Figure 1

Netrin-1 mutants show cranial motor axon guidance defects. E11.5 mouse hindbrains from wild-type, heterozygous and homozygous Netrin-1 mutants; genotypes as indicated. (A-D) Facial motor neurons in r4 and r5 retrogradely labelled using DiI. Rhombomeres 4 and 5 are numbered in (A) and (B); asterisks indicate r4 exit points. Arrows indicate width of fascicles growing towards exit points. Note increased width and defasiculation of axon bundles in homozygotes, with many separate axon bundles near the exit points. (E,F) Wholemount anti-neurofilament staining of motor neurons in E11.5 mouse hindbrains. Note longitudinal axon fascicle in homozygote (arrow in (F)). (G-I) Motor axon pathfinding defects in DiI-labelled hindbrains of Netrin mutant mice. Yellow arrows indicate boundaries of the floor plate, and white arrows indicate defects. (G) Axon fascicles projecting at an angle rather than crossing the floor plate directly. (H) Axon turning prematurely towards exit point. (I) Fascicle projecting longitudinally within floor plate. fp, floor plate. Scale bar in (H) = 150 μm in (A-D,G-I) and 300 μm in (E,F).