Figure 2.

Biochemical properties of tau species. A, Schematic diagram of the tau extraction procedure that is based on previously published methology (Greenberg and Davies, 1990). For details, see Material and Methods. B, Brain extracts from 6.5-month-old rTg4510 were processed as described in A. Tau ∼55 kDa and tau 64 kDa are present in total extracts at 6.5 months of age (assessed by E1 antibody). Tau ∼55 kDa is found in soluble (S1) fraction, whereas hyperphosphorylated tau 64 kDa is found in the sarkosyl-insoluble (P3) fraction. Tau170 and tau140 are present in total lysate from 6.5-month-old rTg4510. Tau140 is mostly found in soluble (S1) fraction, whereas tau170 is mostly in the sarkosyl-insoluble (P3) fraction, as assessed by E1 antibody. Tau170 kDa, present in the sarkosyl-insoluble (P3) fraction, is strongly immunoreactive with AT8, whereas tau140, present in soluble (S1) fraction, exhibits very little immunoreactivity with AT8 antibody. C, Summary of how the various tau species are extracted into the different fractions. D, Analysis of the size of the different tau species in vivo. Size-exclusion chromatography was performed with total extracts from 4.5-month-old rTg4510. Tau140 and tau 55 kDa elute at a similar size and appear relatively small, whereas tau170 and tau 64 kDa are part of larger aggregates. Tau140 and tau170 have distinct sizes that do not overlap at this time point. Molecular weight scale corresponds to standards (see Materials and Methods) eluting at respective fractions shown on the graph (∼67 kDa eluted in fraction 34). E, Size-exclusion chromatography analysis using extracts of older 6.5-month-old rTg4510. Hyperphosphorylated species (64 kDa, tau170) are characterized by two distinct elution peaks, suggesting they are derived from two distinct populations of small and large aggregated species. Tau140 and tau170 have overlapping size ranges at 6.5 months of age.