Ectopic expression of Toddler in toddler−/− embryos according to the schematic representation of embryos at 75% epiboly (top). Animal pole source: transplantation of Toddler-overexpressing cells to the animal pole of sphere stage toddler−/− embryos; ubiquitous expression: injection of 2 pg of toddler mRNA (rescuing concentration) into one-cell stage toddler−/− embryos; marginal source: injection of 10 pg of toddler mRNA into the YSL of 1k-cell stage toddler−/− embryos. Toddler (red); Dextran control (gray). Mesoderm spread was assessed using in situ hybridization for aplnrb (middle; lateral view, dorsal on the right; white line indicates measurement of ventral mesoderm spread) and quantified relative to the average spread in wild-type embryos (bottom). Data are means ± SD. Significance was determined using one-way ANOVA with multiple comparison; ****P < 0.0001; **P < 0.01. Scale bars, 20 μm.