to bind. We discuss that the ectopic deposition of CENP-A in cancer by H3.3 chaperones HIRA and DAXX may fortuitously result in hybrid nucleosome formation. Using these results, we propose biological outcomes that might arise when such heterotypic nucleosomes occupy large regions of the genome.
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Affiliation(s)
- Mary Pitman
- Laboratory of Receptor Biology and Gene Expression, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland; Department of Chemistry and Biochemistry, Institute for Physical Science and Technology, University of Maryland, College Park, Maryland
| | - Yamini Dalal
- Laboratory of Receptor Biology and Gene Expression, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland.
| | - Garegin A Papoian
- Department of Chemistry and Biochemistry, Institute for Physical Science and Technology, University of Maryland, College Park, Maryland.
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16
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Yan THK, Wu Z, Kwok ACM, Wong JTY. Knockdown of Dinoflagellate Condensin CcSMC4 Subunit Leads to S-Phase Impediment and Decompaction of Liquid Crystalline Chromosomes. Microorganisms 2020; 8:microorganisms8040565. [PMID: 32295294 PMCID: PMC7232253 DOI: 10.3390/microorganisms8040565] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2020] [Revised: 03/30/2020] [Accepted: 04/10/2020] [Indexed: 01/01/2023] Open
Abstract
Dinoflagellates have some of the largest genomes, and their liquid-crystalline chromosomes (LCCs) have high degrees of non-nucleosomal superhelicity with cation-mediated DNA condensation. It is currently unknown if condensins, pentameric protein complexes containing structural maintenance of chromosomes 2/4, commonly involved in eukaryotic chromosomes condensation in preparation for M phase, may be involved in the LCC structure. We find that CcSMC4p (dinoflagellate SMC4 homolog) level peaked at S/G2 phase, even though LCCs do not undergo global-decondensation for replication. Despite the differences in the chromosomal packaging system, heterologous CcSMC4p expression suppressed conditional lethality of the corresponding fission yeast mutant, suggesting conservation of some canonical condensin functions. CcSMC4p-knockdown led to sustained expression of the S-phase marker PCNAp, S-phase impediment, and distorted nuclei in the early stage of CcSMC4p depletion. Prolonged CcSMC4p-knockdown resulted in aneuploidal cells and nuclear swelling with increasing LCC decompaction-decondensation. Cumulatively, our data suggested CcSMC4p function was required for dinoflagellate S-phase progression, and we propose that condensin-mediated higher-order compaction provisioning is involved in the provision of local rigidity for the replisome.
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17
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Chromatin and Cytoskeletal Tethering Determine Nuclear Morphology in Progerin-Expressing Cells. Biophys J 2020; 118:2319-2332. [PMID: 32320674 DOI: 10.1016/j.bpj.2020.04.001] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2019] [Revised: 03/18/2020] [Accepted: 04/03/2020] [Indexed: 12/13/2022] Open
Abstract
The nuclear morphology of eukaryotic cells is determined by the interplay between the lamina forming the nuclear skeleton, the chromatin inside the nucleus, and the coupling with the cytoskeleton. Nuclear alterations are often associated with pathological conditions as in Hutchinson-Gilford progeria syndrome, in which a mutation in the lamin A gene yields an altered form of the protein, named progerin, and an aberrant nuclear shape. Here, we introduce an inducible cellular model of Hutchinson-Gilford progeria syndrome in HeLa cells in which increased progerin expression leads to alterations in the coupling of the lamin shell with cytoskeletal or chromatin tethers as well as with polycomb group proteins. Furthermore, our experiments show that progerin expression leads to enhanced nuclear shape fluctuations in response to cytoskeletal activity. To interpret the experimental results, we introduce a computational model of the cell nucleus that explicitly includes chromatin fibers, the nuclear shell, and coupling with the cytoskeleton. The model allows us to investigate how the geometrical organization of the chromatin-lamin tether affects nuclear morphology and shape fluctuations. In sum, our findings highlight the crucial role played by lamin-chromatin and lamin-cytoskeletal alterations in determining nuclear shape morphology and in affecting cellular functions and gene regulation.
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18
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Zhou CY, Heald R. Emergent properties of mitotic chromosomes. Curr Opin Cell Biol 2020; 64:43-49. [PMID: 32151949 DOI: 10.1016/j.ceb.2020.02.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2019] [Revised: 01/21/2020] [Accepted: 02/01/2020] [Indexed: 12/27/2022]
Abstract
As a cell prepares to divide, its genetic material changes dramatically in both form and function. During interphase, a dynamic interplay between DNA compartmentalization and transcription functions to program cell identity. During mitosis, this purpose is put on hold and instead chromosomes function to facilitate their accurate segregation to daughter cells. Chromatin loops are rearranged, stacked, and compressed to form X-shaped chromosomes that are neatly aligned at the center of the mitotic spindle and ready to withstand the forces of anaphase. Many factors that contribute to mitotic chromosome assembly have now been identified, but how the plethora of molecular mechanisms operate in concert to give rise to the distinct form and physical properties of mitotic chromosomes at the cellular scale remains under active investigation. In this review, we discuss recent work that addresses a major challenge for the field: How to connect the molecular-level activities to large-scale changes in whole-chromosome architecture that determine mitotic chromosome size, shape, and function.
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Affiliation(s)
- Coral Y Zhou
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, 94720 USA.
| | - Rebecca Heald
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, 94720 USA.
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19
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Singh PB, Newman AG. On the relations of phase separation and Hi-C maps to epigenetics. ROYAL SOCIETY OPEN SCIENCE 2020; 7:191976. [PMID: 32257349 PMCID: PMC7062049 DOI: 10.1098/rsos.191976] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2019] [Accepted: 02/03/2020] [Indexed: 05/10/2023]
Abstract
The relationship between compartmentalization of the genome and epigenetics is long and hoary. In 1928, Heitz defined heterochromatin as the largest differentiated chromatin compartment in eukaryotic nuclei. Müller's discovery of position-effect variegation in 1930 went on to show that heterochromatin is a cytologically visible state of heritable (epigenetic) gene repression. Current insights into compartmentalization have come from a high-throughput top-down approach where contact frequency (Hi-C) maps revealed the presence of compartmental domains that segregate the genome into heterochromatin and euchromatin. It has been argued that the compartmentalization seen in Hi-C maps is owing to the physiochemical process of phase separation. Oddly, the insights provided by these experimental and conceptual advances have remained largely silent on how Hi-C maps and phase separation relate to epigenetics. Addressing this issue directly in mammals, we have made use of a bottom-up approach starting with the hallmarks of constitutive heterochromatin, heterochromatin protein 1 (HP1) and its binding partner the H3K9me2/3 determinant of the histone code. They are key epigenetic regulators in eukaryotes. Both hallmarks are also found outside mammalian constitutive heterochromatin as constituents of larger (0.1-5 Mb) heterochromatin-like domains and smaller (less than 100 kb) complexes. The well-documented ability of HP1 proteins to function as bridges between H3K9me2/3-marked nucleosomes contributes to polymer-polymer phase separation that packages epigenetically heritable chromatin states during interphase. Contacts mediated by HP1 'bridging' are likely to have been detected in Hi-C maps, as evidenced by the B4 heterochromatic subcompartment that emerges from contacts between large KRAB-ZNF heterochromatin-like domains. Further, mutational analyses have revealed a finer, innate, compartmentalization in Hi-C experiments that probably reflect contacts involving smaller domains/complexes. Proteins that bridge (modified) DNA and histones in nucleosomal fibres-where the HP1-H3K9me2/3 interaction represents the most evolutionarily conserved paradigm-could drive and generate the fundamental compartmentalization of the interphase nucleus. This has implications for the mechanism(s) that maintains cellular identity, be it a terminally differentiated fibroblast or a pluripotent embryonic stem cell.
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Affiliation(s)
- Prim B. Singh
- Nazarbayev University School of Medicine, 5/1 Kerei, Zhanibek Khandar Street, Nur-Sultan Z05K4F4, Kazakhstan
- Epigenetics Laboratory, Department of Natural Sciences, Novosibirsk State University, Pirogov Street 2, Novosibirsk 630090, Russian Federation
| | - Andrew G. Newman
- Institute of Cell and Neurobiology, Charité—Universitätsmedizin Berlin, Corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin and Berlin Institute of Health, Berlin, Germany
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20
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Marko JF. Physics and Biology (of Chromosomes). J Mol Biol 2020; 432:621-631. [PMID: 31866291 PMCID: PMC6948178 DOI: 10.1016/j.jmb.2019.11.022] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Revised: 11/26/2019] [Accepted: 11/27/2019] [Indexed: 12/18/2022]
Abstract
Advances in molecular biology, optics, genetics, and bioinformatics have opened the door to mapping, in molecular detail, processes inside living cells. With the ability to observe the individual moving parts of cellular machinery, concepts formerly confined to physics are entering mainstream biology. This article discusses a few ideas of this sort related to chromosome biology, to illustrate what kinds of insights physics might yet bring to our understanding of living systems.
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Affiliation(s)
- John F Marko
- Department of Physics & Astronomy and Department of Molecular Biosciences, Northwestern University, Evanston, IL, 60208, USA; CNRS, Laboratoire de Physique Théorique de la Matière Condensée (LPTMC), Sorbonne Université, Paris, 75005, France.
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21
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Chromosome disentanglement driven via optimal compaction of loop-extruded brush structures. Proc Natl Acad Sci U S A 2019; 116:24956-24965. [PMID: 31757850 DOI: 10.1073/pnas.1906355116] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Eukaryote cell division features a chromosome compaction-decompaction cycle that is synchronized with their physical and topological segregation. It has been proposed that lengthwise compaction of chromatin into mitotic chromosomes via loop extrusion underlies the compaction-segregation/resolution process. We analyze this disentanglement scheme via considering the chromosome to be a succession of DNA/chromatin loops-a polymer "brush"-where active extrusion of loops controls the brush structure. Given type-II DNA topoisomerase (Topo II)-catalyzed topology fluctuations, we find that interchromosome entanglements are minimized for a certain "optimal" loop that scales with the chromosome size. The optimal loop organization is in accord with experimental data across species, suggesting an important structural role of genomic loops in maintaining a less entangled genome. Application of the model to the interphase genome indicates that active loop extrusion can maintain a level of chromosome compaction with suppressed entanglements; the transition to the metaphase state requires higher lengthwise compaction and drives complete topological segregation. Optimized genomic loops may provide a means for evolutionary propagation of gene-expression patterns while simultaneously maintaining a disentangled genome. We also find that compact metaphase chromosomes have a densely packed core along their cylindrical axes that explains their observed mechanical stiffness. Our model connects chromosome structural reorganization to topological resolution through the cell cycle and highlights a mechanism of directing Topo II-mediated strand passage via loop extrusion-driven lengthwise compaction.
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22
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Nuclear failure, DNA damage, and cell cycle disruption after migration through small pores: a brief review. Essays Biochem 2019; 63:569-577. [PMID: 31366473 DOI: 10.1042/ebc20190007] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2019] [Revised: 07/15/2019] [Accepted: 07/17/2019] [Indexed: 01/14/2023]
Abstract
In many contexts of development, regeneration, or disease such as cancer, a cell squeezes through a dense tissue or a basement membrane, constricting its nucleus. Here, we describe how the severity of nuclear deformation depends on a nucleus' mechanical properties that are mostly determined by the density of chromatin and by the nuclear lamina. We explain how constriction-induced nuclear deformation affects nuclear contents by causing (i) local density changes in chromatin and (ii) rupture of the nuclear lamina and envelope. Both processes mislocalize diffusible nuclear factors including key DNA repair and regulatory proteins. Importantly, these effects of constricted migration are accompanied by excess DNA damage, marked by phosphorylated histone γH2AX in fixed cells. Rupture has a number of downstream consequences that include a delayed cell cycle-consistent with a damage checkpoint-and modulation of differentiation, both of which are expected to affect migration-dependent processes ranging from wound healing to tumorigenic invasion.
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23
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Pfeifer CR, Irianto J, Discher DE. Nuclear Mechanics and Cancer Cell Migration. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019; 1146:117-130. [PMID: 31612457 DOI: 10.1007/978-3-030-17593-1_8] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
As a cancer cell invades adjacent tissue, penetrates a basement membrane barrier, or squeezes into a blood capillary, its nucleus can be greatly constricted. Here, we examine: (1) the passive and active deformation of the nucleus during 3D migration; (2) the nuclear structures-namely, the lamina and chromatin-that govern nuclear deformability; (3) the effect of large nuclear deformation on DNA and nuclear factors; and (4) the downstream consequences of mechanically stressing the nucleus. We focus especially on recent studies showing that constricted migration causes nuclear envelope rupture and excess DNA damage, leading to cell cycle suppression, possibly cell death, and ultimately it seems to heritable genomic variation. We first review the latest understanding of nuclear dynamics during cell migration, and then explore the functional effects of nuclear deformation, especially in relation to genome integrity and potentially cancerous mutations.
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Affiliation(s)
- Charlotte R Pfeifer
- Biophysical Engineering Labs: Molecular & Cell Biophysics and NanoBio-Polymers, University of Pennsylvania, Philadelphia, PA, USA
| | - Jerome Irianto
- Biophysical Engineering Labs: Molecular & Cell Biophysics and NanoBio-Polymers, University of Pennsylvania, Philadelphia, PA, USA
| | - Dennis E Discher
- Biophysical Engineering Labs: Molecular & Cell Biophysics and NanoBio-Polymers, University of Pennsylvania, Philadelphia, PA, USA.
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24
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Michieletto D, Fitzpatrick R, Robertson-Anderson RM. Maximally stiffening composites require maximally coupled rather than maximally entangled polymer species. SOFT MATTER 2019; 15:6703-6717. [PMID: 31386738 DOI: 10.1039/c9sm01461f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Polymer composites are ideal candidates for next generation biomimetic soft materials because of their exquisite bottom-up designability. However, the richness of behaviours comes at a price: the need for precise and extensive characterisation of material properties over a highly-dimensional parameter space, as well as a quantitative understanding of the physical principles underlying desirable features. Here we couple large-scale Molecular Dynamics simulations with optical tweezers microrheology to characterise the viscoelastic response of DNA-actin composites. We discover that the previously observed non-monotonic stress-stiffening of these composites is robust, yet tunable, in a broad range of the parameter space that spans two orders of magnitude in DNA length. Importantly, we discover that the most pronounced stiffening is achieved when the species are maximally coupled, i.e., have similar number of entanglements, and not when the number of entanglements per DNA chain is largest. We further report novel dynamical oscillations of the microstructure of the composites, alternating between mixed and bundled phases, opening the door to future investigations. The generic nature of our system renders our results applicable to the behaviour of a broad class of polymer composites.
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Affiliation(s)
- Davide Michieletto
- School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK.
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25
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Abstract
We review the current understanding of the mechanics of DNA and DNA-protein complexes, from scales of base pairs up to whole chromosomes. Mechanics of the double helix as revealed by single-molecule experiments will be described, with an emphasis on the role of polymer statistical mechanics. We will then discuss how topological constraints- entanglement and supercoiling-impact physical and mechanical responses. Models for protein-DNA interactions, including effects on polymer properties of DNA of DNA-bending proteins will be described, relevant to behavior of protein-DNA complexes in vivo. We also discuss control of DNA entanglement topology by DNA-lengthwise-compaction machinery acting in concert with topoisomerases. Finally, the chapter will conclude with a discussion of relevance of several aspects of physical properties of DNA and chromatin to oncology.
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26
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Potapova TA, Unruh JR, Yu Z, Rancati G, Li H, Stampfer MR, Gerton JL. Superresolution microscopy reveals linkages between ribosomal DNA on heterologous chromosomes. J Cell Biol 2019; 218:2492-2513. [PMID: 31270138 PMCID: PMC6683752 DOI: 10.1083/jcb.201810166] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2018] [Revised: 03/14/2019] [Accepted: 06/03/2019] [Indexed: 12/15/2022] Open
Abstract
Potapova et al. use superresolution microscopy to describe linkages between ribosomal DNA on heterologous human chromosomes whose formation depends on the transcription factor UBF and topoisomerase II. Linkages persist in the absence of cohesion but require topoisomerase II for resolution. The spatial organization of the genome is enigmatic. Direct evidence of physical contacts between chromosomes and their visualization at nanoscale resolution has been limited. We used superresolution microscopy to demonstrate that ribosomal DNA (rDNA) can form linkages between chromosomes. We observed rDNA linkages in many different human cell types and demonstrated their resolution in anaphase. rDNA linkages are coated by the transcription factor UBF and their formation depends on UBF, indicating that they regularly occur between transcriptionally active loci. Overexpression of c-Myc increases rDNA transcription and the frequency of rDNA linkages, further suggesting that their formation depends on active transcription. Linkages persist in the absence of cohesion, but inhibition of topoisomerase II prevents their resolution in anaphase. We propose that linkages are topological intertwines occurring between transcriptionally active rDNA loci spatially colocated in the same nucleolar compartment. Our findings suggest that active DNA loci engage in physical interchromosomal connections that are an integral and pervasive feature of genome organization.
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Affiliation(s)
| | - Jay R Unruh
- Stowers Institute for Medical Research, Kansas City, MO
| | - Zulin Yu
- Stowers Institute for Medical Research, Kansas City, MO
| | - Giulia Rancati
- Institute of Medical Biology, Agency for Science, Technology and Research, Singapore
| | - Hua Li
- Stowers Institute for Medical Research, Kansas City, MO
| | - Martha R Stampfer
- Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, CA
| | - Jennifer L Gerton
- Stowers Institute for Medical Research, Kansas City, MO .,Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS
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27
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Condensin controls mitotic chromosome stiffness and stability without forming a structurally contiguous scaffold. Chromosome Res 2018; 26:277-295. [PMID: 30143891 DOI: 10.1007/s10577-018-9584-1] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2018] [Revised: 08/03/2018] [Accepted: 08/07/2018] [Indexed: 01/26/2023]
Abstract
During cell division, chromosomes must be folded into their compact mitotic form to ensure their segregation. This process is thought to be largely controlled by the action of condensin SMC protein complexes on chromatin fibers. However, how condensins organize metaphase chromosomes is not understood. We have combined micromanipulation of single human mitotic chromosomes, sub-nanonewton force measurement, siRNA interference of condensin subunit expression, and fluorescence microscopy, to analyze the role of condensin in large-scale chromosome organization. Condensin depletion leads to a dramatic (~ 10-fold) reduction in chromosome elastic stiffness relative to the native, non-depleted case. We also find that prolonged metaphase stalling of cells leads to overloading of chromosomes with condensin, with abnormally high chromosome stiffness. These results demonstrate that condensin is a main element controlling the stiffness of mitotic chromosomes. Isolated, slightly stretched chromosomes display a discontinuous condensing staining pattern, suggesting that condensins organize mitotic chromosomes by forming isolated compaction centers that do not form a continuous scaffold.
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28
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Sakai Y, Mochizuki A, Kinoshita K, Hirano T, Tachikawa M. Modeling the functions of condensin in chromosome shaping and segregation. PLoS Comput Biol 2018; 14:e1006152. [PMID: 29912867 PMCID: PMC6005465 DOI: 10.1371/journal.pcbi.1006152] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2017] [Accepted: 04/24/2018] [Indexed: 11/18/2022] Open
Abstract
The mechanistic details underlying the assembly of rod-shaped chromosomes during mitosis and how they segregate from each other to act as individually mobile units remain largely unknown. Here, we construct a coarse-grained physical model of chromosomal DNA and condensins, a class of large protein complexes that plays key roles in these processes. We assume that condensins have two molecular activities: consecutive loop formation in DNA and inter-condensin attractions. Our simulation demonstrates that both of these activities and their balancing acts are essential for the efficient shaping and segregation of mitotic chromosomes. Our results also demonstrate that the shaping and segregation processes are strongly correlated, implying their mechanistic coupling during mitotic chromosome assembly. Our results highlight the functional importance of inter-condensin attractions in chromosome shaping and segregation. Immediately before a cell divides, chromosomal DNA in a eukaryotic cell is packaged into a discrete set of rod-shaped chromosomes. This process, known as mitotic chromosome assembly or condensation, secures the faithful segregation of genetic information into daughter cells. Central to this mechanistically complex process is a class of protein complexes known as condensins. However, how condensins support the assembly and segregation of mitotic chromosomes at a mechanistic level remains elusive. Here we construct a coarse-grained physical model of chromosomal DNA fibers and condensin molecules, and study how condensins work in the mitotic chromosome assembly using computer simulations. Our results show that two activities of condensins, formation of consecutive loops in chromosomal DNA fibers and inter-condensin attractions, are necessary for both the shaping and segregation of mitotic chromosomes, and balancing acts of these activities help to coordinate the efficient progress of the processes. Importantly, chromosome shaping and segregation in our results are strongly correlated, implying that they are controlled by the same underlying mechanism mediated by condensins.
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Affiliation(s)
- Yuji Sakai
- iTHES Research Group, RIKEN, Wako, Japan.,Theoretical Biology Laboratory, RIKEN, Wako, Japan.,Department of Biochemistry and Molecular Biology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | - Atsushi Mochizuki
- iTHES Research Group, RIKEN, Wako, Japan.,Theoretical Biology Laboratory, RIKEN, Wako, Japan.,iTHEMS Program, RIKEN, Wako, Japan.,CREST, JST 4-1-8 Honcho, Kawaguchi, Japan
| | | | | | - Masashi Tachikawa
- iTHES Research Group, RIKEN, Wako, Japan.,Theoretical Biology Laboratory, RIKEN, Wako, Japan.,iTHEMS Program, RIKEN, Wako, Japan
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29
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Szczesny SE, Mauck RL. The Nuclear Option: Evidence Implicating the Cell Nucleus in Mechanotransduction. J Biomech Eng 2017; 139:2592356. [PMID: 27918797 DOI: 10.1115/1.4035350] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2016] [Indexed: 02/06/2023]
Abstract
Biophysical stimuli presented to cells via microenvironmental properties (e.g., alignment and stiffness) or external forces have a significant impact on cell function and behavior. Recently, the cell nucleus has been identified as a mechanosensitive organelle that contributes to the perception and response to mechanical stimuli. However, the specific mechanotransduction mechanisms that mediate these effects have not been clearly established. Here, we offer a comprehensive review of the evidence supporting (and refuting) three hypothetical nuclear mechanotransduction mechanisms: physical reorganization of chromatin, signaling at the nuclear envelope, and altered cytoskeletal structure/tension due to nuclear remodeling. Our goal is to provide a reference detailing the progress that has been made and the areas that still require investigation regarding the role of nuclear mechanotransduction in cell biology. Additionally, we will briefly discuss the role that mathematical models of cell mechanics can play in testing these hypotheses and in elucidating how biophysical stimulation of the nucleus drives changes in cell behavior. While force-induced alterations in signaling pathways involving lamina-associated polypeptides (LAPs) (e.g., emerin and histone deacetylase 3 (HDAC3)) and transcription factors (TFs) located at the nuclear envelope currently appear to be the most clearly supported mechanism of nuclear mechanotransduction, additional work is required to examine this process in detail and to more fully test alternative mechanisms. The combination of sophisticated experimental techniques and advanced mathematical models is necessary to enhance our understanding of the role of the nucleus in the mechanotransduction processes driving numerous critical cell functions.
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Affiliation(s)
- Spencer E Szczesny
- Department of Orthopaedic Surgery, University of Pennsylvania, 424 Stemmler Hall, 36th Street and Hamilton Walk, Philadelphia, PA 19104; Translational Musculoskeletal Research Center, Corporal Michael J. Crescenz Veterans Affairs Medical Center, 3900 Woodland Avenue, Philadelphia, PA 19104
| | - Robert L Mauck
- Department of Orthopaedic Surgery, University of Pennsylvania, 424 Stemmler Hall, 36th Street and Hamilton Walk, Philadelphia, PA 19104; Translational Musculoskeletal Research Center, Corporal Michael J. Crescenz Veterans Affairs Medical Center, 3900 Woodland Avenue, Philadelphia, PA 19104;Department of Bioengineering, University of Pennsylvania, 240 Skirkanich Hall, 210 South 33rd Street, Philadelphia, PA 19104 e-mail:
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30
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Wang X, Brandão HB, Le TBK, Laub MT, Rudner DZ. Bacillus subtilis SMC complexes juxtapose chromosome arms as they travel from origin to terminus. Science 2017; 355:524-527. [PMID: 28154080 DOI: 10.1126/science.aai8982] [Citation(s) in RCA: 196] [Impact Index Per Article: 28.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2016] [Accepted: 01/05/2017] [Indexed: 01/18/2023]
Abstract
Structural maintenance of chromosomes (SMC) complexes play critical roles in chromosome dynamics in virtually all organisms, but how they function remains poorly understood. In the bacterium Bacillus subtilis, SMC-condensin complexes are topologically loaded at centromeric sites adjacent to the replication origin. Here we provide evidence that these ring-shaped assemblies tether the left and right chromosome arms together while traveling from the origin to the terminus (>2 megabases) at rates >50 kilobases per minute. Condensin movement scales linearly with time, providing evidence for an active transport mechanism. These data support a model in which SMC complexes function by processively enlarging DNA loops. Loop formation followed by processive enlargement provides a mechanism by which condensin complexes compact and resolve sister chromatids in mitosis and by which cohesin generates topologically associating domains during interphase.
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Affiliation(s)
- Xindan Wang
- Department of Microbiology and Immunobiology, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA.
| | - Hugo B Brandão
- Graduate Program in Biophysics, Harvard University, Cambridge, MA 02138, USA
| | - Tung B K Le
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Michael T Laub
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.,Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - David Z Rudner
- Department of Microbiology and Immunobiology, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA.
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31
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Ono T, Sakamoto C, Nakao M, Saitoh N, Hirano T. Condensin II plays an essential role in reversible assembly of mitotic chromosomes in situ. Mol Biol Cell 2017; 28:2875-2886. [PMID: 28835373 PMCID: PMC5638589 DOI: 10.1091/mbc.e17-04-0252] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2017] [Revised: 08/15/2017] [Accepted: 08/16/2017] [Indexed: 01/31/2023] Open
Abstract
A modified protocol for inducing reversible assembly of mitotic chromosomes in situ is developed. As judged by this assay, which is combined with quantitative morphological analyses using a supervised machine-learning algorithm, condensin II plays a crucial role in both the recovery of chromatin shapes and the reorganization of chromosome axes. Condensins I and II are multisubunit complexes that play a central role in mitotic chromosome assembly. Although both complexes become concentrated along the axial region of each chromatid by metaphase, it remains unclear exactly how such axes might assemble and contribute to chromosome shaping. To address these questions from a physico-chemical point of view, we have established a set of two-step protocols for inducing reversible assembly of chromosome structure in situ, namely within a whole cell. In this assay, mitotic chromosomes are first expanded in a hypotonic buffer containing a Mg2+-chelating agent and then converted into different shapes in a NaCl concentration-dependent manner. Both chromatin and condensin-positive chromosome axes are converted into near-original shapes at 100 mM NaCl. This assay combined with small interfering RNA depletion demonstrates that the recovery of chromatin shapes and the reorganization of axes are highly sensitive to depletion of condensin II but less sensitive to depletion of condensin I or topoisomerase IIα. Furthermore, quantitative morphological analyses using the machine-learning algorithm wndchrm support the notion that chromosome shaping is tightly coupled to the reorganization of condensin II-based axes. We propose that condensin II makes a primary contribution to mitotic chromosome architecture and maintenance in human cells.
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Affiliation(s)
- Takao Ono
- Chromosome Dynamics Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Chiyomi Sakamoto
- Department of Medical Cell Biology, Institute of Molecular Embryology and Genetics, Kumamoto University, 2-2-1 Honjo, Chuo-ku, Kumamoto 860-0811, Japan
| | - Mitsuyoshi Nakao
- Department of Medical Cell Biology, Institute of Molecular Embryology and Genetics, Kumamoto University, 2-2-1 Honjo, Chuo-ku, Kumamoto 860-0811, Japan
| | - Noriko Saitoh
- Department of Medical Cell Biology, Institute of Molecular Embryology and Genetics, Kumamoto University, 2-2-1 Honjo, Chuo-ku, Kumamoto 860-0811, Japan
| | - Tatsuya Hirano
- Chromosome Dynamics Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
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32
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Goloborodko A, Marko JF, Mirny LA. Chromosome Compaction by Active Loop Extrusion. Biophys J 2017; 110:2162-8. [PMID: 27224481 PMCID: PMC4880799 DOI: 10.1016/j.bpj.2016.02.041] [Citation(s) in RCA: 168] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2015] [Revised: 01/21/2016] [Accepted: 02/23/2016] [Indexed: 12/20/2022] Open
Abstract
During cell division, chromosomes are compacted in length by more than a 100-fold. A wide range of experiments demonstrated that in their compacted state, mammalian chromosomes form arrays of closely stacked consecutive ∼100 kb loops. The mechanism underlying the active process of chromosome compaction into a stack of loops is unknown. Here we test the hypothesis that chromosomes are compacted by enzymatic machines that actively extrude chromatin loops. When such loop-extruding factors (LEF) bind to chromosomes, they progressively bridge sites that are further away along the chromosome, thus extruding a loop. We demonstrate that collective action of LEFs leads to formation of a dynamic array of consecutive loops. Simulations and an analytically solved model identify two distinct steady states: a sparse state, where loops are highly dynamic but provide little compaction; and a dense state, where there are more stable loops and dramatic chromosome compaction. We find that human chromosomes operate at the border of the dense steady state. Our analysis also shows how the macroscopic characteristics of the loop array are determined by the microscopic properties of LEFs and their abundance. When the number of LEFs are used that match experimentally based estimates, the model can quantitatively reproduce the average loop length, the degree of compaction, and the general loop-array morphology of compact human chromosomes. Our study demonstrates that efficient chromosome compaction can be achieved solely by an active loop-extrusion process.
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Affiliation(s)
- Anton Goloborodko
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts
| | - John F Marko
- Department of Molecular Biosciences and Department of Physics and Astronomy, Northwestern University, Evanston, Illinois
| | - Leonid A Mirny
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts; Institute for Medical Engineering & Science, Massachusetts Institute of Technology, Cambridge, Massachusetts.
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33
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Zhang B, Wolynes PG. Genomic Energy Landscapes. Biophys J 2017; 112:427-433. [PMID: 27692923 PMCID: PMC5300775 DOI: 10.1016/j.bpj.2016.08.046] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2016] [Revised: 08/03/2016] [Accepted: 08/17/2016] [Indexed: 12/30/2022] Open
Abstract
Energy landscape theory, developed in the context of protein folding, provides, to our knowledge, a new perspective on chromosome architecture. We review what has been learned concerning the topology and structure of both the interphase and mitotic chromosomes from effective energy landscapes constructed using Hi-C data. Energy landscape thinking raises new questions about the nonequilibrium dynamics of the chromosome and gene regulation.
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Affiliation(s)
- Bin Zhang
- Department of Chemistry and Center for Theoretical Biological Physics, Rice University, Houston, Texas
| | - Peter G Wolynes
- Department of Chemistry and Center for Theoretical Biological Physics, Rice University, Houston, Texas; Department of Physics and Astronomy, Rice University, Houston, Texas.
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Booth DG, Beckett AJ, Molina O, Samejima I, Masumoto H, Kouprina N, Larionov V, Prior IA, Earnshaw WC. 3D-CLEM Reveals that a Major Portion of Mitotic Chromosomes Is Not Chromatin. Mol Cell 2016; 64:790-802. [PMID: 27840028 PMCID: PMC5128728 DOI: 10.1016/j.molcel.2016.10.009] [Citation(s) in RCA: 62] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2016] [Revised: 08/24/2016] [Accepted: 10/05/2016] [Indexed: 11/20/2022]
Abstract
Recent studies have revealed the importance of Ki-67 and the chromosome periphery in chromosome structure and segregation, but little is known about this elusive chromosome compartment. Here we used correlative light and serial block-face scanning electron microscopy, which we term 3D-CLEM, to model the entire mitotic chromosome complement at ultra-structural resolution. Prophase chromosomes exhibit a highly irregular surface appearance with a volume smaller than metaphase chromosomes. This may be because of the absence of the periphery, which associates with chromosomes only after nucleolar disassembly later in prophase. Indeed, the nucleolar volume almost entirely accounts for the extra volume found in metaphase chromosomes. Analysis of wild-type and Ki-67-depleted chromosomes reveals that the periphery comprises 30%–47% of the entire chromosome volume and more than 33% of the protein mass of isolated mitotic chromosomes determined by quantitative proteomics. Thus, chromatin makes up a surprisingly small percentage of the total mass of metaphase chromosomes. 3D-CLEM combines light and serial block-face scanning electron microscopy The complete architecture of all 46 human chromosomes has been defined A large portion of mitotic chromosomes is not composed of chromatin Chromosome volumes determined by light and electron microscopy differ dramatically
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Affiliation(s)
- Daniel G Booth
- Wellcome Trust Centre for Cell Biology, Institute of Cell Biology, University of Edinburgh, EH9 3BF Edinburgh, UK.
| | - Alison J Beckett
- Biomedical Electron Microscopy Unit, Division of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Crown Street, L69 3BX Liverpool, UK
| | - Oscar Molina
- Wellcome Trust Centre for Cell Biology, Institute of Cell Biology, University of Edinburgh, EH9 3BF Edinburgh, UK
| | - Itaru Samejima
- Wellcome Trust Centre for Cell Biology, Institute of Cell Biology, University of Edinburgh, EH9 3BF Edinburgh, UK
| | - Hiroshi Masumoto
- Department of Frontier Research, Laboratory of Cell Engineering, Kazusa DNA Research Institute, Kisarazu, 292-0818 Chiba, Japan
| | - Natalay Kouprina
- Developmental Therapeutics Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4264, USA
| | - Vladimir Larionov
- Developmental Therapeutics Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4264, USA
| | - Ian A Prior
- Biomedical Electron Microscopy Unit, Division of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Crown Street, L69 3BX Liverpool, UK
| | - William C Earnshaw
- Wellcome Trust Centre for Cell Biology, Institute of Cell Biology, University of Edinburgh, EH9 3BF Edinburgh, UK.
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35
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Irianto J, Xia Y, Pfeifer CR, Greenberg RA, Discher DE. As a Nucleus Enters a Small Pore, Chromatin Stretches and Maintains Integrity, Even with DNA Breaks. Biophys J 2016; 112:446-449. [PMID: 28341535 DOI: 10.1016/j.bpj.2016.09.047] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2016] [Revised: 09/17/2016] [Accepted: 09/30/2016] [Indexed: 10/20/2022] Open
Abstract
As a cell pushes or pulls its nucleus through a small constriction, the chromatin must distort and somehow maintain genomic stability despite ever-present double-strand breaks in the DNA. Here we visualize within a living cell the pore-size dependent deformation of a specific locus engineered into chromosome-1 and cleaved. An mCherry-tagged nuclease targets the submicron locus, causing DNA cleavage and recruiting repair factors such as GFP-53BP1 to a large region around the locus. Aspiration of a cell and its nucleus into a micropipette shows that chromatin aligns and stretches parallel to the pore. Extension is largest in small pores, increasing >10-fold but remaining 30-fold shorter than the DNA contour length in the locus. Brochard and de Gennes' blob model for tube geometry fits the data, with a simple modification for chromatin crowding. Continuity of the highly extended, cleaved chromatin is also maintained, consistent with folding and cross bridging of the DNA. Surprisingly, extensional integrity is unaffected by an inhibitor of the DNA repair scaffold.
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Affiliation(s)
- Jerome Irianto
- Physical Sciences Oncology Center at Penn, University of Pennsylvania, Philadelphia, Pennsylvania; Molecular & Cell Biophysics Lab, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Yuntao Xia
- Physical Sciences Oncology Center at Penn, University of Pennsylvania, Philadelphia, Pennsylvania; Molecular & Cell Biophysics Lab, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Charlotte R Pfeifer
- Physical Sciences Oncology Center at Penn, University of Pennsylvania, Philadelphia, Pennsylvania; Molecular & Cell Biophysics Lab, University of Pennsylvania, Philadelphia, Pennsylvania; Graduate Group/Department of Physics & Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Roger A Greenberg
- Physical Sciences Oncology Center at Penn, University of Pennsylvania, Philadelphia, Pennsylvania; Cancer Biology, Abramson Family Cancer Research Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Dennis E Discher
- Physical Sciences Oncology Center at Penn, University of Pennsylvania, Philadelphia, Pennsylvania; Molecular & Cell Biophysics Lab, University of Pennsylvania, Philadelphia, Pennsylvania; Graduate Group/Department of Physics & Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania.
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36
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Yoshimura SH, Hirano T. HEAT repeats - versatile arrays of amphiphilic helices working in crowded environments? J Cell Sci 2016; 129:3963-3970. [PMID: 27802131 DOI: 10.1242/jcs.185710] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Cellular proteins do not work in isolation. Instead, they often function as part of large macromolecular complexes, which are transported and concentrated into specific cellular compartments and function in a highly crowded environment. A central theme of modern cell biology is to understand how such macromolecular complexes are assembled efficiently and find their destinations faithfully. In this Opinion article, we will focus on HEAT repeats, flexible arrays of amphiphilic helices found in many eukaryotic proteins, such as karyopherins and condensins, and discuss how these uniquely designed helical repeats might underlie dynamic protein-protein interactions and support cellular functions in crowded environments. We will make bold speculations on functional similarities between the action of HEAT repeats and intrinsically disordered regions (IDRs) in macromolecular phase separation. Potential contributions of HEAT-HEAT interactions, as well as cooperation between HEATs and IDRs, to mesoscale organelle assembly will be discussed.
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Affiliation(s)
- Shige H Yoshimura
- Graduate School of Biostudies, Kyoto University, Kyoto 606-8501, Japan
| | - Tatsuya Hirano
- Chromosome Dynamics Laboratory, RIKEN, Saitama 351-0198, Japan
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37
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Eastland A, Hornick J, Kawamura R, Nanavati D, Marko JF. Dependence of the structure and mechanics of metaphase chromosomes on oxidized cysteines. Chromosome Res 2016; 24:339-53. [PMID: 27145786 PMCID: PMC4970972 DOI: 10.1007/s10577-016-9528-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2016] [Revised: 04/09/2016] [Accepted: 04/26/2016] [Indexed: 11/28/2022]
Abstract
We have found that reagents that reduce oxidized cysteines lead to destabilization of metaphase chromosome folding, suggesting that chemically linked cysteine residues may play a structural role in mitotic chromosome organization, in accord with classical studies by Dounce et al. (J Theor Biol 42:275-285, 1973) and Sumner (J Cell Sci 70:177-188, 1984a). Human chromosomes isolated into buffer unfold when exposed to dithiothreitol (DTT) or tris(2-carboxyethyl)phosphine (TCEP). In micromanipulation experiments which allow us to examine the mechanics of individual metaphase chromosomes, we have found that the gel-like elastic stiffness of native metaphase chromosomes is dramatically suppressed by DTT and TCEP, even before the chromosomes become appreciably unfolded. We also report protein labeling experiments on human metaphase chromosomes which allow us to tag oxidized and reduction-sensitive cysteine residues. PAGE analysis using fluorescent labels shows a small number of labeled bands. Mass spectrometry analysis of similarly labeled proteins provides a list of candidates for proteins with oxidized cysteines involved in chromosome organization, notably including components of condensin I, cohesin, the nucleosome-interacting proteins RCC1 and RCC2, as well as the RNA/DNA-binding protein NONO/p54NRB.
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Affiliation(s)
- Adrienne Eastland
- Department of Molecular Biosciences, Northwestern University, Evanston, IL, 60208, USA
| | - Jessica Hornick
- Department of Molecular Biosciences, Northwestern University, Evanston, IL, 60208, USA
| | - Ryo Kawamura
- Department of Molecular Biosciences, Northwestern University, Evanston, IL, 60208, USA
- Department of Physics and Astronomy, Northwestern University, Evanston, IL, 60208, USA
| | - Dhaval Nanavati
- Proteomics Core, Chemistry of Life Processes Institute, Northwestern University, Evanston, IL, 60208, USA
| | - John F Marko
- Department of Molecular Biosciences, Northwestern University, Evanston, IL, 60208, USA.
- Department of Physics and Astronomy, Northwestern University, Evanston, IL, 60208, USA.
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38
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Vijayraghavan S, Tsai FL, Schwacha A. A Checkpoint-Related Function of the MCM Replicative Helicase Is Required to Avert Accumulation of RNA:DNA Hybrids during S-phase and Ensuing DSBs during G2/M. PLoS Genet 2016; 12:e1006277. [PMID: 27556397 PMCID: PMC4996524 DOI: 10.1371/journal.pgen.1006277] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2016] [Accepted: 08/04/2016] [Indexed: 01/10/2023] Open
Abstract
The Mcm2-7 complex is the catalytic core of the eukaryotic replicative helicase. Here, we identify a new role for this complex in maintaining genome integrity. Using both genetic and cytological approaches, we find that a specific mcm allele (mcm2DENQ) causes elevated genome instability that correlates with the appearance of numerous DNA-damage associated foci of γH2AX and Rad52. We further find that the triggering events for this genome instability are elevated levels of RNA:DNA hybrids and an altered DNA topological state, as over-expression of either RNaseH (an enzyme specific for degradation of RNA in RNA:DNA hybrids) or Topoisomerase 1 (an enzyme that relieves DNA supercoiling) can suppress the mcm2DENQ DNA-damage phenotype. Moreover, the observed DNA damage has several additional unusual properties, in that DNA damage foci appear only after S-phase, in G2/M, and are dependent upon progression into metaphase. In addition, we show that the resultant DNA damage is not due to spontaneous S-phase fork collapse. In total, these unusual mcm2DENQ phenotypes are markedly similar to those of a special previously-studied allele of the checkpoint sensor kinase ATR/MEC1, suggesting a possible regulatory interplay between Mcm2-7 and ATR during unchallenged growth. As RNA:DNA hybrids primarily result from transcription perturbations, we suggest that surveillance-mediated modulation of the Mcm2-7 activity plays an important role in preventing catastrophic conflicts between replication forks and transcription complexes. Possible relationships among these effects and the recently discovered role of Mcm2-7 in the DNA replication checkpoint induced by HU treatment are discussed.
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Affiliation(s)
- Sriram Vijayraghavan
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - Feng-Ling Tsai
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - Anthony Schwacha
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
- * E-mail:
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39
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A repetitive DNA-directed program of chromosome packaging during mitosis. J Genet Genomics 2016; 43:471-6. [PMID: 27567067 DOI: 10.1016/j.jgg.2016.04.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2016] [Revised: 03/26/2016] [Accepted: 04/04/2016] [Indexed: 11/20/2022]
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40
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Zhang B, Wolynes PG. Shape Transitions and Chiral Symmetry Breaking in the Energy Landscape of the Mitotic Chromosome. PHYSICAL REVIEW LETTERS 2016; 116:248101. [PMID: 27367409 DOI: 10.1103/physrevlett.116.248101] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2015] [Indexed: 05/18/2023]
Abstract
We derive an unbiased information theoretic energy landscape for chromosomes at metaphase using a maximum entropy approach that accurately reproduces the details of the experimentally measured pairwise contact probabilities between genomic loci. Dynamical simulations using this landscape lead to cylindrical, helically twisted structures reflecting liquid crystalline order. These structures are similar to those arising from a generic ideal homogenized chromosome energy landscape. The helical twist can be either right or left handed so chiral symmetry is broken spontaneously. The ideal chromosome landscape when augmented by interactions like those leading to topologically associating domain formation in the interphase chromosome reproduces these behaviors. The phase diagram of this landscape shows that the helical fiber order and the cylindrical shape persist at temperatures above the onset of chiral symmetry breaking, which is limited by the topologically associating domain interaction strength.
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Affiliation(s)
- Bin Zhang
- Department of Chemistry, Rice University, Houston, Texas 77005, USA
- Center for Theoretical Biological Physics, Rice University, Houston, Texas 77005, USA
| | - Peter G Wolynes
- Department of Chemistry, Rice University, Houston, Texas 77005, USA
- Center for Theoretical Biological Physics, Rice University, Houston, Texas 77005, USA
- Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA
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41
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Abstract
The nucleus is physically distinct from the cytoplasm in ways that suggest new ideas and approaches for interrogating the operation of this organelle. Chemical bond formation and breakage underlie the lives of cells, but as this special issue of Molecular Biology of the Cell attests, the nonchemical aspects of cell nuclei present a new frontier to biologists and biophysicists.
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Affiliation(s)
- Thoru Pederson
- Program in Cell and Developmental Dynamics, Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605
| | - John F Marko
- Department of Molecular Biosciences and Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208
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42
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Serra F, Di Stefano M, Spill YG, Cuartero Y, Goodstadt M, Baù D, Marti-Renom MA. Restraint-based three-dimensional modeling of genomes and genomic domains. FEBS Lett 2015; 589:2987-95. [PMID: 25980604 DOI: 10.1016/j.febslet.2015.05.012] [Citation(s) in RCA: 65] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2015] [Revised: 05/05/2015] [Accepted: 05/05/2015] [Indexed: 10/23/2022]
Abstract
Chromosomes are large polymer molecules composed of nucleotides. In some species, such as humans, this polymer can sum up to meters long and still be properly folded within the nuclear space of few microns in size. The exact mechanisms of how the meters long DNA is folded into the nucleus, as well as how the regulatory machinery can access it, is to a large extend still a mystery. However, and thanks to newly developed molecular, genomic and computational approaches based on the Chromosome Conformation Capture (3C) technology, we are now obtaining insight on how genomes are spatially organized. Here we review a new family of computational approaches that aim at using 3C-based data to obtain spatial restraints for modeling genomes and genomic domains.
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Affiliation(s)
- François Serra
- Genome Biology Group, Centre Nacional d'Anàlisi Genòmica (CNAG), Barcelona, Spain; Gene Regulation, Stem Cells and Cancer Program, Centre for Genomic Regulation (CRG), Barcelona, Spain
| | - Marco Di Stefano
- Genome Biology Group, Centre Nacional d'Anàlisi Genòmica (CNAG), Barcelona, Spain; Gene Regulation, Stem Cells and Cancer Program, Centre for Genomic Regulation (CRG), Barcelona, Spain
| | - Yannick G Spill
- Genome Biology Group, Centre Nacional d'Anàlisi Genòmica (CNAG), Barcelona, Spain; Gene Regulation, Stem Cells and Cancer Program, Centre for Genomic Regulation (CRG), Barcelona, Spain
| | - Yasmina Cuartero
- Genome Biology Group, Centre Nacional d'Anàlisi Genòmica (CNAG), Barcelona, Spain; Gene Regulation, Stem Cells and Cancer Program, Centre for Genomic Regulation (CRG), Barcelona, Spain
| | - Michael Goodstadt
- Genome Biology Group, Centre Nacional d'Anàlisi Genòmica (CNAG), Barcelona, Spain; Gene Regulation, Stem Cells and Cancer Program, Centre for Genomic Regulation (CRG), Barcelona, Spain
| | - Davide Baù
- Genome Biology Group, Centre Nacional d'Anàlisi Genòmica (CNAG), Barcelona, Spain; Gene Regulation, Stem Cells and Cancer Program, Centre for Genomic Regulation (CRG), Barcelona, Spain
| | - Marc A Marti-Renom
- Genome Biology Group, Centre Nacional d'Anàlisi Genòmica (CNAG), Barcelona, Spain; Gene Regulation, Stem Cells and Cancer Program, Centre for Genomic Regulation (CRG), Barcelona, Spain; Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain.
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43
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Abstract
Chromosome conformation capture experiments provide a rich set of data concerning the spatial organization of the genome. We use these data along with a maximum entropy approach to derive a least-biased effective energy landscape for the chromosome. Simulations of the ensemble of chromosome conformations based on the resulting information theoretic landscape not only accurately reproduce experimental contact probabilities, but also provide a picture of chromosome dynamics and topology. The topology of the simulated chromosomes is probed by computing the distribution of their knot invariants. The simulated chromosome structures are largely free of knots. Topologically associating domains are shown to be crucial for establishing these knotless structures. The simulated chromosome conformations exhibit a tendency to form fibril-like structures like those observed via light microscopy. The topologically associating domains of the interphase chromosome exhibit multistability with varying liquid crystalline ordering that may allow discrete unfolding events and the landscape is locally funneled toward "ideal" chromosome structures that represent hierarchical fibrils of fibrils.
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44
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Robellet X, Thattikota Y, Wang F, Wee TL, Pascariu M, Shankar S, Bonneil É, Brown CM, D'Amours D. A high-sensitivity phospho-switch triggered by Cdk1 governs chromosome morphogenesis during cell division. Genes Dev 2015; 29:426-39. [PMID: 25691469 PMCID: PMC4335297 DOI: 10.1101/gad.253294.114] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The initiation of chromosome morphogenesis marks the beginning of mitosis in eukaryotic cells. Robellet et al. found that multisite phosphorylation of the chromatin-binding sensor Smc4 integrates the activation state of Cdk1 with the dynamic binding of the condensation machinery to chromatin. Abrogation of this event leads to chromosome segregation defects and lethality, while moderate reduction reveals the existence of a novel chromatin transition state specific to mitosis, the intertwist configuration. The initiation of chromosome morphogenesis marks the beginning of mitosis in all eukaryotic cells. Although many effectors of chromatin compaction have been reported, the nature and design of the essential trigger for global chromosome assembly remain unknown. Here we reveal the identity of the core mechanism responsible for chromosome morphogenesis in early mitosis. We show that the unique sensitivity of the chromosome condensation machinery for the kinase activity of Cdk1 acts as a major driving force for the compaction of chromatin at mitotic entry. This sensitivity is imparted by multisite phosphorylation of a conserved chromatin-binding sensor, the Smc4 protein. The multisite phosphorylation of this sensor integrates the activation state of Cdk1 with the dynamic binding of the condensation machinery to chromatin. Abrogation of this event leads to chromosome segregation defects and lethality, while moderate reduction reveals the existence of a novel chromatin transition state specific to mitosis, the intertwist configuration. Collectively, our results identify the mechanistic basis governing chromosome morphogenesis in early mitosis and how distinct chromatin compaction states can be established via specific thresholds of Cdk1 kinase activity.
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Affiliation(s)
- Xavier Robellet
- Institute for Research in Immunology and Cancer (IRIC), Département de Pathologie et Biologie Cellulaire, Université de Montréal, Montréal, Quebec H3C 3J7, Canada
| | - Yogitha Thattikota
- Institute for Research in Immunology and Cancer (IRIC), Département de Pathologie et Biologie Cellulaire, Université de Montréal, Montréal, Quebec H3C 3J7, Canada
| | - Fang Wang
- Institute for Research in Immunology and Cancer (IRIC), Département de Pathologie et Biologie Cellulaire, Université de Montréal, Montréal, Quebec H3C 3J7, Canada
| | - Tse-Luen Wee
- Advanced BioImaging Facility (ABIF), Department of Physiology, McGill University, Montréal, Quebec H3G 0B1, Canada
| | - Mirela Pascariu
- Institute for Research in Immunology and Cancer (IRIC), Département de Pathologie et Biologie Cellulaire, Université de Montréal, Montréal, Quebec H3C 3J7, Canada
| | - Sahana Shankar
- Institute for Research in Immunology and Cancer (IRIC), Département de Pathologie et Biologie Cellulaire, Université de Montréal, Montréal, Quebec H3C 3J7, Canada
| | - Éric Bonneil
- Institute for Research in Immunology and Cancer (IRIC)
| | - Claire M Brown
- Advanced BioImaging Facility (ABIF), Department of Physiology, McGill University, Montréal, Quebec H3G 0B1, Canada
| | - Damien D'Amours
- Institute for Research in Immunology and Cancer (IRIC), Département de Pathologie et Biologie Cellulaire, Université de Montréal, Montréal, Quebec H3C 3J7, Canada
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45
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Lopez V, Barinova N, Onishi M, Pobiega S, Pringle JR, Dubrana K, Marcand S. Cytokinesis breaks dicentric chromosomes preferentially at pericentromeric regions and telomere fusions. Genes Dev 2015; 29:322-36. [PMID: 25644606 PMCID: PMC4318148 DOI: 10.1101/gad.254664.114] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Dicentric chromosomes are unstable products of erroneous DNA repair events that can lead to further genome rearrangements and extended gene copy number variations. Lopez et al. find that dicentrics without internal telomere sequences preferentially break at pericentromeric regions. In all cases, cleavage does not occur in anaphase but instead requires cytokinesis. Dicentrics cause the spindle pole bodies and centromeres to relocate to the bud neck during cytokinesis, explaining how cytokinesis can sever dicentrics near centromeres. Dicentric chromosomes are unstable products of erroneous DNA repair events that can lead to further genome rearrangements and extended gene copy number variations. During mitosis, they form anaphase bridges, resulting in chromosome breakage by an unknown mechanism. In budding yeast, dicentrics generated by telomere fusion break at the fusion, a process that restores the parental karyotype and protects cells from rare accidental telomere fusion. Here, we observed that dicentrics lacking telomere fusion preferentially break within a 25- to 30-kb-long region next to the centromeres. In all cases, dicentric breakage requires anaphase exit, ruling out stretching by the elongated mitotic spindle as the cause of breakage. Instead, breakage requires cytokinesis. In the presence of dicentrics, the cytokinetic septa pinch the nucleus, suggesting that dicentrics are severed after actomyosin ring contraction. At this time, centromeres and spindle pole bodies relocate to the bud neck, explaining how cytokinesis can sever dicentrics near centromeres.
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Affiliation(s)
- Virginia Lopez
- Laboratoire Télomères et Réparation du Chromosome, Service Instabilité Génétique Réparation et Recombinaison, Institut de Radiobiologie Moléculaire et Cellulaire, Commissariat à l'Energie Atomique et aux Energies Alternatives, 92265 Fontenay-aux-Roses, France; UMR967, Institut National de la Santé et de la Recherche Médicale, 92265 Fontenay-aux-Roses, France
| | - Natalja Barinova
- Laboratoire Télomères et Réparation du Chromosome, Service Instabilité Génétique Réparation et Recombinaison, Institut de Radiobiologie Moléculaire et Cellulaire, Commissariat à l'Energie Atomique et aux Energies Alternatives, 92265 Fontenay-aux-Roses, France; UMR967, Institut National de la Santé et de la Recherche Médicale, 92265 Fontenay-aux-Roses, France
| | - Masayuki Onishi
- Department of Genetics, Stanford University School of Medicine, Stanford, California 94305, USA
| | - Sabrina Pobiega
- Laboratoire Télomères et Réparation du Chromosome, Service Instabilité Génétique Réparation et Recombinaison, Institut de Radiobiologie Moléculaire et Cellulaire, Commissariat à l'Energie Atomique et aux Energies Alternatives, 92265 Fontenay-aux-Roses, France; UMR967, Institut National de la Santé et de la Recherche Médicale, 92265 Fontenay-aux-Roses, France
| | - John R Pringle
- Department of Genetics, Stanford University School of Medicine, Stanford, California 94305, USA
| | - Karine Dubrana
- UMR967, Institut National de la Santé et de la Recherche Médicale, 92265 Fontenay-aux-Roses, France; Laboratoire Instabilité Génétique et Organisation Nucléaire, Service Instabilité Génétique Réparation et Recombinaison, Institut de Radiobiologie Moléculaire et Cellulaire, Commissariat à l'Energie Atomique et aux Energies Alternatives, 92265 Fontenay-aux-Roses, France
| | - Stéphane Marcand
- Laboratoire Télomères et Réparation du Chromosome, Service Instabilité Génétique Réparation et Recombinaison, Institut de Radiobiologie Moléculaire et Cellulaire, Commissariat à l'Energie Atomique et aux Energies Alternatives, 92265 Fontenay-aux-Roses, France; UMR967, Institut National de la Santé et de la Recherche Médicale, 92265 Fontenay-aux-Roses, France;
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46
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Age-associated alterations in the micromechanical properties of chromosomes in the mammalian egg. J Assist Reprod Genet 2015; 32:765-9. [PMID: 25758987 DOI: 10.1007/s10815-015-0453-y] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2014] [Accepted: 02/19/2015] [Indexed: 01/08/2023] Open
Abstract
PURPOSE The incidence of aneuploidy in eggs from women of advanced reproductive age can exceed 60%, making the mammalian egg a unique model system to study the mechanisms of chromosome segregation errors. METHODS Here we applied a novel biophysical chromosome stretching approach to quantify mechanical stiffness of meiotic chromosomes in the mammalian egg and then documented how these properties changed in a mouse model of physiologic reproductive aging. RESULTS We found significant differences in chromosome micromechanics, and thus in higher order chromosome structure, coincident with advanced reproductive age, a time that is also unequivocally associated with an increase in egg aneuploidy. CONCLUSIONS These findings have important implications for both reproductive and cancer biology where aneuploidy plays a central role in aging related disease states.
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47
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Abstract
The primary goal of mitosis is to partition duplicated chromosomes into daughter cells. Eukaryotic chromosomes are equipped with two distinct classes of intrinsic machineries, cohesin and condensins, that ensure their faithful segregation during mitosis. Cohesin holds sister chromatids together immediately after their synthesis during S phase until the establishment of bipolar attachments to the mitotic spindle in metaphase. Condensins, on the other hand, attempt to "resolve" sister chromatids by counteracting cohesin. The products of the balancing acts of cohesin and condensins are metaphase chromosomes, in which two rod-shaped chromatids are connected primarily at the centromere. In anaphase, this connection is released by the action of separase that proteolytically cleaves the remaining population of cohesin. Recent studies uncover how this series of events might be mechanistically coupled with each other and intricately regulated by a number of regulatory factors.
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Affiliation(s)
- Tatsuya Hirano
- Chromosome Dynamics Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
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Abstract
The function of DNA in cells depends on its interactions with protein molecules, which recognize and act on base sequence patterns along the double helix. These notes aim to introduce basic polymer physics of DNA molecules, biophysics of protein-DNA interactions and their study in single-DNA experiments, and some aspects of large-scale chromosome structure. Mechanisms for control of chromosome topology will also be discussed.
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Affiliation(s)
- John F Marko
- Department of Physics & Astronomy and Department of Molecular Biosciences, Northwestern University, Evanston, Illinois USA 60208
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Hirano T. Condensins and the evolution of torsion-mediated genome organization. Trends Cell Biol 2014; 24:727-33. [PMID: 25092191 DOI: 10.1016/j.tcb.2014.06.007] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2014] [Revised: 06/14/2014] [Accepted: 06/26/2014] [Indexed: 12/20/2022]
Abstract
At first glance, bacteria and eukaryotes appear to use different strategies to pack and organize their genomes. At the basal level, bacterial genome compaction relies on unconstrained, negative supercoils, whereas eukaryotic genomes are packaged into nucleosomes via constrained, negative supercoils. Here, I integrate the action of condensins, chromosome-packaging complexes conserved from bacteria to humans, into this picture, and discuss how torsional stress on DNA might have dual impacts on genome organization and function. A common theme is that organisms have evolved flexible and reversible strategies to pack their genomes while keeping them readily accessible to many activities such as gene expression.
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Affiliation(s)
- Tatsuya Hirano
- Chromosome Dynamics Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
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50
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The higher-order structure in the cells nucleus as the structural basis of the post-mitotic state. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2014; 114:137-45. [DOI: 10.1016/j.pbiomolbio.2014.02.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2013] [Accepted: 02/09/2014] [Indexed: 11/19/2022]
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