FIGURE 11. The role of racE in cortical tension and cytokinesis. We postulate that racE plays a role in organizing the cortical actin cytoskeleton by an attachment independent process.

(A) Cells on a substrate receive a signal through attachment that stimulates the polymerization of F-actin. The increase in F-actin may be sufficient to suppress any cytoskeletal organization defects in racE null cells. Alternatively, the attachment signal may also organize the cytoskeleton in a racE-independent manner.

(B) In suspension conditions cells are not stimulated by attachment and have less F-actin. RacE is required under these conditions to organize the cytoskeleton and preserve cortical integrity. In the absence of racE, the cortical cytoskeleton is less organized, leading to breaches in the cortex and formation of blebs. Similarly, the contractile ring to forms but fails to constrict to completion.