Fig. 5. Intermediate stages of notochord formation in dorsal anterior quadrants. (A-D) A dorsal anterior quadrant stained with Bodipy and imaged at (A)10 minutes, (B) 30 minutes, (C) 50 minutes, and (D) 70 minutes after completion of the final notochord cell division. Posterior is left in all panels. The larger cells to the right are anterior endoderm. The darker cells lining the edge are epidermal cells. The posterior-most notochord cells constrict their apices and many enter the interior of the notochord plate as they do during blastopore closure in whole embryos (arrows). But those that remain at the boundary never elongate or intercalate perpendicular to the AP axis. Scale bar, 20 µm. (E,F) Posterior (E) and anterior (F) cross-sectional views of dorsal anterior quadrants at approximately 3 hours PFD, when control embryos have completed formation of a cylindrical rod. Dorsal is up in both views. Arrows indicate the boundary between the neural plate and lateral epidermal cells. Note the downward curvature of the neural plate, which has normally closed to form a tube by this stage.