Shaggy, the Homolog of Glycogen Synthase Kinase 3, Controls Neuromuscular Junction Growth inDrosophila

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Abstract
A protein-trap screen using theDrosophilaneuromuscular junction (NMJ) as a model synapse was performed to identify genes that control synaptic structure or plasticity. We found that Shaggy (Sgg), theDrosophilahomolog of the mammalian glycogen synthase kinases 3 α and β, two serine-threonine kinases, was concentrated at this synapse. Using various combinations of mutant alleles ofshaggy, we found that Shaggy negatively controlled the NMJ growth. Moreover, tissue-specific expression of a dominant-negative Sgg indicated that this kinase is required in the motoneuron, but not in the muscle, to control NMJ growth. Finally, we show that Sgg controlled the microtubule cytoskeleton dynamics in the motoneuron and that Futsch, a microtubule-associated protein, was required for Shaggy function on synaptic growth.