Herpes simplex virus-mediated expression of the axonal protein tau in human model neurons (NT2-N cells)

The establishment of axonal-somatodendritic polarity is an important event during neuronal development. The analysis of the underlying molecular events requires experimental models that display characteristic steps in the development of polarity and that are accessible for experimental manipulations. Here we show that human model neurons (NT2-N cells) can be efficiently infected with an amplicon-based herpes simplex virus (HSV) system that expresses the axonal microtubule-associated protein tau. We demonstrate that the neurons express a high level of exogenous tau, which persists for several days, thus allowing us to analyze the morphological effects of the expressed protein. The intracellular interactions of tau and the effects on the microtubule structure of infected neurons, which were processed for immunocytochemistry, were determined using laser scanning microscopy (LSM). Exogenous tau expression does not result in an increased axon growth of the neurons but promotes neuronal microtubule assembly as indicated by an increased amount of total microtubule polymer as well as a labile, detyrosinated microtubule subpopulation. In contrast, tau expression does not induce a significant microtubule stabilization as judged from the quantitation of acetylated microtubule staining 24 hours after infection. The data demonstrate that HSV-mediated expression of proteins in human model neurons provides a useful system for analysis of the effect of neuronal proteins on the morphology and cytoskeletal organization of terminally differentiated polar neurons. In addition, it suggests a role for tau as a factor which locally promotes tubulin polymerization while the dynamics of axonal microtubules are preserved.