Albertson et al. report, the cell bundles two ingredients needed for division and then speeds them along a microtubule highway to their destination.
Cell division begins when a structure called the contractile ring tightens, creating a furrow that expands to eventually cut the cell in two. Deepening the furrow requires a continual supply of actin filaments, which drive constriction of the contractile ring, as well as a supply of new membrane. Where the fresh actin filaments come from has puzzled researchers. One possibility is that actin monomers already in the furrow polymerize. Alternatively, cells could truck in preformed filaments. How cells target new membrane to the furrow was also unclear.
Both components travel together, Albertson et al. discovered when they followed fluorescently labeled vesicles in Drosophila embryo cells. The researchers observed tagged vesicles sliding toward the furrow and embedding in its edge. Actin rode on the outside of the vesicles. During mitosis, microtubule bundles at the center of the cell combine to form a structure called the central spindle. The vesicles and their actin cargo cruised to the cleavage furrow along these microtubules. Presumably, one of the motor proteins attached to the vesicles dragged them along. The researchers now want to determine which motor powers the vesicles.