Figure 1.

Development of the metanephric kidney. The development of the kidney is initiated when the ureteric bud (shown here in red) invades the metanephric mesenchyme. The mesenchyme consists of two distinct cell populations: the nephron progenitors (light gray) and a layer of fibroblasts known as the stroma (blue). Signals from the bud induce differentiation in a progenitor-subset (dark gray) to form the renal vesicle (gray ball), while signals from the mesenchyme induce branching morphogenesis of the ureteric bud. At the same time, the stromal population is patterned and segregates itself as the cortical stroma (in blue) and medullary stroma (in green). Wnt5a and the PCP determinants Fat4 and Dachsous are primarity expressed in the stromal population, while Four-jointed, Vangl2 and Celsr1 are expressed primarily in the renal vesicles and ureteric buds. Wnt4 is also expressed in the renal vesicles. Wnt9b and Wnt7b are expressed in the ureteric bud epithelium.