Microtubule-associated protein 2 (MAP2) is a neuronal phosphoprotein that regulates the structure and stability of microtubules, neuronal morphogenesis, cytoskeleton dynamics, and organelle trafficking in axons and dendrites. Multiple MAP2 isoforms are expressed in neurons, including high molecular weight MAP2A and MAP2B (280 and 270 kDa), and low molecular weight MAP2C and MAP2D (70 and 75 kDa). Phosphorylation of MAP2 modulates its association with the cytoskeleton and is developmentally regulated. GSK-3 and p44/42 MAP kinase phosphorylate MAP2 at Ser136, Thr1620, and Thr1623. Phosphorylation at Thr1620/1623 by GSK-3 inhibits MAP2 association with microtubules and microtubule stability.