Two studies, published online this week, demonstrate the importance of Cdc42, a Rho-type guanosine triphosphatase (GTPase), in cell polarization. In the January 30 Sciencexpress, Roland Wedlich-Soldner and colleagues used a fusion protein of green fluorescent protein linked to a constitutively activated form of Cdc42 in yeast cells (Sciencexpress, DOI:10.1126/science.1080944, 30 January, 2003). They observed that F-actin and actinomyosin-directed vesicle transport were essential for the establishment and maintenance of Cdc42-induced polar cap formation in growth-arrested cells.

In an Advanced Online Publication in Nature, Etienne-Manneville and Hall describe how Cdc42 participates in cell polarity in mammalian cells (Nature, DOI:10.1038/nature01423, January 29, 2003). They used a scratch-induced cell migration assay with primary rat astrocytes to show that Cdc42 regulates the phosphorylation of glycogen synthase kinase-3β (GSK-3β) at the leading edge of migrating cells. This leads to the interaction of adenomatous polyposis coli (Apc) with the plus ends of microtubules — an essential step in cell polarization. Thus, experiments in completely different systems have demonstrated a key role for Cdc42 in regulating the actin cytoskeleton and cell polarity.