Movie 1

The onset of dorsal convergence. DIC time-lapse imaging of wild-type lateral hypoblast/mesendodermal cells located 90° from the notochord and near the embryo equator as shown in Fig. 2A (15 min time-lapse/30 s imaging intervals). Anterior is to the top and dorsal to the right. At the beginning of imaging, the embryo is at approximately the 75% epiboly stage. The cells initially migrate anteriorly and then make an abrupt right turn toward the dorsal body axis.