Figure 4. Prickle 2 controls the frequency of actomyosin pulses.

(A, B) Cells expressing membrane (Mem) -GFP in the Xenopus dorsal mesoderm display an elongate and aligned morphology in control (A). Pk2-KD disrupts elongation and orientation of cells (B). (C, D) Quantification of cell shapes and orientations by measuring length-width ratio (ellipticity) of each cell and cell angle from mediorateral axis, respectively. (Cell elongation index: **** p < 0.0001, Student t-test, control: n = 100 from three embryos, Pk2-KD: n = 51 from three embryos; Orientation: **** p < 0.0001, Mann Whitney U-test, control: n = 97 from three embryos, Pk2-KD: n = 51 from three embryos). (E, F) Still images from time-lapse movies of Myl9-GFP and Mem-RFP in control (E) or Pk2-KD (F). (G, H) Representative oscillations of Myl9 intensity in two apposed cells (cell1 and cell2, see Figure S4B) in a control (G) or Pk2-KD (Η). (I) Normalized intensities of Myl9-GFP and LifeAct-RFP, measured along mediolaterally aligned cell junctions in Pk2-KD embryos. (I’) Cross-correlation of normalized intensities of Myl9 and LifeAct along medioraterally aligned cell junctions in Pk2-KD embryos revealed their synchronized oscillations (black line with SE). Each blue line is from each cell junction. (J) Peaks in apposed cells generally display a one-to-one ration, suggesting a roughly asynchronous and alternate relationship between cell neighbors. To compare, the result from control embryos in Figure 1E is added. See also Figure S6. (K) Time between peaks is significantly reduced after Pk2-KD. **** p < 0.0001, Mann Whitney U-test, control: n = 76 from three embryos, Pk2-KD: n = 138 from three embryos. Scale bar = 20 μm.