Fig. 2. Cell-autonomous impairment of the multipolar-to-bipolar transformation within the SVZ-IZ in neurons expressing Cdk5-DN. Mixtures of CRC-Cdk5-DN and CAG-RFP were used in different ratios for in utero electroporation of E14.5 mouse embryos. (A,A') The distribution and morphology of RFP-positive cells (red) were analysed in coronal sections at E18.5. Higher magnifications of the indicated areas of 100% (a) and 50% Cdk5-DN (b) are shown in A'. Dose-dependent disturbance of neuronal migration by CRC-Cdk5-DN was also cell-autonomous. When only Cdk5-DN was used (100%), RFP-positive neurons arrested within the SVZ-IZ in the multipolar shape (arrows in A'). This result matched the phenotype of Cdk5^-/- neurons, indicating that defective Cdk5 activity in migrating neurons caused migration arrest in a cell-autonomous manner. When Cdk5-DN was used at 50%, migration delay was observed. RFP-positive neurons have bipolar shape in CP but some of the RFP-positive neurons have branched leading processes (arrows in A'b). MZ, marginal zone; CP, cortical plate; SVZ-IZ, subventricular zone-intermediate zone; VZ, ventricular zone. Scale bar: 100 µm. (B) Bin distribution of RFP-positive neurons at each ratio of Cdk5-DN. The cortical mantle was divided into ten equally spaced bins and the percentage of cells in each bin calculated.