Cdc42 depletion disrupts mitotic spindle orientation. (A) Diagram depicting spindle angle measurement. The centroid of the cyst (dark blue circle) and the center of the spindle axis (pink circles) of a metaphase cell were drawn using ImageJ. The angle (red) between the spindle axis (black lines) and the line connecting the centroid of the cyst to the center of the spindle (dashed lines) was determined. To analyze spindle poles in different z sections, three z sections were taken so as to include both spindle poles and were merged as shown. Three schematic spindles are shown. The right and middle spindle examples represent correctly oriented spindles whose poles are positioned in one section (z2; middle spindle) or in different sections (z1 and z3; right spindle). The left spindle represents a misoriented spindle whose poles are in different z sections. Spindle microtubules, green; centrosomes, yellow; DNA, light blue. (B) Scatter diagram of metaphase spindle angles in cysts that were transfected with control or two Cdc42 siRNA duplexes from three independent experiments. Pink circles indicate mean values, green circles indicate individual data points, and error bars represent the SEM of the total number of spindles analyzed (N). (C) Caco-2 was transfected with control or Cdc42 siRNA and was fixed and stained for DNA (blue), tubulin (green), and filamentous actin (F-actin; red). Single confocal sections through the center of the cysts are shown. Three z sections are shown for the Cdc42 siRNA cyst to reveal both poles of the misoriented spindle. (D and E) Caco-2 transfected with control or Cdc42 siRNA was fixed and stained for DNA (blue) and aPKC (green). (D) Cdc42 siRNA structures contain cells in the middle, with apical domains present between inner and outer cells. (E) Cdc42 siRNA structures possess apical domains that are not in the center and single cells with more than one apical domain. Arrows indicate cells with multiple distinct apical patches on their surface. Bars, 10 μm.