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Biophys. J. BioFAST: First Published October 20, 2005. doi:10.1529/biophysj.105.062224
© 2005 by the Biophysical Society.

A more recent version of this article appeared on January 15, 2006.
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MEMBRANES

Dynamics of membranes driven by actin polymerization

Nir S Gov 1* and Ajay Gopinathan 2

1 Weizmann Institute of Science
2 University of California Santa Barbara

* To whom correspondence should be addressed. E-mail: nirgov{at}wisemail.weizmann.ac.il.

Submitted on March 2, 2005
Revised on May 4, 2005
Accepted on 18 August 2005


  Abstract
A motile cell, when stimulated, shows a dramatic increase in the activity of it's membrane, manifested by the appearance of dynamic membrane structures such as lamellipodia, filopodia and membrane ruffles. The external stimulus turns on membrane bound activators, like Cdc42 and PIP2, which cause increased branching and polymerization of the actin cytoskeleton in their vicinity leading to a local protrusive force on the membrane. The emergence of the complex membrane structures is a result of the coupling between the dynamics of the membrane, the activators and the protrusive forces. We present a simple model that treats the dynamics of a membrane under the action of actin polymerization forces that depend on the local density of freely diffusing activators on the membrane. We show that, depending on the spontaneous membrane curvature associated with the activators, the resulting membrane motion can be wave-like, corresponding to membrane ruffling and actin-waves, or unstable, indicating the tendency of filopodia to form. Our model also quantitatively explains a variety of related experimental observations and makes several testable predictions.

Key Words: Actin polymerization, Filopodia, Lamellipodia, Membrane diffusion, Membrane fluctuations, Spontaneous curvature




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Copyright © 2005 by the Biophysical Society.