Localized collapsing cues can steer growth cones without inducing their full collapse.

Collapsing factors are proteins that induce growth cone collapse and paralysis when added in a soluble form to cultured embryonic neurons. Here we examine the responses of growth cones to localized collapsing signals. Temporal retinal ganglion cell growth cones exposed to a localized collapsing stimulus from nasal retinal ganglion cell axons frequently turn smoothly away from the axons without collapsing. Turning is rare on contact with retinal axons that are unable to induce collapse. In a separate series of experiments, dorsal root ganglion growth cones tend to turn away from beads coated with a brain extract enriched for the motility-inhibiting protein collapsin. Many turns are accomplished with filopodial contact alone. Growth cones do not turn away from control beads coated with heat-inactivated collapsin. These results suggest that inhibitory guidance cues can steer growth cones through a localized inhibition of lamellipodial protrusion.