Rx1 morphants but not rx2 morphants exhibit significant changes in retinal progenitor proliferation. (A–H) Retinal cryosections stained with anti-PH3, a marker for cells in M-phase, from embryos fixed at 25 hpf (A, B), 34 hpf (C, D), 53 hpf (E, F), and 72 hpf (G, H), injected with control MOs (A, C, E, G) or rx1-depleting MOs (B, D, F, H). Staining is markedly reduced in the rx1 morphants at the early times, but increased at the later times; arrow in D indicates disorganized mitotic cells that were occasionally observed in the morphants. I. Average numbers of PH3-positive cells as a function of treatment and time of assessment. Significant differences were evident following rx1 depletion for all times evaluated (***p < 0.001) but rx2 depletion caused no changes. Scale bar = 50 μm; error bars indicate ± 1 SD.