Qiang, Sun, et al. show that cultured rat neurons depleted of tau undergo microtubule loss that is not explicable on the basis of microtubule destabilization. Rather, the loss is due to the diminution of the labile domains of microtubules, indicating that tau's actual role in the axon is to allow microtubules to have long labile domains.
Qiang, L., Sun, X., Austin, T. O., Muralidharan, H., Jean, D. C., Liu, M., … Baas, P. W. (2018). Tau Does Not Stabilize Axonal Microtubules but Rather Enables Them to Have Long Labile Domains. Current Biology, 28(13), 2181-2189.e4. https://doi.org/10.1016/j.cub.2018.05.045