Cell Biology

Push Me Pull You

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Science  03 Feb 2012:
Vol. 335, Issue 6068, pp. 505
DOI: 10.1126/science.335.6068.505-a

A contractile ring composed of actin and myosin promotes cytokinesis—the final stage of cell division when daughter cells are physically separated from one another. The small GTPase RhoA regulates the contraction of this actomyosin ring. A Rho-family GTPase-activating protein (GAP), CYK-4 helps RhoA localize to the cleavage furrow, in part by binding to the guanine nucleotide exchange factor (GEF) for RhoA, ECT2. The cytokinetic role of the GAP domain of CYK-4, however, is unclear. Previously, Rac1 inactivation was proposed to be the primary function of the GAP domain. Now, working in C. elegans embryos, Loria et al. suggest that the CYK-4 GAP domain also contributes to activating RhoA during cytokinesis. Some defects in furrow ingression could be relieved by relaxation of the Rac1-dependent cortical actin network, bypassing to a certain extent the need for activated RhoA and a functional GAP domain in CYK-4. Cleavage furrow ingression thus reflects the balance of forces between the contractile ring and the cell cortex outside of the furrow region, allowing the cell to complete cytokinesis even when some of the cytokinetic machinery has been compromised.

Curr. Biol. 22, 10.1016/j.cub.2011.12.019 (2012).

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