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Chikireddy J, Lengagne L, Le Borgne R, Durieu C, Wioland H, Romet-Lemonne G, Jégou A. Fascin-induced bundling protects actin filaments from disassembly by cofilin. J Cell Biol 2024; 223:e202312106. [PMID: 38497788 PMCID: PMC10949937 DOI: 10.1083/jcb.202312106] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2023] [Revised: 02/26/2024] [Accepted: 02/29/2024] [Indexed: 03/19/2024] Open
Abstract
Actin filament turnover plays a central role in shaping actin networks, yet the feedback mechanism between network architecture and filament assembly dynamics remains unclear. The activity of ADF/cofilin, the main protein family responsible for filament disassembly, has been mainly studied at the single filament level. This study unveils that fascin, by crosslinking filaments into bundles, strongly slows down filament disassembly by cofilin. We show that this is due to a markedly slower initiation of the first cofilin clusters, which occurs up to 100-fold slower on large bundles compared with single filaments. In contrast, severing at cofilin cluster boundaries is unaffected by fascin bundling. After the formation of an initial cofilin cluster on a filament within a bundle, we observed the local removal of fascin. Notably, the formation of cofilin clusters on adjacent filaments is highly enhanced, locally. We propose that this interfilament cooperativity arises from the local propagation of the cofilin-induced change in helicity from one filament to the other filaments of the bundle. Overall, taking into account all the above reactions, we reveal that fascin crosslinking slows down the disassembly of actin filaments by cofilin. These findings highlight the important role played by crosslinkers in tuning actin network turnover by modulating the activity of other regulatory proteins.
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Affiliation(s)
| | - Léana Lengagne
- Université Paris Cité, CNRS, Institut Jacques Monod, Paris, France
| | - Rémi Le Borgne
- Université Paris Cité, CNRS, Institut Jacques Monod, Paris, France
| | - Catherine Durieu
- Université Paris Cité, CNRS, Institut Jacques Monod, Paris, France
| | - Hugo Wioland
- Université Paris Cité, CNRS, Institut Jacques Monod, Paris, France
| | | | - Antoine Jégou
- Université Paris Cité, CNRS, Institut Jacques Monod, Paris, France
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2
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Cowan AE, Loew LM. Beyond analytic solution: Analysis of FRAP experiments by spatial simulation of the forward problem. Biophys J 2023; 122:3722-3737. [PMID: 37353932 PMCID: PMC10541496 DOI: 10.1016/j.bpj.2023.06.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2023] [Revised: 05/25/2023] [Accepted: 06/20/2023] [Indexed: 06/25/2023] Open
Abstract
Fluorescence redistribution after photobleaching is a commonly used method to understand the dynamic behavior of molecules within cells. Analytic solutions have been developed for specific, well-defined models of dynamic behavior in idealized geometries, but these solutions are inaccurate in complex geometries or when complex binding and diffusion behaviors exist. We demonstrate the use of numerical reaction-diffusion simulations using the Virtual Cell software platform to model fluorescence redistribution after photobleaching experiments. Multiple simulations employing parameter scans and varying bleaching locations and sizes can help to bracket diffusion coefficients and kinetic rate constants in complex image-based geometries. This approach is applied to problems in membrane surface diffusion as well as diffusion and binding in cytosolic volumes in complex cell geometries. In addition, we model diffusion and binding within phase-separated biomolecular condensates (liquid droplets). These are modeled as spherical low-affinity binding domains that also define a high viscosity medium for exchange of the free fluorescently labeled ligand with the external cytosol.
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Affiliation(s)
- Ann E Cowan
- Richard D. Berlin Center for Cell Analysis and Modeling, University of Connecticut School of Medicine, Farmington, Connecticut
| | - Leslie M Loew
- Richard D. Berlin Center for Cell Analysis and Modeling, University of Connecticut School of Medicine, Farmington, Connecticut.
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3
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Saito T, Matsunaga D, Deguchi S. Long-Term Fluorescence Recovery After Photobleaching (FRAP). Methods Mol Biol 2023; 2600:311-322. [PMID: 36587107 DOI: 10.1007/978-1-0716-2851-5_21] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Numerous models have been developed for the analysis of fluorescence recovery after photobleaching (FRAP), by which intracellular diffusion and turnover rate are quantitatively evaluated. FRAP analyses typically focus on such events that occur within several minutes, but to precisely evaluate a slow turnover rate of particularly actin stress fibers, achieving long-term FRAP observations of more than 10 min is necessary. In such long-term observations, the effect of intracellular advection is no longer ignored, which motivated us to develop a novel method to decouple the multiple factors associated with the long FRAP response. This method allows us to distinguish the origin of mechanobiological responses of stress fibers that come from either the level of individual actin filaments or that of actin monomers.
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Affiliation(s)
- Takumi Saito
- Division of Bioengineering, Graduate School of Engineering Science, Osaka University, Osaka, Japan.,Graduate School of Biomedical Engineering, Tohoku University, Miyagi, Japan.,JSPS Research Fellowship for Young Scientists, Osaka, Japan
| | - Daiki Matsunaga
- Division of Bioengineering, Graduate School of Engineering Science, Osaka University, Osaka, Japan
| | - Shinji Deguchi
- Division of Bioengineering, Graduate School of Engineering Science, Osaka University, Osaka, Japan.
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4
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Saito T, Deguchi S. CM-FRAP-Continuum Mechanics-Based Fluorescence Recovery After Photobleaching. Curr Protoc 2023; 3:e655. [PMID: 36689324 DOI: 10.1002/cpz1.655] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Fluorescence recovery after photobleaching (FRAP) is widely used to evaluate intracellular molecular turnover or repeated translocation of molecules using confocal laser scanning microscopy. While numerous models have been developed for the analysis of FRAP responses, in which chemical interactions and/or fast diffusion processes are involved, it is inherently difficult to evaluate the long-term behavior of molecular turnover because of the presence of intracellular flow and microscopic deformation of bleached regions. To overcome these difficulties, we have developed a novel continuum mechanics-based FRAP (CM-FRAP) approach that enables simultaneous evaluation of long-term molecular turnover and intracellular flow/deformation. Here we demonstrate the utility of CM-FRAP by using actin molecules associated with stress fibers in rat aortic smooth muscle cells with clarification of the experimental setup and data analysis. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Plasmid construction and sample preparation Basic Protocol 2: How to perform FRAP experiments Basic Protocol 3: Data analysis based on CM-FRAP.
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Affiliation(s)
- Takumi Saito
- Division of Bioengineering, Graduate School of Engineering Science, Osaka University, Japan.,Graduate School of Biomedical Engineering, Tohoku University, Japan.,Department of Molecular Biophysics and Biochemistry, Yale University, USA.,Nanobiology Institute, Yale University, USA
| | - Shinji Deguchi
- Division of Bioengineering, Graduate School of Engineering Science, Osaka University, Japan
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5
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Saito T, Matsunaga D, Deguchi S. Long-term molecular turnover of actin stress fibers revealed by advection-reaction analysis in fluorescence recovery after photobleaching. PLoS One 2022; 17:e0276909. [PMCID: PMC9639824 DOI: 10.1371/journal.pone.0276909] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2022] [Accepted: 10/15/2022] [Indexed: 11/09/2022] Open
Abstract
Fluorescence recovery after photobleaching (FRAP) is a versatile technique to evaluate the intracellular molecular exchange called turnover. Mechanochemical models of FRAP typically consider the molecular diffusion and chemical reaction that simultaneously occur on a time scale of seconds to minutes. Particularly for long-term measurements, however, a mechanical advection effect can no longer be ignored, which transports the proteins in specific directions within the cells and accordingly shifts the spatial distribution of the local chemical equilibrium. Nevertheless, existing FRAP models have not considered the spatial shift, and as such, the turnover rate is often analyzed without considering the spatiotemporally updated chemical equilibrium. Here we develop a new FRAP model aimed at long-term measurements to quantitatively determine the two distinct effects of the advection and chemical reaction, i.e., the different major sources of the change in fluorescence intensity. To validate this approach, we carried out FRAP experiments on actin in stress fibers over a time period of more than 900 s, and the advection rate was shown to be comparable in magnitude to the chemical dissociation rate. We further found that the actin–myosin interaction and actin polymerization differently affect the advection and chemical dissociation. Our results suggest that the distinction between the two effects is indispensable to extract the intrinsic chemical properties of the actin cytoskeleton from the observations of complicated turnover in cells.
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Affiliation(s)
- Takumi Saito
- Division of Bioengineering, Graduate School of Engineering Science, Osaka University, Osaka, Japan
- Graduate School of Biomedical Engineering, Tohoku University, Tohoku, Japan
- JSPS Research Fellowship for Young Scientists, Tokyo, Japan
| | - Daiki Matsunaga
- Division of Bioengineering, Graduate School of Engineering Science, Osaka University, Osaka, Japan
| | - Shinji Deguchi
- Division of Bioengineering, Graduate School of Engineering Science, Osaka University, Osaka, Japan
- * E-mail:
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6
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Saito T, Matsunaga D, Deguchi S. Analysis of chemomechanical behavior of stress fibers by continuum mechanics-based FRAP. Biophys J 2022; 121:2921-2930. [PMID: 35778840 PMCID: PMC9388576 DOI: 10.1016/j.bpj.2022.06.032] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2022] [Revised: 06/07/2022] [Accepted: 06/27/2022] [Indexed: 11/18/2022] Open
Abstract
Fluorescence recovery after photobleaching (FRAP) is a common technique to analyze the turnover of molecules in living cells. Numerous physicochemical models have been developed to quantitatively evaluate the rate of turnover driven by chemical reaction and diffusion that occurs in a few seconds to minutes. On the other hand, they have limitations in interpreting long-term FRAP responses where intracellular active movement inevitably provides target molecular architectures with additional effects other than chemical reaction and diffusion, namely directed transport and structural deformation. To overcome the limitations, we develop a continuum mechanics-based model that allows for decoupling FRAP response into the intrinsic turnover rate and subcellular mechanical characteristics such as displacement vector and strain tensor. Our approach was validated using fluorescently labeled β-actin in an actomyosin-mediated contractile apparatus called stress fibers, revealing spatially distinct patterns of the multi-physicochemical events, in which the turnover rate, which represents effective off-rate of β-actin, was significantly higher at the center of the cell. We also found that the turnover rate is negatively correlated with the rate of displacement or velocity along stress fibers but, interestingly, not with the absolute magnitude of strain. Moreover, stress fibers are subjected to centripetal flow that is facilitated by the circulation of actin molecules. Taken together, this novel framework for long-term FRAP analysis allows for unveiling the contribution of overlooked microscopic mechanics to molecular turnover in living cells.
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Affiliation(s)
- Takumi Saito
- Division of Bioengineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan; Graduate School of Biomedical Engineering, Tohoku University, Sendai, Japan.
| | - Daiki Matsunaga
- Division of Bioengineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan
| | - Shinji Deguchi
- Division of Bioengineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan.
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7
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Determining the domain-level reaction-diffusion properties of an actin-binding protein transgelin-2 within cells. Exp Cell Res 2021; 404:112619. [PMID: 33965400 DOI: 10.1016/j.yexcr.2021.112619] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2021] [Revised: 03/18/2021] [Accepted: 04/19/2021] [Indexed: 11/21/2022]
Abstract
Proteins in cells undergo repeated binding to other molecules, thereby reducing the apparent extent of their intracellular diffusion. While much effort has been made to analytically decouple these combined effects of pure diffusion and chemical binding, it is difficult with conventional approaches to attribute the measured quantities to the nature of specific domains of the proteins. Motivated by the common goal in cell signaling research aimed at identifying the domains responsible for particular intermolecular interactions, here we describe a framework for determining the local physicochemical properties of cellular proteins associated with immobile scaffolds. To validate this new approach, we apply it to transgelin-2, an actin-binding protein whose intracellular dynamics remains elusive. We develop a fluorescence recovery after photobleaching (FRAP)-based framework, in which comprehensive combinations of domain-deletion mutants are created, and the difference among them in FRAP response is analyzed. We demonstrate that transgelin-2 in actin stress fibers (SFs) interacts with F-actin via two separate domains, and the chemical properties are determined for the individual domains. Its pure diffusion properties independent of the association to F-actin is also obtained. Our approach will thus be useful, as presented here for transgelin-2, in addressing the signaling mechanism of cellular proteins associated with SFs.
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8
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Vohnoutka RB, Gulvady AC, Goreczny G, Alpha K, Handelman SK, Sexton JZ, Turner CE. The focal adhesion scaffold protein Hic-5 regulates vimentin organization in fibroblasts. Mol Biol Cell 2019; 30:3037-3056. [PMID: 31644368 PMCID: PMC6880880 DOI: 10.1091/mbc.e19-08-0442] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Focal adhesion (FA)-stimulated reorganization of the F-actin cytoskeleton regulates cellular size, shape, and mechanical properties. However, FA cross-talk with the intermediate filament cytoskeleton is poorly understood. Genetic ablation of the FA-associated scaffold protein Hic-5 in mouse cancer-associated fibroblasts (CAFs) promoted a dramatic collapse of the vimentin network, which was rescued following EGFP-Hic-5 expression. Vimentin collapse correlated with a loss of detergent-soluble vimentin filament precursors and decreased vimentin S72/S82 phosphorylation. Additionally, fluorescence recovery after photobleaching analysis indicated impaired vimentin dynamics. Microtubule (MT)-associated EB1 tracking and Western blotting of MT posttranslational modifications indicated no change in MT dynamics that could explain the vimentin collapse. However, pharmacological inhibition of the RhoGTPase Cdc42 in Hic-5 knockout CAFs rescued the vimentin collapse, while pan-formin inhibition with SMIFH2 promoted vimentin collapse in Hic-5 heterozygous CAFs. Our results reveal novel regulation of vimentin organization/dynamics by the FA scaffold protein Hic-5 via modulation of RhoGTPases and downstream formin activity.
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Affiliation(s)
- Rishel B Vohnoutka
- Department of Cell and Developmental Biology, State University of New York Upstate Medical University, Syracuse, NY 13210
| | - Anushree C Gulvady
- Department of Cell and Developmental Biology, State University of New York Upstate Medical University, Syracuse, NY 13210
| | - Gregory Goreczny
- Department of Cell and Developmental Biology, State University of New York Upstate Medical University, Syracuse, NY 13210
| | - Kyle Alpha
- Department of Cell and Developmental Biology, State University of New York Upstate Medical University, Syracuse, NY 13210
| | - Samuel K Handelman
- Division of Gastroenterology, Department of Internal Medicine, Michigan Medicine at the University of Michigan, Ann Arbor, MI 48109
| | - Jonathan Z Sexton
- Department of Medicinal Chemistry, College of Pharmacy, University of Michigan, Ann Arbor, MI 48109
| | - Christopher E Turner
- Department of Cell and Developmental Biology, State University of New York Upstate Medical University, Syracuse, NY 13210
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9
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Rottner K, Faix J, Bogdan S, Linder S, Kerkhoff E. Actin assembly mechanisms at a glance. J Cell Sci 2018; 130:3427-3435. [PMID: 29032357 DOI: 10.1242/jcs.206433] [Citation(s) in RCA: 178] [Impact Index Per Article: 29.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The actin cytoskeleton and associated motor proteins provide the driving forces for establishing the astonishing morphological diversity and dynamics of mammalian cells. Aside from functions in protruding and contracting cell membranes for motility, differentiation or cell division, the actin cytoskeleton provides forces to shape and move intracellular membranes of organelles and vesicles. To establish the many different actin assembly functions required in time and space, actin nucleators are targeted to specific subcellular compartments, thereby restricting the generation of specific actin filament structures to those sites. Recent research has revealed that targeting and activation of actin filament nucleators, elongators and myosin motors are tightly coordinated by conserved protein complexes to orchestrate force generation. In this Cell Science at a Glance article and the accompanying poster, we summarize and discuss the current knowledge on the corresponding protein complexes and their modes of action in actin nucleation, elongation and force generation.
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Affiliation(s)
- Klemens Rottner
- Division of Molecular Cell Biology, Zoological Institute, Technische Universität Braunschweig, 38106 Braunschweig, Germany.,Department of Cell Biology, Helmholtz Centre for Infection Research, 38124 Braunschweig, Germany
| | - Jan Faix
- Institute for Biophysical Chemistry, Hannover Medical School, 30625 Hannover, Germany
| | - Sven Bogdan
- Institute for Physiology and Pathophysiology, Department of Molecular Cell Physiology, Philipps-University of Marburg, 35032 Marburg, Germany
| | - Stefan Linder
- Institute for Medical Microbiology, Virology and Hygiene, University Medical Center Eppendorf, 20246 Hamburg, Germany
| | - Eugen Kerkhoff
- Department of Neurology, University Hospital Regensburg, 93053 Regensburg, Germany
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10
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Livne A, Geiger B. The inner workings of stress fibers - from contractile machinery to focal adhesions and back. J Cell Sci 2016; 129:1293-304. [PMID: 27037413 DOI: 10.1242/jcs.180927] [Citation(s) in RCA: 116] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Ventral stress fibers and focal adhesions are physically coupled structures that play key roles in cellular mechanics and force sensing. The tight functional interdependence between the two is manifested not only by their apparent proximity but also by the fact that ventral stress fibers and focal adhesions are simultaneously diminished upon actomyosin relaxation, and grow when subjected to external stretching. However, whereas the apparent co-regulation of the two structures is well-documented, the underlying mechanisms remains poorly understood. In this Commentary, we discuss some of the fundamental, yet still open questions regarding ventral stress fiber structure, its force-dependent assembly, as well as its capacity to generate force. We also challenge the common approach - i.e. ventral stress fibers are variants of the well-studied striated or smooth muscle machinery - by presenting and critically discussing alternative venues. By highlighting some of the less-explored aspects of the interplay between stress fibers and focal adhesions, we hope that this Commentary will encourage further investigation in this field.
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Affiliation(s)
- Ariel Livne
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Benjamin Geiger
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 7610001, Israel
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11
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Stem cell differentiation increases membrane-actin adhesion regulating cell blebability, migration and mechanics. Sci Rep 2014; 4:7307. [PMID: 25471686 PMCID: PMC4255193 DOI: 10.1038/srep07307] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Accepted: 11/10/2014] [Indexed: 11/25/2022] Open
Abstract
This study examines how differentiation of human mesenchymal stem cells regulates the interaction between the cell membrane and the actin cortex controlling cell behavior. Micropipette aspiration was used to measure the pressure required for membrane-cortex detachment which increased from 0.15 kPa in stem cells to 0.71 kPa following chondrogenic differentiation. This effect was associated with reduced susceptibility to mechanical and osmotic bleb formation, reduced migration and an increase in cell modulus. Theoretical modelling of bleb formation demonstrated that the increased stiffness of differentiated cells was due to the increased membrane-cortex adhesion. Differentiated cells exhibited greater F-actin density and slower actin remodelling. Differentiated cells also expressed greater levels of the membrane-cortex ezrin, radixin, moeisin (ERM) linker proteins which was responsible for the reduced blebability, as confirmed by transfection of stem cells with dominant active ezrin-T567D-GFP. This study demonstrates that stem cells have an inherently weak membrane-cortex adhesion which increases blebability thereby regulating cell migration and stiffness.
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12
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Responses to cell loss become restricted as the supporting cells in mammalian vestibular organs grow thick junctional actin bands that develop high stability. J Neurosci 2014; 34:1998-2011. [PMID: 24478379 DOI: 10.1523/jneurosci.4355-13.2014] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Sensory hair cell (HC) loss is a major cause of permanent hearing and balance impairments for humans and other mammals. Yet, fish, amphibians, reptiles, and birds readily replace HCs and recover from such sensory deficits. It is unknown what prevents replacement in mammals, but cell replacement capacity declines contemporaneously with massive postnatal thickening of F-actin bands at the junctions between vestibular supporting cells (SCs). In non-mammals, SCs can give rise to regenerated HCs, and the bands remain thin even in adults. Here we investigated the stability of the F-actin bands between SCs in ears from chickens and mice and Madin-Darby canine kidney cells. Pharmacological experiments and fluorescence recovery after photobleaching (FRAP) of SC junctions in utricles from mice that express a γ-actin-GFP fusion protein showed that the thickening F-actin bands develop increased resistance to depolymerization and exceptional stability that parallels a sharp decline in the cell replacement capacity of the maturing mammalian ear. The FRAP recovery rate and the mobile fraction of γ-actin-GFP both decreased as the bands thickened with age and became highly stabilized. In utricles from neonatal mice, time-lapse recordings in the vicinity of dying HCs showed that numerous SCs change shape and organize multicellular actin purse strings that reseal the epithelium. In contrast, adult SCs appeared resistant to deformation, with resealing responses limited to just a few neighboring SCs that did not form purse strings. The exceptional stability of the uniquely thick F-actin bands at the junctions of mature SCs may play an important role in restricting dynamic repair responses in mammalian vestibular epithelia.
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13
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Staras K, Mikulincer D, Gitler D. Monitoring and quantifying dynamic physiological processes in live neurons using fluorescence recovery after photobleaching. J Neurochem 2013; 126:213-22. [PMID: 23496032 DOI: 10.1111/jnc.12240] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2013] [Revised: 03/12/2013] [Accepted: 03/13/2013] [Indexed: 12/27/2022]
Abstract
The direct visualization of subcellular dynamic processes is often hampered by limitations in the resolving power achievable with conventional microscopy techniques. Fluorescence recovery after photobleaching has emerged as a highly informative approach to address this challenge, permitting the quantitative measurement of the movement of small organelles and proteins in living functioning cells, and offering detailed insights into fundamental cellular phenomena of physiological importance. In recent years, its implementation has benefited from the increasing availability of confocal microscopy systems and of powerful labeling techniques based on genetically encoded fluorescent proteins or other chemical markers. In this review, we present fluorescence recovery after photobleaching and related techniques in the context of contemporary neurobiological research and discuss quantitative and semi-quantitative approaches to their interpretation.
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Affiliation(s)
- Kevin Staras
- School of Life Sciences, University of Sussex, Brighton, UK
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14
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Irving AT, Wang D, Vasilevski O, Latchoumanin O, Kozer N, Clayton AHA, Szczepny A, Morimoto H, Xu D, Williams BRG, Sadler AJ. Regulation of actin dynamics by protein kinase R control of gelsolin enforces basal innate immune defense. Immunity 2012; 36:795-806. [PMID: 22633459 DOI: 10.1016/j.immuni.2012.02.020] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2011] [Revised: 12/30/2011] [Accepted: 02/29/2012] [Indexed: 10/28/2022]
Abstract
Primary resistance to pathogens is reliant on both basal and inducible immune defenses. To date, research has focused upon inducible innate immune responses. In contrast to resistance via cytokine induction, basal defense mechanisms are less evident. Here we showed that the antiviral protein kinase R (PKR) inhibited the key actin-modifying protein gelsolin to regulate actin dynamics and control cytoskeletal cellular functions under homeostatic conditions. Through this mechanism, PKR controlled fundamental innate immune, actin-dependent processes that included membrane ruffling and particle engulfment. Accordingly, PKR counteracted viral entry into the cell. These findings identify a layer of host resistance, showing that the regulation of actin-modifying proteins during the innate immune response bolsters first-line defense against intracellular pathogens and has a sustained effect on virus production. Moreover, these data provide proof of principle for a concept in which the cell cytoskeleton could be targeted to elicit broad antiviral protection.
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Affiliation(s)
- Aaron T Irving
- Centre for Cancer Research, Monash Institute of Medical Research, Monash University, Clayton, Victoria 3168, Australia
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15
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Hardy LR. Fluorescence Recovery After Photobleaching (FRAP) with a Focus on F‐actin. ACTA ACUST UNITED AC 2012; Chapter 2:Unit 2.17. [DOI: 10.1002/0471142301.ns0217s61] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Lori R. Hardy
- Department of Basic Sciences, Philadelphia College of Osteopathic Medicine Suwanee Georgia
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16
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Pravincumar P, Bader DL, Knight MM. Viscoelastic cell mechanics and actin remodelling are dependent on the rate of applied pressure. PLoS One 2012; 7:e43938. [PMID: 22984454 PMCID: PMC3439462 DOI: 10.1371/journal.pone.0043938] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2012] [Accepted: 07/27/2012] [Indexed: 12/11/2022] Open
Abstract
Background Living cells are subjected to external and internal mechanical stresses. The effects of these stresses on the deformation and subsequent biological response of the cells remains unclear. This study tested the hypothesis that the rate at which pressure (or stress) is applied influence the viscoelastic properties of the cell associated with differences in the dynamics of the actin cytoskeleton. Principal Finding Micropipette aspiration was used to determine the instantaneous and equilibrium moduli and the viscosity of isolated chondrocytes based on the standard linear solid (SLS) model and a variation of this incorporating Boltzmann superposition. Cells were visualised for 180 seconds following aspiration to 7 cmH2O at 0.35, 0.70 and 5.48 cmH2O/sec. Cell recovery was then examined for a further 180 seconds once the pressure had been removed. Reducing the rate of application of pressure reduced the levels of cell deformation and recovery associated with a significant increase in modulus and viscosity. Using GFP transfection and confocal microscopy, we show that chondrocyte deformation involves distortion, disassembly and subsequent reassembly of the cortical actin cytoskeleton. At faster pressure rates, cell deformation produced an increase in cell volume associated with membrane bleb formation. GFP-actin transfection inhibited the pressure rate dependent variation in cell mechanics indicating that this behaviour is regulated by GFP-sensitive actin dynamics. Conclusion We suggest that slower rates of aspiration pressure enable greater levels of cortical actin distortion. This is partially inhibited by GFP or faster aspiration rates leading to membrane bleb formation and an increase in cell volume. Thus the rate of application of pressure regulates the viscoelastic mechanical properties of living cells through pressure rate sensitive differences in actin dynamics. Therefore cells appear softer when aspirated at a faster rate in contrast to what is expected of a normal viscoelastic material.
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Affiliation(s)
- Priyanka Pravincumar
- Institute of Bioengineering, School of Engineering and Material Science, Queen Mary University of London, London, United Kingdom
| | - Dan L. Bader
- Institute of Bioengineering, School of Engineering and Material Science, Queen Mary University of London, London, United Kingdom
| | - Martin M. Knight
- Institute of Bioengineering, School of Engineering and Material Science, Queen Mary University of London, London, United Kingdom
- * E-mail:
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17
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Guolla L, Bertrand M, Haase K, Pelling AE. Force transduction and strain dynamics in actin stress fibres in response to nanonewton forces. J Cell Sci 2012; 125:603-13. [PMID: 22389400 DOI: 10.1242/jcs.088302] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
It is becoming clear that mechanical stimuli are crucial factors in regulating the biology of the cell, but the short-term structural response of a cell to mechanical forces remains relatively poorly understood. We mechanically stimulated cells transiently expressing actin-EGFP with controlled forces (0-20 nN) in order to investigate the structural response of the cell. Two clear force-dependent responses were observed: a short-term (seconds) local deformation of actin stress fibres and a long-term (minutes) force-induced remodelling of stress fibres at cell edges, far from the point of contact. By photobleaching markers along stress fibres we were also able to quantify strain dynamics occurring along the fibres throughout the cell. The results reveal that the cell exhibits complex heterogeneous negative and positive strain fluctuations along stress fibres in resting cells that indicate localized contraction and stretch dynamics. The application of mechanical force results in the activation of myosin contractile activity reflected in an ~50% increase in strain fluctuations. This approach has allowed us to directly observe the activation of myosin in response to mechanical force and the effects of cytoskeletal crosslinking on local deformation and strain dynamics. The results demonstrate that force application does not result in simplistic isotropic deformation of the cytoarchitecture, but rather a complex and localized response that is highly dependent on an intact microtubule network. Direct visualization of force-propagation and stress fibre strain dynamics have revealed several crucial phenomena that take place and ultimately govern the downstream response of a cell to a mechanical stimulus.
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Affiliation(s)
- Louise Guolla
- Department of Physics, MacDonald Hall, 150 Louis Pasteur, University of Ottawa, Ottawa, ON, K1N 6N5, Canada
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Abstract
Cross-linked actomyosin bundles retract when severed in vivo by laser ablation, or when isolated from the cell and micromanipulated in vitro in the presence of ATP. We identify the timescale for contraction as a viscoelastic time τ, where the viscosity is due to (internal) protein friction. We obtain an estimate of the order of magnitude of the contraction time τ ≈ 10-100 s, consistent with available experimental data for circumferential microfilament bundles and stress fibers. Our results are supported by an exactly solvable, hydrodynamic model of a retracting bundle as a cylinder of isotropic, active matter, from which the order of magnitude of the active stress is estimated.
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Affiliation(s)
- Natsuhiko Yoshinaga
- WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
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Visualization of actin polymerization in invasive structures of macrophages and carcinoma cells using photoconvertible β-actin-Dendra2 fusion proteins. PLoS One 2011; 6:e16485. [PMID: 21339827 PMCID: PMC3038862 DOI: 10.1371/journal.pone.0016485] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2010] [Accepted: 12/22/2010] [Indexed: 11/26/2022] Open
Abstract
Actin polymerization controls a range of cellular processes, from intracellular trafficking to cell motility and invasion. Generation and elongation of free barbed ends defines the regions of actively polymerizing actin in cells and, consequently, is of importance in the understanding of the mechanisms through which actin dynamics are regulated. Herein we present a method that does not involve cell permeabilization and provides direct visualization of growing barbed ends using photoswitchable β-actin - Dendra2 constructs expressed in murine macrophage and rat mammary adenocarcinoma cell lines. The method exploits the ability of photoconverted (red) G-actin species to become incorporated into pre-existing (green) actin filaments, visualized in two distinct wavelengths using TIRF microscopy. In growing actin filaments, photoconverted (red) monomers are added to the barbed end while only green monomers are recycled from the pointed end. We demonstrate that incorporation of actin into intact podosomes of macrophages occurs constitutively and is amenable to inhibition by cytochalasin D indicating barbed end incorporation. Additionally, actin polymerization does not occur in quiescent invadopodial precursors of carcinoma cells suggesting that the filaments are capped and following epidermal growth factor stimulation actin incorporation occurs in a single but extended peak. Finally, we show that Dendra2 fused to either the N- or the C-terminus of β-actin profoundly affects its localization and incorporation in distinct F-actin structures in carcinoma cells, thus influencing the ability of monomers to be photoconverted. These data support the use of photoswitchable actin-Dendra2 constructs as powerful tools in the visualization of free barbed ends in living cells.
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Gliem M, Heupel WM, Spindler V, Harms GS, Waschke J. Actin reorganization contributes to loss of cell adhesion in pemphigus vulgaris. Am J Physiol Cell Physiol 2010; 299:C606-13. [PMID: 20554911 DOI: 10.1152/ajpcell.00075.2010] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In the human autoimmune blistering skin disease pemphigus vulgaris autoantibodies (PV-IgG), which are mainly directed against keratinocyte cell adhesion molecules desmoglein (Dsg) 3 and Dsg1, cause keratinocyte cell dissociation (acantholysis). Recent studies reported that loss of keratinocyte cell adhesion was accompanied by profound alterations of the actin cytoskeleton. Nevertheless, the relevance of actin reorganization in this process is unclear at present. In this study, we provide evidence for an important role of actin reorganization in pemphigus pathogenesis. In parallel to loss of cell adhesion and fragmentation of Dsg3 staining along cell borders, PV-IgG treatment resulted in striking changes in actin cytoskeleton organization. Moreover, in experiments using fluorescence recovery after photobleaching (FRAP), PV-IgG were detected to interfere with actin dynamics. Therefore, we investigated whether pharmacological manipulation of actin polymerization modulates pathogenic effects of PV-IgG. Pharmacological stabilization of actin filaments via jasplakinolide significantly blocked cell dissociation and Dsg3 fragmentation, whereas cytochalasin D-induced actin depolymerization strongly enhanced pathogenic effects of PV-IgG. To substantiate these findings, we studied whether the protective effects of Rho GTPases, which are potent regulators of the actin cytoskeleton and were shown to be involved in pemphigus pathogenesis, were dependent on modulation of actin dynamics. Cytotoxic necrotizing factor-1 (CNF-1)-mediated activation of Rho-GTPases enhanced the cortical junction-associated actin belt and blunted PV-IgG-induced cell dissociation. However, when actin polymerization was blocked under these conditions via addition of latrunculin B, the protective effects of CNF-1 were abrogated. Taken together, these experiments indicate that reorganization of cortical actin filaments is a critical step in PV-IgG-induced keratinocyte dissociation.
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Affiliation(s)
- Martin Gliem
- Institute of Anatomy and Cell Biology, Univ. of Würzburg, Würzburg, Germany
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A mathematical model of actin filament turnover for fitting FRAP data. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2009; 39:669-77. [PMID: 19921173 DOI: 10.1007/s00249-009-0558-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2009] [Revised: 08/24/2009] [Accepted: 10/19/2009] [Indexed: 10/20/2022]
Abstract
A novel mathematical model of the actin dynamics in living cells under steady-state conditions has been developed for fluorescence recovery after photobleaching (FRAP) experiments. As opposed to other FRAP fitting models, which use the average lifetime of actins in filaments and the actin turnover rate as fitting parameters, our model operates with unbiased actin association/dissociation rate constants and accounts for the filament length. The mathematical formalism is based on a system of stochastic differential equations. The derived equations were validated on synthetic theoretical data generated by a stochastic simulation algorithm adapted for the simulation of FRAP experiments. Consistent with experimental findings, the results of this work showed that (1) fluorescence recovery is a function of the average filament length, (2) the F-actin turnover and the FRAP are accelerated in the presence of actin nucleating proteins, (3) the FRAP curves may exhibit both a linear and non-linear behaviour depending on the parameters of actin polymerisation, and (4) our model resulted in more accurate parameter estimations of actin dynamics as compared with other FRAP fitting models. Additionally, we provide a computational tool that integrates the model and that can be used for interpretation of FRAP data on actin cytoskeleton.
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