Triphasic NICD response to rPrPSc accumulation corresponds with delayed increased expression of Nicastrin. A. Western blots during the course of RML scrapie show decreased amount of PS-1 (Presenilin 1) and increased amount of Nicastrin relative to GAPDH standard. B. NICD and Nicastrin are plotted as a function of incubation time. The initial steep rise in NICD corresponds to rPrPSc accumulation, followed by relatively flat NICD level. The late occurring rise in NICD corresponds to increased expression of Nicastrin. n = 3 mice at each time point.