Fig. 5.

Myosin II localization to the equatorial cortex involves two steps, recruitment and retention, that have different molecular determinants. (A) Schematic of known proteins involved in cytokinesis, their relationships to one another, and their effect on myosin II localization. Proteins that are essential for myosin II recruitment are marked in green, those necessary for myosin II retention in the equatorial cortex are marked in red, and those essential for both myosin II retention and significant contraction are indicated in magenta. In black are proteins not assayed for their effect on myosin II localization. The two signaling pathways downstream of rho1 have different effects on myosin II localization. The pathway that leads to F-actin stimulation is necessary only for retention, whereas the pathway that leads to RLC phosphorylation is necessary for the initial recruitment of myosin II. (B) Model for the recruitment and retention of myosin II to the cleavage furrow. Localized activation of rho kinase by rho1 is necessary for the initial recruitment of myosin II to the equatorial cortex at anaphase. At later stages, rho1-activated diaphanous, in conjunction with chickadee, mediates the assembly of parallel F-actin filament structures that are necessary for the retention of myosin II in the equatorial cortex.