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Biophys. J. BioFAST: First Published May 6, 2005. doi:10.1529/biophysj.104.056515
© 2005 by the Biophysical Society.

A more recent version of this article appeared on August 1, 2005.
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BIOPHYSICAL THEORY AND MODELING

The Physics of Filopodial Protrusion

Alexander Mogilner 1* and Boris Rubinstein 1

1 University of California - Davis

* To whom correspondence should be addressed. E-mail: mogilner{at}math.ucdavis.edu.

Submitted on November 17, 2004
Revised on February 18, 2005
Accepted on 29 April 2005


  Abstract
Filopodium, a spike-like actin protrusion at the leading edge of migrating cells, functions as a sensor of the local environment and has a mechanical role in protrusion. We use modeling to examine mechanics and spatial-temporal dynamics of filopodia. We find that more than 10 actin filaments have to be bundled to overcome the membrane resistance, that the filopodial length is limited by buckling for 10 -- 30 filaments, and by G-actin diffusion for more than 30 filaments. There is an optimal number of bundled filaments ~ 30, at which the filopodial length can reach a few microns. The model explains characteristic inter-filopodial distance of a few microns as a balance of initiation, lateral drift and merging of the filopodia. The theory suggests that F-actin barbed ends have to be focussed and protected from capping (the capping rate has to decrease one order of magnitude) once every hundred seconds per micron of the leading edge in order to initiate the observed number of filopodia. The model generates testable predictions about how filopodial length, rate of growth and inter-filopodial distance should depend on the number of bundled filaments, membrane resistance, lamellipodial protrusion rate and G-actin diffusion coefficient.

Key Words: actin dynamics, cell motility, diffusion, mathematical model, protrusion force




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Copyright © 2005 by the Biophysical Society.