Rho GTPases in animal cell mitosis.

The Rho GTPases have been thought to influence cell morphogenesis through remodeling of the actin cytoskeleton. Consistently, downstream targets such as the mDia family of formins and the WASP family proteins induce actin nucleation and polymerization, and another set of downstream effectors, the ROCK family protein kinases, are involved in regulation of actomyosin contractility. However, evidence has now accumulated that Rho GTPases also regulate local dynamics of microtubules. The mDia family proteins, for example, function downstream of Rho to stabilize and align microtubules in interphase cells. Concomitantly, the role of Rho GTPases in animal cell division, once thought to be limited to cytokinesis, has now been shown to extend to mitosis. Recent work indicates that they may function during both spindle orientation and chromosome congression. However, their involvement is cell-type-specific, raising arguments for and against a mitotic role for Rho GTPases.