Fig. 2. Observations of two clones expanding throughout embryogenesis. (A) Dorsal view of an embryo at 20 hpf. Two elongated progenitor cells are seen, one on each side of the embryonic midline. Scale bar: 20 µm. (B) Dorsal view of the same specimen at 28 hpf. Both cells have divided. On the left-hand side daughter cells remain close to the ventricular zone, whereas on the other side two cells are seen further from the ventricular surface, suggesting they will become neurons. Scale bar: 20 µm. (C) Lateral view of cells on the left-hand side of the midline at 38 hpf. Four cells are now visible, suggesting that both cells seen at 28 hpf divided once more. The ventricular surface is indicated by a broken line. Scale bar: 20 µm. (D) Lateral view of cells on the right-hand side of the midline at 38 hpf. These two cells have moved further from the ventricular zone, indicating a neuronal phenotype. The ventricular surface is indicated by a broken line. Scale bar: 20 µm. (E) Confocal projection of the specimen fixed at 48 hpf. There are four cells (see inset) on the left side of the embryonic midline and two on the right, showing that none of the cells observed at 38 hpf divided. Transverse section with dorsal to the top. Scale bar: 50 µm. Arrows in inset indicate two cell bodies very close together. (F) Same section as in E but revealing underlying HuC-GFP expression. All dextran-labelled cells express HuC-GFP, indicating they are neurons. The ventricular surface is indicated by a broken line. Scale bar: 50 µm. (G) Magnified image of four cells on the left side of the midline showing all four co-express HuC-GFP and dextran. (H) Same image as in G showing the GFP channel alone.