Fig. 3. Summary plots of nuclei positions in time-lapse 1. (A,B) Otx-positive and negative nuclei form coherent groups at the end (B, 24-somite stage) and at the beginning (A, 5-somite stage) of the time-lapse. The lines in B indicate the mhb on the basis of the posterior Otx2 boundary. (C,D) Upon shifting the Otx-positive/Otx-negative interface artificially by about one cell row anterior at the five-somite stage (C), the sharp interface of the two cell populations is lost at the 24-somite stage (D). The bracket indicates the zone of overlap. (E,F) Example of cell behavior at an arbitrary boundary in the middle of the tectum. Even though the cell populations are well separated at the five-somite stage (E), they show a marked zone of overlap at the 24-somite stage (F). (G,H) Plots showing the relative movement of cells with respect to their interface at the mhb from the beginning to the end of the time-lapse, expressed in rows (y-axis). The arrows indicate the position at the start of the time-lapse to the position at the end. Diamonds stand for cells that do not change their row position. Upper light-gray arrows represent Otx-positive cells, lower dark-gray arrows represent Otx-negative cells. Each daughter cell is treated as a separate cell (x-axis). (G) Cell movement over 10 hours. (H) Cell movement over 12 hours. Notice that cells move 10 and more cell rows away from their common interface. Most non-moving cells are found in the first cell rows (both Otx positive and Otx negative). Otx-positive nuclei are light grey, Otx-negative nuclei dark grey. Broken lines show the midline. (A-F) Dorsal views, anterior is towards the top, units are in µm in A-F. For ease of understanding, only a subset (leaving out the most dorsal and ventral planes) of the data of time-lapse 1 is shown in A-D. The plots are 2D projections along the z-axis and nuclei sizes are not drawn to scale.