Fig. 2.
Characterization of 4R and 3R isoform aggregation induced by arachidonic acid in vitro. (A) After 6 hours of polymerization, scattered laser light signal (Is) from all three 4R isoforms is significantly greater than the 3R isoforms. Among the 4R isoforms, hT40 signal was significantly higher than hT34 and hT24, and within the 3R isoforms, all 3R constructs produced similar light scattering (one-way ANOVA, Holm-Sidak post-hoc comparisons: **p < 0.05 vs. hT40 all other groups and *p < 0.05 vs. all 3R isoforms, n = 4/group). (B) Thioflavin S (ThS) fluorescence, a marker for β-sheet structures in aggregated tau, was significantly higher in all 4R tau isoforms compared to each 3R isoform. No differences were found between the different 4R or between the different 3R tau isoforms (one-way ANOVA, Holm-Sidak post-hoc comparisons: *p < 0.05 vs. all 3R isoforms, n = 4/group). All graphed values represent mean ± SEM. (C–H) Representative electron micrographs of hT40 (C), hT34 (D), hT24 (E), hT39 (F), hT37 (G) and hT23 (H) aggregates polymerized in the presence of arachidonic acid. The 4R tau isoforms formed a range of short, intermediate and longer filaments compared to 3R tau isoforms, which formed mostly globular oligomeric aggregates and only rare filaments. Scale bar = 600 nm (applies to all panels).