Developmental Roles of the Stroma

The renal stroma is a broad term describing all non-epithelial or endothelial cells in the kidney. Stromal cells arise from a mesenchymal progenitor population distinct from the nephron progenitor cells and differentiate into a variety of cell types including pericytes and interstitial fibroblasts. During development, the stroma is patterned on the cortico-medullary axis with progenitor stromal cells on the cortical edge of the kidney in the nephrogenic zone. Over the past several years, it has been determined that signals from the stroma affect the branching of the ureteric bud, the balance between nephron progenitor differentiation and renewal, the integrity of the vasculature, and the gross patterning of the entire organ, and it is likely that there are additional, undiscovered roles for this underappreciated cell type. This chapter will summarize the known roles and speculate on further roles for the stroma in kidney development.