Epithelial cell layers within the larval zebrafish epidermis exhibit distinct morphological wound closure mechanisms. (a) Time-lapse images of a representative 2.5–3-dpf zebrafish larva at the indicated times after UV laser–induced injury. (a, top) Transgenic Tg(krt4:AKT-PH-GFP) expression of AKT-PH-GFP driven in the suprabasal cell layer (green) is observed simultaneously with mosaic AKT-PH-mKate2 in underlying basal epidermal cells (4–8-cell-stage mRNA injection; red) after puncture wounding in hypotonic E3 medium. Basal cells form lamellipodia and translocate collectively toward the wound, whereas the suprabasal cells translocate and elongate without visible lamellipodia. Note that basal cells at the margin can protrude across the wound opening (yellow arrow), whereas suprabasal cells at the margin align to form a smooth wound edge indicative of contractile “purse string” closure (white arrow). Basal and suprabasal cells maintain a largely consistent proximity; representative center of mass tracks for basal (yellow) and suprabasal (white) cells are shown (10’, top right panel). Bars, 50 µm. (a, bottom) Enlargement of a region in the top panel; basal cell (yellow x) and neighboring suprabasal cell (white x) correspond to upper tracks in top right panel. Bars, 25 µm. All images are from a partial z projection to capture an individual epidermal bilayer. See Video 4. (b) Representative images of a 2.5–3-dpf zebrafish larva mosaically expressing GFP under the control of a basal cell–specific ΔNp63 promoter, immersed in hypotonic bathing solutions shown at indicated times after UV laser cut injury. Broken white line, position of wound. Broken yellow lines, outlines of representative lamellipodial protrusions. Bars, 25 µm.