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UV cone photoreceptor ablation by prodrug application to transgenic fish. Fish were engineered with inducible cell ablation transgenes expressed in UV cone photoreceptors, Tg(SWS1:Gal4-VP16)ua3016;Tg(UAS-E1b:NfsB-mCherry)c264 (“UV:nfsb-mCherry”). Fish treated with a vehicle control DMSO solution maintained nitroreductase- (nfsb-) mCherry expression in UV cones and cell death was not induced (A, A′). Siblings of these fish, treated with prodrug metronidazole (MTZ) for 48 hrs, lost the mCherry fluorescence due to ablation of the targeted UV cones (B, B′). Note the red fluorescence in panels B and B′ is auto-fluorescence due to a longer exposure compared to panel A. Quantification of UV cones in these cryosections after treatment with the prodrug MTZ (C) revealed a significant decrease in the number of cones expressing mCherry fluorescence in the ONL compared to vehicle-treated controls (***p<0.0001; DMSO treated n = 10, MTZ treated n = 8). Similar observations were made on flat-mounted retina (D,E) wherein the UV cones expressing nfsb-mCherry decreased in abundance relative to the number of UV cones expressing GFP (F, **p<0.001; n = 9 DMSO-treated, n = 10 MTZ-treated) or when considering the absolute density of all UV cones per unit area (G, **p<0.001). Scale bar = 50 µm in A,B and 100 µm in D,E.
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