Figure 8. Tau lacking the microtubule-binding domain (ΔTau) mislocalizes to dendritic spines but does not affect Fyn mobility in dendrites and spines.

(a) Representative epifluorescence images of Tau KO neurons co-expressing either full-length Tau (TauWT-GFP) and mCardinal or Tau lacking the microtubule-binding domain (ΔTau-GFP) and mCardinal. Arrows denote reduced localization of TauWT-GFP in dendritic spines and arrowheads denote increased mislocalization of ΔTau-GFP in dendritic spines. Scale bar, 1 μm. (b–i) Comparison of Fyn mobility in the dendrites (b–e) and spines (f–i) of Tau KO neurons expressing Fyn-mEos2, TauWT-GFP and GFP (blue) and Tau KO neurons expressing Fyn-mEos2, ΔTau-GFP and GFP. (b, f) The average mean square displacement (MSD) as a function of time. (c, g) The corresponding area under the MSD curves (AUC). (d, h) The distribution of diffusion coefficients (D) shown in a semi-log plot. (e i,) The corresponding immobile fraction. (j) The average mean square displacement (MSD) of Fyn- mEos2 trajectories from individual spines of Tau KO neurons expressing TauWT-GFP (n = 99 spines) or ΔTau-GFP (n = 181 spines). (k) The effective diffusion coefficient computed from the MSD of individual spines. (l) The distribution of the moment scaling spectrum slope (S_MSS) of trajectories lasting for at least 20 frames (n = 2561 trajectories from the spines of 8 Tau KO neurons expressing TauWT-GFP and n = 4943 trajectories from the spines of 11 Tau KO neurons expressing ΔTau-GFP). (m) The comparison of the state occupancies estimated using a three-state model. In (b–i) and (m), mean ± SEM values were obtained from n = 8 Tau KO neurons expressing Fyn-mEos2, TauWT-GFP and GFP and n = 11 Tau KO neurons expressing Fyn- mEos2, ΔTau-GFP and GFP. Statistical comparisons were performed using the Mann-Whitney U test (c, e and k), Student’s t-test with Welch’s correction (g, i), the Kolmogorov-Smirnov test (l) and Student’s t-test (m).