Moesin negatively regulates Crumbs at the marginal zone in Drosophila follicle cells. Kristin Sherrard, Richard Fehon. Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL.

   Epithelial polarity is crucial for both maintenance of organ function and for morphogenetic movements. The transmembrane protein Crumbs (Crb) has emerged as a key regular of apical and junctional polarity through PDZ-binding interactions with the apical Par complex and Stardust and PATJ. In addition, Crb can bind to FERM domain proteins such as Moesin (Moe), Expanded, and Yurt, though the function of this binding is not well understood. We have been investigating interactions between Moe and Crb in the Drosophila follicular epithelium. We have found that Crb and aPKC levels increase in Moe-depleted follicle cells, and also that Crb is essential for localization of Moe during a stage of oogenesis when the apical and junctional regions of follicle cells are undergoing rapid expansion. In cells expressing a mutant form of Crb unable to bind FERM proteins, phosphorylated Moe and Actin are absent from the marginal zone, a region of the lateral membrane just apical to the adherens junctions. Bazooka/Par3 and Ecadherin are similarly reduced and form discontinuous bands. In contrast, depleting Moe causes a number of effects, including a Rho-dependent decrease in cell size and upregulation of aPKC, Patj, and Crb. We are currently investigating the functional significance of Crb recruiting Moe to the MZ, including possible competition for binding between Moe and Par6. Ultimately we hope to gain a better understanding of how the organization of proteins in the marginal zone contributes to polarity and junctional stability, particularly during morphogenesis.