NICD does not ameliorate neuronal loss in Pen‐2 cKO mice. A, Experimental plan for the generation of Pen‐2 cKO mice expressing N1ICD conditionally in a Cre‐dependent manner. B, qPCR analysis on Notch1 and N1ICD. Relative mRNA levels of Notch1 and N1ICD were highly significantly increased in the cortex of Pen‐2 cKO;NICD mice as compared to Pen‐2 cKOs (***P < 0.001; n = 4 mice per group). C, Nissl staining. Brain sections of control, Pen‐2 cKO, and Pen‐2 cKO;NICD mice at 5‐7 mo were used. Note that there was decreased cortical thickness in Pen‐2 cKO mice with and without NICD expression compared with controls. Boxed areas in (a‐c) were enlarged as (d‐f). Scale bar is 1 mm in (a‐c) or 100 μm in (d‐f). D, Representative images for fluorescence IHC on NeuN. Images were taken from the cortex. Note that there was decreased cortical thickness in Pen‐2 cKO and Pen‐2 cKO;NICD mice compared with controls. Scale bar is 200 μm. E, Averaged number of NeuN+ cells in the cortex. There was no significant difference between Pen‐2 cKO and Pen‐2 cKO;NICD mice. There was significant difference between Pen‐2 cKO and control mice (ns, not significant; **P < 0.01; n = 3 per group)