Abstract
Cells are sensitive to mechanical cues from their environment and at the same time generate and transmit forces to their surroundings. To test quantitatively forces generated by cells not attached to a substrate, we used a dual optical trap to suspend 3T3 fibroblasts between two fibronectin-coated beads. In this simple geometry, we measured both the cells' elastic properties and the force fluctuations they generate with high bandwidth. Cell stiffness decreased substantially with both myosin inhibition by blebbistatin and serum-starvation, but not with microtubule depolymerization by nocodazole. We show that cortical forces generated by non-muscle myosin II deform the cell from its rounded shape in the frequency regime from 0.1 to 10 Hz. The amplitudes of these forces were strongly reduced by blebbistatin and serum starvation, but were unaffected by depolymerization of microtubules. Force fluctuations show a spectrum that is characteristic for an elastic network activated by random sustained stresses with abrupt transitions.
Highlights
Many cellular processes such as substrate– or cell–cell adhesion, locomotion or cell division [1,2,3,4,5,6] depend critically on mechanical interactions and the forces cells exert and experience
We show that cortical forces generated by non-muscle myosin II deform the cell from its rounded shape in the frequency regime from 0.1 to 10 Hz
Blocking the motor activity of non-muscle myosin II motors (NMM IIs) with 100 mM blebbistatin led to a threefold decrease in cell stiffness kcell 1⁄4 3.1 + 1.5 Â 1025 N m21 compared to the cells in control conditions (t-test, significance level 99.9%)
Summary
Many cellular processes such as substrate– or cell–cell adhesion, locomotion or cell division [1,2,3,4,5,6] depend critically on mechanical interactions and the forces cells exert and experience. The accurate measurement of mechanical properties of living cells and of the forces they generate remains challenging. Most work in this direction has been done on substrate-adherent cultured cells [15], a rather non-physiological situation for most cell types. Laser interferometry is used to track the motion of the beads with high bandwidth (figure 1b) This approach allows us, on the one hand, to measure the force fluctuations generated by the cells. We demonstrate that the cortical acto-myosin network is the key cytoskeletal component generating contractile force fluctuations and providing mechanical strength, whereas the contribution of the microtubule network is negligible
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Schedule a callMore From: Philosophical transactions of the Royal Society of London. Series B, Biological sciences
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