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Abstract
This report deals with actin waves that are spontaneously generated on the planar, substrate-attached surface of Dictyostelium cells. These waves have the following characteristics. (1) They are circular structures of varying shape, capable of changing the direction of propagation. (2) The waves propagate by treadmilling with a recovery of actin incorporation after photobleaching of less than 10 seconds. (3) The waves are associated with actin-binding proteins in an ordered 3-dimensional organization: with myosin-IB at the front and close to the membrane, the Arp2/3 complex throughout the wave, and coronin at the cytoplasmic face and back of the wave. Coronin is a marker of disassembling actin structures. (4) The waves separate two areas of the cell cortex that differ in actin structure and phosphoinositide composition of the membrane. The waves arise at the border of membrane areas rich in phosphatidylinositol (3,4,5) trisphosphate (PIP3). The inhibition of PIP3 synthesis reversibly inhibits wave formation. (5) The actin wave and PIP3 patterns resemble 2-dimensional projections of phagocytic cups, suggesting that they are involved in the scanning of surfaces for particles to be taken up.PACS Codes: 87.16.Ln, 87.19.lp, 89.75.Fb
Highlights
This article is an overview of work supported by the Deutsche Forschungsgemeinschaft in the Priority Program “Optical analysis of the structure and dynamics of supramolecular biological complexes”
The starting question we addressed was: how are actin structures organized de novo in cells that have been depleted of polymerized actin? To inhibit actin polymerization, we have used latrunculinA (LatA)
The disassembly and re-assembly of actin structures has been monitored in Dictyostelium cells using a GFP- tagged construct (LimEΔ) that proved to be an appropriate label for recording the dynamics of filamentous actin structures in these cells [1]
Summary
This article is an overview of work supported by the Deutsche Forschungsgemeinschaft in the Priority Program “Optical analysis of the structure and dynamics of supramolecular biological complexes”. Subject of our studies has been the self-organization of actin into propagating waves. The starting question we addressed was: how are actin structures organized de novo in cells that have been depleted of polymerized actin? In living cells, this scavenger of actin monomers results in the depolymerization of actin filaments at a rate determined by their turnover. The actin structures rapidly turn over, resulting in microscopically detectable breakdown of the actin network in the cell cortex within less than 20 seconds after LatA addition [2]
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