Mechanisms of Dendrite‐Specific Pruning in Drosophila Sensory Neurons

Abstract

Abstract During animal development, pruning of unwanted or exuberant neurites is essential for the precise wiring of the nervous system. Holometabolous insects, such as the fruit fly Drosophila , undergo complete metamorphosis to replace their larval nervous systems with distinct adult ones. Many neurons in the central and peripheral nervous systems selectively prune away their larval dendrites and/or axons and regenerate their adult‐specific processes. Dendritic arborisation sensory neurons, ddaCs, specifically remove their larval dendrites in response to the steroid moulting hormone ecdysone and however keep their axons intact. Owing to their peripheral location, effectiveness of RNAi knockdown and convenience of single‐cell clonal analysis, ddaC neurons have emerged as an attractive system to dissect the pruning process for a decade. Some important genes and pathways, acting downstream of ecdysone signalling, have been discovered to enrich our understanding of neuronal pruning. Key Concepts Pruning is a mechanism for the refinement and maturation of the nervous system in various organisms including nematode, fruit fly and mammals. ddaC sensory neurons undergo large‐scale dendrite‐specific pruning during early metamorphosis. Ecdysone signalling is the master regulator of dendrite pruning in ddaC neurons. A genetic pathway composed of Sox14 and Mical governs dendrite pruning in ddaC neurons. Epigenetic factors regulate Sox14 expression and dendrite pruning in ddaC neurons. Ubiquitin‐proteasome system (UPS) regulates different types of neurite pruning. Endolysosomal degradation pathway downregulates the cell‐surface molecule Neuroglian (Nrg) to promote dendrite pruning. Phagocytosis regulates fragmentation and clearance of severed dendrites. Caspase is locally activated in the dendrites of ddaC neurons during pruning. Calcium signalling is activated in the dendritic compartments to regulate dendrite pruning.