Abstract
We present a model to estimate intracellular force variations from live-cell images of actin filament (F-actin) flow during protrusion-retraction cycles of epithelial cells in a wound healing response. To establish a mechanistic relationship between force development and cytoskelal dynamics, force fluctuations were correlated with fluctuations in F-actin turnover, flow and F-actin–vinculin coupling. Our analyses suggest that force transmission at focal adhesions requires binding of vinculin to F-actin and integrin (indirectly), which is modulated at the vinculin–integrin but not the vinculin–F-actin interface. Force transmission at focal adhesions is colocalized in space and synchronized in time with transient increases in the boundary force at the cell edge. Surprisingly, the maxima in adhesion and boundary forces lag behind maximal edge advancement by about 40 s. Maximal F-actin assembly was observed about 20 s after maximal edge advancement. On the basis of these findings, we propose that protrusion events are limited by membrane tension and that the characteristic duration of a protrusion cycle is determined by the efficiency in reinforcing F-actin assembly and adhesion formation as tension increases.
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Acknowledgements
We thank Clare Waterman and Ke Hu for continued discussion of and encouragement for this study. We gratefully acknowledge funding from NIH R01 GM71868 and the Cell Migration Consortium, Grant No U54 GM064346 from NIGMS.
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L.J. designed and implemented the force reconstruction algorithm and performed all image analyses; J.L. acquired fluorescent speckle microscopy data of F-actin and myosin II, and assisted with the preparation of the figures and manuscript; G.D. proposed the idea of force reconstruction from speckle movies and wrote the manuscript.
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Ji, L., Lim, J. & Danuser, G. Fluctuations of intracellular forces during cell protrusion. Nat Cell Biol 10, 1393–1400 (2008). https://doi.org/10.1038/ncb1797
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DOI: https://doi.org/10.1038/ncb1797
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