Fig. 2.

Contribution of the actin and microtubule cytoskeleton to the spatially averaged mechanical properties of the cytoplasm. (A) Relaxation curves for control cells (black) and for cells treated with drugs destabilizing microtubules (nocodazole, Taxol) or microfilaments (LatA and CytoD) (red). Note that the CytoD and control curves superimpose. (B) Average values of the shear modulus G₀, the storage modulus G′, and the loss modulus G″ in the presence of the indicated drug. Data shown in A and B are averages from n = 152, 44, 56, 24, and 34 beads in control cells, nocodazole-, Taxol-, LatA-, and CytoD-treated cells, respectively. (C) Mean-square displacement (MSD) analysis of the motion of 2-µm-diameter beads diffusing inside the optical trap in control cells (black) and in cells treated with LatA (red) or CytoD (blue). The averaged MSD plots as a function of time (Left) were fitted using a caged diffusion model (SI Materials and Methods) to obtain the diffusion coefficient (Right). Data shown are averages from n = 54, 27, and 38 beads for control cells and LatA- and CytoD-treated cells, respectively. Error bars represent SEs. P values are determined from Student’s t test for unpaired samples with respect to control cells (***P < 0.0001; **P < 0.001; and *P < 0.01).