Cease-fire at the leading edge: New perspectives on actin filament branching, debranching, and cross-linking (original) (raw)
A role for actin arcs in the leading-edge advance of migrating cells
Nature Cell Biology, 2011
The migration of epithelial cells requires coordination of two actin modules at the leading edge: one in the lamellipodium and one in the lamella. How the two modules connect mechanistically to regulate directed edge motion is not understood. Using a combination of live-cell imaging and photoactivation approaches, we demonstrate that the actin network of the lamellipodium evolves spatio-temporally into the lamella. This occurs during the retraction phase of edge motion when myosin II redistributes to the cell edge and condenses the lamellipodial-actin into an arc-like bundle (i.e., actin arc) parallel to the edge. The newly formed actin arc moves rearward and couples to focal adhesions as it enters the lamella. We propose net edge extension occurs by nascent focal adhesions advancing the site at which new actin arcs slow down and form the base of the next protrusion event. The actin arc thus serves as a structural element underlying the temporal and spatial connection between the lamellipodium and lamella to drive directed cell motion.
Regulation of directional cell migration by membrane-induced actin bundling
Journal of Cell Science, 2013
During embryonic development and in metastatic cancers, cells detach from the epithelium and migrate with persistent directionality. Directional cell migration is also crucial for the regeneration and maintenance of the epithelium and an impaired ability of epithelial cells for directional migration are linked to chronic inflammatory diseases. Despite its significance, the mechanisms controlling epithelial cell migration remain poorly understood. Villin is an epithelial cell specific actin modifying protein that regulates epithelial cell plasticity and motility. In motile cells villin is associated with the highly branched as well as the unbranched actin filaments of lamellipodia and filopodia, respectively. In this study we demonstrate for the first time that villin regulates directionally persistent epithelial cell migration. Functional characterization of wild-type and mutant villin proteins reveals that villin's ability to self-associate and bundle actin as well as its direc...
1 Regulation of directional cell migration by membrane-induced actin bundling
2016
During embryonic development and in metastatic cancers, cells detach from the epithelium and migrate with persistent directionality. Directional cell migration is also crucial for the regeneration and maintenance of the epithelium and an impaired ability of epithelial cells for directional migration are linked to chronic inflammatory diseases. Despite its significance, the mechanisms controlling epithelial cell migration remain poorly understood. Villin is an epithelial cell specific actin modifying protein that regulates epithelial cell plasticity and motility. In motile cells villin is associated with the highly branched as well as the unbranched actin filaments of lamellipodia and filopodia, respectively. In this study we demonstrate for the first time that villin regulates directionally persistent epithelial cell migration. Functional characterization of wild-type and mutant villin proteins reveals that villin’s ability to self-associate and bundle actin as well as its direct in...
Actin dynamics in cell migration
Essays In Biochemistry
Cell migration is an essential process, both in unicellular organisms such as amoeba and as individual or collective motility in highly developed multicellular organisms like mammals. It is controlled by a variety of activities combining protrusive and contractile forces, normally generated by actin filaments. Here, we summarize actin filament assembly and turnover processes, and how respective biochemical activities translate into different protrusion types engaged in migration. These actin-based plasma membrane protrusions include actin-related protein 2/3 complex-dependent structures such as lamellipodia and membrane ruffles, filopodia as well as plasma membrane blebs. We also address observed antagonisms between these protrusion types, and propose a model – also inspired by previous literature – in which a complex balance between specific Rho GTPase signaling pathways dictates the protrusion mechanism employed by cells. Furthermore, we revisit published work regarding the fascin...
Imaging the Molecular Machines That Power Cell Migration
Methods in Molecular Biology, 2018
Animal cell migration constitutes a complex process involving a multitude of forces generated and maintained by the actin cytoskeleton. Dynamic changes of the cell surface, for instance to effect cell edge protrusion, are at the core of initiating migratory processes, both in tissue culture models and whole animals. Here we sketch different aspects of imaging representative molecular constituents in such actin-driven processes, which power and regulate the polymerisation of actin filaments into bundles and networks, constituting the building blocks of such protrusions. The examples presented illustrate both the diversity of subcellular distributions of distinct molecular components, according to their function, and the complexity of dynamic changes in protrusion size, shape, and/or orientation in 3D. Considering these dynamics helps mechanistically connecting subcellular distributions of molecular machines driving protrusion and migration with their biochemical function.
Emergence of Large-Scale Cell Morphology and Movement from Local Actin Filament Growth Dynamics
PLoS Biology, 2007
Variations in cell migration and morphology are consequences of changes in underlying cytoskeletal organization and dynamics. We investigated how these large-scale cellular events emerge as direct consequences of small-scale cytoskeletal molecular activities. Because the properties of the actin cytoskeleton can be modulated by actinremodeling proteins, we quantitatively examined how one such family of proteins, enabled/vasodilator-stimulated phosphoprotein (Ena/VASP), affects the migration and morphology of epithelial fish keratocytes. Keratocytes generally migrate persistently while exhibiting a characteristic smooth-edged ''canoe'' shape, but may also exhibit less regular morphologies and less persistent movement. When we observed that the smooth-edged canoe keratocyte morphology correlated with enrichment of Ena/VASP at the leading edge, we mislocalized and overexpressed Ena/VASP proteins and found that this led to changes in the morphology and movement persistence of cells within a population. Thus, local changes in actin filament dynamics due to Ena/VASP activity directly caused changes in cell morphology, which is coupled to the motile behavior of keratocytes. We also characterized the range of natural cell-to-cell variation within a population by using measurable morphological and behavioral features-cell shape, leading-edge shape, filamentous actin (F-actin) distribution, cell speed, and directional persistence-that we have found to correlate with each other to describe a spectrum of coordinated phenotypes based on Ena/VASP enrichment at the leading edge. This spectrum stretched from smooth-edged, canoe-shaped keratocytes-which had VASP highly enriched at their leading edges and migrated fast with straight trajectories-to more irregular, rounder cells migrating slower with less directional persistence and low levels of VASP at their leading edges. We developed a mathematical model that accounts for these coordinated cell-shape and behavior phenotypes as large-scale consequences of kinetic contributions of VASP to actin filament growth and protection from capping at the leading edge. This work shows that the local effects of actinremodeling proteins on cytoskeletal dynamics and organization can manifest as global modifications of the shape and behavior of migrating cells and that mathematical modeling can elucidate these large-scale cell behaviors from knowledge of detailed multiscale protein interactions. Citation: Lacayo CI, Pincus Z, VanDuijn MM, Wilson CA, Fletcher DA, et al. (2007) Emergence of large-scale cell morphology and movement from local actin filament growth dynamics. PLoS Biol 5(9): e233.
Mechanical Regulation of Actin Network Dynamics in Migrating Cells
Journal of Biomechanical Science and Engineering, 2010
Cell migration is fundamental to various physiological processes, including metastasis, wound healing and tissue development. The complex processes involved in cell migration; polymerization, adhesion, and retraction, are mediated by highly orchestrated structure-function interactions that occur within the actin cytoskeletal structure. Thus understanding how migrating cells regulate the global dynamics of their cytoskeletal components, which result from rather localized protein-protein interactions, is fundamental to elucidating the mechanisms of cell motility. The objective of this review is to explore the mechanical regulation of actin network dynamics in migrating cells, and to discuss its regulatory role in cell migration. Specifically, we examine the various mechanical forces involved in cell migration, and how they couple with biomechanical factors to spatiotemporally regulate the dynamics of the actin cytoskeleton during cell motility. Two aspects of actin network dynamics are addressed, namely, network turnover by polymerization and depolymerization, and network flow resulting from actomyosin activity. We begin by highlighting the fundamental features of actin network dynamics in migrating cells. We then examine the coupling relationship between actin network flow and traction forces, as well as the mechanism underlying the regulation of traction forces by actin network flow. Finally, we integrate the various motility processes into a mechanical pathway in order to elucidate the importance of mechanical regulation of actin network dynamics to cell migration.
Mechanical Integration of Actin and Adhesion Dynamics in Cell Migration
Annual Review of Cell and Developmental Biology, 2010
Directed cell migration is a physical process that requires dramatic changes in cell shape and adhesion to the extracellular matrix. For efficient movement, these processes must be spatiotemporally coordinated. To a large degree, the morphological changes and physical forces that occur during migration are generated by a dynamic filamentous actin (F-actin) cytoskeleton. Adhesion is regulated by dynamic assemblies of structural and signaling proteins that couple the F-actin cytoskeleton to the extracellular matrix. Here, we review current knowledge of the dynamic organization of the F-actin cytoskeleton in cell migration and the regulation of focal adhesion assembly and disassembly with an emphasis on how mechanical and biochemical signaling between these two systems regulate the coordination of physical processes in cell migration.
bioRxiv (Cold Spring Harbor Laboratory), 2023
Cells migrate by adapting their leading-edge behaviours to heterogeneous extracellular microenvironments (ECMs) during cancer invasions and immune responses. Yet it remains poorly understood how such complicated dynamic behaviours emerge from millisecond-scale assembling activities of protein molecules, which are hard to probe experimentally. To address this gap, we established a spatiotemporal "resistance-adaptive propulsion" theory based on the protein interactions between Arp2/3 complexes and polymerizing actin filaments, and a multiscale dynamic modelling system spanning from molecular proteins to the cell. Combining spatiotemporal simulations with experiments, we quantitatively find that cells can accurately self-adapt propulsive forces to overcome heterogeneous ECMs via a resistance-triggered positive feedback mechanism, dominated by polymerization-induced actin filament bending and the bending-regulated actin-Arp2/3 binding. However, for high resistance regions, resistance triggered a negative feedback, hindering branched filament assembly, which adapts cellular morphologies to circumnavigate the obstacles. Strikingly, the synergy of the two opposite feedbacks not only empowers cells with both powerful and flexible migratory capabilities to deal with complex ECMs, but also endows cells to use their intracellular proteins efficiently. In addition, we identify that the nature of cell migration velocity depending on ECM history stems from the inherent temporal hysteresis of cytoskeleton remodelling. We also quantitatively show that directional cell migration is dictated by the competition between the local stiffness of ECMs and the local polymerizing rate of actin network caused by chemotactic cues. Our results reveal that it is the polymerization force-regulated actin filament-Arp2/3 complex binding interaction that dominates self-adaptive cell migrations in complex ECMs, and we provide a predictive theory and a spatiotemporal multiscale modelling system at the protein level. .
A “Primer”-Based Mechanism Underlies Branched Actin Filament Network Formation and Motility
Current Biology, 2010
Cells use actin assembly to generate forces for membrane protrusions during movement or, in the case of pathogens, to propel themselves in the host cells, in crude extracts , or in mixtures of actin and other purified proteins [3]. Significant progress has been made in understanding the mechanism of actin-based motility at a macroscopic level by using biomimetic systems in vitro . Here, we combined such a system with evanescent wave microscopy to visualize Arp2/3-mediated actin network formation at single-actin-filament resolution. We found that actin filaments that we call ''primers'' determine the origin of the autocatalytic and propagative formation of the actin network. In the presence of capping protein, multiple ''primers'' generate independent networks that merge around the object to form an outer ''shell'' made of entangled and capped filaments. Simultaneously, newly created filaments on the surface of the particle initiate mechanical stress, which develops until symmetry breaking. Our results and extensive modeling support that the stress, which releases into propulsive forces [7], is controlled not by any specific orientation of actin filaments toward the nucleation sites but only by new monomers added near the load surface.
Roles for Actin Dynamics in Cell Movements During Development
Actin-dependent cellular movements and rearrangements are crucial for development. Studies in vitro have contributed much to the knowledge of actin biology. However, interesting environmental influences common in developing systems can differentially regulate actin dynamics and organization. In this chapter, we highlight several selected examples of directed cell migration during morphogenesis, in which actin dynamics have been observed directly in live-imaging studies. We discuss similarities and differences between collective cell and single cell migration during development, and we compare what has been learned from in vivo studies in developmental systems with in vitro studies of single cells.
The Actin-Based Nanomachine at the Leading Edge of Migrating Cells
Biophysical Journal, 1999
Two fundamental parameters of the highly dynamic, ultrathin lamellipodia of migrating fibroblasts have been determined-its thickness in living cells (176 Ϯ 14 nm), by standing-wave fluorescence microscopy, and its F-actin density (1580 Ϯ 613 m of F-actin/m 3 ), via image-based photometry. In combination with data from previous studies, we have computed the density of growing actin filament ends at the lamellipodium margin (241 Ϯ 100/m) and the maximum force (1.86 Ϯ 0.83 nN/m) and pressure (10.5 Ϯ 4.8 kPa) obtainable via actin assembly. We have used cell deformability measurements (Erickson, 1980. J. Cell Sci. 44:187-200; Petersen et al., 1982. Proc. Natl. Acad. Sci. USA. 79:5327-5331) and an estimate of the force required to stall the polymerization of a single filament (Hill, 1981. Proc. Natl. Acad. Sci. USA. 78:5613-5617; Peskin et al., 1993. Biophys. J. 65:316 -324) to argue that actin assembly alone could drive lamellipodial extension directly.
Actin-driven Golgi apparatus dispersal during collective migration of epithelial cells
Proceedings of the National Academy of Sciences
As a sedentary epithelium turns motile during wound healing, morphogenesis, and metastasis, the Golgi apparatus moves from an apical position, above the nucleus, to a basal position. This apical-to-basal repositioning of Golgi is critical for epithelial cell migration. Yet the molecular mechanism underlying it remains elusive, although microtubules are believed to play a role. Using live-cell and super-resolution imaging, we show that at the onset of collective migration of epithelial cells, Golgi stacks get dispersed to create an unpolarized transitional structure, and surprisingly, this dispersal process depends not on microtubules but on actin cytoskeleton. Golgi–actin interaction involves Arp2/3-driven actin projections emanating from the actin cortex, and a Golgi-localized actin elongation factor, MENA. While in sedentary epithelial cells, actin projections intermittently interact with the apically located Golgi, and the frequency of this event increases before the dispersion o...
Control of Actin Filament Treadmilling in Cell Motility
Recent advances in structural, biochemical, biophysical, and live cell imaging approaches have furthered our understanding of the molecular mechanisms by which regulated assembly dynamics of actin filaments drive motile processes. Attention is focused on lamellipodium protrusion, powered by the turnover of a branched filament array. ATP hydrolysis on actin is the key reaction that allows filament treadmilling. It regulates barbed-end dynamics and length fluctuations at steady state and specifies the functional interaction of actin with essential regulatory proteins such as profilin and ADF/cofilin. ATP hydrolysis on actin and Arp2/3 acts as a timer, regulating the assembly and disassembly of the branched array to generate tropomyosin-mediated heterogeneity in the structure and dynamics of the lamellipodial network. The detailed molecular mechanisms of ATP hydrolysis/Pi release on F-actin remain elusive, as well as the mechanism of filament branching with Arp2/3 complex or that of the formin-driven processive actin assembly. Novel biophysical methods involving single-molecule measurements should foster progress in these crucial issues. 449 Annu. Rev. Biophys. 2010.39:449-470. Downloaded from arjournals.annualreviews.org by 89.133.73.22 on 05/25/10. For personal use only.
Actomyosin contractility spatiotemporally regulates actin network dynamics in migrating cells
Journal of Biomechanics, 2009
Coupling interactions among mechanical and biochemical factors are important for the realization of various cellular processes that determine cell migration. Although F-actin network dynamics has been the focus of many studies, it is not yet clear how mechanical forces generated by actomyosin contractility spatiotemporally regulate this fundamental aspect of cell migration. In this study, using a combination of fluorescent speckle microscopy and particle imaging velocimetry techniques, we perturbed the actomyosin system and examined quantitatively the consequence of actomyosin contractility on F-actin network flow and deformation in the lamellipodia of actively migrating fish keratocytes. F-actin flow fields were characterized by retrograde flow at the front and anterograde flow at the back of the lamellipodia, and the two flows merged to form a convergence zone of reduced flow intensity. Interestingly, activating or inhibiting actomyosin contractility altered network flow intensity and convergence, suggesting that network dynamics is directly regulated by actomyosin contractility. Moreover, quantitative analysis of F-actin network deformation revealed that the deformation was significantly negative and predominant in the direction of cell migration. Furthermore, perturbation experiments revealed that the deformation was a function of actomyosin contractility. Based on these results, we suggest that the actin cytoskeletal structure is a mechanically self-regulating system, and we propose an elaborate pathway for the spatiotemporal self-regulation of the actin cytoskeletal structure during cell migration. In the proposed pathway, mechanical forces generated by actomyosin interactions are considered central to the realization of the various mechanochemical processes that determine cell motility.
Comparative Maps of Motion and Assembly of Filamentous Actin and Myosin II in Migrating Cells
Molecular Biology of the Cell, 2007
To understand the mechanism of cell migration, one needs to know how the parts of the motile machinery of the cell are assembled and how they move with respect to each other. Actin and myosin II are thought to be the major structural and force-generating components of this machinery (Mitchison and Cramer, 1996; Parent, 2004). The movement of myosin II along actin filaments is thought to generate contractile force contributing to cell translocation, but the relative motion of the two proteins has not been investigated. We use fluorescence speckle and conventional fluorescence microscopy, image analysis, and computer tracking techniques to generate comparative velocity and assembly maps of actin and myosin II over the entire cell in a simple model system of persistently migrating fish epidermal keratocytes. The results demonstrate contrasting polarized assembly patterns of the two components, indicate force generation at the lamellipodium-cell body transition zone, and suggest a mechanism of anisotropic network contraction via sliding of myosin II assemblies along divergent actin filaments.
Regulation of Cortical Actin Networks in Cell Migration
International Review of Cytology-a Survey of Cell Biology, 2003
The actin cytoskeleton is a primary determinant of cell shape and motility. Studies on actin regulatory proteins are now coupled with studies of the signal transduction that directs actin cytoskeleton reorganization, and we have gained insights into how external stimuli such as chemoattractants drive changes in actin cytoskeleton. Chemoattractants regulate actin regulatory proteins such as the Arp2⧸3 complex through WASP family proteins, ADF⧸cofilin downstream of LIM-kinase, and various other phosphoinositide-dependent or -independent pathways. Through branching of actin filaments, Arp2⧸3 complex-dependent actin polymerization is suffcient to generate the force necessary for protrusion.
Assembling actin filaments for protrusion
Current Opinion in Cell Biology, 2019
Cell migration entails a plethora of activities combining the productive exertion of protrusive and contractile forces to allow cells to push and squeeze themselves through cell clumps, interstitial tissues or tissue borders. All these activities require the generation and turnover of actin filaments that arrange into specific, subcellular structures. The most prominent structures mediating the protrusion at the leading edges of cells include lamellipodia and filopodia as well as plasma membrane blebs. Moreover, in cells migrating on planar substratum, mechanical support is being provided by an additional, more proximally located structure termed the lamella. Here, we systematically dissect the literature concerning the mechanisms driving actin filament nucleation and elongation in the best-studied protrusive structure, the lamellipodium. Recent work has shed light on open questions in lamellipodium protrusion, including the relative contributions of nucleation versus elongation to the assembly of both individual filaments and the lamellipodial network as a whole. However, much remains to be learned concerning the specificity and relevance of individual factors, their cooperation and their site-specific functions relative to the importance of global actin monomer and filament homeostasis.