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Fig. S1 Further evidence that inhibition of GSK3β blocks retinal differentiation and maintains proliferative progenitors. A pulse of BrdU provided 2 h prior to fixation at 72 hpf of fish treated with DMSO starting at 12 hpf shows the progenitors at the CMZ are actively moving through S-phase, while at the back of the retina zpr3 labels the rod photoreceptors (A). Treatment with 2.5 µM 1-azakenpaullone beginning at 12 hpf prevents rod differentiation and BrdU-positive cells are found throughout the retina (B). Treatment with 1-azakenpaullone beginning at 24 or 36 hpf allows some rods to differentiate, though there are still expanded pools of proliferating progenitors (C, D). Fish treated with 1-azakenpaullone beginning at 24 hpf also have expanded PCNA-positive domains, loss of calretinin-positive neurons, loss of GFP-positive Müller glia, and loss of zpr-1 labeled double cones (E, F). Inhibition of GSK3β with a 1 h treatment of 0.3 M LiCl at 48 hpf shows effects on retinal development similar to treatment with 1-azakenpaullone, with a reduced number of calretinin-positive neurons and an expanded CMZ (PCNA-labeled) compared with controls treated with 0.3 M NaCl (G,H). Scale bar.