ABSTRACT Specifying the Renal Epithelial Phenotype in Development and Disease. This application investigates the genetic and biochemical control of renal function in adults, with particular emphasis on urine concentration and the function of Pax proteins. The Dressler Lab has developed genetically engineered mouse lines and epithelia cell derivatives that can delete either Pax2, Pax8, or both genes and their protein products. These Pax proteins are critical for the development of the nephrons, but their functions in adult terminally differentiated epithelia has not been studied. Preliminary data show a significant effect on water, urea, and sodium transporters in adult kidneys upon deletion of both Pax proteins. These data suggest a transcriptional or maintenance role for Pax genes in renal epithelial cells that will be characterized at multiple levels. How Pax proteins impact promoters and enhancers, modify and maintain patterns of histone methylation, and activate or repress target gene transcription will be studied in vivo and in cell culture models. Direct targets of Pax proteins will be identified by chromatin precipitation and bioinformatic analyses. Whether the related proteins Pax2 and Pax8 have redundant functions in the collecting ducts and renal medulla will be determined by individual single and double mutants. How Pax proteins specify the genomic landscape by recruiting histone methyltransferase complexes will also be studied in cell cultures that can delete either or both proteins in response to tamoxifen. These studies will determine fundamental regulatory mechanisms governing renal function and epithelial cell specification, and can identify new pathways for intervention to address both chronic and acute renal disease.