Fly division

S Tumps in animal cells (reviewed by Rappaport, 1986; Satterwhite and Pollard, 1992; Fishkind and Wang, 1995) provide a view of cytokinesis whereby in each dividing cell, a contractile ring of interdigitated anti-parallel actin and bipolar myosin (nonmuscle myosin II) filaments forms in the equatorial region of the cell cortex, and then constricts, in purse string-like fashion, to pinch the cell in two. A number of key questions about this process remain unresolved. An understanding of the signal(s?) that spatially and temporally orchestrate ring formation is lacking. A comprehensive catalog of the proteins that act in concert with actin and myosin to form the ring is also not yet available. In addition, our knowledge of how the ring is integrated into the cortex at large and is associated with the plasma membrane is only rudimentary. Finally, molecular mechanisms by which each protein contributes to the assembly of the complex, supramolecular structure of the ring and functions in chemomechanical force production are far from clear. The multidisciplinary approaches that are being applied in Drosophila are likely to provide insight into the many aspects of furrow function that remain poorly understood. Recently, genetic approaches have identified several new proteins that are required for cytokinesis and cell biological and biochemical methods have revealed proteins that localize in cytokinetic structures. Together, these findings have expanded the list of the molecules implicated in cytokinesis and are harbingers of a new understanding of cytokinesis at the molecular level.