Hyperphosphorylated forms of the microtubule-associated protein (MAP) tau accumulate in Alzheimer's disease and related tauopathies and are thought to have an important role in neurodegeneration. However, the mechanisms through which phosphorylated tau induces neurodegeneration have remained elusive. Here, we show that tau-induced neurodegeneration is associated with accumulation of filamentous actin (F-actin) and the formation of actin-rich rods in Drosophila and mouse models of tauopathy. Importantly, modulating F-actin levels genetically leads to dramatic modification of tau-induced neurodegeneration. The ability of tau to interact with F-actin in vivo and in vitro provides a molecular mechanism for the observed phenotypes. Finally, we show that the Alzheimer's disease-linked human beta-amyloid protein (Abeta) synergistically enhances the ability of wild-type tau to promote alterations in the actin cytoskeleton and neurodegeneration. These findings raise the possibility that a direct interaction between tau and actin may be a critical mediator of tau-induced neurotoxicity in Alzheimer's disease and related disorders.

TOR-mediated cell-cycle activation causes neurodegeneration in a Drosophila tauopathy model, identifying TOR and the cell cycle as potential therapeutic targets in tauopathies and AD.

Tau is a microtubule binding protein implicated in a number of human neurodegenerative disorders, including Alzheimer's disease. Phosphorylation of serine-proline/threonine-proline sites, targeted by proline-directed kinases, coincides temporally with neurodegeneration in the human diseases. Recently, we demonstrated that this unique group of serines and threonines has a critical role in controlling tau toxicity in a Drosophila model of tauopathy. Here, we use a combination of genetic and biochemical approaches to examine these sites individually and to determine which of them is primarily responsible for controlling tau neurotoxicity. Despite the importance placed on individual phosphoepitopes and their contributions to disease pathogenesis, our results indicate that no single phosphorylation residue plays a dominant role in controlling tau toxicity. These findings suggest that serine-proline/threonine-proline sites cooperate to mediate neurodegeneration in vivo.