Dev111617 1228..1241

Contrary to its classic role in restraining cell proliferation, we demonstrate here a divergent function of p53 in themaintenanceof self-renewal of the nephron progenitor pool in the embryonic mouse kidney. Nephron endowment is regulated by progenitor availability and differentiation potential. Conditional deletion of p53 in nephron progenitor cells (Six2Cre;p53) induces progressive depletion of Cited1/Six2 selfrenewing progenitors and loss of cap mesenchyme (CM) integrity. The Six2(p53-null) CM is disorganized, with interspersed stromal cells and an absence of a distinct CM-epithelia and CM-stroma interface. Impaired cell adhesion and epithelialization are indicated by decreased E-cadherin and NCAM expression and by ineffective differentiation in response to Wnt induction. The Six2Cre;p53 cap has 30% fewer Six2(GFP) cells. Apoptotic index is unchanged, whereas proliferation index is significantly reduced in accordancewith cell cycle analysis showing disproportionately fewer Six2Cre;p53 cells in the S and G2/M phases compared with Six2Cre;p53 cells. Mutant kidneys are hypoplastic with fewer generations of nascent nephrons. A significant increase inmean arterial pressure is observed in early adulthood in both germline and conditional Six2(p53-null) mice, linking p53-mediated defects in kidney development to hypertension. RNA-Seq analyses of FACS-isolated wild-type and Six2(GFP) CM cells revealed that the top downregulated genes in Six2Cre;p53CMbelong to glucosemetabolism and adhesion and/ or migration pathways. Mutant cells exhibit a ∼50% decrease in ATP levels and a 30% decrease in levels of reactive oxygen species, indicating energy metabolism dysfunction. In summary, our data indicate a novel role for p53 in enabling the metabolic fitness and selfrenewal of nephron progenitors.