During the establishment of cell polarity, a central feature of development, mRNAs and proteins are localized to restricted cellular domains through asymmetric transport along a polarized microtubule cytoskeleton. Interactions between this cytoskeleton and the plasma membrane establish polarized transport, but what regulates these interactions? On , Gervais and colleagues identify Skittles (a phosphatidylinositol 4-phosphate 5-kinase) as a regulator of these interactions in Drosophila oocytes by showing that Skittles sustains the organization of the microtubule cytoskeleton that asymmetrically localizes several axis-determining mRNAs and thus helps to establish cell polarity. They report that Skittles activity controls phosphatidylinositol 4,5 bisphosphate (PIP2) levels in the oocyte's plasma membrane and that PIP2 synthesis is required to activate Moesin, an adaptor protein that links the plasma membrane to the actin-based cytoskeleton. Furthermore, Skittles activity is needed for the cortical recruitment of several PAR polarity proteins. Thus, by controlling PIP2 synthesis, Skittles may regulate the interactions between the plasma membrane, PAR proteins and the cytoskeleton that are essential for cell polarization.
