Figure 8

Summary of the present results. Schematics showing growing cerebellofugal (CF) axons in open book preparations of the rat hindbrain. (A) At embryonic day (E)13, CF axons extend circumferentially and have not arrived at the ventral midline floor plate, while Robo1 and Robo2 immunoreactivities are largely confined to the longitudinal axons. (B) At E14, CF axons reach the floor plate. At this stage, immunoreactivity for Robo1 and 2 can be detected for CF axons in the midline region. (C) At E16, CF axons extend longitudinally but weak or no expression of Robo1, Robo2 or Rig-1 can be detected on the post-crossing portion of CF axons. In the Rig-1 mutant, CF axons fail to reach the midline and extend longitudinally on the ipsilateral side. Circles represent Robo1/2 mRNA expression, arrows CF axon trajectories, green lines Rig-1, and purple lines Robo1/2. The yellow strip represents distribution of a presumptive favourable cue. In Robo1/2 double knockout mice, many CF axons stall at the floor plate. mRNA expression has not been tested at E16. E represents embryonic day in rat.