Fig. 6. Chick FBM neurones reproduce a caudal and lateral migratory pathway characteristic of mouse FBM cells in mouse-chick chimaeras. (A) Schematic of ventral aspect of facial nerve and their projections into the periphery (adapted from Jacob and Guthrie, 2000). The red and green lines indicate the branchiomotor (FBM) axonal projections towards the hyoid nerve and the visceromotor (VMN) axonal projections towards the palatine nerve, respectively. (B-D) Ventral views of flat-mounted HH stage 23-24 hindbrains after retrograde labelling of facial motoneurones. Labelling of FBM and VMN subpopulations after rhodamine-dextran fills of the facial nerve (B) and of the hyoid nerve (C). An arrowhead in C marks the presence of a few neurones in r5, as previously reported (Jacob and Guthrie, 2000). Labelling of FBM neurones after rhodamine-dextran fills of the hyoid nerve in a chimaeric embryo after chick r5/6 were replaced with mouse r5/6 (D). Only a small subpopulation of FBM neurones in r4 migrates laterally (arrowheads in D), whereas the majority of FBM neurones remain either close to the ventral midline or migrate caudally. The arrow in D shows how within the caudal migration cells are oriented caudolaterally. Ba1, first branchial arch; Ba2, second branchial arch; ct, chorda tympani; ep, r4 exit point; fp, floor plate; h, hyoid nerve; Mx, maxilla; P, palatine nerve.
