scholarly journals Acto-myosin network geometry defines centrosome position

2020 ◽  
Author(s):  
Ana Joaquina Jimenez ◽  
Chiara de Pascalis ◽  
Gaelle Letort ◽  
Benoit Vianay ◽  
Robert D. Goldman ◽  
...  
Keyword(s):  
Actin Network ◽  
Microtubule Network ◽  
Cell Functions ◽  
Geometrical Center ◽  
Network Geometry ◽  
Zone Cell ◽  
Spatial Boundary ◽  
Microtubule Networks ◽  
Contractile Forces ◽  
Adhesion Pattern

AbstractThe centrosome is the main organizer of microtubules and as such, its position is a key determinant of polarized cell functions. As the name says, the default position of the centrosome is considered to be the cell geometrical center. However, the mechanism regulating centrosome positioning is still unclear and often confused with the mechanism regulating the position of the nucleus to which it is linked. Here we used enucleated cells plated on adhesive micropatterns to impose regular and precise geometrical conditions to centrosome-microtubule networks. Although frequently observed there, the equilibrium position of the centrosome is not systematically at the cell geometrical center and can be close to cell edge. Centrosome positioning appears to respond accurately to the architecture and anisotropy of the actin network, which constitutes, rather than cell shape, the actual spatial boundary conditions the microtubule network is sensitive to. We found that the contraction of the actin network defines a peripheral margin, in which microtubules appeared bent by compressive forces. The disassembly of the actin network away from the cell edges defines an inner zone where actin bundles were absent and microtubules were more radially organized. The production of dynein-based forces on microtubules places the centrosome at the center of this inner zone. Cell adhesion pattern and contractile forces define the shape and position of the inner zone in which the centrosome-microtubule network is centered.

scholarly journals An Epidermal Plakin That Integrates Actin and Microtubule Networks at Cellular Junctions

2000 ◽  
Vol 149 (1) ◽  
pp. 195-208 ◽  
Author(s):  
Iakowos Karakesisoglou ◽  
Yanmin Yang ◽  
Elaine Fuchs
Keyword(s):  
Intermediate Filaments ◽  
Actin Filaments ◽  
Neuromuscular Junctions ◽  
Binding Domain ◽  
Epidermal Keratinocytes ◽  
Cell Periphery ◽  
Microtubule Network ◽  
Clear Explanation ◽  
Cellular Junctions ◽  
Microtubule Networks

Plakins are cytoskeletal linker proteins initially thought to interact exclusively with intermediate filaments (IFs), but recently were found to associate additionally with actin and microtubule networks. Here, we report on ACF7, a mammalian orthologue of the Drosophila kakapo plakin genetically involved in epidermal–muscle adhesion and neuromuscular junctions. While ACF7/kakapo is divergent from other plakins in its IF-binding domain, it has at least one actin (Kd = 0.35 μM) and one microtubule (Kd ∼6 μM) binding domain. Similar to its fly counterpart, ACF7 is expressed in the epidermis. In well spread epidermal keratinocytes, ACF7 discontinuously decorates the cytoskeleton at the cell periphery, including microtubules (MTs) and actin filaments (AFs) that are aligned in parallel converging at focal contacts. Upon calcium induction of intercellular adhesion, ACF7 and the cytoskeleton reorganize at cell–cell borders but with different kinetics from adherens junctions and desmosomes. Treatments with cytoskeletal depolymerizing drugs reveal that ACF7's cytoskeletal association is dependent upon the microtubule network, but ACF7 also appears to stabilize actin at sites where microtubules and microfilaments meet. We posit that ACF7 may function in microtubule dynamics to facilitate actin–microtubule interactions at the cell periphery and to couple the microtubule network to cellular junctions. These attributes provide a clear explanation for the kakapo mutant phenotype in flies.

scholarly journals Quantitative regulation of the dynamic steady state of actin networks

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Angelika Manhart ◽  
Téa Aleksandra Icheva ◽  
Christophe Guerin ◽  
Tobbias Klar ◽  
Rajaa Boujemaa-Paterski ◽  
...  
Keyword(s):  
Mathematical Model ◽  
Steady State ◽  
Heterogeneous Networks ◽  
In Silico ◽  
Actin Network ◽  
Network Nodes ◽  
Actin Networks ◽  
Cell Functions ◽  
Selective Disassembly

Principles of regulation of actin network dimensions are fundamentally important for cell functions, yet remain unclear. Using both in vitro and in silico approaches, we studied the effect of key parameters, such as actin density, ADF/Cofilin concentration and network width on the network length. In the presence of ADF/Cofilin, networks reached equilibrium and became treadmilling. At the trailing edge, the network disintegrated into large fragments. A mathematical model predicts the network length as a function of width, actin and ADF/Cofilin concentrations. Local depletion of ADF/Cofilin by binding to actin is significant, leading to wider networks growing longer. A single rate of breaking network nodes, proportional to ADF/Cofilin density and inversely proportional to the square of the actin density, can account for the disassembly dynamics. Selective disassembly of heterogeneous networks by ADF/Cofilin controls steering during motility. Our results establish general principles on how the dynamic steady state of actin network emerges from biochemical and structural feedbacks.

scholarly journals Active contraction of microtubule networks

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Peter J Foster ◽  
Sebastian Fürthauer ◽  
Michael J Shelley ◽  
Daniel J Needleman
Keyword(s):  
Large Scale ◽  
Quantitative Agreement ◽  
Self Organization ◽  
Cellular Processes ◽  
Network Geometry ◽  
Initial Network ◽  
Fluid Theory ◽  
Scale Structures ◽  
Density Inhomogeneities ◽  
Microtubule Networks

Many cellular processes are driven by cytoskeletal assemblies. It remains unclear how cytoskeletal filaments and motor proteins organize into cellular scale structures and how molecular properties of cytoskeletal components affect the large-scale behaviors of these systems. Here, we investigate the self-organization of stabilized microtubules in Xenopus oocyte extracts and find that they can form macroscopic networks that spontaneously contract. We propose that these contractions are driven by the clustering of microtubule minus ends by dynein. Based on this idea, we construct an active fluid theory of network contractions, which predicts a dependence of the timescale of contraction on initial network geometry, a development of density inhomogeneities during contraction, a constant final network density, and a strong influence of dynein inhibition on the rate of contraction, all in quantitative agreement with experiments. These results demonstrate that the motor-driven clustering of filament ends is a generic mechanism leading to contraction.

scholarly journals Tracking Retrograde Flow in Keratocytes: News from the Front

2005 ◽  
Vol 16 (3) ◽  
pp. 1223-1231 ◽  
Author(s):  
Pascal Vallotton ◽  
Gaudenz Danuser ◽  
Sophie Bohnet ◽  
Jean-Jacques Meister ◽  
Alexander B. Verkhovsky
Keyword(s):  
Actin Polymerization ◽  
Leading Edge ◽  
Membrane Resistance ◽  
Retrograde Flow ◽  
Actin Assembly ◽  
Actin Network ◽  
Freely Moving ◽  
Contractile Forces ◽  
Cell Motion ◽  
Shape Changes

Actin assembly at the leading edge of the cell is believed to drive protrusion, whereas membrane resistance and contractile forces result in retrograde flow of the assembled actin network away from the edge. Thus, cell motion and shape changes are expected to depend on the balance of actin assembly and retrograde flow. This idea, however, has been undermined by the reported absence of flow in one of the most spectacular models of cell locomotion, fish epidermal keratocytes. Here, we use enhanced phase contrast and fluorescent speckle microscopy and particle tracking to analyze the motion of the actin network in keratocyte lamellipodia. We have detected retrograde flow throughout the lamellipodium at velocities of 1–3 μm/min and analyzed its organization and relation to the cell motion during both unobstructed, persistent migration and events of cell collision. Freely moving cells exhibited a graded flow velocity increasing toward the sides of the lamellipodium. In colliding cells, the velocity decreased markedly at the site of collision, with striking alteration of flow in other lamellipodium regions. Our findings support the universality of the flow phenomenon and indicate that the maintenance of keratocyte shape during locomotion depends on the regulation of both retrograde flow and actin polymerization.

Syk-dependent phosphorylation of microtubules in activated B-lymphocytes

2000 ◽  
Vol 113 (14) ◽  
pp. 2557-2565 ◽  
Author(s):  
S. Faruki ◽  
R.L. Geahlen ◽  
D.J. Asai
Keyword(s):  
B Cell ◽  
Protein Tyrosine Kinase ◽  
B Lymphocyte ◽  
Dependent Manner ◽  
Microtubule Network ◽  
Alpha Tubulin ◽  
B Cell Signaling ◽  
Low Concentrations ◽  
Microtubule Networks

Syk is a protein-tyrosine kinase that is essential for B-lymphocyte development and B-cell signaling. Syk phosphorylates tubulin on tyrosine both in vitro and in intact lymphocytes. Here we show that (alpha)-tubulin present within the cytoskeletal microtubule network was phosphorylated in a Syk-dependent manner following the activation of B-cells by engagement of the B-cell antigen receptor or by treatment with the phosphotyrosine phosphatase inhibitor, pervanadate. Immunofluorescence staining of microtubule cytoskeletons and western blotting studies with antibodies to phosphotyrosine confirmed the phosphorylation of polymerized tubulin in Syk-expressing, but not Syk-deficient, cells. At low concentrations of pervanadate, centrosomes appeared to be preferentially tyrosine-phosphorylated. Tubulin phosphorylated to a high stoichiometry on tyrosine assembled into microtubules in vitro, and preassembled microtubules were also phosphorylated by Syk kinase in vitro. Thus, Syk has the capacity to interact with microtubule networks within the B-lymphocyte and catalyzes the phosphorylation of the (alpha)-tubulin subunit. Syk-dependent phosphorylation of microtubules may affect the ability of the microtubule cytoskeleton to serve as a platform upon which signaling complexes are assembled.

Purines regulate adult brain subventricular zone cell functions: Contribution of reactive astrocytes

Glia ◽  
2013 ◽  
Vol 62 (3) ◽  
pp. 428-439 ◽  
Author(s):  
Marta Boccazzi ◽  
Chiara Rolando ◽  
Maria P. Abbracchio ◽  
Annalisa Buffo ◽  
Stefania Ceruti
Keyword(s):  
Subventricular Zone ◽  
Reactive Astrocytes ◽  
Adult Brain ◽  
Cell Functions ◽  
Zone Cell

scholarly journals The self-organization of plant microtubules in three dimensions enable stable cortical localization and sensitivity to external cues

2017 ◽  
Author(s):  
Vincent Mirabet ◽  
Pawel Krupinski ◽  
Olivier Hamant ◽  
Elliot M Meyerowitz ◽  
Henrik Jönsson ◽  
...  
Keyword(s):  
Cell Surface ◽  
Cell Shape ◽  
Dimensional Space ◽  
Three Dimensions ◽  
Mechanical Anisotropy ◽  
Cellulose Microfibrils ◽  
Microtubule Cytoskeleton ◽  
Microtubule Network ◽  
Cell Functions ◽  
Cell Shapes

AbstractMany cell functions rely on the ability of microtubules to self-organize as complex networks. In plants, cortical microtubules are essential to determine cell shape as they guide the deposition of cellulose microfibrils, and thus control mechanical anisotropy in the cell wall. Here we analyze how, in turn, cell shape may influence microtubule behavior. Using a computational model of microtubules enclosed in a three-dimensional space, We show that the microtubule network has spontaneous configurations that could explain many experimental observations without resorting to specific regulation. In particular, we find that the preferred localization of microtubules at the cortex emerges from directional persistence of the microtubules, combined with their growth mode. We identified microtubule parameters that seem relatively insensitive to cell shape, such as length or number. In contrast, microtubule array anisotropy depends strongly on local curvature of the cell surface and global orientation follows robustly the longest axis of the cell. Lastly, we found that the network is capable of reorienting toward weak external directional cues. Altogether our simulations show that the microtubule network is a good transducer of weak external polarity, while at the same time, it easily reaches stable global configurations.Author summaryPlants exhibit an astonishing diversity in architecture and shape. A key to such diversity is the ability of their cells to coordinate and grow to reach a broad spectrum of sizes and shapes. Cell growth in plants is guided by the microtubule cytoskeleton. Here, we seek to understand how microtubules self-organize close to the cell surface. We build upon previous two-dimensional models and we consider microtubules as lines growing in three dimensions, accounting for interactions between microtubules or between microtubules and the cell surface. We show that microtubule arrays are able to adapt to various cell shapes and to reorient in response to factors such as signals or environment. Altogether, our results help to understand how the microtubule cytoskeleton contributes to the diversity of plant shapes and to how these shapes adapt to environment.

scholarly journals A proteomic-informed view of the changes induced by loss of cellular adherence: The example of mouse macrophages

PLoS ONE ◽  
2021 ◽  
Vol 16 (5) ◽  
pp. e0252450
Author(s):  
Sacnite Ramirez Rios ◽  
Anaelle Torres ◽  
Hélène Diemer ◽  
Véronique Collin-Faure ◽  
Sarah Cianférani ◽  
...  
Keyword(s):  
Cancer Biology ◽  
Glucose Consumption ◽  
Cytoskeletal Proteins ◽  
Mitochondrial Activity ◽  
Cell Physiology ◽  
Adherent Cells ◽  
Microtubule Network ◽  
Actin Organization ◽  
Cell Functions ◽  
Proteomic Approach

Except cells circulating in the bloodstream, most cells in vertebrates are adherent. Studying the repercussions of adherence per se in cell physiology is thus very difficult to carry out, although it plays an important role in cancer biology, e.g. in the metastasis process. In order to study how adherence impacts major cell functions, we used a murine macrophage cell line. Opposite to the monocyte/macrophage system, where adherence is associated with the acquisition of differentiated functions, these cells can be grown in both adherent or suspension conditions without altering their differentiated functions (phagocytosis and inflammation signaling). We used a proteomic approach to cover a large panel of proteins potentially modified by the adherence status. Targeted experiments were carried out to validate the proteomic results, e.g. on metabolic enzymes, mitochondrial and cytoskeletal proteins. The mitochondrial activity was increased in non-adherent cells compared with adherent cells, without differences in glucose consumption. Concerning the cytoskeleton, a rearrangement of the actin organization (filopodia vs sub-cortical network) and of the microtubule network were observed between adherent and non-adherent cells. Taken together, these data show the mechanisms at play for the modification of the cytoskeleton and also modifications of the metabolic activity between adherent and non-adherent cells.

scholarly journals Multiple Pathways Involved in Porcine Parvovirus Cellular Entry and Trafficking toward the Nucleus

2010 ◽  
Vol 84 (15) ◽  
pp. 7782-7792 ◽  
Author(s):  
Maude Boisvert ◽  
Sandra Fernandes ◽  
Peter Tijssen
Keyword(s):  
Sialic Acids ◽  
Porcine Parvovirus ◽  
Actin Network ◽  
Cellular Mechanisms ◽  
Microtubule Network ◽  
Late Endosomes ◽  
Chemical Inhibitors ◽  
Endosomal Acidification ◽  
Infected Cells ◽  
Gain Access

ABSTRACT Porcine parvovirus (PPV) is a major cause of reproductive failure in swine. The mechanisms implicated in the first steps of infection that lead to the delivery of the PPV genome to the nucleus are poorly understood. In the present work, a panel of chemical inhibitors was used to dissect the cellular mechanisms involved in establishing a PPV infection. The results demonstrated that following binding to sialic acids on cell surface glycoproteins, the virus used both clathrin-mediated endocytosis and macropinocytosis pathways to gain access into cells. Virus obtained from infected cells was present either as isolated particles or as aggregates, and these two forms could be separated by low-speed centrifugation. Isolated and purified particles strongly preferred entry by clathrin-mediated endocytosis, whereas aggregates clearly favored macropinocytosis. Subsequent endosomal acidification and traffic to the late endosomes were also shown to be essential for infection. The microtubule network was found to be important during the first 10 h of infection, whereas an intact actin network was required for almost the whole viral cycle. Proteasome processing was found to be essential, and capsid proteins were ubiquitinated relatively early during infection. Taken together, these results provided new insights into the first steps of PPV infection, including the use of alternative entry pathways, unique among members of this viral family.

Cellular Logistics: Unraveling the Interplay Between Microtubule Organization and Intracellular Transport

2019 ◽  
Vol 35 (1) ◽  
pp. 29-54 ◽  
Author(s):  
Mithila Burute ◽  
Lukas C. Kapitein
Keyword(s):  
Intracellular Transport ◽  
Spatial Organization ◽  
Animal Cell ◽  
Cell Types ◽  
Microtubule Organization ◽  
Microtubule Network ◽  
Core Components ◽  
Cell Type Specific ◽  
Microtubule Networks ◽  
Different Cell Types

Microtubules are core components of the cytoskeleton and serve as tracks for motor protein–based intracellular transport. Microtubule networks are highly diverse across different cell types and are believed to adapt to cell type–specific transport demands. Here we review how the spatial organization of different subsets of microtubules into higher-order networks determines the traffic rules for motor-based transport in different animal cell types. We describe the interplay between microtubule network organization and motor-based transport within epithelial cells, oocytes, neurons, cilia, and the spindle apparatus.

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