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Actin Dynamics and Cell Motility: Minimal Models for the Initiation of Cell Movement
Jan Fuhrmann, Josef Käs and Angela Stevens
The actin driven motility of eukaryotic cells has been one of the most rapidly developing research areas in biology over the last decades. Polymerization and depolymerization of filaments is the driving force behind the crawling motion of individual cells. There is a large variety of proteins known or suspected to be involved in this polymerization machinery. The question arises which of them are essential for the ability of a cell to move directionally. Many studies have been conducted on cells which are already in motion - or at least polarized with established lamellipods, and several mechanisms have been shown to be essential for sustaining the large movement velocities observed in vivo. The question we addressed here is what minimal requirements have to be met by a non polarized resting cell to react to an external stimulus in a prescribed direction.
For that purpose, we develop a minimal model for actin turnover, examine its steady states, and try to figure out which types of perturbations are most appropriate to turn the cytoskeleton into a polarized state which may be viewed as the beginning of directed motion. We analyze a one dimensional model for a resting cell describing the actin network therein. For the time being we restrict ourselves to describing the dynamics of barbed ends accumulating near the cell membrane. Pushing the membrane forward and establishing a lamellipod would be the next step in the initiation of movement and shall be investigated in future. In our simulations we found that very few mechanisms are sufficient to create a significant modification of the cytoskeleton. Moreover we see a striking effect of the diffusion coefficient for the actin monomers on the strength of this modification.