Fig. 1. Representative frames (A-C) from a movie of a cultured 5.5 dpc embryo (see Movie 1 at http://dev.biologists.org/supplemental/). (D) Drawing depicting the orientation of the embryo. The embryo was imaged every 15 minutes with phase-contrast and fluorescence optics. Time from the start of imaging is indicated in hours at the bottom right of each frame. EGFP fluorescence (green) marks the anterior visceral endoderm (AVE). The embryo develops normally and the AVE moves unilaterally to the extra-embryonic ectoderm in approximately 4 hours. It does not move beyond the epiblast for the remainder of the culture period. A, prospective anterior; P, prospective posterior. Scale bar in A: 50 µm for A-D.