scholarly journals Analysis of the local organization and dynamics of cellular actin networks

2013 ◽  
Vol 202 (7) ◽  
pp. 1057-1073 ◽  
Author(s):  
Weiwei Luo ◽  
Cheng-han Yu ◽  
Zi Zhao Lieu ◽  
Jun Allard ◽  
Alex Mogilner ◽  
...  
Keyword(s):  
Myosin Ii ◽  
Spatial Arrangement ◽  
Filamin A ◽  
Actin Network ◽  
Drift Diffusion ◽  
Superresolution Microscopy ◽  
Actin Networks ◽  
Latrunculin A ◽  
Diffusion Motion ◽  
Network Patterns

A ctin filaments, with the aid of multiple accessory proteins, self-assemble into a variety of network patterns. We studied the organization and dynamics of the actin network in nonadhesive regions of cells bridging fibronectin-coated adhesive strips. The network was formed by actin nodes associated with and linked by myosin II and containing the formin disheveled-associated activator of morphogenesis 1 (DAAM1) and the cross-linker filamin A (FlnA). After Latrunculin A (LatA) addition, actin nodes appeared to be more prominent and demonstrated drift-diffusion motion. Superresolution microscopy revealed that, in untreated cells, DAAM1 formed patches with a similar spatial arrangement to the actin nodes. Node movement (diffusion coefficient and velocity) in LatA-treated cells was dependent on the level and activity of myosin IIA, DAAM1, and FlnA. Based on our results, we developed a computational model of the dynamic formin-filamin-actin asters that can self-organize into a contractile actomyosin network. We suggest that such networks are critical for connecting distant parts of the cell to maintain the mechanical coherence of the cytoplasm.

scholarly journals Myosin IIA interacts with the spectrin-actin membrane skeleton to control red blood cell membrane curvature and deformability

2017 ◽  
Author(s):  
Alyson S. Smith ◽  
Roberta B. Nowak ◽  
Sitong Zhou ◽  
Michael Giannetto ◽  
David S. Gokhin ◽  
...  
Keyword(s):  
Motor Activity ◽  
Myosin Ii ◽  
Control Cell ◽  
Cell Types ◽  
Membrane Skeleton ◽  
Membrane Curvature ◽  
General Function ◽  
Actin Network ◽  
Actin Networks ◽  
Cell Shapes

AbstractThe biconcave disc shape and deformability of mammalian red blood cells (RBCs) relies upon the membrane skeleton, a viscoelastic network of short, membrane-associated actin filaments (F-actin) cross-linked by long, flexible spectrin tetramers. Nonmuscle myosin II (NMII) motors exert force on diverse F-actin networks to control cell shapes, but a function for NMII contractility in the 2D spectrin-F-actin network in RBCs has not been tested. Here, we show that RBCs contain membrane skeleton-associated NMIIA puncta, identified as bipolar filaments by super-resolution fluorescence microscopy. NMIIA association with the membrane skeleton is ATP-dependent, consistent with NMIIA motor domains binding to membrane skeleton F-actin and contributing to membrane mechanical stability. In addition, the NMIIA heavy and light chains are phosphorylatedin vivoin RBCs, indicating active regulation of NMIIA motor activity and filament assembly, while reduced heavy chain phosphorylation of membrane skeleton-associated NMIIA indicates assembly of stable filaments at the membrane. Treatment of RBCs with blebbistatin, an inhibitor of NMII motor activity, decreases the number of NMIIA filaments associated with the membrane and enhances local, nanoscale membrane oscillations, suggesting decreased membrane tension. Blebbistatin-treated RBCs also exhibit elongated shapes, loss of membrane curvature, and enhanced deformability, indicating a role for NMIIA contractility in promoting membrane stiffness and maintaining RBC biconcave disc cell shape. As structures similar to the RBC membrane skeleton are conserved in many metazoan cell types, these data demonstrate a general function for NMII in controlling specialized membrane morphology and mechanical properties through contractile interactions with short F-actin in spectrin-F-actin networks.Significance statementThe biconcave disc shape and deformability of the mammalian RBC is vital to its circulatory function, relying upon a 2D viscoelastic spectrin-F-actin network attached to the membrane. A role for myosin II (NMII) contractility in generating tension in this network and controlling RBC shape has never been tested. We show that NMIIA forms phosphorylated bipolar filaments in RBCs, which associate with F-actin at the membrane. NMIIA motor activity is required for interactions with the spectrin-F-actin network, and regulates RBC biconcave shape and deformability. These results provide a novel mechanism for actomyosin force generation at the plasma membrane, and may be applicable to other cell types such as neurons and polarized epithelial cells with a spectrin-F-actin-based membrane skeleton.

scholarly journals Dynamic actin crosslinking governs the cytoplasm’s transition to fluid-like behavior

2019 ◽  
Author(s):  
Loïc Chaubet ◽  
Abdullah R. Chaudhary ◽  
Hossein K. Heris ◽  
Allen J. Ehrlicher ◽  
Adam G. Hendricks
Keyword(s):  
Viscoelastic Properties ◽  
Myosin Ii ◽  
Optical Trap ◽  
Living Cells ◽  
Actin Network ◽  
Wild Type ◽  
Actin Networks ◽  
Long Timescales

AbstractCells precisely control their mechanical properties to organize and differentiate into tissues. The architecture and connectivity of cytoskeletal filaments changes in response to mechanical and biochemical cues, allowing the cell to rapidly tune its mechanics from highly-crosslinked, elastic networks to weakly-crosslinked viscous networks. While the role of actin crosslinking in controlling actin network mechanics is well-characterized in purified actin networks, its mechanical role in the cytoplasm of living cells remains unknown. Here, we probe the frequency-dependent intracellular viscoelastic properties of living cells using multifrequency excitation and in situ optical trap calibration. At long timescales in the intracellular environment, we observe that the cytoskeleton becomes fluid-like. The mechanics are well-captured by a model in which actin filaments are dynamically connected by a single dominant crosslinker. A disease-causing point mutation (K255E) of the actin crosslinker α-actinin 4 (ACTN4) causes its binding kinetics to be insensitive to tension. Under normal conditions, the viscoelastic properties of wild type (WT) and K255E+/- cells are similar. However, when tension is reduced through myosin II inhibition, WT cells relax 3x faster to the fluid-like regime while K255E+/- cells are not affected. These results indicate that dynamic actin crosslinking enables the cytoplasm to flow at long timescales.

scholarly journals Filamin A Regulates Cardiovascular Remodeling

2021 ◽  
Vol 22 (12) ◽  
pp. 6555
Author(s):  
Sashidar Bandaru ◽  
Chandu Ala ◽  
Alex-Xianghua Zhou ◽  
Levent M. Akyürek
Keyword(s):  
Transcription Factors ◽  
Respiratory Diseases ◽  
Cell Function ◽  
Actin Binding ◽  
Cardiovascular Development ◽  
Filamin A ◽  
Cardiovascular Malformations ◽  
Experimental Animal Models ◽  
Actin Networks ◽  
Cardiovascular Remodeling

Filamin A (FLNA) is a large actin-binding cytoskeletal protein that is important for cell motility by stabilizing actin networks and integrating them with cell membranes. Interestingly, a C-terminal fragment of FLNA can be cleaved off by calpain to stimulate adaptive angiogenesis by transporting multiple transcription factors into the nucleus. Recently, increasing evidence suggests that FLNA participates in the pathogenesis of cardiovascular and respiratory diseases, in which the interaction of FLNA with transcription factors and/or cell signaling molecules dictate the function of vascular cells. Localized FLNA mutations associate with cardiovascular malformations in humans. A lack of FLNA in experimental animal models disrupts cell migration during embryogenesis and causes anomalies, including heart and vessels, similar to human malformations. More recently, it was shown that FLNA mediates the progression of myocardial infarction and atherosclerosis. Thus, these latest findings identify FLNA as an important novel mediator of cardiovascular development and remodeling, and thus a potential target for therapy. In this update, we summarized the literature on filamin biology with regard to cardiovascular cell function.

scholarly journals Contribution of Filopodia to Cell Migration: A Mechanical Link between Protrusion and Contraction

2010 ◽  
Vol 2010 ◽  
pp. 1-13 ◽  
Author(s):  
Fei Xue ◽  
Deanna M. Janzen ◽  
David A. Knecht
Keyword(s):  
Cell Migration ◽  
Actin Polymerization ◽  
Myosin Ii ◽  
Temporal Distribution ◽  
Leading Edge ◽  
Distal Portion ◽  
Actin Binding ◽  
Actin Networks ◽  
Motile Cells ◽  
A Cell

Numerous F-actin containing structures are involved in regulating protrusion of membrane at the leading edge of motile cells. We have investigated the structure and dynamics of filopodia as they relate to events at the leading edge and the function of the trailing actin networks. We have found that although filopodia contain parallel bundles of actin, they contain a surprisingly nonuniform spatial and temporal distribution of actin binding proteins. Along the length of the actin filaments in a single filopodium, the most distal portion contains primarily T-plastin, while the proximal portion is primarily bound byα-actinin and coronin. Some filopodia are stationary, but lateral filopodia move with respect to the leading edge. They appear to form a mechanical link between the actin polymerization network at the front of the cell and the myosin motor activity in the cell body. The direction of lateral filopodial movement is associated with the direction of cell migration. When lateral filopodia initiate from and move toward only one side of a cell, the cell will turn opposite to the direction of filopodial flow. Therefore, this filopodia-myosin II system allows actin polymerization driven protrusion forces and myosin II mediated contractile force to be mechanically coordinated.

scholarly journals A Cellular Automaton Model as a First Model-Based Assessment of Interacting Mechanisms for Insulin Granule Transport in Beta Cells

Cells ◽  
2020 ◽  
Vol 9 (6) ◽  
pp. 1487
Author(s):  
Michael Müller ◽  
Mathias Glombek ◽  
Jeldrick Powitz ◽  
Dennis Brüning ◽  
Ingo Rustenbeck
Keyword(s):  
Cellular Automaton ◽  
Beta Cells ◽  
Transport Processes ◽  
Cellular Automaton Model ◽  
Special Role ◽  
Actin Network ◽  
Cell Interior ◽  
Actin Networks ◽  
Insulin Granules ◽  
Secretion Rates

In this paper a first model is derived and applied which describes the transport of insulin granules through the cell interior and at the membrane of a beta cell. A special role is assigned to the actin network, which significantly influences the transport. For this purpose, microscopically measured actin networks are characterized and then further ones are artificially generated. In a Cellular Automaton model, phenomenological laws for granule movement are formulated and implemented. Simulation results are compared with experiments, primarily using TIRF images and secretion rates. In this respect, good similarities are already apparent. The model is a first useful approach to describe complex granule transport processes in beta cells, and offers great potential for future extensions. Furthermore, the model can be used as a tool to validate hypotheses and associated mechanisms regarding their effect on exocytosis or other processes. For this purpose, the source code for the model is provided online.

scholarly journals Directional Transport of a Bead Bound to Lamellipodial Surface Is Driven by Actin Polymerization

2017 ◽  
Vol 2017 ◽  
pp. 1-14 ◽  
Author(s):  
Daisuke Nobezawa ◽  
Sho-ichi Ikeda ◽  
Eitaro Wada ◽  
Takashi Nagano ◽  
Hidetake Miyata
Keyword(s):  
Actin Polymerization ◽  
Cancer Metastasis ◽  
Myosin Ii ◽  
Optical Trap ◽  
Cell Movement ◽  
Cytochalasin D ◽  
The Other ◽  
Other Hand ◽  
Latrunculin A ◽  
Actin Turnover

The force driving the retrograde flow of actin cytoskeleton is important in the cellular activities involving cell movement (e.g., growth cone motility in axon guidance, wound healing, or cancer metastasis). However, relative importance of the forces generated by actin polymerization and myosin II in this process remains elusive. We have investigated the retrograde movement of the poly-D-lysine-coated bead attached with the optical trap to the edge of lamellipodium of Swiss 3T3 fibroblasts. The velocity of the attached bead drastically decreased by submicromolar concentration of cytochalasin D, latrunculin A, or jasplakinolide, indicating the involvement of actin turnover. On the other hand, the velocity decreased only slightly in the presence of 50 μM (−)-blebbistatin and Y-27632. Comparative fluorescence microscopy of the distribution of actin filaments and that of myosin II revealed that the inhibition of actin turnover by cytochalasin D, latrunculin A, or jasplakinolide greatly diminished the actin filament network. On the other hand, inhibition of myosin II activity by (−)-blebbistatin or Y-27632 little affected the actin network but diminished stress fibers. Based on these results, we conclude that the actin polymerization/depolymerization plays the major role in the retrograde movement, while the myosin II activity is involved in the maintenance of the dynamic turnover of actin in lamellipodium.

scholarly journals Release of myosin II from the membrane-cytoskeleton of Dictyostelium discoideum mediated by heavy-chain phosphorylation at the foci within the cortical actin network

1992 ◽  
Vol 117 (6) ◽  
pp. 1231-1239 ◽  
Author(s):  
S Yumura ◽  
T Kitanishi-Yumura
Keyword(s):  
Heavy Chain ◽  
Myosin Ii ◽  
Cortical Region ◽  
Actin Network ◽  
Cortical Actin ◽  
Filamentous Form ◽  
Heavy Chains ◽  
Membrane Cytoskeleton ◽  
Myosin Filaments ◽  
Gamma S

Membrane-cytoskeletons were prepared from Dictyostelium amebas, and networks of actin and myosin II filaments were visualized on the exposed cytoplasmic surfaces of the cell membranes by fluorescence staining (Yumura, S., and T. Kitanishi-Yumura. 1990. Cell Struct. Funct. 15:355-364). Addition of ATP caused contraction of the cytoskeleton with aggregation of part of actin into several foci within the network, but most of myosin II was released via the foci. However, in the presence of 10 mM MgCl2, which stabilized myosin II filaments, myosin II remained at the foci. Ultrastructural examination revealed that, after contraction, only traces of monomeric myosin II remained at the foci. By contrast, myosin II filaments remained in the foci in the presence of 10 mM MgCl2. These observations suggest that myosin II was released not in a filamentous form but in a monomeric form. Using [gamma 32P]ATP, we found that the heavy chains of myosin II released from membrane-cytoskeletons were phosphorylated, and this phosphorylation resulted in disassembly of myosin filaments. Using ITP (a substrate for myosin II ATPase) and/or ATP gamma S (a substrate for myosin II heavy-chain kinase [MHCK]), we demonstrated that phosphorylation of myosin heavy chains occurred at the foci within the actin network, a result that suggests that MHCK was localized at the foci. These results together indicate that, during contraction, the heavy chains of myosin II that have moved toward the foci within the actin network are phosphorylated by a specific MHCK, with the resultant disassembly of filaments which are finally released from membrane-cytoskeletons. This series of reactions could represent the mechanism for the relocation of myosin II from the cortical region to the endoplasm.

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