Astrocyte-dependent local neurite pruning in Beat-Va neurons

Developmental neuronal remodeling is extensive and mechanistically diverse across the nervous system. We sought to identify Drosophila pupal neurons that underwent mechanistically new types of neuronal remodeling and describe remodeling Beat-Va_M and Beat-Va_L neurons. We show that Beat-Va_M neurons produce highly branched neurites in the CNS during larval stages that undergo extensive local pruning. Surprisingly, although the ecdysone receptor (EcR) is essential for pruning in all other cell types studied, Beat-Va_M neurons remodel their branches extensively despite cell autonomous blockade EcR or caspase signaling. Proper execution of local remodeling in Beat-Va_M neurons instead depends on extrinsic signaling from astrocytes converging with intrinsic and less dominant EcR-regulated mechanisms. In contrast, Beat-Va_L neurons undergo steroid hormone–dependent, apoptotic cell death, which we show relies on the segment-specific expression of the Hox gene Abd-B. Our work provides new cell types 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.