Schematic representation of normal development of the human kidney. (a) Invasion of the metanephric mesenchyme (MM) by the ureteric bud (UB) induces MM cells to aggregate around the UB tip. (b) MM cell aggregates undergo mesenchymal-to-epithelial transformation (MET) to form the renal vesicle (RV). (c) RV elongates along the proximal-distal axis to form comma-shaped and then S-shaped nephron. Distal ends of S-shaped nephrons fuse with UB-derived collecting ducts, whereas proximal clefts form glomeruli. Endothelial cells migrate into the proximal cleft. (d) Patterning of the S-shaped nephron and UB result in formation of mature nephron which contains glomerular capillary tuft, podocytes, proximal tubule (PT), loop of Henle, distal tubule (DT), and collecting duct. Please see text for details.
