Figure 1.

Stereotypical, open-loop cytokinesis. (A) Cartoon depicts the series of shapes that cells undergo during cytokinesis. Region of myosin-II enrichment is shown in green. Microtubules are shown in red and depict the microtubule rearrangements typical of Dictyostelium. Nuclei are shown as blue circles. Dictyostelium cells have a closed mitosis (similar to yeast) in which the nuclear envelope does not completely disassemble as in higher metazoans. (B) Diagram depicts an open loop system in which the mitotic spindle delivers signals that direct the accumulation of contractile proteins to the equatorial cortex. The contractile proteins generate force, which changes the cell shape until cytokinesis is completed, producing two daughter cells. However, mechanical perturbations can also affect the forces acting on the cell, and if these disturbances go undetected, cytokinesis can be defective.