Highly phosphorylated soluble tau was rapidly aggregated into sarkosyl-insoluble fraction in Tg30xtau−/− mouse brain. The phosphorylation of tau in the sarkosyl-soluble fraction S2 (A–F) and sarkosyl-insoluble A68 fraction (H–M) was analyzed by immunoblotting with phosphotau antibodies AT270 (A and H), CP13 (B and I), AT180 (C and J), PHF-1 (D and K), and the conformational antibodies MC1 (E and L) and the polyclonal tau antibody B19 (F and M). The mean relative levels of each phosphotau species estimated by densitometry analysis (normalized to total tau estimated with the B19 antibody) are shown in panels G and N. The majority of pathological phosphotau species were reduced in sarkosyl-soluble fraction, whereas the levels of certain phosphotau species were increased in sarkosyl-insoluble fraction of Tg30xtau−/− mice. *P < 0.05 and ***P < 0.001 by Student's t-test (Tg30, n = 5; Tg30xtau−/−, n = 7).