Extended Data Figure 9. Measuring the rate of apical constriction.

(a, d) Kymograph of apical Sqh-GFP videos along the ML axis (compensated for the curvature of the embryos) demonstrating the movement of apical myosin towards the ventral midline. x-axis: ML-axis, Scale bar: 50 μm; y-axis: time, Scale bar: 5 min. (b, e) Kymographs processed with a bandpass filter. (c, f) Trajectories of apical myosin moving towards the ventral midline were tracked from the processed kymographs (showing results tracked from multiple kymographs). Colors are used to distinguish individual trajectories. (g, h) The rate of apical constriction (i.e., the rate of convergent movement of the apical cortex) at different time during VF formation as a function of ML positions. The rate of apical constriction (magenta) was averaged from measurement of individual myosin trajectories over 2-min intervals (blue dots). Red dots are outliers. (i) Average rate of apical constriction over time. For each time point, rates were averaged across the mid-ventral region (x = −50-50 μm). Insert shows the ratio of rates between the wild type and acellular embryos over time. Dashed line corresponds to 1.6×. Error bars indicate s.e.m. (j) Average V_x near the ventral cortex (y = 10–14 μm, t = 6–12 min) as a function of ML positions. (k) Average V_y near the ventral midline (x = −16-16 μm, t = 6–12 min) as a function of AB positions. Error bars indicate s.d. in (j) and (k).