P-cadherin–induced mechanical force generation requires β-PIX and Cdc42. (a) Intercellular stress maps parallel to the migration direction (stress xx) measured at the indicated migration time and corresponding histograms of the maximum principal stress measured over 10 h. n = 6 for C2C12 Pcad Cdc42 shRNA cells and for C2C12 Pcad β-PIX shRNA cells from three independent experiments. (b) Rose plots of the angle between the principal stress direction and velocity at 8 h after removal of the PDMS membrane. Arrows indicate the migration direction. n = 6. (c) Cumulative probability distribution of the angle between cellular velocity and the maximum principal stress for the highest quintile of stress anisotropy (measured using the maximum shear stress). (d) The Tx/Ty ratio measured every 20 µm from the multicellular leading row toward the center of the layer 4–10 h after removal of the PDMS membrane. Error bars show 95% confidence interval of the mean (95% SEM); all nonoverlapping error bars are statistically significant with P < 0.05. (e) Overall orientation of traction forces 0–40 or 60–140 µm from the multicellular leading row. n = 6 from three independent experiments. For all panels, data are the mean ± SEM: **, P < 0.005; ***, P < 0.0005.