PSEN1 and infection: To determine exactly when PS1 was eliminated in this system, we performed Western blot analysis using fPS1/fPS1;PS2+/+ neuronal cell lysates at 5–85 d after infection with the lentivirus expressing ΔCre or Cre. The levels of PS1 proteins were robustly decreased at 15 d after Cre transduction (day 35), and the extent of reduction progressively increased (Fig. 4B), whereas the levels of APP protein were relatively comparable.