Fig. 2. Levels of Medea in dorsal nuclei increase sharply at the onset of gastrulation. Optical sections of wild-type (WT) embryos co-stained for Medea (green) and with the DNA dye ToPro3 (red). Dorsal (D) and ventral (V) midline cells from a single embryo are shown as paired images for each stage, with Medea staining alone (top pair) and merged with DNA dye (bottom pair). (A) Most stage 5 embryos have a subcellular distribution of Medea that is indistinguishable between dorsal and ventral cells, but a few (B) show uniform distribution of Medea between the nuclei and cytoplasm within a broad domain of dorsal cells. (C) At the onset of gastrulation, all embryos show strong nuclear accumulation of Medea within a narrow stripe of cells at the dorsal midline.