Fig. 6. Cortex-specific Cdk5 knockout mice. (A) Loss of Cdk5 in the cerebral cortex and hippocampus was confirmed by western blot analysis. Samples from each brain region were dissected from embryonic or postnatal mouse brains at the indicated stages and subjected to western blot analysis for Cdk5 proteins. Cdk5 protein levels in the cerebral cortex (cc) were low compared with those in other brain regions (ex) at E15.5 and P2. At P10, brains were separated into the cerebral cortex (CC), hippocampus (Hipp), thalamus (Th), and brain stem (BS) and analysed for Cdk5 and actin by western blot. (B) Reduction in the Cdk5 protein level (Cdk5/actin) was confirmed in cerebral cortex at P10. Mean±s.d.; n=6; ^*, P<0.01. (C) Immunostaining of the coronal section of the cerebral cortex from control and CxCdk5KO mice at P10 with anti-Cdk5 antibody. Cdk5 staining was observed in all regions of the control mouse brain at P10. This staining pattern was missing in the cerebral cortex and hippocampus from CxCdk5KO mice. Higher magnification of the area indicated by the arrow in the right-hand panel reveals the presence of Cdk5-positive interneurons, which derive from the ganglionic eminence where Cre recombinase is not expressed; these are also GABA positive (data not shown). Scale bar: 200 µm; inset, 100 µm. (D) Comparison of cerebral cortex in Nissl-stained sagittal sections revealed abnormal laminar structure in CxCdk5KO mice. In the cerebral cortex, cell-sparse structures of layer I (I) and white matter (W.M.) observed in the control were not evident in the cerebral cortex in CxCdk5KO mice. In the hippocampus, pyramidal neurons failed to form a confined layer in CxCdk5KO mice. Scale bar: 100 µm.