Fig. 6. (A) Hypothetical responses of metanephroi to DAPT. At 14.5 dpc, the metanephros contains mature structures in the center (D, podocytes) and immature ones at the periphery (A, uninduced mesenchyme). The peripheral tissue progressively differentiates (vertical box), flanked with mesenchymal stem cells at more peripheral positions. If DAPT only blocks the induction but not differentiation of proximal epithelia (model 1), induced epithelia can still progress to podocytes. If DAPT also blocks podocyte differentiation (model 2), the deficiency in podocytes (Wt1^HIGH cells) will manifest earlier, at day 3 (D-D-D-B-B-A in model 1; D-D-B-B-B-A in model 2). After 3 days in culture, there is no appreciable difference in formation of podocyte/glomeruli near the periphery between the control and DAPT-treated cultures (green circles in B), compatible with model 1. (C) Twenty-four hours later, peripheral regions (green arrows in C) have produced mature Wt1^HIGH cells in DMSO but not in DAPT. We therefore assign the DAPT-sensitive step at the formation of proximal renal epithelia, with a possible secondary effect reducing the number of distal epithelia. The affected cell population is the one containing NICD.