Impaired neuronal differentiation by specific knockdown of Numb-12ex. (A) Isoform specificity of siRNAs targeting Numb. Diagrams show the locations targeted by siRNAs specific for the Numb-12in mRNA (siN12in) and for the Numb-12ex mRNA (siN12ex). SiRNAs indicated at the top of the blots were transfected together with the expression constructs indicated at the bottom of the blots into P19 cells. Cell lysates were analyzed by immunoblotting using anti-Numb. (B–M) Immunostaining of the E4 neural tube for neuronal markers. The right side of the neural tube in each panel has been transfected with the indicated siRNA and the GFP construct, as demonstrated by GFP in B–D. Bars, 50 µm. (N) Quantification of marker⁺ cells. Quantification was performed by the same procedure as Fig. 4 K (mean ± SD, 5 embryos, 3 sections/embryo). *, P < 0.00005 compared with siCont. There is no significant difference between siCont and siN12in.