Fig. 2. Fate mapping in Krox20-null embryos. Reporter gene expression was assayed by X-gal staining in Krox20^lacZ/lacZ (A,C), Krox20^lacZ/Cre R26R (B,D,F) and Krox20^Cre/+ R26R (H) embryos and by AP staining in Krox20^lacZ/Cre Z/AP (E) and Krox20^Cre/+ Z/AP (G) embryos of the indicated stages. (A-E,G) Flat-mounted hindbrains with rostral towards the top; (F,H) Parasagittal sections of the hindbrain region with rostral towards the left. In B, expression from the Krox20lacZ allele and from the R26R reporter are superimposed in r5. In C, labelled neural crest (nc) cells that migrate rostrally and caudally to r5 have not been totally removed. In D, note that r3 blue cells are localised both rostral and caudal to the r2/r4 boundary (visible on the right side). In G, note that an unstained territory corresponding to r4 is present but is not observed on the picture because the rhombomeres are not perfectly perpendicular to the AP axis at this stage.