Taxol improves the polarization of cortical neurons impaired by perturbation of the DLK–JNK pathway. A, Polarization of E16 cortical neurons at 3 DIV in the presence or absence of 5 nm Taxol. Cells were transfected with a plasmid vector encoding nonsilencing shRNA (NC) or DLK shRNA (DLK#1 or DLK#2) before seeding. A JNK inhibitor (10 μm SP600125), Taxol (5 nm), or vehicle (DMSO) was added separately or in combination to the culture medium at 1 DIV. A plasmid vector encoding nonsilencing shRNA was transfected to monitor the effects of the JNK inhibitor. The arrows indicate stage 1 neurons. Scale bar, 100 μm. B, C, Quantitative analysis of the effects of Taxol on the polarization of (B) DLK RNAi or (C) JNK inhibitor-treated cells. The median length of the longest neurite (n = 100) at 3 DIV is shown graphically. The bars represent the average of values obtained from four (B) or three (C) independent experiments. Error bars represent the SD. *p < 0.0005; **p < 0.005. The average of values obtained from control neurons was expressed as 100. D, Western blot analysis monitoring the effects of Taxol on JNK activity and microtubule stability. Primary cultures of E16 cortical neurons were treated with 5 nm Taxol or vehicle at 1 DIV. Cell lysates were prepared at 3 DIV, and proteins were analyzed by Western blotting using antibodies against phosphorylated (active) JNK, acetylated tubulin, and tyrosinated tubulin. A CBB-stained membrane is shown as a loading control.