scholarly journals Membrane-mediated interactions induce spontaneous filament bundling

2018 ◽  
Author(s):  
Afshin Vahid ◽  
George Dadunashvili ◽  
Timon Idema
Keyword(s):  
Actin Filaments ◽  
Living Cells ◽  
Natural Consequence ◽  
Microtubule Network ◽  
Parallel Structures ◽  
Pulling Forces ◽  
Membrane Protrusions ◽  
A Cell ◽  
Cytoskeletal Elements ◽  
Pushing And Pulling

AbstractThe plasma membrane and cytoskeleton of living cells are closely coupled dynamical systems. Internal cytoskeletal elements such as actin filaments and microtubules continually exert forces on the membrane, resulting in the formation of membrane protrusions. In this paper we investigate the interplay between the shape of a cell distorted by pushing and pulling forces generated by microtubules and the resulting rearrangement of the microtubule network. From analytical calculations, we find that two microtubules that deform the vesicle can both attract or repel each other, depending on their angular separations and the direction of the imposed forces. We also show how the existence of attractive interactions between multiple microtubules can be deduced analytically, and further explore general interactions through Monte Carlo simulations. Our results suggest that the commonly reported parallel structures of microtubules in both biological and artificial systems can be a natural consequence of membrane mediated interactions.

scholarly journals Helical buckling of actin inside filopodia generates traction

2014 ◽  
Vol 112 (1) ◽  
pp. 136-141 ◽  
Author(s):  
Natascha Leijnse ◽  
Lene B. Oddershede ◽  
Poul M. Bendix
Keyword(s):  
Cell Membrane ◽  
Rotational Motion ◽  
Actin Filaments ◽  
Cell Communication ◽  
Confocal Imaging ◽  
Actin Bundle ◽  
Cellular Processes ◽  
Membrane Protrusions ◽  
A Cell ◽  
Helical Buckling

Cells can interact with their surroundings via filopodia, which are membrane protrusions that extend beyond the cell body. Filopodia are essential during dynamic cellular processes like motility, invasion, and cell–cell communication. Filopodia contain cross-linked actin filaments, attached to the surrounding cell membrane via protein linkers such as integrins. These actin filaments are thought to play a pivotal role in force transduction, bending, and rotation. We investigated whether, and how, actin within filopodia is responsible for filopodia dynamics by conducting simultaneous force spectroscopy and confocal imaging of F-actin in membrane protrusions. The actin shaft was observed to periodically undergo helical coiling and rotational motion, which occurred simultaneously with retrograde movement of actin inside the filopodium. The cells were found to retract beads attached to the filopodial tip, and retraction was found to correlate with rotation and coiling of the actin shaft. These results suggest a previously unidentified mechanism by which a cell can use rotation of the filopodial actin shaft to induce coiling and hence axial shortening of the filopodial actin bundle.

scholarly journals Force dependence of filopodia adhesion: involvement of myosin II and formins

2017 ◽  
Author(s):  
N. O. Alieva ◽  
A. K. Efremov ◽  
S. Hu ◽  
D. Oh ◽  
Z. Chen ◽  
...  
Keyword(s):  
Optical Tweezers ◽  
Actin Filaments ◽  
Adhesion Force ◽  
Preferential Attachment ◽  
Cell Orientation ◽  
Pulling Forces ◽  
Membrane Protrusions ◽  
Myosin Iia ◽  
Pulling Force

AbstractFilopodia are dynamic membrane protrusions driven by polymerization of an actin filament core, mediated by formin molecules at the filopodia tips. Filopodia can adhere to the extracellular matrix and experience both external and cell generated pulling forces. The role of such forces in filopodia adhesion is however insufficiently understood. Here, we induced sustained growth of filopodia by applying pulling force to their tips via attached fibronectin-coated beads trapped by optical tweezers. Strikingly, pharmacological inhibition or knockdown of myosin IIA, which localized to the base of filopodia, resulted in weakening of filopodia adherence strength. Inhibition of formins, which caused detachment of actin filaments from formin molecules, produced similar effect. Thus, myosin IIA-generated centripetal force transmitted to the filopodia tips through interactions between formins and actin filaments are required for filopodia adhesion. Force-dependent adhesion led to preferential attachment of filopodia to rigid versus fluid substrates, which may underlie cell orientation and polarization.

scholarly journals Centrosome centering and decentering by microtubule network rearrangement

2016 ◽  
Vol 27 (18) ◽  
pp. 2833-2843 ◽  
Author(s):  
Gaëlle Letort ◽  
Francois Nedelec ◽  
Laurent Blanchoin ◽  
Manuel Théry
Keyword(s):  
Molecular Motors ◽  
Cell Polarization ◽  
Cell Cortex ◽  
Cell Periphery ◽  
Microtubule Network ◽  
Abrupt Transition ◽  
External Cues ◽  
Pulling Forces ◽  
Number Dynamics ◽  
Pushing And Pulling

The centrosome is positioned at the cell center by pushing and pulling forces transmitted by microtubules (MTs). Centrosome decentering is often considered to result from asymmetric, cortical pulling forces exerted in particular by molecular motors on MTs and controlled by external cues affecting the cell cortex locally. Here we used numerical simulations to investigate the possibility that it could equally result from the redistribution of pushing forces due to a reorientation of MTs. We first showed that MT gliding along cell edges and pivoting around the centrosome regulate MT rearrangement and thereby direct the spatial distribution of pushing forces, whereas the number, dynamics, and stiffness of MTs determine the magnitude of these forces. By modulating these parameters, we identified different regimes, involving both pushing and pulling forces, characterized by robust centrosome centering, robust off-centering, or “reactive” positioning. In the last-named conditions, weak asymmetric cues can induce a misbalance of pushing and pulling forces, resulting in an abrupt transition from a centered to an off-centered position. Taken together, these results point to the central role played by the configuration of the MTs on the distribution of pushing forces that position the centrosome. We suggest that asymmetric external cues should not be seen as direct driver of centrosome decentering and cell polarization but instead as inducers of an effective reorganization of the MT network, fostering centrosome motion to the cell periphery.

scholarly journals Centrosome centering and Decentering by microtubule network rearrangement

2016 ◽  
Author(s):  
Gaëlle Letort ◽  
Francois Nedelec ◽  
Laurent Blanchoin ◽  
Manuel Théry
Keyword(s):  
Molecular Motors ◽  
Cell Polarization ◽  
Cell Cortex ◽  
Cell Periphery ◽  
Microtubule Network ◽  
Abrupt Transition ◽  
External Cues ◽  
Pulling Forces ◽  
Number Dynamics ◽  
Pushing And Pulling

AbstractThe centrosome is positioned at the cell center by pushing and pulling forces transmitted by microtubules (MTs). Centrosome decentering is often considered to result from asymmetric, cortical pulling forces exerted in particular by molecular motors on MTs, and controlled by external cues affecting the cell cortex locally. Here we used numerical simulations to investigate the possibility that it could equally result from the redistribution of pushing forces due to a reorientation of MTs. We first showed that MT gliding along cell edges and pivoting around the centrosome regulate MT rearrangement and thereby direct the spatial distribution of pushing forces, while the number, dynamics and stiffness of MTs determine the magnitude of these forces. By modulating these parameters, we identified different regimes, involving both pushing and pulling forces, characterized either by robust centrosome centering, robust off-centering or “reactive” positioning. In those latter conditions weak asymmetric cues can induce a misbalance of pushing and pulling forces resulting in an abrupt transition from a centered to an off-centered position. Altogether these results point at the central role played by the configuration of the MTs on the distribution of pushing forces that position the centrosome. We suggest that asymmetric external cues should not be seen as direct driver of centrosome decentering and cell polarization, but rather as inducers of an effective reorganization of the MT network, fostering centrosome motion to the cell periphery.

Modulated polarization microscopy displays the dynamics of cytoskeletal structures in living, motile cells

1995 ◽  
Vol 53 ◽  
pp. 902-903
Author(s):  
J. R. Kuhn ◽  
M. Poenie
Keyword(s):  
Mitotic Spindle ◽  
Actin Filaments ◽  
Cell Shape ◽  
Dynamic Structure ◽  
Living Cells ◽  
Cytoskeletal Proteins ◽  
Polarization Microscopy ◽  
Video Enhancement ◽  
Ultrastructural Studies ◽  
Motile Cells

Cell shape and movement are controlled by elements of the cytoskeleton including actin filaments an microtubules. Unfortunately, it is difficult to visualize the cytoskeleton in living cells and hence follow it dynamics. Immunofluorescence and ultrastructural studies of fixed cells while providing clear images of the cytoskeleton, give only a static picture of this dynamic structure. Microinjection of fluorescently Is beled cytoskeletal proteins has proved useful as a way to follow some cytoskeletal events, but long terry studies are generally limited by the bleaching of fluorophores and presence of unassembled monomers.Polarization microscopy has the potential for visualizing the cytoskeleton. Although at present, it ha mainly been used for visualizing the mitotic spindle. Polarization microscopy is attractive in that it pro vides a way to selectively image structures such as cytoskeletal filaments that are birefringent. By combing ing standard polarization microscopy with video enhancement techniques it has been possible to image single filaments. In this case, however, filament intensity depends on the orientation of the polarizer and analyzer with respect to the specimen.

scholarly journals Contact formation during fibroblast locomotion: involvement of membrane ruffles and microtubules.

1988 ◽  
Vol 106 (3) ◽  
pp. 747-760 ◽  
Author(s):  
G Rinnerthaler ◽  
B Geiger ◽  
J V Small
Keyword(s):  
Actin Filaments ◽  
Leading Edge ◽  
Fiber Assembly ◽  
Contact Formation ◽  
Contact Patterns ◽  
Fluorescence And Electron Microscopy ◽  
Cell Substrate ◽  
History Of ◽  
Cytoskeletal Elements ◽  
Primordial Cell

We have correlated the motility of the leading edge of fibroblasts, monitored by phase-contrast cinematography, with the relative distributions of several cytoskeletal elements (vinculin, tubulin, and actin) as well as with the contact patterns determined by interference reflection microscopy. This analysis has revealed the involvement of both ruffles and microspikes, as well as microtubules in the initiation of focal contact formation. Nascent vinculin sites within the leading edge or at its base, taken as primordial cell-substrate contacts, were invariably colocalized with sites that showed a history of transient, prolonged, or cyclic ruffling activity. Extended microspike structures, often preceded the formation of ruffles. Immunofluorescent labeling indicated that some of these primordial contacts were in close apposition to the ends of microtubules that penetrated into the leading edge. By fluorescence and electron microscopy short bundles of actin filaments found at the base of the leading edge were identified as presumptive, primordial contacts. It is concluded that ruffles and microspikes, either independently or in combination, initiate and mark the sites for future contact. Plaque proteins then accumulate (within 10-30 s) at the contract site and, beneath ruffles, induce localized bundling of actin filaments. We propose that all primordial contacts support traction for leading edge protrusion but that only some persist long enough to nucleate stress fiber assembly. Microtubules are postulated as the elements that select, stabilize, and potentiate the formation of these latter, long-lived contacts.

scholarly journals Subcellular optogenetic activation of Cdc42 controls local and distal signaling to drive immune cell migration

2016 ◽  
Vol 27 (9) ◽  
pp. 1442-1450 ◽  
Author(s):  
Patrick R. O’Neill ◽  
Vani Kalyanaraman ◽  
N. Gautam
Keyword(s):  
Cell Migration ◽  
Intracellular Signaling ◽  
Immune Cell ◽  
Leading Edge ◽  
Signaling Networks ◽  
Membrane Protrusions ◽  
A Cell ◽  
Immune Cell Migration ◽  
Directional Cell Migration ◽  
Rhoa Signaling

Migratory immune cells use intracellular signaling networks to generate and orient spatially polarized responses to extracellular cues. The monomeric G protein Cdc42 is believed to play an important role in controlling the polarized responses, but it has been difficult to determine directly the consequences of localized Cdc42 activation within an immune cell. Here we used subcellular optogenetics to determine how Cdc42 activation at one side of a cell affects both cell behavior and dynamic molecular responses throughout the cell. We found that localized Cdc42 activation is sufficient to generate polarized signaling and directional cell migration. The optically activated region becomes the leading edge of the cell, with Cdc42 activating Rac and generating membrane protrusions driven by the actin cytoskeleton. Cdc42 also exerts long-range effects that cause myosin accumulation at the opposite side of the cell and actomyosin-mediated retraction of the cell rear. This process requires the RhoA-activated kinase ROCK, suggesting that Cdc42 activation at one side of a cell triggers increased RhoA signaling at the opposite side. Our results demonstrate how dynamic, subcellular perturbation of an individual signaling protein can help to determine its role in controlling polarized cellular responses.

scholarly journals Methods and applications of label-free cell-based systems

2016 ◽  
Vol 1 (1) ◽  
Author(s):  
Joachim Wiest
Keyword(s):  
Environmental Monitoring ◽  
Morphological Changes ◽  
Free Cell ◽  
Living Cells ◽  
Label Free ◽  
Controlled System ◽  
Chip Technology ◽  
Cell Monitoring ◽  
A Cell ◽  
On Chip

Label-free monitoring of living cells is used in various applications such as drug development, toxicology, regenerative medicine or environmental monitoring. The most prominent methods for monitoring the extracellular acidification, oxygen consumption, electrophysiological activity and morphological changes of living cells are described. Furthermore, the intelligent mobile lab (IMOLA) – a computer controlled system integrating cell monitoring and automated cell cultivation – is described as an example of a cell-based system for microphysiometry. Results from experiments in the field of environmental monitoring using algae are presented. An outlook toward the development of an organ-on-chip technology is given.

scholarly journals A dual-labeling probe to track functional mitochondria–lysosome interactions in live cells

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Qixin Chen ◽  
Hongbao Fang ◽  
Xintian Shao ◽  
Zhiqi Tian ◽  
Shanshan Geng ◽  
...  
Keyword(s):  
Fluorescence Intensity ◽  
Fluorescent Probes ◽  
Living Cells ◽  
Molecular Probe ◽  
Live Cells ◽  
Blue Fluorescence ◽  
Red Fluorescence ◽  
Dynamic Tracking ◽  
A Cell

AbstractMitochondria–lysosome interactions are essential for maintaining intracellular homeostasis. Although various fluorescent probes have been developed to visualize such interactions, they remain unable to label mitochondria and lysosomes simultaneously and dynamically track their interaction. Here, we introduce a cell-permeable, biocompatible, viscosity-responsive, small organic molecular probe, Coupa, to monitor the interaction of mitochondria and lysosomes in living cells. Through a functional fluorescence conversion, Coupa can simultaneously label mitochondria with blue fluorescence and lysosomes with red fluorescence, and the correlation between the red–blue fluorescence intensity indicates the progress of mitochondria–lysosome interplay during mitophagy. Moreover, because its fluorescence is sensitive to viscosity, Coupa allowed us to precisely localize sites of mitochondria–lysosome contact and reveal increases in local viscosity on mitochondria associated with mitochondria–lysosome contact. Thus, our probe represents an attractive tool for the localization and dynamic tracking of functional mitochondria–lysosome interactions in living cells.

scholarly journals Effect of Cyclic Stretch on Tissue Maturation in Myoblast-Laden Hydrogel Fibers

Micromachines ◽  
2019 ◽  
Vol 10 (6) ◽  
pp. 399 ◽  
Author(s):  
Shinako Bansai ◽  
Takashi Morikura ◽  
Hiroaki Onoe ◽  
Shogo Miyata
Keyword(s):  
Skeletal Muscle ◽  
Muscle Tissue ◽  
Skeletal Muscles ◽  
Malignant Tumors ◽  
Three Dimensional ◽  
Living Cells ◽  
Cyclic Stretch ◽  
Core Shell ◽  
Custom Made ◽  
A Cell

Engineering of the skeletal muscles has attracted attention for the restoration of damaged muscles from myopathy, injury, and extraction of malignant tumors. Reconstructing a three-dimensional muscle using living cells could be a promising approach. However, the regenerated tissue exhibits a weak construction force due to the insufficient tissue maturation. The purpose of this study is to establish the reconstruction system for the skeletal muscle. We used a cell-laden core-shell hydrogel microfiber as a three-dimensional culture to control the cellular orientation. Moreover, to mature the muscle tissue in the microfiber, we also developed a custom-made culture device for imposing cyclic stretch stimulation using a motorized stage and the fiber-grab system. As a result, the directions of the myotubes were oriented and the mature myotubes could be formed by cyclic stretch stimulation.

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