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Heyn JCJ, Rädler JO, Falcke M. Mesenchymal cell migration on one-dimensional micropatterns. Front Cell Dev Biol 2024; 12:1352279. [PMID: 38694822 PMCID: PMC11062138 DOI: 10.3389/fcell.2024.1352279] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2023] [Accepted: 03/29/2024] [Indexed: 05/04/2024] Open
Abstract
Quantitative studies of mesenchymal cell motion are important to elucidate cytoskeleton function and mechanisms of cell migration. To this end, confinement of cell motion to one dimension (1D) significantly simplifies the problem of cell shape in experimental and theoretical investigations. Here we review 1D migration assays employing micro-fabricated lanes and reflect on the advantages of such platforms. Data are analyzed using biophysical models of cell migration that reproduce the rich scenario of morphodynamic behavior found in 1D. We describe basic model assumptions and model behavior. It appears that mechanical models explain the occurrence of universal relations conserved across different cell lines such as the adhesion-velocity relation and the universal correlation between speed and persistence (UCSP). We highlight the unique opportunity of reproducible and standardized 1D assays to validate theory based on statistical measures from large data of trajectories and discuss the potential of experimental settings embedding controlled perturbations to probe response in migratory behavior.
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Affiliation(s)
- Johannes C. J. Heyn
- Fakultät für Physik, Ludwig-Maximilians-Universität München (LMU), Munich, Germany
| | - Joachim O. Rädler
- Fakultät für Physik, Ludwig-Maximilians-Universität München (LMU), Munich, Germany
| | - Martin Falcke
- Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany
- Department of Physics, Humboldt University, Berlin, Germany
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2
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Grudtsyna V, Packirisamy S, Bidone TC, Swaminathan V. Extracellular matrix sensing via modulation of orientational order of integrins and F-actin in focal adhesions. Life Sci Alliance 2023; 6:e202301898. [PMID: 37463754 PMCID: PMC10355215 DOI: 10.26508/lsa.202301898] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2023] [Revised: 06/30/2023] [Accepted: 07/03/2023] [Indexed: 07/20/2023] Open
Abstract
Specificity of cellular responses to distinct cues from the ECM requires precise and sensitive decoding of physical information. However, how known mechanisms of mechanosensing like force-dependent catch bonds and conformational changes in FA proteins can confer that this sensitivity is not known. Using polarization microscopy and computational modeling, we identify dynamic changes in an orientational order of FA proteins as a molecular organizational mechanism that can fine-tune cell sensitivity to the ECM. We find that αV integrins and F-actin show precise changes in the orientational order in an ECM-mediated integrin activation-dependent manner. These changes are sensitive to ECM density and are regulated independent of myosin-II activity though contractility can enhance this sensitivity. A molecular-clutch model demonstrates that the orientational order of integrin-ECM binding coupled to directional catch bonds can capture cellular responses to changes in ECM density. This mechanism also captures decoupling of ECM density sensing from stiffness sensing thus elucidating specificity. Taken together, our results suggest relative geometric organization of FA molecules as an important molecular architectural feature and regulator of mechanotransduction.
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Affiliation(s)
- Valeriia Grudtsyna
- Division of Oncology, Department of Clinical Sciences, Lund University, Lund, Sweden
- Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
| | - Swathi Packirisamy
- Division of Oncology, Department of Clinical Sciences, Lund University, Lund, Sweden
| | - Tamara C Bidone
- Department of Biomedical Engineering, The University of Utah, Salt Lake City, UT, USA
| | - Vinay Swaminathan
- Division of Oncology, Department of Clinical Sciences, Lund University, Lund, Sweden
- Wallenberg Centre for Molecular Medicine, Lund University, Lund, Sweden
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3
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Maksudov F, Jones LK, Barsegov V. Statistical Learning from Single-Molecule Experiments: Support Vector Machines and Expectation-Maximization Approaches to Understanding Protein Unfolding Data. J Phys Chem B 2021; 125:5794-5808. [PMID: 34075752 DOI: 10.1021/acs.jpcb.1c02334] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Single-molecule force spectroscopy has become a powerful tool for the exploration of dynamic processes that involve proteins; yet, meaningful interpretation of the experimental data remains challenging. Owing to low signal-to-noise ratio, experimental force-extension spectra contain force signals due to nonspecific interactions, tip or substrate detachment, and protein desorption. Unravelling of complex protein structures results in the unfolding transitions of different types. Here, we test the performance of Support Vector Machines (SVM) and Expectation Maximization (EM) approaches in statistical learning from dynamic force experiments. When the output from molecular modeling in silico (or other studies) is used as a training set, SVM and EM can be applied to understand the unfolding force data. The maximal margin or maximum likelihood classifier can be used to separate experimental test observations into the unfolding transitions of different types, and EM optimization can then be utilized to resolve the statistics of unfolding forces: weights, average forces, and standard deviations. We designed an EM-based approach, which can be directly applied to the experimental data without data classification and division into training and test observations. This approach performs well even when the sample size is small and when the unfolding transitions are characterized by overlapping force ranges.
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4
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Wiener GI, Kadosh D, Weihs D. Two- and three-dimensional de-drifting algorithms for fiducially marked image stacks. J Biomech 2020; 110:109967. [DOI: 10.1016/j.jbiomech.2020.109967] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2020] [Revised: 07/16/2020] [Accepted: 07/16/2020] [Indexed: 12/15/2022]
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5
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Bolado-Carrancio A, Rukhlenko OS, Nikonova E, Tsyganov MA, Wheeler A, Garcia-Munoz A, Kolch W, von Kriegsheim A, Kholodenko BN. Periodic propagating waves coordinate RhoGTPase network dynamics at the leading and trailing edges during cell migration. eLife 2020; 9:58165. [PMID: 32705984 PMCID: PMC7380942 DOI: 10.7554/elife.58165] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Accepted: 07/02/2020] [Indexed: 12/27/2022] Open
Abstract
Migrating cells need to coordinate distinct leading and trailing edge dynamics but the underlying mechanisms are unclear. Here, we combine experiments and mathematical modeling to elaborate the minimal autonomous biochemical machinery necessary and sufficient for this dynamic coordination and cell movement. RhoA activates Rac1 via DIA and inhibits Rac1 via ROCK, while Rac1 inhibits RhoA through PAK. Our data suggest that in motile, polarized cells, RhoA–ROCK interactions prevail at the rear, whereas RhoA-DIA interactions dominate at the front where Rac1/Rho oscillations drive protrusions and retractions. At the rear, high RhoA and low Rac1 activities are maintained until a wave of oscillatory GTPase activities from the cell front reaches the rear, inducing transient GTPase oscillations and RhoA activity spikes. After the rear retracts, the initial GTPase pattern resumes. Our findings show how periodic, propagating GTPase waves coordinate distinct GTPase patterns at the leading and trailing edge dynamics in moving cells.
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Affiliation(s)
- Alfonso Bolado-Carrancio
- Edinburgh Cancer Research Centre, Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom
| | - Oleksii S Rukhlenko
- Systems Biology Ireland, School of Medicine and Medical Science, University College Dublin, Belfield, Ireland
| | - Elena Nikonova
- Systems Biology Ireland, School of Medicine and Medical Science, University College Dublin, Belfield, Ireland
| | - Mikhail A Tsyganov
- Systems Biology Ireland, School of Medicine and Medical Science, University College Dublin, Belfield, Ireland.,Institute of Theoretical and Experimental Biophysics, Pushchino, Russian Federation
| | - Anne Wheeler
- Edinburgh Cancer Research Centre, Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom
| | - Amaya Garcia-Munoz
- Systems Biology Ireland, School of Medicine and Medical Science, University College Dublin, Belfield, Ireland
| | - Walter Kolch
- Systems Biology Ireland, School of Medicine and Medical Science, University College Dublin, Belfield, Ireland.,Conway Institute of Biomolecular & Biomedical Research, University College Dublin, Belfield, Ireland
| | - Alex von Kriegsheim
- Edinburgh Cancer Research Centre, Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom.,Systems Biology Ireland, School of Medicine and Medical Science, University College Dublin, Belfield, Ireland
| | - Boris N Kholodenko
- Systems Biology Ireland, School of Medicine and Medical Science, University College Dublin, Belfield, Ireland.,Conway Institute of Biomolecular & Biomedical Research, University College Dublin, Belfield, Ireland.,Department of Pharmacology, Yale University School of Medicine, New Haven, United States
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6
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Saha S, Nagy TL, Weiner OD. Joining forces: crosstalk between biochemical signalling and physical forces orchestrates cellular polarity and dynamics. Philos Trans R Soc Lond B Biol Sci 2019; 373:rstb.2017.0145. [PMID: 29632270 DOI: 10.1098/rstb.2017.0145] [Citation(s) in RCA: 40] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/30/2017] [Indexed: 12/11/2022] Open
Abstract
Dynamic processes like cell migration and morphogenesis emerge from the self-organized interaction between signalling and cytoskeletal rearrangements. How are these molecular to sub-cellular scale processes integrated to enable cell-wide responses? A growing body of recent studies suggest that forces generated by cytoskeletal dynamics and motor activity at the cellular or tissue scale can organize processes ranging from cell movement, polarity and division to the coordination of responses across fields of cells. To do so, forces not only act mechanically but also engage with biochemical signalling. Here, we review recent advances in our understanding of this dynamic crosstalk between biochemical signalling, self-organized cortical actomyosin dynamics and physical forces with a special focus on the role of membrane tension in integrating cellular motility.This article is part of the theme issue 'Self-organization in cell biology'.
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Affiliation(s)
- Suvrajit Saha
- Cardiovascular Research Institute, University of California, San Francisco, CA 94158, USA
| | - Tamas L Nagy
- Cardiovascular Research Institute, University of California, San Francisco, CA 94158, USA.,Biological and Medical Informatics Graduate Program, University of California, San Francisco, CA 94158, USA
| | - Orion D Weiner
- Cardiovascular Research Institute, University of California, San Francisco, CA 94158, USA .,Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94158, USA
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7
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Rossy J, Laufer JM, Legler DF. Role of Mechanotransduction and Tension in T Cell Function. Front Immunol 2018; 9:2638. [PMID: 30519239 PMCID: PMC6251326 DOI: 10.3389/fimmu.2018.02638] [Citation(s) in RCA: 62] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2018] [Accepted: 10/26/2018] [Indexed: 12/23/2022] Open
Abstract
T cell migration from blood to, and within lymphoid organs and tissue, as well as, T cell activation rely on complex biochemical signaling events. But T cell migration and activation also take place in distinct mechanical environments and lead to drastic morphological changes and reorganization of the acto-myosin cytoskeleton. In this review we discuss how adhesion proteins and the T cell receptor act as mechanosensors to translate these mechanical contexts into signaling events. We further discuss how cell tension could bring a significant contribution to the regulation of T cell signaling and function.
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Affiliation(s)
- Jérémie Rossy
- Biotechnology Institute Thurgau (BITg) at the University of Konstanz, Kreuzlingen, Switzerland.,Department of Biology, University of Konstanz, Konstanz, Germany
| | - Julia M Laufer
- Biotechnology Institute Thurgau (BITg) at the University of Konstanz, Kreuzlingen, Switzerland
| | - Daniel F Legler
- Biotechnology Institute Thurgau (BITg) at the University of Konstanz, Kreuzlingen, Switzerland.,Department of Biology, University of Konstanz, Konstanz, Germany
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8
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Autenrieth TJ, Frank SC, Greiner AM, Klumpp D, Richter B, Hauser M, Lee SI, Levine J, Bastmeyer M. Actomyosin contractility and RhoGTPases affect cell-polarity and directional migration during haptotaxis. Integr Biol (Camb) 2017; 8:1067-1078. [PMID: 27713970 DOI: 10.1039/c6ib00152a] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Although much is known about chemotaxis- induced by gradients of soluble chemical cues - the molecular mechanisms involved in haptotaxis (migration induced by substrate-bound protein gradients) are largely unknown. We used micropatterning to produce discontinuous gradients consisting of μm-sized fibronectin-dots arranged at constant lateral but continuously decreasing axial spacing. Parameters like gradient slope, protein concentration and size or shape of the fibronectin dots were modified to determine optimal conditions for directional cell migration in gradient patterns. We demonstrate that fibroblasts predominantly migrate uphill towards a higher fibronectin density in gradients with a dot size of 2 × 2 μm, a 2% and 6% slope, and a low fibronectin concentration of 1 μg ml-1. Increasing dot size to 3.5 × 3.5 μm resulted in stationary cells, whereas rectangular dots (2 × 3 μm) orientated perpendicular to the gradient axis preferentially induce lateral migration. During haptotaxis, the Golgi apparatus reorients to a posterior position between the nucleus and the trailing edge. Using pharmacological inhibitors, we demonstrate that actomyosin contractility and microtubule dynamics are a prerequisite for gradient recognition indicating that asymmetric intracellular forces are necessary to read the axis of adhesive gradients. In the haptotaxis signalling cascade, RhoA and Cdc42, and the atypical protein kinase C zeta (aPKCζ), but not Rac, are located upstream of actomyosin contractility.
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Affiliation(s)
- Tatjana J Autenrieth
- Zoological Institute, Department of Cell- and Neurobiology, Karlsruhe Institute of Technology (KIT), Fritz-Haber-Weg 4, 76131 Karlsruhe, Germany. and DFG-Center for Functional Nanostructures (CFN), Karlsruhe Institute of Technology (KIT), Wolfgang-Gaede-Straße 1, 76131 Karlsruhe, Germany and Institute of Functional Interfaces, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
| | - Stephanie C Frank
- Zoological Institute, Department of Cell- and Neurobiology, Karlsruhe Institute of Technology (KIT), Fritz-Haber-Weg 4, 76131 Karlsruhe, Germany. and Institute of Functional Interfaces, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
| | - Alexandra M Greiner
- Zoological Institute, Department of Cell- and Neurobiology, Karlsruhe Institute of Technology (KIT), Fritz-Haber-Weg 4, 76131 Karlsruhe, Germany.
| | - Dominik Klumpp
- Zoological Institute, Department of Cell- and Neurobiology, Karlsruhe Institute of Technology (KIT), Fritz-Haber-Weg 4, 76131 Karlsruhe, Germany.
| | - Benjamin Richter
- Zoological Institute, Department of Cell- and Neurobiology, Karlsruhe Institute of Technology (KIT), Fritz-Haber-Weg 4, 76131 Karlsruhe, Germany. and Institute of Applied Physics, Karlsruhe Institute of Technology (KIT), Wolfgang-Gaede-Straße 1, 76131 Karlsruhe, Germany
| | - Mario Hauser
- Institute of Applied Physics, Karlsruhe Institute of Technology (KIT), Wolfgang-Gaede-Straße 1, 76131 Karlsruhe, Germany
| | - Seong-Il Lee
- Department of Neurobiology and Behavior, Stony Brook University, Stony Brook NY, USA
| | - Joel Levine
- Department of Neurobiology and Behavior, Stony Brook University, Stony Brook NY, USA
| | - Martin Bastmeyer
- Zoological Institute, Department of Cell- and Neurobiology, Karlsruhe Institute of Technology (KIT), Fritz-Haber-Weg 4, 76131 Karlsruhe, Germany. and DFG-Center for Functional Nanostructures (CFN), Karlsruhe Institute of Technology (KIT), Wolfgang-Gaede-Straße 1, 76131 Karlsruhe, Germany and Institute of Functional Interfaces, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
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9
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Wu CY, Tsai YY, Chen SY, Lin YP, Shin JW, Wu CC, Yang BC. Interaction of Zap70 and CXCR4 receptor at lamellipodia that determines the directionality during Jurkat T cells chemotaxis. Mol Immunol 2017; 90:245-254. [DOI: 10.1016/j.molimm.2017.08.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2017] [Revised: 07/21/2017] [Accepted: 08/13/2017] [Indexed: 10/19/2022]
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10
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Srivastava N, Kay RR, Kabla AJ. Method to study cell migration under uniaxial compression. Mol Biol Cell 2017; 28:809-816. [PMID: 28122819 PMCID: PMC5349787 DOI: 10.1091/mbc.e16-08-0575] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2016] [Revised: 12/06/2016] [Accepted: 01/17/2017] [Indexed: 12/23/2022] Open
Abstract
A method is described for imposing mechanical compression on individual cells while monitoring their morphology and migratory phenotype. A compression of the order of 500 Pa flattens the cells by up to 50% and triggers a transition in the mode of migration. This approach is convenient for studying mechanotransduction in confined environments. The chemical, physical, and mechanical properties of the extracellular environment have a strong effect on cell migration. Aspects such as pore size or stiffness of the matrix influence the selection of the mechanism used by cells to propel themselves, including by pseudopods or blebbing. How a cell perceives its environment and how such a cue triggers a change in behavior are largely unknown, but mechanics is likely to be involved. Because mechanical conditions are often controlled by modifying the composition of the environment, separating chemical and physical contributions is difficult and requires multiple controls. Here we propose a simple method to impose a mechanical compression on individual cells without altering the composition of the matrix. Live imaging during compression provides accurate information about the cell's morphology and migratory phenotype. Using Dictyostelium as a model, we observe that a compression of the order of 500 Pa flattens the cells under gel by up to 50%. This uniaxial compression directly triggers a transition in the mode of migration from primarily pseudopodial to bleb driven in <30 s. This novel device is therefore capable of influencing cell migration in real time and offers a convenient approach with which to systematically study mechanotransduction in confined environments.
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Affiliation(s)
- Nishit Srivastava
- Department of Engineering, University of Cambridge, Cambridge CB2 1PZ, United Kingdom
| | - Robert R Kay
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom
| | - Alexandre J Kabla
- Department of Engineering, University of Cambridge, Cambridge CB2 1PZ, United Kingdom
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11
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Carbon Ion-Irradiated Hepatoma Cells Exhibit Coupling Interplay between Apoptotic Signaling and Morphological and Mechanical Remodeling. Sci Rep 2016; 6:35131. [PMID: 27731354 PMCID: PMC5059721 DOI: 10.1038/srep35131] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2016] [Accepted: 09/22/2016] [Indexed: 12/27/2022] Open
Abstract
A apoptotic model was established based on the results of five hepatocellular carcinoma cell (HCC) lines irradiated with carbon ions to investigate the coupling interplay between apoptotic signaling and morphological and mechanical cellular remodeling. The expression levels of key apoptotic proteins and the changes in morphological characteristics and mechanical properties were systematically examined in the irradiated HCC lines. We observed that caspase-3 was activated and that the Bax/Bcl-2 ratio was significantly increased over time. Cellular morphology and mechanics analyses indicated monotonic decreases in spatial sizes, an increase in surface roughness, a considerable reduction in stiffness, and disassembly of the cytoskeletal architecture. A theoretical model of apoptosis revealed that mechanical changes in cells induce the characteristic cellular budding of apoptotic bodies. Statistical analysis indicated that the projected area, stiffness, and cytoskeletal density of the irradiated cells were positively correlated, whereas stiffness and caspase-3 expression were negatively correlated, suggesting a tight coupling interplay between the cellular structures, mechanical properties, and apoptotic protein levels. These results help to clarify a novel arbitration mechanism of cellular demise induced by carbon ions. This biomechanics strategy for evaluating apoptosis contributes to our understanding of cancer-killing mechanisms in the context of carbon ion radiotherapy.
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12
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Cooperative Interactions between 480 kDa Ankyrin-G and EB Proteins Assemble the Axon Initial Segment. J Neurosci 2016; 36:4421-33. [PMID: 27098687 DOI: 10.1523/jneurosci.3219-15.2016] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2015] [Accepted: 02/04/2016] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED The axon initial segment (AIS) is required for generating action potentials and maintaining neuronal polarity. Significant progress has been made in deciphering the basic building blocks composing the AIS, but the underlying mechanisms required for AIS formation remains unclear. The scaffolding protein ankyrin-G is the master-organizer of the AIS. Microtubules and their interactors, particularly end-binding proteins (EBs), have emerged as potential key players in AIS formation. Here, we show that the longest isoform of ankyrin-G (480AnkG) selectively associates with EBs via its specific tail domain and that this interaction is crucial for AIS formation and neuronal polarity in cultured rodent hippocampal neurons. EBs are essential for 480AnkG localization and stabilization at the AIS, whereas 480AnkG is required for the specific accumulation of EBs in the proximal axon. Our findings thus provide a conceptual framework for understanding how the cooperative relationship between 480AnkG and EBs induces the assembly of microtubule-AIS structures in the proximal axon. SIGNIFICANCE STATEMENT Neuronal polarity is crucial for the proper function of neurons. The assembly of the axon initial segment (AIS), which is the hallmark of early neuronal polarization, relies on the longest 480 kDa ankyrin-G isoform. The microtubule cytoskeleton and its interacting proteins were suggested to be early key players in the process of AIS formation. In this study, we show that the crosstalk between 480 kDa ankyrin-G and the microtubule plus-end tracking proteins, EBs, at the proximal axon is decisive for AIS assembly and neuronal polarity. Our work thus provides insight into the functional mechanisms used by 480 kDa ankyrin-G to drive the AIS formation and thereby to establish neuronal polarity.
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13
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Abstract
Understanding the forces controlling vascular network properties and morphology can enhance in vitro tissue vascularization and graft integration prospects. This work assessed the effect of uniaxial cell-induced and externally applied tensile forces on the morphology of vascular networks formed within fibroblast and endothelial cell-embedded 3D polymeric constructs. Force intensity correlated with network quality, as verified by inhibition of force and of angiogenesis-related regulators. Tensile forces during vessel formation resulted in parallel vessel orientation under static stretching and diagonal orientation under cyclic stretching, supported by angiogenic factors secreted in response to each stretch protocol. Implantation of scaffolds bearing network orientations matching those of host abdominal muscle tissue improved graft integration and the mechanical properties of the implantation site, a critical factor in repair of defects in this area. This study demonstrates the regulatory role of forces in angiogenesis and their capacities in vessel structure manipulation, which can be exploited to improve scaffolds for tissue repair.
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14
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Ennomani H, Letort G, Guérin C, Martiel JL, Cao W, Nédélec F, De La Cruz EM, Théry M, Blanchoin L. Architecture and Connectivity Govern Actin Network Contractility. Curr Biol 2016; 26:616-26. [PMID: 26898468 DOI: 10.1016/j.cub.2015.12.069] [Citation(s) in RCA: 155] [Impact Index Per Article: 19.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2015] [Revised: 11/25/2015] [Accepted: 12/24/2015] [Indexed: 01/03/2023]
Abstract
Actomyosin contractility plays a central role in a wide range of cellular processes, including the establishment of cell polarity, cell migration, tissue integrity, and morphogenesis during development. The contractile response is variable and depends on actomyosin network architecture and biochemical composition. To determine how this coupling regulates actomyosin-driven contraction, we used a micropatterning method that enables the spatial control of actin assembly. We generated a variety of actin templates and measured how defined actin structures respond to myosin-induced forces. We found that the same actin filament crosslinkers either enhance or inhibit the contractility of a network, depending on the organization of actin within the network. Numerical simulations unified the roles of actin filament branching and crosslinking during actomyosin contraction. Specifically, we introduce the concept of "network connectivity" and show that the contractions of distinct actin architectures are described by the same master curve when considering their degree of connectivity. This makes it possible to predict the dynamic response of defined actin structures to transient changes in connectivity. We propose that, depending on the connectivity and the architecture, network contraction is dominated by either sarcomeric-like or buckling mechanisms. More generally, this study reveals how actin network contractility depends on its architecture under a defined set of biochemical conditions.
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Affiliation(s)
- Hajer Ennomani
- Biosciences & Biotechnology Institute of Grenoble, Laboratoire de Physiologie Cellulaire et Vegétale, CNRS/CEA/UGA/INRA, Grenoble 38054, France
| | - Gaëlle Letort
- Biosciences & Biotechnology Institute of Grenoble, Laboratoire de Physiologie Cellulaire et Vegétale, CNRS/CEA/UGA/INRA, Grenoble 38054, France
| | - Christophe Guérin
- Biosciences & Biotechnology Institute of Grenoble, Laboratoire de Physiologie Cellulaire et Vegétale, CNRS/CEA/UGA/INRA, Grenoble 38054, France
| | - Jean-Louis Martiel
- Biosciences & Biotechnology Institute of Grenoble, Laboratoire de Physiologie Cellulaire et Vegétale, CNRS/CEA/UGA/INRA, Grenoble 38054, France
| | - Wenxiang Cao
- Department of Molecular Biophysics and Biochemistry, Yale University, 260 Whitney Avenue, New Haven, CT 06520-8114, USA
| | - François Nédélec
- Cell Biology and Biophysics Unit, EMBL, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Enrique M De La Cruz
- Department of Molecular Biophysics and Biochemistry, Yale University, 260 Whitney Avenue, New Haven, CT 06520-8114, USA
| | - Manuel Théry
- Biosciences & Biotechnology Institute of Grenoble, Laboratoire de Physiologie Cellulaire et Vegétale, CNRS/CEA/UGA/INRA, Grenoble 38054, France; Unité de thérapie Cellulaire, Hopital Saint-Louis, Avenue Claude Vellefaux, Paris 75010, France.
| | - Laurent Blanchoin
- Biosciences & Biotechnology Institute of Grenoble, Laboratoire de Physiologie Cellulaire et Vegétale, CNRS/CEA/UGA/INRA, Grenoble 38054, France.
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15
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Moshe M, Sharon E, Kupferman R. Elastic interactions between two-dimensional geometric defects. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2015; 92:062403. [PMID: 26764699 DOI: 10.1103/physreve.92.062403] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2015] [Indexed: 06/05/2023]
Abstract
In this paper, we introduce a methodology applicable to a wide range of localized two-dimensional sources of stress. This methodology is based on a geometric formulation of elasticity. Localized sources of stress are viewed as singular defects-point charges of the curvature associated with a reference metric. The stress field in the presence of defects can be solved using a scalar stress function that generalizes the classical Airy stress function to the case of materials with nontrivial geometry. This approach allows the calculation of interaction energies between various types of defects. We apply our methodology to two physical systems: shear-induced failure of amorphous materials and the mechanical interaction between contracting cells.
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Affiliation(s)
- Michael Moshe
- Department of Physics, Syracuse University, Syracuse, New York 13244-1130, USA and Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Eran Sharon
- Racah Institute of Physics, The Hebrew University, Jerusalem
| | - Raz Kupferman
- Einstein Institute of Mathematics, The Hebrew University, Jerusalem
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16
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Verkhovsky AB. The mechanisms of spatial and temporal patterning of cell-edge dynamics. Curr Opin Cell Biol 2015; 36:113-21. [PMID: 26432504 DOI: 10.1016/j.ceb.2015.09.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2015] [Revised: 09/11/2015] [Accepted: 09/11/2015] [Indexed: 01/14/2023]
Abstract
Adherent cells migrate and change their shape by means of protrusion and retraction at their edges. When and where these activities occur defines the shape of the cell and the way it moves. Despite a great deal of knowledge about the structural organization, components, and biochemical reactions involved in protrusion and retraction, the origins of their spatial and temporal patterns are still poorly understood. Chemical signaling circuitry is believed to be an important source of patterning, but recent studies highlighted mechanisms based on physical forces, motion, and mechanical feedback.
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Affiliation(s)
- Alexander B Verkhovsky
- Laboratory of Physics of Living Matter, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
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17
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Changes in renal tissue proteome induced by mesenteric lymph drainage in rats after hemorrhagic shock with resuscitation. Shock 2015; 42:350-5. [PMID: 24978890 DOI: 10.1097/shk.0000000000000214] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Kidney injury commonly occurs after hemorrhagic shock. Previous studies have shown that post-hemorrhagic shock mesenteric lymph (PHSML) return negatively affects the kidneys and may induce injury. This study investigates the effect of PHSML drainage on the proteome in renal tissue. A controlled hemorrhagic shock model was established in the shock and shock+drainage groups. After 1 h of hypotension, fluid resuscitation was implemented within 30 min. Meanwhile, PHSML was drained in the shock+drainage group. After 3 h of resuscitation, renal tissue was extracted for proteome analysis using two-dimensional fluorescence difference gel electrophoresis. Differential proteins with intensities that either increased or decreased by 1.5-fold or greater were selected for trypsin digestion and analyzed by matrix-assisted laser desorption/ionization time-of-flight (TOF) mass spectrometry and tandem TOF/TOF mass spectrometry. Enzyme-linked immunosorbent assay was used to validate the identified partial proteins. Compared with the sham group, hnRNPC and Starp decreased in the shock group, whereas Hadha, Slc25a13, Atp5b, hnRNPC, Starp, Rps3, and actin were downregulated in the shock+drainage group. Meanwhile, Atp5b and actin decreased in the shock+drainage group relative to the shock group. The identified proteins can be classified into different categories, such as cell proliferation (hnRNPC, Strap, and Rps3), energy metabolism (Hadha, Atp5b, and Slc25a13), cell motility, and cytoskeleton (actin). Moreover, enzyme-linked immunosorbent assay measurement validated the changed levels of Atp5b and Actg2. Our findings provide a starting point for investigating the functions of differentially expressed proteins in acute kidney injury induced by hemorrhagic shock. These findings hold great potential for the development of therapeutic interventions.
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Abstract
Here we demonstrate that interleukin-2-inducible T-cell kinase (Itk) signaling in cluster of differentiation 4-positive (CD4(+)) T cells promotes experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis (MS). We show that Itk(-/-) mice exhibit reduced disease severity, and transfer of Itk(-/-) CD4(+) T cells into T cell-deficient recipients results in lower disease severity. We observed a significant reduction of CD4(+) T cells in the CNS of Itk(-/-) mice or recipients of Itk(-/-) CD4(+) T cells during EAE, which is consistent with attenuated disease. Itk(-/-) CD4(+) T cells exhibit defective response to myelin antigen stimulation attributable to displacement of filamentous actin from the CD4(+) coreceptor. This results in inadequate transmigration of Itk(-/-) CD4(+) T cells into the CNS and across brain endothelial barriers in vitro. Finally, Itk(-/-) CD4(+) T cells show significant reduction in production of T-helper 1 (Th1) and Th17 cytokines and exhibit skewed T effector/T regulatory cell ratios. These results indicate that signaling by Itk promotes autoimmunity and CNS inflammation, suggesting that it may be a viable target for treatment of MS.
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19
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Ben-Yaakov D, Golkov R, Shokef Y, Safran SA. Response of adherent cells to mechanical perturbations of the surrounding matrix. SOFT MATTER 2015; 11:1412-1424. [PMID: 25604950 DOI: 10.1039/c4sm01817f] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We present a generic and unified theory to explain how cells respond to perturbations of their mechanical environment such as the presence of neighboring cells, slowly applied stretch, or gradients of matrix rigidity. Motivated by experiments, we calculate the local balance of forces that give rise to a tendency for the cell to locally move or reorient, with a focus on the contribution of feedback and homeostasis to cell contractility (manifested by a fixed displacement, strain or stress) that acts on the adhesions at the cell boundary. These forces can be either reinforced or diminished by elastic stresses due to mechanical perturbations of the matrix. Our model predicts these changes and how their balance with local protrusive forces that act on the cell's leading edge either increase or decrease the tendency of the cell to locally move (toward neighboring cells or rigidity gradients) or reorient (in the direction of slowly applied stretch or rigidity gradients).
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Affiliation(s)
- Dan Ben-Yaakov
- Dept. Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel.
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20
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Fuse M, Hayakawa T, Hashizume-Takizawa T, Takeuchi R, Kurita-Ochiai T, Fujita-Yoshigaki J, Fukumoto M. MC3T3-E1 Cell Assay on Collagen or Fibronectin Immobilized Poly (Lactic Acid-ε-Caprolactone) Film. J HARD TISSUE BIOL 2015. [DOI: 10.2485/jhtb.24.249] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- Megumi Fuse
- Department of Laboratory Medicine for Dentistry, Nihon University School of Dentistry at Matsudo
| | - Tohru Hayakawa
- Department of Dental Engineering, Tsurumi University School of Dental Medicine
| | | | - Reiri Takeuchi
- Department of Biochemistry and Molecular Biology, Nihon University School of Dentistry at Matsudo
| | | | | | - Masahiko Fukumoto
- Department of Laboratory Medicine for Dentistry, Nihon University School of Dentistry at Matsudo
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21
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Bella A, Shaw M, Ray S, Ryadnov MG. Filming protein fibrillogenesis in real time. Sci Rep 2014; 4:7529. [PMID: 25519825 PMCID: PMC4269891 DOI: 10.1038/srep07529] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2014] [Accepted: 12/01/2014] [Indexed: 12/28/2022] Open
Abstract
Protein fibrillogenesis is a universal tool of nano-to-micro scale construction supporting different forms of biological function. Its exploitable potential in nanoscience and technology is substantial, but the direct observation of homogeneous fibre growth able to underpin a kinetic-based rationale for building customized nanostructures in situ is lacking. Here we introduce a kinetic model of de novo protein fibrillogenesis which we imaged at the nanoscale and in real time, filmed. The model helped to reveal that, in contrast to heterogeneous amyloid assemblies, homogeneous protein recruitment is principally characterized by uniform rates of cooperative growth at both ends of growing fibers, bi-directional growth, with lateral growth arrested at a post-seeding stage. The model provides a foundation for in situ engineering of sequence-prescribed fibrous architectures.
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Affiliation(s)
- Angelo Bella
- National Physical Laboratory, Hampton Road, Teddington, TW11 0LW, UK
| | - Michael Shaw
- National Physical Laboratory, Hampton Road, Teddington, TW11 0LW, UK
| | - Santanu Ray
- National Physical Laboratory, Hampton Road, Teddington, TW11 0LW, UK
| | - Maxim G Ryadnov
- 1] National Physical Laboratory, Hampton Road, Teddington, TW11 0LW, UK [2] School of Physics and Astronomy, University of Edinburgh, UK EH9 3JZ, UK
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22
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Power transduction of actin filaments ratcheting in vitro against a load. Proc Natl Acad Sci U S A 2014; 111:17845-50. [PMID: 25453075 DOI: 10.1073/pnas.1414184111] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The actin cytoskeleton has the unique capability of producing pushing forces at the leading edge of motile cells without the implication of molecular motors. This phenomenon has been extensively studied theoretically, and molecular models, including the widely known Brownian ratchet, have been proposed. However, supporting experimental work is lacking, due in part to hardly accessible molecular length scales. We designed an experiment to directly probe the mechanism of force generation in a setup where a population of actin filaments grows against a load applied by magnetic microparticles. The filaments, arranged in stiff bundles by fascin, are constrained to point toward the applied load. In this protrusion-like geometry, we are able to directly measure the velocity of filament elongation and its dependence on force. Using numerical simulations, we provide evidence that our experimental data are consistent with a Brownian ratchet-based model. We further demonstrate the existence of a force regime far below stalling where the mechanical power transduced by the ratcheting filaments to the load is maximal. The actin machinery in migrating cells may tune the number of filaments at the leading edge to work in this force regime.
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23
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Shamloo A. Cell-cell interactions mediate cytoskeleton organization and collective endothelial cell chemotaxis. Cytoskeleton (Hoboken) 2014; 71:501-12. [DOI: 10.1002/cm.21185] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Revised: 06/28/2014] [Accepted: 07/21/2014] [Indexed: 01/03/2023]
Affiliation(s)
- Amir Shamloo
- Center of Excellence in Energy Conversion (CEEC); Department of Mechanical Engineering, Sharif University of Technology; Tehran Iran
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24
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Osmulski P, Mahalingam D, Gaczynska ME, Liu J, Huang S, Horning AM, Wang CM, Thompson IM, Huang THM, Chen CL. Nanomechanical biomarkers of single circulating tumor cells for detection of castration resistant prostate cancer. Prostate 2014; 74:1297-307. [PMID: 25065737 PMCID: PMC4142568 DOI: 10.1002/pros.22846] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/21/2014] [Accepted: 06/04/2014] [Indexed: 01/22/2023]
Abstract
BACKGROUND Emerging evidence shows that nanomechanical phenotypes of circulating tumor cells (CTC) could become potential biomarkers for metastatic castration resistant prostate cancer (mCRPC). METHODS To determine the nanomechanical phenotypes of CTCs we applied atomic force microscopy (AFM) employing the PeakForce quantitative nanomechanical (QNM) imaging. We assessed biophysical parameters (elasticity, deformation, and adhesion) of 130 CTCs isolated from blood samples from five castration sensitive (CS) and 12 castration resistant prostate cancer (CRPCa) patients. RESULTS We found that CTCs from CRPCa patients are three times softer, three times more deformable, and seven times more adhesive than counterparts from CSPCa patients. Both nonsupervised hierarchical clustering and principle component analysis show that three combined nanomechanical parameters could constitute a valuable set to distinguish between CSPCa and CRPCa. CONCLUSIONS [corrected] Our study indicates that nanomechanical phenotypes of CTCs may serve as novel and effective biomarkers for mCRPC.
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Affiliation(s)
- Pawel Osmulski
- Departments of Molecular Medicine, University of Texas Health Science Center, San Antonio, Texas
| | - Devalingam Mahalingam
- Cancer Therapy and Research Center, University of Texas Health Science Center, San Antonio, Texas
- Department of Medicine, University of Texas Health Science Center, San Antonio, Texas
| | - Maria E Gaczynska
- Departments of Molecular Medicine, University of Texas Health Science Center, San Antonio, Texas
| | - Joseph Liu
- Departments of Molecular Medicine, University of Texas Health Science Center, San Antonio, Texas
| | - Susan Huang
- Departments of Molecular Medicine, University of Texas Health Science Center, San Antonio, Texas
| | - Aaron M Horning
- Integrated Biomedical Science Graduate Program, University of Texas Health Science Center, San Antonio, Texas
| | - Chiou-Miin Wang
- Departments of Molecular Medicine, University of Texas Health Science Center, San Antonio, Texas
| | - Ian M. Thompson
- Cancer Therapy and Research Center, University of Texas Health Science Center, San Antonio, Texas
- Department of Urology, University of Texas Health Science Center, San Antonio, Texas
| | - Tim H-M Huang
- Departments of Molecular Medicine, University of Texas Health Science Center, San Antonio, Texas
- Cancer Therapy and Research Center, University of Texas Health Science Center, San Antonio, Texas
| | - Chun-Liang Chen
- Departments of Molecular Medicine, University of Texas Health Science Center, San Antonio, Texas
- Cancer Therapy and Research Center, University of Texas Health Science Center, San Antonio, Texas
- Correspondence: Chun-Liang Chen, PhD, Department of Molecular Medicine, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr., Mail code: 8257, San Antonio, Tx 78229-3900.
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25
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Novak IL, Slepchenko BM. A conservative algorithm for parabolic problems in domains with moving boundaries. JOURNAL OF COMPUTATIONAL PHYSICS 2014; 270:203-213. [PMID: 25067852 PMCID: PMC4107334 DOI: 10.1016/j.jcp.2014.03.014] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We describe a novel conservative algorithm for parabolic problems in domains with moving boundaries developed for modeling in cell biology. The spatial discretization is accomplished by applying Voronoi decomposition to a fixed rectangular grid. In the vicinity of the boundary, the procedure generates irregular Voronoi cells that conform to the domain shape and merge seamlessly with regular control volumes in the domain interior. Consequently, our algorithm is free of the CFL stability issue due to moving interfaces and does not involve cell-merging or mass redistribution. Local mass conservation is ensured by finite-volume discretization and natural-neighbor interpolation. Numerical experiments with two-dimensional geometries demonstrate exact mass conservation and indicate an order of convergence in space between one and two. The use of standard meshing techniques makes extension of the method to three dimensions conceptually straightforward.
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Affiliation(s)
- Igor L Novak
- Richard D. Berlin Center for Cell Analysis and Modeling, Department of Cell Biology, University of Connecticut Health Center, Farmington, Connecticut 06030
| | - Boris M Slepchenko
- Richard D. Berlin Center for Cell Analysis and Modeling, Department of Cell Biology, University of Connecticut Health Center, Farmington, Connecticut 06030
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26
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Mkrtchyan A, Åström J, Karttunen M. A new model for cell division and migration with spontaneous topology changes. SOFT MATTER 2014; 10:4332-4339. [PMID: 24793724 DOI: 10.1039/c4sm00489b] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Tissue topology, in particular proliferating epithelium topology, is remarkably similar between various species. Understanding the mechanisms that result in the observed topologies is needed for better insight into the processes governing tissue formation. We present a two-dimensional single-cell based model for cell divisions and tissue growth. The model accounts for cell mechanics and allows cell migration. Cells do not have pre-existing shapes or topologies. Shape changes and local rearrangements occur naturally as a response to the evolving cellular environment and cell-cell interactions. We show that the commonly observed tissue topologies arise spontaneously from this model. We consider different cellular rearrangements that accompany tissue growth and study their effects on tissue topology.
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Affiliation(s)
- Anna Mkrtchyan
- Department of Applied Mathematics, University of Western Ontario, London, Ontario, Canada
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27
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Reichman-Fried M, Raz E. Small proteins, big roles: The signaling protein Apela extends the complexity of developmental pathways in the early zebrafish embryo. Bioessays 2014; 36:741-5. [DOI: 10.1002/bies.201400048] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Michal Reichman-Fried
- Institute of Cell Biology; Center for Molecular Biology of Inflammation; Münster Germany
| | - Erez Raz
- Institute of Cell Biology; Center for Molecular Biology of Inflammation; Münster Germany
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28
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Bacterial twitching motility is coordinated by a two-dimensional tug-of-war with directional memory. Nat Commun 2014; 5:3759. [PMID: 24806757 DOI: 10.1038/ncomms4759] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2013] [Accepted: 03/31/2014] [Indexed: 02/07/2023] Open
Abstract
Type IV pili are ubiquitous bacterial motors that power surface motility. In peritrichously piliated species, it is unclear how multiple pili are coordinated to generate movement with directional persistence. Here we use a combined theoretical and experimental approach to test the hypothesis that multiple pili of Neisseria gonorrhoeae are coordinated through a tug-of-war. Based on force-dependent unbinding rates and pilus retraction speeds measured at the level of single pili, we build a tug-of-war model. Whereas the one-dimensional model robustly predicts persistent movement, the two-dimensional model requires a mechanism of directional memory provided by re-elongation of fully retracted pili and pilus bundling. Experimentally, we confirm memory in the form of bursts of pilus retractions. Bursts are seen even with bundling suppressed, indicating re-elongation from stable core complexes as the key mechanism of directional memory. Directional memory increases the surface range explored by motile bacteria and likely facilitates surface colonization.
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