Fig. 3. Defects in branchio-motoneuron migration and axonal pathfinding in the hindbrain of Nkx6.1 mutant embryos. Application of DiI to the facial (A,B,E,F,G,H) and trigeminal nerve (C,D) in wild-type (A,C,G) and Nkx6.1 mutant embryos (B,D,E,F,H) at E12.5. While facial branchiomotor (bm) neurons are backlabeled along their entire migratory stream from r4 into dorsal r6 in wild-type embryos (A), most facial bm neurons are clustered close to the ventral midline in r4 and few in the rostral third of r5 in Nkx6.1 mutants (B). No difference in the location of facial visceromotor (vm) neurons is observed between wild-type and Nkx6.1 mutant embryos (A,B). In wild-type embryos, trigeminal motoneurons are found at the trigeminal nerve exit point (C), but scattered between the floor plate and the exit point in Nkx6.1 mutants (D). Note the backlabeling of an additional nerve process in Nkx6.1 mutants (D). DiI application to the facial nerve labeled neurons in r2/r3 (E) and r6/r7 (arrowheads in B,F) in Nkx6.1 mutants, but not in wild-type embryos. Simultaneous application of DiI (red) to the facial and DiA (green) to the glossopharyngeal/vagal nerve shows that neurons, which project through the facial nerve in Nkx6.1 mutants (arrowheads in H), are localized within the territory of the inferior salivatory nucleus (nIS) and nucleus ambiguous (nA). (I,J) Lateral view of E10.5 embryos stained with 2H3 anti-neurofilament antibody. The branching pattern of the cranial nerves does not differ between wild-type (I) and Nkx6.1 mutant embryos (J). (K) Schematic summary of the differences in the position and axonal projections of hindbrain motoneurons between wild-type and Nkx6.1 mutant embryos. Trigeminal (V), facial (VII), vestibuloacoustic (VIII), glossopharyngeal (IX), vagal (X), spinal accessory (XI) and hypoglossal (XII) nerves; branchial arch (BA); otic vesicle (OV).