LAUSR

ABSTRACT Cilia are cellular antennae that are essential for human development and physiology. A large number of genetic disorders linked to cilium dysfunction are associated with proteins that localize to the ciliary transition zone (TZ), a structure at the base of cilia that regulates trafficking in and out of the cilium. Despite substantial effort to identify TZ proteins and their roles in cilium assembly and function, processes underlying maturation of TZs are not well understood. Here, we report a role for the membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP2) in TZ maturation in the Drosophila melanogaster male germline. We show that reduction of cellular PIP2 levels through ectopic expression of a phosphoinositide phosphatase or mutation of the type I phosphatidylinositol phosphate kinase Skittles induces formation of longer than normal TZs. These hyperelongated TZs exhibit functional defects, including loss of plasma membrane tethering. We also report that the onion rings (onr) allele of Drosophila Exo84 decouples TZ hyperelongation from loss of cilium–plasma membrane tethering. Our results reveal a requirement for PIP2 in supporting ciliogenesis by promoting proper TZ maturation. Summary: The membrane phospholipid PIP2, and the kinase that produces PIP2, called Skittles, are needed for normal ciliary transition zone morphology and function in the Drosophila male germline.