Figure 8

Schematic summaries of axon guidance errors and role of repulsion in cranial motor axon pathfinding. (A) Schematic diagram of chick hindbrain with grey axons on control (right) representing correct trajectories, away from the floor plate towards the dorsal exit points (grey ellipses). On the left side (pathfinding errors) blue axons represent axon guidance errors induced by loss of ROCK or MLCK function in vitro and loss of RhoA or MRLC function in vivo. (B-D) Schematic diagrams showing operation of repulsive mechanisms during BM cranial motor axon pathfinding in even and odd-numbered rhombomeres during (B) initial polarisation and outgrowth, (C) onward growth and suppression of ectopic branching/turning, and (D) roof plate repulsion (especially via MLCK and myosin II), which hems in axon trajectories dorsally and ensures correct axon turning towards exit points. EP, exit point; FP, floor plate; RP, roof plate.