Abstract
During cytokinesis, the cell membrane furrows inward along a cleavage plane. The positioning of the cleavage plane is critical to faithful cell division and is determined by the Rho guanine nucleotide exchange factor (RhoGEF)-mediated activation of the small guanosine triphosphatase RhoA and the conserved motor protein complex centralspindlin. Here, we explored whether and how centralspindlin mediates the positioning of RhoGEF. In dividing neuroblasts from Drosophila melanogaster, we observed that immediately before cleavage, first centralspindlin and then RhoGEF localized to the sites where cleavage subsequently initiated. Using in vitro assays with purified Drosophila proteins and stabilized microtubules, we found that centralspindlin directly transported RhoGEF as cargo along single microtubules and sequestered it at microtubule plus-ends for prolonged periods of time. In addition, the binding of RhoGEF to centralspindlin appeared to stimulate centralspindlin motor activity. Thus, the motor activity and microtubule association of centralspindlin can translocate RhoGEF to areas where microtubule plus-ends are abundant, such as at overlapping astral microtubules, to locally activate RhoA and accurately position the cleavage plane during cell division.
