Renal Stroma: Where Is It and What Is It?
In the mouse, metanephric development begins at approximately E10.5 with formation of the ureteric bud. By E11, the ureteric bud has invaded the surrounding blastema (mesenchyme), and the cells are induced to survive and proliferate. At this stage, the blastema consists of a group of morphologically similar cells (fig. 1a). The ureteric bud then induces the blastemal cells to condense around the ureteric bud tip (fig. 1b), and two regions of the metanephric mesenchyme can be morphologically distinguished: (1) the region surrounding the ureteric bud tip is condensing cap mesenchymal cells which are Pax2 positive and will ultimately form nephrons, and (2) the region peripheral to the cap mesenchyme is a looser domain of cells which express the winged helix transcription factor Foxd1 (formerly BF2 – [20]) (fig. 1b). These latter cells are the presumptive stromal progenitor cells [20]. Within the nephrogenic zone is a 3rd population of cells (fig. 1b) which are Foxd1 negative and appear sm
