Apical nuclear migration in the hindbrain is faster and more directed than in the retina. (A) Neuroepithelial nuclei move stochastically in G1 and S and occupy diverse apicobasal positions. In G2 (highlighted in purple in the schematic and all montages), nuclei migrate to the apical side where cells divide. (B) Schematic of hindbrain and retinal neuroepithelia in the zebrafish embryo. Hindbrain is shown in green and retina in blue in all figures. (B’) Morphology of hindbrain at 18 hpf and retina at 24 hpf. Nuclear staining: DAPI (cyan); actin staining: phalloidin (gray); mitotic cells: pH3 (magenta). Solid lines mark the apical and dashed lines mark the basal tissue surface in all figures. (C) Example of apical nuclear migration in maximum projection of hindbrain and retinal cells, imaged with LSFM (Video 1). Staining: mKate2-PCNA labels nuclei (cyan), GFP-UtrophinCH labels actin (gray). (D) Apical migration trajectories. Start: 0 min = entry in G2. Finish: onset of cell rounding (nuclear position at cell rounding = 0 µm from the apical side). (E) Starting positions of hindbrain and retinal nuclei shown as mean ± SD. Variances comparison: P = 0.0485, Levene’s test. (F) Directionality ratios shown as mean of all tracks; error bars represent SD. Hindbrain = 0.63 ± 0.06, Retina = 0.36 ± 0.07. (G) Pooled instantaneous velocity distributions in hindbrain and retina. P < 0.0001, Mann-Whitney test. Scale bars: 20 µm (B’), 5 µm (C).