Figure 2: Lattice expansion induces disassembly of tau envelopes.

a. Fluorescence micrographs of tau-mCherry envelopes on GMPCPP-capped GDP-lattice microtubules before, during, and after hydrodynamic flow removing tau at t=0 sec. During the hydrodynamic flow we either added 10 μM taxol (top panels) or kept the measurement buffer taxol-free (bottom panels). Yellow arrows indicate the location of the bend induced by the flow and the subsequent local decrease in tau density. Scale bars: 5 μm. b. Relative density of tau-mCherry in the bend of GMPCPP-capped GDP-lattice microtubules, during and after the flow. With taxol in solution the density dropped to 45.9 ± 15.9% during flow (mean ± s.d., n = 11 microtubules, 5 experiments) and decreased further to 3.6 ± 2.8% after flow (mean ± s.d., n = 11 microtubules, 5 experiments). Without taxol in solution the density dropped to 53.5 ± 10.4% during hydrodynamic flow (mean ± s.d.; n=11 microtubules, 4 experiments) and recovered to 77.3 ± 10.8% after flow (mean ± s.d.; n=11 microtubules, 4 experiments). c. Schematics of the optical tweezers assay. d. Fluorescence micrographs of a biotin-HiLyte647-labeled taxol-lattice microtubule suspended between two beads after addition of 60 nM tau-mCherry. Yellow arrows indicate locations of the tau envelopes. Scale bar: 2 μm. e. Compaction of taxol-lattice microtubules measured after the addition of either 60 nM tau-mCherry (green) or 0 nM tau-mCherry (grey). Compaction with tau in was 0.48 ± 0.32% (mean ± s.d., n = 26 microtubules, 26 experiments). Without tau in solution the microtubule did not compact; −0.01 ± 0.07% (mean ± s.d., n = 23 microtubules, 23 experiments, two-sided t-test, p<0.001). f. Representative force-time (blue) and distance-time (purple) graphs of a single taxol-lattice microtubule after addition of 60 nM tau-mCherry. After tau addition (green arrow) a decrease in the distance and an increase in the force is detected. After tau was removed from the channel (grey arrow) an increase in the distance, and a decrease in the force is detected, indicating relaxation of the microtubule lattice as tau envelopes disassembled. g. Fluorescence micrographs of tau envelope disassembly where the microtubule is stretched using external force. Sketches of the micrographs (left panels) indicate the size and positions of the tau envelopes (green lines). Scale bars: 2 μm. h. Disassembly rate of tau envelopes on taxol-lattice microtubules either stretched by an external force (blue, 0.11 ± 0.06 μm/s, mean ± s.d., n = 24 microtubules, 24 experiments) or relaxed when no external force is applied (grey, 0.05 ± 0.02 μm/s, mean ± s.d., n = 18 microtubules, 18 experiments, two-sided t-test, p<0.001). i. Fluorescence micrographs of a tau envelope disassembly experiment where the microtubule is relaxed in absence of external force. Sketches of the micrographs (left panels) indicate the sizes and positions of the tau envelopes (green lines). Scale bars: 2 μm.