Fig. 6. A schematic diagram depicting two pathways leading to cell-cycle-coupled cell division in Dictyostelium cells. (A) Cytokinesis A. Mitotic AmiA^- or coronin^- cell carries out cytokinesis by active contraction of the cleavage furrow which depends on actin and myosin II. (B) Cytokinesis B. A mitotic myosin II-null cell divides by passive contraction of the cleavage furrow. In this case, cytoplasm in equatorial region is withdrawn indirectly (white arrows inside the cell) by traction forces generated along polar peripheries (black arrows). (C) Summary of three methods of cytokinesis in Dictyostelium. Cytokinesis A requires myosin II expression, but adhesion to a substrate is not necessary. Cytokinesis B is not dependent on myosin II but adhesion is indispensable. These two mechanisms of cell division occur immediately following nuclear division and are somehow coordinated in wild-type cells. The third pathway, cytokinesis C, is cell cycle independent and occurs during interphase.