Nonmuscle Myosin IIA-dependent Force Inhibits Cell Spreading and Drives F-actin Flow

¹ Columbia University
² Universite Bordeaux
³ Université Paris

^* To whom correspondence should be addressed. E-mail: ms2001{at}columbia.edu.

Submitted on March 9, 2006
Revised on April 19, 2006
Accepted on 20 July 2006

	Abstract

Nonmuscle myosin IIA (NMM-IIA) is involved in the formation of focal adhesions and neurite retraction. However, the role of NMM-IIA in these functions remains largely unknown. Using RNA interference (RNAi) as a tool to decrease NMM-IIA expression, we have found that NMM-IIA is the major myosin involved in traction force generation and retrograde F-actin flow in mouse embryonic fibroblast (MEF) cells. Quantitative analyses revealed that ~60% of traction force on fibronectin-coated surfaces is contributed by NMM-IIA and ~30% by NMM-IIB. The retrograde F-actin flow decreased dramatically in NMM-IIA-depleted cells, but seemed unaffected by NMM-IIB deletion. In addition, we found that depletion of NMM-IIA caused cells to spread at a higher rate and to a greater area on fibronectin substrates during the early spreading period, whereas deletion of NMM-IIB appeared to have no effect on spreading. The distribution of NMM-IIA was concentrated on the dorsal surface and approached the ventral surface in the periphery whereas NMM-IIB was primarily concentrated around the nucleus and to a lesser extent at the ventral surface. Our results suggest that NMM-IIA is involved in generating a coherent cytoplasmic contractile force from one side of the cell to the other through the crosslinking and the contraction of dorsal actin filaments.

Key Words: RNA interference, cytoskeleton, deformable micro-post, fibroblast, motility, total internal reflection fluorescence microscopy

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