Myosin II transport, organization, and phosphorylation: evidence for cortical flow/solation-contraction coupling during cytokinesis and cell locomotion.

Abstract

The mechanism of cytokinesis has been difficult to define because of the short duration and the temporal-spatial dynamics involved in the formation, activation, force production, and disappearance of the cleavage furrow. We have investigated the structural and chemical dynamics of myosin II in living Swiss 3T3 cells from prometaphase through the separation and migration of daughter cells. The structural and chemical dynamics of myosin II have been defined using the semiautomated, multimode light microscope, together with a fluorescent analogue of myosin II and a fluorescent biosensor of myosin II regulatory light chain (RLC) phosphorylation at serine 19. The correlation of image data from live cells using different modes of light microscopy allowed interpretations not possible from single-mode investigations. Myosin II transported toward the equatorial plane from adjacent regions, forming three-dimensional fibers that spanned the volume of the equator during anaphase and telophase. A global phosphorylation of myosin II at serine 19 of the RLC was initiated at anaphase when cortical myosin II transport started. The phosphorylation of myosin II remained high near the equatorial plane through telophase and into cytokinesis, whereas the phosphorylation of myosin II at serine 19 of the RLC decreased at the poles. The timing and pattern of phosphorylation was the same as the shortening of myosin II-based fibers in the cleavage furrow. Myosin II-based fibers shortened and transported out of the cleavage furrow into the tails of the two daughter cells late in cytokinesis. The patterns of myosin II transport, phosphorylation, and shortening of fibers in the migrating daughter cells were similar to that previously defined for cells migrating in a wound in vitro. The temporal-spatial patterns and dynamics of myosin II transport, phosphorylation at serine 19 of the RLC, and the shortening and disappearance of myosin II-based fibers support the proposal that a combination of the cortical flow hypothesis and the solation-contraction coupling hypothesis explain key aspects of cytokinesis and polarized cell locomotion.

A Specific Isoform of Nonmuscle Myosin II-C Is Required for Cytokinesis in a Tumor Cell Line

“…Our findings that blebbistatin treatment causes a loss of furrow ingression leading to binucleation suggest that the process of cell adhesion and attachment of the dividing A549 cells are myosin-dependent events and that we are not observing a myosin-independent form of cytokinesis. In a number of ways, the mechanism outlined above for myosin II playing a role in formation and retraction of the cytoplasmic bridge as well as in cell adhesion and spreading agrees with the mechanism suggested by Taylor's laboratory using Swiss 3T3 cells, where they measured traction force during the late stages of cytokinesis (32,33). Our data support the idea that this traction force is generated by nonmuscle myosin II.…”

Asymmetric Flows in the Intercellular Membrane during Cytokinesis

“…Formation of the contractile ring and the membrane partition require a supply of actin, myosin, and phospholipids. This material can either be directly recruited from the cytoplasm or can flow into the furrow through actomyosin-based cortical flows (14)(15)(16)(17). Cortical flows are known to facilitate alignment of actin filaments in the contractile ring (14,18).…”

Active multistage coarsening of actin networks driven by myosin motors

“…Interestingly, similar dense condensates appear in cells during myosin-driven shape changes of the actin cytoskeleton. Formation of the contractile ring in dividing fibroblasts (19) and Caenorhabditis elegans embryos (20) both involve large-scale flows and coalescence of dense actomyosin condensates. Similarly, the lamellipodium of migrating cells displays dense myosin aggregates (21,22).…”