Fig. 4.

Western blotting analysis of tau isoforms and their phosphorylation status in cat brains. a Western blotting of TBS-soluble fractions obtained from the hippocampus of various ages and treated with alkaline phosphatase (AP). The left lane (tau) shows the six isoforms of human tau (recombinantly produced): three 3-repeat tau isoforms (2N3R, 1N3R, 0N3R) and three 4-repeat tau isoforms (2N4R, 1N4R, 0N4R). In the fetal brain, only the 3-repeat tau isoforms are expressed. In the adult cat brains, all six isoforms are detected using anti-tau antibody (TAU-5) and also 3-repeat tau (RD3), and 4-repeat tau (RD4) antibodies. b Western blotting of sarkosyl-insoluble guanidine HCl-soluble fractions obtained from the hippocampus of aged cat brains without AP treatment (left) and with AP treatment (right). In cat hippocampi that were immunohistochemically positive for hyperphosphorylated tau (cases No. 12 and 22), AT8- and AT100-positive tau proteins are detected. In these cats, the smear-like band pattern resolved into clear lower molecular weight bands consisting of both 3-repeat and 4-repeat tau isoforms after dephosphorylation treatment