Purple sea urchin embryos undergoing mitosis. Embryos are expressing GFP-rhotekin GTPase binding domain, which is a probe for active Rho, with 3xmCherry-Ensconsin (a microtubule asociated protein shown in blue). Embryos were imaged with a laser scanning confocal microscope (Radiance 2000; Bio-Rad Laboratories) mounted on a compound microscope (E800; Nikon) using a 40× 1.3 NA Plan-Fluor oil lens. Room temperature was maintained at 14–17°C