Figure 1. Schematic representation of the epiboly progression during early zebrafish development. During epiboly, the blastomeres, migrate toward the vegetal pole to envelope the yolk cell. This morphogenic movement is orchestrated by the coordinate changes in the yolk syncitial layer (YSL) cytoskeleton mainly composed of microtubules and F-actin cables. Parallel microtubule meshwork originating from the yolk syncitial nuclei (YSN) are extending toward the vegetal embryo pole, and participates actively in the epiboly progression. The margin actin-myosin ring formed at 75% epiboly is important for the completion of the epiboly. EVL: enveloping layer; DCL: deep cell layer.