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Fig. 5 ERT2-GAL4-driven expression is sufficient to generate gain-of-function phenotypes in vivo. (A-O) Embryos from a Ubiquitin::ERT2-GAL4 fish crossed to UAS::GFP-dnCasp9 fish were treated with ethanol (A,B,F,G,K,L) or 0.625 μM 4-OHT (C-E,H-J,M-O) from 50% epiboly to 18 hpf, followed by added treatment with 10 μM HA14-1 for 2 hours. Staining for activated caspase 3 (red channel) and GFP (green channel) reveals a rescue of HA14-1-induced apoptosis by widespread GAL4-induced expression of dominant-negative caspase 9 (compare K,L with M,N, red channel) in embryonic trunk. In embryos with mosaic GAL4 activity (E,J,O, GFP in green channel), the rescue of apoptosis is cell-autonomous to the GFP-dnCasp9-expressing cells (E,J,O, compare non-overlapping green and red). Samples were co-stained with DAPI (A-E, blue channel) to reveal nuclei of all cells. All images are side views of the trunk at 20 hpf.