Fig. 10. Blebbistatin treatment triggers the reorientation of cortical microtubules. (A) Caco-2 cells growing on Matrigel-coated coverslips were treated for 12 hours with either blebbistatin (100 µM) or vehicle, fixed, and double-labeled for F-actin (green) and -tubulin (red). In vehicle-treated cells, cortical microtubules are positioned in parallel to the cell surface behind thick actomyosin bundles (arrows). Blebbistatin treatment induces the disassembly of actomyosin bundles and reorientation of cortical microtubules so that they are perpendicular to the edge of epithelial colonies (arrowheads). Scale bar: 20 µm. (B) Quantification of changes in microtubule distribution. The average pixel intensity ratios were calculated for -tubulin signal at the front versus the back of F-actin cables in control Caco-2 colonies and in the distal versus proximal parts of peripheral protrusions in blebbistatin-treated colonies. The pixel intensity ratio was significantly higher in blebbistatin-treated cells, thus indicating the accumulation of microtubules in close vicinity to the plasma membrane (^*P<0.05).