Astrocyte-dependent local neurite pruning and Hox gene-mediated cell death in Beat-Va neurons

Neuronal remodeling is extensive and mechanistically diverse across the nervous systems of complex metazoans. To explore circuit refinement mechanisms, we screened for new neuronal subtypes in the Drosophila nervous system that undergo remodeling early in metamorphosis. We find Beat-VaM neurons elaborate a highly branched neurite network during larval stages that undergoes local neurite pruning during early metamorphosis. Surprisingly, Beat-VaM neurons remodel their branches despite blockade of steroid hormone signaling and instead depend on signaling from astrocytes to activate pruning. We show Beat-VaL neurons undergo steroid hormone-dependent cell death in posterior but not anterior abdominal segments. Correct activation of apoptotic cell death relies on segment-specific expression of the hox gene Abd-B, which is capable of activating cell death in any Beat-VaL neuron. Our work provides new model cells in which to study neuronal remodeling, highlights an important role for astrocytes in activating local pruning in Drosophila independent of steroid signaling, and defines a Hox gene-mediated mechanism for segment-specific cell elimination. SummaryLehmann et al. characterize two new populations of neurons that undergo remodeling during Drosophila metamorphosis. Beat-VaM neurons undergo drastic neurite pruning that is largely independent of ecdysone signaling and instead is driven by astrocytes. Beat-VaL neurons undergo Abd-B mediated, caspase driven cell death in a segmentally restricted manner.