Subsecond reorganization of the actin network in cell motility and chemotaxis

Abstract

Actin networks are continuously reorganized in cells that rapidly change their shape. Applying total internal reflection fluorescence microscopy at acquisition rates of 10 -20 Hz, we measured an average growth rate of 3 m⅐sec ؊1 for filamentous actin structures throughout the entire substrate-attached cortex of Dictyostelium cells. New filaments often proceed along preexisting ones, resulting in bundle formation concurrent with filament growth. In cells that orientate in a gradient of chemoattractant, prominent assemblies of actin enriched in the Arp2͞3 complex are inserted into the network, primarily at the base of filopods that point into the direction of the gradient. We propose that high turnover rates of actin filaments confer the plasticity to the cell cortex that is required for rapid accommodation to external stimuli.actin polymerization ͉ Arp2͞3 complex ͉ Dictyostelium ͉ latrunculin ͉ total internal reflection fluorescence

Actin cytoskeleton of chemotactic amoebae operates close to the onset of oscillations

“…We will therefore present a simplified heuristic model, in which the detailed processes are summarized into a small number of effective kinetic terms. The ongoing buildup and degradation of filamentous actin allow for a quick rearrangement of the cortical structures, essential for the rapid responses of motile cells to extracellular cues (1,21). We will describe this process on the basis of a simple effective kinetic rate equation:…”

“…Due to its excellent fluorescence properties and low cytosolic background levels, LimE-GFP became a popular in vivo marker for F-actin structures. It was successfully used in high-speed recordings of cortical actin reorganization (21) as well as in studies of actin waves (22,23) and phagocytosis (24). We generated cAMP stimuli by using microfluidic flow photolysis, an approach to address individual cells with well-controlled chemical signals (25).…”

Structural transition of actin filament in a cell-sized water droplet with a phospholipid membrane

“…1,2 Actin filament shows a variety of morphologies in cytoplasm, especially in conjunction with membrane. It has been considered that actin filaments form assembly together with structural proteins such as α-actinin, fimbrin and scruin.…”

Toward the Structure of Dynamic Membrane-Anchored Actin Networks

“…The rate in fast growing filopodia is thus close to the average polymerization rate of actin filaments in the cortical network of Dictyostelium cells, which corresponds to 11 x 10 2 subunits per second and is thought to be a formin mediated process. 2 The localization of DdDia2 to the filopod tip and its involvement in the formation of filopodia 10 strongly suggests a role of this formin in actin polymerization at the terminal cone of actin filaments.…”

“…In highly motile cells such as those of Dictyostelium, organization of actin networks does change on the sub-second scale. 2 There are two major difficulties in preserving the structure of such networks for electron microscopic investigation: the networks are membrane-anchored and the filaments are highly dynamic because regulatory proteins will rapidly bind and dissociate. Moreover, actin filaments are not easily seen in thin sections.…”