1
|
Kwok ML, Geyer M, Chan WC, Zhao S, Gu L, Huang F, Vogel SM, Petukhov PA, Komarova Y. Targeting EB3-IP 3R3 Interface with Cognate Peptide Protects from Acute Respiratory Distress Syndrome. Am J Respir Cell Mol Biol 2023; 69:391-403. [PMID: 37290041 PMCID: PMC10557916 DOI: 10.1165/rcmb.2022-0217oc] [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: 05/24/2022] [Accepted: 06/08/2023] [Indexed: 06/10/2023] Open
Abstract
Acute respiratory distress syndrome (ARDS) is a lung disease characterized by acute onset of noncardiogenic pulmonary edema, hypoxemia, and respiratory insufficiency. The current treatment for ARDS is mainly supportive in nature, providing a critical need for targeted pharmacological management. We addressed this medical problem by developing a pharmacological treatment for pulmonary vascular leakage, a culprit of alveolar damage and lung inflammation. Our novel therapeutic target is the microtubule accessory factor EB3 (end binding protein 3), which contributes to pulmonary vascular leakage by amplifying pathological calcium signaling in endothelial cells in response to inflammatory stimuli. EB3 interacts with IP3R3 (inositol 1,4,5-trisphosphate receptor 3) and orchestrates calcium release from endoplasmic reticulum stores. Here, we designed and tested the therapeutic benefits of a 14-aa peptide named CIPRI (cognate IP3 receptor inhibitor), which disrupted EB3-IP3R3 interaction in vitro and in lungs of mice challenged with endotoxin. Treatment with CIPRI or depletion of IP3R3 in lung microvascular endothelial monolayers mitigated calcium release from endoplasmic reticulum stores and prevented a disassembly of vascular endothelial cadherin junctions in response to the proinflammatory mediator α-thrombin. Furthermore, intravenous administration of CIPRI in mice mitigated inflammation-induced lung injury, blocked pulmonary microvascular leakage, prevented activation of NFAT (nuclear factor of activated T cells) signaling, and reduced production of proinflammatory cytokines in the lung tissue. CIPRI also improved survival of mice from endotoxemia and polymicrobial sepsis. Together, these data demonstrate that targeting EB3-IP3R3 interaction with a cognate peptide is a promising strategy to address hyperpermeability of microvessels in inflammatory lung diseases.
Collapse
Affiliation(s)
- Man Long Kwok
- Department of Pharmacology and Regenerative Medicine, College of Medicine, and
| | - Melissa Geyer
- Department of Pharmacology and Regenerative Medicine, College of Medicine, and
| | - Wan Ching Chan
- Department of Pharmacology and Regenerative Medicine, College of Medicine, and
| | - Shuangping Zhao
- Department of Pharmacology and Regenerative Medicine, College of Medicine, and
| | - Lianzhi Gu
- Department of Pharmacology and Regenerative Medicine, College of Medicine, and
| | - Fei Huang
- Department of Pharmacology and Regenerative Medicine, College of Medicine, and
| | - Steven M. Vogel
- Department of Pharmacology and Regenerative Medicine, College of Medicine, and
| | - Pavel A. Petukhov
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Illinois at Chicago, Chicago, Illinois
| | - Yulia Komarova
- Department of Pharmacology and Regenerative Medicine, College of Medicine, and
| |
Collapse
|
2
|
Appalabhotla R, Butler MT, Bear JE, Haugh JM. G-actin diffusion is insufficient to achieve F-actin assembly in fast-treadmilling protrusions. Biophys J 2023; 122:3816-3829. [PMID: 37644720 PMCID: PMC10541494 DOI: 10.1016/j.bpj.2023.08.022] [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: 04/01/2023] [Revised: 07/07/2023] [Accepted: 08/25/2023] [Indexed: 08/31/2023] Open
Abstract
To generate forces that drive migration of a eukaryotic cell, arrays of actin filaments (F-actin) are assembled at the cell's leading membrane edge. To maintain cell propulsion and respond to dynamic external cues, actin filaments must be disassembled to regenerate the actin monomers (G-actin), and transport of G-actin from sites of disassembly back to the leading edge completes the treadmilling cycle and limits the flux of F-actin assembly. Whether or not molecular diffusion is sufficient for G-actin transport has been a long-standing topic of debate, in part because the dynamic nature of cell motility and migration hinders the estimation of transport parameters. In this work, we applied an experimental system in which cells adopt an approximately constant and symmetrical shape; they cannot migrate but exhibit fast, steady treadmilling in the thin region protruding from the cell. Using fluorescence recovery after photobleaching, we quantified the relative concentrations and corresponding fluxes of F- and G-actin in this system. In conjunction with mathematical modeling, constrained by measured features of each region of interest, this approach revealed that diffusion alone cannot account for the transport of G-actin to the leading edge. Although G-actin diffusion and vectorial transport might vary with position in the protruding region, good agreement with the fluorescence recovery after photobleaching measurements was achieved by a model with constant G-actin diffusivity ∼2 μm2/s and anterograde G-actin velocity less than 1 μm/s.
Collapse
Affiliation(s)
- Ravikanth Appalabhotla
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina
| | - Mitchell T Butler
- Department of Cell Biology and Physiology, UNC Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, North Carolina
| | - James E Bear
- Department of Cell Biology and Physiology, UNC Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, North Carolina.
| | - Jason M Haugh
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina.
| |
Collapse
|
3
|
Demosthene B, Lee M, Marracino RR, Heidings JB, Kang EH. Molecular Basis for Actin Polymerization Kinetics Modulated by Solution Crowding. Biomolecules 2023; 13:biom13050786. [PMID: 37238656 DOI: 10.3390/biom13050786] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2023] [Revised: 04/18/2023] [Accepted: 04/25/2023] [Indexed: 05/28/2023] Open
Abstract
Actin polymerization drives cell movement and provides cells with structural integrity. Intracellular environments contain high concentrations of solutes, including organic compounds, macromolecules, and proteins. Macromolecular crowding has been shown to affect actin filament stability and bulk polymerization kinetics. However, the molecular mechanisms behind how crowding influences individual actin filament assembly are not well understood. In this study, we investigated how crowding modulates filament assembly kinetics using total internal reflection fluorescence (TIRF) microscopy imaging and pyrene fluorescence assays. The elongation rates of individual actin filaments analyzed from TIRF imaging depended on the type of crowding agent (polyethylene glycol, bovine serum albumin, and sucrose) as well as their concentrations. Further, we utilized all-atom molecular dynamics (MD) simulations to evaluate the effects of crowding molecules on the diffusion of actin monomers during filament assembly. Taken together, our data suggest that solution crowding can regulate actin assembly kinetics at the molecular level.
Collapse
Affiliation(s)
- Bryan Demosthene
- NanoScience Technology Center, University of Central Florida, Orlando, FL 32826, USA
- Burnett School of Biomedical Sciences, University of Central Florida, Orlando, FL 32827, USA
| | - Myeongsang Lee
- NanoScience Technology Center, University of Central Florida, Orlando, FL 32826, USA
| | - Ryan R Marracino
- NanoScience Technology Center, University of Central Florida, Orlando, FL 32826, USA
- Burnett School of Biomedical Sciences, University of Central Florida, Orlando, FL 32827, USA
| | - James B Heidings
- NanoScience Technology Center, University of Central Florida, Orlando, FL 32826, USA
- Burnett School of Biomedical Sciences, University of Central Florida, Orlando, FL 32827, USA
| | - Ellen Hyeran Kang
- NanoScience Technology Center, University of Central Florida, Orlando, FL 32826, USA
- Department of Physics, University of Central Florida, Orlando, FL 32816, USA
- Department of Materials Science and Engineering, University of Central Florida, Orlando, FL 32816, USA
| |
Collapse
|
4
|
Das S, Ippolito A, McGarry P, Deshpande VS. Cell reorientation on a cyclically strained substrate. PNAS NEXUS 2022; 1:pgac199. [PMID: 36712366 PMCID: PMC9802216 DOI: 10.1093/pnasnexus/pgac199] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/22/2022] [Accepted: 09/17/2022] [Indexed: 06/18/2023]
Abstract
Cyclic strain avoidance, the phenomenon of cell and cytoskeleton alignment perpendicular to the direction of cyclic strain of the underlying 2D substrate, is an important characteristic of the adherent cell organization. This alignment has typically been attributed to the stress-fiber reorganization although observations clearly show that stress-fiber reorganization under cyclic loading is closely coupled to cell morphology and reorientation of the cells. Here, we develop a statistical mechanics framework that couples the cytoskeletal stress-fiber organization with cell morphology under imposed cyclic straining and make quantitative comparisons with observations. The framework accurately predicts that cyclic strain avoidance stems primarily from cell reorientation away from the cyclic straining rather than cytoskeletal reorganization within the cell. The reorientation of the cell is a consequence of the cell lowering its free energy by largely avoiding the imposed cyclic straining. Furthermore, we investigate the kinetics of the cyclic strain avoidance mechanism and demonstrate that it emerges primarily due to the rigid body rotation of the cell rather than via a trajectory involving cell straining. Our results provide clear physical insights into the coupled dynamics of cell morphology and stress-fibers, which ultimately leads to cellular organization in cyclically strained tissues.
Collapse
Affiliation(s)
- Shuvrangsu Das
- Department of Engineering, Cambridge University, Trumpington St, Cambridge CB2 1PZ, UK
| | - Alberto Ippolito
- Department of Engineering, Cambridge University, Trumpington St, Cambridge CB2 1PZ, UK
| | - Patrick McGarry
- Department of Mechanical and Biomedical Engineering, National University of Ireland, University Road, Galway H91 CF50, Ireland
| | | |
Collapse
|
5
|
A statistical mechanics model for determining the length distribution of actin filaments under cellular tensional homeostasis. Sci Rep 2022; 12:14466. [PMID: 36002503 PMCID: PMC9402564 DOI: 10.1038/s41598-022-18833-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Accepted: 08/22/2022] [Indexed: 11/08/2022] Open
Abstract
Tensional homeostasis is a cellular process whereby nonmuscle cells such as fibroblasts keep a constant level of intracellular tension and signaling activities. Cells are allowed thanks to tensional homeostasis to adapt to mechanical stress, but the detailed mechanism remains unclear. Here we address from a theoretical point of view what is required for maintaining cellular tensional homeostasis. A constrained optimization problem is formulated to analytically determine the probability function of the length of individual actin filaments (AFs) responsible for sustaining cellular tension. An objective function composed of two entropic quantities measuring the extent of formation and dispersion of AFs within cells is optimized under two constraint functions dictating a constant amount of actin molecules and tension that are arguably the two most salient features of tensional homeostasis. We then derive a specific probability function of AFs that is qualitatively consistent with previous experimental observations, in which short AF populations preferably appear. Regarding the underlying mechanism, our analyses suggest that the constraint for keeping the constant tension level makes long AF populations smaller in number because long AFs have a higher chance to be involved in bearing larger forces. The specific length distribution of AFs is thus required for achieving the constrained objectives, by which individual cells are endowed with the ability to stably maintain a homeostatic tension throughout the cell, thereby potentially allowing cells to locally detect deviation in the tension, keep resulting biological functions, and hence enable subsequent adaptation to mechanical stress. Although minimal essential factors are included given the actual complexity of cells, our approach would provide a theoretical basis for understanding complicated homeostatic and adaptive behavior of the cell.
Collapse
|
6
|
Deviri D, Safran SA. Balance of osmotic pressures determines the nuclear-to-cytoplasmic volume ratio of the cell. Proc Natl Acad Sci U S A 2022; 119:e2118301119. [PMID: 35580183 PMCID: PMC9173802 DOI: 10.1073/pnas.2118301119] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2021] [Accepted: 04/05/2022] [Indexed: 01/06/2023] Open
Abstract
The volume of the cell nucleus varies across cell types and species and is commonly thought to be determined by the size of the genome and degree of chromatin compaction. However, this notion has been challenged over the years by much experimental evidence. Here, we consider the physical condition of mechanical force balance as a determining condition of the nuclear volume and use quantitative, order-of-magnitude analysis to estimate the forces from different sources of nuclear and cytoplasmic pressure. Our estimates suggest that the dominant pressure within the nucleus and cytoplasm of nonstriated muscle cells originates from the osmotic pressure of proteins and RNA molecules that are localized to the nucleus or cytoplasm by out-of-equilibrium, active nucleocytoplasmic transport rather than from chromatin or its associated ions. This motivates us to formulate a physical model for the ratio of the cell and nuclear volumes in which osmotic pressures of localized proteins determine the relative volumes. In accordance with unexplained observations that are a century old, our model predicts that the ratio of the cell and nuclear volumes is a constant, robust to a wide variety of biochemical and biophysical manipulations, and is changed only if gene expression or nucleocytoplasmic transport is modulated.
Collapse
Affiliation(s)
- Dan Deviri
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovet 76100, Israel
| | - Samuel A. Safran
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovet 76100, Israel
| |
Collapse
|
7
|
Vimentin intermediate filaments and filamentous actin form unexpected interpenetrating networks that redefine the cell cortex. Proc Natl Acad Sci U S A 2022; 119:e2115217119. [PMID: 35235449 PMCID: PMC8915831 DOI: 10.1073/pnas.2115217119] [Citation(s) in RCA: 19] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Filamentous actin (F-actin) and vimentin intermediate filaments (VIFs) are two major cytoskeletal components; they are generally thought to be spatially compartmentalized and to have distinctly different and independent functions. Here we combine two imaging methods, high-resolution structured illumination microscopy and cryo-electron tomography, as well as functional characterizations, to show that unexpectedly, VIFs and F-actin have extensive structural interactions within the cell cortex and form interpenetrating networks. These interactions have very important functional consequences for cells, which are broadly significant given the wide range of processes attributed to F-actin. These results profoundly alter our understanding of the contributions of cytoskeletal components and counter the common belief that VIFs and F-actin are independent in both structure and function. The cytoskeleton of eukaryotic cells is primarily composed of networks of filamentous proteins, F-actin, microtubules, and intermediate filaments. Interactions among the cytoskeletal components are important in determining cell structure and in regulating cell functions. For example, F-actin and microtubules work together to control cell shape and polarity, while the subcellular organization and transport of vimentin intermediate filament (VIF) networks depend on their interactions with microtubules. However, it is generally thought that F-actin and VIFs form two coexisting but separate networks that are independent due to observed differences in their spatial distribution and functions. In this paper, we present a closer investigation of both the structural and functional interplay between the F-actin and VIF cytoskeletal networks. We characterize the structure of VIFs and F-actin networks within the cell cortex using structured illumination microscopy and cryo-electron tomography. We find that VIFs and F-actin form an interpenetrating network (IPN) with interactions at multiple length scales, and VIFs are integral components of F-actin stress fibers. From measurements of recovery of cell contractility after transient stretching, we find that the IPN structure results in enhanced contractile forces and contributes to cell resilience. Studies of reconstituted networks and dynamic measurements in cells suggest direct and specific associations between VIFs and F-actin. From these results, we conclude that VIFs and F-actin work synergistically, both in their structure and in their function. These results profoundly alter our understanding of the contributions of the components of the cytoskeleton, particularly the interactions between intermediate filaments and F-actin.
Collapse
|
8
|
Rapid ensemble measurement of protein diffusion and probe blinking dynamics in cells. BIOPHYSICAL REPORTS 2021; 1:100015. [PMID: 36425455 PMCID: PMC9680803 DOI: 10.1016/j.bpr.2021.100015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Accepted: 08/30/2021] [Indexed: 12/25/2022]
Abstract
We present a fluorescence fluctuation image correlation analysis method that can rapidly and simultaneously measure the diffusion coefficient, photoblinking rates, and fraction of diffusing particles of fluorescent molecules in cells. Unlike other image correlation techniques, we demonstrated that our method could be applied irrespective of a nonuniformly distributed, immobile blinking fluorophore population. This allows us to measure blinking and transport dynamics in complex cell morphologies, a benefit for a range of super-resolution fluorescence imaging approaches that rely on probe emission blinking. Furthermore, we showed that our technique could be applied without directly accounting for photobleaching. We successfully employed our technique on several simulations with realistic EMCCD noise and photobleaching models, as well as on Dronpa-C12-labeled β-actin in living NIH/3T3 and HeLa cells. We found that the diffusion coefficients measured using our method were consistent with previous literature values. We further found that photoblinking rates measured in the live HeLa cells varied as expected with changing excitation power.
Collapse
|
9
|
Membrane Homeostasis: The Role of Actin Cytoskeleton. J Indian Inst Sci 2021. [DOI: 10.1007/s41745-020-00217-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
|
10
|
Targeting the cytoskeleton against metastatic dissemination. Cancer Metastasis Rev 2021; 40:89-140. [PMID: 33471283 DOI: 10.1007/s10555-020-09936-0] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/19/2020] [Accepted: 10/08/2020] [Indexed: 02/08/2023]
Abstract
Cancer is a pathology characterized by a loss or a perturbation of a number of typical features of normal cell behaviour. Indeed, the acquisition of an inappropriate migratory and invasive phenotype has been reported to be one of the hallmarks of cancer. The cytoskeleton is a complex dynamic network of highly ordered interlinking filaments playing a key role in the control of fundamental cellular processes, like cell shape maintenance, motility, division and intracellular transport. Moreover, deregulation of this complex machinery contributes to cancer progression and malignancy, enabling cells to acquire an invasive and metastatic phenotype. Metastasis accounts for 90% of death from patients affected by solid tumours, while an efficient prevention and suppression of metastatic disease still remains elusive. This results in the lack of effective therapeutic options currently available for patients with advanced disease. In this context, the cytoskeleton with its regulatory and structural proteins emerges as a novel and highly effective target to be exploited for a substantial therapeutic effort toward the development of specific anti-metastatic drugs. Here we provide an overview of the role of cytoskeleton components and interacting proteins in cancer metastasis with a special focus on small molecule compounds interfering with the actin cytoskeleton organization and function. The emerging involvement of microtubules and intermediate filaments in cancer metastasis is also reviewed.
Collapse
|
11
|
Senra D, Páez A, Gueron G, Bruno L, Guisoni N. Following the footprints of variability during filopodial growth. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2020; 49:643-659. [PMID: 33141270 DOI: 10.1007/s00249-020-01473-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2020] [Revised: 10/06/2020] [Accepted: 10/19/2020] [Indexed: 01/09/2023]
Abstract
Filopodia are actin-built finger-like dynamic structures that protrude from the cell cortex. These structures can sense the environment and play key roles in migration and cell-cell interactions. The growth-retraction cycle of filopodia is a complex process exquisitely regulated by intra- and extra-cellular cues, whose nature remains elusive. Filopodia present wide variation in length, lifetime and growth rate. Here, we investigate the features of filopodia patterns in fixed prostate tumor cells by confocal microscopy. Analysis of almost a thousand filopodia suggests the presence of two different populations: one characterized by a narrow distribution of lengths and the other with a much more variable pattern with very long filopodia. We explore a stochastic model of filopodial growth which takes into account diffusion and reactions involving actin and the regulatory proteins formin and capping, and retrograde flow. Interestingly, we found an inverse dependence between the filopodial length and the retrograde velocity. This result led us to propose that variations in the retrograde velocity could explain the experimental lengths observed for these tumor cells. In this sense, one population involves a wider range of retrograde velocities than the other population, and also includes low values of this velocity. It has been hypothesized that cells would be able to regulate retrograde flow as a mechanism to control filopodial length. Thus, we propound that the experimental filopodia pattern is the result of differential retrograde velocities originated from heterogeneous signaling due to cell-substrate interactions or prior cell-cell contacts.
Collapse
Affiliation(s)
- Daniela Senra
- Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, Universidad Nacional de La Plata, CONICET, La Plata, Argentina
| | - Alejandra Páez
- Laboratorio de Inflamación y Cáncer, Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, C1428EGA, Buenos Aires, Argentina
- CONICET, Universidad de Buenos Aires, Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales (IQUIBICEN), C1428EGA, Buenos Aires, Argentina
- Unidad de Transferencia Genética, Instituto de Oncología "Ángel H. Roffo", Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Geraldine Gueron
- Laboratorio de Inflamación y Cáncer, Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, C1428EGA, Buenos Aires, Argentina
- CONICET, Universidad de Buenos Aires, Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales (IQUIBICEN), C1428EGA, Buenos Aires, Argentina
| | - Luciana Bruno
- Instituto de Cálculo, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, CONICET, Pabellón 2, Ciudad Universitaria (1428), Buenos Aires, Argentina
| | - Nara Guisoni
- Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, Universidad Nacional de La Plata, CONICET, La Plata, Argentina.
| |
Collapse
|
12
|
Kopfer KH, Jäger W, Matthäus F. A mechanochemical model for rho GTPase mediated cell polarization. J Theor Biol 2020; 504:110386. [DOI: 10.1016/j.jtbi.2020.110386] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2020] [Revised: 06/15/2020] [Accepted: 06/17/2020] [Indexed: 01/13/2023]
|
13
|
Pimm ML, Hotaling J, Henty-Ridilla JL. Profilin choreographs actin and microtubules in cells and cancer. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2020; 355:155-204. [PMID: 32859370 PMCID: PMC7461721 DOI: 10.1016/bs.ircmb.2020.05.005] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Actin and microtubules play essential roles in aberrant cell processes that define and converge in cancer including: signaling, morphology, motility, and division. Actin and microtubules do not directly interact, however shared regulators coordinate these polymers. While many of the individual proteins important for regulating and choreographing actin and microtubule behaviors have been identified, the way these molecules collaborate or fail in normal or disease contexts is not fully understood. Decades of research focus on Profilin as a signaling molecule, lipid-binding protein, and canonical regulator of actin assembly. Recent reports demonstrate that Profilin also regulates microtubule dynamics and polymerization. Thus, Profilin can coordinate both actin and microtubule polymer systems. Here we reconsider the biochemical and cellular roles for Profilin with a focus on the essential cytoskeletal-based cell processes that go awry in cancer. We also explore how the use of model organisms has helped to elucidate mechanisms that underlie the regulatory essence of Profilin in vivo and in the context of disease.
Collapse
Affiliation(s)
- Morgan L Pimm
- Department of Cell and Developmental Biology, State University of New York (SUNY) Upstate Medical University, Syracuse, NY, United States
| | - Jessica Hotaling
- Department of Cell and Developmental Biology, State University of New York (SUNY) Upstate Medical University, Syracuse, NY, United States
| | - Jessica L Henty-Ridilla
- Department of Cell and Developmental Biology, State University of New York (SUNY) Upstate Medical University, Syracuse, NY, United States; Department of Biochemistry and Molecular Biology, State University of New York (SUNY) Upstate Medical University, Syracuse, NY, United States.
| |
Collapse
|
14
|
The Arp2/3 complex and the formin, Diaphanous, are both required to regulate the size of germline ring canals in the developing egg chamber. Dev Biol 2020; 461:75-85. [PMID: 31945342 DOI: 10.1016/j.ydbio.2020.01.007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2019] [Revised: 01/10/2020] [Accepted: 01/10/2020] [Indexed: 01/30/2023]
Abstract
Intercellular bridges are an essential structural feature found in both germline and somatic cells throughout the animal kingdom. Because of their large size, the germline intercellular bridges, or ring canals, in the developing fruit fly egg chamber are an excellent model to study the formation, stabilization, and growth of these structures. Within the egg chamber, the germline ring canals connect 15 supporting nurse cells to the developing oocyte, facilitating the transfer of materials required for successful oogenesis. The ring canals are derived from a stalled actomyosin contractile ring; once formed, additional actin and actin-binding proteins are recruited to the ring to support the 20-fold growth that accompanies oogenesis. These behaviors provide a unique model system to study the actin regulators that control incomplete cytokinesis, intercellular bridge formation, and growth. By temporally controlling their expression in the germline, we have demonstrated that the Arp2/3 complex and the formin, Diaphanous (Dia), coordinately regulate ring canal size and growth throughout oogenesis. Dia is required for successful incomplete cytokinesis and the initial stabilization of the germline ring canals. Once ring canals have formed, the Arp2/3 complex and Dia cooperate to determine ring canal size and maintain stability. Our data suggest that nurse cells must maintain a precise balance between the activity of these two nucleators during oogenesis.
Collapse
|
15
|
Dos-Santos Carvalho S, Moreau MM, Hien YE, Garcia M, Aubailly N, Henderson DJ, Studer V, Sans N, Thoumine O, Montcouquiol M. Vangl2 acts at the interface between actin and N-cadherin to modulate mammalian neuronal outgrowth. eLife 2020; 9:51822. [PMID: 31909712 PMCID: PMC6946565 DOI: 10.7554/elife.51822] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2019] [Accepted: 12/16/2019] [Indexed: 12/13/2022] Open
Abstract
Dynamic mechanical interactions between adhesion complexes and the cytoskeleton are essential for axon outgrowth and guidance. Whether planar cell polarity (PCP) proteins, which regulate cytoskeleton dynamics and appear necessary for some axon guidance, also mediate interactions with membrane adhesion is still unclear. Here we show that Vangl2 controls growth cone velocity by regulating the internal retrograde actin flow in an N-cadherin-dependent fashion. Single molecule tracking experiments show that the loss of Vangl2 decreased fast-diffusing N-cadherin membrane molecules and increased confined N-cadherin trajectories. Using optically manipulated N-cadherin-coated microspheres, we correlated this behavior to a stronger mechanical coupling of N-cadherin with the actin cytoskeleton. Lastly, we show that the spatial distribution of Vangl2 within the growth cone is selectively affected by an N-cadherin-coated substrate. Altogether, our data show that Vangl2 acts as a negative regulator of axonal outgrowth by regulating the strength of the molecular clutch between N-cadherin and the actin cytoskeleton.
Collapse
Affiliation(s)
- Steve Dos-Santos Carvalho
- INSERM, Neurocentre Magendie, U1215, Bordeaux, France.,Univ. Bordeaux, Neurocentre Magendie, U1215, Bordeaux, France
| | - Maite M Moreau
- INSERM, Neurocentre Magendie, U1215, Bordeaux, France.,Univ. Bordeaux, Neurocentre Magendie, U1215, Bordeaux, France
| | - Yeri Esther Hien
- INSERM, Neurocentre Magendie, U1215, Bordeaux, France.,Univ. Bordeaux, Neurocentre Magendie, U1215, Bordeaux, France
| | - Mikael Garcia
- CNRS, Interdisciplinary Institute for Neuroscience, UMR 5297, Bordeaux, France.,Univ. Bordeaux, Interdisciplinary Institute for Neuroscience, UMR 5297, Bordeaux, France
| | - Nathalie Aubailly
- INSERM, Neurocentre Magendie, U1215, Bordeaux, France.,Univ. Bordeaux, Neurocentre Magendie, U1215, Bordeaux, France
| | - Deborah J Henderson
- Biosciences Institute, Newcastle University, Centre for Life, Newcastle upon Tyne, United Kingdom
| | - Vincent Studer
- CNRS, Interdisciplinary Institute for Neuroscience, UMR 5297, Bordeaux, France.,Univ. Bordeaux, Interdisciplinary Institute for Neuroscience, UMR 5297, Bordeaux, France
| | - Nathalie Sans
- INSERM, Neurocentre Magendie, U1215, Bordeaux, France.,Univ. Bordeaux, Neurocentre Magendie, U1215, Bordeaux, France
| | - Olivier Thoumine
- CNRS, Interdisciplinary Institute for Neuroscience, UMR 5297, Bordeaux, France.,Univ. Bordeaux, Interdisciplinary Institute for Neuroscience, UMR 5297, Bordeaux, France
| | - Mireille Montcouquiol
- INSERM, Neurocentre Magendie, U1215, Bordeaux, France.,Univ. Bordeaux, Neurocentre Magendie, U1215, Bordeaux, France
| |
Collapse
|
16
|
Motahari F, Carlsson AE. Pulling-force generation by ensembles of polymerizing actin filaments. Phys Biol 2019; 17:016005. [PMID: 31747656 DOI: 10.1088/1478-3975/ab59bd] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The process by which actin polymerization generates pulling forces in cellular processes such as endocytosis is less well understood than pushing-force generation. To clarify the basic mechanisms of pulling-force generation, we perform stochastic polymerization simulations for a square array of polymerizing semiflexible actin filaments, having different interactions with the membrane. The filaments near the array center have a strong attractive component. Filament bending and actin-network elasticity are treated explicitly. We find that the outer filaments push on the membrane and the inner filaments pull, with a net balance of forces. The total calculated pulling force is maximized when the central filaments have a very deep potential well, and the outer filaments have no well. The steady-state force is unaffected by the gel rigidity, but equilibration takes longer for softer gels. The force distributions are flat over the pulling and pushing regions. Actin polymerization is enhanced by softening the gel or reducing the filament binding to the membrane. Filament-membrane detachment can occur for softer gels, even if the total binding energy of the filaments to the membrane is 100 [Formula: see text] or more. It propagates via a stress-concentration mechanism similar to that of a brittle crack in a solid, and the breaking stress is determined by a criterion similar to that of the 'Griffith' theory of crack propagation.
Collapse
Affiliation(s)
- F Motahari
- Department of Physics and Center for Engineering Mechanobiology, Washington University, St. Louis, MO 63130, United States of America
| | | |
Collapse
|
17
|
Yamashiro S, Watanabe N. Quantitative high-precision imaging of myosin-dependent filamentous actin dynamics. J Muscle Res Cell Motil 2019; 41:163-173. [PMID: 31313218 DOI: 10.1007/s10974-019-09541-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2019] [Accepted: 07/10/2019] [Indexed: 12/20/2022]
Abstract
Over recent decades, considerable effort has been made to understand how mechanical stress applied to the actin network alters actin assembly and disassembly dynamics. However, there are conflicting reports concerning the issue both in vitro and in cells. In this review, we discuss concerns regarding previous quantitative live-cell experiments that have attempted to evaluate myosin regulation of filamentous actin (F-actin) turnover. In particular, we highlight an error-generating mechanism in quantitative live-cell imaging, namely convection-induced misdistribution of actin-binding probes. Direct observation of actin turnover at the single-molecule level using our improved electroporation-based Single-Molecule Speckle (eSiMS) microscopy technique overcomes these concerns. We introduce our recent single-molecule analysis that unambiguously demonstrates myosin-dependent regulation of F-actin stability in live cells. We also discuss the possible application of eSiMS microscopy in the analysis of actin remodeling in striated muscle cells.
Collapse
Affiliation(s)
- Sawako Yamashiro
- Laboratory of Single-Molecule Cell Biology, Kyoto University Graduate School of Biostudies, Yoshida Konoe-cho, Sakyo-ku, Kyoto, 606-8501, Japan. .,Department of Pharmacology, Kyoto University Graduate School of Medicine, Kyoto, Japan.
| | - Naoki Watanabe
- Laboratory of Single-Molecule Cell Biology, Kyoto University Graduate School of Biostudies, Yoshida Konoe-cho, Sakyo-ku, Kyoto, 606-8501, Japan.,Department of Pharmacology, Kyoto University Graduate School of Medicine, Kyoto, Japan
| |
Collapse
|
18
|
Chakrabarty N, Jung P. Stochastic models of polymerization-based axonal actin transport. Phys Biol 2019; 16:056001. [PMID: 31195374 DOI: 10.1088/1478-3975/ab29cd] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Recent advances in live cell imaging of F-actin structures, combined with pulse-chase imaging and computational modeling have suggested that actin is transported along the axon via biased polymerization of metastable actin fibers (actin trails). This mechanism is distinct from motor driven polymer transport, such as for neurofilaments and can be best described as molecular hitchhiking, where G-actin molecules are intermittently incorporated into actin fibers which grow preferentially in the anterograde direction. In this paper, we discuss how various axonal and actin trail parameters like axon diameter, trail nucleation rates, basal G-actin concentration, and trail length influence the transport rate. These predictions can help guide future experiments to verify this novel protein transport mechanism. We introduce a simplified, analytically solvable model of actin transport which relates these parameters to experimentally measurable quantities. We also discuss why a simple diffusion-based transport mechanism cannot explain bulk actin transport in the axon.
Collapse
Affiliation(s)
- Nilaj Chakrabarty
- Department of Physics and Astronomy, Neuroscience Program and Quantitative Biology Institute, Athens, OH 45701, United States of America
| | | |
Collapse
|
19
|
Yamashiro S, Taniguchi D, Tanaka S, Kiuchi T, Vavylonis D, Watanabe N. Convection-Induced Biased Distribution of Actin Probes in Live Cells. Biophys J 2018; 116:142-150. [PMID: 30558885 DOI: 10.1016/j.bpj.2018.11.022] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2018] [Revised: 11/02/2018] [Accepted: 11/16/2018] [Indexed: 11/20/2022] Open
Abstract
Fluorescent markers that bind endogenous target proteins are frequently employed for quantitative live-cell imaging. To visualize the actin cytoskeleton in live cells, several actin-binding probes have been widely used. Among them, Lifeact is the most popular probe with ideal properties, including fast exchangeable binding kinetics. Because of its fast kinetics, Lifeact is generally believed to distribute evenly throughout cellular actin structures. In this study, however, we demonstrate misdistribution of Lifeact toward the rear of lamellipodia where actin filaments continuously move inward along the retrograde flow. Similarly, phalloidin showed biased misdistribution toward the rear of lamellipodia in live cells. We show evidence of convection-induced misdistribution of actin probes by both experimental data and physical models. Our findings warn about the potential error arising from the use of target-binding probes in quantitative live imaging.
Collapse
Affiliation(s)
- Sawako Yamashiro
- Laboratory of Single-Molecule Cell Biology, Kyoto University Graduate School of Medicine, Kyoto Japan; Department of Pharmacology, Kyoto University Graduate School of Medicine, Kyoto Japan.
| | - Daisuke Taniguchi
- Department of Pharmacology, Kyoto University Graduate School of Medicine, Kyoto Japan
| | - Soichiro Tanaka
- Laboratory of Single-Molecule Cell Biology, Tohoku University Graduate School of Life Sciences, Sendai, Miyagi, Japan
| | - Tai Kiuchi
- Department of Pharmacology, Kyoto University Graduate School of Medicine, Kyoto Japan
| | | | - Naoki Watanabe
- Laboratory of Single-Molecule Cell Biology, Kyoto University Graduate School of Medicine, Kyoto Japan; Department of Pharmacology, Kyoto University Graduate School of Medicine, Kyoto Japan.
| |
Collapse
|
20
|
Chakrabarty N, Dubey P, Tang Y, Ganguly A, Ladt K, Leterrier C, Jung P, Roy S. Processive flow by biased polymerization mediates the slow axonal transport of actin. J Cell Biol 2018; 218:112-124. [PMID: 30401699 PMCID: PMC6314539 DOI: 10.1083/jcb.201711022] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2017] [Revised: 09/02/2018] [Accepted: 10/25/2018] [Indexed: 12/15/2022] Open
Abstract
Chakrabarty et al. propose a model in which slow axonal transport of actin can occur by a biased polymerization of actin filaments along the axon shaft without the involvement of microtubules (MTs) or MT-based motors. These dynamics are distinct from polymer sliding—the canonical mechanism thought to convey cytoskeletal cargoes in slow transport. Classic pulse-chase studies have shown that actin is conveyed in slow axonal transport, but the mechanistic basis for this movement is unknown. Recently, we reported that axonal actin was surprisingly dynamic, with focal assembly/disassembly events (“actin hotspots”) and elongating polymers along the axon shaft (“actin trails”). Using a combination of live imaging, superresolution microscopy, and modeling, in this study, we explore how these dynamic structures can lead to processive transport of actin. We found relatively more actin trails elongated anterogradely as well as an overall slow, anterogradely biased flow of actin in axon shafts. Starting with first principles of monomer/filament assembly and incorporating imaging data, we generated a quantitative model simulating axonal hotspots and trails. Our simulations predict that the axonal actin dynamics indeed lead to a slow anterogradely biased flow of the population. Collectively, the data point to a surprising scenario where local assembly and biased polymerization generate the slow axonal transport of actin without involvement of microtubules (MTs) or MT-based motors. Mechanistically distinct from polymer sliding, this might be a general strategy to convey highly dynamic cytoskeletal cargoes.
Collapse
Affiliation(s)
- Nilaj Chakrabarty
- Department of Physics and Astronomy, Neuroscience Program and Quantitative Biology Institute, Ohio University, Athens, OH
| | - Pankaj Dubey
- Department of Pathology and Laboratory Medicine, University of Wisconsin-Madison, Madison, WI
| | - Yong Tang
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA
| | - Archan Ganguly
- Department of Neurosciences, University of California, San Diego, La Jolla, CA
| | - Kelsey Ladt
- Department of Neurosciences, University of California, San Diego, La Jolla, CA
| | - Christophe Leterrier
- Aix-Marseille Université, Centre National de la Recherche Scientifique, Institut Neurophysiopathol, NeuroCyto, Marseille, France
| | - Peter Jung
- Department of Physics and Astronomy, Neuroscience Program and Quantitative Biology Institute, Ohio University, Athens, OH
| | - Subhojit Roy
- Department of Pathology and Laboratory Medicine, University of Wisconsin-Madison, Madison, WI .,Department of Neuroscience, University of Wisconsin-Madison, Madison, WI
| |
Collapse
|
21
|
The homeostatic ensemble for cells. Biomech Model Mechanobiol 2018; 17:1631-1662. [PMID: 29987699 DOI: 10.1007/s10237-018-1048-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2018] [Accepted: 06/26/2018] [Indexed: 12/12/2022]
Abstract
Cells are quintessential examples of out-of-equilibrium systems, but they maintain a homeostatic state over a timescale of hours to days. As a consequence, the statistics of all observables is remarkably consistent. Here, we develop a statistical mechanics framework for living cells by including the homeostatic constraint that exists over the interphase period of the cell cycle. The consequence is the introduction of the concept of a homeostatic ensemble and an associated homeostatic temperature, along with a formalism for the (dynamic) homeostatic equilibrium that intervenes to allow living cells to evade thermodynamic decay. As a first application, the framework is shown to accurately predict the observed effect of the mechanical environment on the in vitro response of smooth muscle cells. This includes predictions that both the mean values and diversity/variability in the measured values of observables such as cell area, shape and tractions decrease with decreasing stiffness of the environment. Thus, we argue that the observed variabilities are inherent to the entropic nature of the homeostatic equilibrium of cells and not a result of in vitro experimental errors.
Collapse
|
22
|
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: 77] [Impact Index Per Article: 12.8] [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.
Collapse
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
| |
Collapse
|
23
|
Raz-Ben Aroush D, Ofer N, Abu-Shah E, Allard J, Krichevsky O, Mogilner A, Keren K. Actin Turnover in Lamellipodial Fragments. Curr Biol 2017; 27:2963-2973.e14. [PMID: 28966086 DOI: 10.1016/j.cub.2017.08.066] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2016] [Revised: 07/21/2017] [Accepted: 08/29/2017] [Indexed: 10/18/2022]
Abstract
Actin turnover is the central driving force underlying lamellipodial motility. The molecular components involved are largely known, and their properties have been studied extensively in vitro. However, a comprehensive picture of actin turnover in vivo is still missing. We focus on fragments from fish epithelial keratocytes, which are essentially stand-alone motile lamellipodia. The geometric simplicity of the fragments and the absence of additional actin structures allow us to characterize the spatiotemporal lamellipodial actin organization with unprecedented detail. We use fluorescence recovery after photobleaching, fluorescence correlation spectroscopy, and extraction experiments to show that about two-thirds of the lamellipodial actin diffuses in the cytoplasm with nearly uniform density, whereas the rest forms the treadmilling polymer network. Roughly a quarter of the diffusible actin pool is in filamentous form as diffusing oligomers, indicating that severing and debranching are important steps in the disassembly process generating oligomers as intermediates. The remaining diffusible actin concentration is orders of magnitude higher than the in vitro actin monomer concentration required to support the observed polymerization rates, implying that the majority of monomers are transiently kept in a non-polymerizable "reserve" pool. The actin network disassembles and reassembles throughout the lamellipodium within seconds, so the lamellipodial network turnover is local. The diffusible actin transport, on the other hand, is global: actin subunits typically diffuse across the entire lamellipodium before reassembling into the network. This combination of local network turnover and global transport of dissociated subunits through the cytoplasm makes actin transport robust yet rapidly adaptable and amenable to regulation.
Collapse
Affiliation(s)
- Dikla Raz-Ben Aroush
- Department of Physics, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Noa Ofer
- Department of Physics, Technion-Israel Institute of Technology, Haifa 32000, Israel; Russell Berrie Nanotechnology Institute, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Enas Abu-Shah
- Department of Physics, Technion-Israel Institute of Technology, Haifa 32000, Israel; Russell Berrie Nanotechnology Institute, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Jun Allard
- Department of Mathematics, Center for Complex Biological Systems and Department of Physics and Astronomy, University of California at Irvine, Irvine, CA 92697, USA
| | - Oleg Krichevsky
- Physics Department and Ilse Kats Center for Nanoscience, Ben-Gurion University, Beer-Sheva 84105, Israel
| | - Alex Mogilner
- Courant Institute of Mathematical Sciences and Department of Biology, New York University, New York, NY 10012, USA.
| | - Kinneret Keren
- Department of Physics, Technion-Israel Institute of Technology, Haifa 32000, Israel; Russell Berrie Nanotechnology Institute, Technion-Israel Institute of Technology, Haifa 32000, Israel; Network Biology Research Laboratories, Technion-Israel Institute of Technology, Haifa 32000, Israel.
| |
Collapse
|
24
|
Yamashiro S, Watanabe N. Overview of Single-Molecule Speckle (SiMS) Microscopy and Its Electroporation-Based Version with Efficient Labeling and Improved Spatiotemporal Resolution. SENSORS 2017; 17:s17071585. [PMID: 28684722 PMCID: PMC5539652 DOI: 10.3390/s17071585] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/01/2017] [Revised: 06/30/2017] [Accepted: 07/03/2017] [Indexed: 12/19/2022]
Abstract
Live-cell single-molecule imaging was introduced more than a decade ago, and has provided critical information on remodeling of the actin cytoskeleton, the motion of plasma membrane proteins, and dynamics of molecular motor proteins. Actin remodeling has been the best target for this approach because actin and its associated proteins stop diffusing when assembled, allowing visualization of single-molecules of fluorescently-labeled proteins in a state specific manner. The approach based on this simple principle is called Single-Molecule Speckle (SiMS) microscopy. For instance, spatiotemporal regulation of actin polymerization and lifetime distribution of actin filaments can be monitored directly by tracking actin SiMS. In combination with fluorescently labeled probes of various actin regulators, SiMS microscopy has contributed to clarifying the processes underlying recycling, motion and remodeling of the live-cell actin network. Recently, we introduced an electroporation-based method called eSiMS microscopy, with high efficiency, easiness and improved spatiotemporal precision. In this review, we describe the application of live-cell single-molecule imaging to cellular actin dynamics and discuss the advantages of eSiMS microscopy over previous SiMS microscopy.
Collapse
Affiliation(s)
- Sawako Yamashiro
- Laboratory of Single-Molecule Cell Biology, Kyoto University Graduate School of Biostudies, Kyoto 606-8501, Japan.
| | - Naoki Watanabe
- Laboratory of Single-Molecule Cell Biology, Kyoto University Graduate School of Biostudies, Kyoto 606-8501, Japan.
- Department of Pharmacology, Kyoto University Graduate School of Medicine, Kyoto 606-8501, Japan.
| |
Collapse
|
25
|
Abstract
In this study we present a steady-state adaptation of the thermodynamically motivated stress fiber (SF) model of Vigliotti et al. (2015). We implement this steady-state formulation in a non-local finite element setting where we also consider global conservation of the total number of cytoskeletal proteins within the cell, global conservation of the number of binding integrins on the cell membrane, and adhesion limiting ligand density on the substrate surface. We present a number of simulations of cell spreading in which we consider a limited subset of the possible deformed spread-states assumed by the cell in order to examine the hypothesis that free energy minimization drives the process of cell spreading. Simulations suggest that cell spreading can be viewed as a competition between (i) decreasing cytoskeletal free energy due to strain induced assembly of cytoskeletal proteins into contractile SFs, and (ii) increasing elastic free energy due to stretching of the mechanically passive components of the cell. The computed minimum free energy spread area is shown to be lower for a cell on a compliant substrate than on a rigid substrate. Furthermore, a low substrate ligand density is found to limit cell spreading. The predicted dependence of cell spread area on substrate stiffness and ligand density is in agreement with the experiments of Engler et al. (2003). We also simulate the experiments of Théry et al. (2006), whereby initially circular cells deform and adhere to "V-shaped" and "Y-shaped" ligand patches. Analysis of a number of different spread states reveals that deformed configurations with the lowest free energy exhibit a SF distribution that corresponds to experimental observations, i.e. a high concentration of highly aligned SFs occurs along free edges, with lower SF concentrations in the interior of the cell. In summary, the results of this study suggest that cell spreading is driven by free energy minimization based on a competition between decreasing cytoskeletal free energy and increasing passive elastic free energy.
Collapse
Affiliation(s)
- Eóin McEvoy
- Biomedical Engineering, National University of Ireland Galway, Galway, Ireland.
| | | | - Patrick McGarry
- Biomedical Engineering, National University of Ireland Galway, Galway, Ireland.
| |
Collapse
|
26
|
Dimchev G, Steffen A, Kage F, Dimchev V, Pernier J, Carlier MF, Rottner K. Efficiency of lamellipodia protrusion is determined by the extent of cytosolic actin assembly. Mol Biol Cell 2017; 28:1311-1325. [PMID: 28331069 PMCID: PMC5426846 DOI: 10.1091/mbc.e16-05-0334] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2016] [Revised: 02/10/2017] [Accepted: 03/17/2017] [Indexed: 11/26/2022] Open
Abstract
Lamellipodia protrusion requires actin network formation driven by the Arp2/3 complex and its upstream regulators WAVE complex and Rac. Actin assembly factors of the formin and Ena/VASP families can influence protrusion, in particular by maintaining a balance between lamellipodial and cytosolic actin filament assembly. Cell migration and cell–cell communication involve the protrusion of actin-rich cell surface projections such as lamellipodia and filopodia. Lamellipodia are networks of actin filaments generated and turned over by filament branching through the Arp2/3 complex. Inhibition of branching is commonly agreed to eliminate formation and maintenance of lamellipodial actin networks, but the regulation of nucleation or elongation of Arp2/3-independent filament populations within the network by, for example, formins or Ena/VASP family members and its influence on the effectiveness of protrusion have been unclear. Here we analyzed the effects of a set of distinct formin fragments and VASP on site-specific, lamellipodial versus cytosolic actin assembly and resulting consequences on protrusion. Surprisingly, expression of formin variants but not VASP reduced lamellipodial protrusion in B16-F1 cells, albeit to variable extents. The rates of actin network polymerization followed a similar trend. Unexpectedly, the degree of inhibition of both parameters depended on the extent of cytosolic but not lamellipodial actin assembly. Indeed, excess cytosolic actin assembly prevented actin monomer from rapid translocation to and efficient incorporation into lamellipodia. Thus, as opposed to sole regulation by actin polymerases operating at their tips, the protrusion efficiency of lamellipodia is determined by a finely tuned balance between lamellipodial and cytosolic actin assembly.
Collapse
Affiliation(s)
- Georgi Dimchev
- 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
| | - Anika Steffen
- Department of Cell Biology, Helmholtz Centre for Infection Research, 38124 Braunschweig, Germany
| | - Frieda Kage
- 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
| | - Vanessa Dimchev
- 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
| | - Julien Pernier
- Cytoskeleton Dynamics and Motility, Centre National de la Recherche Scientifique, 91198 Gif-sur-Yvette, France
| | - Marie-France Carlier
- Cytoskeleton Dynamics and Motility, Centre National de la Recherche Scientifique, 91198 Gif-sur-Yvette, France
| | - 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
| |
Collapse
|
27
|
Wang X, Galletta BJ, Cooper JA, Carlsson AE. Actin-Regulator Feedback Interactions during Endocytosis. Biophys J 2016; 110:1430-43. [PMID: 27028652 DOI: 10.1016/j.bpj.2016.02.018] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2015] [Revised: 01/20/2016] [Accepted: 02/08/2016] [Indexed: 01/22/2023] Open
Abstract
Endocytosis mediated by clathrin, a cellular process by which cells internalize membrane receptors and their extracellular ligands, is an important component of cell signaling regulation. Actin polymerization is involved in endocytosis in varying degrees depending on the cellular context. In yeast, clathrin-mediated endocytosis requires a pulse of polymerized actin and its regulators, which recruit and activate the Arp2/3 complex. In this article, we seek to identify the main protein-protein interactions that 1) cause actin and its regulators to appear in pulses, and 2) determine the effects of key mutations and drug treatments on actin and regulator assembly. We perform a joint modeling/experimental study of actin and regulator dynamics during endocytosis in the budding yeast Saccharomyces cerevisiae. We treat both a stochastic model that grows an explicit three-dimensional actin network, and a simpler two-variable Fitzhugh-Nagumo type model. The models include a negative-feedback interaction of F-actin onto the Arp2/3 regulators. Both models explain the pulse time courses and the effects of interventions on actin polymerization: the surprising increase in the peak F-actin count caused by reduced regulator branching activity, the increase in F-actin resulting from slowing of actin disassembly, and the increased Arp2/3 regulator lifetime resulting from latrunculin treatment. In addition, they predict that decreases in the regulator branching activity lead to increases in accumulation of regulators, and we confirmed this prediction with experiments on yeast harboring mutations in the Arp2/3 regulators, using quantitative fluorescence microscopy. Our experimental measurements suggest that the regulators act quasi-independently, in the sense that accumulation of a particular regulator is most strongly affected by mutations of that regulator, as opposed to the others.
Collapse
Affiliation(s)
- Xinxin Wang
- Department of Physics, Washington University, St. Louis, Missouri
| | - Brian J Galletta
- Cell Biology and Physiology Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
| | - John A Cooper
- Department of Cell Biology and Physiology, Washington University School of Medicine, St Louis, Missouri
| | | |
Collapse
|
28
|
McMillen LM, Vavylonis D. Model of turnover kinetics in the lamellipodium: implications of slow- and fast- diffusing capping protein and Arp2/3 complex. Phys Biol 2016; 13:066009. [PMID: 27922825 DOI: 10.1088/1478-3975/13/6/066009] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Cell protrusion through polymerization of actin filaments at the leading edge of motile cells may be influenced by spatial gradients of diffuse actin and regulators. Here we study the distribution of two of the most important regulators, capping protein and Arp2/3 complex, which regulate actin polymerization in the lamellipodium through capping and nucleation of free barbed ends. We modeled their kinetics using data from prior single molecule microscopy experiments on XTC cells. These experiments have provided evidence for a broad distribution of diffusion coefficients of both capping protein and Arp2/3 complex. The slowly diffusing proteins appear as extended 'clouds' while proteins bound to the actin filament network appear as speckles that undergo retrograde flow. Speckle appearance and disappearance events correspond to assembly and dissociation from the actin filament network and speckle lifetimes correspond to the dissociation rate. The slowly diffusing capping protein could represent severed capped actin filament fragments or membrane-bound capping protein. Prior evidence suggests that slowly diffusing Apr2/3 complex associates with the membrane. We use the measured rates and estimates of diffusion coefficients of capping protein and Arp2/3 complex in a Monte Carlo simulation that includes particles in association with a filament network and diffuse in the cytoplasm. We consider two separate pools of diffuse proteins, representing fast and slowly diffusing species. We find a steady state with concentration gradients involving a balance of diffusive flow of fast and slow species with retrograde flow. We show that simulations of FRAP are consistent with prior experiments performed on different cell types. We provide estimates for the ratio of bound to diffuse complexes and calculate conditions where Arp2/3 complex recycling by diffusion may become limiting. We discuss the implications of slowly diffusing populations and suggest experiments to distinguish among mechanisms that influence long range transport.
Collapse
Affiliation(s)
- Laura M McMillen
- Department of Physics, Lehigh University, Bethlehem PA 18015, USA
| | | |
Collapse
|
29
|
Kapustina M, Read TA, Vitriol EA. Simultaneous quantification of actin monomer and filament dynamics with modeling-assisted analysis of photoactivation. J Cell Sci 2016; 129:4633-4643. [PMID: 27831495 PMCID: PMC5201019 DOI: 10.1242/jcs.194670] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2016] [Accepted: 11/02/2016] [Indexed: 01/30/2023] Open
Abstract
Photoactivation allows one to pulse-label molecules and obtain quantitative data about their behavior. We have devised a new modeling-based analysis for photoactivatable actin experiments that simultaneously measures properties of monomeric and filamentous actin in a three-dimensional cellular environment. We use this method to determine differences in the dynamic behavior of β- and γ-actin isoforms, showing that both inhabit filaments that depolymerize at equal rates but that β-actin exists in a higher monomer-to-filament ratio. We also demonstrate that cofilin (cofilin 1) equally accelerates depolymerization of filaments made from both isoforms, but is only required to maintain the β-actin monomer pool. Finally, we used modeling-based analysis to assess actin dynamics in axon-like projections of differentiating neuroblastoma cells, showing that the actin monomer concentration is significantly depleted as the axon develops. Importantly, these results would not have been obtained using traditional half-time analysis. Given that parameters of the publicly available modeling platform can be adjusted to suit the experimental system of the user, this method can easily be used to quantify actin dynamics in many different cell types and subcellular compartments.
Collapse
Affiliation(s)
- Maryna Kapustina
- Department of Cell Biology and Physiology, School of Medicine, University of North Carolina, Chapel Hill, NC 27599, 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
| |
Collapse
|
30
|
Hartzell CA, Jankowska KI, Burkhardt JK, Lewis RS. Calcium influx through CRAC channels controls actin organization and dynamics at the immune synapse. eLife 2016; 5. [PMID: 27440222 PMCID: PMC4956410 DOI: 10.7554/elife.14850] [Citation(s) in RCA: 62] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2016] [Accepted: 06/13/2016] [Indexed: 11/21/2022] Open
Abstract
T cell receptor (TCR) engagement opens Ca2+ release-activated Ca2+ (CRAC) channels and triggers formation of an immune synapse between T cells and antigen-presenting cells. At the synapse, actin reorganizes into a concentric lamellipod and lamella with retrograde actin flow that helps regulate the intensity and duration of TCR signaling. We find that Ca2+ influx is required to drive actin organization and dynamics at the synapse. Calcium acts by promoting actin depolymerization and localizing actin polymerization and the actin nucleation promotion factor WAVE2 to the periphery of the lamellipod while suppressing polymerization elsewhere. Ca2+-dependent retrograde actin flow corrals ER tubule extensions and STIM1/Orai1 complexes to the synapse center, creating a self-organizing process for CRAC channel localization. Our results demonstrate a new role for Ca2+ as a critical regulator of actin organization and dynamics at the synapse, and reveal potential feedback loops through which Ca2+ influx may modulate TCR signaling. DOI:http://dx.doi.org/10.7554/eLife.14850.001 An effective immune response requires the immune system to rapidly recognize and respond to foreign invaders. Immune cells known as T cells recognize infection through a protein on their surface known as the T cell receptor. The T cell receptor binds to foreign proteins displayed on the surface of other cells. This interaction initiates a chain of events, including the opening of calcium channels embedded in the T cell membrane known as CRAC channels, which allows calcium ions to flow into the cell. These events ultimately lead to the activation of the T cell, enabling it to mount an immune response against the foreign invader. As part of the activation process, the T cell spreads over the surface of the cell that is displaying foreign proteins to form an extensive interface known as an immune synapse. The movement of the T cell's internal skeleton (the cytoskeleton) is crucial for the formation and function of the synapse. Actin filaments, a key component of the cytoskeleton, flow from the edge of the synapse toward the center; these rearrangements of the actin cytoskeleton help to transport clusters of T cell receptors to the center of the synapse and enable the T cell receptors to transmit signals that lead to the T cell being activated. It is not entirely clear how the binding of T cell receptors to foreign proteins drives the actin rearrangements, but there is indirect evidence suggesting that calcium ions may be involved. Hartzell et al. have now investigated the interactions between calcium and the actin cytoskeleton at the immune synapse in human T cells. T cells were placed on glass so that they formed immune synapse-like connections with the surface, and actin movements at the synapse were visualized using a specialized type of fluorescence microscopy. When calcium ions were prevented from entering the T cell, the movement of actin stopped almost entirely. Thus, the flow of calcium ions into the T cell through CRAC channels is essential for driving the actin movements that underlie immune synapse development and T cell activation. In further experiments, Hartzell et al. tracked the movements of CRAC channels and actin at the synapse and found that actin filaments create a constricting “corral” that concentrates CRAC channels in the center of the synapse. Thus, by driving cytoskeleton movement, calcium ions also help to organize calcium channels at the immune synapse. Future work will focus on identifying the actin remodeling proteins that enable calcium ions to control this process. DOI:http://dx.doi.org/10.7554/eLife.14850.002
Collapse
Affiliation(s)
- Catherine A Hartzell
- Immunology Program, Stanford University, Stanford, United States.,Department of Molecular and Cellular Physiology, Stanford University, Stanford, United States
| | - Katarzyna I Jankowska
- Department of Pathology and Laboratory Medicine, Children's Hospital of Philadelphia Research Institute, Philadelphia, United States.,Department of Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, United States
| | - Janis K Burkhardt
- Department of Pathology and Laboratory Medicine, Children's Hospital of Philadelphia Research Institute, Philadelphia, United States.,Department of Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, United States
| | - Richard S Lewis
- Immunology Program, Stanford University, Stanford, United States.,Department of Molecular and Cellular Physiology, Stanford University, Stanford, United States
| |
Collapse
|
31
|
Lipchinsky A. Osmophoresis—a possible mechanism for vesicle trafficking in tip-growing cells. Phys Biol 2015; 12:066012. [DOI: 10.1088/1478-3975/12/6/066012] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
|
32
|
Chetta J, Love JM, Bober BG, Shah SB. Bidirectional actin transport is influenced by microtubule and actin stability. Cell Mol Life Sci 2015; 72:4205-20. [PMID: 26043972 PMCID: PMC11113749 DOI: 10.1007/s00018-015-1933-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2014] [Revised: 05/14/2015] [Accepted: 05/19/2015] [Indexed: 12/16/2022]
Abstract
Local and long-distance transport of cytoskeletal proteins is vital to neuronal maintenance and growth. Though recent progress has provided insight into the movement of microtubules and neurofilaments, mechanisms underlying the movement of actin remain elusive, in large part due to rapid transitions between its filament states and its diverse cellular localization and function. In this work, we integrated live imaging of rat sensory neurons, image processing, multiple regression analysis, and mathematical modeling to perform the first quantitative, high-resolution investigation of GFP-actin identity and movement in individual axons. Our data revealed that filamentous actin densities arise along the length of the axon and move short but significant distances bidirectionally, with a net anterograde bias. We directly tested the role of actin and microtubules in this movement. We also confirmed a role for actin densities in extension of axonal filopodia, and demonstrated intermittent correlation of actin and mitochondrial movement. Our results support a novel mechanism underlying slow component axonal transport, in which the stability of both microtubule and actin cytoskeletal components influence the mobility of filamentous actin.
Collapse
Affiliation(s)
- Joshua Chetta
- Fischell Department of Bioengineering, University of Maryland, College Park, MD, USA
| | - James M Love
- Fischell Department of Bioengineering, University of Maryland, College Park, MD, USA
| | - Brian G Bober
- Department of Bioengineering, University of California, San Diego, La Jolla, CA, USA
| | - Sameer B Shah
- Fischell Department of Bioengineering, University of Maryland, College Park, MD, USA.
- Departments of Orthopaedic Surgery and Bioengineering, University of California, San Diego, 9500 Gilman Drive, MC 0863, La Jolla, CA, 92093, USA.
| |
Collapse
|
33
|
Tabdanov E, Gondarenko S, Kumari S, Liapis A, Dustin ML, Sheetz MP, Kam LC, Iskratsch T. Micropatterning of TCR and LFA-1 ligands reveals complementary effects on cytoskeleton mechanics in T cells. Integr Biol (Camb) 2015; 7:1272-84. [PMID: 26156536 PMCID: PMC4593733 DOI: 10.1039/c5ib00032g] [Citation(s) in RCA: 66] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The formation of the immunological synapse between a T cell and the antigen-presenting cell (APC) is critically dependent on actin dynamics, downstream of T cell receptor (TCR) and integrin (LFA-1) signalling. There is also accumulating evidence that mechanical forces, generated by actin polymerization and/or myosin contractility regulate T cell signalling. Because both receptor pathways are intertwined, their contributions towards the cytoskeletal organization remain elusive. Here, we identify the specific roles of TCR and LFA-1 by using a combination of micropatterning to spatially separate signalling systems and nanopillar arrays for high-precision analysis of cellular forces. We identify that Arp2/3 acts downstream of TCRs to nucleate dense actin foci but propagation of the network requires LFA-1 and the formin FHOD1. LFA-1 adhesion enhances actomyosin forces, which in turn modulate actin assembly downstream of the TCR. Together our data shows a mechanically cooperative system through which ligands presented by an APC modulate T cell activation.
Collapse
Affiliation(s)
- Erdem Tabdanov
- Department of Biomedical Engineering, Columbia University, New York, NY, USA
| | - Sasha Gondarenko
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Sudha Kumari
- Department of Pathology, New York University, New York, NY, USA
| | | | - Michael L. Dustin
- Department of Pathology, New York University, New York, NY, USA
- Kennedy Institute of Rheumatology, University of Oxford, Headington, Oxon, UK
| | - Michael P. Sheetz
- Department of Biological Sciences, Columbia University, New York, NY, USA
- Mechanobiology Institute, National University of Singapore, Singapore 117411, Singapore
| | - Lance C. Kam
- Department of Biomedical Engineering, Columbia University, New York, NY, USA
| | - Thomas Iskratsch
- Department of Biological Sciences, Columbia University, New York, NY, USA
| |
Collapse
|
34
|
A thermodynamically motivated model for stress-fiber reorganization. Biomech Model Mechanobiol 2015; 15:761-89. [DOI: 10.1007/s10237-015-0722-9] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2015] [Accepted: 08/24/2015] [Indexed: 10/23/2022]
|
35
|
Fluorescence recovery after photobleaching in material and life sciences: putting theory into practice. Q Rev Biophys 2015; 48:323-87. [PMID: 26314367 DOI: 10.1017/s0033583515000013] [Citation(s) in RCA: 89] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
AbstractFluorescence recovery after photobleaching (FRAP) is a versatile tool for determining diffusion and interaction/binding properties in biological and material sciences. An understanding of the mechanisms controlling the diffusion requires a deep understanding of structure–interaction–diffusion relationships. In cell biology, for instance, this applies to the movement of proteins and lipids in the plasma membrane, cytoplasm and nucleus. In industrial applications related to pharmaceutics, foods, textiles, hygiene products and cosmetics, the diffusion of solutes and solvent molecules contributes strongly to the properties and functionality of the final product. All these systems are heterogeneous, and accurate quantification of the mass transport processes at the local level is therefore essential to the understanding of the properties of soft (bio)materials. FRAP is a commonly used fluorescence microscopy-based technique to determine local molecular transport at the micrometer scale. A brief high-intensity laser pulse is locally applied to the sample, causing substantial photobleaching of the fluorescent molecules within the illuminated area. This causes a local concentration gradient of fluorescent molecules, leading to diffusional influx of intact fluorophores from the local surroundings into the bleached area. Quantitative information on the molecular transport can be extracted from the time evolution of the fluorescence recovery in the bleached area using a suitable model. A multitude of FRAP models has been developed over the years, each based on specific assumptions. This makes it challenging for the non-specialist to decide which model is best suited for a particular application. Furthermore, there are many subtleties in performing accurate FRAP experiments. For these reasons, this review aims to provide an extensive tutorial covering the essential theoretical and practical aspects so as to enable accurate quantitative FRAP experiments for molecular transport measurements in soft (bio)materials.
Collapse
|
36
|
Vitriol EA, McMillen LM, Kapustina M, Gomez SM, Vavylonis D, Zheng JQ. Two functionally distinct sources of actin monomers supply the leading edge of lamellipodia. Cell Rep 2015. [PMID: 25865895 DOI: 10.1016/j.celrep.2015.03] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/26/2023] Open
Abstract
Lamellipodia, the sheet-like protrusions of motile cells, consist of networks of actin filaments (F-actin) regulated by the ordered assembly from and disassembly into actin monomers (G-actin). Traditionally, G-actin is thought to exist as a homogeneous pool. Here, we show that there are two functionally and molecularly distinct sources of G-actin that supply lamellipodial actin networks. G-actin originating from the cytosolic pool requires the monomer-binding protein thymosin β4 (Tβ4) for optimal leading-edge localization, is targeted to formins, and is responsible for creating an elevated G/F-actin ratio that promotes membrane protrusion. The second source of G-actin comes from recycled lamellipodia F-actin. Recycling occurs independently of Tβ4 and appears to regulate lamellipodia homeostasis. Tβ4-bound G-actin specifically localizes to the leading edge because it does not interact with Arp2/3-mediated polymerization sites found throughout the lamellipodia. These findings demonstrate that actin networks can be constructed from multiple sources of monomers with discrete spatiotemporal functions.
Collapse
Affiliation(s)
- Eric A Vitriol
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322, USA.
| | - Laura M McMillen
- Department of Physics, Lehigh University, Bethlehem, PA 18015, USA
| | - Maryna Kapustina
- Department of Cell Biology and Physiology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Shawn M Gomez
- Department of Computer Science, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA; Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | | | - James Q Zheng
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322, USA; Department of Neurology, Emory University School of Medicine, Atlanta, GA 30322, USA; Center for Neurodegenerative Diseases, Emory University School of Medicine, Atlanta, GA 30322, USA.
| |
Collapse
|
37
|
Vitriol EA, McMillen LM, Kapustina M, Gomez SM, Vavylonis D, Zheng JQ. Two functionally distinct sources of actin monomers supply the leading edge of lamellipodia. Cell Rep 2015; 11:433-45. [PMID: 25865895 DOI: 10.1016/j.celrep.2015.03.033] [Citation(s) in RCA: 58] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2014] [Revised: 11/20/2014] [Accepted: 03/13/2015] [Indexed: 12/21/2022] Open
Abstract
Lamellipodia, the sheet-like protrusions of motile cells, consist of networks of actin filaments (F-actin) regulated by the ordered assembly from and disassembly into actin monomers (G-actin). Traditionally, G-actin is thought to exist as a homogeneous pool. Here, we show that there are two functionally and molecularly distinct sources of G-actin that supply lamellipodial actin networks. G-actin originating from the cytosolic pool requires the monomer-binding protein thymosin β4 (Tβ4) for optimal leading-edge localization, is targeted to formins, and is responsible for creating an elevated G/F-actin ratio that promotes membrane protrusion. The second source of G-actin comes from recycled lamellipodia F-actin. Recycling occurs independently of Tβ4 and appears to regulate lamellipodia homeostasis. Tβ4-bound G-actin specifically localizes to the leading edge because it does not interact with Arp2/3-mediated polymerization sites found throughout the lamellipodia. These findings demonstrate that actin networks can be constructed from multiple sources of monomers with discrete spatiotemporal functions.
Collapse
Affiliation(s)
- Eric A Vitriol
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322, USA.
| | - Laura M McMillen
- Department of Physics, Lehigh University, Bethlehem, PA 18015, USA
| | - Maryna Kapustina
- Department of Cell Biology and Physiology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Shawn M Gomez
- Department of Computer Science, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA; Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | | | - James Q Zheng
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322, USA; Department of Neurology, Emory University School of Medicine, Atlanta, GA 30322, USA; Center for Neurodegenerative Diseases, Emory University School of Medicine, Atlanta, GA 30322, USA.
| |
Collapse
|
38
|
Kiuchi T, Nagai T, Ohashi K, Watanabe N, Mizuno K. Live-cell imaging of G-actin dynamics using sequential FDAP. BIOARCHITECTURE 2014; 1:240-244. [PMID: 22754616 PMCID: PMC3384577 DOI: 10.4161/bioa.18471] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Various microscopic techniques have been developed to understand the mechanisms that spatiotemporally control actin filament dynamics in live cells. Kinetic data on the processes of actin assembly and disassembly on F-actin have been accumulated. However, the kinetics of cytoplasmic G-actin, a key determinant for actin polymerization, has remained unclear because of a lack of appropriate methods to measure the G-actin concentration quantitatively. We have developed two new microscopic techniques based on the fluorescence decay after photoactivation (FDAP) time-lapse imaging of photoswitchable Dronpa-labeled actin. These techniques, sequential FDAP (s-FDAP) and multipoint FDAP, were used to measure the time-dependent changes in and spatial distribution of the G-actin concentration in live cells. Use of s-FDAP provided data on changes in the G-actin concentration with high temporal resolution; these data were useful for the model analysis of actin assembly processes in live cells. The s-FDAP analysis also provided evidence that the cytoplasmic G-actin concentration substantially decreases after cell stimulation and that the extent of stimulus-induced actin assembly and cell size extension are linearly correlated with the G-actin concentration before cell stimulation. The advantages of using s-FDAP and multipoint FDAP to measure spatiotemporal G-actin dynamics and the roles of G-actin concentration and ADF/cofilin in stimulus-induced actin assembly and lamellipodium extension in live cells are discussed.
Collapse
Affiliation(s)
- Tai Kiuchi
- Department of Biomolecular Sciences; Graduate School of Life Sciences; Tohoku University; Sendai, Japan
| | | | | | | | | |
Collapse
|
39
|
Abstract
Directed cell migration requires a spatially polarized distribution of polymerized actin. We develop and treat a mechanical model of cell polarization based on polymerization and depolymerization of actin filaments at the two ends of a cell, modulated by forces at either end that are coupled by the cell membrane. We solve this model using both a simulation approach that treats filament nucleation, polymerization, and depolymerization stochastically, and a rate-equation approach based on key properties such as the number of filaments N and the number of polymerized subunits F at either end of the cell. The rate-equation approach agrees closely with the stochastic approach at steady state and, when appropriately generalized, also predicts the dynamic behavior accurately. The calculated transitions from symmetric to polarized states show that polarization is enhanced by a high free-actin concentration, a large pointed-end off-rate, a small barbed-end off-rate, and a small spontaneous nucleation rate. The rate-equation approach allows us to perform a linear-stability analysis to pin down the key interactions that drive the polarization. The polarization is driven by a positive-feedback loop having two interactions. First, an increase in F at one side of the cell lengthens the filaments and thus reduces the decay rate of N (increasing N); second, increasing N enhances F because the force per growing filament tip is reduced. We find that the transitions induced by changing system properties result from supercritical pitchfork bifurcations. The filament lifetime depends strongly on the average filament length, and this effect is crucial for obtaining polarization correctly.
Collapse
Affiliation(s)
- Xinxin Wang
- Department of Physics, Washington University, One Brookings Drive, Campus Box 1105, USA
| | | |
Collapse
|
40
|
Koskinen M, Hotulainen P. Measuring F-actin properties in dendritic spines. Front Neuroanat 2014; 8:74. [PMID: 25140131 PMCID: PMC4122166 DOI: 10.3389/fnana.2014.00074] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2014] [Accepted: 07/16/2014] [Indexed: 12/28/2022] Open
Abstract
During the last decade, numerous studies have demonstrated that the actin cytoskeleton plays a pivotal role in the control of dendritic spine shape. Synaptic stimulation rapidly changes the actin dynamics and many actin regulators have been shown to play roles in neuron functionality. Accordingly, defects in the regulation of the actin cytoskeleton in neurons have been implicated in memory disorders. Due to the small size of spines, it is difficult to detect changes in the actin structures in dendritic spines by conventional light microscopy imaging. Instead, to know how tightly actin filaments are bundled together, and how fast the filaments turnover, we need to use advanced microscopy techniques, such as fluorescence recovery after photobleaching (FRAP), photoactivatable green fluorescent protein (PAGFP) fluorescence decay and fluorescence anisotropy. Fluorescence anisotropy, which measures the Förster resonance energy transfer (FRET) between two GFP fluorophores, has been proposed as a method to measure the level of actin polymerization. Here, we propose a novel idea that fluorescence anisotropy could be more suitable to study the level of actin filament bundling instead of actin polymerization. We validate the method in U2OS cell line where the actin structures can be clearly distinguished and apply to analyze how actin filament organization in dendritic spines changes during neuronal maturation. In addition to fluorescence anisotropy validation, we take a critical look at the properties and limitations of FRAP and PAGFP fluorescence decay methods and offer our proposals for the analysis methods for these approaches. These three methods complement each other, each providing additional information about actin dynamics and organization in dendritic spines.
Collapse
Affiliation(s)
- Mikko Koskinen
- Neuroscience Center, University of Helsinki Helsinki, Finland
| | | |
Collapse
|
41
|
Chiu CL, Aguilar JS, Tsai CY, Wu G, Gratton E, Digman MA. Nanoimaging of focal adhesion dynamics in 3D. PLoS One 2014; 9:e99896. [PMID: 24959851 PMCID: PMC4069057 DOI: 10.1371/journal.pone.0099896] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2014] [Accepted: 05/20/2014] [Indexed: 01/13/2023] Open
Abstract
Organization and dynamics of focal adhesion proteins have been well characterized in cells grown on two-dimensional (2D) cell culture surfaces. However, much less is known about the dynamic association of these proteins in the 3D microenvironment. Limited imaging technologies capable of measuring protein interactions in real time and space for cells grown in 3D is a major impediment in understanding how proteins function under different environmental cues. In this study, we applied the nano-scale precise imaging by rapid beam oscillation (nSPIRO) technique and combined the scaning-fluorescence correlation spectroscopy (sFCS) and the number and molecular brightness (N&B) methods to investigate paxillin and actin dynamics at focal adhesions in 3D. Both MDA-MB-231 cells and U2OS cells produce elongated protrusions with high intensity regions of paxillin in cell grown in 3D collagen matrices. Using sFCS we found higher percentage of slow diffusing proteins at these focal spots, suggesting assembling/disassembling processes. In addition, the N&B analysis shows paxillin aggregated predominantly at these focal contacts which are next to collagen fibers. At those sites, actin showed slower apparent diffusion rate, which indicated that actin is either polymerizing or binding to the scaffolds in these locals. Our findings demonstrate that by multiplexing these techniques we have the ability to spatially and temporally quantify focal adhesion assembly and disassembly in 3D space and allow the understanding tumor cell invasion in a more complex relevant environment.
Collapse
Affiliation(s)
- Chi-Li Chiu
- Department of Developmental and Cell Biology, University of California Irvine, Irvine, California, United States of America
| | - Jose S. Aguilar
- Department of Biomedical Engineering, Laboratory for Fluorescence Dynamics, University of California Irvine, Irvine, California, United States of America
| | - Connie Y. Tsai
- Department of Biological Chemistry, University of California Irvine, Irvine, California, United States of America
| | - GuiKai Wu
- Department of Biological Chemistry, University of California Irvine, Irvine, California, United States of America
| | - Enrico Gratton
- Department of Developmental and Cell Biology, University of California Irvine, Irvine, California, United States of America
- Department of Biomedical Engineering, Laboratory for Fluorescence Dynamics, University of California Irvine, Irvine, California, United States of America
| | - Michelle A. Digman
- Department of Developmental and Cell Biology, University of California Irvine, Irvine, California, United States of America
- Department of Biomedical Engineering, Laboratory for Fluorescence Dynamics, University of California Irvine, Irvine, California, United States of America
- * E-mail:
| |
Collapse
|
42
|
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.
Collapse
|
43
|
Wolff K, Barrett-Freeman C, Evans MR, Goryachev AB, Marenduzzo D. Modelling the effect of myosin X motors on filopodia growth. Phys Biol 2014; 11:016005. [PMID: 24464797 DOI: 10.1088/1478-3975/11/1/016005] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We present a numerical simulation study of the dynamics of filopodial growth in the presence of active transport by myosin X motors. We employ both a microscopic agent-based model, which captures the stochasticity of the growth process, and a continuum mean-field theory which neglects fluctuations. We show that in the absence of motors, filopodia growth is overestimated by the continuum mean-field theory. Thus fluctuations slow down the growth, especially when the protrusions are driven by a small number (10 or less) of F-actin fibres, and when the force opposing growth (coming from membrane elasticity) is large enough. We also show that, with typical parameter values for eukaryotic cells, motors are unlikely to provide an actin transport mechanism which enhances filopodial size significantly, unless the G-actin concentration within the filopodium greatly exceeds that of the cytosol bulk. We explain these observations in terms of order-of-magnitude estimates of diffusion-induced and advection-induced growth of a bundle of Brownian ratchets.
Collapse
Affiliation(s)
- K Wolff
- Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstraße 36, D-10623 Berlin, Germany. SUPA, School of Physics and Astronomy, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JZ, UK
| | | | | | | | | |
Collapse
|
44
|
Lorente G, Syriani E, Morales M. Actin filaments at the leading edge of cancer cells are characterized by a high mobile fraction and turnover regulation by profilin I. PLoS One 2014; 9:e85817. [PMID: 24465723 PMCID: PMC3895011 DOI: 10.1371/journal.pone.0085817] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2013] [Accepted: 12/03/2013] [Indexed: 11/18/2022] Open
Abstract
Cellular motility is the basis for cancer cell invasion and metastasis. In the case of breast cancer, the most common type of cancer among women, metastasis represents the most devastating stage of the disease. The central role of cellular motility in cancer development emphasizes the importance of understanding the specific mechanisms involved in this process. In this context, tumor development and metastasis would be the consequence of a loss or defect of the mechanisms that control cytoskeletal remodeling. Profilin I belongs to a family of small actin binding proteins that are thought to assist in actin filament elongation at the leading edge of migrating cells. Traditionally, Profilin I has been considered to be an essential control element for actin polymerization and cell migration. Expression of Profilin I is down-regulated in breast and various other cancer cells. In MDA-MB-231 cells, a breast cancer cell line, further inhibition of Profilin I expression promotes hypermotility and metastatic spread, a finding that contrasts with the proposed role of Profilin in enhancing polymerization. In this report, we have taken advantage of the fluorescence recovery after photobleaching (FRAP) of GFP-actin to quantify and compare actin dynamics at the leading edge level in both cancer and non-cancer cell models. Our results suggest that (i) a high level of actin dynamics (i.e., a large mobile fraction of actin filaments and a fast turnover) is a common characteristic of some cancer cells; (ii) actin polymerization shows a high degree of independence from the presence of extracellular growth factors; and (iii) our results also corroborate the role of Profilin I in regulating actin polymerization, as raising the intracellular levels of Profilin I decreased the mobile fraction ratio of actin filaments and slowed their polymerization rate; furthermore, increased Profilin levels also led to reduced individual cell velocity and directionality.
Collapse
Affiliation(s)
- Gisela Lorente
- Neurophysiology Laboratory, Deptartment of Physiological Sciences I, School of Medicine, University of Barcelona, Barcelona, Spain
| | - Emilio Syriani
- Structural Synaptic Plasticity Lab, Department of Neurodegenerative Diseases, CIBIR Piqueras 98, Logroño, La Rioja, Spain
| | - Miguel Morales
- Structural Synaptic Plasticity Lab, Department of Neurodegenerative Diseases, CIBIR Piqueras 98, Logroño, La Rioja, Spain
- * E-mail:
| |
Collapse
|
45
|
Fritzsche M, Lewalle A, Duke T, Kruse K, Charras G. Analysis of turnover dynamics of the submembranous actin cortex. Mol Biol Cell 2013; 24:757-67. [PMID: 23345594 PMCID: PMC3596247 DOI: 10.1091/mbc.e12-06-0485] [Citation(s) in RCA: 145] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Two filament subpopulations with very different turnover rates make up the actin cortex in living cells: one with fast turnover dynamics and polymerization resulting from addition of monomers to free barbed ends, and one with slow turnover dynamics with polymerization resulting from formin-mediated filament growth. The cell cortex is a thin network of actin, myosin motors, and associated proteins that underlies the plasma membrane in most eukaryotic cells. It enables cells to resist extracellular stresses, perform mechanical work, and change shape. Cortical structural and mechanical properties depend strongly on the relative turnover rates of its constituents, but quantitative data on these rates remain elusive. Using photobleaching experiments, we analyzed the dynamics of three classes of proteins within the cortex of living cells: a scaffold protein (actin), a cross-linker (α-actinin), and a motor (myosin). We found that two filament subpopulations with very different turnover rates composed the actin cortex: one with fast turnover dynamics and polymerization resulting from addition of monomers to free barbed ends, and one with slow turnover dynamics with polymerization resulting from formin-mediated filament growth. Our data suggest that filaments in the second subpopulation are on average longer than those in the first and that cofilin-mediated severing of formin-capped filaments contributes to replenishing the filament subpopulation with free barbed ends. Furthermore, α-actinin and myosin minifilaments turned over significantly faster than F-actin. Surprisingly, only one-fourth of α-actinin dimers were bound to two actin filaments. Taken together, our results provide a quantitative characterization of essential mechanisms underlying actin cortex homeostasis.
Collapse
Affiliation(s)
- Marco Fritzsche
- London Centre for Nanotechnology, University College London, London, United Kingdom
| | | | | | | | | |
Collapse
|
46
|
Distributed actin turnover in the lamellipodium and FRAP kinetics. Biophys J 2013; 104:247-57. [PMID: 23332077 DOI: 10.1016/j.bpj.2012.11.3819] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2012] [Revised: 10/01/2012] [Accepted: 11/21/2012] [Indexed: 10/27/2022] Open
Abstract
Studies of actin dynamics at the leading edge of motile cells with single-molecule speckle (SiMS) microscopy have shown a broad distribution of EGFP-actin speckle lifetimes and indicated actin polymerization and depolymerization over an extended region. Other experiments using FRAP with the same EGFP-actin as a probe have suggested, by contrast, that polymerization occurs exclusively at the leading edge. We performed FRAP experiments on XTC cells to compare SiMS to FRAP on the same cell type. We used speckle statistics obtained by SiMS to model the steady-state distribution and kinetics of actin in the lamellipodium. We demonstrate that a model with a single diffuse actin species is in good agreement with FRAP experiments. A model including two species of diffuse actin provides an even better agreement. The second species consists of slowly diffusing oligomers that associate to the F-actin network throughout the lamellipodium or break up into monomers after a characteristic time. Our work motivates studies to test the presence and composition of slowly diffusing actin species that may contribute to local remodeling of the actin network and increase the amount of soluble actin.
Collapse
|
47
|
Caby M, Hardas P, Ramachandran S, Ryckaert JP. Hybrid molecular dynamics simulations of living filaments. J Chem Phys 2012; 136:114901. [PMID: 22443794 DOI: 10.1063/1.3694672] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
We propose a hybrid molecular dynamics/multi-particle collision dynamics model to simulate a set of self-assembled semiflexible filaments and free monomers. Further, we introduce a Monte Carlo scheme to deal with single monomer addition (polymerization) or removal (depolymerization), satisfying the detailed balance condition within a proper statistical mechanical framework. This model of filaments, based on the wormlike chain, aims to represent equilibrium polymers with distinct reaction rates at both ends, such as self-assembled adenosine diphosphate-actin filaments in the absence of adenosine triphosphate (ATP) hydrolysis and other proteins. We report the distribution of filament lengths and the corresponding dynamical fluctuations on an equilibrium trajectory. Potential generalizations of this method to include irreversible steps like ATP-actin hydrolysis are discussed.
Collapse
Affiliation(s)
- Mathieu Caby
- Physique des Polymères, Université Libre de Bruxelles, Campus Plaine, CP 223, B-1050 Brussels, Belgium
| | | | | | | |
Collapse
|
48
|
Fan Y, Eswarappa SM, Hitomi M, Fox PL. Myo1c facilitates G-actin transport to the leading edge of migrating endothelial cells. ACTA ACUST UNITED AC 2012; 198:47-55. [PMID: 22778278 PMCID: PMC3392929 DOI: 10.1083/jcb.201111088] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Addition of actin monomer (G-actin) to growing actin filaments (F-actin) at the leading edge generates force for cell locomotion. The polymerization reaction and its regulation have been studied in depth. However, the mechanism responsible for transport of G-actin substrate to the cell front is largely unknown; random diffusion, facilitated transport via myosin II contraction, local synthesis as a result of messenger ribonucleic acid localization, or F-actin turnover all might contribute. By tracking a photoactivatable, nonpolymerizable actin mutant, we show vectorial transport of G-actin in live migrating endothelial cells (ECs). Mass spectrometric analysis identified Myo1c, an unconventional F-actin-binding motor protein, as a major G-actin-interacting protein. The cargo-binding tail domain of Myo1c interacted with G-actin, and the motor domain was required for the transport. Local microinjection of Myo1c promoted G-actin accumulation and plasma membrane ruffling, and Myo1c knockdown confirmed its contribution to G-actin delivery to the leading edge and for cell motility. In addition, there is no obvious requirement for myosin II contractile-based transport of G-actin in ECs. Thus, Myo1c-facilitated G-actin transport might be a critical node for control of cell polarity and motility.
Collapse
Affiliation(s)
- Yi Fan
- Department of Cell Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA
| | | | | | | |
Collapse
|
49
|
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.
Collapse
Affiliation(s)
- Louise Guolla
- Department of Physics, MacDonald Hall, 150 Louis Pasteur, University of Ottawa, Ottawa, ON, K1N 6N5, Canada
| | | | | | | |
Collapse
|
50
|
Jaqaman K, Grinstein S. Regulation from within: the cytoskeleton in transmembrane signaling. Trends Cell Biol 2012; 22:515-26. [PMID: 22917551 DOI: 10.1016/j.tcb.2012.07.006] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2012] [Revised: 07/17/2012] [Accepted: 07/17/2012] [Indexed: 12/16/2022]
Abstract
There is mounting evidence that the plasma membrane is highly dynamic and organized in a complex manner. The cortical cytoskeleton is proving to be a particularly important regulator of plasmalemmal organization, modulating the mobility of proteins and lipids in the membrane, facilitating their segregation, and influencing their clustering. This organization plays a critical role in receptor-mediated signaling, especially in the case of immunoreceptors, which require lateral clustering for their activation. Based on recent developments, we discuss the structures and mechanisms whereby the cortical cytoskeleton regulates membrane dynamics and organization, and how the nonuniform distribution of immunoreceptors and their self-association may affect activation and signaling.
Collapse
Affiliation(s)
- Khuloud Jaqaman
- Department of Systems Biology, Harvard Medical School, Boston, MA, USA
| | | |
Collapse
|