Structural and seeding property analysis of TDP-43 PFFs. Transmission electron microscope (TEM) images of TDP-43 PFFs before sonication (a) and after sonication (b). The statistics of the length of TDP-43 PFFs ranging from 120 nm to 800 nm before sonication (c) and 40 nm to 480 nm after sonication (d). n = 10 samples/group. Bar, 100 nm. Characteristic increase in ThT fluorescence upon binding to TDP-43 PFFs (e). A seeded fibrillation of TDP-43 fibrils monitored by the ThT fluorescence intensity (f). n = 10 samples/group. The fibril nature of the TDP-43 PFFs was confirmed by analysis of proteinase K (PK) resistance using the dot-blot (g). An SDS-PAGE analysis has shown that a higher level of insoluble TDP-43 was detected in the pellet fraction, but less TDP-43 remained in the soluble fraction after a seeding reaction (h).