Pk1 knockdown disrupts cell rearrangement in the PCM. (A) WT and Pk1-MO cells in PCM explants in contact with BCR (dashed lines, PCM-BCR boundary). Red and yellow arrows indicate migration of unlabeled cell over red and yellow cells, respectively. Time in minutes. Scale bars, 20 μm. (A′) Quantification of cell intercalation events summed over time in PCM explants. (B) Cell length/width ratio (WT, n = 109; Pk1-MO, n = 109) and circularity (WT, n = 135; Pk1-MO, n = 128). Bars indicate the mean in all figures. ****, P ≤ 0.0001 in a two-tailed Student’s t test. Data distribution was assumed to be normal but was not formally tested. (C) Cell orientation in WT (n = 126) and Pk1-MO PCM (n = 126). 0° indicates orientation toward BCR. (D) Tracks of individual cells in WT, Pk1-MO, and Dvl2-MO PCM-BCR explants. Blue and red dashed lines, initial and final tissue boundaries. (E) From Videos 1 and 2. Velocity gradient in WT and Pk1-MO PCM. BCR on the right; dashed lines indicate initial tissue boundaries. Scale bars, 20 μm. (F) Net translocation of WT (n = 22) and Pk1-MO (n = 22) cells in explants over 90 min. ***, P ≤ 0.001 in a two-tailed Student’s t test. Data distribution was assumed to be normal but was not formally tested. (G) Migration persistence (WT, n = 22; Pk1-MO, n = 22). ****, P ≤ 0.0001 in a two-tailed Student’s t test. Data distribution was assumed to be normal but was not formally tested.