Fig. 2. The ZLI forms from cells in the diencephalic alar plate. (A) Strategy to ascertain whether cells in the basal plate contribute to the ZLI. (B-H) The relative positions of labeled cells along the dorsoventral axis of the diencephalon were assessed immediately following DiI injection (relative initial position in B, and C,F) and after 48 hours in culture (relative final position in B, and D,G). DiI was photo-converted to a brown precipitate and analyzed in relation to the ZLI, as marked by Ptc2 expression (E,H). Cells labeled in the ZLI (B, black circles) and elsewhere in the diencephalon (B, gray circles) remained at the same relative dorsoventral position during the experimental period. (C-E) DiI injected in the basal plate was never observed in the ZLI (n=24). (F-H) Labeling in the ZLI observed after focal injection of DiI into the alar plate (n=11).