Figure 7: Rotation is specifically required to maintain tissue-level actin alignment during early stages.

(a) Late expression of Abi RNAi using mirror-Gal4 (mirr-Gal4) does not affect the basal actin pattern at stage six but by stage eight, the leading edge actin network is eliminated without altering basal actin bundle alignment. One copy of SCAR was also removed in this genetic background. Laser-scanning confocal images. (b) Kymographs of rotating egg chambers where the follicle cell membranes are marked with Indy GFP. The slopes of the indivdual lines indicate the rate at which the cell membranes are moving over time. After 20 min, the samples were treated with either with the Arp2/3 inhibitor CK-666 or the control molecule CK-689 (asterisk). The inhibitor stops follicle cell migration within 1 h. n=5 for each condition. Spinning disk confocal images. (c) Representative images of the basal actin bundle alignment after one hour of drug treatment during each of the given stages with the corresponding order parameter value (S). Yellow lines represent the mean orientation of the actin bundles in each cell. Spinning disk confocal images. (d) Graph showing the average order parameter for the basal actin bundles for stages one through eight after 1 h of drug treatment. The value is reduced in inhibitor-treated samples compared with controls only during early stages. During stages six to eight, the two values are indistinguishable. For stage 1 n≥2, stages 2–3 n≥6, stages 4–7 n≥10, stage 8 n≥4 (exact n values are in Supplementary Table 2). Data points represent mean±s.e.m. The t-test compares the difference between the basal actin bundle order parameter in control and inhibitor-treated samples at each stage (**P=0.009, ***P=7.90 × 10⁻⁵). When stars are not shown, there was no statistically significant difference observed. (e) Representative images of basement membrane polarization (Col IV, Vkg GFP) with the corresponding order parameter value. Spinning disk confocal images. (f) Overlay of graphs from d and Supplementary Fig. S5e showing that the period when rotation becomes dispensable for the tissue-level actin alignment coincides with the period of highest basement membrane polarization. Scale bars, 10 μm.