Contractile pulse and extension dynamics in epithelia with non-deformable nuclei. (A) Still frames of T1 events from a time-lapse kuk movie showing enhanced nuclear dispersion (indicated by the disappearance of nuclei from the given imaging plane at 0 s). Image slice from ∼11 µm below the apical surface. (B) Comparing vertical interface lengths of control (luciferase shRNA) and kuk shRNA during GBE. 0 min indicates the onset of the GBE. Positive lengths indicate T1 interfaces while negative lengths are horizontally extending T3 interfaces. Error envelopes indicate SEM. (B′) The rate of vertical interface length change is shown in B′, negative values indicate contraction of vertical interfaces; n = 133 interfaces for control (luciferase) and n = 95 interfaces for kuk from k = 3 embryos for each background. (C) Centroid distances for AB (blue) and CD (red) cells over the course of 20 min for control (luciferase) (left) and kuk (right) embryos during GBE indicating cell convergence and extension. Inset shows labeling scheme of AB and CD cells during T1 to T3 transitions. Error envelopes indicate SD. (D) Extension rate of AB cells in control (luciferase) and kuk embryos. For C and D, n = 158 for control (luciferase) and n = 159 transitions for kuk from k = 3 embryos for each background. (E) FFT analysis of oscillatory dynamics in control (luciferase) and kuk embryos. The dotted line indicates where the amplitude percent change was calculated in F. Color bar indicates the FFT amplitude in the frequency space. (F) FFT amplitude percent change (decrease in cell oscillation amplitude from the nucleus midplane to 4 μm basal to the nucleus midplane) in control (luciferase) and kuk embryos. For E and F, n = 961 cells for control and n = 580 cells for kuk from k = 3 embryos for each background. Error bars indicate SEM. The measured n values are regardless of time points. Scale bar = 5 µm. Statistical significance was calculated using the Mann–Whitney U-test. *P < 0.05, ****P < 0.0001.