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Figure S4. Taxol induces the protrusion of polymerizing dynamic MTs to the growth cone periphery. (A–D) An unpolarized neuron (1 DIV) expressing the MT plus end–binding protein EB3 tagged with GFP. Phase and fluorescent images of the untreated neuron (A and B) were acquired every 10 s. Dynamic MTs marked by EB3-GFP are present along the whole length of all processes (B). Subsequently, taxol was added to the medium to a final concentration of 10 nM (C and D) and imaging was continued. Dynamic MTs become localized to the tips of the processes upon taxol addition (D, arrows). Bars, 20 µm. (E) Kymographs showing the movement of EB3-GFP in the selected regions of interest marked in the inset in D, which allows taxol-induced changes in distribution and dynamics of GFP-tagged EB3 to be followed. The horizontal axis represents time and the vertical axis represents distance. In all panels, the top represents the distal part of the region of interest and the bottom corresponds to the proximal part. EB3-GFP diagonal streaks directed to the upper right therefore represent dynamic MTs facing the growth cone with their plus ends, whereas diagonal streaks aiming at the lower right stand for dynamic MTs facing the cell body with their plus ends. Briefly after addition of taxol, practically all dynamic MTs face the growth cones with their plus ends (EB3-GFP streaks directed to the upper right; a, c, and d). Upon taxol addition, dynamic MTs become localized to the tips of the processes (a–d) and rapid neurite outgrowth begins (a, c, and d).