1
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Chandrasekaran A, Graham K, Stachowiak JC, Rangamani P. Kinetic trapping organizes actin filaments within liquid-like protein droplets. Nat Commun 2024; 15:3139. [PMID: 38605007 PMCID: PMC11009352 DOI: 10.1038/s41467-024-46726-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2023] [Accepted: 03/07/2024] [Indexed: 04/13/2024] Open
Abstract
Several actin-binding proteins (ABPs) phase separate to form condensates capable of curating the actin network shapes. Here, we use computational modeling to understand the principles of actin network organization within VASP condensate droplets. Our simulations reveal that the different actin shapes, namely shells, rings, and mixture states are highly dependent on the kinetics of VASP-actin interactions, suggesting that they arise from kinetic trapping. Specifically, we show that reducing the residence time of VASP on actin filaments reduces degree of bundling, thereby promoting assembly of shells rather than rings. We validate the model predictions experimentally using a VASP-mutant with decreased bundling capability. Finally, we investigate the ring opening within deformed droplets and found that the sphere-to-ellipsoid transition is favored under a wide range of filament lengths while the ellipsoid-to-rod transition is only permitted when filaments have a specific range of lengths. Our findings highlight key mechanisms of actin organization within phase-separated ABPs.
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Affiliation(s)
- Aravind Chandrasekaran
- Department of Mechanical and Aerospace Engineering, University of California San Diego, La Jolla, CA, 92093-0411, USA
| | - Kristin Graham
- Department of Biomedical Engineering, University of Texas at Austin, Austin, TX, 78712, USA
| | - Jeanne C Stachowiak
- Department of Biomedical Engineering, University of Texas at Austin, Austin, TX, 78712, USA.
- Department of Chemical Engineering, University of Texas at Austin, Austin, TX, 78712, USA.
| | - Padmini Rangamani
- Department of Mechanical and Aerospace Engineering, University of California San Diego, La Jolla, CA, 92093-0411, USA.
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2
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Ni H, Ni Q, Papoian GA, Trache A, Jiang Y. Myosin and [Formula: see text]-actinin regulation of stress fiber contractility under tensile stress. Sci Rep 2023; 13:8662. [PMID: 37248294 PMCID: PMC10227020 DOI: 10.1038/s41598-023-35675-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2023] [Accepted: 05/19/2023] [Indexed: 05/31/2023] Open
Abstract
Stress fibers are actomyosin bundles that regulate cellular mechanosensation and force transduction. Interacting with the extracellular matrix through focal adhesion complexes, stress fibers are highly dynamic structures regulated by myosin motors and crosslinking proteins. Under external mechanical stimuli such as tensile forces, the stress fiber remodels its architecture to adapt to external cues, displaying properties of viscoelastic materials. How the structural remodeling of stress fibers is related to the generation of contractile force is not well understood. In this work, we simulate mechanochemical dynamics and force generation of stress fibers using the molecular simulation platform MEDYAN. We model stress fiber as two connecting bipolar bundles attached at the ends to focal adhesion complexes. The simulated stress fibers generate contractile force that is regulated by myosin motors and [Formula: see text]-actinin crosslinkers. We find that stress fibers enhance contractility by reducing the distance between actin filaments to increase crosslinker binding, and this structural remodeling ability depends on the crosslinker turnover rate. Under tensile pulling force, the stress fiber shows an instantaneous increase of the contractile forces followed by a slow relaxation into a new steady state. While the new steady state contractility after pulling depends only on the overlap between actin bundles, the short-term contractility enhancement is sensitive to the tensile pulling distance. We further show that this mechanical response is also sensitive to the crosslinker turnover rate. Our results provide new insights into the stress fiber mechanics that have significant implications for understanding cellular adaptation to mechanical signaling.
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Affiliation(s)
- Haoran Ni
- Institute for Physical Science and Technology, University of Maryland, College Park, MD, USA
| | - Qin Ni
- Institute for NanoBioTechnology, Johns Hopkins University, Baltimore, MD, USA
| | - Garegin A. Papoian
- Institute for Physical Science and Technology, University of Maryland, College Park, MD, USA
- Department of Chemistry and Biochemistry, University of Maryland, College Park, MD, USA
| | - Andreea Trache
- Department of Medical Physiology, Texas A &M University Health Science Center, Bryan, TX, USA
- Department of Biomedical Engineering, Texas A &M University, College Station, TX, USA
| | - Yi Jiang
- Department of Mathematics and Statistics, Georgia State University, Atlanta, GA, USA
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3
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Akenuwa OH, Abel SM. Organization and dynamics of cross-linked actin filaments in confined environments. Biophys J 2023; 122:30-42. [PMID: 36461638 PMCID: PMC9822838 DOI: 10.1016/j.bpj.2022.11.2944] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2022] [Revised: 11/02/2022] [Accepted: 11/28/2022] [Indexed: 12/03/2022] Open
Abstract
The organization of the actin cytoskeleton is impacted by the interplay between physical confinement, features of cross-linking proteins, and deformations of semiflexible actin filaments. Some cross-linking proteins preferentially bind filaments in parallel, although others bind more indiscriminately. However, a quantitative understanding of how the mode of binding influences the assembly of actin networks in confined environments is lacking. Here we employ coarse-grained computer simulations to study the dynamics and organization of semiflexible actin filaments in confined regions upon the addition of cross-linkers. We characterize how the emergent behavior is influenced by the system shape, the number and type of cross-linking proteins, and the length of filaments. Structures include isolated clusters of filaments, highly connected filament bundles, and networks of interconnected bundles and loops. Elongation of one dimension of the system promotes the formation of long bundles that align with the elongated axis. Dynamics are governed by rapid cross-linking into aggregates, followed by a slower change in their shape and connectivity. Cross-linking decreases the average bending energy of short or sparsely connected filaments by suppressing shape fluctuations. However, it increases the average bending energy in highly connected networks because filament bundles become deformed, and small numbers of filaments exhibit long-lived, highly unfavorable configurations. Indiscriminate cross-linking promotes the formation of high-energy configurations due to the increased likelihood of unfavorable, difficult-to-relax configurations at early times. Taken together, this work demonstrates physical mechanisms by which cross-linker binding and physical confinement impact the emergent behavior of actin networks, which is relevant both in cells and in synthetic environments.
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Affiliation(s)
- Oghosa H Akenuwa
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee
| | - Steven M Abel
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee.
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4
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Baldauf L, van Buren L, Fanalista F, Koenderink GH. Actomyosin-Driven Division of a Synthetic Cell. ACS Synth Biol 2022; 11:3120-3133. [PMID: 36164967 PMCID: PMC9594324 DOI: 10.1021/acssynbio.2c00287] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2022] [Indexed: 01/24/2023]
Abstract
One of the major challenges of bottom-up synthetic biology is rebuilding a minimal cell division machinery. From a reconstitution perspective, the animal cell division apparatus is mechanically the simplest and therefore attractive to rebuild. An actin-based ring produces contractile force to constrict the membrane. By contrast, microbes and plant cells have a cell wall, so division requires concerted membrane constriction and cell wall synthesis. Furthermore, reconstitution of the actin division machinery helps in understanding the physical and molecular mechanisms of cytokinesis in animal cells and thus our own cells. In this review, we describe the state-of-the-art research on reconstitution of minimal actin-mediated cytokinetic machineries. Based on the conceptual requirements that we obtained from the physics of the shape changes involved in cell division, we propose two major routes for building a minimal actin apparatus capable of division. Importantly, we acknowledge both the passive and active roles that the confining lipid membrane can play in synthetic cytokinesis. We conclude this review by identifying the most pressing challenges for future reconstitution work, thereby laying out a roadmap for building a synthetic cell equipped with a minimal actin division machinery.
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Affiliation(s)
| | | | - Federico Fanalista
- Department of Bionanoscience,
Kavli Institute of Nanoscience Delft, Delft
University of Technology, 2629 HZ Delft, The Netherlands
| | - Gijsje Hendrika Koenderink
- Department of Bionanoscience,
Kavli Institute of Nanoscience Delft, Delft
University of Technology, 2629 HZ Delft, The Netherlands
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5
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Vasudevan J, Zheng C, Wan JG, Cham TJ, Teck LC, Fernandez JG. From qualitative data to correlation using deep generative networks: Demonstrating the relation of nuclear position with the arrangement of actin filaments. PLoS One 2022; 17:e0271056. [PMID: 35905093 PMCID: PMC9337686 DOI: 10.1371/journal.pone.0271056] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2022] [Accepted: 06/22/2022] [Indexed: 11/18/2022] Open
Abstract
The cell nucleus is a dynamic structure that changes locales during cellular processes such as proliferation, differentiation, or migration, and its mispositioning is a hallmark of several disorders. As with most mechanobiological activities of adherent cells, the repositioning and anchoring of the nucleus are presumed to be associated with the organization of the cytoskeleton, the network of protein filaments providing structural integrity to the cells. However, demonstrating this correlation between cytoskeleton organization and nuclear position requires the parameterization of the extraordinarily intricate cytoskeletal fiber arrangements. Here, we show that this parameterization and demonstration can be achieved outside the limits of human conceptualization, using generative network and raw microscope images, relying on machine-driven interpretation and selection of parameterizable features. The developed transformer-based architecture was able to generate high-quality, completed images of more than 8,000 cells, using only information on actin filaments, predicting the presence of a nucleus and its exact localization in more than 70 per cent of instances. Our results demonstrate one of the most basic principles of mechanobiology with a remarkable level of significance. They also highlight the role of deep learning as a powerful tool in biology beyond data augmentation and analysis, capable of interpreting—unconstrained by the principles of human reasoning—complex biological systems from qualitative data.
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Affiliation(s)
- Jyothsna Vasudevan
- Engineering and Product Development, Singapore University of Technology and Design, Singapore, Singapore
- Department of Biomedical Engineering, National University of Singapore, Singapore, Singapore
| | - Chuanxia Zheng
- School of Computer Science and Engineering, Nanyang Technological University, Singapore, Singapore
| | - James G. Wan
- Engineering Systems and Design, Singapore University of Technology and Design, Singapore, Singapore
| | - Tat-Jen Cham
- School of Computer Science and Engineering, Nanyang Technological University, Singapore, Singapore
| | - Lim Chwee Teck
- Department of Biomedical Engineering, National University of Singapore, Singapore, Singapore
- Mechanobiology Institute, National University of Singapore, Singapore, Singapore
- Institute for Health Innovation and Technology, National University of Singapore, Singapore, Singapore
| | - Javier G. Fernandez
- Engineering and Product Development, Singapore University of Technology and Design, Singapore, Singapore
- * E-mail:
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6
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Rutkowski DM, Vavylonis D. Discrete mechanical model of lamellipodial actin network implements molecular clutch mechanism and generates arcs and microspikes. PLoS Comput Biol 2021; 17:e1009506. [PMID: 34662335 PMCID: PMC8553091 DOI: 10.1371/journal.pcbi.1009506] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Revised: 10/28/2021] [Accepted: 09/30/2021] [Indexed: 01/03/2023] Open
Abstract
Mechanical forces, actin filament turnover, and adhesion to the extracellular environment regulate lamellipodial protrusions. Computational and mathematical models at the continuum level have been used to investigate the molecular clutch mechanism, calculating the stress profile through the lamellipodium and around focal adhesions. However, the forces and deformations of individual actin filaments have not been considered while interactions between actin networks and actin bundles is not easily accounted with such methods. We develop a filament-level model of a lamellipodial actin network undergoing retrograde flow using 3D Brownian dynamics. Retrograde flow is promoted in simulations by pushing forces from the leading edge (due to actin polymerization), pulling forces (due to molecular motors), and opposed by viscous drag in cytoplasm and focal adhesions. Simulated networks have densities similar to measurements in prior electron micrographs. Connectivity between individual actin segments is maintained by permanent and dynamic crosslinkers. Remodeling of the network occurs via the addition of single actin filaments near the leading edge and via filament bond severing. We investigated how several parameters affect the stress distribution, network deformation and retrograde flow speed. The model captures the decrease in retrograde flow upon increase of focal adhesion strength. The stress profile changes from compression to extension across the leading edge, with regions of filament bending around focal adhesions. The model reproduces the observed reduction in retrograde flow speed upon exposure to cytochalasin D, which halts actin polymerization. Changes in crosslinker concentration and dynamics, as well as in the orientation pattern of newly added filaments demonstrate the model's ability to generate bundles of filaments perpendicular (actin arcs) or parallel (microspikes) to the protruding direction.
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7
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Bashirzadeh Y, Redford SA, Lorpaiboon C, Groaz A, Moghimianavval H, Litschel T, Schwille P, Hocky GM, Dinner AR, Liu AP. Actin crosslinker competition and sorting drive emergent GUV size-dependent actin network architecture. Commun Biol 2021. [PMID: 34584211 DOI: 10.1101/2020.10.03.322354v1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/22/2023] Open
Abstract
The proteins that make up the actin cytoskeleton can self-assemble into a variety of structures. In vitro experiments and coarse-grained simulations have shown that the actin crosslinking proteins α-actinin and fascin segregate into distinct domains in single actin bundles with a molecular size-dependent competition-based mechanism. Here, by encapsulating actin, α-actinin, and fascin in giant unilamellar vesicles (GUVs), we show that physical confinement can cause these proteins to form much more complex structures, including rings and asters at GUV peripheries and centers; the prevalence of different structures depends on GUV size. Strikingly, we found that α-actinin and fascin self-sort into separate domains in the aster structures with actin bundles whose apparent stiffness depends on the ratio of the relative concentrations of α-actinin and fascin. The observed boundary-imposed effect on protein sorting may be a general mechanism for creating emergent structures in biopolymer networks with multiple crosslinkers.
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Affiliation(s)
- Yashar Bashirzadeh
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Steven A Redford
- James Franck Institute, University of Chicago, Chicago, IL, 60637, USA
- The graduate program in Biophysical Sciences, University of Chicago, Chicago, IL, 60637, USA
| | | | - Alessandro Groaz
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, 77030, USA
| | | | - Thomas Litschel
- Department of Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, 82152, Martinsried, Germany
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, 02138, USA
| | - Petra Schwille
- Department of Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, 82152, Martinsried, Germany
| | - Glen M Hocky
- Department of Chemistry, New York University, New York, NY, 10003, USA
| | - Aaron R Dinner
- James Franck Institute, University of Chicago, Chicago, IL, 60637, USA.
- Department of Chemistry, University of Chicago, Chicago, IL, 60637, USA.
| | - Allen P Liu
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA.
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA.
- Department of Biophysics, University of Michigan, Ann Arbor, MI, 48109, USA.
- Cellular and Molecular Biology Program, University of Michigan, Ann Arbor, MI, 48109, USA.
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8
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Bashirzadeh Y, Redford SA, Lorpaiboon C, Groaz A, Moghimianavval H, Litschel T, Schwille P, Hocky GM, Dinner AR, Liu AP. Actin crosslinker competition and sorting drive emergent GUV size-dependent actin network architecture. Commun Biol 2021; 4:1136. [PMID: 34584211 PMCID: PMC8478941 DOI: 10.1038/s42003-021-02653-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Accepted: 09/08/2021] [Indexed: 02/07/2023] Open
Abstract
The proteins that make up the actin cytoskeleton can self-assemble into a variety of structures. In vitro experiments and coarse-grained simulations have shown that the actin crosslinking proteins α-actinin and fascin segregate into distinct domains in single actin bundles with a molecular size-dependent competition-based mechanism. Here, by encapsulating actin, α-actinin, and fascin in giant unilamellar vesicles (GUVs), we show that physical confinement can cause these proteins to form much more complex structures, including rings and asters at GUV peripheries and centers; the prevalence of different structures depends on GUV size. Strikingly, we found that α-actinin and fascin self-sort into separate domains in the aster structures with actin bundles whose apparent stiffness depends on the ratio of the relative concentrations of α-actinin and fascin. The observed boundary-imposed effect on protein sorting may be a general mechanism for creating emergent structures in biopolymer networks with multiple crosslinkers. By encapsulating proteins in giant unilamellar vesicles, Bashirzadeh et al find that actin crosslinkers, α-actinin and fascin, can self-assemble with actin into complex structures that depend on the degree of confinement. Further analysis and modeling show that α-actinin and fascin sort to separate domains of these structures. These insights may be generalizable to other biopolymer networks containing crosslinkers.
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Affiliation(s)
- Yashar Bashirzadeh
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Steven A Redford
- James Franck Institute, University of Chicago, Chicago, IL, 60637, USA.,The graduate program in Biophysical Sciences, University of Chicago, Chicago, IL, 60637, USA
| | | | - Alessandro Groaz
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA.,Department of Neuroscience, Baylor College of Medicine, Houston, TX, 77030, USA
| | | | - Thomas Litschel
- Department of Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, 82152, Martinsried, Germany.,John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, 02138, USA
| | - Petra Schwille
- Department of Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, 82152, Martinsried, Germany
| | - Glen M Hocky
- Department of Chemistry, New York University, New York, NY, 10003, USA
| | - Aaron R Dinner
- James Franck Institute, University of Chicago, Chicago, IL, 60637, USA. .,Department of Chemistry, University of Chicago, Chicago, IL, 60637, USA.
| | - Allen P Liu
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA. .,Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA. .,Department of Biophysics, University of Michigan, Ann Arbor, MI, 48109, USA. .,Cellular and Molecular Biology Program, University of Michigan, Ann Arbor, MI, 48109, USA.
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9
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Waizumi T, Sakuta H, Hayashi M, Tsumoto K, Takiguchi K, Yoshikawa K. Polymerization/depolymerization of actin cooperates with the morphology and stability of cell-sized droplets generated in a polymer solution under a depletion effect. J Chem Phys 2021; 155:075101. [PMID: 34418942 DOI: 10.1063/5.0055460] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Intercellular fluids in living organisms contain high concentrations of macromolecules such as nucleic acid and protein. Over the past few decades, several studies have examined membraneless organelles in terms of liquid-liquid phase separation. These studies have investigated aggregation/attraction among a rich variety of biomolecules. Here, we studied the association between the polymerization/depolymerization of actin, interconversion between monomeric (G-actin) and filamentous states (F-actin), and water/water phase separation in a binary polymer solution using polyethylene glycol (PEG) and dextran (DEX). We found that actin, which is a representative cytoskeleton, changes its distribution in a PEG/DEX binary solution depending on its polymerization state: monomeric G-actin is distributed homogeneously throughout the solution, whereas polymerized F-actin is localized only within the DEX-rich phase. We extended our study by using fragmin, which is a representative actin-severing and -depolymerizing factor. It took hours to restore a homogeneous actin distribution from localization within the DEX-rich phase, even with the addition of fragmin in an amount that causes complete depolymerization. In contrast, when actin that had been depolymerized by fragmin in advance was added to a solution with microphase-separation, F-actin was found in DEX-rich phase droplets. The micro-droplets tended to deform into a non-spherical morphology under conditions where they contained F-actin. These findings suggest that microphase-separation is associated with the dynamics of polymerization and localization of the actin cytoskeleton. We discuss our observations by taking into consideration the polymer depletion effect.
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Affiliation(s)
- Tatsuyuki Waizumi
- Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan
| | - Hiroki Sakuta
- Faculty of Life and Medical Sciences, Doshisha University, Tatara, Kyotanabe, Kyoto 610-0394, Japan
| | - Masahito Hayashi
- Department of Frontier Bioscience, Hosei University, Koganei, Tokyo 184-8584, Japan
| | - Kanta Tsumoto
- Division of Chemistry for Materials, Graduate School of Engineering, Mie University, Kurimamachiya-cho 1577, Tsu, Mie 514-8507, Japan
| | - Kingo Takiguchi
- Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan
| | - Kenichi Yoshikawa
- Faculty of Life and Medical Sciences, Doshisha University, Tatara, Kyotanabe, Kyoto 610-0394, Japan
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10
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Litschel T, Kelley CF, Holz D, Adeli Koudehi M, Vogel SK, Burbaum L, Mizuno N, Vavylonis D, Schwille P. Reconstitution of contractile actomyosin rings in vesicles. Nat Commun 2021; 12:2254. [PMID: 33859190 PMCID: PMC8050101 DOI: 10.1038/s41467-021-22422-7] [Citation(s) in RCA: 66] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2020] [Accepted: 03/04/2021] [Indexed: 12/31/2022] Open
Abstract
One of the grand challenges of bottom-up synthetic biology is the development of minimal machineries for cell division. The mechanical transformation of large-scale compartments, such as Giant Unilamellar Vesicles (GUVs), requires the geometry-specific coordination of active elements, several orders of magnitude larger than the molecular scale. Of all cytoskeletal structures, large-scale actomyosin rings appear to be the most promising cellular elements to accomplish this task. Here, we have adopted advanced encapsulation methods to study bundled actin filaments in GUVs and compare our results with theoretical modeling. By changing few key parameters, actin polymerization can be differentiated to resemble various types of networks in living cells. Importantly, we find membrane binding to be crucial for the robust condensation into a single actin ring in spherical vesicles, as predicted by theoretical considerations. Upon force generation by ATP-driven myosin motors, these ring-like actin structures contract and locally constrict the vesicle, forming furrow-like deformations. On the other hand, cortex-like actin networks are shown to induce and stabilize deformations from spherical shapes. Cytoskeletal networks support and direct cell shape and guide intercellular transport, but relatively little is understood about the self-organization of cytoskeletal components on the scale of an entire cell. Here, authors use an in vitro system and observe the assembly of different types of actin networks and the condensation of membrane-bound actin into single rings.
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Affiliation(s)
- Thomas Litschel
- Department of Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Charlotte F Kelley
- Department of Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, Martinsried, Germany.,Department of Structural Cell Biology, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Danielle Holz
- Department of Physics, Lehigh University, Bethlehem, PA, USA
| | | | - Sven K Vogel
- Department of Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Laura Burbaum
- Department of Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Naoko Mizuno
- Department of Structural Cell Biology, Max Planck Institute of Biochemistry, Martinsried, Germany
| | | | - Petra Schwille
- Department of Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, Martinsried, Germany.
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11
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Grekas G, Proestaki M, Rosakis P, Notbohm J, Makridakis C, Ravichandran G. Cells exploit a phase transition to mechanically remodel the fibrous extracellular matrix. J R Soc Interface 2021; 18:20200823. [PMID: 33593211 DOI: 10.1098/rsif.2020.0823] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Through mechanical forces, biological cells remodel the surrounding collagen network, generating striking deformation patterns. Tethers-tracts of high densification and fibre alignment-form between cells, thinner bands emanate from cell clusters. While tethers facilitate cell migration and communication, how they form is unclear. Combining modelling, simulation and experiment, we show that tether formation is a densification phase transition of the extracellular matrix, caused by buckling instability of network fibres under cell-induced compression, featuring unexpected similarities with martensitic microstructures. Multiscale averaging yields a two-phase, bistable continuum energy landscape for fibrous collagen, with a densified/aligned second phase. Simulations predict strain discontinuities between the undensified and densified phase, which localizes within tethers as experimentally observed. In our experiments, active particles induce similar localized patterns as cells. This shows how cells exploit an instability to mechanically remodel the extracellular matrix simply by contracting, thereby facilitating mechanosensing, invasion and metastasis.
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Affiliation(s)
- Georgios Grekas
- Aerospace Engineering and Mechanics, University of Minnesota, Minneapolis, MN, USA
| | - Maria Proestaki
- Department of Engineering Physics, University of Wisconsin-Madison, Madison, WI, USA
| | - Phoebus Rosakis
- Department of Mathematics and Applied Mathematics, University of Crete, Heraklion, Greece.,Institute of Applied and Computational Mathematics, Foundation for Research and Technology-Hellas, Heraklion, Greece
| | - Jacob Notbohm
- Department of Engineering Physics, University of Wisconsin-Madison, Madison, WI, USA
| | - Charalambos Makridakis
- Department of Mathematics and Applied Mathematics, University of Crete, Heraklion, Greece.,Institute of Applied and Computational Mathematics, Foundation for Research and Technology-Hellas, Heraklion, Greece.,Department of Mathematics, MPS, University of Sussex, Brighton, UK
| | - Guruswami Ravichandran
- Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA, USA
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