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.

Dynamin is a large GTPase responsible for diverse cellular processes, such as endocytosis, division of organelles, and cytokinesis. The social amoebozoan, Dictyostelium discoideum, has five dynamin-like proteins: dymA, dymB, dlpA, dlpB, and dlpC. DymA, dlpA, or dlpB-deficient cells exhibited defects in cytokinesis. DlpA and dlpB were found to colocalize at cleavage furrows from the early phase, and dymA localized at the intercellular bridge connecting the two daughter cells, indicating that these dynamins contribute to cytokinesis at distinct dividing stages. Total internal reflection fluorescence microscopy revealed that dlpA and dlpB colocalized at individual dots at the furrow cortex. However, dlpA and dlpB did not colocalize with clathrin, suggesting that they are not involved in clathrin-mediated endocytosis. The fact that dlpA did not localize at the furrow in dlpB null cells and vice versa, as well as other several lines of evidence, suggests that hetero-oligomerization of dlpA and dlpB is required for them to bind to the furrow. The hetero-oligomers directly or indirectly associate with actin filaments, stabilizing them in the contractile rings. Interestingly, dlpA, but not dlpB, accumulated at the phagocytic cups independently of dlpB. Our results suggest that the hetero-oligomers of dlpA and dlpB contribute to cytokinesis cooperatively with dymA.

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