Sdk localization to vertices and cell contacts is dynamic. (Refers to Video 4.) (A–B′) Dynamics of Sdk::GFP localization relative to MyoII (A and A′) and F-actin (B and B′). (A and B) Upper panels: Snapshots from a video at 28 h APF. (A′ and B′) Lower panels: Kymographs of the contacts shown above. Note increased Sdk::GFP accumulation at vertices during contraction and decreased accumulation and dispersal along LC–LC contacts during expansion. (C) Trace of Sdk::GFP signal intensity at vertices relative to contact length in a single LC–LC contact. Sdk::GFP intensity increases as length decreases and vice versa. (D) Correlation between Sdk::GFP intensity and contact length. r = −0.68, P < 0.0001. (E) Schematics of contact length fluctuations and measurement scheme of Sdk::GFP levels relative to the fluctuations in contact length. A, amplitude. (F–J) The intensity values of Sdk::GFP between the different phases of contact length fluctuations were compared using Wilcoxon tests. Sdk::GFP is higher in shorter contacts with the largest difference in intensities when comparing late expansion versus late contraction. *, P < 0.05; **, P < 0.01; ***, P < 0.001. Scale bar, 5 μm.