Kidney disease affects more than 20 million people in the United States and is the 8th leading cause of death. It is also one of the costliest complications of chronic illness, such as hypertension and diabetes. Advances in kidney regeneration that could slow or reverse progression to kidney failure will have a major impact on human health. A long-term goal of cell-based therapies for kidney regeneration is to use engineered renal progenitor cells to generate new nephrons and replace damaged nephrons in injured kidneys. Renal progenitor cells are also being explored for use in generating nephrons ex vivo in engineered or natural organ scaffolds. In either case, nephron function requires a patent lumen for filtrate flow, processing, and homeostasis; i.e., proper plumbing. Tubule lumen interconnections are established normally during renal development by invasion of the ureter epithelium by cells of the distal S-shaped body. However, in a mature kidney, implanted renal progenitor cells may differentiate into tubules but fail to connect to an existing branched collecting system and do not contribute to kidney function. This proposal aims to overcome this hurdle by identifying growth factors that mediate nephron tubule-collecting duct fusion and determine how tubule interconnection can be induced during renal regeneration. Using the zebrafish adult kidney as a model of synchronous nephron tubule-collecting duct fusion we will 1) screen well-established Wnt and FGF signaling pathways with small molecule inhibitors and assay tubule interconnection and 2) test the effect of spatially and temporally restricted expression of growth factors or dominant negative small GTPase signaling inhibitors on nephron tubule- collecting duct fusion. These studies will provide important new insights about an essential but understudied cellular mechanism that is required for cell and tissue-based renal regeneration therapies.