ATP reconstitutes basal cell migration and epithelial sheet movement in the absence of a transepithelial osmotic gradient. (a) Representative time-lapse images of zebrafish larvae exhibiting mosaic plasma membrane AKT-PH-mKate2 labeling of predominately basal cells (4–8-cell-stage mRNA injection). Larvae were subjected to UV-laser-cut wounding in isotonic mounting agarose. After 10 min of isotonic preincubation (red time indices), a bolus of isotonic solution ± 5 mM ATP was added to the imaging dish. Yellow x, representative morphological response after addition of isotonic solution ± 5 mM ATP. Note that formation of AKT-PH-mKate2–rich membrane protrusions (yellow broken line) after iso-iso/ATP, but not iso-iso shifting. The same representative iso-iso control and data set were used in Fig. S5 a. See also Video 9. Bars: (main panels) 50 µm; (inset) 10 µm. (b) Global PIV analysis of the indicated number of larvae exhibiting ubiquitous plasma membrane labeling (one-cell stage AKT-PH-mKate2 mRNA yolk injection). Larvae were subjected to UV-laser-cut wounding in isotonic mounting agarose. After 10 min of isotonic incubation, a bolus of isotonic medium ± 5 mM ATP was added to the sample. (c) Proposed circuitry scheme of tissue intrinsic and environmentally triggered branches of the wound response in zebrafish tail fins. Tissue-intrinsic mechanisms include purse-string contraction (not depicted). Environmentally dependent osmotic surveillance through secretion of nucleotides (epithelial cells) and eicosanoids (leukocytes) is depicted.