Complementary distribution of tau proteins in different phosphorylation states within growing axons.

Microtubule-associated tau proteins are hyperphosphorylated in brains from patients with Alzheimer's disease compared with normal adult human brain. At least some of the phosphorylated residues are also transiently phosphorylated in juvenile brain, but not in more mature stages. Using the monoclonal anti-tau antibodies TAU-1 and AT8, we found in cultured embryonic chicken and rat neurones a clear differential distribution of immunostaining within growing axons. Tau proteins that are phosphorylated at Ser202 (recognized by AT8) appear to be concentrated in the axonal portion that is close to the cell body and they decrease in proximal-distal direction. In contrast, tau proteins carrying an epitope that contains dephospho-Ser202 (recognized by TAU-1) are enriched in the distal axon and the growth cone. In colchicine-treated, growth-inhibited neurones there was an intense TAU-1 staining of the perikarya, but no longer any staining by AT8.