Drosophila Stardust is a partner of Crumbs in the control of epithelial cell polarity

The polarized architecture of epithelial cells depends on the highly stereo typic distribution of cellular junctions and other membrane-associated prot ein complexes. In epithelial cells of the Drosophila embryo, three distinct domains subdivide the lateral plasma membrane. The most apical one compris es the subapical complex (SAC). It is followed by the zonula adherens (ZA) and, further basally, by the septate junction(1). A core component of the S AC is the transmembrane protein Crumbs, the cytoplasmic domain of which rec ruits the PDZ-protein Discs Lost into the complex(2,3). Cells lacking crumb s or the functionally related gene stardust fail to organize a continuous Z A and to maintain cell polarity(4-6). Here we show that stardust provides a n essential component of the SAC. Stardust proteins colocalize with Crumbs and bind to the carboxy-terminal amino acids of its cytoplasmic tail. We in troduce two different Stardust proteins here: one MAGUK protein, characteri zed by a PDZ domain, an SH3 domain and a guanylate kinase domain; and a sec ond isoform comprising only the guanylate kinase domain. The Stardust prote ins represent versatile candidates as structural and possibly regulatory co nstituents of the SAC, a crucial element in the control of epithelial cell polarity.