Analysis of tau species in aged delta NP73 null mice. A: Histochemical analysis of the hippocampus of 17 month-old DeltaNp73 homozygous mutant mouse (middle row) and a wildtype littermate control (bottom row). Immunohistochemitry with AT8 and PHF-1 antibodies (left and middle columns, respectively) and Gallyas staining (right column) were used to examine tau pathology in these mice. Tau transgenic Tg30 mice were used as a positive control for staining (top row) with Gallyas-positive aggregates and a somatodendritic accumulation of phosphotau being observed in TgTau but not in DeltaNp73 mice. B: Immunoblot analysis of 17 month-old DeltaNp73 hemizygous and homozygous mutant mice using phosphotau specific antibodies. Tau transgenic Tg30 mice were used as a positive control (left lane). Loading controls (bottom row) consist of images of Ponceau red-stained membranes taken immediately after blotting.