Moesin inactivation impairs mitotic spindle organization and positioning. (A) In the absence of moesin, abnormally long astral microtubules (arrowheads) contact the cortex at locations of actin-rich cell deformations (arrows). α-Tubulin, green; actin, red; DNA, blue. (B) Quantification of spindle defects in metaphase cells. L, mitotic spindle length (n = 100); c1/c2, ratio between distances of the centrosomes to their respective polar cortex (n = 25); d, distance between the geometrical center of the cell and the center of the spindle (n = 25). Each blue dot represents the calculated value for one cell. Horizontal bars represent the mean value of these data. ***, P < 0.005. (C) Time-lapse frames of S2 cells expressing α-tubulin–GFP treated with the indicated dsRNA. Arrowheads indicate astral microtubules associated with cortex bulges. The red lines show maximal deviations of the spindle orientation from its initial position (green lines). Bars, 10 μm.