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G. Cortés JC, Ramos M, Konomi M, Barragán I, Moreno MB, Alcaide-Gavilán M, Moreno S, Osumi M, Pérez P, Ribas JC. Specific detection of fission yeast primary septum reveals septum and cleavage furrow ingression during early anaphase independent of mitosis completion. PLoS Genet 2018; 14:e1007388. [PMID: 29813053 PMCID: PMC5993333 DOI: 10.1371/journal.pgen.1007388] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2017] [Revised: 06/08/2018] [Accepted: 05/01/2018] [Indexed: 11/27/2022] Open
Abstract
It is widely accepted in eukaryotes that the cleavage furrow only initiates after mitosis completion. In fission yeast, cytokinesis requires the synthesis of a septum tightly coupled to cleavage furrow ingression. The current cytokinesis model establishes that simultaneous septation and furrow ingression only initiate after spindle breakage and mitosis exit. Thus, this model considers that although Cdk1 is inactivated at early-anaphase, septation onset requires the long elapsed time until mitosis completion and full activation of the Hippo-like SIN pathway. Here, we studied the precise timing of septation onset regarding mitosis by exploiting both the septum-specific detection with the fluorochrome calcofluor and the high-resolution electron microscopy during anaphase and telophase. Contrarily to the existing model, we found that both septum and cleavage furrow start to ingress at early anaphase B, long before spindle breakage, with a slow ingression rate during anaphase B, and greatly increasing after telophase onset. This shows that mitosis and cleavage furrow ingression are not concatenated but simultaneous events in fission yeast. We found that the timing of septation during early anaphase correlates with the cell size and is regulated by the corresponding levels of SIN Etd1 and Rho1. Cdk1 inactivation was directly required for timely septation in early anaphase. Strikingly the reduced SIN activity present after Cdk1 loss was enough to trigger septation by immediately inducing the medial recruitment of the SIN kinase complex Sid2-Mob1. On the other hand, septation onset did not depend on the SIN asymmetry establishment, which is considered a hallmark for SIN activation. These results recalibrate the timing of key cytokinetic events in fission yeast; and unveil a size-dependent control mechanism that synchronizes simultaneous nuclei separation with septum and cleavage furrow ingression to safeguard the proper chromosome segregation during cell division. Fission yeast cytokinesis requires the invagination of the equatorial plasma membrane (cleavage furrow ingression) coupled to the synthesis of a special wall structure named septum (septation). Despite Cdk1 kinase is inactivated in early anaphase, it is believed that cleavage furrow ingression and septation onset require anaphase progression and mitosis completion, only initiating after the complete activation of the Hippo-like septation initiation network (SIN) after telophase onset. Here, we studied the precise timing of septation start with respect to mitosis through specific septum-staining and electron microscopy. We found that septum and cleavage furrow ingression initiate in early anaphase, showing first a slow ingression rate during anaphase B, and increasing to a fast ingression rate after telophase onset. Thus, mitosis and cleavage furrow ingression are not concatenated but simultaneous events in fission yeast. The timing of septation correlated with cell size and depended on the level of cytoplasmic activators like SIN Etd1 and Rho1. We further analyzed the mitotic mechanisms that control the septation onset during early anaphase. Cdk1 directly regulated the timing of septation onset during early anaphase, and the low SIN activity present after Cdk1 inactivation was enough to trigger septation. Globally, these results recalibrate the timing of the main cytokinetic events of fission yeast and reveal a size-dependent control mechanism that synchronizes simultaneous nuclei separation with septum and cleavage furrow ingression.
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Affiliation(s)
- Juan Carlos G. Cortés
- Instituto de Biología Funcional y Genómica and Departamento de Microbiología y Genética, Consejo Superior de Investigaciones Científicas (CSIC) / Universidad de Salamanca, Salamanca, Spain
- * E-mail:
| | - Mariona Ramos
- Instituto de Biología Funcional y Genómica and Departamento de Microbiología y Genética, Consejo Superior de Investigaciones Científicas (CSIC) / Universidad de Salamanca, Salamanca, Spain
| | - Mami Konomi
- Laboratory of Electron Microscopy/Bio-imaging Centre, and Department of Chemical and Biological Sciences, Japan Women's University, Mejirodai, Bunkyo-ku, Tokyo, Japan
| | - Iris Barragán
- Instituto de Biología Funcional y Genómica and Departamento de Microbiología y Genética, Consejo Superior de Investigaciones Científicas (CSIC) / 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 (CSIC) / Universidad de Salamanca, Salamanca, Spain
| | - María Alcaide-Gavilán
- Centro Andaluz de Biología del Desarrollo, Universidad Pablo de Olavide/Consejo Superior de Investigaciones Científicas, Sevilla, Spain
| | - Sergio Moreno
- Instituto de Biología Funcional y Genómica and Departamento de Microbiología y Genética, Consejo Superior de Investigaciones Científicas (CSIC) / Universidad de Salamanca, Salamanca, Spain
| | - Masako Osumi
- Laboratory of Electron Microscopy/Bio-imaging Centre, and Department of Chemical and Biological Sciences, Japan Women's University, Mejirodai, Bunkyo-ku, Tokyo, Japan
- NPO: Integrated Imaging Research Support, Hirakawa-cho, Chiyoda-ku, Tokyo, Japan
| | - Pilar Pérez
- Instituto de Biología Funcional y Genómica and Departamento de Microbiología y Genética, Consejo Superior de Investigaciones Científicas (CSIC) / 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 (CSIC) / Universidad de Salamanca, Salamanca, Spain
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Hattersley N, Lara-Gonzalez P, Cheerambathur D, Gomez-Cavazos JS, Kim T, Prevo B, Khaliullin R, Lee KY, Ohta M, Green R, Oegema K, Desai A. Employing the one-cell C. elegans embryo to study cell division processes. Methods Cell Biol 2018; 144:185-231. [PMID: 29804670 DOI: 10.1016/bs.mcb.2018.03.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The one-cell Caenorhabditis elegans embryo offers many advantages for mechanistic analysis of cell division processes. Conservation of key genes and pathways involved in cell division makes findings in C. elegans broadly relevant. A key technical advantage of this system is the ability to penetrantly deplete essential gene products by RNA interference (RNAi) and replace them with wild-type or mutant versions expressed at endogenous levels from single copy RNAi-resistant transgene insertions. This ability to precisely perturb essential genes is complemented by the inherently highly reproducible nature of the zygotic division that facilitates development of quantitative imaging assays. Here, we detail approaches to generate targeted single copy transgene insertions that are RNAi-resistant, to engineer variants of individual genes employing transgene insertions as well as at the endogenous locus, and to in situ tag genes with fluorophores/purification tags. We also describe imaging assays and common image analysis tools employed to quantitatively monitor phenotypic effects of specific perturbations on meiotic and mitotic chromosome segregation, centrosome assembly/function, and cortical dynamics/cytokinesis.
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Affiliation(s)
- Neil Hattersley
- Ludwig Institute for Cancer Research, La Jolla, CA, United States; Department of Cellular & Molecular Medicine, University of California San Diego, La Jolla, CA, United States
| | - Pablo Lara-Gonzalez
- Ludwig Institute for Cancer Research, La Jolla, CA, United States; Department of Cellular & Molecular Medicine, University of California San Diego, La Jolla, CA, United States
| | - Dhanya Cheerambathur
- Ludwig Institute for Cancer Research, La Jolla, CA, United States; Department of Cellular & Molecular Medicine, University of California San Diego, La Jolla, CA, United States
| | - J Sebastian Gomez-Cavazos
- Ludwig Institute for Cancer Research, La Jolla, CA, United States; Department of Cellular & Molecular Medicine, University of California San Diego, La Jolla, CA, United States
| | - Taekyung Kim
- Ludwig Institute for Cancer Research, La Jolla, CA, United States; Department of Cellular & Molecular Medicine, University of California San Diego, La Jolla, CA, United States
| | - Bram Prevo
- Ludwig Institute for Cancer Research, La Jolla, CA, United States; Department of Cellular & Molecular Medicine, University of California San Diego, La Jolla, CA, United States
| | - Renat Khaliullin
- Ludwig Institute for Cancer Research, La Jolla, CA, United States; Department of Cellular & Molecular Medicine, University of California San Diego, La Jolla, CA, United States
| | - Kian-Yong Lee
- Ludwig Institute for Cancer Research, La Jolla, CA, United States; Department of Cellular & Molecular Medicine, University of California San Diego, La Jolla, CA, United States
| | - Midori Ohta
- Ludwig Institute for Cancer Research, La Jolla, CA, United States; Department of Cellular & Molecular Medicine, University of California San Diego, La Jolla, CA, United States
| | - Rebecca Green
- Ludwig Institute for Cancer Research, La Jolla, CA, United States; Department of Cellular & Molecular Medicine, University of California San Diego, La Jolla, CA, United States
| | - Karen Oegema
- Ludwig Institute for Cancer Research, La Jolla, CA, United States; Department of Cellular & Molecular Medicine, University of California San Diego, La Jolla, CA, United States
| | - Arshad Desai
- Ludwig Institute for Cancer Research, La Jolla, CA, United States; Department of Cellular & Molecular Medicine, University of California San Diego, La Jolla, CA, United States.
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53
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Segal D, Zaritsky A, Schejter ED, Shilo BZ. Feedback inhibition of actin on Rho mediates content release from large secretory vesicles. J Cell Biol 2018; 217:1815-1826. [PMID: 29496739 PMCID: PMC5940311 DOI: 10.1083/jcb.201711006] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2017] [Revised: 12/24/2017] [Accepted: 01/30/2018] [Indexed: 12/02/2022] Open
Abstract
This work identified a cycle of actin assembly and disassembly in large secretory vesicles of Drosophila salivary glands. Actin disassembly is triggered by actin-dependent recruitment of a RhoGAP protein and is essential for the contractility of the vesicle, leading to content release to the lumen. Secretion of adhesive glycoproteins to the lumen of Drosophila melanogaster larval salivary glands is performed by contraction of an actomyosin network assembled around large secretory vesicles, after their fusion to the apical membranes. We have identified a cycle of actin coat nucleation and disassembly that is independent of myosin. Recruitment of active Rho1 to the fused vesicle triggers activation of the formin Diaphanous and actin nucleation. This leads to actin-dependent localization of a RhoGAP protein that locally shuts off Rho1, promoting disassembly of the actin coat. When contraction of vesicles is blocked, the strict temporal order of the recruited elements generates repeated oscillations of actin coat formation and disassembly. Interestingly, different blocks to actin coat disassembly arrested vesicle contraction, indicating that actin turnover is an integral part of the actomyosin contraction cycle. The capacity of F-actin to trigger a negative feedback on its own production may be widely used to coordinate a succession of morphogenetic events or maintain homeostasis.
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Affiliation(s)
- Dagan Segal
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Assaf Zaritsky
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, Israel.,Lyda Hill Department of Bioinformatics, University of Texas Southwestern Medical Center, Dallas, TX
| | - Eyal D Schejter
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Ben-Zion Shilo
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
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54
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Capping protein regulates actin dynamics during cytokinetic midbody maturation. Proc Natl Acad Sci U S A 2018; 115:2138-2143. [PMID: 29439200 DOI: 10.1073/pnas.1722281115] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
During cytokinesis, a cleavage furrow generated by actomyosin ring contraction is restructured into the midbody, a platform for the assembly of the abscission machinery that controls the final separation of daughter cells. The polymerization state of F-actin is important during assembly, ingression, disassembly, and closure of the contractile ring and for the cytoskeletal remodeling that accompanies midbody formation and progression to abscission. Actin filaments must be cleared from the abscission sites before the final cut can take place. Although many conserved proteins interact with and influence the polymerization state of actin filaments, it is poorly understood how they regulate cytokinesis in higher eukaryotes. We report here that the actin capping protein (CP), a barbed end actin binding protein, participates in the control of actin polymerization during later stages of cytokinesis in human cells. Cells depleted of CP furrow and form early midbodies, but they fail cytokinesis. Appropriate recruitment of the ESCRT-III abscission machinery to the midbody is impaired, preventing the cell from progressing to the abscission stage. To generate actin filaments of optimal length, different actin nucleators, such as formins, balance CP's activity. Loss of actin capping activity leads to excessive accumulation of formin-based linear actin filaments. Depletion of the formin FHOD1 results in partial rescue of CP-induced cytokinesis failure, suggesting that it can antagonize CP activity during midbody maturation. Our work suggests that the actin cytoskeleton is remodeled in a stepwise manner during cytokinesis, with different regulators at different stages required for successful progression to abscission.
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55
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Lee S. Mathematical Model of Contractile Ring-Driven Cytokinesis in a Three-Dimensional Domain. Bull Math Biol 2018; 80:583-597. [PMID: 29344759 DOI: 10.1007/s11538-018-0390-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2017] [Accepted: 01/05/2018] [Indexed: 12/22/2022]
Abstract
In this paper, a mathematical model of contractile ring-driven cytokinesis is presented by using both phase-field and immersed-boundary methods in a three-dimensional domain. It is one of the powerful hypotheses that cytokinesis happens driven by the contractile ring; however, there are only few mathematical models following the hypothesis, to the author's knowledge. I consider a hybrid method to model the phenomenon. First, a cell membrane is represented by a zero-contour of a phase-field implicitly because of its topological change. Otherwise, immersed-boundary particles represent a contractile ring explicitly based on the author's previous work. Here, the multi-component (or vector-valued) phase-field equation is considered to avoid the emerging of each cell membrane right after their divisions. Using a convex splitting scheme, the governing equation of the phase-field method has unique solvability. The numerical convergence of contractile ring to cell membrane is proved. Several numerical simulations are performed to validate the proposed model.
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Affiliation(s)
- Seunggyu Lee
- National Institute for Mathematical Sciences, Daejeon, 34047, Republic of Korea.
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56
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Skruber K, Read TA, Vitriol EA. Reconsidering an active role for G-actin in cytoskeletal regulation. J Cell Sci 2018; 131:131/1/jcs203760. [PMID: 29321224 DOI: 10.1242/jcs.203760] [Citation(s) in RCA: 65] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Globular (G)-actin, the actin monomer, assembles into polarized filaments that form networks that can provide structural support, generate force and organize the cell. Many of these structures are highly dynamic and to maintain them, the cell relies on a large reserve of monomers. Classically, the G-actin pool has been thought of as homogenous. However, recent work has shown that actin monomers can exist in distinct groups that can be targeted to specific networks, where they drive and modify filament assembly in ways that can have profound effects on cellular behavior. This Review focuses on the potential factors that could create functionally distinct pools of actin monomers in the cell, including differences between the actin isoforms and the regulation of G-actin by monomer binding proteins, such as profilin and thymosin β4. Owing to difficulties in studying and visualizing G-actin, our knowledge over the precise role that specific actin monomer pools play in regulating cellular actin dynamics remains incomplete. Here, we discuss some of these unanswered questions and also provide a summary of the methodologies currently available for the imaging of G-actin.
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Affiliation(s)
- Kristen Skruber
- Department of Anatomy and Cell Biology, University of Florida, Gainesville, FL 32610, USA
| | - Tracy-Ann Read
- Department of Anatomy and Cell Biology, University of Florida, Gainesville, FL 32610, USA
| | - Eric A Vitriol
- Department of Anatomy and Cell Biology, University of Florida, Gainesville, FL 32610, USA
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57
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Menon VV, Soumya SS, Agarwal A, Naganathan SR, Inamdar MM, Sain A. Asymmetric Flows in the Intercellular Membrane during Cytokinesis. Biophys J 2018; 113:2787-2795. [PMID: 29262371 DOI: 10.1016/j.bpj.2017.10.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2017] [Revised: 09/06/2017] [Accepted: 10/11/2017] [Indexed: 12/26/2022] Open
Abstract
Eukaryotic cells undergo shape changes during their division and growth. This involves flow of material both in the cell membrane and in the cytoskeletal layer beneath the membrane. Such flows result in redistribution of phospholipid at the cell surface and actomyosin in the cortex. Here we focus on the growth of the intercellular surface during cell division in a Caenorhabditis elegans embryo. The growth of this surface leads to the formation of a double-layer of separating membranes between the two daughter cells. The division plane typically has a circular periphery and the growth starts from the periphery as a membrane invagination, which grows radially inward like the shutter of a camera. The growth is typically not concentric, in the sense that the closing internal ring is located off-center. Cytoskeletal proteins anillin and septin have been found to be responsible for initiating and maintaining the asymmetry of ring closure but the role of possible asymmetry in the material flow into the growing membrane has not been investigated yet. Motivated by experimental evidence of such flow asymmetry, here we explore the patterns of internal ring closure in the growing membrane in response to asymmetric boundary fluxes. We highlight the importance of the flow asymmetry by showing that many of the asymmetric growth patterns observed experimentally can be reproduced by our model, which incorporates the viscous nature of the membrane and contractility of the associated cortex.
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Affiliation(s)
- Vidya V Menon
- Center for Research in Nanotechnology and Science, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
| | - S S Soumya
- Department of Civil Engineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
| | - Amal Agarwal
- Department of Physics, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
| | | | - Mandar M Inamdar
- Department of Civil Engineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India.
| | - Anirban Sain
- Department of Physics, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India.
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58
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Li J, Jiang H. Regulating positioning and orientation of mitotic spindles via cell size and shape. Phys Rev E 2018; 97:012407. [PMID: 29448469 DOI: 10.1103/physreve.97.012407] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2017] [Indexed: 06/08/2023]
Abstract
Proper location of the mitotic spindle is critical for chromosome segregation and the selection of the cell division plane. However, how mitotic spindles sense cell size and shape to regulate their own position and orientation is still largely unclear. To investigate this question systematically, we used a general model by considering chromosomes, microtubule dynamics, and forces of various molecular motors. Our results show that in cells of various sizes and shapes, spindles can always be centered and oriented along the long axis robustly in the absence of other specified mechanisms. We found that the characteristic time of positioning and orientation processes increases with cell size. Spindles sense the cell size mainly by the cortical force in small cells and by the cytoplasmic force in large cells. In addition to the cell size, the cell shape mainly influences the orientation process. We found that more slender cells have a faster orientation process, and the final orientation is not necessarily along the longest axis but is determined by the radial profile and the symmetry of the cell shape. Finally, our model also reproduces the separation and repositioning of the spindle poles during the anaphase. Therefore, our work provides a general tool for studying the mitotic spindle across the whole mitotic phase.
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Affiliation(s)
- Jingchen Li
- Department of Modern Mechanics, CAS Key Laboratory of Mechanical Behavior and Design of Materials, University of Science and Technology of China, Hefei, Anhui 230027, China
| | - Hongyuan Jiang
- Department of Modern Mechanics, CAS Key Laboratory of Mechanical Behavior and Design of Materials, University of Science and Technology of China, Hefei, Anhui 230027, China
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59
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Chang M, Li Z, Huang S. Monomeric G-actin is uniformly distributed in pollen tubes and is rapidly redistributed via cytoplasmic streaming during pollen tube growth. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2017; 92:509-519. [PMID: 28845534 DOI: 10.1111/tpj.13668] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2017] [Revised: 08/11/2017] [Accepted: 08/18/2017] [Indexed: 05/25/2023]
Abstract
Dynamic assembly and disassembly of the actin cytoskeleton has been implicated in the regulation of pollen germination and subsequent tube growth. It is widely accepted that actin filaments are arrayed into distinct structures within different regions of the pollen tube. Maintenance of the equilibrium between monomeric globular actin (G-actin) and filamentous actin (F-actin) is crucial for actin assembly and array construction, and the local concentration of G-actin thus directly impacts actin assembly. The localization and dynamics of G-actin in the pollen tube, however, remain to be determined conclusively. To address this question, we created a series of fusion proteins between green fluorescent protein (GFP) and the Arabidopsis reproductive actin ACT11. Expression of a fusion protein with GFP inserted after methionine at position 49 within the DNase I-binding loop of ACT11 (GFPMet49 -ACT11) rescued the phenotypes in act11 mutants. Consistent with the notion that the majority of actin is in its monomeric form, GFPMet49 -ACT11 and GFP fusion proteins of four other reproductive actins generated with the same strategy do not obviously label filamentous structures. In further support of the functionality of these fusion proteins, we found that they can be incorporated into filamentous structures in jasplakinolide (Jasp)-treated pollen tubes. Careful observations showed that G-actin is distributed uniformly in the pollen tube and is rapidly redistributed via cytoplasmic streaming during pollen tube growth. Our study suggests that G-actin is readily available in the cytoplasm to support continuous actin polymerization during rapid pollen tube growth.
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Affiliation(s)
- Ming Chang
- Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing, 100084, China
| | - Zhankun Li
- Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing, 100084, China
| | - Shanjin Huang
- Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing, 100084, China
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60
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Pachong SM, Müller-Nedebock KK. Active force maintains the stability of a contractile ring. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2017; 40:91. [PMID: 29046990 DOI: 10.1140/epje/i2017-11581-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2017] [Accepted: 10/09/2017] [Indexed: 06/07/2023]
Abstract
We investigate a system of sufficiently dense polar actin filaments considered rigid and cross-linked by dimer myosin II protein within the contractile ring. The Langevin dynamics of this system is cast in a functional integral formalism and then transformed into density variables. Using the dynamical Random Phase Approximation (RPA) along with the a one-dimensional Langevin dynamics simulation (LDS), we investigate the structural integrity of the actin bundle network. The active force and the networking force reveal a non-trivial diffusive behaviour of the filaments within the ring. We conclude on when the active and networking forces lead to the contractile ring breaking down. The non-equilibrium active force is predominantly responsible for the prevention of the gaps in the ring.
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Affiliation(s)
- Stanard Mebwe Pachong
- Institute of Theoretical Physics, Department of Physics, Stellenbosch University, 7600, Stellenbosch, South Africa.
| | - Kristian K Müller-Nedebock
- Institute of Theoretical Physics, Department of Physics, Stellenbosch University, 7600, Stellenbosch, South Africa
- National Institute for Theoretical Physics, 7600, Stellenbosch, South Africa
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61
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Abstract
SUMMARYCell division-cytokinesis-involves large-scale rearrangements of the entire cell. Primarily driven by cytoskeletal proteins, cytokinesis also depends on topological rearrangements of the plasma membrane, which are coordinated with nuclear division in both space and time. Despite the fundamental nature of the process, different types of eukaryotic cells show variations in both the structural mechanisms of cytokinesis and the regulatory controls. In animal cells and fungi, a contractile actomyosin-based structure plays a central, albeit flexible, role. Here, the underlying molecular mechanisms are summarized and integrated and common themes are highlighted.
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Affiliation(s)
- Michael Glotzer
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois 60637
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62
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Rubinstein BY, Mogilner A. Myosin Clusters of Finite Size Develop Contractile Stress in 1D Random Actin Arrays. Biophys J 2017; 113:937-947. [PMID: 28834729 DOI: 10.1016/j.bpj.2017.07.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Revised: 06/29/2017] [Accepted: 07/05/2017] [Indexed: 01/08/2023] Open
Abstract
Myosin-powered force generation and contraction in nonmuscle cells underlies many cell biological processes and is based on contractility of random actin arrays. This contractility must rely on a microscopic asymmetry, the precise mechanism of which is not completely clear. A number of models of mechanical and structural asymmetries in actomyosin contraction have been posited. Here, we examine a contraction mechanism based on a finite size of myosin clusters and anisotropy of force generation by myosin heads at the ends of the myosin clusters. We use agent-based numerical simulations to demonstrate that if average lengths of actin filaments and myosin clusters are similar, then the proposed microscopic asymmetry leads to effective contraction of random 1D actomyosin arrays. We discuss the model's implication for mechanics of contractile rings and stress fibers.
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Affiliation(s)
- Boris Y Rubinstein
- Stowers Institute, Kansas City, Missouri, New York University, New York, New York
| | - Alex Mogilner
- Courant Institute of Mathematical Sciences, New York University, New York, New York; Department of Biology, New York University, New York, New York.
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63
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Price KL, Rose LS. LET-99 functions in the astral furrowing pathway, where it is required for myosin enrichment in the contractile ring. Mol Biol Cell 2017; 28:2360-2373. [PMID: 28701343 PMCID: PMC5576900 DOI: 10.1091/mbc.e16-12-0874] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2016] [Revised: 06/16/2017] [Accepted: 06/27/2017] [Indexed: 11/11/2022] Open
Abstract
LET-99 is required for furrowing during cytokinesis in both symmetrically and asymmetrically dividing cells. This function is distinct from the role of LET-99 in spindle positioning with Gα signaling. LET-99 is localized to the furrow, where it acts to promote myosin enrichment. The anaphase spindle determines the position of the cytokinesis furrow, such that the contractile ring assembles in an equatorial zone between the two spindle poles. Contractile ring formation is mediated by RhoA activation at the equator by the centralspindlin complex and midzone microtubules. Astral microtubules also inhibit RhoA accumulation at the poles. In the Caenorhabditis elegans one-cell embryo, the astral microtubule–dependent pathway requires anillin, NOP-1, and LET-99. LET-99 is well characterized for generating the asymmetric cortical localization of the Gα-dependent force-generating complex that positions the spindle during asymmetric division. However, whether the role of LET-99 in cytokinesis is specific to asymmetric division and whether it acts through Gα to promote furrowing are unclear. Here we show that LET-99 contributes to furrowing in both asymmetrically and symmetrically dividing cells, independent of its function in spindle positioning and Gα regulation. LET-99 acts in a pathway parallel to anillin and is required for myosin enrichment into the contractile ring. These and other results suggest a positive feedback model in which LET-99 localizes to the presumptive cleavage furrow in response to the spindle and myosin. Once positioned there, LET-99 enhances myosin accumulation to promote furrowing in both symmetrically and asymmetrically dividing cells.
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Affiliation(s)
- Kari L Price
- Department of Molecular and Cellular Biology and Biochemistry, Molecular, Cellular and Developmental Biology Graduate Program, University of California, Davis, Davis, CA 95616
| | - Lesilee S Rose
- Department of Molecular and Cellular Biology and Biochemistry, Molecular, Cellular and Developmental Biology Graduate Program, University of California, Davis, Davis, CA 95616
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64
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Montembault E, Claverie MC, Bouit L, Landmann C, Jenkins J, Tsankova A, Cabernard C, Royou A. Myosin efflux promotes cell elongation to coordinate chromosome segregation with cell cleavage. Nat Commun 2017; 8:326. [PMID: 28835609 PMCID: PMC5569077 DOI: 10.1038/s41467-017-00337-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Accepted: 06/21/2017] [Indexed: 12/02/2022] Open
Abstract
Chromatid segregation must be coordinated with cytokinesis to preserve genomic stability. Here we report that cells clear trailing chromatids from the cleavage site by undergoing two phases of cell elongation. The first phase relies on the assembly of a wide contractile ring. The second phase requires the activity of a pool of myosin that flows from the ring and enriches the nascent daughter cell cortices. This myosin efflux is a novel feature of cytokinesis and its duration is coupled to nuclear envelope reassembly and the nuclear sequestration of the Rho-GEF Pebble. Trailing chromatids induce a delay in nuclear envelope reassembly concomitant with prolonged cortical myosin activity, thus providing forces for the second elongation. We propose that the modulation of cortical myosin dynamics is part of the cellular response triggered by a “chromatid separation checkpoint” that delays nuclear envelope reassembly and, consequently, Pebble nuclear sequestration when trailing chromatids are present at the midzone. Chromatid segregation must be coordinated with cytokinesis to preserve genomic stability. Here the authors show that cells clear trailing chromatids from the cleavage site in a two-step cell elongation and demonstrate the role of myosin efflux in the second phase.
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Affiliation(s)
- Emilie Montembault
- University of Bordeaux, CNRS, UMR5095, Institut Européen de Chimie et Biologie, 2 Rue Robert Escarpit, Pessac, 33607, France.
| | - Marie-Charlotte Claverie
- University of Bordeaux, CNRS, UMR5095, Institut Européen de Chimie et Biologie, 2 Rue Robert Escarpit, Pessac, 33607, France
| | - Lou Bouit
- University of Bordeaux, CNRS, UMR5095, Institut Européen de Chimie et Biologie, 2 Rue Robert Escarpit, Pessac, 33607, France
| | - Cedric Landmann
- University of Bordeaux, CNRS, UMR5095, Institut Européen de Chimie et Biologie, 2 Rue Robert Escarpit, Pessac, 33607, France
| | - James Jenkins
- University of Bordeaux, CNRS, UMR5095, Institut Européen de Chimie et Biologie, 2 Rue Robert Escarpit, Pessac, 33607, France
| | - Anna Tsankova
- Department of Biology, University of Washington, Seattle, WA, 98195, USA
| | - Clemens Cabernard
- Department of Biology, University of Washington, Seattle, WA, 98195, USA
| | - Anne Royou
- University of Bordeaux, CNRS, UMR5095, Institut Européen de Chimie et Biologie, 2 Rue Robert Escarpit, Pessac, 33607, France.
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65
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Chew TG, Huang J, Palani S, Sommese R, Kamnev A, Hatano T, Gu Y, Oliferenko S, Sivaramakrishnan S, Balasubramanian MK. Actin turnover maintains actin filament homeostasis during cytokinetic ring contraction. J Cell Biol 2017; 216:2657-2667. [PMID: 28655757 PMCID: PMC5584170 DOI: 10.1083/jcb.201701104] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2017] [Revised: 05/04/2017] [Accepted: 06/01/2017] [Indexed: 11/30/2022] Open
Abstract
Many cytokinetic actomyosin ring components undergo dynamic turnover, but its function is unclear. Chew et al. show that continuous actin polymerization ensures crucial F-actin homeostasis during ring contraction, without which ring proteins organize into noncontractile clusters. Cytokinesis in many eukaryotes involves a tension-generating actomyosin-based contractile ring. Many components of actomyosin rings turn over during contraction, although the significance of this turnover has remained enigmatic. Here, using Schizosaccharomyces japonicus, we investigate the role of turnover of actin and myosin II in its contraction. Actomyosin ring components self-organize into ∼1-µm-spaced clusters instead of undergoing full-ring contraction in the absence of continuous actin polymerization. This effect is reversed when actin filaments are stabilized. We tested the idea that the function of turnover is to ensure actin filament homeostasis in a synthetic system, in which we abolished turnover by fixing rings in cell ghosts with formaldehyde. We found that these rings contracted fully upon exogenous addition of a vertebrate myosin. We conclude that actin turnover is required to maintain actin filament homeostasis during ring contraction and that the requirement for turnover can be bypassed if homeostasis is achieved artificially.
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Affiliation(s)
- Ting Gang Chew
- Warwick Medical School, University of Warwick, Coventry, UK
| | - Junqi Huang
- Warwick Medical School, University of Warwick, Coventry, UK .,Key Laboratory of Regenerative Medicine, Ministry of Education, Jinan University, Guangzhou, China
| | | | - Ruth Sommese
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN
| | - Anton Kamnev
- Warwick Medical School, University of Warwick, Coventry, UK
| | | | - Ying Gu
- Randall Division of Cell and Molecular Biophysics, King's College London, London, UK
| | - Snezhana Oliferenko
- Randall Division of Cell and Molecular Biophysics, King's College London, London, UK.,Francis Crick Institute, London, UK
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66
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Antagonistic Behaviors of NMY-1 and NMY-2 Maintain Ring Channels in the C. elegans Gonad. Biophys J 2017; 111:2202-2213. [PMID: 27851943 DOI: 10.1016/j.bpj.2016.10.011] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2015] [Revised: 09/30/2016] [Accepted: 10/05/2016] [Indexed: 11/23/2022] Open
Abstract
Contractile rings play critical roles in a number of biological processes, including oogenesis, wound healing, and cytokinesis. In many cases, the activity of motor proteins such as nonmuscle myosins is required for appropriate constriction of these contractile rings. In the gonad of the nematode worm Caenorhabditis elegans, ring channels are a specialized form of contractile ring that are maintained at a constant diameter before oogenesis. We propose a model of ring channel maintenance that explicitly incorporates force generation by motor proteins that can act normally or tangentially to the ring channel opening. We find that both modes of force generation are needed to maintain the ring channels. We demonstrate experimentally that the type II myosins NMY-1 and NMY-2 antagonize each other in the ring channels by producing force in perpendicular directions: the experimental depletion of NMY-1/theoretical decrease in orthogonal force allows premature ring constriction and cellularization, whereas the experimental depletion of NMY-2/theoretical decrease in tangential force opens the ring channels and prevents cellularization. Together, our experimental and theoretical results show that both forces, mediated by NMY-1 and NMY-2, are crucial for maintaining the appropriate ring channel diameter and dynamics throughout the gonad.
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67
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Bermudez JG, Chen H, Einstein LC, Good MC. Probing the biology of cell boundary conditions through confinement of Xenopus cell-free cytoplasmic extracts. Genesis 2017; 55. [PMID: 28132422 DOI: 10.1002/dvg.23013] [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: 11/14/2016] [Revised: 12/04/2016] [Accepted: 12/05/2016] [Indexed: 11/11/2022]
Abstract
Cell-free cytoplasmic extracts prepared from Xenopus eggs and embryos have for decades provided a biochemical system with which to interrogate complex cell biological processes in vitro. Recently, the application of microfabrication and microfluidic strategies in biology has narrowed the gap between in vitro and in vivo studies by enabling formation of cell-size compartments containing functional cytoplasm. These approaches provide numerous advantages over traditional biochemical experiments performed in a test tube. Most notably, the cell-free cytoplasm is confined using a two- or three-dimensional boundary, which mimics the natural configuration of a cell. This strategy enables characterization of the spatial organization of a cell, and the role that boundaries play in regulating intracellular assembly and function. In this review, we describe the marriage of Xenopus cell-free cytoplasm and confinement technologies to generate synthetic cell-like systems, the recent biological insights they have enabled, and the promise they hold for future scientific discovery.
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Affiliation(s)
- Jessica G Bermudez
- Department of Bioengineering, University of Pennsylvania, 421 Curie Blvd, 1151 BRB II/III, Philadelphia, Pennsylvania, 19104
| | - Hui Chen
- Department of Cell and Developmental Biology, University of Pennsylvania, 421 Curie Blvd, 1151 BRB II/III, Philadelphia, Pennsylvania, 19104
| | - Lily C Einstein
- Department of Cell and Developmental Biology, University of Pennsylvania, 421 Curie Blvd, 1151 BRB II/III, Philadelphia, Pennsylvania, 19104
| | - Matthew C Good
- Department of Bioengineering, University of Pennsylvania, 421 Curie Blvd, 1151 BRB II/III, Philadelphia, Pennsylvania, 19104.,Department of Cell and Developmental Biology, University of Pennsylvania, 421 Curie Blvd, 1151 BRB II/III, Philadelphia, Pennsylvania, 19104
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68
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Spencer AK, Schaumberg AJ, Zallen JA. Scaling of cytoskeletal organization with cell size in Drosophila. Mol Biol Cell 2017; 28:1519-1529. [PMID: 28404752 PMCID: PMC5449150 DOI: 10.1091/mbc.e16-10-0691] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2016] [Revised: 03/31/2017] [Accepted: 04/05/2017] [Indexed: 11/11/2022] Open
Abstract
Actin-rich denticle precursors are regularly distributed in the Drosophila embryo. Cytoskeletal scaling occurs through changes in denticle number and spacing. Denticle spacing scales with cell length over a 10-fold range. Accurate denticle positioning requires the microtubule cytoskeleton. Spatially organized macromolecular complexes are essential for cell and tissue function, but the mechanisms that organize micron-scale structures within cells are not well understood. Microtubule-based structures such as mitotic spindles scale with cell size, but less is known about the scaling of actin structures within cells. Actin-rich denticle precursors cover the ventral surface of the Drosophila embryo and larva and provide templates for cuticular structures involved in larval locomotion. Using quantitative imaging and statistical modeling, we demonstrate that denticle number and spacing scale with cell length over a wide range of cell sizes in embryos and larvae. Denticle number and spacing are reduced under space-limited conditions, and both features robustly scale over a 10-fold increase in cell length during larval growth. We show that the relationship between cell length and denticle spacing can be recapitulated by specific mathematical equations in embryos and larvae and that accurate denticle spacing requires an intact microtubule network and the microtubule minus end–binding protein, Patronin. These results identify a novel mechanism of microtubule-dependent actin scaling that maintains precise patterns of actin organization during tissue growth.
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Affiliation(s)
- Alison K Spencer
- Gerstner Sloan Kettering Graduate School of Biomedical Sciences.,Howard Hughes Medical Institute and Developmental Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, NY 10065
| | - Andrew J Schaumberg
- Weill Cornell Graduate School of Medical Sciences and the Tri-Institutional PhD Program in Computational Biology and Medicine, Memorial Sloan Kettering Cancer Center, New York, NY 10065
| | - Jennifer A Zallen
- Howard Hughes Medical Institute and Developmental Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, NY 10065
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69
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Abstract
Actin functions in a multitude of cellular processes owing to its ability to polymerize into filaments, which can be further organized into higher-order structures by an array of actin-binding and regulatory proteins. Therefore, research on actin and actin-related functions relies on the visualization of actin structures without interfering with the cycles of actin polymerization and depolymerization that underlie cellular actin dynamics. In this Cell Science at a Glance and the accompanying poster, we briefly evaluate the different techniques and approaches currently applied to analyze and visualize cellular actin structures, including in the nuclear compartment. Referring to the gold standard F-actin marker phalloidin to stain actin in fixed samples and tissues, we highlight methods for visualization of actin in living cells, which mostly apply the principle of genetically fusing fluorescent proteins to different actin-binding domains, such as LifeAct, utrophin and F-tractin, as well as anti-actin-nanobody technology. In addition, the compound SiR-actin and the expression of GFP-actin are also applicable for various types of live-cell analyses. Overall, the visualization of actin within a physiological context requires a careful choice of method, as well as a tight control of the amount or the expression level of a given detection probe in order to minimize its influence on endogenous actin dynamics.
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Affiliation(s)
- Michael Melak
- Institute of Pharmacology, Biochemical-Pharmacological Center (BPC), University of Marburg, Karl-von-Frisch-Straße 1, Marburg 35043, Germany
| | - Matthias Plessner
- Institute of Pharmacology, Biochemical-Pharmacological Center (BPC), University of Marburg, Karl-von-Frisch-Straße 1, Marburg 35043, Germany
| | - Robert Grosse
- Institute of Pharmacology, Biochemical-Pharmacological Center (BPC), University of Marburg, Karl-von-Frisch-Straße 1, Marburg 35043, Germany
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70
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Abstract
The midbody is a protein-dense assembly that forms during cytokinesis when the actomyosin ring constricts around bundling central spindle microtubules. After its initial description by Walther Flemming in the late nineteenth century and its rediscovery through electron microscopy in the 1960s and 1970s, its ultrastructural organization and the sequential recruitment of its molecular constituents has only been elucidated in the past decade. Recently, it has become clear that the midbody can serve as a polarity cue during asymmetric cell division, cell polarization, and spindle orientation by coordinating cytoskeletal organization, vesicular transport, and localized cortical cues. In this chapter, these newly emerging functions will be discussed as well as asymmetries during midbody formation and their consequences for cellular organization in tissues.
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Affiliation(s)
- Christian Pohl
- Buchmann Institute for Molecular Life Sciences, Institute of Biochemistry II, Goethe University Medical School, Max-von-Laue-Strasse 15, 60438, Frankfurt (Main), Germany.
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71
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Silva AM, Osório DS, Pereira AJ, Maiato H, Pinto IM, Rubinstein B, Gassmann R, Telley IA, Carvalho AX. Robust gap repair in the contractile ring ensures timely completion of cytokinesis. J Cell Biol 2016; 215:789-799. [PMID: 27974482 PMCID: PMC5166501 DOI: 10.1083/jcb.201605080] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2016] [Revised: 09/14/2016] [Accepted: 11/02/2016] [Indexed: 11/22/2022] Open
Abstract
Using laser microsurgery, Silva et al. show that gaps in the contractile ring can be repaired at any stage of constriction, allowing for successful and timely cytokinesis. Their results support a contractile unit model for constriction of the cytokinetic ring. Cytokinesis in animal cells requires the constriction of an actomyosin contractile ring, whose architecture and mechanism remain poorly understood. We use laser microsurgery to explore the biophysical properties of constricting rings in Caenorhabditis elegans embryos. Laser cutting causes rings to snap open. However, instead of disintegrating, ring topology recovers and constriction proceeds. In response to severing, a finite gap forms and is repaired by recruitment of new material in an actin polymerization–dependent manner. An open ring is able to constrict, and rings repair from successive cuts. After gap repair, an increase in constriction velocity allows cytokinesis to complete at the same time as controls. Our analysis demonstrates that tension in the ring increases while net cortical tension at the site of ingression decreases throughout constriction and suggests that cytokinesis is accomplished by contractile modules that assemble and contract autonomously, enabling local repair of the actomyosin network. Consequently, cytokinesis is a highly robust process impervious to discontinuities in contractile ring structure.
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Affiliation(s)
- Ana M Silva
- Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200-135 Porto, Portugal.,Instituto de Biologia Molecular e Celular, 4200-135 Porto, Portugal
| | - Daniel S Osório
- Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200-135 Porto, Portugal.,Instituto de Biologia Molecular e Celular, 4200-135 Porto, Portugal
| | - Antonio J Pereira
- Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200-135 Porto, Portugal.,Instituto de Biologia Molecular e Celular, 4200-135 Porto, Portugal
| | - Helder Maiato
- Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200-135 Porto, Portugal.,Instituto de Biologia Molecular e Celular, 4200-135 Porto, Portugal
| | - Inês Mendes Pinto
- International Iberian Nanotechnology Laboratory, 4715-330 Braga, Portugal
| | | | - Reto Gassmann
- Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200-135 Porto, Portugal.,Instituto de Biologia Molecular e Celular, 4200-135 Porto, Portugal
| | - Ivo Andreas Telley
- Instituto Gulbenkian de Ciência, Fundação Calouste Gulbenkian, 2780-156 Oeiras, Portugal
| | - Ana Xavier Carvalho
- Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4200-135 Porto, Portugal .,Instituto de Biologia Molecular e Celular, 4200-135 Porto, Portugal
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72
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Fickentscher R, Struntz P, Weiss M. Setting the Clock for Fail-Safe Early Embryogenesis. PHYSICAL REVIEW LETTERS 2016; 117:188101. [PMID: 27835015 DOI: 10.1103/physrevlett.117.188101] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2016] [Indexed: 06/06/2023]
Abstract
The embryogenesis of the small nematode Caenorhabditis elegans is a remarkably robust self-organization phenomenon. Cell migration trajectories in the early embryo, for example, are well explained by mechanical cues that push cells into positions where they experience the least repulsive forces. Yet, how this mechanically guided progress in development is properly timed has remained elusive so far. Here, we show that cell volumes and division times are strongly anticorrelated during the early embryogenesis of C. elegans with significant differences between somatic cells and precursors of the germline. Our experimental findings are explained by a simple model that in conjunction with mechanical guidance can account for the fail-safe early embryogenesis of C. elegans.
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Affiliation(s)
- Rolf Fickentscher
- Experimental Physics I, University of Bayreuth, Universitätsstrasse 30, D-95447 Bayreuth, Germany
| | - Philipp Struntz
- Experimental Physics I, University of Bayreuth, Universitätsstrasse 30, D-95447 Bayreuth, Germany
| | - Matthias Weiss
- Experimental Physics I, University of Bayreuth, Universitätsstrasse 30, D-95447 Bayreuth, Germany
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73
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Kim K, Sikora A, Nakazawa H, Umetsu M, Hwang W, Teizer W. Isomorphic coalescence of aster cores formed in vitro from microtubules and kinesin motors. Phys Biol 2016; 13:056002. [PMID: 27652512 DOI: 10.1088/1478-3975/13/5/056002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We report fluorescence microscopy studies of the formation of aster-like structures emerging from a cellular element-based active system and a novel analysis of the aster condensation. The system consists of rhodamine labeled microtubules which are dynamically coupled by functionalized kinesin motor proteins cross-linked via streptavidin-coated quantum dots (QDs). The aster-shaped objects contain core structures. The cores are aggregates of the QD-motor protein complexes, and result from the dynamic condensation of sub-clusters that are connected to each other randomly. The structural specificity of the aster core reflects a configuration of the initial connectivity between sub-clusters. Detailed image analysis allows us to extract a novel correlation between the condensation speed and the sub-cluster separation. The size of the core is scaled down during the condensation process, following a power law dependence on the distance between sub-clusters. The exponent of the power law is close to two, as expected from a geometric model. This single exponent common to all the contractile lines implies that there exists a time regime during which an isomorphic contraction of the aster core continues during the condensation process. We analyze the observed contraction by using a model system with potential applicability in a wide range of emergent phenomena in randomly coupled active networks, which are prevalent in the cellular environment.
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Affiliation(s)
- K Kim
- WPI-Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Japan
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74
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A Combination of Actin Treadmilling and Cross-Linking Drives Contraction of Random Actomyosin Arrays. Biophys J 2016; 109:1818-29. [PMID: 26536259 DOI: 10.1016/j.bpj.2015.09.013] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2015] [Revised: 09/14/2015] [Accepted: 09/18/2015] [Indexed: 01/02/2023] Open
Abstract
We investigate computationally the self-organization and contraction of an initially random actomyosin ring. In the framework of a detailed physical model for a ring of cross-linked actin filaments and myosin-II clusters, we derive the force balance equations and solve them numerically. We find that to contract, actin filaments have to treadmill and to be sufficiently cross linked, and myosin has to be processive. The simulations reveal how contraction scales with mechanochemical parameters. For example, they show that the ring made of longer filaments generates greater force but contracts slower. The model predicts that the ring contracts with a constant rate proportional to the initial ring radius if either myosin is released from the ring during contraction and actin filaments shorten, or if myosin is retained in the ring, while the actin filament number decreases. We demonstrate that a balance of actin nucleation and compression-dependent disassembly can also sustain contraction. Finally, the model demonstrates that with time pattern formation takes place in the ring, worsening the contractile process. The more random the actin dynamics are, the higher the contractility will be.
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75
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Cheffings T, Burroughs N, Balasubramanian M. Actomyosin Ring Formation and Tension Generation in Eukaryotic Cytokinesis. Curr Biol 2016; 26:R719-R737. [DOI: 10.1016/j.cub.2016.06.071] [Citation(s) in RCA: 77] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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76
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Wollrab V, Thiagarajan R, Wald A, Kruse K, Riveline D. Still and rotating myosin clusters determine cytokinetic ring constriction. Nat Commun 2016; 7:11860. [PMID: 27363521 PMCID: PMC4932180 DOI: 10.1038/ncomms11860] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2015] [Accepted: 05/06/2016] [Indexed: 12/27/2022] Open
Abstract
The cytokinetic ring is essential for separating daughter cells during division. It consists of actin filaments and myosin motors that are generally assumed to organize as sarcomeres similar to skeletal muscles. However, direct evidence is lacking. Here we show that the internal organization and dynamics of rings are different from sarcomeres and distinct in different cell types. Using micro-cavities to orient rings in single focal planes, we find in mammalian cells a transition from a homogeneous distribution to a periodic pattern of myosin clusters at the onset of constriction. In contrast, in fission yeast, myosin clusters rotate prior to and during constriction. Theoretical analysis indicates that both patterns result from acto-myosin self-organization and reveals differences in the respective stresses. These findings suggest distinct functional roles for rings: contraction in mammalian cells and transport in fission yeast. Thus self-organization under different conditions may be a generic feature for regulating morphogenesis in vivo.
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Affiliation(s)
- Viktoria Wollrab
- Laboratory of Cell Physics ISIS/IGBMC, ISIS &icFRC, Université de Strasbourg &CNRS, 8 allée Gaspard Monge, Strasbourg 67000, France.,Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.,Centre National de la Recherche Scientifique, UMR7104, Illkirch, France.,Institut National de la Santé et de la Recherche Médicale, U964, Illkirch, France.,Université de Strasbourg, Illkirch, France.,Theoretical Physics, Saarland University 66123, Saarbrücken, Germany
| | - Raghavan Thiagarajan
- Laboratory of Cell Physics ISIS/IGBMC, ISIS &icFRC, Université de Strasbourg &CNRS, 8 allée Gaspard Monge, Strasbourg 67000, France.,Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.,Centre National de la Recherche Scientifique, UMR7104, Illkirch, France.,Institut National de la Santé et de la Recherche Médicale, U964, Illkirch, France.,Université de Strasbourg, Illkirch, France
| | - Anne Wald
- Theoretical Physics, Saarland University 66123, Saarbrücken, Germany
| | - Karsten Kruse
- Theoretical Physics, Saarland University 66123, Saarbrücken, Germany
| | - Daniel Riveline
- Laboratory of Cell Physics ISIS/IGBMC, ISIS &icFRC, Université de Strasbourg &CNRS, 8 allée Gaspard Monge, Strasbourg 67000, France.,Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.,Centre National de la Recherche Scientifique, UMR7104, Illkirch, France.,Institut National de la Santé et de la Recherche Médicale, U964, Illkirch, France.,Université de Strasbourg, Illkirch, France
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77
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Denning D, Roos WH. Elucidating the molecular mechanisms underlying cellular response to biophysical cues using synthetic biology approaches. Cell Adh Migr 2016; 10:540-553. [PMID: 27266767 DOI: 10.1080/19336918.2016.1170259] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The use of synthetic surfaces and materials to influence and study cell behavior has vastly progressed our understanding of the underlying molecular mechanisms involved in cellular response to physicochemical and biophysical cues. Reconstituting cytoskeletal proteins and interfacing them with a defined microenvironment has also garnered deep insight into the engineering mechanisms existing within the cell. This review presents recent experimental findings on the influence of several parameters of the extracellular environment on cell behavior and fate, such as substrate topography, stiffness, chemistry and charge. In addition, the use of synthetic environments to measure physical properties of the reconstituted cytoskeleton and their interaction with intracellular proteins such as molecular motors is discussed, which is relevant for understanding cell migration, division and structural integrity, as well as intracellular transport. Insight is provided regarding the next steps to be taken in this interdisciplinary field, in order to achieve the global aim of artificially directing cellular response.
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Affiliation(s)
- Denise Denning
- a Moleculaire Biofysica , Zernike instituut, Rijksuniversiteit Groningen , Groningen , The Netherlands
| | - Wouter H Roos
- a Moleculaire Biofysica , Zernike instituut, Rijksuniversiteit Groningen , Groningen , The Netherlands
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78
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Schwayer C, Sikora M, Slováková J, Kardos R, Heisenberg CP. Actin Rings of Power. Dev Cell 2016; 37:493-506. [DOI: 10.1016/j.devcel.2016.05.024] [Citation(s) in RCA: 67] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2016] [Revised: 05/24/2016] [Accepted: 05/25/2016] [Indexed: 12/21/2022]
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79
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Avoiding artefacts when counting polymerized actin in live cells with LifeAct fused to fluorescent proteins. Nat Cell Biol 2016; 18:676-83. [PMID: 27159499 DOI: 10.1038/ncb3351] [Citation(s) in RCA: 96] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2015] [Accepted: 03/31/2016] [Indexed: 11/08/2022]
Abstract
When tagged with a fluorescent protein, actin is not fully functional, so the LifeAct peptide fused to a fluorescent protein is widely used to localize actin filaments in live cells. However, we find that these fusion proteins have many concentration-dependent effects on actin assembly in vitro and in fission yeast cells. mEGFP-LifeAct inhibits actin assembly during endocytosis as well as assembly and constriction of the cytokinetic contractile ring. Purified mEGFP-LifeAct and LifeAct-mCherry bind actin filaments with Kd values of ∼10 μM. LifeAct-mCherry can promote actin filament nucleation and either promote or inhibit filament elongation. Both separately and together, profilin and formins suppress these effects. LifeAct-mCherry can also promote or inhibit actin filament severing by cofilin. These concentration-dependent effects mean that caution is necessary when overexpressing LifeAct fusion proteins to label actin filaments in cells. Therefore, we used low micromolar concentrations of tagged LifeAct to follow assembly and disassembly of actin filaments in cells. Careful titrations also gave an estimate of a peak of ∼190,000 actin molecules (∼500 μm) in the fission yeast contractile ring. These filaments shorten from ∼500 to ∼100 subunits as the ring constricts.
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80
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Oelz D, Mogilner A. Actomyosin contraction, aggregation and traveling waves in a treadmilling actin array. PHYSICA D. NONLINEAR PHENOMENA 2016; 318-319:70-83. [PMID: 26989275 PMCID: PMC4789780 DOI: 10.1016/j.physd.2015.10.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We use perturbation theory to derive a continuum model for the dynamic actomyosin bundle/ring in the regime of very strong crosslinking. Actin treadmilling is essential for contraction. Linear stability analysis and numerical solutions of the model equations reveal that when the actin treadmilling is very slow, actin and myosin aggregate into equidistantly spaced peaks. When treadmilling is significant, actin filament of one polarity are distributed evenly, while filaments of the opposite polarity develop a shock wave moving with the treadmilling velocity. Myosin aggregates into a sharp peak surfing the crest of the actin wave. Any actomyosin aggregation diminishes contractile stress. The easiest way to maintain higher contraction is to upregulate the actomyosin turnover which destabilizes nontrivial patterns and stabilizes the homogeneous actomyosin distributions. We discuss the model's implications for the experiment.
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Affiliation(s)
- Dietmar Oelz
- Courant Inst. of Math. Sciences, New York University, 251
Mercer St, New York, NY 10012
| | - Alex Mogilner
- Courant Inst. of Math. Sciences, New York University, 251
Mercer St, New York, NY 10012
- Department of Biology, New York University
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81
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Dorn JF, Zhang L, Phi TT, Lacroix B, Maddox PS, Liu J, Maddox AS. A theoretical model of cytokinesis implicates feedback between membrane curvature and cytoskeletal organization in asymmetric cytokinetic furrowing. Mol Biol Cell 2016; 27:1286-99. [PMID: 26912796 PMCID: PMC4831882 DOI: 10.1091/mbc.e15-06-0374] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Accepted: 02/16/2016] [Indexed: 11/11/2022] Open
Abstract
Furrow ingression is asymmetric in cytokinesis in the Caenorhabditis elegans zygote. A combination of quantitative high-resolution live-cell microscopy and theoretical modeling revealed a mechanistic basis for asymmetry: feedback among membrane curvature, cytoskeletal alignment, and contractility. The model also suggests that asymmetry promotes energy efficiency. During cytokinesis, the cell undergoes a dramatic shape change as it divides into two daughter cells. Cell shape changes in cytokinesis are driven by a cortical ring rich in actin filaments and nonmuscle myosin II. The ring closes via actomyosin contraction coupled with actin depolymerization. Of interest, ring closure and hence the furrow ingression are nonconcentric (asymmetric) within the division plane across Metazoa. This nonconcentricity can occur and persist even without preexisting asymmetric cues, such as spindle placement or cellular adhesions. Cell-autonomous asymmetry is not explained by current models. We combined quantitative high-resolution live-cell microscopy with theoretical modeling to explore the mechanistic basis for asymmetric cytokinesis in the Caenorhabditis elegans zygote, with the goal of uncovering basic principles of ring closure. Our theoretical model suggests that feedback among membrane curvature, cytoskeletal alignment, and contractility is responsible for asymmetric cytokinetic furrowing. It also accurately predicts experimental perturbations of conserved ring proteins. The model further suggests that curvature-mediated filament alignment speeds up furrow closure while promoting energy efficiency. Collectively our work underscores the importance of membrane–cytoskeletal anchoring and suggests conserved molecular mechanisms for this activity.
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Affiliation(s)
- Jonas F Dorn
- Institute for Research in Immunology and Cancer, Université de Montréal, Montréal, QC H3T 1J4, Canada
| | - Li Zhang
- Institute for Research in Immunology and Cancer, Université de Montréal, Montréal, QC H3T 1J4, Canada
| | - Tan-Trao Phi
- Institute for Research in Immunology and Cancer, Université de Montréal, Montréal, QC H3T 1J4, Canada
| | | | - Paul S Maddox
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Jian Liu
- Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20814
| | - Amy Shaub Maddox
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
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82
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Abstract
Cytokinesis is the final process in the cell cycle that physically divides one cell into two. In budding yeast, cytokinesis is driven by a contractile actomyosin ring (AMR) and the simultaneous formation of a primary septum, which serves as template for cell wall deposition. AMR assembly, constriction, primary septum formation and cell wall deposition are successive processes and tightly coupled to cell cycle progression to ensure the correct distribution of genetic material and cell organelles among the two rising cells prior to cell division. The role of the AMR in cytokinesis and the molecular mechanisms that drive AMR constriction and septation are the focus of current research. This review summarizes the recent progresses in our understanding of how budding yeast cells orchestrate the multitude of molecular mechanisms that control AMR driven cytokinesis in a spatio-temporal manner to achieve an error free cell division.
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83
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Vuković LD, Jevtić P, Edens LJ, Levy DL. New Insights into Mechanisms and Functions of Nuclear Size Regulation. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2016; 322:1-59. [PMID: 26940517 DOI: 10.1016/bs.ircmb.2015.11.001] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Nuclear size is generally maintained within a defined range in a given cell type. Changes in cell size that occur during cell growth, development, and differentiation are accompanied by dynamic nuclear size adjustments in order to establish appropriate nuclear-to-cytoplasmic volume relationships. It has long been recognized that aberrations in nuclear size are associated with certain disease states, most notably cancer. Nuclear size and morphology must impact nuclear and cellular functions. Understanding these functional implications requires an understanding of the mechanisms that control nuclear size. In this review, we first provide a general overview of the diverse cellular structures and activities that contribute to nuclear size control, including structural components of the nucleus, effects of DNA amount and chromatin compaction, signaling, and transport pathways that impinge on the nucleus, extranuclear structures, and cell cycle state. We then detail some of the key mechanistic findings about nuclear size regulation that have been gleaned from a variety of model organisms. Lastly, we review studies that have implicated nuclear size in the regulation of cell and nuclear function and speculate on the potential functional significance of nuclear size in chromatin organization, gene expression, nuclear mechanics, and disease. With many fundamental cell biological questions remaining to be answered, the field of nuclear size regulation is still wide open.
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Affiliation(s)
- Lidija D Vuković
- Department of Molecular Biology, University of Wyoming, Laramie, WY, United States of America
| | - Predrag Jevtić
- Department of Molecular Biology, University of Wyoming, Laramie, WY, United States of America
| | - Lisa J Edens
- Department of Molecular Biology, University of Wyoming, Laramie, WY, United States of America
| | - Daniel L Levy
- Department of Molecular Biology, University of Wyoming, Laramie, WY, United States of America.
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84
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Mitchison TJ, Ishihara K, Nguyen P, Wühr M. Size Scaling of Microtubule Assemblies in Early Xenopus Embryos. Cold Spring Harb Perspect Biol 2015; 7:a019182. [PMID: 26261283 DOI: 10.1101/cshperspect.a019182] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The first 12 cleavage divisions in Xenopus embryos provide a natural experiment in size scaling, as cell radius decreases ∼16-fold with little change in biochemistry. Analyzing both natural cleavage and egg extract partitioned into droplets revealed that mitotic spindle size scales with cell size, with an upper limit in very large cells. We discuss spindle-size scaling in the small- and large-cell regimes with a focus on the "limiting-component" hypotheses. Zygotes and early blastomeres show a scaling mismatch between spindle and cell size. This problem is solved, we argue, by interphase asters that act to position the spindle and transport chromosomes to the center of daughter cells. These tasks are executed by the spindle in smaller cells. We end by discussing possible mechanisms that limit mitotic aster size and promote interphase aster growth to cell-spanning dimensions.
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Affiliation(s)
- Timothy J Mitchison
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts 02115 Marine Biological Laboratory, Woods Hole, Massachusetts 02543
| | - Keisuke Ishihara
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts 02115 Marine Biological Laboratory, Woods Hole, Massachusetts 02543
| | - Phuong Nguyen
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts 02115 Marine Biological Laboratory, Woods Hole, Massachusetts 02543
| | - Martin Wühr
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts 02115 Marine Biological Laboratory, Woods Hole, Massachusetts 02543
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85
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Abstract
Organelle function is often directly related to organelle size. However, it is not necessarily absolute size but the organelle-to-cell-size ratio that is critical. Larger cells generally have increased metabolic demands, must segregate DNA over larger distances, and require larger cytokinetic rings to divide. Thus, organelles often must scale to the size of the cell. The need for scaling is particularly acute during early development during which cell size can change rapidly. Here, we highlight scaling mechanisms for cellular structures as diverse as centrosomes, nuclei, and the mitotic spindle, and distinguish them from more general mechanisms of size control. In some cases, scaling is a consequence of the underlying mechanism of organelle size control. In others, size-control mechanisms are not obviously related to cell size, implying that scaling results indirectly from cell-size-dependent regulation of size-control mechanisms.
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Affiliation(s)
- Simone Reber
- Max Planck Institute of Molecular Genetics and Cell Biology, 01307 Dresden, Germany Integrative Research Institute (IRI) for the Life Sciences, Humboldt-Universität zu Berlin, 10115 Berlin, Germany
| | - Nathan W Goehring
- The Francis Crick Institute, WC2A 3LY London, United Kingdom MRC Laboratory of Molecular Cell Biology, University College London, WC1E 6BT London, United Kingdom
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86
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Jung YW, Mascagni M. Constriction model of actomyosin ring for cytokinesis by fission yeast using a two-state sliding filament mechanism. J Chem Phys 2015; 141:125101. [PMID: 25273478 DOI: 10.1063/1.4896164] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
We developed a model describing the structure and contractile mechanism of the actomyosin ring in fission yeast, Schizosaccharomyces pombe. The proposed ring includes actin, myosin, and α-actinin, and is organized into a structure similar to that of muscle sarcomeres. This structure justifies the use of the sliding-filament mechanism developed by Huxley and Hill, but it is probably less organized relative to that of muscle sarcomeres. Ring contraction tension was generated via the same fundamental mechanism used to generate muscle tension, but some physicochemical parameters were adjusted to be consistent with the proposed ring structure. Simulations allowed an estimate of ring constriction tension that reproduced the observed ring constriction velocity using a physiologically possible, self-consistent set of parameters. Proposed molecular-level properties responsible for the thousand-fold slower constriction velocity of the ring relative to that of muscle sarcomeres include fewer myosin molecules involved, a less organized contractile configuration, a low α-actinin concentration, and a high resistance membrane tension. Ring constriction velocity is demonstrated as an exponential function of time despite a near linear appearance. We proposed a hypothesis to explain why excess myosin heads inhibit constriction velocity rather than enhance it. The model revealed how myosin concentration and elastic resistance tension are balanced during cytokinesis in S. pombe.
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Affiliation(s)
- Yong-Woon Jung
- Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255, USA
| | - Michael Mascagni
- Departments of Computer Science, Mathematics and Scientific Computing, and Graduate Program in Molecular Biophysics, Florida State University, Tallahassee, Florida 32306-4530, USA
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87
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Kumar M, Pushpa K, Mylavarapu SVS. Splitting the cell, building the organism: Mechanisms of cell division in metazoan embryos. IUBMB Life 2015; 67:575-87. [PMID: 26173082 PMCID: PMC5937677 DOI: 10.1002/iub.1404] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2015] [Accepted: 06/18/2015] [Indexed: 11/12/2022]
Abstract
The unicellular metazoan zygote undergoes a series of cell divisions that are central to its development into an embryo. Differentiation of embryonic cells leads eventually to the development of a functional adult. Fate specification of pluripotent embryonic cells occurs during the early embryonic cleavage divisions in several animals. Early development is characterized by well-known stages of embryogenesis documented across animals--morulation, blastulation, and morphogenetic processes such as gastrulation, all of which contribute to differentiation and tissue specification. Despite this broad conservation, there exist clearly discernible morphological and functional differences across early embryonic stages in metazoans. Variations in the mitotic mechanisms of early embryonic cell divisions play key roles in governing these gross differences that eventually encode developmental patterns. In this review, we discuss molecular mechanisms of both karyokinesis (nuclear division) and cytokinesis (cytoplasmic separation) during early embryonic divisions. We outline the broadly conserved molecular pathways that operate in these two stages in early embryonic mitoses. In addition, we highlight mechanistic variations in these two stages across different organisms. We finally discuss outstanding questions of interest, answers to which would illuminate the role of divergent mitotic mechanisms in shaping early animal embryogenesis.
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Affiliation(s)
- Megha Kumar
- Laboratory of Cellular Dynamics, Regional Centre for Biotechnology, NCR Biotech Science Cluster, Faridabad, Haryana, India
| | - Kumari Pushpa
- Laboratory of Cellular Dynamics, Regional Centre for Biotechnology, NCR Biotech Science Cluster, Faridabad, Haryana, India
| | - Sivaram V. S. Mylavarapu
- Laboratory of Cellular Dynamics, Regional Centre for Biotechnology, NCR Biotech Science Cluster, Faridabad, Haryana, India
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88
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Abstract
Actomyosin-mediated contractility is a highly conserved mechanism for generating mechanical stress in animal cells and underlies muscle contraction, cell migration, cell division and tissue morphogenesis. Whereas actomyosin-mediated contractility in striated muscle is well understood, the regulation of such contractility in non-muscle and smooth muscle cells is less certain. Our increased understanding of the mechanics of actomyosin arrays that lack sarcomeric organization has revealed novel modes of regulation and force transmission. This work also provides an example of how diverse mechanical behaviours at cellular scales can arise from common molecular components, underscoring the need for experiments and theories to bridge the molecular to cellular length scales.
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89
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Takaine M, Numata O, Nakano K. An actin-myosin-II interaction is involved in maintaining the contractile ring in fission yeast. J Cell Sci 2015; 128:2903-18. [PMID: 26092938 DOI: 10.1242/jcs.171264] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2015] [Accepted: 06/12/2015] [Indexed: 01/26/2023] Open
Abstract
The actomyosin-based contractile ring, which assembles at the cell equator, maintains its circularity during cytokinesis in many eukaryotic cells, ensuring its efficient constriction. Although consistent maintenance of the ring is one of the mechanisms underpinning cytokinesis, it has not yet been fully addressed. We here investigated the roles of fission yeast myosin-II proteins [Myo2 and Myo3 (also known as Myp2)] in ring maintenance during cytokinesis, with a focus on Myo3. A site-directed mutational analysis showed that the motor properties of Myo3 were involved in its accumulation in the contractile ring. The assembled ring was often deformed and not properly maintained under conditions in which the activities of myosin-II proteins localizing to the contractile ring were decreased, leading to inefficient cell division. Moreover, Myo3 appeared to form motile clusters on the ring. We propose that large assemblies of myosin-II proteins consolidate the contractile ring by continuously binding to F-actin in the ring, thereby contributing to its maintenance.
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Affiliation(s)
- Masak Takaine
- Department of Biological Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8577, Japan
| | - Osamu Numata
- Department of Biological Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8577, Japan
| | - Kentaro Nakano
- Department of Biological Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8577, Japan
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90
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Stam S, Alberts J, Gardel ML, Munro E. Isoforms Confer Characteristic Force Generation and Mechanosensation by Myosin II Filaments. Biophys J 2015; 108:1997-2006. [PMID: 25902439 PMCID: PMC4407263 DOI: 10.1016/j.bpj.2015.03.030] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2014] [Revised: 01/27/2015] [Accepted: 03/02/2015] [Indexed: 12/21/2022] Open
Abstract
Myosin II isoforms with varying mechanochemistry and filament size interact with filamentous actin (F-actin) arrays to generate contractile forces in muscle and nonmuscle cells. How myosin II force production is shaped by isoform-specific motor properties and environmental stiffness remains poorly understood. Here, we used computer simulations to analyze force production by an ensemble of myosin motors against an elastically tethered actin filament. We found that force output depends on two timescales: the duration of F-actin attachment, which varies sharply with the ensemble size, motor duty ratio, and external load; and the time to build force, which scales with the ensemble stall force, gliding speed, and environmental stiffness. Although force-dependent kinetics were not required to sense changes in stiffness, the myosin catch bond produced positive feedback between the attachment time and force to trigger switch-like transitions from transient attachments, generating small forces, to high-force-generating runs. Using parameters representative of skeletal muscle myosin, nonmuscle myosin IIB, and nonmuscle myosin IIA revealed three distinct regimes of behavior, respectively: 1) large assemblies of fast, low-duty ratio motors rapidly build stable forces over a large range of environmental stiffness; 2) ensembles of slow, high-duty ratio motors serve as high-affinity cross-links with force buildup times that exceed physiological timescales; and 3) small assemblies of low-duty ratio motors operating at intermediate speeds are poised to respond sharply to changes in mechanical context-at low force or stiffness, they serve as low-affinity cross-links, but they can transition to force production via the positive-feedback mechanism described above. Together, these results reveal how myosin isoform properties may be tuned to produce force and respond to mechanical cues in their environment.
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Affiliation(s)
- Samantha Stam
- Biophysical Sciences Graduate Program, University of Washington, Friday Harbor, Washington; Institute for Biophysical Dynamics, University of Washington, Friday Harbor, Washington
| | - Jon Alberts
- Center for Cell Dynamics, University of Washington, Friday Harbor, Washington
| | - Margaret L Gardel
- Institute for Biophysical Dynamics, University of Washington, Friday Harbor, Washington; Physics Department, University of Chicago, Chicago, Illinois; James Franck Institute, University of Chicago, Chicago, Illinois; Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois.
| | - Edwin Munro
- Institute for Biophysical Dynamics, University of Washington, Friday Harbor, Washington; Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois.
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91
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Cell-sized spherical confinement induces the spontaneous formation of contractile actomyosin rings in vitro. Nat Cell Biol 2015; 17:480-9. [DOI: 10.1038/ncb3142] [Citation(s) in RCA: 102] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2014] [Accepted: 02/19/2015] [Indexed: 12/13/2022]
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92
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Abstract
Cytokinesis mediates the physical separation of dividing cells after chromosome segregation. In animal cell cytokinesis, a contractile ring, mainly composed of actin and myosin filaments, ingresses a cleavage furrow midway between the two spindle poles. A distinct machinery, involving the endosomal sorting complex required for transport III (ESCRT-III), subsequently splits the plasma membrane of nascent daughter cells in a process termed abscission. Here, we provide a brief overview of early cytokinesis events in animal cells and then cover in depth recently emerging models for the assembly and function of the abscission machinery and its temporal coordination with chromosome segregation.
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Affiliation(s)
- Beata Mierzwa
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), 1030 Vienna, Austria
| | - Daniel W Gerlich
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), 1030 Vienna, Austria.
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93
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Sain A, Inamdar MM, Jülicher F. Dynamic force balances and cell shape changes during cytokinesis. PHYSICAL REVIEW LETTERS 2015; 114:048102. [PMID: 25679910 DOI: 10.1103/physrevlett.114.048102] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2013] [Indexed: 06/04/2023]
Abstract
During the division of animal cells, an actomyosin ring is formed in the cell cortex. The contraction of this ring induces shape changes of the cell and the formation of a cytokinesis furrow. In many cases, a cell-cell interface forms that separates the two new cells. Here we present a simple physical description of the cell shape changes and the dynamics of the interface closure, based on force balances involving active stresses and viscous friction. We discuss conditions in which the interface closure is either axially symmetric or asymmetric. We show that our model can account for the observed dynamics of ring contraction and interface closure in the C. elegans embryo.
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Affiliation(s)
- Anirban Sain
- Physics Department, Indian Institute of Technology-Bombay, Powai, Mumbai 400076, India
| | - Mandar M Inamdar
- Department of Civil Engineering, Indian Institute of Technology-Bombay, Powai, Mumbai 400076, India
| | - Frank Jülicher
- Max-Planck-Institute for the Physics of Complex Systems Nöthnitzer Strasse 38, 01187 Dresden, Germany
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94
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Bidone TC, Tang H, Vavylonis D. Dynamic network morphology and tension buildup in a 3D model of cytokinetic ring assembly. Biophys J 2014; 107:2618-28. [PMID: 25468341 DOI: 10.1016/j.bpj.2014.10.034] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2014] [Revised: 10/15/2014] [Accepted: 10/23/2014] [Indexed: 11/19/2022] Open
Abstract
During fission yeast cytokinesis, actin filaments nucleated by cortical formin Cdc12 are captured by myosin motors bound to a band of cortical nodes and bundled by cross-linking proteins. The myosin motors exert forces on the actin filaments, resulting in a net pulling of the nodes into a contractile ring, while cross-linking interactions help align actin filaments and nodes into a single bundle. We used these mechanisms in a three-dimensional computational model of contractile ring assembly, with semiflexible actin filaments growing from formins at cortical nodes, capturing of filaments by neighboring nodes, and cross-linking among filaments through attractive interactions. The model was used to predict profiles of actin filament density at the cell cortex, morphologies of condensing node-filament networks, and regimes of cortical tension by varying the node pulling force and strength of cross-linking among actin filaments. Results show that cross-linking interactions can lead to confinement of actin filaments at the simulated cortical boundary. We show that the ring-formation region in parameter space lies close to regions leading to clumps, meshworks or double rings, and stars/cables. Since boundaries between regions are not sharp, transient structures that resemble clumps, stars, and meshworks can appear in the process of ring assembly. These results are consistent with prior experiments with mutations in actin-filament turnover regulators, myosin motor activity, and changes in the concentration of cross-linkers that alter the morphology of the condensing network. Transient star shapes appear in some simulations, and these morphologies offer an explanation for star structures observed in prior experimental images. Finally, we quantify tension along actin filaments and forces on nodes during ring assembly and show that the mechanisms describing ring assembly can also drive ring constriction once the ring is formed.
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Affiliation(s)
- Tamara C Bidone
- Department of Physics, Lehigh University, Bethlehem, Pennsylvania
| | - Haosu Tang
- Department of Physics, Lehigh University, Bethlehem, Pennsylvania
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95
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Pollard TD. The value of mechanistic biophysical information for systems-level understanding of complex biological processes such as cytokinesis. Biophys J 2014; 107:2499-507. [PMID: 25468329 PMCID: PMC4255220 DOI: 10.1016/j.bpj.2014.10.031] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2014] [Revised: 10/06/2014] [Accepted: 10/08/2014] [Indexed: 12/15/2022] Open
Abstract
This review illustrates the value of quantitative information including concentrations, kinetic constants and equilibrium constants in modeling and simulating complex biological processes. Although much has been learned about some biological systems without these parameter values, they greatly strengthen mechanistic accounts of dynamical systems. The analysis of muscle contraction is a classic example of the value of combining an inventory of the molecules, atomic structures of the molecules, kinetic constants for the reactions, reconstitutions with purified proteins and theoretical modeling to account for the contraction of whole muscles. A similar strategy is now being used to understand the mechanism of cytokinesis using fission yeast as a favorable model system.
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Affiliation(s)
- Thomas D Pollard
- Departments of Molecular Cellular and Developmental Biology, Molecular Biophysics and Biochemistry, and Cell Biology, Yale University, New Haven, Connecticut.
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96
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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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97
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Bourdages KG, Lacroix B, Dorn JF, Descovich CP, Maddox AS. Quantitative analysis of cytokinesis in situ during C. elegans postembryonic development. PLoS One 2014; 9:e110689. [PMID: 25329167 PMCID: PMC4203819 DOI: 10.1371/journal.pone.0110689] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2014] [Accepted: 09/24/2014] [Indexed: 12/20/2022] Open
Abstract
The physical separation of a cell into two daughter cells during cytokinesis requires cell-intrinsic shape changes driven by a contractile ring. However, in vivo, cells interact with their environment, which includes other cells. How cytokinesis occurs in tissues is not well understood. Here, we studied cytokinesis in an intact animal during tissue biogenesis. We used high-resolution microscopy and quantitative analysis to study the three rounds of division of the C. elegans vulval precursor cells (VPCs). The VPCs are cut in half longitudinally with each division. Contractile ring breadth, but not the speed of ring closure, scales with cell length. Furrowing speed instead scales with division plane dimensions, and scaling is consistent between the VPCs and C. elegans blastomeres. We compared our VPC cytokinesis kinetics data with measurements from the C. elegans zygote and HeLa and Drosophila S2 cells. Both the speed dynamics and asymmetry of ring closure are qualitatively conserved among cell types. Unlike in the C. elegans zygote but similar to other epithelial cells, Anillin is required for proper ring closure speed but not asymmetry in the VPCs. We present evidence that tissue organization impacts the dynamics of cytokinesis by comparing our results on the VPCs with the cells of the somatic gonad. In sum, this work establishes somatic lineages in post-embryonic C. elegans development as cell biological models for the study of cytokinesis in situ.
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Affiliation(s)
- Karine G. Bourdages
- Institute for Research in Immunology and Cancer, Université de Montréal, Montréal, Québec, Canada
| | - Benjamin Lacroix
- Institute for Research in Immunology and Cancer, Université de Montréal, Montréal, Québec, Canada
| | - Jonas F. Dorn
- Institute for Research in Immunology and Cancer, Université de Montréal, Montréal, Québec, Canada
- Advanced Quantitative Sciences, Novartis Pharma AG, Basel, Switzerland
| | - Carlos P. Descovich
- Department of Biology, University of North Carolina, Chapel Hill, North Carolina, United States of America
| | - Amy S. Maddox
- Department of Biology, University of North Carolina, Chapel Hill, North Carolina, United States of America
- * E-mail:
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98
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Davies T, Jordan SN, Chand V, Sees JA, Laband K, Carvalho AX, Shirasu-Hiza M, Kovar DR, Dumont J, Canman JC. High-resolution temporal analysis reveals a functional timeline for the molecular regulation of cytokinesis. Dev Cell 2014; 30:209-23. [PMID: 25073157 DOI: 10.1016/j.devcel.2014.05.009] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2013] [Revised: 03/17/2014] [Accepted: 05/12/2014] [Indexed: 02/08/2023]
Abstract
To take full advantage of fast-acting temperature-sensitive mutations, thermal control must be extremely rapid. We developed the Therminator, a device capable of shifting sample temperature in ~17 s while simultaneously imaging cell division in vivo. Applying this technology to six key regulators of cytokinesis, we found that each has a distinct temporal requirement in the Caenorhabditis elegans zygote. Specifically, myosin-II is required throughout cytokinesis until contractile ring closure. In contrast, formin-mediated actin nucleation is only required during assembly and early contractile ring constriction. Centralspindlin is required to maintain division after ring closure, although its GAP activity is only required until just prior to closure. Finally, the chromosomal passenger complex is required for cytokinesis only early in mitosis, but not during metaphase or cytokinesis. Together, our results provide a precise functional timeline for molecular regulators of cytokinesis using the Therminator, a powerful tool for ultra-rapid protein inactivation.
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Affiliation(s)
- Tim Davies
- Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
| | - Shawn N Jordan
- Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
| | - Vandana Chand
- Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
| | - Jennifer A Sees
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA
| | - Kimberley Laband
- CNRS, Institut Jacques Monod, Univ. P7, 75205 Paris CEDEX 13, France
| | - Ana X Carvalho
- Molecular and Cellular Biology Unit, Instituto de Biologia Molecular e Celular (IBMC), 4150-180 Porto, Portugal
| | - Mimi Shirasu-Hiza
- Department of Genetics and Development, Columbia University, New York, NY 10032, USA
| | - David R Kovar
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA; Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL 60637, USA
| | - Julien Dumont
- CNRS, Institut Jacques Monod, Univ. P7, 75205 Paris CEDEX 13, France
| | - Julie C Canman
- Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA.
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99
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Turlier H, Audoly B, Prost J, Joanny JF. Furrow constriction in animal cell cytokinesis. Biophys J 2014; 106:114-23. [PMID: 24411243 DOI: 10.1016/j.bpj.2013.11.014] [Citation(s) in RCA: 106] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2013] [Revised: 11/08/2013] [Accepted: 11/11/2013] [Indexed: 10/25/2022] Open
Abstract
Cytokinesis is the process of physical cleavage at the end of cell division; it proceeds by ingression of an acto-myosin furrow at the equator of the cell. Its failure leads to multinucleated cells and is a possible cause of tumorigenesis. Here, we calculate the full dynamics of furrow ingression and predict cytokinesis completion above a well-defined threshold of equatorial contractility. The cortical acto-myosin is identified as the main source of mechanical dissipation and active forces. Thereupon, we propose a viscous active nonlinear membrane theory of the cortex that explicitly includes actin turnover and where the active RhoA signal leads to an equatorial band of myosin overactivity. The resulting cortex deformation is calculated numerically, and reproduces well the features of cytokinesis such as cell shape and cortical flows toward the equator. Our theory gives a physical explanation of the independence of cytokinesis duration on cell size in embryos. It also predicts a critical role of turnover on the rate and success of furrow constriction. Scaling arguments allow for a simple interpretation of the numerical results and unveil the key mechanism that generates the threshold for cytokinesis completion: cytoplasmic incompressibility results in a competition between the furrow line tension and the cell poles' surface tension.
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Affiliation(s)
- Hervé Turlier
- Physicochimie Curie (Centre National de la Recherche Scientifique-UMR168), Institut Curie, Section de Recherche, Paris, France.
| | - Basile Audoly
- Institut Jean Le Rond d'Alembert (Centre National de la Recherche Scientifique-UMR7190), Université Pierre-et-Marie-Curie, Université Paris VI, Paris, France
| | - Jacques Prost
- Physicochimie Curie (Centre National de la Recherche Scientifique-UMR168), Institut Curie, Section de Recherche, Paris, France; École Supérieure de Physique et de Chimie Industrielles de la Ville de Paris-ParisTech, Paris, France
| | - Jean-François Joanny
- Physicochimie Curie (Centre National de la Recherche Scientifique-UMR168), Institut Curie, Section de Recherche, Paris, France
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100
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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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