Fig. 2: Isoform-specific seeding pattern is unaltered during repeated propagation.

a Schematic showing in vivo propagation paradigm in 6hTau mice. Similar amounts of human tau strains (P0) were injected into the hippocampus of naive 6hTau mice for 1st round transmission and 3 months later, the hippocampi were dissected and extracted using detergent to obtain the induced tau strain (P1). The P1 tau strain was re-injected into the hippocampus of naive 2nd round transmission 6hTau mice, and the induced P2 tau pathologies were extracted similarly as P1 and injected into the hippocampus of 3rd round of 6hTau mice. Representative IHC staining in panel b using MAbs AT8, MAb RD3 (3R isoform tau-selective) and MAb RD4 (4R tau isoform-specific) on adjacent brain sections from 6hTau mice injected with equal amounts of P0-tau from different human tau strains; or c with control lysate from normal human brains Ctrl_P0 or non-injected aged 6hTau mouse brains Ctrl_P1; or d with induced P1-tau; or e with induced P2-tau at 3 m.p.i. The P1 injection doses were 0.1–0.5 μg per site, and P2 were 0.01–0.03 μg per site, while the P0 were 1 μg per site. Biochemical extraction of induced f P1 from strain_P0–6hTau and g P2 from strain_P1–6hTau mice with 0.1% sarkosyl. The sarkosyl-insoluble tau were probed with Mab RD3, Mab RD4, and polyclonal anti-4R Tau-specific antibody to examine the isoform compositions in the induced pathologies. Open arrowheads indicate 3R Tau immunobands, and solid arrowheads indicate 4R Tau bands. Asterisks indicate the non-specific immunoreactive bands near 50 KDa, respectively, shown in RD3 and 4RTau blots. Equal proportion of sarkosyl-soluble fractions were loaded, and f 15-fold fraction from strain_P1 or g 40-fold fraction from strain_P2 mice were loaded as sarkosyl-insoluble fraction. h Quantification of b from strain_P0; i quantification of d from strain_P1, and j quantification of e from strain_P2 induced neuronal tau pathologies, respectively, indicated by AT8, RD3, and RD4. Only ipsilateral hippocampus (iHpx) were quantified for each mouse. Data are presented as mean ± s.e.m. n = 3–6 mice per each group. Multiple t-tests were performed. Source data is available as a Source Data file.