Fig. 2

Tau-tau interaction is detected by tau-PLA. a Inducible homomeric tau complexes are detected by tau-PLA. Tau was fused to FKBP or FRB which form a ternary complex with rapamycin. Tau complexes are forced to conditionally associate in the presence of rapamycin. b HEK293 cells were transfected with both constructs and incubated with or without rapamycin for 1 h after transfection (left). Quantification of tau-PLA puncta (right). Tau-PLA puncta significantly increased in the presence of rapamycin, as determined by unpaired two-tailed Student’s t-test (*p < 0.05), indicating tau-PLA detects tau–tau interactions. Data are mean ± SEM, N = 20 cells per condition. Nuclei were identified by DAPI staining (blue). Images are maximum projections of z-stacks. Scale bar: 10 μm. All experiments were performed in triplicates. c Tau-PLA detects tau–tau interaction of recombinant tau but not monomeric tau. Aggregation of recombinant full-length unphosphorylated tau4R was induced by shaking in the presence of heparin. After 16 h of shaking, both amorphous and spherical/globular tau accumulations are seen on TEM analysis. After 360 h of shaking tau assembled into a mixed population of shaped species, including globular structures and filaments, mostly of short or intermediate length. Alpha- synuclein assembled into fibrils after 120 h of shaking (without heparin). The obtained recombinant protein preparations were subjected to TEM (all images at 18.500 x) and tau-PLA