Schematic illustration of the assay on micropatterned substrate. Tubulin was first added alone to measure the nucleation capacity of each micropattern, and then washed out. Later on, actin was added followed by actin and tubulin. Finally, actin was rinsed out and gelsolin was added to fully disassemble actin filaments. Representative images showing microtubules (top line) and the merged images of actin and microtubules (bottom line) during the four steps of the assay; in the presence of tubulin only, in the absence of tubulin and presence of actin, in the presence of tubulin and actin, and finally in the presence of tubulin and gelsolin but in the absence of actin filaments (from left to right). Scale bar: 10 μm. 