Figure 1.

Activity of Rho GTPase family members is compartementalized during cell division. (A) During mitosis and cytokinesis, the activity and localization of RhoA, Rac1 and Cdc42 is compartimentalized. Cdc42 activity peaks during metaphase where it is involved in the attachement of microtubules to the kinetochores. While the overall levels of active Rac1 do not change during cell division, its inactivation at the equatorial cortex is necessary for cytokinesis completions. Here, RhoA activity peaks during anaphase and telophase and drives the ingression of the cleavage furrow. Rac1 activity at the polar regions is thought to contribute to cell spreading and adhesion during and/or after cytokinesis. Both positive (including the RhoGEF Ect2) and negative regulators (including p120 and its interaction partner the RhoGAP MP-GAP; see text for more details) of RhoA localize to the equatorial cortex during cleavage furrow ingression to allow for rapid GTPase cycling to restrict and focus activity of RhoA. (B) Our recent data suggest that an inactive RhoA pool (marked by phosphorylation of Ser188) exists directly adjacent to the active membrane-associated RhoA pool during furrow ingression (anaphase to telophase)³⁸ _. The presence of this substantial pool of inactive RhoA might enable rapid GTPase cycling of RhoA to maintain heavily restricted RhoA activity at the eqeatorial cortex to drive the ingression of the cleavage furrow. The molecular mechanisms underlying phosphorylation of RhoA during cytokineses remain undetermined. The two future daughter cells are indicated with I. and II. Error bar = 2 μm. Immunofluorescence images depicted here are reproduced from³⁸.