Reduced percentage of neural progenitor cells reentering the cell cycle in PS cDKO embryos. Immunofluorescent staining of BrdU (green) and the proliferating cell marker Ki67 (red, staining all cell cycle stages except G0). (A-D) E13.5 embryos labeled by BrdU at E12.5. (E-H) E14.5 embryos labeled by BrdU at E13.5. (I, J) The proportions of cells which reentered cell cycle are shown as (%). Much less portion of the neural progenitor cells reentered the cell cycle in the PS cDKO embryonic brain (*, p < 0.05). Scale bar: 100 μm.