Transmission electron micrographs of human Tau fragment samples at physiological pH after incubation under different conditions.

Tau_244–372 (A and B) and GSK-3β phosphorylated Tau_244–441 (C and D) samples were incubated for 1 h (A and B) or 2 h (C and D) in the absence of a crowding agent (A and C) and in the presence of 150 g/l Ficoll 70 (B) or 300 g/l Ficoll 70 (D), respectively. A 2% (w/v) uranyl acetate solution was used to negatively stain the fibrils. The scale bars represent 200 nm.