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Abstract
A universal feature of mitosis is that all chromosomes become aligned at the spindle equator--the halfway point between the two spindle poles--prior to anaphase onset. This migratory event is called congression, and is powered by centromere-bound protein machines called kinetochores. This Commentary aims to document recent advances concerning the two kinetochore-based force-generating mechanisms that drive mitotic chromosome congression in vertebrate cells: depolymerisation-coupled pulling (DCP) and lateral sliding. We aim to explore how kinetochores can 'read-out' their spatial position within the spindle, and adjust these force-generating mechanisms to ensure chromosomes reach, and then remain, at the equator. Finally, we will describe the 'life history' of a chromosome, and provide a working model for how individual mechanisms are integrated to ensure efficient and successful congression.
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Affiliation(s)
- Philip Auckland
- Mechanochemical Cell Biology Building, Division of Biomedical Cell Biology, Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK
| | - Andrew D McAinsh
- Mechanochemical Cell Biology Building, Division of Biomedical Cell Biology, Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK
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52
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Tan CH, Gasic I, Huber-Reggi SP, Dudka D, Barisic M, Maiato H, Meraldi P. The equatorial position of the metaphase plate ensures symmetric cell divisions. eLife 2015; 4. [PMID: 26188083 PMCID: PMC4536468 DOI: 10.7554/elife.05124] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2014] [Accepted: 07/17/2015] [Indexed: 12/16/2022] Open
Abstract
Chromosome alignment in the middle of the bipolar spindle is a hallmark of metazoan cell divisions. When we offset the metaphase plate position by creating an asymmetric centriole distribution on each pole, we find that metaphase plates relocate to the middle of the spindle before anaphase. The spindle assembly checkpoint enables this centering mechanism by providing cells enough time to correct metaphase plate position. The checkpoint responds to unstable kinetochore-microtubule attachments resulting from an imbalance in microtubule stability between the two half-spindles in cells with an asymmetric centriole distribution. Inactivation of the checkpoint prior to metaphase plate centering leads to asymmetric cell divisions and daughter cells of unequal size; in contrast, if the checkpoint is inactivated after the metaphase plate has centered its position, symmetric cell divisions ensue. This indicates that the equatorial position of the metaphase plate is essential for symmetric cell divisions.
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Affiliation(s)
- Chia Huei Tan
- Department of Physiology and Metabolism, Medical Faculty, University of Geneva, Geneva, Switzerland
| | - Ivana Gasic
- Department of Physiology and Metabolism, Medical Faculty, University of Geneva, Geneva, Switzerland
| | | | - Damian Dudka
- Department of Physiology and Metabolism, Medical Faculty, University of Geneva, Geneva, Switzerland
| | - Marin Barisic
- Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal
| | - Helder Maiato
- Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal
| | - Patrick Meraldi
- Department of Physiology and Metabolism, Medical Faculty, University of Geneva, Geneva, Switzerland
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53
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Armond JW, Vladimirou E, Erent M, McAinsh AD, Burroughs NJ. Probing microtubule polymerisation state at single kinetochores during metaphase chromosome motion. J Cell Sci 2015; 128:1991-2001. [PMID: 25908867 PMCID: PMC4457160 DOI: 10.1242/jcs.168682] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2015] [Accepted: 03/18/2015] [Indexed: 11/20/2022] Open
Abstract
Kinetochores regulate the dynamics of attached microtubule bundles (kinetochore-fibres, K-fibres) to generate the forces necessary for chromosome movements in mitosis. Current models suggest that poleward-moving kinetochores are attached to depolymerising K-fibres and anti-poleward-moving kinetochores to polymerising K-fibres. How the dynamics of individual microtubules within the K-fibre relate to poleward and anti-poleward movements is poorly understood. To investigate this, we developed a live-cell imaging assay combined with computational image analysis that allows eGFP-tagged EB3 (also known as MAPRE3) to be quantified at thousands of individual metaphase kinetochores as they undergo poleward and anti-poleward motion. Surprisingly, we found that K-fibres are incoherent, containing both polymerising and depolymerising microtubules – with a small polymerisation bias for anti-poleward-moving kinetochores. K-fibres also display bursts of EB3 intensity, predominantly on anti-poleward-moving kinetochores, equivalent to more coherent polymerisation, and this was associated with more regular oscillations. The frequency of bursts and the polymerisation bias decreased upon loss of kinesin-13, whereas loss of kinesin-8 elevated polymerisation bias. Thus, kinetochores actively set the balance of microtubule polymerisation dynamics in the K-fibre while remaining largely robust to fluctuations in microtubule polymerisation.
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Affiliation(s)
- Jonathan W Armond
- Warwick Systems Biology Centre and Mathematics Institute, University of Warwick, Coventry CV4 7AL, UK
| | - Elina Vladimirou
- Mechanochemical Cell Biology Building, Division of Biomedical Cell Biology, Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK
| | - Muriel Erent
- Mechanochemical Cell Biology Building, Division of Biomedical Cell Biology, Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK
| | - Andrew D McAinsh
- Mechanochemical Cell Biology Building, Division of Biomedical Cell Biology, Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK
| | - Nigel J Burroughs
- Warwick Systems Biology Centre and Mathematics Institute, University of Warwick, Coventry CV4 7AL, UK
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54
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Abstract
In order to understand the three-dimensional structure of the functional kinetochore in vertebrates, we require a complete list and stoichiometry for the protein components of the kinetochore, which can be provided by genetic and proteomic experiments. We also need to know how the chromatin-containing CENP-A, which makes up the structural foundation for the kinetochore, is folded, and how much of that DNA is involved in assembling the kinetochore. In this MS, we demonstrate that functioning metaphase kinetochores in chicken DT40 cells contain roughly 50 kb of DNA, an amount that corresponds extremely closely to the length of chromosomal DNA associated with CENP-A in ChIP-seq experiments. Thus, during kinetochore assembly, CENP-A chromatin is compacted into the inner kinetochore plate without including significant amounts of flanking pericentromeric heterochromatin.
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Affiliation(s)
- Susana Abreu Ribeiro
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, Michael Swann Building, King's Buildings, Mayfield Road, Edinburgh, EH9 3JR, Scotland, UK
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55
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Regulation of kinetochore-microtubule attachments through homeostatic control during mitosis. Nat Rev Mol Cell Biol 2014; 16:57-64. [PMID: 25466864 DOI: 10.1038/nrm3916] [Citation(s) in RCA: 112] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Faithful chromosome segregation during mitosis is essential for genome integrity and is mediated by the bi-oriented attachment of replicated chromosomes to spindle microtubules through kinetochores. Errors in kinetochore-microtubule (k-MT) attachment that could cause chromosome mis-segregation are frequent and are corrected by the dynamic turnover of k-MT attachments. Thus, regulating the rate of spindle microtubule attachment and detachment to kinetochores is crucial for mitotic fidelity and is frequently disrupted in cancer cells displaying chromosomal instability. A model based on homeostatic principles involving receptors, a core control network, effectors and feedback control may explain the precise regulation of k-MT attachment stability during mitotic progression to ensure error-free mitosis.
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56
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Häfner J, Mayr MI, Möckel MM, Mayer TU. Pre-anaphase chromosome oscillations are regulated by the antagonistic activities of Cdk1 and PP1 on Kif18A. Nat Commun 2014; 5:4397. [PMID: 25048371 DOI: 10.1038/ncomms5397] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2013] [Accepted: 06/13/2014] [Indexed: 12/16/2022] Open
Abstract
Upon congression at the spindle equator, vertebrate chromosomes display oscillatory movements which typically decline as cells progress towards anaphase. Kinesin-8 Kif18A has been identified as a suppressor of chromosome movements, but how its activity is temporally regulated to dampen chromosome oscillations before anaphase onset remained mysterious. Here, we identify a regulatory network composed of cyclin-dependent kinase-1 (Cdk1) and protein phosphatase-1 (PP1) that antagonistically regulate Kif18A. Cdk1-mediated inhibitory phosphorylation of Kif18A promotes chromosome oscillations in early metaphase. PP1 induces metaphase plate thinning by directly dephosphorylating Kif18A. Chromosome attachment induces Cdk1 inactivation and kinetochore recruitment of PP1α/γ. Thus, we propose that chromosome biorientation mediates the alignment of chromosomes at the metaphase plate by tipping the balance in favour of dephosphorylated Kif18A capable of suppressing the oscillatory movements of chromosomes. Notably, interfering with chromosome oscillations severely impairs the fidelity of sister chromatid segregation demonstrating the importance of timely controlled chromosome dynamics for the maintenance of genome integrity.
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Affiliation(s)
- Julia Häfner
- Department of Molecular Genetics, University of Konstanz, Universitätsstr. 10, 78457 Konstanz, Germany
| | - Monika I Mayr
- Department of Biology, Institute of Biochemistry, ETH Zurich, Schafmattstrasse 18, 8093 Zurich, Switzerland
| | - Martin M Möckel
- Department of Molecular Genetics, University of Konstanz, Universitätsstr. 10, 78457 Konstanz, Germany
| | - Thomas U Mayer
- Department of Molecular Genetics, University of Konstanz, Universitätsstr. 10, 78457 Konstanz, Germany
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57
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Bissonette S, Stumpff J. Quantifying Mitotic Chromosome Dynamics and Positioning. J Cell Physiol 2014; 229:1301-5. [PMID: 24683081 DOI: 10.1002/jcp.24634] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2014] [Accepted: 03/26/2014] [Indexed: 11/05/2022]
Affiliation(s)
- Samantha Bissonette
- Department of Molecular Physiology and Biophysics; University of Vermont; Burlington Vermont
| | - Jason Stumpff
- Department of Molecular Physiology and Biophysics; University of Vermont; Burlington Vermont
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58
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Cross RA, McAinsh A. Prime movers: the mechanochemistry of mitotic kinesins. Nat Rev Mol Cell Biol 2014; 15:257-71. [PMID: 24651543 DOI: 10.1038/nrm3768] [Citation(s) in RCA: 138] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Mitotic spindles are self-organizing protein machines that harness teams of multiple force generators to drive chromosome segregation. Kinesins are key members of these force-generating teams. Different kinesins walk directionally along dynamic microtubules, anchor, crosslink, align and sort microtubules into polarized bundles, and influence microtubule dynamics by interacting with microtubule tips. The mechanochemical mechanisms of these kinesins are specialized to enable each type to make a specific contribution to spindle self-organization and chromosome segregation.
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Affiliation(s)
- Robert A Cross
- Warwick Medical School, Gibbet Hill, Coventry CV4 7AL, UK
| | - Andrew McAinsh
- Warwick Medical School, Gibbet Hill, Coventry CV4 7AL, UK
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59
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Kim JH, Zhang T, Wong NC, Davidson N, Maksimovic J, Oshlack A, Earnshaw WC, Kalitsis P, Hudson DF. Condensin I associates with structural and gene regulatory regions in vertebrate chromosomes. Nat Commun 2014; 4:2537. [PMID: 24088984 DOI: 10.1038/ncomms3537] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2013] [Accepted: 09/03/2013] [Indexed: 11/09/2022] Open
Abstract
The condensin complex is essential for correct packaging and segregation of chromosomes during mitosis and meiosis in all eukaryotes. To date, the genome-wide location and the nature of condensin-binding sites have remained elusive in vertebrates. Here we report the genome-wide map of condensin I in chicken DT40 cells. Unexpectedly, we find that condensin I binds predominantly to promoter sequences in mitotic cells. We also find a striking enrichment at both centromeres and telomeres, highlighting the importance of the complex in chromosome segregation. Taken together, the results show that condensin I is largely absent from heterochromatic regions. This map of the condensin I binding sites on the chicken genome reveals that patterns of condensin distribution on chromosomes are conserved from prokaryotes, through yeasts to vertebrates. Thus in three kingdoms of life, condensin is enriched on promoters of actively transcribed genes and at loci important for chromosome segregation.
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Affiliation(s)
- Ji Hun Kim
- 1] Murdoch Childrens Research Institute, Royal Children's Hospital, Parkville, Melbourne, Victoria 3052, Australia [2] Department of Paediatrics, University of Melbourne, Parkville, Melbourne, Victoria 3052, Australia
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60
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Messin LJ, Millar JBA. Role and regulation of kinesin-8 motors through the cell cycle. SYSTEMS AND SYNTHETIC BIOLOGY 2014; 8:205-13. [PMID: 25136382 DOI: 10.1007/s11693-014-9140-z] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2014] [Revised: 03/11/2014] [Accepted: 03/15/2014] [Indexed: 10/25/2022]
Abstract
Members of the kinesin-8 motor family play a central role in controlling microtubule length throughout the eukaryotic cell cycle. Inactivation of kinesin-8 causes defects in cell polarity during interphase and astral and mitotic spindle length, metaphase chromosome alignment, timing of anaphase onset and accuracy of chromosome segregation. Although the biophysical mechanism by which kinesin-8 molecules influence microtubule dynamics has been studied extensively in a variety of species, a consensus view has yet to emerge. One reason for this might be that some members of the kinesin-8 family can associate to other microtubule-associated proteins, cell cycle regulatory proteins and other kinesin family members. In this review we consider how cell cycle specific modification and its association to other regulatory proteins may modulate the function of kinesin-8 to enable it to function as a master regulator of microtubule dynamics.
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Affiliation(s)
- Liam J Messin
- Mechanochemical Cell Biology Building, Division of Biomedical Cell Biology, Warwick Medical School, University of Warwick, Gibbet Hill, Coventry, CV4 7AL UK
| | - Jonathan B A Millar
- Mechanochemical Cell Biology Building, Division of Biomedical Cell Biology, Warwick Medical School, University of Warwick, Gibbet Hill, Coventry, CV4 7AL UK
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61
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Ferraro-Gideon J, Hoang C, Forer A. Meiosis-I in Mesostoma ehrenbergii spermatocytes includes distance segregation and inter-polar movements of univalents, and vigorous oscillations of bivalents. PROTOPLASMA 2014; 251:127-143. [PMID: 23921676 DOI: 10.1007/s00709-013-0532-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2013] [Accepted: 07/10/2013] [Indexed: 06/02/2023]
Abstract
In this article, we describe meiosis-I in spermatocytes of the free-living freshwater flatworm Mesostoma ehrenbergii. The original observations of Oakley (1983, 1985) and Fuge (Eur J Cell Biol 44:294-298, 1987, Cell Motil Cytoskeleton 13:212-220, 1989, Protoplasma 160:39-48, 1991), the first to describe these cells, challenge our understanding of cell division, and we have expanded on these descriptions with the aim of laying the framework for further experimental work. These cells contain three bivalents and four univalent chromosomes (two pairs). Bivalent kinetochores oscillate vigorously and regularly throughout prometaphase, for up to several hours, until anaphase. Anaphase onset usually begins in the middle of the kinetochore oscillation cycle. Precocious cleavage furrows form at the start of prometaphase, ingress and then remain arrested until the end of anaphase. The four univalents do not pair, yet by anaphase there is one of each kind at each pole, an example of "distance segregation" (Hughes-Schrader in Chromosoma 27:109-129, 1969). Until proper segregation is achieved, univalents move between spindle poles up to seven times in an individual cell; they move with velocities averaging 9 μm/min, which is faster than the oscillatory motions of the bivalent kinetochores (5-6 μm/min), and much faster than the anaphase movements of the segregating half-bivalents (1 μm/min). Bipolar bivalents periodically reorient, most often resulting in the partner kinetochores exchanging poles. We suggest that the large numbers of inter-polar movements of univalents, and the reorientations of bivalents that lead to partners exchanging poles, might be because there is non-random segregation of chromosomes, as in some other cell types.
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62
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Marco E, Dorn JF, Hsu PH, Jaqaman K, Sorger PK, Danuser G. S. cerevisiae chromosomes biorient via gradual resolution of syntely between S phase and anaphase. Cell 2013; 154:1127-1139. [PMID: 23993100 DOI: 10.1016/j.cell.2013.08.008] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2012] [Revised: 05/01/2013] [Accepted: 08/07/2013] [Indexed: 01/08/2023]
Abstract
Following DNA replication, eukaryotic cells must biorient all sister chromatids prior to cohesion cleavage at anaphase. In animal cells, sister chromatids gradually biorient during prometaphase, but current models of mitosis in S. cerevisiae assume that biorientation is established shortly after S phase. This assumption is based on the observation of a bilobed distribution of yeast kinetochores early in mitosis and suggests fundamental differences between yeast mitosis and mitosis in animal cells. By applying super-resolution imaging methods, we show that yeast and animal cells share the key property of gradual and stochastic chromosome biorientation. The characteristic bilobed distribution of yeast kinetochores, hitherto considered synonymous for biorientation, arises from kinetochores in mixed attachment states to microtubules, the length of which discriminates bioriented from syntelic attachments. Our results offer a revised view of mitotic progression in S. cerevisiae that augments the relevance of mechanistic information obtained in this powerful genetic system for mammalian mitosis.
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Affiliation(s)
- Eugenio Marco
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA; Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Jonas F Dorn
- Institute for Research in Immunology and Cancer, University of Montreal, Montreal QC H3C 3J7, Canada
| | - Pei-Hsin Hsu
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Khuloud Jaqaman
- Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Peter K Sorger
- Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Gaudenz Danuser
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.
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63
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Vladimirou E, Mchedlishvili N, Gasic I, Armond J, Samora C, Meraldi P, McAinsh A. Nonautonomous Movement of Chromosomes in Mitosis. Dev Cell 2013; 27:60-71. [DOI: 10.1016/j.devcel.2013.08.004] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2013] [Revised: 06/17/2013] [Accepted: 08/05/2013] [Indexed: 01/19/2023]
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64
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Shrestha R, Draviam V. Lateral to end-on conversion of chromosome-microtubule attachment requires kinesins CENP-E and MCAK. Curr Biol 2013; 23:1514-26. [PMID: 23891108 PMCID: PMC3748344 DOI: 10.1016/j.cub.2013.06.040] [Citation(s) in RCA: 92] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2013] [Revised: 05/14/2013] [Accepted: 06/17/2013] [Indexed: 11/28/2022]
Abstract
BACKGROUND Proper attachment of chromosomes to microtubules is crucial for the accurate segregation of chromosomes. Human chromosomes attach initially to lateral walls of microtubules. Subsequently, attachments to lateral walls disappear and attachments to microtubule ends (end-on attachments) predominate. While it is known in yeasts that lateral to end-on conversion of attachments occurs through a multistep process, equivalent conversion steps in humans remain unknown. RESULTS By developing a high-resolution imaging assay to visualize intermediary steps of the lateral to end-on conversion process, we show that the mechanisms that bring a laterally bound chromosome and its microtubule end closer to each other are indispensable for proper end-on attachment because laterally attached chromosomes seldom detach. We show that end-on conversion requires (1) the plus-end-directed motor CENP-E to tether the lateral kinetochore onto microtubule walls and (2) the microtubule depolymerizer MCAK to release laterally attached microtubules after a partial end-on attachment is formed. CONCLUSIONS By uncovering a CENP-E mediated wall-tethering event and a MCAK-mediated wall-removing event, we establish that human chromosome-microtubule attachment is achieved through a set of deterministic sequential events rather than stochastic direct capture of microtubule ends.
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Affiliation(s)
| | - Viji M. Draviam
- Department of Genetics, University of Cambridge, Cambridge, CB2 3EH, UK
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65
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Civelekoglu-Scholey G, He B, Shen M, Wan X, Roscioli E, Bowden B, Cimini D. Dynamic bonds and polar ejection force distribution explain kinetochore oscillations in PtK1 cells. ACTA ACUST UNITED AC 2013; 201:577-93. [PMID: 23671311 PMCID: PMC3653364 DOI: 10.1083/jcb.201301022] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
A computational model of kinetochore dynamics suggests that differences in the distribution of polar ejection forces at the periphery and in the middle of PtK1 cell spindles underlie the observed position-dependence of metaphase chromosome behavior. Duplicated mitotic chromosomes aligned at the metaphase plate maintain dynamic attachments to spindle microtubules via their kinetochores, and multiple motor and nonmotor proteins cooperate to regulate their behavior. Depending on the system, sister chromatids may display either of two distinct behaviors, namely (1) the presence or (2) the absence of oscillations about the metaphase plate. Significantly, in PtK1 cells, in which chromosome behavior appears to be dependent on the position along the metaphase plate, both types of behavior are observed within the same spindle, but how and why these distinct behaviors are manifested is unclear. Here, we developed a new quantitative model to describe metaphase chromosome dynamics via kinetochore–microtubule interactions mediated by nonmotor viscoelastic linkages. Our model reproduces all the key features of metaphase sister kinetochore dynamics in PtK1 cells and suggests that differences in the distribution of polar ejection forces at the periphery and in the middle of PtK1 cell spindles underlie the observed dichotomy of chromosome behavior.
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Affiliation(s)
- Gul Civelekoglu-Scholey
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
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66
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Charnley M, Anderegg F, Holtackers R, Textor M, Meraldi P. Effect of Cell Shape and Dimensionality on Spindle Orientation and Mitotic Timing. PLoS One 2013; 8:e66918. [PMID: 23825020 PMCID: PMC3688943 DOI: 10.1371/journal.pone.0066918] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2013] [Accepted: 05/13/2013] [Indexed: 01/13/2023] Open
Abstract
The formation and orientation of the mitotic spindle is a critical feature of mitosis. The morphology of the cell and the spatial distribution and composition of the cells' adhesive microenvironment all contribute to dictate the position of the spindle. However, the impact of the dimensionality of the cells' microenvironment has rarely been studied. In this study we present the use of a microwell platform, where the internal surfaces of the individual wells are coated with fibronectin, enabling the three-dimensional presentation of adhesive ligands to single cells cultured within the microwells. This platform was used to assess the effect of dimensionality and cell shape in a controlled microenvironment. Single HeLa cells cultured in circular microwells exhibited greater tilting of the mitotic spindle, in comparison to cells cultured in square microwells. This correlated with an increase in the time required to align the chromosomes at the metaphase plate due to prolonged activation of the spindle checkpoint in an actin dependent process. The comparison to 2D square patterns revealed that the dimensionality of cell adhesions alone affected both mitotic timings and spindle orientation; in particular the role of actin varied according to the dimensionality of the cells' microenvironment. Together, our data revealed that cell shape and the dimensionality of the cells' adhesive environment impacted on both the orientation of the mitotic spindle and progression through mitosis.
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Affiliation(s)
- Mirren Charnley
- Laboratory for Surface Science and Technology, ETH Zurich, Zurich, Switzerland
- * E-mail:
| | - Fabian Anderegg
- Laboratory for Surface Science and Technology, ETH Zurich, Zurich, Switzerland
| | | | - Marcus Textor
- Laboratory for Surface Science and Technology, ETH Zurich, Zurich, Switzerland
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67
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Ferraro-Gideon J, Hoang C, Forer A. Mesostoma ehrenbergii spermatocytes--a unique and advantageous cell for studying meiosis. Cell Biol Int 2013; 37:892-8. [PMID: 23686688 DOI: 10.1002/cbin.10130] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2013] [Accepted: 04/21/2013] [Indexed: 01/06/2023]
Abstract
Mesostoma ehrenbergii have a unique male meiosis: their spermatocytes have three large bivalents that oscillate for 1-2 h before entering into anaphase without having formed a metaphase plate, have a precocious ('pre-anaphase') cleavage furrow, and have four univalents that segregate between spindle poles without physical interaction between them, that is via 'distance segregation'. These unique and unconventional features make Mesostoma spermatocytes an ideal organism for studying the force produced by the spindle to move chromosomes, and to study cleavage furrow control and 'distance segregation'. We review the literature on meiosis in Mesostoma spermatocytes and describe our current research with Mesostoma spermatocytes, rearing the animals in the laboratory using methods that described in our companion article [Hoang et al. (2013); Cell Biol Int].
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68
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Cheeseman LP, Harry EF, McAinsh AD, Prior IA, Royle SJ. Specific removal of TACC3-ch-TOG-clathrin at metaphase deregulates kinetochore fiber tension. J Cell Sci 2013; 126:2102-13. [PMID: 23532825 PMCID: PMC3666260 DOI: 10.1242/jcs.124834] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/01/2013] [Indexed: 12/19/2022] Open
Abstract
Microtubule-associated proteins of the mitotic spindle are thought to be important for the initial assembly and the maintenance of spindle structure and function. However, distinguishing assembly and maintenance roles for a given protein is difficult. Most experimental methods for protein inactivation are slow and therefore affect both assembly and maintenance. Here, we have used 'knocksideways' to rapidly (∼5 minutes) and specifically remove TACC3-ch-TOG-clathrin non-motor complexes from kinetochore fibers (K-fibers). This method allows the complex to be inactivated at defined stages of mitosis. Removal of TACC3-ch-TOG-clathrin after nuclear envelope breakdown caused severe delays in chromosome alignment. Inactivation at metaphase, following a normal prometaphase, significantly delayed progression to anaphase. In these cells, K-fiber tension was reduced and the spindle checkpoint was not satisfied. Surprisingly, there was no significant loss of K-fiber microtubules, even after prolonged removal. TACC3-ch-TOG-clathrin removal during metaphase also resulted in a decrease in spindle length and significant alteration in kinetochore dynamics. Our results indicate that TACC3-ch-TOG-clathrin complexes are important for the maintenance of spindle structure and function as well as for initial spindle assembly.
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Affiliation(s)
- Liam P. Cheeseman
- Department of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Crown Street, Liverpool L69 3BX, UK
| | - Edward F. Harry
- Centre for Mechanochemical Cell Biology, Division of Biomedical Cell Biology, Warwick Medical School, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
- Molecular Organization and Assembly in Cells Doctoral Training Centre, University of Warwick, Coventry CV4 7AL, UK
| | - Andrew D. McAinsh
- Centre for Mechanochemical Cell Biology, Division of Biomedical Cell Biology, Warwick Medical School, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
| | - Ian A. Prior
- Department of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Crown Street, Liverpool L69 3BX, UK
| | - Stephen J. Royle
- Department of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Crown Street, Liverpool L69 3BX, UK
- Centre for Mechanochemical Cell Biology, Division of Biomedical Cell Biology, Warwick Medical School, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
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69
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Abstract
Regulating physical size is an essential problem that biological organisms must solve from the subcellular to the organismal scales, but it is not well understood what physical principles and mechanisms organisms use to sense and regulate their size. Any biophysical size-regulation scheme operates in a noisy environment and must be robust to other cellular dynamics and fluctuations. This work develops theory of filament length regulation inspired by recent experiments on kinesin-8 motor proteins, which move with directional bias on microtubule filaments and alter microtubule dynamics. Purified kinesin-8 motors can depolymerize chemically-stabilized microtubules. In the length-dependent depolymerization model, the rate of depolymerization tends to increase with filament length, because long filaments accumulate more motors at their tips and therefore shorten more quickly. When balanced with a constant filament growth rate, this mechanism can lead to a fixed polymer length. However, the mechanism by which kinesin-8 motors affect the length of dynamic microtubules in cells is less clear. We study the more biologically realistic problem of microtubule dynamic instability modulated by a motor-dependent increase in the filament catastrophe frequency. This leads to a significant decrease in the mean filament length and a narrowing of the filament length distribution. The results improve our understanding of the biophysics of length regulation in cells.
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Affiliation(s)
- Hui-Shun Kuan
- Program in Chemical Physics and Biofrontiers Institute, University of Colorado at Boulder, Boulder, CO, USA
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70
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Wandke C, Barisic M, Sigl R, Rauch V, Wolf F, Amaro AC, Tan CH, Pereira AJ, Kutay U, Maiato H, Meraldi P, Geley S. Human chromokinesins promote chromosome congression and spindle microtubule dynamics during mitosis. ACTA ACUST UNITED AC 2013; 198:847-63. [PMID: 22945934 PMCID: PMC3432768 DOI: 10.1083/jcb.201110060] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Human chromokinesins hKID and KIF4A contribute to proper attachment of chromosomes by controlling the positioning of the chromosome arms and microtubule dynamics, respectively. Chromokinesins are microtubule plus end–directed motor proteins that bind to chromosome arms. In Xenopus egg cell-free extracts, Xkid and Xklp1 are essential for bipolar spindle formation but the functions of the human homologues, hKID (KIF22) and KIF4A, are poorly understood. By using RNAi-mediated protein knockdown in human cells, we find that only co-depletion delayed progression through mitosis in a Mad2-dependent manner. Depletion of hKID caused abnormal chromosome arm orientation, delayed chromosome congression, and sensitized cells to nocodazole. Knockdown of KIF4A increased the number and length of microtubules, altered kinetochore oscillations, and decreased kinetochore microtubule flux. These changes were associated with failures in establishing a tight metaphase plate and an increase in anaphase lagging chromosomes. Co-depletion of both chromokinesins aggravated chromosome attachment failures, which led to mitotic arrest. Thus, hKID and KIF4A contribute independently to the rapid and correct attachment of chromosomes by controlling the positioning of chromosome arms and the dynamics of microtubules, respectively.
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Affiliation(s)
- Cornelia Wandke
- Biocenter, Division of Molecular Pathophysiology, Innsbruck Medical University, A-6020 Innsbruck, Austria
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71
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Tanaka K. Regulatory mechanisms of kinetochore-microtubule interaction in mitosis. Cell Mol Life Sci 2013; 70:559-79. [PMID: 22752158 PMCID: PMC11113415 DOI: 10.1007/s00018-012-1057-7] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2012] [Revised: 05/29/2012] [Accepted: 06/11/2012] [Indexed: 12/17/2022]
Abstract
Interaction of microtubules with kinetochores is fundamental to chromosome segregation. Kinetochores initially associate with lateral surfaces of microtubules and subsequently become attached to microtubule ends. During these interactions, kinetochores can move by sliding along microtubules or by moving together with depolymerizing microtubule ends. The interplay between kinetochores and microtubules leads to the establishment of bi-orientation, which is the attachment of sister kinetochores to microtubules from opposite spindle poles, and subsequent chromosome segregation. Molecular mechanisms underlying these processes have been intensively studied over the past 10 years. Emerging evidence suggests that the KNL1-Mis12-Ndc80 (KMN) network plays a central role in connecting kinetochores to microtubules, which is under fine regulation by a mitotic kinase, Aurora B. However, a growing number of additional molecules are being shown to be involved in the kinetochore-microtubule interaction. Here I overview the current range of regulatory mechanisms of the kinetochore-microtubule interaction, and discuss how these multiple molecules contribute cooperatively to allow faithful chromosome segregation.
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Affiliation(s)
- Kozo Tanaka
- Department of Molecular Oncology, Institute of Development, Aging and Cancer, Tohoku University, 4-1 Seiryo-machi, Aoba-ku, Sendai, 980-8575, Miyagi, Japan.
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72
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Vagnarelli P. Chromatin reorganization through mitosis. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2013; 90:179-224. [PMID: 23582205 DOI: 10.1016/b978-0-12-410523-2.00006-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Chromosome condensation is one of the major chromatin-remodeling events that occur during cell division. The changes in chromatin compaction and higher-order structure organization are essential requisites for ensuring a faithful transmission of the replicated genome to daughter cells. Although the observation of mitotic chromosome condensation has fascinated Scientists for a century, we are still far away from understanding how the process works from a molecular point of view. In this chapter, I will analyze our current understanding of chromatin condensation during mitosis with particular attention to the major molecular players that trigger and maintain this particular chromatin conformation. However, within the chromosome, not all regions of the chromatin are organized in the same manner. I will address separately the structure and functions of particular chromatin domains such as the centromere. Finally, the transition of the chromatin through mitosis represents just an interlude for gene expression between two cell cycles. How the transcriptional information that governs cell linage identity is transmitted from mother to daughter represents a big and interesting question. I will present how cells take care of the aspect ensuring that mitotic chromosome condensation and the block of transcription does not wipe out the cell identity.
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Affiliation(s)
- Paola Vagnarelli
- Heinz Wolff Building, Brunel University, Uxbridge, United Kingdom.
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73
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Pereira AJ, Maiato H. Maturation of the kinetochore-microtubule interface and the meaning of metaphase. Chromosome Res 2012; 20:563-77. [PMID: 22801775 DOI: 10.1007/s10577-012-9298-8] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Chromosome positioning at the equator of the mitotic spindle emerges out of a relatively entropic background. At this moment, termed metaphase, all kinetochores have typically captured microtubules leading to satisfaction of the spindle-assembly checkpoint, but the cell does not enter anaphase immediately. The waiting time in metaphase is related to the kinetics of securin and cyclin B1 degradation, which trigger sister-chromatid separation and promote anaphase processivity, respectively. Yet, as judged by metaphase duration, such kinetics vary widely between cell types and organisms, with no evident correlation to ploidy or cell size. During metaphase, many animal and plant spindles are also characterized by a conspicuous "flux" activity characterized by continuous poleward translocation of spindle microtubules, which maintain steady-state length and position. Whether spindle microtubule flux plays a specific role during metaphase remains arguable. Based on known experimental parameters, we have performed a comparative analysis amongst different cell types from different organisms and show that spindle length, metaphase duration and flux velocity combine within each system to obey a quasi-universal rule. As so, knowledge of two of these parameters is enough to estimate the third. This trend indicates that metaphase duration is tuned to allow approximately one kinetochore-to-pole round of microtubule flux. We propose that the time cells spend in metaphase evolved as a quality enhancement step that allows for the uniform stabilization/correction of kinetochore-microtubule attachments, thereby promoting mitotic fidelity.
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Affiliation(s)
- António J Pereira
- Chromosome Instability and Dynamics Laboratory, Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal.
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74
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Samejima K, Samejima I, Vagnarelli P, Ogawa H, Vargiu G, Kelly DA, de Lima Alves F, Kerr A, Green LC, Hudson DF, Ohta S, Cooke CA, Farr CJ, Rappsilber J, Earnshaw WC. Mitotic chromosomes are compacted laterally by KIF4 and condensin and axially by topoisomerase IIα. ACTA ACUST UNITED AC 2012; 199:755-70. [PMID: 23166350 PMCID: PMC3514791 DOI: 10.1083/jcb.201202155] [Citation(s) in RCA: 128] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
During the shaping of mitotic chromosomes, KIF4 and condensin work in parallel to promote lateral chromatid compaction and in opposition to topoisomerase IIα, which shortens the chromatid arms. Mitotic chromosome formation involves a relatively minor condensation of the chromatin volume coupled with a dramatic reorganization into the characteristic “X” shape. Here we report results of a detailed morphological analysis, which revealed that chromokinesin KIF4 cooperated in a parallel pathway with condensin complexes to promote the lateral compaction of chromatid arms. In this analysis, KIF4 and condensin were mutually dependent for their dynamic localization on the chromatid axes. Depletion of either caused sister chromatids to expand and compromised the “intrinsic structure” of the chromosomes (defined in an in vitro assay), with loss of condensin showing stronger effects. Simultaneous depletion of KIF4 and condensin caused complete loss of chromosome morphology. In these experiments, topoisomerase IIα contributed to shaping mitotic chromosomes by promoting the shortening of the chromatid axes and apparently acting in opposition to the actions of KIF4 and condensins. These three proteins are major determinants in shaping the characteristic mitotic chromosome morphology.
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Affiliation(s)
- Kumiko Samejima
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, King's Buildings, Edinburgh EH9 3JR, Scotland, UK
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75
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Tamura N, Draviam VM. Microtubule plus-ends within a mitotic cell are 'moving platforms' with anchoring, signalling and force-coupling roles. Open Biol 2012; 2:120132. [PMID: 23226599 PMCID: PMC3513837 DOI: 10.1098/rsob.120132] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2012] [Accepted: 11/01/2012] [Indexed: 12/21/2022] Open
Abstract
The microtubule polymer grows and shrinks predominantly from one of its ends called the 'plus-end'. Plus-end regulation during interphase is well understood. However, mitotic regulation of plus-ends is only beginning to be understood in mammalian cells. During mitosis, the plus-ends are tethered to specialized microtubule capture sites. At these sites, plus-end-binding proteins are loaded and unloaded in a regulated fashion. Proper tethering of plus-ends to specialized sites is important so that the microtubule is able to translate its growth and shrinkage into pushing and pulling forces that move bulky subcellular structures. We discuss recent advances on how mitotic plus-ends are tethered to distinct subcellular sites and how plus-end-bound proteins can modulate the forces that move subcellular structures. Using end binding 1 (EB1) as a prototype plus-end-binding protein, we highlight the complex network of plus-end-binding proteins and their regulation through phosphorylation. Finally, we develop a speculative 'moving platform' model that illustrates the plus-end's role in distinguishing correct versus incorrect microtubule interactions.
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Affiliation(s)
| | - Viji M. Draviam
- Department of Genetics, University of Cambridge, Downing Site, Downing Street, Cambridge CB2 3EH, UK
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76
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Gardner MK, Zanic M, Howard J. Microtubule catastrophe and rescue. Curr Opin Cell Biol 2012; 25:14-22. [PMID: 23092753 DOI: 10.1016/j.ceb.2012.09.006] [Citation(s) in RCA: 107] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2012] [Revised: 09/25/2012] [Accepted: 09/27/2012] [Indexed: 11/28/2022]
Abstract
Microtubules are long cylindrical polymers composed of tubulin subunits. In cells, microtubules play an essential role in architecture and motility. For example, microtubules give shape to cells, serve as intracellular transport tracks, and act as key elements in important cellular structures such as axonemes and mitotic spindles. To accomplish these varied functions, networks of microtubules in cells are very dynamic, continuously remodeling through stochastic length fluctuations at the ends of individual microtubules. The dynamic behavior at the end of an individual microtubule is termed 'dynamic instability'. This behavior manifests itself by periods of persistent microtubule growth interrupted by occasional switching to rapid shrinkage (called microtubule 'catastrophe'), and then by switching back from shrinkage to growth (called microtubule 'rescue'). In this review, we summarize recent findings which provide new insights into the mechanisms of microtubule catastrophe and rescue, and discuss the impact of these findings in regards to the role of microtubule dynamics inside of cells.
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Affiliation(s)
- Melissa K Gardner
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455, USA.
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77
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Stumpff J, Wagenbach M, Franck A, Asbury CL, Wordeman L. Kif18A and chromokinesins confine centromere movements via microtubule growth suppression and spatial control of kinetochore tension. Dev Cell 2012; 22:1017-29. [PMID: 22595673 DOI: 10.1016/j.devcel.2012.02.013] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2011] [Revised: 12/08/2011] [Accepted: 02/28/2012] [Indexed: 10/28/2022]
Abstract
Alignment of chromosomes at the metaphase plate is a signature of cell division in metazoan cells, yet the mechanisms controlling this process remain ambiguous. Here we use a combination of quantitative live-cell imaging and reconstituted dynamic microtubule assays to investigate the molecular control of mitotic centromere movements. We establish that Kif18A (kinesin-8) attenuates centromere movement by directly promoting microtubule pausing in a concentration-dependent manner. This activity provides the dominant mechanism for restricting centromere movement to the spindle midzone. Furthermore, polar ejection forces spatially confine chromosomes via position-dependent regulation of kinetochore tension and centromere switch rates. We demonstrate that polar ejection forces are antagonistically modulated by chromokinesins. These pushing forces depend on Kid (kinesin-10) activity and are antagonized by Kif4A (kinesin-4), which functions to directly suppress microtubule growth. These data support a model in which Kif18A and polar ejection forces synergistically promote centromere alignment via spatial control of kinetochore-microtubule dynamics.
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Affiliation(s)
- Jason Stumpff
- Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195, USA.
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78
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Wurzenberger C, Held M, Lampson MA, Poser I, Hyman AA, Gerlich DW. Sds22 and Repo-Man stabilize chromosome segregation by counteracting Aurora B on anaphase kinetochores. ACTA ACUST UNITED AC 2012; 198:173-83. [PMID: 22801782 PMCID: PMC3410419 DOI: 10.1083/jcb.201112112] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Repo-Man and Sds22 counteract Aurora B phosphorylation of Dsn1 and thus regulate the kinetochore–microtubule interface during anaphase. During mitotic spindle assembly, Aurora B kinase is part of an error correction mechanism that detaches microtubules from kinetochores that are under low mechanical tension. During anaphase, however, kinetochore–microtubule attachments must be maintained despite a drop of tension after removal of sister chromatid cohesion. Consistent with this requirement, Aurora B relocates away from chromosomes to the central spindle at the metaphase–anaphase transition. By ribonucleic acid interference screening using a phosphorylation biosensor, we identified two PP1-targeting subunits, Sds22 and Repo-Man, which counteracted Aurora B–dependent phosphorylation of the outer kinetochore component Dsn1 during anaphase. Sds22 or Repo-Man depletion induced transient pauses during poleward chromosome movement and a high incidence of chromosome missegregation. Thus, our study identifies PP1-targeting subunits that regulate the microtubule–kinetochore interface during anaphase for faithful chromosome segregation.
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Affiliation(s)
- Claudia Wurzenberger
- Institute of Biochemistry, Swiss Federal Institute of Technology Zurich, CH-8093 Zurich, Switzerland
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79
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Schilling Z, Frank E, Magidson V, Wason J, Lončarek J, Boyer K, Wen J, Khodjakov A. Predictive-focus illumination for reducing photodamage in live-cell microscopy. J Microsc 2012; 246:160-7. [PMID: 22429382 PMCID: PMC3582196 DOI: 10.1111/j.1365-2818.2012.03605.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Due to photobleaching and phototoxicity induced by high-intensity excitation light, the number of fluorescence images that can be obtained in live cells is always limited. This limitation becomes particularly prominent in multidimensional recordings when multiple Z-planes are captured at every time point. Here we present a simple technique, termed predictive-focus illumination (PFI), which helps to minimize cells' exposure to light by decreasing the number of Z-planes that need to be captured in live-cell 3D time-lapse recordings. PFI utilizes computer tracking to predict positions of objects of interest (OOIs) and restricts image acquisition to small dynamic Z-regions centred on each OOI. Importantly, PFI does not require hardware modifications and it can be easily implemented on standard wide-field and spinning-disc confocal microscopes.
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Affiliation(s)
- Z. Schilling
- Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA
| | - E. Frank
- Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA
| | - V. Magidson
- Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA
| | - J. Wason
- Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA
| | - J. Lončarek
- Wadsworth Center, NY State Dept. of Health, Albany, NY, USA
| | - K. Boyer
- Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA
| | - J. Wen
- Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA
- Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA
| | - A. Khodjakov
- Wadsworth Center, NY State Dept. of Health, Albany, NY, USA
- Department of Biology, Rensselaer Polytechnic Institute, Troy, NY, USA
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80
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Lane SIR, Yun Y, Jones KT. Timing of anaphase-promoting complex activation in mouse oocytes is predicted by microtubule-kinetochore attachment but not by bivalent alignment or tension. Development 2012; 139:1947-55. [PMID: 22513370 DOI: 10.1242/dev.077040] [Citation(s) in RCA: 110] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Homologous chromosome segregation errors during meiosis I are common and generate aneuploid embryos. Here, we provide a reason for this susceptibility to mis-segregation by live cell imaging of mouse oocytes. Our results show that stable kinetochore-microtubule attachments form in mid-prometaphase, 3-4 hours before anaphase. This coincided with the loss of Mad2 from kinetochores and with the start of anaphase-promoting complex/cyclosome (APC/C)-mediated cyclin B1 destruction. Therefore, the spindle assembly checkpoint (SAC) ceased to inhibit the APC/C from mid-prometaphase. This timing did not coincide with bivalent congression in one-third of all oocytes examined. Non-aligned bivalents were weakly positive for Mad2, under less tension than congressed bivalents and, by live-cell imaging, appeared to be in the process of establishing correct bi-orientation. The time from when the APC/C became active until anaphase onset was affected by the rate of loss of CDK1 activity, rather than by these non-aligned bivalents, which occasionally persisted until anaphase, resulting in homolog non-disjunction. We conclude that, in oocytes, a few erroneous attachments of bivalent kinetochores to microtubules do not generate a sufficient SAC 'wait anaphase' signal to inhibit the APC/C.
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Affiliation(s)
- Simon I R Lane
- School of Biomedical Sciences and Pharmacy, University of Newcastle, Callaghan, NSW 2308, Australia
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81
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Earley S, Vinegoni C, Dunham J, Gorbatov R, Feruglio PF, Weissleder R. In vivo imaging of drug-induced mitochondrial outer membrane permeabilization at single-cell resolution. Cancer Res 2012; 72:2949-56. [PMID: 22505651 DOI: 10.1158/0008-5472.can-11-4096] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Observing drug responses in the tumor microenvironment in vivo can be technically challenging. As a result, cellular responses to molecularly targeted cancer drugs are often studied in cell culture, which does not accurately represent the behavior of cancer cells growing in vivo. Using high-resolution microscopy and fluorescently labeled genetic reporters for apoptosis, we developed an approach to visualize drug-induced cell death at single-cell resolution in vivo. Stable expression of the mitochondrial intermembrane protein IMS-RP was established in human breast and pancreatic cancer cells. Image analysis was then used to quantify release of IMS-RP into the cytoplasm upon apoptosis and irreversible mitochondrial permeabilization. Both breast and pancreatic cancer cells showed higher basal apoptotic rates in vivo than in culture. To study drug-induced apoptosis, we exposed tumor cells to navitoclax (ABT-263), an inhibitor of Bcl-2, Bcl-xL, and Bcl-w, both in vitro and in vivo. Although the tumors responded to Bcl-2 inhibition in vivo, inducing apoptosis in around 20% of cancer cells, the observed response was much higher in cell culture. Together, our findings show an imaging technique that can be used to directly visualize cell death within the tumor microenvironment in response to drug treatment.
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Affiliation(s)
- Sarah Earley
- Center for Systems Biology, Massachusetts General Hospital, Boston 02114, USA
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82
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Arora R, Brun CM, Azzalin CM. Transcription regulates telomere dynamics in human cancer cells. RNA (NEW YORK, N.Y.) 2012; 18:684-93. [PMID: 22357912 PMCID: PMC3312556 DOI: 10.1261/rna.029587.111] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Telomeres are nucleoprotein structures capping the physical ends of linear eukaryotic chromosomes. Although largely heterochromatic, telomeres are transcribed into telomeric repeat-containing RNA (TERRA) molecules by RNA polymerase II. The functions associated with telomere transcription and TERRA remain ill defined. Here we show that the transcriptional activity of human telomeres directly regulates their movement during interphase. We find that chemical inhibition of global transcription dampens telomere motion, while global stimulation promotes it. Likewise, when DNA methyltransferase enzymes are deleted to augment telomere transcription, we observe increased telomere movement. Finally, using a cell line engineered with a unique transcriptionally inducible telomere, we show that transcription of one specific telomere stimulates only its own dynamics without overtly affecting its stability or its length. We reveal a new and unforeseen function for telomere transcription as a regulator of telomere motion, and speculate on the intriguing possibility that transcription-dependent telomere motion sustains the maintenance of functional and dysfunctional telomeres.
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Affiliation(s)
- Rajika Arora
- Institute of Biochemistry, Eidgenössische Technische Hochschule Zürich (ETHZ), CH-8093 Zürich, Switzerland
| | - Catherine M. Brun
- Institute of Biochemistry, Eidgenössische Technische Hochschule Zürich (ETHZ), CH-8093 Zürich, Switzerland
| | - Claus M. Azzalin
- Institute of Biochemistry, Eidgenössische Technische Hochschule Zürich (ETHZ), CH-8093 Zürich, Switzerland
- Corresponding author.E-mail .
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83
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McHedlishvili N, Wieser S, Holtackers R, Mouysset J, Belwal M, Amaro AC, Meraldi P. Kinetochores accelerate centrosome separation to ensure faithful chromosome segregation. J Cell Sci 2012; 125:906-18. [PMID: 22399803 DOI: 10.1242/jcs.091967] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
At the onset of mitosis, cells need to break down their nuclear envelope, form a bipolar spindle and attach the chromosomes to microtubules via kinetochores. Previous studies have shown that spindle bipolarization can occur either before or after nuclear envelope breakdown. In the latter case, early kinetochore-microtubule attachments generate pushing forces that accelerate centrosome separation. However, until now, the physiological relevance of this prometaphase kinetochore pushing force was unknown. We investigated the depletion phenotype of the kinetochore protein CENP-L, which we find to be essential for the stability of kinetochore microtubules, for a homogenous poleward microtubule flux rate and for the kinetochore pushing force. Loss of this force in prometaphase not only delays centrosome separation by 5-6 minutes, it also causes massive chromosome alignment and segregation defects due to the formation of syntelic and merotelic kinetochore-microtubule attachments. By contrast, CENP-L depletion has no impact on mitotic progression in cells that have already separated their centrosomes at nuclear envelope breakdown. We propose that the kinetochore pushing force is an essential safety mechanism that favors amphitelic attachments by ensuring that spindle bipolarization occurs before the formation of the majority of kinetochore-microtubule attachments.
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Affiliation(s)
- Nunu McHedlishvili
- Institute of Biochemistry, ETH Zurich, Schafmattstrasse 18, 8093 Zürich, Switzerland
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84
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Haase J, Stephens A, Verdaasdonk J, Yeh E, Bloom K. Bub1 kinase and Sgo1 modulate pericentric chromatin in response to altered microtubule dynamics. Curr Biol 2012; 22:471-81. [PMID: 22365852 DOI: 10.1016/j.cub.2012.02.006] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2011] [Revised: 12/19/2011] [Accepted: 02/03/2012] [Indexed: 01/25/2023]
Abstract
BACKGROUND Tension sensing of bioriented chromosomes is essential for the fidelity of chromosome segregation. The spindle assembly checkpoint (SAC) conveys lack of tension or attachment to the anaphase promoting complex. Components of the SAC (Bub1) phosphorylate histone H2A (S121) and recruit the protector of cohesin, Shugoshin (Sgo1), to the inner centromere. How the chromatin structural modifications of the inner centromere are integrated into the tension sensing mechanisms and the checkpoint are not known. RESULTS We have identified a Bub1/Sgo1-dependent structural change in the geometry and dynamics of kinetochores and the pericentric chromatin upon reduction of microtubule dynamics. The cluster of inner kinetochores contract, whereas the pericentric chromatin and cohesin that encircle spindle microtubules undergo a radial expansion. Despite its increased spatial distribution, the pericentric chromatin is less dynamic. The change in dynamics is due to histone H2A phosphorylation and Sgo1 recruitment to the pericentric chromatin, rather than microtubule dynamics. CONCLUSIONS Bub1 and Sgo1 act as a rheostat to regulate the chromatin spring and maintain force balance. Through histone H2A S121 phosphorylation and recruitment of Sgo1, Bub1 kinase softens the chromatin spring in response to changes in microtubule dynamics. The geometric alteration of all 16 kinetochores and pericentric chromatin reflect global changes in the pericentromeric region and provide mechanisms for mechanically amplifying damage at a single kinetochore microtubule.
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Affiliation(s)
- Julian Haase
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3280, USA
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85
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Erent M, Drummond DR, Cross RA. S. pombe kinesins-8 promote both nucleation and catastrophe of microtubules. PLoS One 2012; 7:e30738. [PMID: 22363481 PMCID: PMC3282699 DOI: 10.1371/journal.pone.0030738] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2011] [Accepted: 12/23/2011] [Indexed: 11/18/2022] Open
Abstract
The kinesins-8 were originally thought to be microtubule depolymerases, but are now emerging as more versatile catalysts of microtubule dynamics. We show here that S. pombe Klp5-436 and Klp6-440 are non-processive plus-end-directed motors whose in vitro velocities on S. pombe microtubules at 7 and 23 nm s(-1) are too slow to keep pace with the growing tips of dynamic interphase microtubules in living S. pombe. In vitro, Klp5 and 6 dimers exhibit a hitherto-undescribed combination of strong enhancement of microtubule nucleation with no effect on growth rate or catastrophe frequency. By contrast in vivo, both Klp5 and Klp6 promote microtubule catastrophe at cell ends whilst Klp6 also increases the number of interphase microtubule arrays (IMAs). Our data support a model in which Klp5/6 bind tightly to free tubulin heterodimers, strongly promoting the nucleation of new microtubules, and then continue to land as a tubulin-motor complex on the tips of growing microtubules, with the motors then dissociating after a few seconds residence on the lattice. In vivo, we predict that only at cell ends, when growing microtubule tips become lodged and their growth slows down, will Klp5/6 motor activity succeed in tracking growing microtubule tips. This mechanism would allow Klp5/6 to detect the arrival of microtubule tips at cells ends and to amplify the intrinsic tendency for microtubules to catastrophise in compression at cell ends. Our evidence identifies Klp5 and 6 as spatial regulators of microtubule dynamics that enhance both microtubule nucleation at the cell centre and microtubule catastrophe at the cell ends.
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Affiliation(s)
- Muriel Erent
- Centre for Mechanochemical Cell Biology, Warwick Medical School, The University of Warwick, Coventry, United Kingdom
| | - Douglas R. Drummond
- Centre for Mechanochemical Cell Biology, Warwick Medical School, The University of Warwick, Coventry, United Kingdom
| | - Robert A. Cross
- Centre for Mechanochemical Cell Biology, Warwick Medical School, The University of Warwick, Coventry, United Kingdom
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86
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Green LC, Kalitsis P, Chang TM, Cipetic M, Kim JH, Marshall O, Turnbull L, Whitchurch CB, Vagnarelli P, Samejima K, Earnshaw WC, Choo KHA, Hudson DF. Contrasting roles of condensin I and condensin II in mitotic chromosome formation. J Cell Sci 2012; 125:1591-604. [PMID: 22344259 DOI: 10.1242/jcs.097790] [Citation(s) in RCA: 123] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
In vertebrates, two condensin complexes exist, condensin I and condensin II, which have differing but unresolved roles in organizing mitotic chromosomes. To dissect accurately the role of each complex in mitosis, we have made and studied the first vertebrate conditional knockouts of the genes encoding condensin I subunit CAP-H and condensin II subunit CAP-D3 in chicken DT40 cells. Live-cell imaging reveals highly distinct segregation defects. CAP-D3 (condensin II) knockout results in masses of chromatin-containing anaphase bridges. CAP-H (condensin I)-knockout anaphases have a more subtle defect, with chromatids showing fine chromatin fibres that are associated with failure of cytokinesis and cell death. Super-resolution microscopy reveals that condensin-I-depleted mitotic chromosomes are wider and shorter, with a diffuse chromosome scaffold, whereas condensin-II-depleted chromosomes retain a more defined scaffold, with chromosomes more stretched and seemingly lacking in axial rigidity. We conclude that condensin II is required primarily to provide rigidity by establishing an initial chromosome axis around which condensin I can arrange loops of chromatin.
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Affiliation(s)
- Lydia C Green
- Murdoch Childrens Research Institute, Royal Children's Hospital, Melbourne, Victoria 3052, Australia
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87
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Abstract
Mitosis is the process by which eukaryotic cells organize and segregate their chromosomes in preparation for cell division. It is accomplished by a cellular machine composed largely of microtubules (MTs) and their associated proteins. This article reviews literature on mitosis from a biophysical point of view, drawing attention to the assembly and motility processes required to do this complex job with precision. Work from both the recent and the older literature is integrated into a description of relevant biological events and the experiments that probe their mechanisms. Theoretical work on specific subprocesses is also reviewed. Our goal is to provide a document that will expose biophysicists to the fascination of this quite amazing process and provide them with a good background from which they can pursue their own research interests in the subject.
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88
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Wan X, Cimini D, Cameron LA, Salmon ED. The coupling between sister kinetochore directional instability and oscillations in centromere stretch in metaphase PtK1 cells. Mol Biol Cell 2012; 23:1035-46. [PMID: 22298429 PMCID: PMC3302731 DOI: 10.1091/mbc.e11-09-0767] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
High-resolution kinetochore tracking reveals that oscillations in centromere stretch occur at twice the frequency of kinetochore oscillations because of the nonlinear kinetics of kinetochore directional instability, which produce poleward and away-from-the-pole kinetochore oscillations. Kinetochores bound to kinetochore microtubules (kMTs) exhibit directional instability in mammalian and other mitotic vertebrate cells, oscillating between poleward (P) and away-from-the-pole (AP) movements. These oscillations are coupled to changes in length of kMTs in a way that maintains a net stretch of the centromere. To understand how sister kinetochore directional instability and kMT plus-end dynamic instability are coupled to oscillations in centromere stretch, we tracked at high resolution the positions of fluorescent kinetochores and their poles for oscillating chromosomes within spindles of metaphase PtK1 cells. We found that the kinetics of P and AP movement are nonlinear and different. By subtracting contributions from the poleward flux of kMTs, we found that maximum centromere stretch occurred when the leading kinetochore switched from depolymerization to polymerization, whereas minimum centromere stretch occurred on average 7 s after the initially trailing kinetochore switched from polymerization to depolymerization. These differences produce oscillations in centromere stretch at about twice the frequency of kinetochore directional instability and at about twice the frequency of centromere oscillations back and forth across the spindle equator.
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Affiliation(s)
- Xiaohu Wan
- Biology Department, University of North Carolina, Chapel Hill, NC 27599, USA.
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89
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Gardner MK, Zanic M, Gell C, Bormuth V, Howard J. Depolymerizing kinesins Kip3 and MCAK shape cellular microtubule architecture by differential control of catastrophe. Cell 2012; 147:1092-103. [PMID: 22118464 DOI: 10.1016/j.cell.2011.10.037] [Citation(s) in RCA: 136] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2011] [Revised: 07/11/2011] [Accepted: 10/26/2011] [Indexed: 10/15/2022]
Abstract
Microtubules are dynamic filaments whose ends alternate between periods of slow growth and rapid shortening as they explore intracellular space and move organelles. A key question is how regulatory proteins modulate catastrophe, the conversion from growth to shortening. To study this process, we reconstituted microtubule dynamics in the absence and presence of the kinesin-8 Kip3 and the kinesin-13 MCAK. Surprisingly, we found that, even in the absence of the kinesins, the microtubule catastrophe frequency depends on the age of the microtubule, indicating that catastrophe is a multistep process. Kip3 slowed microtubule growth in a length-dependent manner and increased the rate of aging. In contrast, MCAK eliminated the aging process. Thus, both kinesins are catastrophe factors; Kip3 mediates fine control of microtubule length by narrowing the distribution of maximum lengths prior to catastrophe, whereas MCAK promotes rapid restructuring of the microtubule cytoskeleton by making catastrophe a first-order random process.
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Affiliation(s)
- Melissa K Gardner
- Department of Genetics, University of Minnesota, Minneapolis, MN 55455, USA
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90
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Stumpff J, Du Y, English CA, Maliga Z, Wagenbach M, Asbury CL, Wordeman L, Ohi R. A tethering mechanism controls the processivity and kinetochore-microtubule plus-end enrichment of the kinesin-8 Kif18A. Mol Cell 2011; 43:764-75. [PMID: 21884977 DOI: 10.1016/j.molcel.2011.07.022] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2011] [Revised: 06/23/2011] [Accepted: 07/28/2011] [Indexed: 10/17/2022]
Abstract
Metaphase chromosome positioning depends on Kif18A, a kinesin-8 that accumulates at and suppresses the dynamics of K-MT plus ends. By engineering Kif18A mutants that suppress MT dynamics but fail to concentrate at K-MT plus ends, we identify a mechanism that allows Kif18A to accumulate at K-MT plus ends to a level required to suppress chromosome movements. Enrichment of Kif18A at K-MT plus ends depends on its C-terminal tail domain, while the ability of Kif18A to suppress MT growth is conferred by the N-terminal motor domain. The Kif18A tail contains a second MT-binding domain that diffuses along the MT lattice, suggesting that it tethers the motor to the MT track. Consistently, the tail enhances Kif18A processivity and is crucial for it to accumulate at K-MT plus ends. The heightened processivity of Kif18A, conferred by its tail domain, thus promotes concentration of Kif18A at K-MT plus ends, where it suppresses their dynamics to control chromosome movements.
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Affiliation(s)
- Jason Stumpff
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, WA 98195, USA
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91
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McAinsh AD, Meraldi P. The CCAN complex: Linking centromere specification to control of kinetochore–microtubule dynamics. Semin Cell Dev Biol 2011; 22:946-52. [DOI: 10.1016/j.semcdb.2011.09.016] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2011] [Accepted: 09/29/2011] [Indexed: 12/20/2022]
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92
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Meraldi P. Keeping kinetochores on track. Eur J Cell Biol 2011; 91:103-6. [PMID: 22104445 DOI: 10.1016/j.ejcb.2011.10.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2011] [Accepted: 10/06/2011] [Indexed: 11/26/2022] Open
Abstract
The multiple functions of kinetochores are reflected in their complex composition, with over a hundred different proteins, which self-associate in several functional subcomplexes. Most of these kinetochore proteins were identified over the last 10-12 years using a combination of genetic, cell biological, biochemical, and bioinformatic approaches in various model organisms. The key challenge since then has been to determine the structural architecture of kinetochores, define the functions of its different subcomponents, and understand its regulation, both in response to the rapid changes in microtubule dynamics or to sense erroneous attachments for spindle checkpoint signalling. Here, we present some of the key advances obtained in the last six years on the biology of kinetochores, both through our work and through the work of many other groups studying this exciting structure.
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Affiliation(s)
- Patrick Meraldi
- Institute of Biochemistry, ETH Zurich, Schafmattstrasse 18, CH-8093 Zurich, Switzerland.
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93
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A non-motor microtubule binding site is essential for the high processivity and mitotic function of kinesin-8 Kif18A. PLoS One 2011; 6:e27471. [PMID: 22102900 PMCID: PMC3213134 DOI: 10.1371/journal.pone.0027471] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2011] [Accepted: 10/17/2011] [Indexed: 11/19/2022] Open
Abstract
Background Members of the kinesin-8 subfamily are plus end-directed molecular motors that accumulate at the plus-ends of kinetochore-microtubules (kt-MTs) where they regulate MT dynamics. Loss of vertebrate kinesin-8 function induces hyperstable MTs and elongated mitotic spindles accompanied by severe chromosome congression defects. It has been reported that the motility of human kinesin-8, Kif18A, is required for its accumulation at the plus tips of kt-MTs. Methodology/Findings Here, we investigate how Kif18A localizes to the plus-ends of kt-MTs. We find that Kif18A lacking its C-terminus does not accumulate on the tips of kt-MTs and fails to fulfill its mitotic function. In vitro studies reveal that Kif18A possesses a non-motor MT binding site located within its C-proximal 121 residues. Using single molecule measurements we find that Kif18A is a highly processive motor and, furthermore, that the C-terminal tail is essential for the high processivity of Kif18A. Conclusion/Significance These results show that Kif18A like its yeast orthologue is a highly processive motor. The ability of Kif18A to walk on MTs for a long distance without dissociating depends on a non-motor MT binding site located at the C-terminus of Kif18A. This C-proximal tail of Kif18A is essential for its plus-end accumulation and mitotic function. These findings advance our understanding of how Kif18A accumulates at the tips of kt-MTs to fulfill its function in mitosis.
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94
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Chinta R, Wasser M. Three-dimensional segmentation of nuclei and mitotic chromosomes for the study of cell divisions in live Drosophila embryos. Cytometry A 2011; 81:52-64. [PMID: 22069299 DOI: 10.1002/cyto.a.21164] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2011] [Revised: 07/19/2011] [Accepted: 10/06/2011] [Indexed: 11/12/2022]
Abstract
Drosophila embryogenesis is an established model to investigate mechanisms and genes related to cell divisions in an intact multicellular organism. Progression through the cell cycle phases can be monitored in vivo using fluorescently labeled fusion proteins and time-lapse microscopy. To measure cellular properties in microscopic images, accurate and fast image segmentation methods are a critical prerequisite. To quantify static and dynamic features of interphase nuclei and mitotic chromosomes, we developed a three-dimensional (3D) segmentation method based on multiple level sets. We tested our method on 3D time-series images of live embryos expressing histone-2Av-green fluorescence protein. Our method is robust to low signal-to-noise ratios inherent to high-speed imaging, fluorescent signals in the cytoplasm, and dynamic changes of shape and texture. Comparisons with manual ground-truth segmentations showed that our method achieves more than 90% accuracy on the object as well as voxel levels and performs consistently throughout all cell cycle phases and developmental stages from syncytial blastoderm to postblastoderm mitotic domains.
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Affiliation(s)
- Rambabu Chinta
- Bioinformatics Institute, Agency for Science, Technology and Research (A*STAR), Singapore 138671, Republic of Singapore.
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95
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Drummond DR. Regulation of microtubule dynamics by kinesins. Semin Cell Dev Biol 2011; 22:927-34. [PMID: 22001250 DOI: 10.1016/j.semcdb.2011.09.021] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2011] [Accepted: 09/30/2011] [Indexed: 01/14/2023]
Abstract
The simple mechanistic and functional division of the kinesin family into either active translocators or non-motile microtubule depolymerases was initially appropriate but is now proving increasingly unhelpful, given evidence that several translocase kinesins can affect microtubule dynamics, whilst non-translocase kinesins can promote microtubule assembly and depolymerisation. Such multi-role kinesins act either directly on microtubule dynamics, by interaction with microtubules and tubulin, or indirectly, through the transport of other factors along the lattice to the microtubule tip. Here I review recent progress on the mechanisms and roles of these translocase kinesins.
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Affiliation(s)
- Douglas R Drummond
- Centre for Mechanochemical Cell Biology, Warwick Medical School, University of Warwick, Coventry, CV4 7AL, United Kingdom.
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96
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Hagan RS, Manak MS, Buch HK, Meier MG, Meraldi P, Shah JV, Sorger PK. p31(comet) acts to ensure timely spindle checkpoint silencing subsequent to kinetochore attachment. Mol Biol Cell 2011; 22:4236-46. [PMID: 21965286 PMCID: PMC3216650 DOI: 10.1091/mbc.e11-03-0216] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The spindle assembly checkpoint links the onset of anaphase to completion of chromosome-microtubule attachment and is mediated by the binding of Mad and Bub proteins to kinetochores of unattached or maloriented chromosomes. Mad2 and BubR1 traffic between kinetochores and the cytosol, thereby transmitting a "wait anaphase" signal to the anaphase-promoting complex. It is generally assumed that this signal dissipates automatically upon kinetochore-microtubule binding, but it has been shown that under conditions of nocodazole-induced arrest p31(comet), a Mad2-binding protein, is required for mitotic progression. In this article we investigate the localization and function of p31(comet) during normal, unperturbed mitosis in human and marsupial cells. We find that, like Mad2, p31(comet) traffics on and off kinetochores and is also present in the cytosol. Cells depleted of p31(comet) arrest in metaphase with mature bipolar kinetochore-microtubule attachments, a satisfied checkpoint, and high cyclin B levels. Thus p31(comet) is required for timely mitotic exit. We propose that p31(comet) is an essential component of the machinery that silences the checkpoint during each cell cycle.
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Affiliation(s)
- Robert S Hagan
- Center for Cell Decision Processes, Harvard Medical School, Boston, MA 02115, USA
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97
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Weaver LN, Ems-McClung SC, Stout JR, LeBlanc C, Shaw SL, Gardner MK, Walczak CE. Kif18A uses a microtubule binding site in the tail for plus-end localization and spindle length regulation. Curr Biol 2011; 21:1500-6. [PMID: 21885282 DOI: 10.1016/j.cub.2011.08.005] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2011] [Revised: 07/03/2011] [Accepted: 08/02/2011] [Indexed: 01/03/2023]
Abstract
The mitotic spindle is a macromolecular structure utilized to properly align and segregate sister chromatids to two daughter cells. During mitosis, the spindle maintains a constant length, even though the spindle microtubules (MTs) are constantly undergoing polymerization and depolymerization [1]. Members of the kinesin-8 family are important for the regulation of spindle length and for chromosome positioning [2-9]. Kinesin-8 proteins are length-specific, plus-end-directed motors that are proposed to be either MT depolymerases [3, 4, 8, 10, 11] or MT capping proteins [12]. How Kif18A uses its destabilization activity to control spindle morphology is not known. We found that Kif18A controls spindle length independently of its role in chromosome positioning. The ability of Kif18A to control spindle length is mediated by an ATP-independent MT binding site at the C-terminal end of the Kif18A tail that has a strong affinity for MTs in vitro and in cells. We used computational modeling to ask how modulating the motility or binding properties of Kif18A would affect its activity. Our modeling predicts that both fast motility and a low off rate from the MT end are important for Kif18A function. In addition, our studies provide new insight into how depolymerizing and capping enzymes can lead to MT destabilization.
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Affiliation(s)
- Lesley N Weaver
- Department of Biology, Indiana University, Bloomington, IN 47405, USA
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98
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Magidson V, O’Connell CB, Lončarek J, Paul R, Mogilner A, Khodjakov A. The spatial arrangement of chromosomes during prometaphase facilitates spindle assembly. Cell 2011; 146:555-67. [PMID: 21854981 PMCID: PMC3291198 DOI: 10.1016/j.cell.2011.07.012] [Citation(s) in RCA: 226] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2010] [Revised: 04/17/2011] [Accepted: 07/08/2011] [Indexed: 11/19/2022]
Abstract
Error-free chromosome segregation requires stable attachment of sister kinetochores to the opposite spindle poles (amphitelic attachment). Exactly how amphitelic attachments are achieved during spindle assembly remains elusive. We employed photoactivatable GFP and high-resolution live-cell confocal microscopy to visualize complete 3D movements of individual kinetochores throughout mitosis in nontransformed human cells. Combined with electron microscopy, molecular perturbations, and immunofluorescence analyses, this approach reveals unexpected details of chromosome behavior. Our data demonstrate that unstable lateral interactions between kinetochores and microtubules dominate during early prometaphase. These transient interactions lead to the reproducible arrangement of chromosomes in an equatorial ring on the surface of the nascent spindle. A computational model predicts that this toroidal distribution of chromosomes exposes kinetochores to a high density of microtubules which facilitates subsequent formation of amphitelic attachments. Thus, spindle formation involves a previously overlooked stage of chromosome prepositioning which promotes formation of amphitelic attachments.
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Affiliation(s)
| | | | | | - Raja Paul
- Departments of Neurobiology, Physiology, and Behavior, and Mathematics, University of California, Davis, CA 95616, USA
| | - Alex Mogilner
- Departments of Neurobiology, Physiology, and Behavior, and Mathematics, University of California, Davis, CA 95616, USA
| | - Alexey Khodjakov
- Wadsworth Center, PO Box 509, Albany, NY 12201-509, USA
- Rensselaer Polytechnic Institute, Troy NY 12180, USA
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99
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Samora CP, Mogessie B, Conway L, Ross JL, Straube A, McAinsh AD. MAP4 and CLASP1 operate as a safety mechanism to maintain a stable spindle position in mitosis. Nat Cell Biol 2011; 13:1040-50. [PMID: 21822276 DOI: 10.1038/ncb2297] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2011] [Accepted: 06/14/2011] [Indexed: 12/21/2022]
Abstract
Correct positioning of the mitotic spindle is critical to establish the correct cell-division plane. Spindle positioning involves capture of astral microtubules and generation of pushing/pulling forces at the cell cortex. Here we show that the tau-related protein MAP4 and the microtubule rescue factor CLASP1 are essential for maintaining spindle position and the correct cell-division axis in human cells. We propose that CLASP1 is required to correctly capture astral microtubules, whereas MAP4 prevents engagement of excess dynein motors, thereby protecting the system from force imbalance. Consistent with this, MAP4 physically interacts with dynein-dynactin in vivo and inhibits dynein-mediated microtubule sliding in vitro. Depletion of MAP4, but not CLASP1, causes spindle misorientation in the vertical plane, demonstrating that force generators are under spatial control. These findings have wide biological importance, because spindle positioning is essential during embryogenesis and stem-cell homeostasis.
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Affiliation(s)
- Catarina P Samora
- Centre for Mechanochemical Cell Biology, Warwick Medical School, University of Warwick, Coventry, CV4 7AL, UK
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100
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Vladimirou E, Harry E, Burroughs N, McAinsh AD. Springs, clutches and motors: driving forward kinetochore mechanism by modelling. Chromosome Res 2011; 19:409-21. [PMID: 21331796 PMCID: PMC3078324 DOI: 10.1007/s10577-011-9191-x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
As a mechanical system, the kinetochore can be viewed as a set of interacting springs, clutches and motors; the problem of kinetochore mechanism is now one of understanding how these functional modules assemble, disassemble and interact with one another to give rise to the emergent properties of the system. The sheer complexity of the kinetochore system points to a future requirement for data-driven mathematical modelling and statistical analysis based on quantitative empirical measurement of sister kinetochore trajectories. Here, we review existing models of chromosome motion in the context of recent advances in our understanding of kinetochore molecular biology.
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Affiliation(s)
- Elina Vladimirou
- Centre for Mechanochemical Cell Biology, Warwick Medical School, University of Warwick, Coventry, UK
| | - Ed Harry
- Centre for Mechanochemical Cell Biology, Warwick Medical School, University of Warwick, Coventry, UK
- Molecular Organisation and Assembly in Cells (MOAC) Doctoral Training Centre, University of Warwick, Coventry, UK
- Warwick Systems Biology Centre, University of Warwick, Coventry, UK
| | - Nigel Burroughs
- Warwick Systems Biology Centre, University of Warwick, Coventry, UK
| | - Andrew D. McAinsh
- Centre for Mechanochemical Cell Biology, Warwick Medical School, University of Warwick, Coventry, UK
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