Peripheral glia direct axon guidance across the CNS/PNS transition zone

CNS glia have integral roles in directing axon migration of both vertebrate s and insects. In contrast, very little is known about the roles of PNS gli a in axonal pathfinding. in vertebrates and Drosophila, anatomical evidence shows that peripheral glia prefigure the transition zones through which ax ons migrate into and out of the CNS. Therefore, peripheral glia could guide axons at the transition zone. We used the Drosophila model system to test this hypothesis by ablating peripheral glia early in embryonic neurodevelop ment via targeted overexpression of cell death genes grim and ced-3. The ef fects of peripheral glial loss on sensory and motor neuron development were analyzed. Motor axons initially exit the CNS in abnormal patterns in the a bsence of peripheral glia. However, they must use other cues within the per iphery to find their correct target muscles since early pathfinding errors are largely overcome. When peripheral glia are lost, sensory axons show dis rupted migration as they travel centrally. This is not a result of motor ne uron defects, as determined by motor/sensory double-labeling experiments. W e conclude that peripheral glia prefigure the CNS/PNS transition zone and g uide axons as they traverse this region. (C) 2001 Academic Press.