IRSp53 and myosin II function synergistically to regulate epithelial lumen polarity. IRSp53KD (−dox) and control (+dox) subjected to Ca²⁺ switch assays for 24 and 48 h in the presence or absence of 50 µM BB. Lumen polarity was quantified as described in Materials and methods. Statistically significant difference is shown with P < 0.0001 (*). Images represent the 24-h time point. Error bars indicate SEM. Bars, 10 µm.