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First published online April 23, 2007
doi: 10.1242/10.1242/jcs.002527

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Traction force microscopy in Dictyostelium reveals distinct roles for myosin II motor and actin-crosslinking activity in polarized cell movement

¹ Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269, USA
² Department of Biomedical Engineering, Boston University, Boston, MA 02215, USA

^* Author for correspondence (e-mail: juliet.lee{at}uconn.edu)

Accepted 28 February 2007

Continuous cell movement requires the coordination of protrusive forces at the leading edge with contractile forces at the rear of the cell. Myosin II is required to generate the necessary contractile force to facilitate retraction; however, Dictyostelium cells that lack myosin II (mhcA^–) are still motile. To directly investigate the role of myosin II in contractility we used a gelatin traction force assay to measure the magnitude and dynamic redistribution of traction stresses generated by randomly moving wild-type, myosin II essential light chain null (mlcE^–) and mhcA^– cells. Our data show that for each cell type, periods of rapid, directed cell movement occur when an asymmetrical distribution of traction stress is present, in which traction stresses at the rear are significantly higher than those at the front. We found that the major determinants of cell speed are the rate and frequency at which traction stress asymmetry develops, not the absolute magnitude of traction stress. We conclude that traction stress asymmetry is important for rapid, polarized cell movement because high traction stresses at the rear promote retraction, whereas low traction at the front allows protrusion. We propose that myosin II motor activity increases the rate and frequency at which traction stress asymmetry develops, whereas actin crosslinking activity is important for stabilizing it.

Key words: Traction forces, Myosin II, Myosin essential light chain, Movement, Dictyostelium discoideum

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				Y. Iwadate and S. Yumura Actin-based propulsive forces and myosin-II-based contractile forces in migrating Dictyostelium cells J. Cell Sci., April 15, 2008; 121(8): 1314 - 1324. [Abstract] [Full Text] [PDF]