Actin-dependent rheological properties of microtubule-nucleus complex. (a) Creep experiment setup. Magnetic tweezers generate high magnetic force on the ferrofluid injected into the nucleus. The applied force continuously displaces microtubule–nucleus complex (creep phase). After releasing the force, the complex partly moves back and eventually stops (relaxation phase). (b) Time-lapse confocal images of the microtubule–nucleus complex in the creep experiment. Cyan indicates outlines of the cell nucleus (broken line: nucleus outline at t = 0 sec). White line indicates the outline of injected ferrofluid. Scale bar is 10 μm. (c) The position of the nucleus (top) and the amplitude of the magnetic force (bottom) are plotted as a function of time. Shaded area indicates the creep phase. (d and e) Inhibitor experiments. (d) The compliance of control (black), nocodazole (blue), and latrunculin B (red) conditions is plotted as a function of time. Single representative data for each condition is shown. The solid line indicates the fittings using the Burgers model (inset). (e and f) The effective spring constant k (e) and the long-term viscosity η0 (f) of control (n = 15), nocodazole (n = 12), and latrunculin B (n = 10) conditions. Error bars indicate the standard deviation.
