Studies of Cell Lineage in the Developing Kidney

The development of the definitive (metanephric) kidney in mammals depends on the reciprocal inductive interactions between two mesoderm-derived structures: the metanephric mesenchyme (MM) and the epithelial ureteric bud. The ureteric bud secretes factors that induce the mesenchyme to condensate, proliferate, and convert to an epithelium, resulting in the formation of an epithelial vesicle that matures into a glomerulus. The induced mesenchyme in turn sends signals to the ureteric bud, causing its division and growth. When the ureteric bud has branched once, the MM already possesses precursor cells with the ability to differentiate into epithelial, vascular, interstitial, and mesangial cells (1 –3 ). As a result of these processes, the ureteric bud generates the collecting and the pelvic and ureteric epithelia, whereas the MM gives rise to glomeruli, vessels, and proximal tubules.