Supplementary Figure 2: Apical F-actin is dynamic in ventral furrow cells.

(a) Utrophin::GFP (Utr::GFP) labels F-actin throughout the cell, including medioapical, junctional, and subapical structures. Images are from fixed Utr::GFP embryo and stained with phalloidin to label F-actin. Scale bar is 5 m. (b) Orthogonal view/cross-section of same embryo from a. Scale bar is 10 m. (c) Total F-actin levels decrease throughout apical constriction. Quantifications are averages from embryos (n = 4 embryos, at least 35 cells per embryo) expressing Utr::GFP and Myo::ChFP. Area was quantified from sub-apical F-actin images. Total apical F-actin and Myo-II levels were quantified from apical z-projections. Values for individual cells were averaged within an embryo and then averaged across multiple embryos. (d) Quantification of total F-actin levels and area in individual cells from a live embryo expressing Utr::GFP and Gap43::ChFP. F-actin levels during contractile pulses (highlights) are heterogeneous, and can increase (yellow), stabilize (blue), or decrease (magenta). F-actin levels most often increase or remain stable during a contractile pulse. (e) Graph of average behavior of area and F-actin during contractile pulses (n = 44 pulses) from embryo in d. Values are normalized to highest and lowest values during individual pulses. Error bars are standard deviation. On average, F-actin levels are briefly stabilized during contractile pulses. (f) Schematic illustrating the calculation of the time resolved cross-correlation function. Cross-correlation is calculated between constriction rate and myosin rate for various temporal shifts (ΔT). A peak cross-correlation at ΔT∼0 indicates a significant correlation with the value of ΔT indicating the time lag between the two signals.