1
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Ramos M, Cortés JCG, Sato M, Rincón SA, Moreno MB, Clemente-Ramos JÁ, Osumi M, Pérez P, Ribas JC. Two S. pombe septation phases differ in ingression rate, septum structure, and response to F-actin loss. J Cell Biol 2019; 218:4171-4194. [PMID: 31597680 PMCID: PMC6891078 DOI: 10.1083/jcb.201808163] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2018] [Revised: 04/19/2019] [Accepted: 09/10/2019] [Indexed: 12/28/2022] Open
Abstract
Ramos et al. establish that fission yeast septation proceeds in two phases. Initially, the septum is immature and, upon F-actin depolymerization, loses the Bgs1 glucan synthase and fails to ingress. During a second phase, the mature septum can maintain Bgs1 and ingression without F-actin, and ingression becomes Cdc42 and exocyst dependent. In fission yeast, cytokinesis requires a contractile actomyosin ring (CR) coupled to membrane and septum ingression. Septation proceeds in two phases. In anaphase B, the septum ingresses slowly. During telophase, the ingression rate increases, and the CR becomes dispensable. Here, we explore the relationship between the CR and septation by analyzing septum ultrastructure, ingression, and septation proteins in cells lacking F-actin. We show that the two phases of septation correlate with septum maturation and the response of cells to F-actin removal. During the first phase, the septum is immature and, following F-actin removal, rapidly loses the Bgs1 glucan synthase from the membrane edge and fails to ingress. During the second phase, the rapidly ingressing mature septum can maintain a Bgs1 ring and septum ingression without F-actin, but ingression becomes Cdc42 and exocyst dependent. Our results provide new insights into fungal cytokinesis and reveal the dual function of CR as an essential landmark for the concentration of Bgs1 and a contractile structure that maintains septum shape and synthesis.
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Affiliation(s)
- Mariona Ramos
- Instituto de Biología Funcional y Genómica and Departamento de Microbiología y Genética, Consejo Superior de Investigaciones Científicas/Universidad de Salamanca, Salamanca, Spain
| | - Juan Carlos G Cortés
- Instituto de Biología Funcional y Genómica and Departamento de Microbiología y Genética, Consejo Superior de Investigaciones Científicas/Universidad de Salamanca, Salamanca, Spain
| | - Mamiko Sato
- Laboratory of Electron Microscopy/Bio-imaging Center, Japan Women's University, Bunkyo-ku, Tokyo, Japan
| | - Sergio A Rincón
- Instituto de Biología Funcional y Genómica and Departamento de Microbiología y Genética, Consejo Superior de Investigaciones Científicas/Universidad de Salamanca, Salamanca, Spain
| | - M Belén Moreno
- Instituto de Biología Funcional y Genómica and Departamento de Microbiología y Genética, Consejo Superior de Investigaciones Científicas/Universidad de Salamanca, Salamanca, Spain
| | - José Ángel Clemente-Ramos
- Instituto de Biología Funcional y Genómica and Departamento de Microbiología y Genética, Consejo Superior de Investigaciones Científicas/Universidad de Salamanca, Salamanca, Spain
| | - Masako Osumi
- Laboratory of Electron Microscopy/Bio-imaging Center, Japan Women's University, Bunkyo-ku, Tokyo, Japan.,Integrated Imaging Research Support, Chiyoda-ku, Tokyo, Japan
| | - Pilar Pérez
- Instituto de Biología Funcional y Genómica and Departamento de Microbiología y Genética, Consejo Superior de Investigaciones Científicas/Universidad de Salamanca, Salamanca, Spain
| | - Juan Carlos Ribas
- Instituto de Biología Funcional y Genómica and Departamento de Microbiología y Genética, Consejo Superior de Investigaciones Científicas/Universidad de Salamanca, Salamanca, Spain
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2
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Wang S, O’Shaughnessy B. Anchoring of actin to the plasma membrane enables tension production in the fission yeast cytokinetic ring. Mol Biol Cell 2019; 30:2053-2064. [PMID: 31216223 PMCID: PMC6727776 DOI: 10.1091/mbc.e19-03-0173] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2019] [Revised: 05/31/2019] [Accepted: 05/31/2019] [Indexed: 11/11/2022] Open
Abstract
The cytokinetic ring generates tensile force that drives cell division, but how tension emerges from the relatively disordered ring organization remains unclear. Long ago, a musclelike sliding filament mechanism was proposed, but evidence for sarcomeric order is lacking. Here we present quantitative evidence that in fission yeast, ring tension originates from barbed-end anchoring of actin filaments to the plasma membrane, providing resistance to myosin forces that enables filaments to develop tension. The role of anchoring was highlighted by experiments on isolated fission yeast rings, where sections of ring became unanchored from the membrane and shortened ∼30-fold faster than normal. The dramatically elevated constriction rates are unexplained. Here we present a molecularly explicit simulation of constricting partially anchored rings as studied in these experiments. Simulations accurately reproduced the experimental constriction rates and showed that following anchor release, a segment becomes tensionless and shortens via a novel noncontractile reeling-in mechanism at about the velocity of load-free myosin II. The ends are reeled in by barbed end-anchored actin filaments in adjacent segments. Other actin anchoring schemes failed to constrict rings. Our results quantitatively support a specific organization and anchoring scheme that generate tension in the cytokinetic ring.
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Affiliation(s)
- Shuyuan Wang
- Department of Physics, Columbia University, New York, NY 10027
| | - Ben O’Shaughnessy
- Department of Chemical Engineering, Columbia University, New York, NY 10027
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3
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Palani S, Srinivasan R, Zambon P, Kamnev A, Gayathri P, Balasubramanian MK. Steric hindrance in the upper 50 kDa domain of the motor Myo2p leads to cytokinesis defects in fission yeast. J Cell Sci 2018; 131:jcs.205625. [PMID: 29162650 PMCID: PMC5818058 DOI: 10.1242/jcs.205625] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Accepted: 11/06/2017] [Indexed: 02/05/2023] Open
Abstract
Cytokinesis in many eukaryotes requires a contractile actomyosin ring that is placed at the division site. In fission yeast, which is an attractive organism for the study of cytokinesis, actomyosin ring assembly and contraction requires the myosin II heavy chain Myo2p. Although myo2-E1, a temperature-sensitive mutant defective in the upper 50 kDa domain of Myo2p, has been studied extensively, the molecular basis of the cytokinesis defect is not understood. Here, we isolate myo2-E1-Sup2, an intragenic suppressor that contains the original mutation in myo2-E1 (G345R) and a second mutation in the upper 50 kDa domain (Y297C). Unlike myo2-E1-Sup1, a previously characterized myo2-E1 suppressor, myo2-E1-Sup2 reverses actomyosin ring contraction defects in vitro and in vivo Structural analysis of available myosin motor domain conformations suggests that a steric clash in myo2-E1, which is caused by the replacement of a glycine with a bulky arginine, is relieved in myo2-E1-Sup2 by mutation of a tyrosine to a smaller cysteine. Our work provides insight into the function of the upper 50 kDa domain of Myo2p, informs a molecular basis for the cytokinesis defect in myo2-E1, and may be relevant to the understanding of certain cardiomyopathies.
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Affiliation(s)
- Saravanan Palani
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK
| | - Ramanujam Srinivasan
- School of Biological Sciences, National Institute of Science Engineering and Research (NISER), Bhubaneswar, Odisha 752050, India
| | - Paola Zambon
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK
| | - Anton Kamnev
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK
| | - Pananghat Gayathri
- Biology Division, Indian Institute of Science Education and Research (IISER), Pune 411 008, India
| | - Mohan K Balasubramanian
- Centre for Mechanochemical Cell Biology and Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK
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4
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Friend JE, Sayyad WA, Arasada R, McCormick CD, Heuser JE, Pollard TD. Fission yeast Myo2: Molecular organization and diffusion in the cytoplasm. Cytoskeleton (Hoboken) 2017; 75:164-173. [PMID: 29205883 DOI: 10.1002/cm.21425] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2017] [Revised: 11/22/2017] [Accepted: 11/27/2017] [Indexed: 12/20/2022]
Abstract
Myosin-II is required for the assembly and constriction of cytokinetic contractile rings in fungi and animals. We used electron microscopy, fluorescence recovery after photobleaching (FRAP), and fluorescence correlation spectroscopy (FCS) to characterize the physical properties of Myo2 from fission yeast Schizosaccharomyces pombe. By electron microscopy, Myo2 has two heads and a coiled-coiled tail like myosin-II from other species. The first 65 nm of the tail is a stiff rod, followed by a flexible, less-ordered region up to 30 nm long. Myo2 sediments as a 7 S molecule in high salt, but aggregates rather than forming minifilaments at lower salt concentrations; this is unaffected by heavy chain phosphorylation. We used FRAP and FCS to observe the dynamics of Myo2 in live S. pombe cells and in cell extracts at different salt concentrations; both show that Myo2 with an N-terminal mEGFP tag has a diffusion coefficient of ∼ 3 µm2 s-1 in the cytoplasm of live cells during interphase and mitosis. Photon counting histogram analysis of the FCS data confirmed that Myo2 diffuses as doubled-headed molecules in the cytoplasm. FCS measurements on diluted cell extracts showed that mEGFP-Myo2 has a diffusion coefficient of ∼ 30 µm2 s-1 in 50 to 400 mM KCl concentrations.
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Affiliation(s)
- Janice E Friend
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520-8103
| | - Wasim A Sayyad
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520-8103
| | - Rajesh Arasada
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520-8103
| | - Chad D McCormick
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520-8103.,Section on Integrative Biophysics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, Maryland 20892-1855
| | - John E Heuser
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520-8103
| | - Thomas D Pollard
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520-8103.,Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520-8103.,Department of Cell Biology, Yale University, New Haven, Connecticut 06520-8103
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5
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Zimmermann D, Homa KE, Hocky GM, Pollard LW, De La Cruz EM, Voth GA, Trybus KM, Kovar DR. Mechanoregulated inhibition of formin facilitates contractile actomyosin ring assembly. Nat Commun 2017; 8:703. [PMID: 28951543 PMCID: PMC5614989 DOI: 10.1038/s41467-017-00445-3] [Citation(s) in RCA: 56] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2016] [Accepted: 06/27/2017] [Indexed: 11/20/2022] Open
Abstract
Cytokinesis physically separates dividing cells by forming a contractile actomyosin ring. The fission yeast contractile ring has been proposed to assemble by Search-Capture-Pull-Release from cytokinesis precursor nodes that include the molecular motor type-II myosin Myo2 and the actin assembly factor formin Cdc12. By successfully reconstituting Search-Capture-Pull in vitro, we discovered that formin Cdc12 is a mechanosensor, whereby myosin pulling on formin-bound actin filaments inhibits Cdc12-mediated actin assembly. We mapped Cdc12 mechanoregulation to its formin homology 1 domain, which facilitates delivery of new actin subunits to the elongating actin filament. Quantitative modeling suggests that the pulling force of the myosin propagates through the actin filament, which behaves as an entropic spring, and thereby may stretch the disordered formin homology 1 domain and impede formin-mediated actin filament elongation. Finally, live cell imaging of mechano-insensitive formin mutant cells established that mechanoregulation of formin Cdc12 is required for efficient contractile ring assembly in vivo. The fission yeast cytokinetic ring assembles by Search-Capture-Pull-Release from precursor nodes that include formin Cdc12 and myosin Myo2. The authors reconstitute Search-Capture-Pull in vitro and find that Myo2 pulling on Cdc12-associated actin filaments mechano-inhibits Cdc12-mediated assembly, which enables proper ring assembly in vivo.
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Affiliation(s)
- Dennis Zimmermann
- Department of Molecular Genetics and Cell Biology, The University of Chicago, 920 E. 58th St., CSLC 212, Chicago, IL, 60637, USA
| | - Kaitlin E Homa
- Department of Molecular Genetics and Cell Biology, The University of Chicago, 920 E. 58th St., CSLC 212, Chicago, IL, 60637, USA
| | - Glen M Hocky
- Department of Chemistry, The James Franck Institute and Institute for Biophysical Dynamics and Computation Institute, The University of Chicago, 5735 S. Ellis Ave., Searle Chemistry Laboratory 231, Chicago, IL, 60637, USA
| | - Luther W Pollard
- Department of Molecular Physiology and Biophysics, University of Vermont, 149 Beaumont Ave., HSRF 130, Burlington, VT, 05405, USA
| | - Enrique M De La Cruz
- Department of Molecular Biophysics and Biochemistry, Yale University, PO Box 208114, 266 Whitney Ave., New Haven, CT, 06520-8114, USA
| | - Gregory A Voth
- Department of Chemistry, The James Franck Institute and Institute for Biophysical Dynamics and Computation Institute, The University of Chicago, 5735 S. Ellis Ave., Searle Chemistry Laboratory 231, Chicago, IL, 60637, USA.
| | - Kathleen M Trybus
- Department of Molecular Physiology and Biophysics, University of Vermont, 149 Beaumont Ave., HSRF 130, Burlington, VT, 05405, USA.
| | - David R Kovar
- Department of Molecular Genetics and Cell Biology, The University of Chicago, 920 E. 58th St., CSLC 212, Chicago, IL, 60637, USA. .,Department of Biochemistry and Molecular Biology, The University of Chicago, 920 E. 58th St., CSLC 212, Chicago, IL, 60637, USA.
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6
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Li X, Mei Y, Yan B, Vitriol E, Huang S, Ji P, Qiu Y. Histone deacetylase 6 regulates cytokinesis and erythrocyte enucleation through deacetylation of formin protein mDia2. Haematologica 2017; 102:984-994. [PMID: 28255013 PMCID: PMC5451330 DOI: 10.3324/haematol.2016.161513] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2016] [Accepted: 02/27/2017] [Indexed: 11/09/2022] Open
Abstract
The formin protein mDia2 plays a critical role in a number of cellular processes through its ability to promote nucleation and elongation of actin filaments. In erythroblasts, this includes control of cytokinesis and enucleation by regulating contractile actin ring formation. Here we report a novel mechanism of how mDia2 is regulated: through acetylation and deacetylation at lysine 970 in the formin homology 2 domain. Ectopic expression of an acetyl-mimic mDia2 mutant in mouse erythroblasts is sufficient to abolish contractile actin ring formation at the cleavage furrow and subsequent erythrocyte cytokinesis and enucleation. We also identified that class II histone deacetylase 6 deacetylates and subsequently activates mDia2. Knockdown or inhibition of histone deacetylase 6 impairs contractile actin ring formation, and expression of a non-acetyl-mimic mDia2 mutant restores the contractile actin ring and rescues the impairment of enucleation. In addition to revealing a new step in mDia2 regulation, this study may unveil a novel regulatory mechanism of formin-mediated actin assembly, since the K970 acetylation site is conserved among Dia proteins
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Affiliation(s)
- Xuehui Li
- Department of Anatomy and Cell Biology, College of Medicine, University of Florida, Gainesville, FL, USA
| | - Yang Mei
- Department of Pathology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
| | - Bowen Yan
- Department of Anatomy and Cell Biology, College of Medicine, University of Florida, Gainesville, FL, USA
| | - Eric Vitriol
- Department of Anatomy and Cell Biology, College of Medicine, University of Florida, Gainesville, FL, USA
| | - Suming Huang
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, FL, USA.,Macau Institute for Applied Research in Medicine and Health, State Key Laboratory of Quality Research in Chinese Medicine, Macau University of Science and Technology, Avenida Wai Long, Taipa, Macau
| | - Peng Ji
- Department of Pathology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
| | - Yi Qiu
- Department of Anatomy and Cell Biology, College of Medicine, University of Florida, Gainesville, FL, USA
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7
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Brooker HR, Geeves MA, Mulvihill DP. Analysis of biophysical and functional consequences of tropomyosin-fluorescent protein fusions. FEBS Lett 2016; 590:3111-21. [PMID: 27501521 PMCID: PMC5053231 DOI: 10.1002/1873-3468.12346] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2016] [Revised: 08/02/2016] [Accepted: 08/02/2016] [Indexed: 01/14/2023]
Abstract
The dynamic nature of actin polymers is modulated to facilitate a diverse range of cellular processes. These dynamic properties are determined by different isoforms of tropomyosin which are recruited to distinct subpopulations of actin polymers to differentially regulate their functional properties. This makes tropomyosin an attractive target for labelling discrete actin populations. We have assessed the effect of different fluorescent labelling strategies for this protein. Although tropomyosin–fluorescent fusions decorate actin in vivo, they are either nonfunctional or perturb regulation of actin nucleation and cell cycle timings. Thus, conclusions and physiological relevance should be carefully evaluated when using tropomyosin fusions.
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8
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Addario B, Sandblad L, Persson K, Backman L. Characterisation of Schizosaccharomyces pombe α-actinin. PeerJ 2016; 4:e1858. [PMID: 27069798 PMCID: PMC4824898 DOI: 10.7717/peerj.1858] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2015] [Accepted: 03/08/2016] [Indexed: 11/27/2022] Open
Abstract
The actin cytoskeleton plays a fundamental role in eukaryotic cells. Its reorganization is regulated by a plethora of actin-modulating proteins, such as a-actinin. In higher organisms, α-actinin is characterized by the presence of three distinct structural domains: an N-terminal actin-binding domain and a C-terminal region with EF-hand motif separated by a central rod domain with four spectrin repeats. Sequence analysis has revealed that the central rod domain of α-actinin from the fission yeast Schizosaccharomyces pombe consists of only two spectrin repeats. To obtain a firmer understanding of the structure and function of this unconventional α-actinin, we have cloned and characterized each structural domain. Our results show that this a-actinin isoform is capable of forming dimers and that the rod domain is required for this. However, its actin-binding and cross-linking activity appears less efficient compared to conventional α-actinins. The solved crystal structure of the actin-binding domain indicates that the closed state is stabilised by hydrogen bonds and a salt bridge not present in other α-actinins, which may reduce the affinity for actin.
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Affiliation(s)
- Barbara Addario
- Cell Biology Laboratory, School of Biochemistry and Cell Biology, BioScience Institute, University College Cork , Cork , Ireland
| | - Linda Sandblad
- Department of Molecular Biology, UmeåUniversity , Umeå , Sweden
| | - Karina Persson
- Department of Chemistry, Biological Chemistry , Umeå , Sweden
| | - Lars Backman
- Department of Chemistry, Biological Chemistry , Umeå , Sweden
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9
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Srivastava V, Iglesias PA, Robinson DN. Cytokinesis: Robust cell shape regulation. Semin Cell Dev Biol 2015; 53:39-44. [PMID: 26481973 DOI: 10.1016/j.semcdb.2015.10.023] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Accepted: 10/13/2015] [Indexed: 11/25/2022]
Abstract
Cytokinesis, the final step of cell division, is a great example of robust cell shape regulation. A wide variety of cells ranging from the unicellular Dictyostelium to human cells in tissues proceed through highly similar, stereotypical cell shape changes during cell division. Typically, cells first round up forming a cleavage furrow in the middle, which constricts resulting in the formation of two daughter cells. Tight control of cytokinesis is essential for proper segregation of genetic and cellular materials, and its failure is deleterious to cell viability. Thus, biological systems have developed elaborate mechanisms to ensure high fidelity of cytokinesis, including the existence of multiple biochemical and mechanical pathways regulated through feedback. In this review, we focus on the built-in redundancy of the cytoskeletal machinery that allows cells to divide successfully in a variety of biological and mechanical contexts. Using Dictyostelium cytokinesis as an example, we demonstrate that the crosstalk between biochemical and mechanical signaling through feedback ensures correct assembly and function of the cell division machinery.
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Affiliation(s)
- Vasudha Srivastava
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, United States; Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, MD 21218, United States
| | - Pablo A Iglesias
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, United States; Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, MD 21218, United States
| | - Douglas N Robinson
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, United States; Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, MD 21205, United States; Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, MD 21218, United States.
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10
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Laplante C, Berro J, Karatekin E, Hernandez-Leyva A, Lee R, Pollard TD. Three myosins contribute uniquely to the assembly and constriction of the fission yeast cytokinetic contractile ring. Curr Biol 2015; 25:1955-65. [PMID: 26144970 DOI: 10.1016/j.cub.2015.06.018] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2014] [Revised: 05/16/2015] [Accepted: 06/05/2015] [Indexed: 11/30/2022]
Abstract
Cytokinesis in fission yeast cells depends on conventional myosin-II (Myo2) to assemble and constrict a contractile ring of actin filaments. Less is known about the functions of an unconventional myosin-II (Myp2) and a myosin-V (Myo51) that are also present in the contractile ring. Myo2 appears in cytokinetic nodes around the equator 10 min before spindle pole body separation (cell-cycle time, -10 min) independent of actin filaments, followed by Myo51 at time zero and Myp2 at time +20 min, both located between nodes and dependent on actin filaments. We investigated the contributions of these three myosins to cytokinesis using a severely disabled mutation of the essential myosin-II heavy-chain gene (myo2-E1) and deletion mutations of the other myosin heavy-chain genes. Cells with only Myo2 assemble contractile rings normally. Cells with either Myp2 or Myo51 alone can assemble nodes and actin filaments into contractile rings but complete assembly later than normal. Both Myp2 and Myo2 contribute to constriction of fully assembled rings at rates 55% that of normal in cells relying on Myp2 alone and 25% that of normal in cells with Myo2 alone. Myo51 alone cannot constrict rings but increases the constriction rate by Myo2 in Δmyp2 cells or Myp2 in myo2-E1 cells. Three myosins function in a hierarchal, complementary manner to accomplish cytokinesis, with Myo2 and Myo51 taking the lead during contractile ring assembly and Myp2 making the greatest contribution to constriction.
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Affiliation(s)
- Caroline Laplante
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520, USA
| | - Julien Berro
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA; Nanobiology Institute, Yale University, West Haven, CT 06516, USA
| | - Erdem Karatekin
- Nanobiology Institute, Yale University, West Haven, CT 06516, USA; Department of Cellular and Molecular Physiology, Yale University, New Haven, CT 06520, USA; Institut des Sciences Biologiques, Centre National de la Recherche Scientifique (CNRS), Délégation Paris Michel-Ange, 3 rue Michel-Ange, 75794 Paris Cedex 16, France
| | - Ariel Hernandez-Leyva
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520, USA
| | - Rachel Lee
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520, USA
| | - Thomas D Pollard
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520, USA; Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA; Department of Cell Biology, Yale University, New Haven, CT 06520, USA.
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11
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Willet AH, McDonald NA, Bohnert KA, Baird MA, Allen JR, Davidson MW, Gould KL. The F-BAR Cdc15 promotes contractile ring formation through the direct recruitment of the formin Cdc12. ACTA ACUST UNITED AC 2015; 208:391-9. [PMID: 25688133 PMCID: PMC4332253 DOI: 10.1083/jcb.201411097] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Cdc15 contributes to contractile ring formation and cytokinesis by recruiting the formin Cdc12, which defines a novel cytokinetic function for an F-BAR domain. In Schizosaccharomyces pombe, cytokinesis requires the assembly and constriction of an actomyosin-based contractile ring (CR). Nucleation of F-actin for the CR requires a single formin, Cdc12, that localizes to the cell middle at mitotic onset. Although genetic requirements for formin Cdc12 recruitment have been determined, the molecular mechanisms dictating its targeting to the medial cortex during cytokinesis are unknown. In this paper, we define a short motif within the N terminus of Cdc12 that binds directly to the F-BAR domain of the scaffolding protein Cdc15. Mutations preventing the Cdc12–Cdc15 interaction resulted in reduced Cdc12, F-actin, and actin-binding proteins at the CR, which in turn led to a delay in CR formation and sensitivity to other perturbations of CR assembly. We conclude that Cdc15 contributes to CR formation and cytokinesis via formin Cdc12 recruitment, defining a novel cytokinetic function for an F-BAR domain.
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Affiliation(s)
- Alaina H Willet
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Nathan A McDonald
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - K Adam Bohnert
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Michelle A Baird
- National High Magnetic Field Laboratory and Department of Biological Science, The Florida State University, Tallahassee, FL 32306 National High Magnetic Field Laboratory and Department of Biological Science, The Florida State University, Tallahassee, FL 32306
| | - John R Allen
- National High Magnetic Field Laboratory and Department of Biological Science, The Florida State University, Tallahassee, FL 32306 National High Magnetic Field Laboratory and Department of Biological Science, The Florida State University, Tallahassee, FL 32306
| | - Michael W Davidson
- National High Magnetic Field Laboratory and Department of Biological Science, The Florida State University, Tallahassee, FL 32306 National High Magnetic Field Laboratory and Department of Biological Science, The Florida State University, Tallahassee, FL 32306
| | - Kathleen L Gould
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232
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12
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Zhou Z, Munteanu EL, He J, Ursell T, Bathe M, Huang KC, Chang F. The contractile ring coordinates curvature-dependent septum assembly during fission yeast cytokinesis. Mol Biol Cell 2014; 26:78-90. [PMID: 25355954 PMCID: PMC4279231 DOI: 10.1091/mbc.e14-10-1441] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Cytokinesis in fission yeast is accomplished by inward growth of the cell wall septum guided by the contractile ring. The ring promotes local septum growth in a curvature-dependent manner, allowing even a misshapen septum to grow into a more regular shape. This suggests that the ring regulates cell wall assembly through a mechanosensitive mechanism. The functions of the actin-myosin–based contractile ring in cytokinesis remain to be elucidated. Recent findings show that in the fission yeast Schizosaccharomyces pombe, cleavage furrow ingression is driven by polymerization of cell wall fibers outside the plasma membrane, not by the contractile ring. Here we show that one function of the ring is to spatially coordinate septum cell wall assembly. We develop an improved method for live-cell imaging of the division apparatus by orienting the rod-shaped cells vertically using microfabricated wells. We observe that the septum hole and ring are circular and centered in wild-type cells and that in the absence of a functional ring, the septum continues to ingress but in a disorganized and asymmetric manner. By manipulating the cleavage furrow into different shapes, we show that the ring promotes local septum growth in a curvature-dependent manner, allowing even a misshapen septum to grow into a more regular shape. This curvature-dependent growth suggests a model in which contractile forces of the ring shape the septum cell wall by stimulating the cell wall machinery in a mechanosensitive manner. Mechanical regulation of the cell wall assembly may have general relevance to the morphogenesis of walled cells.
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Affiliation(s)
- Zhou Zhou
- Department of Microbiology and Immunology, Columbia University College of Physicians and Surgeons, New York, NY 10032
| | - Emilia Laura Munteanu
- Department of Microbiology and Immunology, Columbia University College of Physicians and Surgeons, New York, NY 10032
| | - Jun He
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Tristan Ursell
- Department of Bioengineering, Stanford University, Stanford, CA 94305
| | - Mark Bathe
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Kerwyn Casey Huang
- Department of Bioengineering, Stanford University, Stanford, CA 94305 Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA 94305
| | - Fred Chang
- Department of Microbiology and Immunology, Columbia University College of Physicians and Surgeons, New York, NY 10032
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13
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Stachowiak MR, Laplante C, Chin HF, Guirao B, Karatekin E, Pollard TD, O'Shaughnessy B. Mechanism of cytokinetic contractile ring constriction in fission yeast. Dev Cell 2014; 29:547-561. [PMID: 24914559 DOI: 10.1016/j.devcel.2014.04.021] [Citation(s) in RCA: 116] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2013] [Revised: 02/28/2014] [Accepted: 04/16/2014] [Indexed: 11/24/2022]
Abstract
Cytokinesis involves constriction of a contractile actomyosin ring. The mechanisms generating ring tension and setting the constriction rate remain unknown because the organization of the ring is poorly characterized, its tension was rarely measured, and constriction is coupled to other processes. To isolate ring mechanisms, we studied fission yeast protoplasts, in which constriction occurs without the cell wall. Exploiting the absence of cell wall and actin cortex, we measured ring tension and imaged ring organization, which was dynamic and disordered. Computer simulations based on the amounts and biochemical properties of the key proteins showed that they spontaneously self-organize into a tension-generating bundle. Together with rapid component turnover, the self-organization mechanism continuously reassembles and remodels the constricting ring. Ring constriction depended on cell shape, revealing that the ring operates close to conditions of isometric tension. Thus, the fission yeast ring sets its own tension, but other processes set the constriction rate.
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Affiliation(s)
- Matthew R Stachowiak
- Department of Chemical Engineering, Columbia University, New York, NY 10027, USA
| | - Caroline Laplante
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520, USA
| | - Harvey F Chin
- Department of Chemical Engineering, Columbia University, New York, NY 10027, USA
| | - Boris Guirao
- Department of Chemical Engineering, Columbia University, New York, NY 10027, USA
| | - Erdem Karatekin
- Department of Cellular and Molecular Physiology, School of Medicine, Yale University, New Haven, CT 06520, USA; Nanobiology Institute, Yale University, New Haven, CT 06520, USA
| | - Thomas D Pollard
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520, USA; Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA; Department of Cell Biology, Yale University, New Haven, CT 06520, USA
| | - Ben O'Shaughnessy
- Department of Chemical Engineering, Columbia University, New York, NY 10027, USA.
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14
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Korobova F, Gauvin TJ, Higgs HN. A role for myosin II in mammalian mitochondrial fission. Curr Biol 2014; 24:409-14. [PMID: 24485837 DOI: 10.1016/j.cub.2013.12.032] [Citation(s) in RCA: 185] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2013] [Revised: 11/11/2013] [Accepted: 12/16/2013] [Indexed: 01/26/2023]
Abstract
Mitochondria are dynamic organelles, undergoing both fission and fusion regularly in interphase cells. Mitochondrial fission is thought to be part of a quality-control mechanism whereby damaged mitochondrial components are segregated from healthy components in an individual mitochondrion, followed by mitochondrial fission and degradation of the damaged daughter mitochondrion. Fission also plays a role in apoptosis. Defects in mitochondrial dynamics can lead to neurodegenerative diseases such as Alzheimer's disease. Mitochondrial fission requires the dynamin GTPase Drp1, which assembles in a ring around the mitochondrion and appears to constrict both outer and inner mitochondrial membranes. However, mechanisms controlling Drp1 assembly on mammalian mitochondria are unclear. Recent results show that actin polymerization, driven by the endoplasmic reticulum-bound formin protein INF2, stimulates Drp1 assembly at fission sites. Here, we show that myosin II also plays a role in fission. Chemical inhibition by blebbistatin or small interfering RNA (siRNA)-mediated suppression of myosin IIA or myosin IIB causes an increase in mitochondrial length in both control cells and cells expressing constitutively active INF2. Active myosin II accumulates in puncta on mitochondria in an actin- and INF2-dependent manner. In addition, myosin II inhibition decreases Drp1 association with mitochondria. Based on these results, we propose a mechanistic model in which INF2-mediated actin polymerization leads to myosin II recruitment and constriction at the fission site, enhancing subsequent Drp1 accumulation and fission.
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Affiliation(s)
- Farida Korobova
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA
| | - Timothy J Gauvin
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA
| | - Henry N Higgs
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA.
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15
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Muñoz J, Cortés JCG, Sipiczki M, Ramos M, Clemente-Ramos JA, Moreno MB, Martins IM, Pérez P, Ribas JC. Extracellular cell wall β(1,3)glucan is required to couple septation to actomyosin ring contraction. ACTA ACUST UNITED AC 2013; 203:265-82. [PMID: 24165938 PMCID: PMC3812973 DOI: 10.1083/jcb.201304132] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
β(1,3)glucan is critical for contractile ring positioning and for coupling septum synthesis to constriction of the contractile ring and plasma membrane extension during cytokinesis. Cytokinesis has been extensively studied in different models, but the role of the extracellular cell wall is less understood. Here we studied this process in fission yeast. The essential protein Bgs4 synthesizes the main cell wall β(1,3)glucan. We show that Bgs4-derived β(1,3)glucan is required for correct and stable actomyosin ring positioning in the cell middle, before the start of septum formation and anchorage to the cell wall. Consequently, β(1,3)glucan loss generated ring sliding, oblique positioned rings and septa, misdirected septum synthesis indicative of relaxed rings, and uncoupling between a fast ring and membrane ingression and slow septum synthesis, suggesting that cytokinesis can progress with defective septum pushing and/or ring pulling forces. Moreover, Bgs4-derived β(1,3)glucan is essential for secondary septum formation and correct primary septum completion. Therefore, our results show that extracellular β(1,3)glucan is required for cytokinesis to connect the cell wall with the plasma membrane and for contractile ring function, as proposed for the equivalent extracellular matrix in animal cells.
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Affiliation(s)
- Javier Muñoz
- Instituto de Biología Funcional y Genómica, Consejo Superior de Investigaciones Científicas/Universidad de Salamanca, 37007 Salamanca, Spain
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16
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Stark BC, James ML, Pollard LW, Sirotkin V, Lord M. UCS protein Rng3p is essential for myosin-II motor activity during cytokinesis in fission yeast. PLoS One 2013; 8:e79593. [PMID: 24244528 PMCID: PMC3828377 DOI: 10.1371/journal.pone.0079593] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2013] [Accepted: 09/27/2013] [Indexed: 12/25/2022] Open
Abstract
UCS proteins have been proposed to operate as co-chaperones that work with Hsp90 in the de novo folding of myosin motors. The fission yeast UCS protein Rng3p is essential for actomyosin ring assembly and cytokinesis. Here we investigated the role of Rng3p in fission yeast myosin-II (Myo2p) motor activity. Myo2p isolated from an arrested rng3-65 mutant was capable of binding actin, yet lacked stability and activity based on its expression levels and inactivity in ATPase and actin filament gliding assays. Myo2p isolated from a myo2-E1 mutant (a mutant hyper-sensitive to perturbation of Rng3p function) showed similar behavior in the same assays and exhibited an altered motor conformation based on limited proteolysis experiments. We propose that Rng3p is not required for the folding of motors per se, but instead works to ensure the activity of intrinsically unstable myosin-II motors. Rng3p is specific to conventional myosin-II and the actomyosin ring, and is not required for unconventional myosin motor function at other actin structures. However, artificial destabilization of myosin-I motors at endocytic actin patches (using a myo1-E1 mutant) led to recruitment of Rng3p to patches. Thus, while Rng3p is specific to myosin-II, UCS proteins are adaptable and can respond to changes in the stability of other myosin motors.
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Affiliation(s)
- Benjamin C. Stark
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont, United States of America
| | - Michael L. James
- Department of Cell and Developmental Biology, State University of New York - Upstate Medical University, Syracuse, New York, United States of America
| | - Luther W. Pollard
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont, United States of America
| | - Vladimir Sirotkin
- Department of Cell and Developmental Biology, State University of New York - Upstate Medical University, Syracuse, New York, United States of America
| | - Matthew Lord
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont, United States of America
- * E-mail:
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17
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Biphasic assembly of the contractile apparatus during the first two cell division cycles in zebrafish embryos. ZYGOTE 2013; 22:218-28. [DOI: 10.1017/s0967199413000051] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
SummaryThe large and optically clear embryos of the zebrafish provide an excellent model system in which to study the dynamic assembly of the essential contractile band components, actin and myosin, via double fluorescent labelling in combination with confocal microscopy. We report the rapid appearance (i.e. within <2 min) of a restricted arc of F-actin patches along the prospective furrow plane in a central, apical region of the blastodisc cortex. These patches then fused with each other end-to-end forming multiple actin cables, which were subsequently bundled together forming an F-actin band. During this initial assembly phase, the F-actin-based structure did not elongate laterally, but was still restricted to an arc extending ~15° either side of the blastodisc apex. This initial assembly phase was then followed by an extension phase, where additional F-actin patches were added to each end of the original arc, thus extending it out to the edges of the blastodisc. The dynamics of phosphorylated myosin light chain 2 (MLC2) recruitment to this F-actin scaffold also reflect the two-phase nature of the contractile apparatus assembly. MLC2 was not associated with the initial F-actin arc, but MLC2 clusters were recruited and assembled into the extending ends of the band. We propose that the MLC2-free central region of the contractile apparatus acts to position and then extend the cleavage furrow in the correct plane, while the actomyosin ends alone generate the force required for furrow ingression. This biphasic assembly strategy may be required to successfully divide the early cells of large embryos.
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18
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Lee IJ, Coffman VC, Wu JQ. Contractile-ring assembly in fission yeast cytokinesis: Recent advances and new perspectives. Cytoskeleton (Hoboken) 2012; 69:751-63. [PMID: 22887981 DOI: 10.1002/cm.21052] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2012] [Accepted: 07/16/2012] [Indexed: 11/07/2022]
Abstract
The fission yeast Schizosaccharomyces pombe is an excellent model organism to study cytokinesis. Here, we review recent advances on contractile-ring assembly in fission yeast. First, we summarize the assembly of cytokinesis nodes, the precursors of a normal contractile ring. IQGAP Rng2 and myosin essential light chain Cdc4 are recruited by the anillin-like protein Mid1, followed by the addition of other cytokinesis node proteins. Mid1 localization on the plasma membrane is stabilized by interphase node proteins. Second, we discuss proteins and processes that contribute to the search, capture, pull, and release mechanism of contractile-ring assembly. Actin filaments nucleated by formin Cdc12, the motor activity of myosin-II, the stiffness of the actin network, and severing of actin filaments by cofilin all play essential roles in contractile-ring assembly. Finally, we discuss the Mid1-independent pathway for ring assembly, and the possible mechanisms underlying the ring maturation and constriction. Collectively, we provide an overview of the current understanding of contractile-ring assembly and uncover future directions in studying cytokinesis in fission yeast.
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Affiliation(s)
- I-Ju Lee
- Department of Molecular Genetics, The Ohio State University, Columbus, Ohio, USA
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19
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Phosphorylation of myosin II regulatory light chain controls its accumulation, not that of actin, at the contractile ring in HeLa cells. Exp Cell Res 2012; 318:915-24. [PMID: 22374324 DOI: 10.1016/j.yexcr.2012.02.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2011] [Revised: 02/02/2012] [Accepted: 02/12/2012] [Indexed: 11/24/2022]
Abstract
During cytokinesis in eukaryotic cells, an actomyosin-based contractile ring (CR) is assembled along the equator of the cell. Myosin II ATPase activity is stimulated by the phosphorylation of the myosin II regulatory light chain (MRLC) in vitro, and phosphorylated MRLC localizes at the CR in various types of cells. Previous studies have determined that phosphorylated MRLC plays an important role in CR furrowing. However, the role of phosphorylated MRLC in CR assembly remains unknown. Here, we have used confocal microscopy to observe dividing HeLa cells expressing fluorescent protein-tagged MRLC mutants and actin during CR assembly near the cortex. Di-phosphomimic MRLC accumulated at the cell equator earlier than non-phosphorylatable MRLC and actin. Interestingly, perturbation of myosin II activity by non-phosphorylatable MRLC expression or treatment with blebbistatin, a myosin II inhibitor, did not alter the time of actin accumulation at the cell equator. Furthermore, inhibition of actin polymerization by treatment with latrunculin A had no effect on MRLC accumulation at the cell equator. Taken together, these data suggest that phosphorylated MRLC temporally controls its own accumulation, but not that of actin, in cultured mammalian cells.
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20
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Uyeda TQP, Iwadate Y, Umeki N, Nagasaki A, Yumura S. Stretching actin filaments within cells enhances their affinity for the myosin II motor domain. PLoS One 2011; 6:e26200. [PMID: 22022566 PMCID: PMC3192770 DOI: 10.1371/journal.pone.0026200] [Citation(s) in RCA: 113] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2011] [Accepted: 09/22/2011] [Indexed: 11/18/2022] Open
Abstract
To test the hypothesis that the myosin II motor domain (S1) preferentially binds to specific subsets of actin filaments in vivo, we expressed GFP-fused S1 with mutations that enhanced its affinity for actin in Dictyostelium cells. Consistent with the hypothesis, the GFP-S1 mutants were localized along specific portions of the cell cortex. Comparison with rhodamine-phalloidin staining in fixed cells demonstrated that the GFP-S1 probes preferentially bound to actin filaments in the rear cortex and cleavage furrows, where actin filaments are stretched by interaction with endogenous myosin II filaments. The GFP-S1 probes were similarly enriched in the cortex stretched passively by traction forces in the absence of myosin II or by external forces using a microcapillary. The preferential binding of GFP-S1 mutants to stretched actin filaments did not depend on cortexillin I or PTEN, two proteins previously implicated in the recruitment of myosin II filaments to stretched cortex. These results suggested that it is the stretching of the actin filaments itself that increases their affinity for the myosin II motor domain. In contrast, the GFP-fused myosin I motor domain did not localize to stretched actin filaments, which suggests different preferences of the motor domains for different structures of actin filaments play a role in distinct intracellular localizations of myosin I and II. We propose a scheme in which the stretching of actin filaments, the preferential binding of myosin II filaments to stretched actin filaments, and myosin II-dependent contraction form a positive feedback loop that contributes to the stabilization of cell polarity and to the responsiveness of the cells to external mechanical stimuli.
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Affiliation(s)
- Taro Q P Uyeda
- National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan.
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21
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East DA, Mulvihill DP. Regulation and function of the fission yeast myosins. J Cell Sci 2011; 124:1383-90. [PMID: 21502135 DOI: 10.1242/jcs.078527] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
It is now quarter of a century since the actin cytoskeleton was first described in the fission yeast, Schizosaccharomyces pombe. Since then, a substantial body of research has been undertaken on this tractable model organism, extending our knowledge of the organisation and function of the actomyosin cytoskeleton in fission yeast and eukaryotes in general. Yeast represents one of the simplest eukaryotic model systems that has been characterised to date, and its genome encodes genes for homologues of the majority of actin regulators and actin-binding proteins found in metazoan cells. The ease with which diverse methodologies can be used, together with the small number of myosins, makes fission yeast an attractive model system for actomyosin research and provides the opportunity to fully understand the biochemical and functional characteristics of all myosins within a single cell type. In this Commentary, we examine the differences between the five S. pombe myosins, and focus on how these reflect the diversity of their functions. We go on to examine the role that the actin cytoskeleton plays in regulating the myosin motor activity and function, and finally explore how research in this simple unicellular organism is providing insights into the substantial impacts these motors can have on development and viability in multicellular higher-order eukaryotes.
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Affiliation(s)
- Daniel A East
- School of Biosciences, University of Kent, Canterbury, Kent CT2 7NJ, UK
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22
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Padmanabhan A, Bakka K, Sevugan M, Naqvi N, D'souza V, Tang X, Mishra M, Balasubramanian M. IQGAP-Related Rng2p Organizes Cortical Nodes and Ensures Position of Cell Division in Fission Yeast. Curr Biol 2011; 21:467-72. [DOI: 10.1016/j.cub.2011.01.059] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2010] [Revised: 12/22/2010] [Accepted: 01/24/2011] [Indexed: 12/01/2022]
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23
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Goyal A, Takaine M, Simanis V, Nakano K. Dividing the spoils of growth and the cell cycle: The fission yeast as a model for the study of cytokinesis. Cytoskeleton (Hoboken) 2011; 68:69-88. [PMID: 21246752 PMCID: PMC3044818 DOI: 10.1002/cm.20500] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2010] [Revised: 12/15/2010] [Accepted: 12/20/2010] [Indexed: 12/12/2022]
Abstract
Cytokinesis is the final stage of the cell cycle, and ensures completion of both genome segregation and organelle distribution to the daughter cells. Cytokinesis requires the cell to solve a spatial problem (to divide in the correct place, orthogonally to the plane of chromosome segregation) and a temporal problem (to coordinate cytokinesis with mitosis). Defects in the spatiotemporal control of cytokinesis may cause cell death, or increase the risk of tumor formation [Fujiwara et al., 2005 (Fujiwara T, Bandi M, Nitta M, Ivanova EV, Bronson RT, Pellman D. 2005. Cytokinesis failure generating tetraploids promotes tumorigenesis in p53-null cells. Nature 437:1043–1047); reviewed by Ganem et al., 2007 (Ganem NJ, Storchova Z, Pellman D. 2007. Tetraploidy, aneuploidy and cancer. Curr Opin Genet Dev 17:157–162.)]. Asymmetric cytokinesis, which permits the generation of two daughter cells that differ in their shape, size and properties, is important both during development, and for cellular homeostasis in multicellular organisms [reviewed by Li, 2007 (Li R. 2007. Cytokinesis in development and disease: variations on a common theme. Cell Mol Life Sci 64:3044–3058)]. The principal focus of this review will be the mechanisms of cytokinesis in the mitotic cycle of the yeast Schizosaccharomyces pombe. This simple model has contributed significantly to our understanding of how the cell cycle is regulated, and serves as an excellent model for studying aspects of cytokinesis. Here we will discuss the state of our knowledge of how the contractile ring is assembled and disassembled, how it contracts, and what we know of the regulatory mechanisms that control these events and assure their coordination with chromosome segregation.
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Affiliation(s)
- Anupama Goyal
- EPFL SV ISREC UPSIMSV2.1830, Station 19, CH 1015 Lausanne, Switzerland
| | - Masak Takaine
- Structural Biosciences, Graduate School of Environmental and Life Sciences, University of Tsukuba1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8577, Japan
| | - Viesturs Simanis
- EPFL SV ISREC UPSIMSV2.1830, Station 19, CH 1015 Lausanne, Switzerland
| | - Kentaro Nakano
- Structural Biosciences, Graduate School of Environmental and Life Sciences, University of Tsukuba1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8577, Japan
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24
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Fang X, Luo J, Nishihama R, Wloka C, Dravis C, Travaglia M, Iwase M, Vallen EA, Bi E. Biphasic targeting and cleavage furrow ingression directed by the tail of a myosin II. J Cell Biol 2010; 191:1333-50. [PMID: 21173112 PMCID: PMC3010076 DOI: 10.1083/jcb.201005134] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2010] [Accepted: 11/29/2010] [Indexed: 02/07/2023] Open
Abstract
Cytokinesis in animal and fungal cells utilizes a contractile actomyosin ring (AMR). However, how myosin II is targeted to the division site and promotes AMR assembly, and how the AMR coordinates with membrane trafficking during cytokinesis, remains poorly understood. Here we show that Myo1 is a two-headed myosin II in Saccharomyces cerevisiae, and that Myo1 localizes to the division site via two distinct targeting signals in its tail that act sequentially during the cell cycle. Before cytokinesis, Myo1 localization depends on the septin-binding protein Bni5. During cytokinesis, Myo1 localization depends on the IQGAP Iqg1. We also show that the Myo1 tail is sufficient for promoting the assembly of a "headless" AMR, which guides membrane deposition and extracellular matrix remodeling at the division site. Our study establishes a biphasic targeting mechanism for myosin II and highlights an underappreciated role of the AMR in cytokinesis beyond force generation.
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Affiliation(s)
- Xiaodong Fang
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
| | - Jianying Luo
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
| | - Ryuichi Nishihama
- Department of Genetics, Stanford University of School of Medicine, Stanford, CA 94305
| | - Carsten Wloka
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
- Department of Biology, Chemistry and Pharmacy, Free University of Berlin, D-14195 Berlin, Germany
| | - Christopher Dravis
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
| | - Mirko Travaglia
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
| | - Masayuki Iwase
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
| | | | - Erfei Bi
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
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25
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Coulton AT, East DA, Galinska-Rakoczy A, Lehman W, Mulvihill DP. The recruitment of acetylated and unacetylated tropomyosin to distinct actin polymers permits the discrete regulation of specific myosins in fission yeast. J Cell Sci 2010; 123:3235-43. [PMID: 20807799 DOI: 10.1242/jcs.069971] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Tropomyosin (Tm) is a conserved dimeric coiled-coil protein, which forms polymers that curl around actin filaments in order to regulate actomyosin function. Acetylation of the Tm N-terminal methionine strengthens end-to-end bonds, which enhances actin binding as well as the ability of Tm to regulate myosin motor activity in both muscle and non-muscle cells. In this study we explore the function of each Tm form within fission yeast cells. Electron microscopy and live cell imaging revealed that acetylated and unacetylated Tm associate with distinct actin structures within the cell, and that each form has a profound effect upon the shape and integrity of the polymeric actin filament. We show that, whereas Tm acetylation is required to regulate the in vivo motility of class II myosins, acetylated Tm had no effect on the motility of class I and V myosins. These findings illustrate a novel Tm-acetylation-state-dependent mechanism for regulating specific actomyosin cytoskeletal interactions.
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Affiliation(s)
- Arthur T Coulton
- School of Biosciences, University of Kent, Canterbury, Kent, CT2 7NJ, UK
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26
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Cooperation between the septins and the actomyosin ring and role of a cell-integrity pathway during cell division in fission yeast. Genetics 2010; 186:897-915. [PMID: 20739711 DOI: 10.1534/genetics.110.119842] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
A major question about cytokinesis concerns the role of the septin proteins, which localize to the division site in all animal and fungal cells but are essential for cytokinesis only in some cell types. For example, in Schizosaccharomyces pombe, four septins localize to the division site, but deletion of the four genes produces only a modest delay in cell separation. To ask if the S. pombe septins function redundantly in cytokinesis, we conducted a synthetic-lethal screen in a septin-deficient strain and identified seven mutations. One mutation affects Cdc4, a myosin light chain that is an essential component of the cytokinetic actomyosin ring. Five others cause frequent cell lysis during cell separation and map to two loci. These mutations and their dosage suppressors define a signaling pathway (including Rho1 and a novel arrestin) for repairing cell-wall damage. The seventh mutation affects the poorly understood RNA-binding protein Scw1 and severely delays cell separation when combined either with a septin mutation or with a mutation affecting the septin-interacting, anillin-like protein Mid2, suggesting that Scw1 functions in a pathway parallel to that of the septins. Taken together, our results suggest that the S. pombe septins participate redundantly in one or more pathways that cooperate with the actomyosin ring during cytokinesis and that a septin defect causes septum defects that can be repaired effectively only when the cell-integrity pathway is intact.
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Differential Regulation of Unconventional Fission Yeast Myosins via the Actin Track. Curr Biol 2010; 20:1423-31. [DOI: 10.1016/j.cub.2010.07.026] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2010] [Revised: 07/13/2010] [Accepted: 07/14/2010] [Indexed: 11/23/2022]
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Coffman VC, Nile AH, Lee IJ, Liu H, Wu JQ. Roles of formin nodes and myosin motor activity in Mid1p-dependent contractile-ring assembly during fission yeast cytokinesis. Mol Biol Cell 2010; 20:5195-210. [PMID: 19864459 DOI: 10.1091/mbc.e09-05-0428] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Two prevailing models have emerged to explain the mechanism of contractile-ring assembly during cytokinesis in the fission yeast Schizosaccharomyces pombe: the spot/leading cable model and the search, capture, pull, and release (SCPR) model. We tested some of the basic assumptions of the two models. Monte Carlo simulations of the SCPR model require that the formin Cdc12p is present in >30 nodes from which actin filaments are nucleated and captured by myosin-II in neighboring nodes. The force produced by myosin motors pulls the nodes together to form a compact contractile ring. Live microscopy of cells expressing Cdc12p fluorescent fusion proteins shows for the first time that Cdc12p localizes to a broad band of 30-50 dynamic nodes, where actin filaments are nucleated in random directions. The proposed progenitor spot, essential for the spot/leading cable model, usually disappears without nucleating actin filaments. alpha-Actinin ain1 deletion cells form a normal contractile ring through nodes in the absence of the spot. Myosin motor activity is required to condense the nodes into a contractile ring, based on slower or absent node condensation in myo2-E1 and UCS rng3-65 mutants. Taken together, these data provide strong support for the SCPR model of contractile-ring formation in cytokinesis.
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Affiliation(s)
- Valerie C Coffman
- Department of Molecular Genetics, Graduate Program of Molecular, Cellular, and Developmental Biology, The Ohio State University, Columbus, OH 43210, USA
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Stark BC, Sladewski TE, Pollard LW, Lord M. Tropomyosin and myosin-II cellular levels promote actomyosin ring assembly in fission yeast. Mol Biol Cell 2010; 21:989-1000. [PMID: 20110347 PMCID: PMC2836979 DOI: 10.1091/mbc.e09-10-0852] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
A combination of in vivo and in vitro approaches were used to show how tropomyosin and myosin-II contribute to contractile ring assembly in fission yeast. Ring assembly is sensitive to changes in the cellular levels of myosin-II, and tropomyosin works to maximize myosin-II motor function during this process by stabilizing actomyosin interactions. Myosin-II (Myo2p) and tropomyosin are essential for contractile ring formation and cytokinesis in fission yeast. Here we used a combination of in vivo and in vitro approaches to understand how these proteins function at contractile rings. We find that ring assembly is delayed in Myo2p motor and tropomyosin mutants, but occurs prematurely in cells engineered to express two copies of myo2. Thus, the timing of ring assembly responds to changes in Myo2p cellular levels and motor activity, and the emergence of tropomyosin-bound actin filaments. Doubling Myo2p levels suppresses defects in ring assembly associated with a tropomyosin mutant, suggesting a role for tropomyosin in maximizing Myo2p function. Correspondingly, tropomyosin increases Myo2p actin affinity and ATPase activity and promotes Myo2p-driven actin filament gliding in motility assays. Tropomyosin achieves this by favoring the strong actin-bound state of Myo2p. This mode of regulation reflects a role for tropomyosin in specifying and stabilizing actomyosin interactions, which facilitates contractile ring assembly in the fission yeast system.
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Affiliation(s)
- Benjamin C Stark
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405, USA
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Cytokinesis and the contractile ring in fission yeast: towards a systems-level understanding. Trends Microbiol 2009; 18:38-45. [PMID: 19959363 DOI: 10.1016/j.tim.2009.10.002] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2009] [Revised: 10/18/2009] [Accepted: 10/20/2009] [Indexed: 11/20/2022]
Abstract
Cytokinesis, the final stage of the cell division cycle, requires the proper placement, assembly and contraction of an actomyosin-based contractile ring. Conserved sets of cytokinesis proteins and pathways have now been identified and characterized functionally. Additionally, fluorescent protein fusion technology enables quantitative high-resolution imaging of protein dynamics in living cells. For these reasons, the study of cytokinesis is now ripe for quantitative, systems-level approaches. Here, we review our current understanding of the molecular mechanisms of contractile ring dynamics in the model organism Schizosaccharomyces pombe (fission yeast), focusing on recent examples that illustrate a synergistic integration of quantitative experimental data with computational modeling. A picture of a highly dynamic and integrated system consisting of overlapping networks is beginning to emerge, the detailed nature of which remains to be elucidated.
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Park JS, Steinbach SK, Desautels M, Hemmingsen SM. Essential role for Schizosaccharomyces pombe pik1 in septation. PLoS One 2009; 4:e6179. [PMID: 19587793 PMCID: PMC2704394 DOI: 10.1371/journal.pone.0006179] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2009] [Accepted: 05/24/2009] [Indexed: 11/29/2022] Open
Abstract
Background Schizosaccharomyces pombe pik1 encodes a phosphatidylinositol 4-kinase, reported to bind Cdc4, but not Cdc4G107S. Principal Findings Gene deletion revealed that pik1 is essential. In cells with pik1 deleted, ectopic expression of a loss-of-function allele, created by fusion to a temperature-sensitive dihydrofolate reductase, allowed normal cell proliferation at 25°C. At 36°C, cells arrested with abnormally thick, misplaced or supernumerary septa, indicating a defect late in septation. In addition to being Golgi associated, ectopically expressed GFP-tagged Pik1 was observed at the medial cell plane late in cytokinesis. New alleles, created by site-directed mutagenesis, were expressed ectopically. Lipid kinase and Cdc4-binding activity assays were performed. Pik1D709A was kinase-dead, but bound Cdc4. Pik1R838A did not bind Cdc4, but was an active kinase. Genomic integration of these substitutions in S. pombe and complementation studies in Saccharomyces cerevisiae pik1-101 cells revealed that D709 is essential in both cases while R838 is dispensable. In S. pombe, ectopic expression of pik1 was dominantly lethal; while, pik1D709A,R838A was innocuous, pik1R838A was almost innocuous, and pik1D709A produced partial lethality and septation defects. The pik1 ectopic expression lethal phenotype was suppressed in cdc4G107S. Thus, D709 is essential for kinase activity and septation. Conclusions Pik1 kinase activity is required for septation. The Pik1 R838 residue is required for important protein-protein interactions, possibly with Cdc4.
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Affiliation(s)
- Jae-Sook Park
- Department of Microbiology and Immunology, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
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Sladewski TE, Previs MJ, Lord M. Regulation of fission yeast myosin-II function and contractile ring dynamics by regulatory light-chain and heavy-chain phosphorylation. Mol Biol Cell 2009; 20:3941-52. [PMID: 19570908 DOI: 10.1091/mbc.e09-04-0346] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
We investigated the role of regulatory light-chain (Rlc1p) and heavy-chain phosphorylation in controlling fission yeast myosin-II (Myo2p) motor activity and function during cytokinesis. Phosphorylation of Rlc1p leads to a fourfold increase in Myo2p's in vitro motility rate, which ensures effective contractile ring constriction and function. Surprisingly, unlike with smooth muscle and nonmuscle myosin-II, RLC phosphorylation does not influence the actin-activated ATPase activity of Myo2p. A truncated form of Rlc1p lacking its extended N-terminal regulatory region (including phosphorylation sites) supported maximal Myo2p in vitro motility rates and normal contractile ring function. Thus, the unphosphorylated N-terminal extension of Rlc1p can uncouple the ATPase and motility activities of Myo2p. We confirmed the identity of one out of two putative heavy-chain phosphorylation sites previously reported to control Myo2p function and cytokinesis. Although in vitro studies indicated that phosphorylation at Ser-1444 is not needed for Myo2p motor activity, phosphorylation at this site promotes the initiation of contractile ring constriction.
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Affiliation(s)
- Thomas E Sladewski
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405, USA
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33
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Asano S, Hamao K, Hosoya H. Direct evidence for roles of phosphorylated regulatory light chain of myosin II in furrow ingression during cytokinesis in HeLa cells. Genes Cells 2009; 14:555-68. [PMID: 19371382 DOI: 10.1111/j.1365-2443.2009.01288.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Phosphorylation of myosin II is thought to play an important role in cytokinesis. Although it is well known that phosphorylated regulatory light chain of myosin II (P-MRLC) localizes along the contractile ring, it is not clear how P-MRLC controls myosin II and F-actin in furrow ingression during cytokinesis. To elucidate roles of P-MRLC in furrow ingression, HeLa cells transfected with EGFP-tagged wild-type or each MRLC mutant were observed using a live-imaging microscope. Time-lapse observation revealed that a delay of furrow ingression was observed in the nonphosphorylatable form of MRLC (AA-MRLC)-expressing cell but not in the wild-type or phospho-mimic MRLC-expressing cell. Among each form of MRLC-expressing cell, the total amount of P-MRLC including phospho-mimic MRLCs was smallest in the cell expressing AA-MRLC. However, the amount of F-actin and myosin II at the contractile ring in the AA-MRLC-expressing cell was the same as that in the normal cell. Interestingly, delay of furrow ingression by a Rho-kinase inhibitor, Y27632, was rescued by phospho-mimic MRLCs. These results suggest that the P-MRLC is essential for the progress of furrow ingression but not the retainment of F-actin and myosin II in the contractile ring of dividing HeLa cells.
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Affiliation(s)
- Satoshi Asano
- Department of Biological Science, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
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Roberts-Galbraith RH, Gould KL. Stepping into the ring: the SIN takes on contractile ring assembly. Genes Dev 2009; 22:3082-8. [PMID: 19056889 DOI: 10.1101/gad.1748908] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The septation initiation network (SIN) regulates the timing of septum formation in Schizosaccharomyces pombe. However, whether and how the SIN functions in contractile ring formation has remained unclear. In this issue of Genes & Development, Hachet and Simanis (3205-3216) demonstrate that the SIN acts downstream from the Plo1 kinase to control a final step in contractile ring assembly. Furthermore, their careful analysis of contractile ring formation may help bridge two existing models of cytokinetic ring formation.
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Affiliation(s)
- Rachel H Roberts-Galbraith
- Howard Hughes Medical Institute, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
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35
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Satoh R, Morita T, Takada H, Kita A, Ishiwata S, Doi A, Hagihara K, Taga A, Matsumura Y, Tohda H, Sugiura R. Role of the RNA-binding protein Nrd1 and Pmk1 mitogen-activated protein kinase in the regulation of myosin mRNA stability in fission yeast. Mol Biol Cell 2009; 20:2473-85. [PMID: 19279143 DOI: 10.1091/mbc.e08-09-0893] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Myosin II is an essential component of the actomyosin contractile ring and plays a crucial role in cytokinesis by generating the forces necessary for contraction of the actomyosin ring. Cdc4 is an essential myosin II light chain in fission yeast and is required for cytokinesis. In various eukaryotes, the phosphorylation of myosin is well documented as a primary means of activating myosin II, but little is known about the regulatory mechanisms of Cdc4. Here, we isolated Nrd1, an RNA-binding protein with RNA-recognition motifs, as a multicopy suppressor of cdc4 mutants. Notably, we demonstrated that Nrd1 binds and stabilizes Cdc4 mRNA, thereby suppressing the cytokinesis defects of the cdc4 mutants. Importantly, Pmk1 mitogen-activated protein kinase (MAPK) directly phosphorylates Nrd1, thereby negatively regulating the binding activity of Nrd1 to Cdc4 mRNA. Consistently, the inactivation of Pmk1 MAPK signaling, as well as Nrd1 overexpression, stabilized the Cdc4 mRNA level, thereby suppressing the cytokinesis defects associated with the cdc4 mutants. In addition, we demonstrated the cell cycle-dependent regulation of Pmk1/Nrd1 signaling. Together, our results indicate that Nrd1 plays a role in the regulation of Cdc4 mRNA stability; moreover, our study is the first to demonstrate the posttranscriptional regulation of myosin expression by MAPK signaling.
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Affiliation(s)
- Ryosuke Satoh
- Laboratory of Molecular Pharmacogenomics, and Laboratory of Pharmaceutical Analytical Chemistry, School of Pharmaceutical Sciences, Kinki University, Higashi-Osaka 577-8502, Japan
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36
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Abstract
Tropomyosins were discovered as regulators of actomyosin contractility in muscle cells, making yeasts and other fungi seem unlikely to harbor such proteins. Fungal cells are encased in a rigid cell wall and do not engage in the same sorts of contractile shape changes of animal cells. However, discovery of actin and myosin in yeast raised the possibility for a role for tropomyosin in regulating their interaction. Through a biochemical search, fungal tropomyosins were identified with strong similarities to their animal counterparts in terms ofprotein structure and physical properties. Two particular fungi, the buddingyeast Saccharomyces cerevisiae and the fission yeast Schizosaccharomyces pombe, have provided powerful genetic systems for studying tropomyosins in nonmetazoans. In these yeasts, tropomyosins associate with subsets ofactin filamentous structures. Mutational studies oftropomyosin genes and biochemical assays of purified proteins point to roles for these proteins as factors that stabilize actin filaments, promote actin-based structures of particular architecture and help maintain distinct biochemical identities among different filament populations. Tropomyosin-enriched filaments are the cytoskeletal structures that promote the major cell shape changes of these organisms: polarized growth and cell division.
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Affiliation(s)
- David Pruyne
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, USA.
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37
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Low CP, Shui G, Liew LP, Buttner S, Madeo F, Dawes IW, Wenk MR, Yang H. Caspase-dependent and -independent lipotoxic cell-death pathways in fission yeast. J Cell Sci 2008; 121:2671-84. [PMID: 18653539 DOI: 10.1242/jcs.028977] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Understanding the mechanisms underlying lipid-induced cell death has significant implications in both cell biology and human diseases. Previously, we showed that fission-yeast Schizosaccharomyces pombe cells deficient in triacylglycerol synthesis display apoptotic markers upon entry into stationary phase. Here, we characterize the sequential molecular events that take place at the onset of cell death in S. pombe, including a surge of diacylglycerol, post-mitotic arrest, alterations in mitochondrial activities and in intracellular redox balance, chromatin condensation, nuclear-envelope fragmentation, and eventually plasma-membrane permeabilization. Our results demonstrated active roles of mitochondria and reactive oxygen species in cell death, and identified novel cell-death regulators--including metacaspase Pca1, BH3-domain protein Rad9, and diacylglycerol-binding proteins Pck1 and Bzz1. Most importantly, we show that, under different conditions and stimuli, failure to maintain intracellular-lipid homeostasis can lead to cell death with different phenotypic manifestations, genetic criteria and cellular mechanisms, pointing to the existence of multiple lipotoxic pathways in this organism. Our study represents the first in-depth analysis of cell-death pathways in S. pombe.
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Affiliation(s)
- Choon Pei Low
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117597, Republic of Singapore
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38
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Yonetani A, Lustig RJ, Moseley JB, Takeda T, Goode BL, Chang F. Regulation and targeting of the fission yeast formin cdc12p in cytokinesis. Mol Biol Cell 2008; 19:2208-19. [PMID: 18305104 DOI: 10.1091/mbc.e07-07-0731] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Formins are conserved actin nucleators which promote the assembly of actin filaments for the formation of diverse actin structures. In fission yeast Schizosaccharomyces pombe, the formin cdc12p is required specifically in assembly of the actin-based contractile ring during cytokinesis. Here, using a mutational analysis of cdc12p, we identify regions of cdc12p responsible for ring assembly and localization. Profilin-binding residues of the FH1 domain regulate actin assembly and processive barbed-end capping by the FH2 domain. Studies using photobleaching (FRAP) and sensitivity to latrunculin A treatment show that profilin binding modulates the rapid dynamics of actin and cdc12p within the ring in vivo. Visualized by functional GFP-fusion constructs expressed from the endogenous promoter, cdc12p appears in a small number of cytoplasmic motile spot structures that deliver the formin to the ring assembly site, without detectable formation of an intermediate band of "nodes." The FH3/DID region directs interphase spot localization, while an N-terminal region and the FH1-FH2 domains of cdc12p can target its localization to the ring. Mutations in putative DID and DAD regions do not alter regulation, suggesting that cdc12p is not regulated by a canonical autoinhibition mechanism. Our findings provide insights into the regulation of formin activity and the mechanisms of contractile ring dynamics and assembly.
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Affiliation(s)
- Ann Yonetani
- Department of Microbiology, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA
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39
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Pinar M, Coll PM, Rincón SA, Pérez P. Schizosaccharomyces pombe Pxl1 is a paxillin homologue that modulates Rho1 activity and participates in cytokinesis. Mol Biol Cell 2008; 19:1727-38. [PMID: 18256290 DOI: 10.1091/mbc.e07-07-0718] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Schizosaccharomyces pombe Rho GTPases regulate actin cytoskeleton organization and cell integrity. We studied the fission yeast gene SPBC4F6.12 based on its ability to suppress the thermosensitivity of cdc42-1625 mutant strain. This gene, named pxl1(+), encodes a protein with three LIM domains that is similar to paxillin. Pxl1 does not interact with Cdc42 but it interacts with Rho1, and it negatively regulates this GTPase. Fission yeast Pxl1 forms a contractile ring in the cell division region and deletion of pxl1(+) causes a delay in cell-cell separation, suggesting that it has a function in cytokinesis. Pxl1 N-terminal region is required and sufficient for its localization to the medial ring, whereas the LIM domains are necessary for its function. Pxl1 localization requires actin polymerization and the actomyosin ring, but it is independent of the septation initiation network (SIN) function. Moreover, Pxl1 colocalizes and interacts with Myo2, and Cdc15, suggesting that it is part of the actomyosin ring. Here, we show that in cells lacking Pxl1, the myosin ring is not correctly assembled and that actomyosin ring contraction is delayed. Together, these data suggest that Pxl1 modulates Rho1 GTPase signaling and plays a role in the formation and contraction of the actomyosin ring during cytokinesis.
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Affiliation(s)
- Mario Pinar
- Instituto de Microbiología Bioquímica, Consejo Superior de Investigaciones Científicas/Departamento de Microbiología y Genética, Universidad de Salamanca, Edificio Departamental, 37007 Salamanca, Spain
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40
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Vjestica A, Tang XZ, Oliferenko S. The actomyosin ring recruits early secretory compartments to the division site in fission yeast. Mol Biol Cell 2008; 19:1125-38. [PMID: 18184749 DOI: 10.1091/mbc.e07-07-0663] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The ultimate goal of cytokinesis is to establish a membrane barrier between daughter cells. The fission yeast Schizosaccharomyces pombe utilizes an actomyosin-based division ring that is thought to provide physical force for the plasma membrane invagination. Ring constriction occurs concomitantly with the assembly of a division septum that is eventually cleaved. Membrane trafficking events such as targeting of secretory vesicles to the division site require a functional actomyosin ring suggesting that it serves as a spatial landmark. However, the extent of polarization of the secretion apparatus to the division site is presently unknown. We performed a survey of dynamics of several fluorophore-tagged proteins that served as markers for various compartments of the secretory pathway. These included markers for the endoplasmic reticulum, the COPII sites, and the early and late Golgi. The secretion machinery exhibited a marked polarization to the division site. Specifically, we observed an enrichment of the transitional endoplasmic reticulum (tER) accompanied by Golgi cisternae biogenesis. These processes required actomyosin ring assembly and the function of the EFC-domain protein Cdc15p. Cdc15p overexpression was sufficient to induce tER polarization in interphase. Thus, fission yeast polarizes its entire secretory machinery to the cell division site by utilizing molecular cues provided by the actomyosin ring.
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41
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Kamasaki T, Osumi M, Mabuchi I. Three-dimensional arrangement of F-actin in the contractile ring of fission yeast. ACTA ACUST UNITED AC 2007; 178:765-71. [PMID: 17724118 PMCID: PMC2064542 DOI: 10.1083/jcb.200612018] [Citation(s) in RCA: 155] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The contractile ring, which is required for cytokinesis in animal and yeast cells, consists mainly of actin filaments. Here, we investigate the directionality of the filaments in fission yeast using myosin S1 decoration and electron microscopy. The contractile ring is composed of around 1,000 to 2,000 filaments each around 0.6 mum in length. During the early stages of cytokinesis, the ring consists of two semicircular populations of parallel filaments of opposite directionality. At later stages, before contraction, the ring filaments show mixed directionality. We consider that the ring is initially assembled from a single site in the division plane and that filaments subsequently rearrange before contraction initiates.
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Affiliation(s)
- Tomoko Kamasaki
- Division of Biology, School of Arts and Sciences, University of Tokyo, Tokyo 153-8902, Japan
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42
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Vavylonis D, Wu JQ, Hao S, O'Shaughnessy B, Pollard TD. Assembly mechanism of the contractile ring for cytokinesis by fission yeast. Science 2007; 319:97-100. [PMID: 18079366 DOI: 10.1126/science.1151086] [Citation(s) in RCA: 291] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Animals and fungi assemble a contractile ring of actin filaments and the motor protein myosin to separate into individual daughter cells during cytokinesis. We used fluorescence microscopy of live fission yeast cells to observe that membrane-bound nodes containing myosin were broadly distributed around the cell equator and assembled into a contractile ring through stochastic motions, after a meshwork of dynamic actin filaments appeared. Analysis of node motions and numerical simulations supported a mechanism whereby transient connections are established when myosins in one node capture and exert force on actin filaments growing from other nodes.
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Affiliation(s)
- Dimitrios Vavylonis
- Department of Chemical Engineering, Columbia University, New York, NY 10027, USA
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43
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Urven LE, Yabe T, Pelegri F. A role for non-muscle myosin II function in furrow maturation in the early zebrafish embryo. J Cell Sci 2007; 119:4342-52. [PMID: 17038547 DOI: 10.1242/jcs.03197] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Cytokinesis in early zebrafish embryos involves coordinated changes in the f-actin- and microtubule-based cytoskeleton, and the recruitment of adhesion junction components to the furrow. We show that exposure to inhibitors of non-muscle myosin II function does not affect furrow ingression during the early cleavage cycles but interferes with the recruitment of pericleavage f-actin and cortical beta-catenin aggregates to the furrow, as well as the remodeling of the furrow microtubule array. This remodeling is in turn required for the distal aggregation of the zebrafish germ plasm. Embryos with reduced myosin activity also exhibit at late stages of cytokinesis a stabilized contractile ring apparatus that appears as a ladder-like pattern of short f-actin cables, supporting a role for myosin function in the disassembly of the contractile ring after furrow formation. Our studies support a role for myosin function in furrow maturation that is independent of furrow ingression and which is essential for the recruitment of furrow components and the remodeling of the cytoskeleton during cytokinesis.
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Affiliation(s)
- Lance E Urven
- Laboratory of Genetics, University of Wisconsin - Madison, WI 53706, USA
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44
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Nakano K, Mabuchi I. Actin-capping protein is involved in controlling organization of actin cytoskeleton together with ADF/cofilin, profilin and F-actin crosslinking proteins in fission yeast. Genes Cells 2006; 11:893-905. [PMID: 16866873 DOI: 10.1111/j.1365-2443.2006.00987.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Actin-capping protein (CP) is a heterodimeric protein which is expressed in various eukaryotic cells. CP binds to the barbed end of the actin filaments in vitro and inhibits both the association and dissociation of actin monomers at this end. However, the cellular role of CP has not been uncovered. Here we investigated the function of CP in fission yeast cells. The fission yeast CP is composed of Acp1 and Acp2. It was found that Acp2 accumulated as cortical dots at the cell ends during interphase and the mid-region of mitotic cells, which disappeared in the absence of Acp1 or F-actin. Acp1 and Acp2, when co-over-expressed, decreased F-actin structures in cells, and cytokinesis was often interrupted in these cells. On the other hand, disruption of one of the CP genes affected the distribution of F-actin patches at cell ends and decreased the rate of actin depolymerization in vivo. Moreover, genetic analysis showed that CP controls actin dynamics together with ADF/cofilin and profilin. In addition, CP is likely involved in assembling the F-actin contractile ring and F-actin patch with F-actin-crosslinking proteins.
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Affiliation(s)
- Kentaro Nakano
- Division of Biology, Department of Life Sciences, School of Arts and Sciences, University of Tokyo, Komaba, Tokyo 153-8902, Japan.
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45
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Wu JQ, Sirotkin V, Kovar DR, Lord M, Beltzner CC, Kuhn JR, Pollard TD. Assembly of the cytokinetic contractile ring from a broad band of nodes in fission yeast. ACTA ACUST UNITED AC 2006; 174:391-402. [PMID: 16864655 PMCID: PMC2064235 DOI: 10.1083/jcb.200602032] [Citation(s) in RCA: 232] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We observed live fission yeast expressing pairs of functional fluorescent fusion proteins to test the popular model that the cytokinetic contractile ring assembles from a single myosin II progenitor or a Cdc12p-Cdc15p spot. Under our conditions, the anillin-like protein Mid1p establishes a broad band of small dots or nodes in the cortex near the nucleus. These nodes mature by the addition of conventional myosin II (Myo2p, Cdc4p, and Rlc1p), IQGAP (Rng2p), pombe Cdc15 homology protein (Cdc15p), and formin (Cdc12p). The nodes coalesce laterally into a compact ring when Cdc12p and profilin Cdc3p stimulate actin polymerization. We did not observe assembly of contractile rings by extension of a leading cable from a single spot or progenitor. Arp2/3 complex and its activators accumulate in patches near the contractile ring early in anaphase B, but are not concentrated in the contractile ring and are not required for assembly of the contractile ring. Their absence delays late steps in cytokinesis, including septum formation and cell separation.
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Affiliation(s)
- Jian-Qiu Wu
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520, USA
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46
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Wachtler V, Huang Y, Karagiannis J, Balasubramanian MK. Cell cycle-dependent roles for the FCH-domain protein Cdc15p in formation of the actomyosin ring in Schizosaccharomyces pombe. Mol Biol Cell 2006; 17:3254-66. [PMID: 16687577 PMCID: PMC1483054 DOI: 10.1091/mbc.e05-11-1086] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Cell division in the fission yeast Schizosaccharomyces pombe requires the formation and constriction of an actomyosin ring at the division site. The actomyosin ring is assembled in metaphase and anaphase A, is maintained throughout mitosis, and constricts after completion of anaphase. Maintenance of the actomyosin ring during late stages of mitosis depends on the septation initiation network (SIN), a signaling cascade that also regulates the deposition of the division septum. However, SIN is not active in metaphase and is not required for the initial assembly of the actomyosin ring early in mitosis. The FER/CIP4-homology (FCH) domain protein Cdc15p is a component of the actomyosin ring. Mutations in cdc15 lead to failure in cytokinesis and result in the formation of elongated, multinucleate cells without a division septum. Here we present evidence that the requirement of Cdc15p for actomyosin ring formation is dependent on the stage of mitosis. Although cdc15 mutants are competent to assemble actomyosin rings in metaphase, they are unable to maintain actomyosin rings late in mitosis when SIN is active. In the absence of functional Cdc15p, ring formation upon metaphase arrest depends on the anillin-like Mid1p. Interestingly, when cytokinesis is delayed due to perturbations to the division machinery, Cdc15p is maintained in a hypophosphorylated form. The dephosphorylation of Cdc15p, which occurs transiently in unperturbed cytokinesis, is partially dependent on the phosphatase Clp1p/Flp1p. This suggests a mechanism where both SIN and Clp1p/Flp1p contribute to maintenance of the actomyosin ring in late mitosis through Cdc15p, possibly by regulating its phosphorylation status.
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Affiliation(s)
- Volker Wachtler
- *Cell Division Laboratory, Temasek Life Sciences Laboratory, Singapore 117604, Singapore; and
- The Department of Biological Sciences, The National University of Singapore, Singapore 117604, Singapore
| | - Yinyi Huang
- *Cell Division Laboratory, Temasek Life Sciences Laboratory, Singapore 117604, Singapore; and
- The Department of Biological Sciences, The National University of Singapore, Singapore 117604, Singapore
| | - Jim Karagiannis
- *Cell Division Laboratory, Temasek Life Sciences Laboratory, Singapore 117604, Singapore; and
| | - Mohan K. Balasubramanian
- *Cell Division Laboratory, Temasek Life Sciences Laboratory, Singapore 117604, Singapore; and
- The Department of Biological Sciences, The National University of Singapore, Singapore 117604, Singapore
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47
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Mulvihill DP, Edwards SR, Hyams JS. A critical role for the type V myosin, Myo52, in septum deposition and cell fission during cytokinesis in Schizosaccharomyces pombe. ACTA ACUST UNITED AC 2006; 63:149-61. [PMID: 16421926 DOI: 10.1002/cm.20113] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Cytokinesis in fission yeast involves the coordination of septum deposition with the contraction of a cytokinetic actomyosin ring. We have examined the role of the type V myosin Myo52 in the coupling of these two events by the construction of a series of deletion mutants of the Myo52 tail and a further mutant within the ATP binding domain of the head. Each mutant protein was ectopically expressed in fission yeast cells. Each truncation was assayed for the ability to localize to the cell poles and septum (the normal cellular locations of Myo52) and to rescue the morphology defects and temperature sensitivity of a myo52Delta strain. A region within the Myo52 tail (amino acids 1320-1503), with a high degree of similarity to the vesicle-binding domain of the budding yeast type V myosin Myo2p, was essential for Myo52's role in the maintenance of growth polarity and cell division. A separate region (amino acids 1180-1320) was required for Myo52 foci to move throughout the cytoplasm; however, constructs lacking this region, but which retained the ability to dimerize still associated with actin at sites of cell growth. Not all of the Myo52 truncations which localized rescued the morphological defects of myo52Delta, demonstrating that loss of function was not simply brought about by an inability of mutant proteins to target the correct cellular location. By contrast, Myo52 motor activity was required for both localization and cellular function. myo52Delta cells were unable to efficiently localize the beta-1,3-glucan synthase, Bgs1, either at the cell poles or at the division septum, regions of cell wall deposition. Bgs1 and Myo52 localized to vesicle-like dots at the poles in interphase and these moved together to the septum at division. These data have led to the formulation of a model in which Myo52 is responsible for the delivery of Bgs1 and associated molecules to polar cell growth regions during interphase. On the commencement of septum formation, Myo52 transports Bgs1 to the cell equator, thus ensuring the accurate deposition of beta-1,3-glucan at the leading edge of the primary septum.
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Affiliation(s)
- Daniel P Mulvihill
- Department of Biology, University College London, London WC1E 6BT, United Kingdom.
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48
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Darenfed H, Mandato CA. Wound-induced contractile ring: a model for cytokinesis. Biochem Cell Biol 2006; 83:711-20. [PMID: 16333322 DOI: 10.1139/o05-164] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The actomyosin-based contractile ring is required for several biological processes, such as wound healing and cytokinesis of animal cells. Despite progress in defining the roles of this structure in both wound closure and cell division, we still do not fully understand how an actomyosin ring is spatially and temporally assembled, nor do we understand the molecular mechanism of its contraction. Recent results have demonstrated that microtubule-dependent local assembly of F-actin and myosin-II is present in wound closure and is similar to that in cytokinesis in animal cells. Furthermore, signalling factors such as small Rho GTPases have been shown to be involved in the regulation of actin dynamics during both processes. In this review we address recent findings in an attempt to better understand the dynamics of actomyosin contractile rings during wound healing as compared with the final step of animal cell division.
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Affiliation(s)
- Hassina Darenfed
- Department of Anatomy and Cell Biology, Mc Gill University, Montreal, QC, Canada
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Escobar-Cabrera E, Venkatesan M, Desautels M, Hemmingsen SM, McIntosh LP. Dissecting the domain structure of Cdc4p, a myosin essential light chain involved in Schizosaccharomyces pombe cytokinesis. Biochemistry 2005; 44:12136-48. [PMID: 16142912 DOI: 10.1021/bi050641c] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cytokinesis is the process by which one cell divides into two. Key in the cytokinetic mechanism of Schizosaccharomyces pombe is the contractile ring myosin, which consists of two heavy chains (Myo2p), two essential light chains (Cdc4p), and two regulatory light chains (Rlc1p). Cdc4p is a dumbbell-shaped EF-hand protein composed of N- and C-terminal domains separated by a flexible linker. The properties of these two domains are of particular interest because each is hypothesized to have independent functions in binding different components of the cytokinesis machinery. To help define these properties, we used NMR spectroscopy to compare the structure, stability, and dynamics of the isolated N- and C-terminal domains with one another and with native Cdc4p. On the basis of invariant chemical shifts, the N-domain retains the same structure in isolation as in the context of the full-length Cdc4p, whereas the C-domain appears markedly perturbed. This perturbation results from intramolecular binding of the residual linker sequence at the N-terminus of the C-domain in a mode similar to that used by native Cdc4p to associate with target polypeptide sequences. NMR relaxation, thermal denaturation, and amide hydrogen exchange experiments also indicate that the C-domain is less stable and more dynamic than the N-domain, both in isolation and in the full-length protein. We hypothesize that these properties reflect a conformational plasticity of the C-domain, which may allow Cdc4p to interact with several regulatory or contractile ring proteins necessary for cytokinesis.
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Affiliation(s)
- Eric Escobar-Cabrera
- Department of Biochemistry and Molecular Biology, The Michael Smith Laboratories, and The Protein Engineering Network of Centres of Excellence, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
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Dean SO, Rogers SL, Stuurman N, Vale RD, Spudich JA. Distinct pathways control recruitment and maintenance of myosin II at the cleavage furrow during cytokinesis. Proc Natl Acad Sci U S A 2005; 102:13473-8. [PMID: 16174742 PMCID: PMC1200093 DOI: 10.1073/pnas.0506810102] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The correct localization of myosin II to the equatorial cortex is crucial for proper cell division. Here, we examine a collection of genes that cause defects in cytokinesis and reveal with live cell imaging two distinct phases of myosin II localization. Three genes in the rho1 signaling pathway, pebble (a Rho guanidine nucleotide exchange factor), rho1, and rho kinase, are required for the initial recruitment of myosin II to the equatorial cortex. This initial localization mechanism does not require F-actin or the two components of the centralspindlin complex, the mitotic kinesin pavarotti/MKLP1 and racGAP50c/CYK-4. However, F-actin, the centralspindlin complex, formin (diaphanous), and profilin (chickadee) are required to stably maintain myosin II at the furrow. In the absence of these latter genes, myosin II delocalizes from the equatorial cortex and undergoes highly dynamic appearances and disappearances around the entire cell cortex, sometimes associated with abnormal contractions or blebbing. Our findings support a model in which a rho kinase-dependent event, possibly myosin II regulatory light chain phosphorylation, is required for the initial recruitment to the furrow, whereas the assembly of parallel, unbranched actin filaments, generated by formin-mediated actin nucleation, is required for maintaining myosin II exclusively at the equatorial cortex.
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Affiliation(s)
- Sara O Dean
- Department of Biochemistry, Stanford University, Stanford, CA 94305, USA
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