Emergence of Large-Scale Cell Morphology and Movement from Local Actin Filament Growth Dynamics

Abstract

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 actin-remodeling 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 actin-remodeling 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.

Mechanism of shape determination in motile cells

“…2b and Supplementary Fig. 2), producing a phenotypic continuum that we have described previously 11 : from rough, slow and rounded 'decoherent' cells, to smooth, fast and wide 'coherent' cells that exhibit a more pronounced peak in actin filament density at the centre.…”

“…1). Furthermore, whereas the shape of an individual cell can be significantly affected by such perturbations 11 , the phase space of cell shapes under the perturbations tested was nearly identical to that spanned by the population of unperturbed cells ( Supplementary Fig. 1).…”

“…The relative simplicity of keratocytes has inspired extensive experimental and theoretical investigations into this cell type [5][6][7][8][9][10][11][12][13][14][15][16][17] , considerably advancing the understanding of cell motility. A notable example is the graded radial extension (GRE) model 12 , which was an early attempt to link the mechanism of motility at the molecular level with overall cell geometry.…”

“…1b), which together account for ,97% of the total variation in shape. Roughly, these modes can be characterized as measures of: the projected cell area (mode 1); whether the cell has a rounded 'D' shape or an elongated 'canoe' shape (mode 2) 11 ; the angle of the rear of the lamellipodium with respect to the cell body (mode 3); and the left-right asymmetry of the side lobes (mode 4). These shape modes provide a meaningful and concise quantitative description of keratocyte morphology using very few parameters.…”

Involvement of vasodilator-stimulated phosphoprotein in UDP-induced microglial actin aggregation via PKC- and Rho-dependent pathways

“…The function of phosphorylated VASP in UDP-stimulated microglia VASP is a member of the Ena/VASP proteins and directly regulates assembly of the actin-filament network, modulates the morphology and behavior of membrane protrusion structures (such as filopodia and lamellipodia) and influences cell motility [45][46][47]. The phosphorylation of VASP negatively regulates actin nucleation/G-actin binding and interaction with F-actin and some cell adhesion regulators [48][49][50].…”