Fig 1: Isolation and electron microscopy of sarkosyl-insoluble tau. (A) Levels of soluble and insoluble tau were determined with the mouse Total Tau Meso Scale kit. Tau levels increased with age in the pellet obtained by centrifuging brain homogenates at 27,000 × g. The resulting supernatant was treated with 1% sarkosyl and centrifuged at 200,000 × g. The solubility of tau in sarkosyl decreased with age, irrespective of genotype. (B) Overview of negatively-stained material in sarkosyl-insoluble lysates from (a) aged wild-type (WT) and (b) aged APPswe/PS1?E9 transgenic (TG) mice. Fibrils of ~20 nm in width, appearing as straight filaments (c) or as two intertwined fibrils (g), each with a diameter of ~10 nm. PHFs with axial periodicities of ~80 nm were present in APPswe/PS1?E9 mice (d; arrows), and more frequently observed in AD patient material (h; arrows). The inserts show ‘stacked’ PHFs, which were denser in the AD preparation. Structures identified in the detergent-insoluble fractions of the mouse and human brain included bent fibrils of ~7 nm in width (e,i), and rod-shaped particles (arrows e & f; insert a). Scale bars: 1 µm (a, b); 200 nm (c,d,g,h); 100 nm (e,f,i,j; insert a).