Figure 2. Model for tau’s role in regulating microtubule stability in the axon.
The upper panel shows tau enriched on the labile domain (light green) of the microtubule and MAP6 enriched on the stable domain (dark green). Shades of green indicate levels of stability, with lighter shades indicating less stability. Lower panels indicate the effects of tau depletion (on the left) and MAP6 depletion (on the right). When tau (pink thread-like structures) is depleted, MAP6 (blue thread-like structures) spreads out along the microtubule, binding more to the labile domain than it normally does, thus partially stabilizing it. When MAP6 is depleted, the stable domain becomes no less stable, suggesting that other stabilizing proteins contribute to its stability, but the labile domain becomes even more labile than it normally is, indicating that the small amount of MAP6 normally on the labile domain makes it slightly less labile than it would otherwise be. Tau depletion leads to shortening of the labile domain, while MAP6 depletion leads to shortening of both domains.