Fig. 6

Pk1b function is required for facial neuron migration. The disposition of the branchiomotor neurons is visualized using islet1-GFP transgenic embryos, (A, C) viewed by fluorescence microscopy, (B, D) same image merged with bright field (DIC optics), or by confocal microscopy (E–H). The hindbrain is seen in dorsal (A–F) or lateral view (G, H); anterior is to the left in all panels. Rhombomeres (r) 2, r4, and r6 are labeled. (A, B) In wild-type 28 hpf embryos, the facial neurons (VII) have migrated most of the way to r6/7. (C, D) In Pk1b-deficient embryos (injected with Pk1b-MO), the facial neurons do not migrate and are instead found in clusters in r4. (E) In wild-type 40 hpf embryos, facial neuron migration is complete. (F) In 40 hpf Pk1b-deficient embryos, the facial neurons remain in r4. (G) In wild-type 48 hpf embryos, the facial neurons lie in r6/7, and their axons project out of r4 to innervate the second pharyngeal arch. The asterisk marks the axons of the VIIIth nerve/octavolateralis efferent (OLe), which project across the otic vesicle. (H) In Pk1b-deficient embryos, the facial (VII) and OLe (asterisk) axons can be seen to project normally. However, the facial neurons (VII) lie in r4, in an unusually dorsal position. MO: morpholino; V: trigeminal neurons; VII: facial neurons; X: vagal neurons.