Taxol directs growing MT plus ends toward the tips of processes. (A–D) After 1 DIV, unpolarized neurons transfected with EB3-GFP (A) were subjected to low doses of taxol. The effect on MT dynamics was examined 30 min after treatment by monitoring the distribution of EB3-GFP (B–D). n = 52 neurons from eight independent experiments. (C) Higher magnification of the growth cones marked in A and B. EB3-GFP is mainly localized at the tips of neurites after a 30-min treatment with 10 nM taxol (a'–d') in comparison to a more even distribution before treatment (a–d). (D) Profiles of EB3-GFP immunofluorescence intensity (arbitrary units) of a representative neurite (neurite “c”) before (red) and after (green) taxol treatment. (E–G) Dynamic MT plus ends in polarizing neurons (1 DIV) visualized by transfection with EB3-GFP. (G) Higher magnification of the growth cones marked in F. The growth cone of the future axon (F and G, asterisk) harbors a high amount of dynamic MTs in comparison to the growth cones of the remaining minor neurites in 64 ± 12% of the cases (n = 14 neurons from more than five independent experiments). Bars: (A and B) 20 μm; (C) 5 μm; (E and F) 20 μm; (G) 5 μm.