SEPT9 repeat motifs are required for MT bundling and asymmetric neurite growth. (A and B) Maximal projections of 3D confocal microscopy images of MDCK cells expressing GFP-tagged SEPT9_i1 and SEPT9_i4 before (A) and after (B) treatment with 5 µM paclitaxel for 1.5 h. (C) Manders coefficients for the colocalization of GFP-tagged SEPT9_i1 and SEPT9_i4 with MTs in MDCK cells (n = 15). High and low colocalization are indicated by coefficients >0.5 and <0.5, respectively. (D and E) Plots show the fluorescence intensity of putative MT bundles with 5× and 10× the mean intensity of single MTs as percentage of total MT intensity in MDCK cells (n = 15) before (D) or after (E) treatment with paclitaxel. (F) Phase-contrast images show PC12 cells transfected with GFP and GFP-tagged SEPT9_i1 and SEPT9_i4 after a 2- and 3-d NGF treatment. Insets show GFP fluorescence in inverted monochrome. Bars, 10 µm. (G) Graph shows percentage of PC12 cells (n = 90) with one or more neurites. Pooled data from three independent experiments are shown.