scholarly journals Cracking up: symmetry breaking in cellular systems

2006 ◽  
Vol 175 (5) ◽  
pp. 687-692 ◽  
Author(s):  
Ewa Paluch ◽  
Jasper van der Gucht ◽  
Cécile Sykes
Keyword(s):  
Cell Membrane ◽  
Cellular Systems ◽  
Common Mechanism ◽  
Cell Cortex ◽  
Actin Network ◽  
Cortical Actin ◽  
Animal Cells ◽  
Actin Cortex ◽  
Myosin Motors ◽  
Local Relaxation

The shape of animal cells is, to a large extent, determined by the cortical actin network that underlies the cell membrane. Because of the presence of myosin motors, the actin cortex is under tension, and local relaxation of this tension can result in cortical flows that lead to deformation and polarization of the cell. Cortex relaxation is often regulated by polarizing signals, but the cortex can also rupture and relax spontaneously. A similar tension-induced polarization is observed in actin gels growing around beads, and we propose that a common mechanism governs actin gel rupture in both systems.

scholarly journals Extent of myosin penetration within the actin cortex regulates cell surface mechanics

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Binh An Truong Quang ◽  
Ruby Peters ◽  
Davide A. D. Cassani ◽  
Priyamvada Chugh ◽  
Andrew G. Clark ◽  
...  
Keyword(s):  
Cell Surface ◽  
Network Architecture ◽  
Super Resolution ◽  
Actin Network ◽  
Cortical Actin ◽  
Animal Cells ◽  
Cortical Tension ◽  
Protein Size ◽  
Myosin Motors ◽  
Surface Mechanics

AbstractIn animal cells, shape is mostly determined by the actomyosin cortex, a thin cytoskeletal network underlying the plasma membrane. Myosin motors generate tension in the cortex, and tension gradients result in cellular deformations. As such, many cell morphogenesis studies have focused on the mechanisms controlling myosin activity and recruitment to the cortex. Here, we demonstrate using super-resolution microscopy that myosin does not always overlap with actin at the cortex, but remains restricted towards the cytoplasm in cells with low cortex tension. We propose that this restricted penetration results from steric hindrance, as myosin minifilaments are considerably larger than the cortical actin meshsize. We identify myosin activity and actin network architecture as key regulators of myosin penetration into the cortex, and show that increasing myosin penetration increases cortical tension. Our study reveals that the spatial coordination of myosin and actin at the cortex regulates cell surface mechanics, and unveils an important mechanism whereby myosin size controls its action by limiting minifilament penetration into the cortical actin network. More generally, our findings suggest that protein size could regulate function in dense cytoskeletal structures.

scholarly journals Mechanism of the formation of contractile ring in dividing cultured animal cells. II. Cortical movement of microinjected actin filaments.

1990 ◽  
Vol 111 (5) ◽  
pp. 1905-1911 ◽  
Author(s):  
L G Cao ◽  
Y L Wang
Keyword(s):  
Actin Filaments ◽  
Average Rate ◽  
Rat Kidney ◽  
Equatorial Region ◽  
Cell Cortex ◽  
Polar Regions ◽  
Cortical Actin ◽  
Animal Cells ◽  
Contractile Ring ◽  
Directional Movement

The contractile ring in dividing animal cells is formed primarily through the reorganization of existing actin filaments (Cao, L.-G., and Y.-L. Wang. 1990. J. Cell Biol. 110:1089-1096), but it is not clear whether the process involves a random recruitment of diffusible actin filaments from the cytoplasm, or a directional movement of cortically associated filaments toward the equator. We have studied this question by observing the distribution of actin filaments that have been labeled with fluorescent phalloidin and microinjected into dividing normal rat kidney (NRK) cells. The labeled filaments are present primarily in the cytoplasm during prometaphase and early metaphase, but become associated extensively with the cell cortex 10-15 min before the onset of anaphase. This process is manifested both as an increase in cortical fluorescence intensity and as movements of discrete aggregates of actin filaments toward the cortex. The concentration of actin fluorescence in the equatorial region, accompanied by a decrease of fluorescence in polar regions, is detected 2-3 min after the onset of anaphase. By directly tracing the distribution of aggregates of labeled actin filaments, we are able to detect, during anaphase and telophase, movements of cortical actin filaments toward the equator at an average rate of 1.0 micron/min. Our results, combined with previous observations, suggest that the organization of actin filaments during cytokinesis probably involves an association of cytoplasmic filaments with the cortex, a movement of cortical filaments toward the cleavage furrow, and a dissociation of filaments from the equatorial cortex.

scholarly journals Coupled myosin VI motors facilitate unidirectional movement on an F-actin network

2009 ◽  
Vol 187 (1) ◽  
pp. 53-60 ◽  
Author(s):  
Sivaraj Sivaramakrishnan ◽  
James A. Spudich
Keyword(s):  
Single Molecule ◽  
Membrane Trafficking ◽  
Cell Periphery ◽  
Myosin Vi ◽  
Actin Network ◽  
Cortical Actin ◽  
Actin Cortex ◽  
Unidirectional Movement ◽  
Transport Vesicle ◽  
Pointed End

Unconventional myosins interact with the dense cortical actin network during processes such as membrane trafficking, cell migration, and mechanotransduction. Our understanding of unconventional myosin function is derived largely from assays that examine the interaction of a single myosin with a single actin filament. In this study, we have developed a model system to study the interaction between multiple tethered unconventional myosins and a model F-actin cortex, namely the lamellipodium of a migrating fish epidermal keratocyte. Using myosin VI, which moves toward the pointed end of actin filaments, we directly determine the polarity of the extracted keratocyte lamellipodium from the cell periphery to the cell nucleus. We use a combination of experimentation and simulation to demonstrate that multiple myosin VI molecules can coordinate to efficiently transport vesicle-size cargo over 10 µm of the dense interlaced actin network. Furthermore, several molecules of monomeric myosin VI, which are nonprocessive in single molecule assays, can coordinate to transport cargo with similar speeds as dimers.

scholarly journals Vimentin filaments interact with the actin cortex in mitosis allowing normal cell division

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Sofia Duarte ◽  
Álvaro Viedma-Poyatos ◽  
Elena Navarro-Carrasco ◽  
Alma E. Martínez ◽  
María A. Pajares ◽  
...  
Keyword(s):  
Cell Division ◽  
Cell Types ◽  
Hiv Protease ◽  
Cell Cortex ◽  
Tail Domain ◽  
Cellular Functions ◽  
Cortical Actin ◽  
Intrinsically Disordered ◽  
Actin Cortex ◽  
Vimentin Filaments

Abstract The vimentin network displays remarkable plasticity to support basic cellular functions and reorganizes during cell division. Here, we show that in several cell types vimentin filaments redistribute to the cell cortex during mitosis, forming a robust framework interwoven with cortical actin and affecting its organization. Importantly, the intrinsically disordered tail domain of vimentin is essential for this redistribution, which allows normal mitotic progression. A tailless vimentin mutant forms curly bundles, which remain entangled with dividing chromosomes leading to mitotic catastrophes or asymmetric partitions. Serial deletions of vimentin tail domain gradually impair cortical association and mitosis progression. Disruption of f-actin, but not of microtubules, causes vimentin bundling near the chromosomes. Pathophysiological stimuli, including HIV-protease and lipoxidation, induce similar alterations. Interestingly, full filament formation is dispensable for cortical association, which also occurs in vimentin particles. These results unveil implications of vimentin dynamics in cell division through its interplay with the actin cortex.

scholarly journals Filopodia formation and endosome clustering induced by mutant plus-end–directed myosin VI

2017 ◽  
Vol 114 (7) ◽  
pp. 1595-1600 ◽  
Author(s):  
Thomas A. Masters ◽  
Folma Buss
Keyword(s):  
Actin Filaments ◽  
Leucine Zipper ◽  
Adaptor Protein ◽  
Cell Cortex ◽  
Myosin Vi ◽  
Actin Network ◽  
Ph Domain ◽  
Cortical Actin ◽  
Directed Movement ◽  
Interacting Protein

Myosin VI (MYO6) is the only myosin known to move toward the minus end of actin filaments. It has roles in numerous cellular processes, including maintenance of stereocilia structure, endocytosis, and autophagosome maturation. However, the functional necessity of minus-end–directed movement along actin is unclear as the underlying architecture of the local actin network is often unknown. To address this question, we engineered a mutant of MYO6, MYO6+, which undergoes plus-end–directed movement while retaining physiological cargo interactions in the tail. Expression of this mutant motor in HeLa cells led to a dramatic reorganization of cortical actin filaments and the formation of actin-rich filopodia. MYO6 is present on peripheral adaptor protein, phosphotyrosine interacting with PH domain and leucine zipper 1 (APPL1) signaling endosomes and MYO6+ expression causes a dramatic relocalization and clustering of this endocytic compartment in the cell cortex. MYO6+ and its adaptor GAIP interacting protein, C terminus (GIPC) accumulate at the tips of these filopodia, while APPL1 endosomes accumulate at the base. A combination of MYO6+ mutagenesis and siRNA-mediated depletion of MYO6 binding partners demonstrates that motor activity and binding to endosomal membranes mediated by GIPC and PI(4,5)P2 are crucial for filopodia formation. A similar reorganization of actin is induced by a constitutive dimer of MYO6+, indicating that multimerization of MYO6 on endosomes through binding to GIPC is required for this cellular activity and regulation of actin network structure. This unique engineered MYO6+ offers insights into both filopodia formation and MYO6 motor function at endosomes and at the plasma membrane.

scholarly journals Dynamic multimerization of Dab2-Myosin VI complexes regulates cargo processivity while minimizing cortical actin reorganization

2020 ◽  
pp. jbc.RA120.012703
Author(s):  
Ashim Rai ◽  
Duha Vang ◽  
Michael Ritt ◽  
Sivaraj Sivaramakrishnan
Keyword(s):  
Lipid Bilayers ◽  
Single Molecule ◽  
High Rate ◽  
Myosin Vi ◽  
Actin Network ◽  
Cortical Actin ◽  
Myosin V ◽  
Kinetic Measurements ◽  
Actin Cortex ◽  
Run Lengths

Myosin VI ensembles on endocytic cargo facilitate directed transport through a dense cortical actin network. Myosin VI is recruited to clathrin-coated endosomes via the cargo adaptor Dab2. Canonically, it has been assumed that the interactions between a motor and its cargo adaptor are stable. However, it has been demonstrated that the force generated by multiple stably attached motors disrupts local cytoskeletal architecture, potentially compromising transport. In this study, we demonstrate that dynamic multimerization of myosin VI-Dab2 complexes facilitates cargo processivity without significant reorganization of cortical actin networks. Specifically, we find that Dab2 myosin interacting region (MIR) binds myosin VI with a moderate affinity (184 nM) and single molecule kinetic measurements demonstrate a high rate of turnover (1 s-1) of the Dab2 MIR-myosin VI interaction. Single molecule motility shows thatsaturating Dab2-MIR concentration (2 μM) promotes myosin VI homodimerization and processivity with run lengths comparable to constitutive myosin VI dimers. Cargo-mimetic DNA origami scaffolds patterned with Dab2 MIR-myosin VI complexes are weakly processive, displaying sparse motility on single actin filaments and “stop-and-go” motion on a cellular actin network. On a minimal actin cortex assembled on lipid bilayers, unregulated processive movement by either constitutive myosin V or VI dimers result in actin remodeling and foci formation. In contrast, Dab2 MIRmyosinVI interactions preserve the integrity of a minimal cortical actin network. Taken together, our study demonstrates the importance of dynamic motor-cargo association in enabling cargo transportation without disrupting cytoskeletal organization.

scholarly journals Dictyostelium myosin IK is involved in the maintenance of cortical tension and affects motility and phagocytosis

2000 ◽  
Vol 113 (4) ◽  
pp. 621-633 ◽  
Author(s):  
E.C. Schwarz ◽  
E.M. Neuhaus ◽  
C. Kistler ◽  
A.W. Henkel ◽  
T. Soldati
Keyword(s):  
Class I ◽  
Actin Binding ◽  
Cell Cortex ◽  
Tail Domain ◽  
Cortical Actin ◽  
Cortical Tension ◽  
Actin Cortex ◽  
Significant Enrichment ◽  
Motor Velocity ◽  
Distinctive Role

Dictyostelium discoideum myosin Ik (MyoK) is a novel type of myosin distinguished by a remarkable architecture. MyoK is related to class I myosins but lacks a cargo-binding tail domain and carries an insertion in a surface loop suggested to modulate motor velocity. This insertion shows similarity to a secondary actin-binding site present in the tail of some class I myosins, and indeed a GST-loop construct binds actin. Probably as a consequence, binding of MyoK to actin was not only ATP- but also salt-dependent. Moreover, as both binding sites reside within its motor domain and carry potential sites of regulation, MyoK might represent a new form of actin crosslinker. MyoK was distributed in the cytoplasm with a significant enrichment in dynamic regions of the cortex. Absence of MyoK resulted in a drop of cortical tension whereas overexpression led to significantly increased tension. Absence and overexpression of MyoK dramatically affected the cortical actin cytoskeleton and resulted in reduced initial rates of phagocytosis. Cells lacking MyoK showed excessive ruffling, mostly in the form of large lamellipodia, accompanied by a thicker basal actin cortex. At early stages of development, aggregation of myoK null cells was slowed due to reduced motility. Altogether, the data indicate a distinctive role for MyoK in the maintenance and dynamics of the cell cortex.

scholarly journals Myosin motors fragment and compact membrane-bound actin filaments

eLife ◽  
2013 ◽  
Vol 2 ◽  
Author(s):  
Sven K Vogel ◽  
Zdenek Petrasek ◽  
Fabian Heinemann ◽  
Petra Schwille
Keyword(s):  
Cell Division ◽  
Compressive Stress ◽  
Actin Filaments ◽  
Cell Cortex ◽  
Tirf Microscopy ◽  
Actin Cortex ◽  
Actin Turnover ◽  
Membrane Bound ◽  
Myosin Motors

Cell cortex remodeling during cell division is a result of myofilament-driven contractility of the cortical membrane-bound actin meshwork. Little is known about the interaction between individual myofilaments and membrane-bound actin filaments. Here we reconstituted a minimal actin cortex to directly visualize the action of individual myofilaments on membrane-bound actin filaments using TIRF microscopy. We show that synthetic myofilaments fragment and compact membrane-bound actin while processively moving along actin filaments. We propose a mechanism by which tension builds up between the ends of myofilaments, resulting in compressive stress exerted to single actin filaments, causing their buckling and breakage. Modeling of this mechanism revealed that sufficient force (∼20 pN) can be generated by single myofilaments to buckle and break actin filaments. This mechanism of filament fragmentation and compaction may contribute to actin turnover and cortex reorganization during cytokinesis.

Actin microfilaments are associated with the migrating nucleus and the cell cortex in the green alga Micrasterias. Studies on living cells

1994 ◽  
Vol 107 (7) ◽  
pp. 1929-1934 ◽  
Author(s):  
U. Meindl ◽  
D. Zhang ◽  
P.K. Hepler
Keyword(s):  
Laser Scanning ◽  
Nuclear Migration ◽  
Laser Scanning Microscopy ◽  
Confocal Laser ◽  
Cell Cortex ◽  
Actin Network ◽  
Cortical Actin ◽  
Electron Microscopic ◽  
Rhodamine Phalloidin ◽  
Growing Cell

Rhodamine-phalloidin or FITC-phalloidin has been injected in small amounts into living, developing cells of Micrasterias denticulata and the stained microfilaments visualized by confocal laser scanning microscopy. The results reveal that two different actin filament systems are present in a growing cell: a cortical actin network that covers the inner surface of the cell and is extended far into the tips of the lobes in both the growing and the nongrowing semicell; it is also associated with the surface of the chloroplast. The second actin system ensheathes the nucleus at the isthmus-facing side during nuclear migration. Its arrangement corresponds to that of the microtubule system that has been described in earlier electron microscopic investigations. The spatial correspondence between the distribution of actin filaments and microtubules suggests a cooperation between both cytoskeleton elements in generating the motive force for nuclear migration. The function of the cortical actin network is not yet clear. It may be involved in processes like transport and fusion of secretory vesicles and may also function in shaping and anchoring the chloroplast.

scholarly journals Actin kinetics shapes cortical network structure and mechanics

2016 ◽  
Vol 2 (4) ◽  
pp. e1501337 ◽  
Author(s):  
Marco Fritzsche ◽  
Christoph Erlenkämper ◽  
Emad Moeendarbary ◽  
Guillaume Charras ◽  
Karsten Kruse
Keyword(s):  
Single Molecule ◽  
Actin Filaments ◽  
Length Distribution ◽  
Living Cells ◽  
Stochastic Simulations ◽  
Cortical Actin ◽  
Animal Cells ◽  
Cellular Mechanics ◽  
Cellular Processes ◽  
Actin Cortex

The actin cortex of animal cells is the main determinant of cellular mechanics. The continuous turnover of cortical actin filaments enables cells to quickly respond to stimuli. Recent work has shown that most of the cortical actin is generated by only two actin nucleators, the Arp2/3 complex and the formin Diaph1. However, our understanding of their interplay, their kinetics, and the length distribution of the filaments that they nucleate within living cells is poor. Such knowledge is necessary for a thorough comprehension of cellular processes and cell mechanics from basic polymer physics principles. We determined cortical assembly rates in living cells by using single-molecule fluorescence imaging in combination with stochastic simulations. We find that formin-nucleated filaments are, on average, 10 times longer than Arp2/3-nucleated filaments. Although formin-generated filaments represent less than 10% of all actin filaments, mechanical measurements indicate that they are important determinants of cortical elasticity. Tuning the activity of actin nucleators to alter filament length distribution may thus be a mechanism allowing cells to adjust their macroscopic mechanical properties to their physiological needs.

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