Fig. 4. Direct observation of an asymmetric division. (A) Single cell at 24 hpf labelled with dextran is shown in red. The cell has retracted its process from the pial surface, indicating that it is about to divide at the ventricular surface. Three non-related neurons expressing HuC-GFP are seen at the pial surface. Arrowhead points to ventricular surface. Scale bar: 10 µm. (B-D) Lateral views of the same specimen as in A. Anterior is to the right and dorsal to the top. Arrowheads point to ventricular surface throughout. All scale bars: 20 µm. (B) Two cells are present at 36 hpf following the earlier division. One has a neuronal morphology and one a radial morphology, which may indicate that it is still in the cell cycle. (C) Three neurons with axonal processes are present at 48 hpf, showing that the radial progenitor cell divided again. (D) Same view as C but with brightfield overlay.