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Vol. 16, Issue 3, 1223-1231, March 2005
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* Laboratory for Biomechanics, ETH Zurich, 8952 Schlieren, Switzerland;
Laboratory for Computational Cell Biology, The Scripps Research Institute, La Jolla, CA 92037; and
Laboratory of Cell Biophysics, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland
Submitted July 21, 2004;
Revised December 14, 2004;
Accepted December 21, 2004
Monitoring Editor: Ted Salmon
Actin assembly at the leading edge of the cell is believed to drive protrusion, whereas membrane resistance and contractile forces result in retrograde flow of the assembled actin network away from the edge. Thus, cell motion and shape changes are expected to depend on the balance of actin assembly and retrograde flow. This idea, however, has been undermined by the reported absence of flow in one of the most spectacular models of cell locomotion, fish epidermal keratocytes. Here, we use enhanced phase contrast and fluorescent speckle microscopy and particle tracking to analyze the motion of the actin network in keratocyte lamellipodia. We have detected retrograde flow throughout the lamellipodium at velocities of 1–3 µm/min and analyzed its organization and relation to the cell motion during both unobstructed, persistent migration and events of cell collision. Freely moving cells exhibited a graded flow velocity increasing toward the sides of the lamellipodium. In colliding cells, the velocity decreased markedly at the site of collision, with striking alteration of flow in other lamellipodium regions. Our findings support the universality of the flow phenomenon and indicate that the maintenance of keratocyte shape during locomotion depends on the regulation of both retrograde flow and actin polymerization.
The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).
These authors contributed equally to this work.
Address correspondence to: Gaudenz Danuser (gdanuser{at}scripps.edu) or Alexander B. Verkhovsky (verkhov{at}dpmail.epfl.ch).
This article has been cited by other articles:
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  T. W. Anderson, A. N. Vaughan, and L. P. Cramer Retrograde Flow and Myosin II Activity within the Leading Cell Edge Deliver F-Actin to the Lamella to Seed the Formation of Graded Polarity Actomyosin II Filament Bundles in Migrating Fibroblasts Mol. Biol. Cell, November 1, 2008; 19(11): 5006 - 5018. [Abstract] [Full Text] [PDF]
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S. Schaub, S. Bohnet, V. M. Laurent, J.-J. Meister, and A. B. Verkhovsky Comparative Maps of Motion and Assembly of Filamentous Actin and Myosin II in Migrating Cells Mol. Biol. Cell, October 1, 2007; 18(10): 3723 - 3732. [Abstract] [Full Text] [PDF]
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 P. T. Yam, C. A. Wilson, L. Ji, B. Hebert, E. L. Barnhart, N. A. Dye, P. W. Wiseman, G. Danuser, and J. A. Theriot Actin myosin network reorganization breaks symmetry at the cell rear to spontaneously initiate polarized cell motility J. Cell Biol., September 24, 2007; 178(7): 1207 - 1221. [Abstract] [Full Text] [PDF]
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 S. Schaub, J.-J. Meister, and A. B. Verkhovsky Analysis of actin filament network organization in lamellipodia by comparing experimental and simulated images J. Cell Sci., April 15, 2007; 120(8): 1491 - 1500. [Abstract] [Full Text] [PDF]
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C. M. Brown, B. Hebert, D. L. Kolin, J. Zareno, L. Whitmore, A. R. Horwitz, and P. W. Wiseman Probing the integrin-actin linkage using high-resolution protein velocity mapping J. Cell Sci., December 15, 2006; 119(24): 5204 - 5214. [Abstract] [Full Text] [PDF]
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