Fig. 3.

Basal tension is higher than apical tension outside folds. a–h Apical (a, c) and basal (e, g) views and cross-sectional images (b, d, f, h) of wing imaginal discs of 72 h AEL larvae co-expressing Utr-GFP and Sqh-cherry to visualize F-actin and Myosin regulatory light chain, respectively. The apical and basal sides of the columnar cells are indicated in the cross sections. In a–d the apical side of the columnar cells was mounted closer to the coverslip, whereas in e–h the basal side was mounted closer to the coverslip. Scale bars are 10 μm. i–l Wing imaginal disc pouch cells of 72 h AEL larvae expressing Indy-GFP before and 20 s after ablation of a single cell edge at the apical (i, j) or basal (k, l) side of the pouch epithelium. Scale bars are 10 μm. Red dots mark vertices of ablated cell edges. m Average recoil velocity of the two vertices at the end of an ablated cell edge within 0.25 s after ablation in the pouch region for wing imaginal discs of the indicated times AEL. Recoil velocities are shown for ablations of apical and basal cell edges, as indicated. Mean and s.e.m. are shown (n = 15 cuts) (***p < 0.001, Student’s t-test)