MAPT and tauopathy: Common sources of tau seeds include: i) full length or truncated forms of recombinant tau protein, with or without associated mutations, where the use of heparin or other adjuvants catalyses the formation of tau fibrils (PFFs: pre-formed fibrils) [10–13]; ii) mouse brain lysates from aged symptomatic transgenic tau animals, which contain hyperphosphorylated and aggregated tau [14–17]; or iii) post-mortem samples from patients with a variety of tauopathies (PHFs: paired helical filaments) [18–22].