Specificity of shKIF13A and shKIF13B knockdown, and effect on axonal polarization. (A) RT-qPCR quantification of KIF13B mRNA levels from dissociated hippocampal neurons infected with the shKIF13A lentivirus (red) or control lentivirus (lacking the shRNA sequence; black) relative to the uninfected condition. Cultures were lysed after 15 DIV and 7 d after infection. Bars show mean ± SEM, together with individual values from each experiment. n, number of independent experiments; not significantly different from uninfected (Wilcoxon test). (B) RT-qPCR quantification of KIF13A mRNA levels from dissociated hippocampal neurons infected with shKIF13B (burgundy) or control (lacking shRNA sequence; black) lentivirus relative to the uninfected condition. Bars show mean ± SEM, together with individual values for each experiment. n = 3 (skKIF13A) and n = 6 (shKIF13B) independent experiments; not significantly different from uninfected (Wilcoxon test). (C) Left: Representative confocal images of 3 DIV dissociated hippocampal neurons infected with a control lentivirus (control; top panels) or lentiviruses expressing shKIF13A (middle panels) and shKIF13B (bottom panels), all expressing mCherry (red, left panels). Tau immunocytochemistry (ICC) was performed to assess neurite length (right panels) in all conditions. Scale bars in right panels are identical to those in left panels. Right: Quantification of axonal polarization was calculated from the ratio between the length of the major neurite compared with the length of the secondary neurite. Bars represent the mean ± SEM, together with individual values for each experiment. shKIF13B neurons (burgundy) show significantly less axonal polarization with respect to control (black) and shKIF13A (red) neurons (P = 0.0001 and P < 0.0001, respectively, Mann–Whitney test). n = 51, 72, or 105 cells for control, shKIF13A- or shKIF13B-expressing neurons, respectively.