Changes in MTs and cell morphology in cultured astrocytes infected with T40-AV. Double-immunofluorescence staining for β-tubulin (red; Tub) and tau (green; 17026) was performed in astrocytes infected with T40-AV. Non-infected cells showed clear mesh-like MT networks but no tau staining (A), whereas a slight disturbance of the MT network was noticeable in some astrocytes just 4 hr after infection (B). Disruption of MT networks increased over time with abnormally thick bundles of MTs and free tau in a subset of cells at 8 hr after infection (C). Sixteen hours after infection, MT networks completely disappeared, and free tau (i.e., unbound to MTs) uniformly filled the cytoplasm (D). No additional changes in astrocyte morphology were detected 24 hr after infection, except for tau deposits near the cell periphery (E, arrowheads). Low-power photomicrographs (insets) clearly show alterations in the morphology of the astrocytes associated with increasing tau expression. Scale bars, 10 μm.