Cell-autonomous requirement of the USP/EcR-B ecdysone receptor for mushroom body neuronal remodeling in Drosophila

Neuronal process remodeling occurs widely in the construction of both inver tebrate and vertebrate nervous systems. During Drosophila metamorphosis, ga mma neurons of the mushroom bodies (MBs), the center for olfactory learning in insects, undergo pruning of larval-specific dendrites and axons followe d by outgrowth of adult-specific processes. To elucidate the underlying mol ecular mechanisms, we conducted a genetic mosaic screen and identified one ultraspiracle (usp) allele defective in larval process pruning. Consistent with the notion that USP forms a heterodimer with the ecdysone receptor (Ec R), we found that the EcR-B1 isoform is specifically expressed in the MB ga mma neurons, and is required for the pruning of larval processes. Surprisin gly, most identified primary EcR/USP targets are dispensable for MB neurona l remodeling. Our study demonstrates cell-autonomous roles for EcR/USP in c ontrolling neuronal remodeling, potentially through novel downstream target s.