Fig. 2

Fig. 2 Glossopharyngeal (nIX)-like motor neurons are found in r6 in trilobite mutant embryos. All panels show dorsal views with anterior to the left. Double arrows in (B) and (D) denote the midline. (A) In a 48-HPF wild-type sibling, the zn5 antibody labels abducens (nVI) motor neurons medially in r5 and r6 (surrounding the asterisk) and the nIX motor neurons medially in r7 (arrowhead). (B) In a tri mutant, the nVI motor neurons (asterisk) develop normally in r5 and r6. However, the nIX motor neurons are absent from r7. Other zn5-labeled cell types such as the hindbrain commissural neurons (white arrows) and other uncharacterized cells (black arrow) develop in a similar fashion in wild-type and mutant embryos. (C) In a 48-HPF wild-type sibling, DiI application in the first gill arch retrogradely labels nIX neuron cell bodies in r7 (arrowhead). (D) By contrast, in a tri mutant, DiI application in the first gill arch labels nIX cell bodies exclusively in r6 (arrowhead). The out-of-focus labeled cells in r7 (asterisk) are seen in some wild-type and mutant embryos and appear to be very anteriorly located nX neurons that contain DiI, due to inadvertent labeling of nX axons at the DiI injection site. Scale bar, 100 (A, B) and 50 μm (C, D).