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First published online April 3, 2008
doi: 10.1242/10.1242/jcs.021576

Journal of Cell Science 121, 1314-1324 (2008)
Published by The Company of Biologists 2008
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Research Article

Actin-based propulsive forces and myosin-II-based contractile forces in migrating Dictyostelium cells

Yoshiaki Iwadate* and Shigehiko Yumura

Department of Functional Molecular Biology, Graduate School of Medicine, Yamaguchi University, Yamaguchi 753-8512, Japan

* Author for correspondence (e-mail: iwadate{at}yamaguchi-u.ac.jp)

Accepted 22 January 2008

It has been suggested that myosin II exerts traction forces at the posterior ends and retracting pseudopodia of migrating cells, but there is no direct evidence. Here, using a combination of total internal reflection fluorescence (TIRF) microscopy and force microscopy with a high spatial resolution of ~400 nm, we simultaneously recorded GFP-myosin II dynamics and traction forces under migrating Dictyostelium cells. Accumulation of filamentous myosin II and a subsequent increase in traction forces were detected in pseudopodia just before retraction. In the case of motorless myosin II, traction forces did not increase after accumulation, suggesting that the source of the retraction force is the motor activity of accumulated myosin II. Simultaneous recording of F-actin and traction forces revealed that traction forces were exerted under spot-like regions where F-actin accumulated. Cells migrated in a direction counter to the sum of the force vectors exerted at each spot, suggesting that the stress spots act as scaffolds to transmit the propulsive forces at the leading edge generated by actin polymerization.

Key words: Amoeboid movement, Cell migration, Pseudopod






© The Company of Biologists Ltd 2008