Scribble acts in the Drosophila Fat-Hippo pathway to regulate Warts activity. Shilpi Verghese1, Indrayani Waghmare1, Hailey Kwon1, Katelin Hanes1, Madhuri Kango-Singh1,2,3. 1) Department of Biology, University of Dayton, Dayton, OH; 2) Pre-Medical Programs, University of Dayton, Dayton OH; 3) Center for Tissue Regeneration and Engineering at Dayton, University of Dayton, Dayton OH.

   Hippo pathway regulates organ size from flies to mammals through the transcriptional co-activator Yorkie (Yki). The pathway controls gene expression and growth regulation by controlling the nuclear availability of Yki by several alternate mechanisms (e.g., sequestration of Yki in the cytoplasm by Warts (Wts) phosphorylation following hyper-activation, or by binding of Expanded (Ex) and Yki resulting in its membrane localization). Several Hippo pathway components (like, Fat (Ft) and Ex) localize to cell junctions organized by three distinct protein complexes that maintain epithelial sheet integrity and aid in signaling interactions. Amongst the junctional proteins, Crumbs (Crb), atypical Protein Kinase C (aPKC), Scribble (Scrib) and Lethal giant larvae (Lgl) are known to interact with Hippo pathway to regulate growth. However the molecular mechanisms of these interactions are largely unknown. scrib is a neoplastic tumor suppressor gene known to regulate growth and apico-basal polarity in cells. Loss of scrib causes neoplastic tumors while scrib mutant cells challenged with wild type cells get eliminated attributing differential growth properties to scrib mutant cells. Recent studies have shown that scrib interacts with the Hippo pathway and loss of scrib affects expression of Hippo target genes. Furthermore, both in flies and mammalian model systems, Scribble has been shown to act upstream or parallel of Warts and Scribble requires Yki to regulate its growth functions. However, the mechanism by which Scribble regulates growth via Hippo pathway remains unclear. Using the GAL4-UAS system and transgenic RNAi approach, we show that Scrib acts downstream of Ft. We also show that Ft requires Scrib to interact with Ex and Dachs (D), and for regulating Wts levels and stability, thus placing Scrib in the Hippo pathway network.