Immunohistochemical analysis of tau species in control and compound mutant young mice. A: Tau pathology was assessed histologically in the hippocampal formation (top; 4 x objective) and cortex (bottom; 10 x objective). The left-hand column shows a control tau transgenic mouse (TgTauP301L) with tau-positive astrocytic plaque and neurofibrillary tangle morphologies. Immunodetected structures are denoted by brown (DAB) staining, in accord with previous analyses of mice of this age (540 days) . No staining is apparent in compound mutant mice aged 60 days (2nd column) or in Trp73+/- or wild type aged matched littermate controls (3rd and 4th columns, respectively) for AT8 and CP13 phospho-tau specific antibodies. B: Detection of neuritic pathology. Left hand field (4x) represents the area of hippocampus and cortex from a sagittal section of 70 day-old compound transgenic mouse bearing a total of 5 amyloid plaques (arrows) visualized with 6E10 antibody. Right hand panel (40x) shows one of the cortical plaques (grey arrow, left panel) that has developed neuritic tau pathology. The plaque vicinity is shown (circle with a dashed line) and the neuritic pathology is manifest by dot-like immunostaining within the plaque (see also Additional file 2: Figure S2).