Figure 2. Nuclear actin forms a soft, viscoelastic network.

(a) Schematic diagram of active microrheology experimental set-up with two opposing electromagnets. Inset shows XY image of Lifeact::GFP labeled actin network (green) with an embedded magnetic microsphere (red, R = 1.5 μm). Scale bar = 10 μm. (b) An example of sinusoidal applied force (black) and response of magnetic microsphere (red). (c) Lissajous (stress-strain) plot of applied magnetic force as a function of measured displacement of microspheres in one nucleus. Error bars are s.e.m. Curves are fit to an ellipse and color denotes applied frequency. (d) Viscoelastic moduli, storage modulus (red) and loss modulus (blue), as a function of frequency in the untreated nucleus (n = 9 nuclei). Error bars represent s.e.m. Solid line is from fit determined by viscoelastic model in Fig. 3 inset.