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Cellular inertia. Sci Rep 2021; 11:23799. [PMID: 34893617 PMCID: PMC8664931 DOI: 10.1038/s41598-021-02384-y] [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: 12/25/2020] [Accepted: 11/09/2021] [Indexed: 11/18/2022] Open
Abstract
It has been experimentally reported that chemotactic cells exhibit cellular memory, that is, a tendency to maintain the migration direction despite changes in the chemoattractant gradient. In this study, we analyzed a phenomenological model assuming the presence of cellular inertia, as well as a response time in motility, resulting in the reproduction of the cellular memory observed in the previous experiments. According to the analysis, the cellular motion is described by the superposition of multiple oscillative functions induced by the multiplication of the oscillative polarity and motility. The cellular intertia generates cellular memory by regulating phase differences between those oscillative functions. By applying the theory to the experimental data, the cellular inertia was estimated at \documentclass[12pt]{minimal}
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\begin{document}$$m=3-6$$\end{document}m=3-6 min. In addition, physiological parameters, such as response time in motility and intracellular processing speed, were also evaluated. The agreement between the experiemental data and theory suggests the possibility of the presence of the response time in motility, which has never been biologically verified and should be explored in the future.
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2
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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]
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Karmakar R, Schich C, Kamprad N, Scheller V, Gutierrez E, Groisman A, Rappel WJ, Tarantola M. Novel micropatterning technique reveals dependence of cell-substrate adhesion and migration of social amoebas on parental strain, development, and fluorescent markers. PLoS One 2020; 15:e0236171. [PMID: 32702047 PMCID: PMC7377449 DOI: 10.1371/journal.pone.0236171] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2020] [Accepted: 06/30/2020] [Indexed: 02/07/2023] Open
Abstract
Cell-substrate adhesion of the social amoeba Dictyostelium discoideum, a model organism often used for the study of chemotaxis, is non-specific and does not involve focal adhesion complexes. Therefore, micropatterned substrates where adherent Dictyostelium cells are constrained to designated microscopic regions are difficult to make. Here we present a micropatterning technique for Dictyostelium cells that relies on coating the substrate with an ∼1μm thick layer of polyethylene glycol (PEG) gel. We show that, when plated on a substrate with narrow parallel stripes of PEG-gel and glass, Dictyostelium cells nearly exclusive adhere to and migrate along the glass stripes, thus providing a model system to study one-dimensional migration of amoeboid cells. Surprisingly, we find substantial differences in the adhesion to PEG-gel and glass stripes between vegetative and developed cells and between two different axenic laboratory strains of Dictyostelium, AX2 and AX4. Even more surprisingly, we find that the distribution of Dictyostelium cells between PEG-gel and glass stripes is significantly affected by the expression of several fluorescent protein markers of the cytoskeleton. We carry out atomic force microscopy based single cell force spectroscopy measurements that confirm that the force of adhesion to PEG-gel substrate can be significantly different between vegetative and developed cells, AX2 and AX4 cells, and cells with and without fluorescent markers. Thus, the choice of parental background, the degree of development, and the expression of fluorescent protein markers can all have a profound effect on cell-substrate adhesion and should be considered when comparing migration of cells and when designing micropatterned substrates.
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Affiliation(s)
- Richa Karmakar
- Department of Physics, University of California, San Diego, La Jolla, California, United States of America
| | | | - Nadine Kamprad
- Institute for Dynamics of Complex Systems, Goettingen, Germany.,Max Planck Institute for Dynamics and Self-Organization, Göttingen, Germany
| | | | - Edgar Gutierrez
- Department of Physics, University of California, San Diego, La Jolla, California, United States of America
| | - Alex Groisman
- Department of Physics, University of California, San Diego, La Jolla, California, United States of America
| | - Wouter-Jan Rappel
- Department of Physics, University of California, San Diego, La Jolla, California, United States of America
| | - Marco Tarantola
- Institute for Dynamics of Complex Systems, Goettingen, Germany.,Max Planck Institute for Dynamics and Self-Organization, Göttingen, Germany
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4
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Whitelaw JA, Swaminathan K, Kage F, Machesky LM. The WAVE Regulatory Complex Is Required to Balance Protrusion and Adhesion in Migration. Cells 2020; 9:E1635. [PMID: 32646006 PMCID: PMC7407199 DOI: 10.3390/cells9071635] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2020] [Revised: 07/02/2020] [Accepted: 07/03/2020] [Indexed: 12/15/2022] Open
Abstract
Cells migrating over 2D substrates are required to polymerise actin at the leading edge to form lamellipodia protrusions and nascent adhesions to anchor the protrusion to the substrate. The major actin nucleator in lamellipodia formation is the Arp2/3 complex, which is activated by the WAVE regulatory complex (WRC). Using inducible Nckap1 floxed mouse embryonic fibroblasts (MEFs), we confirm that the WRC is required for lamellipodia formation, and importantly, for generating the retrograde flow of actin from the leading cell edge. The loss of NCKAP1 also affects cell spreading and focal adhesion dynamics. In the absence of lamellipodium, cells can become elongated and move with a single thin pseudopod, which appears devoid of N-WASP. This phenotype was more prevalent on collagen than fibronectin, where we observed an increase in migratory speed. Thus, 2D cell migration on collagen is less dependent on branched actin.
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Affiliation(s)
| | - Karthic Swaminathan
- CRUK Beatson Institute, Glasgow G61 1BD, UK; (K.S.); (L.M.M.)
- School of Chemistry and Bioscience, University of Bradford, Bradford BD7 1PD, UK
| | - Frieda Kage
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth College, Hanover, NH 03755-3844, USA;
- Zoological Institute, Technische Universität Braunschweig, 38106 Braunschweig, Germany
| | - Laura M. Machesky
- CRUK Beatson Institute, Glasgow G61 1BD, UK; (K.S.); (L.M.M.)
- Institute of Cancer Sciences, University of Glasgow, Glasgow G61 1QH, UK
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5
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Feng J, Levine H, Mao X, Sander LM. Cell motility, contact guidance, and durotaxis. SOFT MATTER 2019; 15:4856-4864. [PMID: 31161163 DOI: 10.1039/c8sm02564a] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Mechanical properties of the substrate play a vital role in cell motility. In particular, cells have been shown to migrate along aligned fibers in the substrate (contact guidance) and up stiffness gradients (durotaxis). Here we present a simple mechanical model for cell migration coupled to substrate properties, by placing a simulated cell on a lattice mimicking biopolymer gels or hydrogels. In our model cells attach to the substrate via focal adhesions (FAs). As the cells contract, forces are generated at the FAs, determining their maturation and detachment. At the same time, the cell was also allowed to move and rotate to maintain force and torque balance. Our model, in which the cells only have access to information regarding forces acting at the FAs, without a prior knowledge of the substrate stiffness or geometry, is able to reproduce both contact guidance and durotaxis.
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Affiliation(s)
- Jingchen Feng
- Center for Theoretical Biological Physics, Rice University, 6100 Main Street, Houston, TX 77005-1892, USA.
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6
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Kamprad N, Witt H, Schröder M, Kreis CT, Bäumchen O, Janshoff A, Tarantola M. Adhesion strategies of Dictyostelium discoideum- a force spectroscopy study. NANOSCALE 2018; 10:22504-22519. [PMID: 30480299 DOI: 10.1039/c8nr07107a] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Biological adhesion is essential for all motile cells and generally limits locomotion to suitably functionalized substrates displaying a compatible surface chemistry. However, organisms that face vastly varying environmental challenges require a different strategy. The model organism Dictyostelium discoideum (D.d.), a slime mould dwelling in the soil, faces the challenge of overcoming variable chemistry by employing the fundamental forces of colloid science. To understand the origin of D.d. adhesion, we realized and modified a variety of conditions for the amoeba comprising the absence and presence of the specific adhesion protein Substrate Adhesion A (sadA), glycolytic degradation, ionic strength, surface hydrophobicity and strength of van der Waals interactions by generating tailored model substrates. By employing AFM-based single cell force spectroscopy we could show that experimental force curves upon retraction exhibit two regimes. The first part up to the critical adhesion force can be described in terms of a continuum model, while the second regime of the curve beyond the critical adhesion force is governed by stochastic unbinding of individual binding partners and bond clusters. We found that D.d. relies on adhesive interactions based on EDL-DLVO (Electrical Double Layer-Derjaguin-Landau-Verwey-Overbeek) forces and contributions from the glycocalix and specialized adhesion molecules like sadA. This versatile mechanism allows the cells to adhere to a large variety of natural surfaces under various conditions.
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Affiliation(s)
- Nadine Kamprad
- Max Planck Institute for Dynamics and Self-Organization, Am Faßberg 17, 37077 Göttingen, Germany.
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Sun X, Hourwitz MJ, Baker EM, Schmidt BUS, Losert W, Fourkas JT. Replication of biocompatible, nanotopographic surfaces. Sci Rep 2018; 8:564. [PMID: 29330498 PMCID: PMC5766624 DOI: 10.1038/s41598-017-19008-z] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2017] [Accepted: 12/20/2017] [Indexed: 01/16/2023] Open
Abstract
The ability of cells to sense and respond to nanotopography is being implicated as a key element in many physiological processes such as cell differentiation, immune response, and wound healing, as well as in pathologies such as cancer metastasis. To understand how nanotopography affects cellular behaviors, new techniques are required for the mass production of biocompatible, rigid nanotopographic surfaces. Here we introduce a method for the rapid and reproducible production of biocompatible, rigid, acrylic nanotopographic surfaces, and for the functionalization of the surfaces with adhesion-promoting molecules for cell experiments. The replica surfaces exhibit high optical transparency, which is advantageous for high-resolution, live-cell imaging. As a representative application, we demonstrate that epithelial cells form focal adhesions on surfaces composed of nanoscale ridges and grooves, and that the focal adhesions prefer to localize on the nanoridges. We further demonstrate that both F-actin and microtubules align along the nanoridges, but only F-actin aligns along the nanogrooves. The mass production of nanotopographic surfaces opens the door to the investigation of the effect of physical cues on the spatial distribution and the dynamics of intracellular proteins, and to the study of the mechanism of mechanosensing in processes such as cell migration, phagocytosis, division, and differentiation.
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Affiliation(s)
- Xiaoyu Sun
- Department of Chemistry and Biochemistry, University of Maryland, College Park, MD, 20742, USA
| | - Matt J Hourwitz
- Department of Chemistry and Biochemistry, University of Maryland, College Park, MD, 20742, USA
| | - Eleni M Baker
- Department of Chemistry and Biochemistry, University of Maryland, College Park, MD, 20742, USA
| | - B U Sebastian Schmidt
- Institute for Physical Science and Technology, University of Maryland, College Park, MD, 20742, USA
| | - Wolfgang Losert
- Institute for Physical Science and Technology, University of Maryland, College Park, MD, 20742, USA. .,Department of Physics, University of Maryland, College Park, MD, 20742, USA. .,Maryland NanoCenter, University of Maryland, College Park, MD, 20742, USA.
| | - John T Fourkas
- Department of Chemistry and Biochemistry, University of Maryland, College Park, MD, 20742, USA. .,Institute for Physical Science and Technology, University of Maryland, College Park, MD, 20742, USA. .,Center for Nanophysics and Advanced Materials, University of Maryland, College Park, MD, 20742, USA. .,Maryland NanoCenter, University of Maryland, College Park, MD, 20742, USA.
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Cherstvy AG, Nagel O, Beta C, Metzler R. Non-Gaussianity, population heterogeneity, and transient superdiffusion in the spreading dynamics of amoeboid cells. Phys Chem Chem Phys 2018; 20:23034-23054. [DOI: 10.1039/c8cp04254c] [Citation(s) in RCA: 51] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
What is the underlying diffusion process governing the spreading dynamics and search strategies employed by amoeboid cells?
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Affiliation(s)
- Andrey G. Cherstvy
- Institute for Physics & Astronomy
- University of Potsdam
- 14476 Potsdam-Golm
- Germany
| | - Oliver Nagel
- Institute for Physics & Astronomy
- University of Potsdam
- 14476 Potsdam-Golm
- Germany
| | - Carsten Beta
- Institute for Physics & Astronomy
- University of Potsdam
- 14476 Potsdam-Golm
- Germany
| | - Ralf Metzler
- Institute for Physics & Astronomy
- University of Potsdam
- 14476 Potsdam-Golm
- Germany
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9
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Eidi Z, Mohammad-Rafiee F, Khorrami M, Gholami A. Modelling of Dictyostelium discoideum movement in a linear gradient of chemoattractant. SOFT MATTER 2017; 13:8209-8222. [PMID: 29058003 DOI: 10.1039/c7sm01568b] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Chemotaxis is a ubiquitous biological phenomenon in which cells detect a spatial gradient of chemoattractant, and then move towards the source. Here we present a position-dependent advection-diffusion model that quantitatively describes the statistical features of the chemotactic motion of the social amoeba Dictyostelium discoideum in a linear gradient of cAMP (cyclic adenosine monophosphate). We fit the model to experimental trajectories that are recorded in a microfluidic setup with stationary cAMP gradients and extract the diffusion and drift coefficients in the gradient direction. Our analysis shows that for the majority of gradients, both coefficients decrease over time and become negative as the cells crawl up the gradient. The extracted model parameters also show that besides the expected drift in the direction of the chemoattractant gradient, we observe a nonlinear dependency of the corresponding variance on time, which can be explained by the model. Furthermore, the results of the model show that the non-linear term in the mean squared displacement of the cell trajectories can dominate the linear term on large time scales.
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Affiliation(s)
- Zahra Eidi
- Department of Physics, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran.
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10
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Shear force-based genetic screen reveals negative regulators of cell adhesion and protrusive activity. Proc Natl Acad Sci U S A 2017; 114:E7727-E7736. [PMID: 28847951 DOI: 10.1073/pnas.1616600114] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The model organism Dictyostelium discoideum has greatly facilitated our understanding of the signal transduction and cytoskeletal pathways that govern cell motility. Cell-substrate adhesion is downstream of many migratory and chemotaxis signaling events. Dictyostelium cells lacking the tumor suppressor PTEN show strongly impaired migratory activity and adhere strongly to their substrates. We reasoned that other regulators of migration could be obtained through a screen for overly adhesive mutants. A screen of restriction enzyme-mediated integration mutagenized cells yielded numerous mutants with the desired phenotypes, and the insertion sites in 18 of the strains were mapped. These regulators of adhesion and motility mutants have increased adhesion and decreased motility. Characterization of seven strains demonstrated decreased directed migration, flatness, increased filamentous actin-based protrusions, and increased signal transduction network activity. Many of the genes share homology to human genes and demonstrate the diverse array of cellular networks that function in adhesion and migration.
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11
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Fukujin F, Nakajima A, Shimada N, Sawai S. Self-organization of chemoattractant waves in Dictyostelium depends on F-actin and cell-substrate adhesion. J R Soc Interface 2016; 13:20160233. [PMID: 27358278 PMCID: PMC4938087 DOI: 10.1098/rsif.2016.0233] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Accepted: 06/01/2016] [Indexed: 12/25/2022] Open
Abstract
In the social amoeba Dictyostelium discoideum, travelling waves of extracellular cyclic adenosine monophosphate (cAMP) self-organize in cell populations and direct aggregation of individual cells to form multicellular fruiting bodies. In contrast to the large body of studies that addressed how movement of cells is determined by spatial and temporal cues encoded in the dynamic cAMP gradients, how cell mechanics affect the formation of a self-generated chemoattractant field has received less attention. Here, we show, by live cell imaging analysis, that the periodicity of the synchronized cAMP waves increases in cells treated with the actin inhibitor latrunculin. Detail analysis of the extracellular cAMP-induced transients of cytosolic cAMP (cAMP relay response) in well-isolated cells demonstrated that their amplitude and duration were markedly reduced in latrunculin-treated cells. Similarly, in cells strongly adhered to a poly-l-lysine-coated surface, the response was suppressed, and the periodicity of the population-level oscillations was markedly lengthened. Our results suggest that cortical F-actin is dispensable for the basic low amplitude relay response but essential for its full amplification and that this enhanced response is necessary to establish high-frequency signalling centres. The observed F-actin dependence may prevent aggregation centres from establishing in microenvironments that are incompatible with cell migration.
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Affiliation(s)
- Fumihito Fukujin
- Department of Basic Science, Graduate School of Arts and Sciences, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
| | - Akihiko Nakajima
- Research Center for Complex Systems Biology, Graduate School of Arts and Sciences, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
| | - Nao Shimada
- Department of Basic Science, Graduate School of Arts and Sciences, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
| | - Satoshi Sawai
- Department of Basic Science, Graduate School of Arts and Sciences, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan Research Center for Complex Systems Biology, Graduate School of Arts and Sciences, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan PRESTO, Japan Science and Technology Agency, Kawaguchi-shi, Saitama 332-0012, Japan
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12
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Zhu X, Bouffanais R, Yue DKP. Interplay between motility and cell-substratum adhesion in amoeboid cells. BIOMICROFLUIDICS 2015; 9:054112. [PMID: 26487898 PMCID: PMC4592429 DOI: 10.1063/1.4931762] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2015] [Accepted: 09/15/2015] [Indexed: 05/07/2023]
Abstract
The effective migration of amoeboid cells requires a fine regulation of cell-substratum adhesion. These entwined processes have been shown to be regulated by a host of biophysical and biochemical cues. Here, we reveal the pivotal role played by calcium-based mechanosensation in the active regulation of adhesion resulting in a high migratory adaptability. Using mechanotactically driven Dictyostelium discoideum amoebae, we uncover the existence of optimal mechanosensitive conditions-corresponding to specific levels of extracellular calcium-for persistent directional migration over physicochemically different substrates. When these optimal mechanosensitive conditions are met, noticeable enhancement in cell migration directionality and speed is achieved, yet with significant differences among the different substrates. In the same narrow range of calcium concentrations that yields optimal cellular mechanosensory activity, we uncovered an absolute minimum in cell-substratum adhesion activity, for all considered substrates, with differences in adhesion strength among them amplified. The blocking of the mechanosensitive ion channels with gadolinium-i.e., the inhibition of the primary mechanosensory apparatus-hampers the active reduction in substrate adhesion, thereby leading to the same undifferentiated and drastically reduced directed migratory response. The adaptive behavioral responses of Dictyostelium cells sensitive to substrates with varying physicochemical properties suggest the possibility of novel surface analyses based on the mechanobiological ability of mechanosensitive and guidable cells to probe substrates at the nanometer-to-micrometer level.
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Affiliation(s)
- Xiaoying Zhu
- Singapore University of Technology and Design , 8 Somapah Road, Singapore 487372
| | - Roland Bouffanais
- Singapore University of Technology and Design , 8 Somapah Road, Singapore 487372
| | - Dick K P Yue
- Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
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13
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Wang C, Chowdhury S, Driscoll M, Parent CA, Gupta SK, Losert W. The interplay of cell-cell and cell-substrate adhesion in collective cell migration. J R Soc Interface 2015; 11:20140684. [PMID: 25165597 DOI: 10.1098/rsif.2014.0684] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Collective cell migration often involves notable cell-cell and cell-substrate adhesions and highly coordinated motion of touching cells. We focus on the interplay between cell-substrate adhesion and cell-cell adhesion. We show that the loss of cell-surface contact does not significantly alter the dynamic pattern of protrusions and retractions of fast migrating amoeboid cells (Dictyostelium discoideum), but significantly changes their ability to adhere to other cells. Analysis of the dynamics of cell shapes reveals that cells that are adherent to a surface may coordinate their motion with neighbouring cells through protrusion waves that travel across cell-cell contacts. However, while shape waves exist if cells are detached from surfaces, they do not couple cell to cell. In addition, our investigation of actin polymerization indicates that loss of cell-surface adhesion changes actin polymerization at cell-cell contacts. To further investigate cell-cell/cell-substrate interactions, we used optical micromanipulation to form cell-substrate contact at controlled locations. We find that both cell-shape dynamics and cytoskeletal activity respond rapidly to the formation of cell-substrate contact.
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Affiliation(s)
- Chenlu Wang
- Biophysics Graduate Program, University of Maryland, College Park, MD 20742, USA Laboratory of Cellular and Molecular Biology, Center for Cancer Research, NCI, NIH, 37 Convent Drive, Bethesda, MD 20892, USA
| | - Sagar Chowdhury
- Department of Mechanical Engineering and the Institute for Systems Research, University of Maryland, College Park, MD 20742, USA
| | - Meghan Driscoll
- Department of Physics, University of Maryland, College Park, MD 20742, USA
| | - Carole A Parent
- Laboratory of Cellular and Molecular Biology, Center for Cancer Research, NCI, NIH, 37 Convent Drive, Bethesda, MD 20892, USA Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742, USA
| | - S K Gupta
- Department of Mechanical Engineering and the Institute for Systems Research, University of Maryland, College Park, MD 20742, USA
| | - Wolfgang Losert
- Department of Physics, University of Maryland, College Park, MD 20742, USA Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742, USA
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