Figure 1. Cell rearrangements during zebrafish gastrulation. (a,c,e) DIC images of wild-type embryos at 30% epiboly (a), 60% epiboly or shield stage (c) and bud stage (e). Lateral views with the animal pole to the top and dorsal (c,e) to the right. Scale bar=250 m. (b,d,f) Schematic views of the main cellular rearrangements at the stages depicted in (a,c,e). (b) Epiboly. Radial intercalations flatten and expand the blastodermal tissue. (d) Internalization. Hypoblast cells move towards the animal pole in a direction opposite to that of the overlying epiblast, EVL and forerunner cells. (e) Convergent extension. Dorsal view of cells undergoing medio-lateral intercalations, which lead to the extension of the tissue in the anterior–posterior direction. The orientations in (b, d, f) correspond to those in (a,c,e); (f) shows a dorsal view on the cells instead of a lateral view in (e). In (b,d,f), black dots indicate the cell nuclei. YSL, yolk syncytial layer; EVL, enveloping layer.

Figure 2. A fate map of early gastrula embryo. Modified from Kimmel et al. (1990).

Figure 3. Model for dorsoventral axis formation in zebrafish. See text for details.