Gamma-secretase activity is dispensable for mesenchyme-to-epithelium transition but required for podocyte and proximal tubule formation in developing mouse kidney.

Notch signaling is involved in pronephros development in Xenopus and in glomerulogenesis in mice. However, owing to early lethality in mice deficient for some Notch pathway genes and functional redundancy for others, a role for Notch signaling during early stages of metanephric development has not been defined. Using an antibody specific to the N-terminal end of gamma-secretase-cleaved Notch1, we found evidence for Notch1 activation in the comma and S-shaped bodies of the mouse metanephros. We therefore cultured mouse metanephroi in the presence of a gamma-secretase inhibitor, N-S-phenyl-glycine-t-butyl ester (DAPT), to block Notch signaling. We observed slightly reduced ureteric bud branching but normal mesenchymal condensation and expression of markers indicating that mesenchyme induction had occurred. However, fewer renal epithelial structures were observed, with a severe deficiency in proximal tubules and glomerular podocytes, which are derived from cells in which activated Notch1 is normally present. Distal tubules were present but in reduced numbers, and this was accompanied by an increase in intervening, non-epithelial cells. After a transient 3-day exposure to DAPT, proximal tubules expanded, but podocyte differentiation failed to recover after removal of DAPT. These observations suggest that gamma-secretase activity, probably through activation of Notch, is required for maintaining a competent progenitor pool as well as for determining the proximal tubule and podocyte fates.