Rapid degeneration of Drosophila olfactory neurons in Orco mutant maxillary palps

Drosophila melanogaster vinegar flies have two olfactory organs: the antenna and maxillary palp. Olfactory neurons in these tissues respond to odorants via odorant receptors. Insect odorant receptors are heterotetramers of two proteins: an odorant binding OrX subunit and an Odorant Receptor Co-Receptor (Orco). Mutation of Orco disrupts odorant receptor formation, and abolishes olfactory responses. Some antennal olfactory neurons in Orco mutants have been previously shown to degenerate. Here, we examine if maxillary palp olfactory neurons also degenerate in Orco mutants. We find degeneration occurs both more broadly and more rapidly in Orco mutant maxillary palp olfactory neurons than reported for antennae, with ~60% of all mutant olfactory neurons absent in maxillary palps by 7 days post eclosion. Interestingly, the subset of Orco mutant olfactory neurons that express the Or42a receptor appear resistant to degeneration. These results suggest the maxillary palp might be a suitable model for examining the molecular mechanisms underlying neurodegeneration in sensory neurons.