Fig. 4.

Hh signaling and Gli1 function are essential for branchiomotor neuron development. Panels A–F and G–O show dorsal and lateral views, respectively, of the hindbrain with anterior to the left. Asterisks in G–O mark the cerebellum. (A) In a 48-hpf wild-type embryo, the nIII, nIV, nV, nVII, and nX motor neurons are found in their characteristic positions. (B–C) In slow muscle-omitted (smu; B) and detour (dtr; C) mutants, GFP-expressing cranial motor neurons are almost completely missing, while the zn5-labeled axons at rhombomere boundaries are unaffected. (D) In a 21-hpf wild-type embryo, nk2.2 is expressed throughout the ventral neural tube at all axial levels. (E–F) In smu (E) and dtr (F) mutants, nk2.2 expression is lost, while krox20 expression in r3 and r5 is unaffected. (G–I) In a 24-hpf wild-type embryo (G), ptc1 is expressed in the ventral hindbrain, while it is expressed diffusely at a reduced level in dtr mutants (I), and not expressed at all in smu mutants (H). (J) In a 30-hpf wild-type embryo, net1a is expressed in the ventral hindbrain and at rhombomere boundaries (arrowhead). (K) In smu mutants, net1a expression is mostly lost, with residual expression in the floor plate (fp). (L) In dtr mutants, net1a expression in the ventral hindbrain is greatly reduced, but expression at rhombomere boundaries (arrowhead) is unaffected. (M–O) In a 21-hpf wild-type embryo (M), gli1 is expressed in the ventral two-thirds of the neural tube, while its expression is greatly reduced in smu mutants (N), and is unaffected in dtr mutants (O). The anterior tip of the notochord (nc) is at the level of r4, and is indicated by arrows.