Homozygous TauEGFP knock-in mice 21 were purchased from the Jackson Laboratories and bred with C57Bl6 mice (Taconic) to generate TauEGFP heterozygous embryos. Balb/c mice were purchased from Taconic. Rosa26-rtTA mice were obtained from Rudolf Jaenisch28. MEFs were isolated from E14.5 embryos under a dissection microscope (Leica). The head, vertebral column (containing the spinal cord), dorsal root ganglia, and all internal organs were removed and discarded to ensure the removal of all cells with neurogenic potential from the cultures. The remaining tissue was manually dissociated and incubated in 0.25% Trypsin (Sigma) for 10–15 minutes to create a single cell suspension. The cells from each embryo were plated onto a 15cm tissue culture dish in MEF media (Dulbecco’s Modified Eagle Medium (Invitrogen) containing 10% Fetal Bovine Serum (FBS) (Hyclone), beta-mercaptoethanol (Sigma-Aldrich), non-essential amino acids, sodium pyruvate, and penicillin/streptomycin (all from Invitrogen). Cells were grown at 37oC for 4–7 days until confluent, and then split once before being frozen. After thawing, cells were cultured on 15cm plates and allowed to become confluent before being split onto plates for infections using 0.25% Trypsin. Postnatal
