Wallerian Degeneration and Clearance of Olfactory Receptor Neuron Axons following Drosophila Antennal Transection.

Neurons extend their axons and dendrites over long distances and rely on evolutionarily conserved mechanisms to maintain the cellular structure and function of neurites at a distance from their cell body. Neurites that lose connection with their cell body following damage or stressors to their cytoskeleton undergo a programmed self-destruction process akin to apoptosis but using different cellular machinery, termed Wallerian degeneration. While first described for vertebrate axons by Augustus Waller in 1850, key discoveries of the enzymes that regulate Wallerian degeneration were made through forward genetic screens in Drosophila melanogaster Powerful techniques for genetic manipulation and visualization of single neurons combined with simple methods for introducing axotomy (neuron severing) to certain neuron types in Drosophila have enabled the discovery and study of the cellular machinery responsible for Wallerian degeneration, in addition to mechanisms that enable clearance of the resulting debris. This protocol describes how to study the degeneration and clearance of axons from olfactory receptor neurons (ORNs). These peripheral neurons reside in the antennae and project axons to olfactory glomeruli of the anterior brain. Simple and nonlethal removal of antennae from adult flies causes axotomy of ORNs, and the fate of the injured axons can be readily visualized in a whole-mount dissected brain. This assay takes advantage of well-characterized genetic methods to robustly and specifically label subsets of ORNs. This method of neurite labeling and axotomy was the first axon injury paradigm to be developed in flies and is still regularly used due to its simplicity to perform, dissect, image, and analyze.