Fig. 4. Neural crest cell migration at hindbrain and rostral trunk levels. (A) Stage 23 embryo in which cells originating from the caudal hindbrain region are located rostral to the site of injection within the rostral branchial arches; b-d indicate planes of section in B-D, respectively. (B-D) Neural crest cells from the mid hindbrain region have migrated ventrally and rostrally to populate the rostral branchial arches. (E) Late stage 23 embryo labeled at the hindbrain and rostral trunk neural tube level; by stage 23, labeled cells have migrated ventrally towards the caudal presumptive branchial arches. (F) At stage 25, labeled cells from the caudal hindbrain region are located throughout two branchial arches, having completely filled both arches along the dorsoventral axis. (G) Neural crest cells originating from the caudal hindbrain to rostral trunk level migrated ventrally toward the most caudal presumptive arch and migrated dorsocaudally into the dorsal fin. fm, fin mesenchyme; white arrows, final position of labeled cells; yellow circle, initial position of DiI; yellow arrow, direction and distance of migration away from initial site. Scale bar: 200 µm.