Watch the movement of granules containing the dark pigment melanin as they travel along microtubules in a fish epidermal cell. This movement of melanin granules enables the fish to change its color to avoid predators. Rotamine labeled tubulin was used to visualize the microtubules. Notice how some of the microtubules appear to move as tubulin monomers are added to one end and removed from the other. Get it! Gary Borisi, Northwestern University Medical School.