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Fig. 9 Multiple retinal cell types engage in retinoic acid signaling in response to retinoic acid treatment during retinal differentiation. (A to E) Embryos carrying the RARE-YFP transgene were treated with 0.3 μM RA at 48 hpf, and at 75 hpf were processed as 5 μm cryosections for indirect immunofluorescence with an anti-GFP antibody (green color in all panels) and the following markers (red color in all panels): zpr1 (stains red and green-sensitive cones; (A), zpr3 (stains rods and green cones; (B), zpr2 (stains RPE; C), zrf1 (stains Müller glia; D), and anti-PKC (stains rod bipolar cells; E). Dorsal is up in all panels; boxed regions in each panel appear at higher magnification in the insets. All types of retinal cells examined are capable of responding directly to RA by activating the RARE-YFP transgene (doubly-labeled cells in each panel; arrowheads; colabeling within the limit of resolution of our objective lens = 1.4 μm), although not all cells of each type respond (singly-labeled cells; arrows). (F) Embryos carrying the RARE-YFP transgene were treated with 0.3 μM RA at 72 hpf, and were fixed at 75 hpf as 5 μm cryosections for indirect immunofluorescence with the anti-GFP antibody. Widespread transgene expression indicates rapid response to RA. Bar = 50 μm.