APPL1 and Alzheimer disease: Satellite bouton production has been observed for certain Drosophila proteins that affect synaptic plasticity, including overexpression of the Drosophila amyloid precursor protein APPL, a pan-neuronal protein implicated in Alzheimer's disease [48] and Shaggy, the Drosophila homolog of the glycogen synthase kinase 3 (GSK3βa kinase that negatively controls NMJ growth via microtubule cytoskeleton dynamics [29].