Fig. 6. space cadet mutant larvae display retinal ganglion cell (RGC) axons pathfinding defects. The RGC layer in wild-type and space cadet larvae was injected with DiI to visualize RGC axon trajectories. (A) All wild-type RGC axons crossed the midline (broken line) and projected to the contralateral optic tectum (cot). (B) space cadet RGC axons projected aberrantly to the ipsilateral optic tectum (iot) or stalled around the midline (arrow, C). (D,E) Histological sections of 120 hpf wild-type (D) and space cadet (E) larvae show that retinal organization as well as cellular morphology are unaffected in space cadet mutants (le, lens; inl, inner nuclear layer; ipl, inner plexiform layer; on, optic nerve; pe, pigment epithelium; prl, photoreceptor cell layer; rgc, retinal ganglion cell layer. Immunostaining of wild-type (F) and space cadet larvae (G) with zn-5 antibody at 50 hpf. The zn-5 antiserum stains the RGC somata and axons. In a small fraction of space cadet mutants, the optic nerve, after exiting the eye (arrow), is markedly thinner when compared with wild-type eyes.