![]() Upon ecdysone release, it binds to the ecdysone receptor (EcR) and its co-receptor Ultraspiracle (Usp) to activate downstream signaling and thereby promote dendrite pruning ( Kuo et al., 2005 Williams and Truman, 2005). In ddaC neurons, the pruning process is initiated by the release of the steroid hormone ecdysone at the late larval stage ( Truman, 1990). Among the four classes of dorsal da neurons, ddaA/F (class III) and ddaB (class II) neurons are eliminated via apoptosis, whereas ddaC (class IV, also known as C4da) and ddaD/E (class I) prune their entire dendrite arbors without a concurrent loss of their axons ( Kuo et al., 2005 Shimono et al., 2009 Williams and Truman, 2005). Dendritic arborization (da) neurons are a group of PNS neurons that undergo extensive remodeling during metamorphosis. Their central (CNS) and peripheral (PNS) nervous systems are required to restructure accordingly as the body transitions from larval to adult stages. Holometabolous insects such as Drosophila experience complete metamorphosis ( Truman and Riddiford, 2019). Thus, Sgg and Par-1 might converge on and phosphorylate a common downstream microtubule-associated protein(s) to disassemble microtubules and thereby facilitate dendrite pruning. We show that Sgg and Par-1 kinases act synergistically to promote microtubule disassembly and dendrite pruning. Moreover, our pharmacological and genetic data suggest that Sgg is required to promote dendrite pruning at least partly via microtubule disassembly. Although Sgg is not required for the minus-end-out microtubule orientation in dendrites, hyperactivated Sgg can disturb the dendritic microtubule orientation. Sgg is necessary and sufficient to promote microtubule depolymerization, turnover and disassembly in the dendrites. Here, we report that the Drosophila GSK3β homologue Shaggy (Sgg) is cell-autonomously required for dendrite pruning of ddaC sensory neurons during metamorphosis. However, it remains unknown whether GSK3β regulates neuronal pruning, which is a regressive process. The evolutionarily conserved Glycogen Synthase Kinase 3β (GSK3β), a negative regulator of microtubules, is crucial for neuronal polarization, growth and migration during animal development.
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