Glycogen synthase kinase 3-alpha is a multifunctional protein serine kinase. GSK-3 phosphorylates and inactivates glycogen synthase. It has also been implicated in the regulation of cell fate in Dictyostelium and is a component of the Wnt signaling pathway required for Drosophila, Xenopus, and mammalian development. GSK-3 has been shown to regulate Cyclin D1 proteolysis and subcellular localization. GSK-3alpha (GSK-3α) regulates the production of amyloid-beta peptides, a major component of the plaques that accumulate with progression of Alzheimer's disease, by phosphorylating Tau proteins. This presents the possibility that defects in GSK-3 signaling can contribute to the onset of Alzheimer’s disease. GSK-3α can be phosphorylated by Akt at Ser21. This phosphorylation of GSK-3α negatively regulates its kinase activity.