Dynamin contributes to cytokinesis by stabilizing actin filaments in the contractile ring

Dynamin has been proposed to play an important role in cytokinesis, although the nature of its contribution has remained unclear. Dictyostelium discoideum has five dynamin-like proteins: DymA, DymB, DlpA, DlpB and DlpC. Cells mutant for dymA, dlpA or dlpB presented defects in cytokinesis that resulted in multinucleation when the cells were cultured in suspension. However, the cells could divide normally when attached to the substratum; this latter process depends on traction-mediated cytokinesis B. A dynamin GTPase inhibitor also blocked cytokinesis in suspension, suggesting an important role for dynamin in cytokinesis A, which requires a contractile ring powered by myosin II. Myosin II did not properly localize to the cleavage furrow in dynamin mutant cells, and the furrow shape was distorted. DymA and DlpA were associated with actin filaments at the furrow. Fluorescence recovery after photobleaching and a DNase I binding assay showed that actin filaments in the contractile ring were significantly fragmented in mutant cells. Dynamin is therefore involved in the stabilization of actin filaments in the furrow, which, in turn, maintain proper myosin II organization. We conclude that the lack of these dynamins disrupts proper actomyosin organization and thereby disables cytokinesis A.