Fig. 1

Facial (nVII) motor neurons are found aberrantly in r4 in trilobite mutants. All panels show dorsal views of the hindbrain with anterior to the left. Double arrows in (B), (D), and (F) denote the midline. (C, D) Composite confocal images of embryos; identify GFP-expressing motor neurons in the fluorescein channel and zn5-labeled commissural neurons and axons in the rhodamine channel. (A) In a 48-HPF wild-type sibling, the islet antibody labels the trigeminal motor neurons (nV) in r2 and r3, the facial motor neurons (nVII) in r6 and r7 (arrows), the glossopharyngeal motor neurons (nIX) in r7 (arrowhead), and the vagal motor neurons (nX) in the caudal hindbrain (chb). The strongly labeled, medially located cells in r5 and r6 surrounding the asterisk are the abducens motor neurons (nVI). (B) In a tri mutant, the nV, nVI, and nX neurons are found in the same locations as in wild-type siblings. A large number of islet-labeled cells are found in r4 (arrow), corresponding to nVII neurons. The nIX neurons in r7 are absent. (C) In a 48-HPF wild-type sibling, the zn5 antibody labels commissural axons at rhombomere boundaries in a characteristic fashion and confirms that the GFP-expressing nVII neurons (arrows) are located in r6 and r7. (D) In a tri mutant, zn5 labeling confirms that nVII neurons (arrow) are located in r4. (E) In a 36-HPF wild-type sibling, application of the lipophilic dye, DiI, to the hyoid arch retrogradely labels nVII cell bodies in r6 and r7 (arrows). (F) By contrast, in a tri mutant, DiI application in the hyoid arch retrogradely labels nVII cell bodies in r4 exclusively (arrow). oto, otocyst. Scale bar, 100 (A–D) and 50 μm (E, F).