Fig 2. Blue cone photoreceptors are efficiently ablated upon addition of prodrug.

(A-C) Prior to treatment with prodrug metronidazole (MTZ) most blue cones (cyan) express the nfsb-mCherry transgene (magenta); some exceptions are noted (dotted lined circles). Wholemount retinae labelled with antisense riboprobes against sws2 blue opsin and against mCherry viewed en face (tangential plane). 78±2% of blue cones express the nfsb-mCherry transgene, considering all 1430±60 blue cones across the entire retina of 7dfp larvae (n = 4), the age at which they begin to receive MTZ in our ablation paradigm. D-K. Retinal sections of larval zebrafish expressing the transgenes Tg[sws2:KalTA4; UAS:nfsb-mCherry-KalTA4] such that blue cones contain the nitroreductase-mCherry fusion protein (pseudocoloured magenta). MTZ was applied via bath treatment for 24 hours beginning at 7 days post-fertilization (dpf); the end of this 24 hour period is denoted in the text and figures as zero hours since the end of drug treatment. Top row: Blue cones are intact in retinal sections of transgenic larvae treated with the vehicle control (DMSO, applied at 7 dpf; time 0h = 8dpf). Bottom row: Blue cones are ablated, as shown in retinal sections of transgenic larvae treated with the prodrug. A decrease in the number of mCherry-positive blue cones (magenta) is apparent through 48 hours post ablation, followed by observation of mCherry-fluorescing blue cones at the ciliary marginal zone (panels G & H). Auto-fluorescence is included for spatial reference (green). L. Blue cones were reduced in abundance four-fold after prodrug MTZ treatment (red bars) relative to vehicle control (DMSO; grey bars). Abundance of cones in the peripheral retina is represented by lighter grey or red bars. Blue cones were gradually added to the periphery (light red bars) on the days following MTZ. Quantification considered cones in the peripheral retina and mature retina (⌘ indicates p<0.0001 when comparing blue cone abundance in mature retina treated with MTZ relative to DMSO, and p<0.05 when comparing peripheral retina treated with MTZ relative to DMSO; ❖ denotes significant difference (p<0.0001) when comparing blue cones in mature retina with MTZ relative to DMSO, but peripheral blue cone abundance is not significantly different between treatments. n≥5 fish for each treatment). Scale bars are 50 μm.