Early organogenesis of the kidney.

The mammalian permanent kidney consists of three cell lineages of different origin: the epithelial cells of the ureter bud, the mesenchymal cells of the nephric blastema and the endothelial cells of the capillaries. Organogenesis is governed by a cascade of morphogenetic interactions between these cell populations, a reciprocal epithelial-mesenchymal interaction between the branching ureter and the metanephric mesenchyme, homotypic interactions between cells of the tubular anlagen, stimulation of angiogenesis by the differentiating blastema and a mesenchymal--endothelial interaction guiding the migration of the capillary endothelial cells. While the biology of these interactive events is well known, as described in this overview, the molecular mechanisms are less well mapped out.