Possible mechanism of cytokinesis of mammalian cells in the absence of myosin II

Adherent mammalian cells experience a series of elaborate, but simple morphological changes during cell division. This complex process was mediated by mechanics and biological molecules. As a kind of motor proteins, myosin II plays an important role in cell division. Recent investigations showed that cells on substrates in the absence of myosin II also could finish cytokinesis. However, its mechanism is still unclear. In this study, morphology of NRK cells treated with 0.3%DMSO and 30 μmol blebbistatin (myosin II inhibitor) were investigated quantitatively by using micro-image collecting and analysis system. Intercellular bridge dynamics was simulated using mechanical model of intercellular bridge thinning coupled with mechanical parameters of NRK cells. The distribution of actin in early cytokinesis was examined using immunofluorescence method. Our results showed that intercellular bridge thinning trajectory and morphology of cells treated with 30 μmol blebbistatin were fundamentally different from cells treated with 0.3%DMSO. The surface tension contributed greatly to the trajectory of 30 μmol blebbistatin group from fluid mechanical considerations and the measured mechanical parameters. Immunofluorescence results indicated that a mass of actin was recruited to the fan-shaped leading lamellipodia of daughter cells from the cytoplasm in cells treated with 30 μmol blebbistatin. Our study indicated that Laplace pressure determined by mechanical properties and the motility of cell orchestrated to dictate a well-controlled cytokinesis of cells in the absence of myosin II.