![]() Pruning proceeds in a stereotypical fashion: Dendrites are first severed at proximal sites close to the cell body between 5 and 10 h after puparium formation (h APF). The sensory class IV dendritic arborization (c4da) neurons completely and specifically prune their long and branched larval dendrites at the onset of the pupal phase, while their axons stay intact (Kuo et al, 2005 Williams & Truman, 2005). In the peripheral nervous system (PNS) of Drosophila, several types of sensory neurons undergo either apoptosis or prune their larval processes in an ecdysone‐dependent manner. In holometabolous insects, the nervous system is remodeled at a large scale during metamorphosis. While the mechanisms of neurite outgrowth and synapse formation have been studied in some detail, comparably little is known about the mechanisms underlying pruning. Pruning is an important developmental mechanism that is used to ensure specificity of neuronal connections, and to remove developmental intermediates (Luo & O'Leary, 2005 Schuldiner & Yaron, 2015). The physiological degeneration of synapses, axons, or dendrites without loss of the parent neuron is known as pruning. Our results shed light on the signaling cascades and epistatic relationships involved in neurite destabilization during dendrite pruning. Finally, PAR‐1 is also required for dendritic thinning, suggesting that microtubule breakdown might precede ensuing plasma membrane alterations. Mammalian PAR‐1 is a known Tau kinase, and genetic interactions suggest that PAR‐1 promotes microtubule breakdown largely via inhibition of Tau also in Drosophila. Our data show that neurons lacking PAR‐1 fail to break down dendritic microtubules, and PAR‐1 is required for an increase in neuronal microtubule dynamics at the onset of metamorphosis. Here, we show that the kinase PAR‐1 is required for pruning and dendritic microtubule breakdown. Microtubule disassembly requires a katanin homologue, but the signals initiating microtubule breakdown are not known. Prior to severing, dendritic microtubules undergo local disassembly, and dendrites thin extensively through local endocytosis. Pruning dendrites are severed in their proximal regions. Drosophila sensory neurons prune their dendrites during metamorphosis. Pruning of unspecific neurites is an important mechanism during neuronal morphogenesis.
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