Study of Axonal Injury and Degeneration in Drosophila

A fundamental feature of nervous systems is a highly specified synaptic connectivity between cells and the ability to adaptively change this connectivity through plasticity mechanisms. Plasticity mechanisms are highly relevant for responding to nervous system damage, and studies using nervous system injury paradigms in Drosophila (as well as other model organisms) have revealed conserved molecular pathways that are triggered by axon damage. Simple assays that introduce injuries to axons in either adult flies or larvae have proven to be particularly powerful for uncovering mechanisms of axonal degeneration and clearance. They have also been used to reveal requirements for regrowth of axons and dendrites, as well as signaling pathways that regulate cellular responses to nerve injury. Here we review commonly used and simple to carry out techniques that enable experimenters to study responses to axonal damage in either adult flies (following antennal transection) or larvae (following nerve crush to segmental nerves). Because axons and dendrites in the larval peripheral nervous system can be readily visualized through the translucent cuticle, another versatile method to probe injury responses is to focus high-energy laser light to a small and specific location in the animal. We therefore discuss a method for immobilizing intact larvae for imaging through the cuticle to carry out injury by pulse dye laser, which can be used to generate many different kinds of injuries and directed ablations within intact larvae. These techniques, combined with powerful genetic tools in Drosophila, make the fruit fly an excellent model system for studying the effects of injury and the mechanisms of axon degeneration, synapse plasticity, and immune response.