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Biophys. J. BioFAST: First Published October 7, 2005. doi:10.1529/biophysj.105.071480
© 2005 by the Biophysical Society.

A more recent version of this article appeared on January 1, 2006.
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BIOPHYSICAL THEORY AND MODELING

Mechanics and Dynamics of Actin-driven Thin Membrane Protrusions

Erdinc Atilgan 1, Denis Wirtz 2 and Sean X. Sun 2*

1 Johns Hopkins Univ.
2 Johns Hopkins University

* To whom correspondence should be addressed. E-mail: ssun{at}jhu.edu.

Submitted on July 26, 2005
Revised on August 22, 2005
Accepted on 22 September 2005


  Abstract
Motile cells explore their surrounding milieu by extending thin dynamic protrusions, or filopodia. The growth of filopodia is driven by actin filament bundles that polymerize underneath the cell membrane.We compute the mechanical and dynamical features of the protrusion growth process by explicitly incorporating the flexible plasma membrane. We find that a critical number of filaments is needed to generate net growth. Without external influences, the filopodium can extend indefinitely up to its buckling length. Dynamical calculations show that the protrusion speed is enhanced by the thermal fluctuations of the membrane; a filament bundle encased in flexible membrane grows much faster. The protrusion speed depends directly on the number and spatial arrangement of the filaments in the bundle and whether the filaments are tethered to the membrane. Filopodia also attract each other through distortions of the membrane. Spatially close filopodia will merge to form a larger one. Force-velocity relationships mimicking possible experimental measurements are computed.

Key Words: F-actin bundle, biological force generation, cell motility, filopodium, mathematical model, plasma membrane




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Copyright © 2005 by the Biophysical Society.