Cell Separation Delay and Membrane Trafficking Defects in Cdc42 GAP Mutants

Cytokinesis is the final step in cell division, where a cell separates into two daughter cells. Cytokinesis involves many steps that must be organized in a spatiotemporal manner. In many eukaryotes, it involves the assembly and constriction of an actomyosin ring. The fission yeast Schizosaccharomyces pombe serves as a good model system to study cytokinesis because they divide via actomyosin-dependent-cytokinesis.

The Rho-family of small GTPases are molecules involved in the regulation of cell growth and division. The GTPase Cdc42 helps promote timely onset of ring constriction and septum formation in fission yeast. Studies with many other organisms show that Cdc42 must also be inactivated at certain points during cell division for proper cytokinesis. Cells lacking rga4 and rga6, the GAPs that inactive Cdc42, exhibit delayed cell separation, due to overactive Cdc42.

We find that the GAP mutants display membrane remodeling defects during cell abscission. Cdc42 is likely involved in the regulation of membrane trafficking. Indeed, fimbrin, an endocytosis marker displays abnormal localization in the GAP mutant. This suggests that there is an endocytic defect in cells lacking both rga4 and rga6. Future directions will investigate how membrane remodeling defects impair cytokinesis.