Rho-dependent control of anillin behavior during cytokinesis.

Anillin is a conserved protein required for cytokinesis but its molecular function is unclear. Anillin accumulation at the cleavage furrow is Rho guanine nucleotide exchange factor (GEF)(Pbl)-dependent but may also be mediated by known anillin interactions with F-actin and myosin II, which are under RhoGEF(Pbl)-dependent control themselves. Microscopy of Drosophila melanogaster S2 cells reveal here that although myosin II and F-actin do contribute, equatorial anillin localization persists in their absence. Using latrunculin A, the inhibitor of F-actin assembly, we uncovered a separate RhoGEF(Pbl)-dependent pathway that, at the normal time of furrowing, allows stable filamentous structures containing anillin, Rho1, and septins to form directly at the equatorial plasma membrane. These structures associate with microtubule (MT) ends and can still form after MT depolymerization, although they are delocalized under such conditions. Thus, a novel RhoGEF(Pbl)-dependent input promotes the simultaneous association of anillin with the plasma membrane, septins, and MTs, independently of F-actin. We propose that such interactions occur dynamically and transiently to promote furrow stability.