Figure 3. Cellular stiffness in response to latrunculin-A.

Two cross sections along the z-axis through a cell before (a) and after (b) exposing the cell to latrunculin-A. A Brillouin image of the same cell taken at higher sampling resolution after drug exposure (c) and the associated phase-contrast image (d). Latrunculin is a toxin that prevents polymerisation of actin filaments and thereby decreases cell stiffness. Note that actin filaments are predominantly found in the cytoplasm and are absent from nucleoli. Indeed, cytoplasmic stiffness is decreased from 2.57 ± 0.05 to 2.46 ± 0.06 GPa (p < 0.0001), whereas nucleolar stiffness is not substantially affected by latrunculin-A exposure with a small decrease from 2.68 ± 0.07 GPa to 2.64 ± 0.06 GPa (p = 0.65) (values reported as mean ± s.d.). A bar-plot represents the change (mean ± SEM) in the longitudinal modulus of the cytoplasm and nucleoli in response to latrunculin-A of all experiments (*p < 0.001) (e). These data show that Brillouin microscopy is capable of measuring both spatial and temporal variations in stiffness in a physiologically relevant stiffness range that facilitates the study of cellular biomechanics.