UC Santa Barbara

Microtubules (MTs) are highly dynamic components of the cell cytoskeleton that are necessary for many functions, including cell division, cellular locomotion, and intracellular transport. An essential mechanistic feature of MT physiology is dynamic instability, which is characterized by the frequent polymerization and depolymerization of tubulin subunits at MT ends. This dynamicity is critical to MT function and is regulated by MT-associated proteins (MAPs), which interact with tubulin dimers and/or the MTs themselves. Tau is a prominent neuronal MAP that stabilizes MTs by promoting growth events, stability, and by suppressing shortening events. On the other hand, dysregulation and mutation of tau are associated with pathogenesis in various neurodegenerative diseases, such as Alzheimer’s disease (AD), frontotemporal dementia with Parkinsonism-17 (FTDP-17), and progressive supranuclear palsy (PSP). Taken together, it is critical to understand both normal tau physiology as well as how altered tau function leads to disease pathogenesis. Previous research has suggested that tau is able to dimerize or oligomerize via its N-terminal projection domain as part of its normal function. One currently proposed model, based on in vitro data, is that two tau molecules form an “electrostatic zipper” in which the N-termini of the two molecules associate in an antiparallel fashion, with the C-termini containing the MT-binding region of each tau molecule extending away from one another. If correct, this model could explain many features of tau action. We investigated this hypothesis in mammalian cells using a split-luciferase strategy in order to (i) test the above stated model for tau oligomerization in cells and (ii) identify and map regions of the protein that are capable of tau-tau oligomerization. We found that constructs containing the N-terminus of tau produce significantly higher luciferase signals indicative of oligomerization compared to constructs containing the C-terminus. More specifically, the construct containing amino acids 1-120 produces the strongest luciferase signal, consistent with our proposed model that the N-terminus of tau is responsible, at least in part, for its oligomerization activity. Interestingly, C-terminal regions of tau are also capable of promoting tau oligomerization. Taken together, our data suggest that both the N- and C- termini of tau are each sufficient to promote tau oligomerization in mammalian cells.