Fig. 2. In space cadet mutants, a subset of hindbrain commissures and the Mauthner axon cap are affected. Low magnification, dorsal views of the head of 120 hpf wild-type (A) and space cadet larvae (B) stained with the neurofilament antibody 3A10. All major trajectories appear unaffected in space cadet mutants. (C) In wild-type larvae, higher magnification reveals two prominent commissures in rhombomere 3 (arrows), the paired Mauthner cells (labeled M) with the characteristic axon cap at the initial segment of the axon (arrowheads) and a series of seven ladder-like commissural tracts in the caudal hindbrain (labeled 1-7). (D) In space cadet mutants the two prominent commissures in rhombomere 3 are strongly diminished or absent and the axon cap structure is not detectable. The ladder-like commissures in the caudal hindbrain appear less organized (black and white asterisks) and the caudal most commissure is missing in 35% of the space cadet larvae (red arrow). (E) High magnification view of the two rhombomere 3 commissures (arrows) and the Mauthner soma with the surrounding axon cap (arrowheads). (F) In space cadet mutants both commissures and the axon cap are strongly reduced. Dorsal view on the hindbrain of wild-type (G) and space cadet larvae (H), in which reticulospinal neurons (arrows) were retrogradely labeled (see also Table 1). Similarly, analysis of commissures in the midbrain revealed no difference between wild-type (I) and space cadet mutant larvae (J).
