Development of the renal interstitium.

The kidney is derived from two tissue sources and develops through a series of mesenchymal-epithelial transitions and epithelial-mesenchymal interactions to form an epithelial tubular organ embedded in an interstitium derived from mesenchyme. The primary interstitium of the embryonic kidney undergoes significant differentiation to form the adult counterpart whose diverse cells have structural and functional characteristics that relate to their local milieu. Whether the adult interstitial cells retain the capacity to transform to other cell types and thus play a role in pathophysiological conditions appears more and more likely as the plasticity of cells becomes apparent. Besides forming the adult interstitium, the primary interstitium is active in metanephric development, with specific roles in nephron growth and collecting duct growth and arborization. Interruptions to the development of the interstitium or amelioration of its developmental capacity result in severely disrupted kidneys. The development of the renal interstitium is an essential component in the process of renal genesis.