Cyclin D1 activation in PS mutant animals. A, Representative images of NeuN and Cyclin D1 immunostaining of 6-month-old control (Ctrl), PS cDKO, PS cDKO; hPS1, and PS cDKO; D257A animals. Inset shows representative NeuN/Cyclin D1 double-positive cells in PS cDKO mice. B, Representative images of NeuN and Cyclin D1 immunostaining of 6-month-old control (Ctrl) and PS1 ΔE10 brains with NeuN/Cyclin D1 double-positive cells shown in inset. C, Western blot analysis of Cyclin D1 protein levels in forebrain samples of PS mutants. γ-Tubulin was used as a loading control.