Figure 4.

Inducible Sall1 deletion phenocopies the conditional Sall1 mutant. Tamoxifen was injected at E12.5 and analyzed later. (A–H) Immunostaining for Six2 (nephron progenitor), WT1 (nephron progenitor and podocyte), LTL (proximal renal tubule), and THP (the loop of Henle) at P0. Development of the nephron components is significantly impaired in the Sall1^CreER/flox mouse kidney. Scale bar, 100 μm. (I–K) Terminal deoxynucleotidyl transferase-mediated digoxigenin-deoxyuridine nick-end labeling (red) and NCAM (green) staining at E14.5. (J and K) Apoptotic cells are detected in differentiating nephrons in the mutant. (K) Apoptosis is more prominent in the differentiating nephrons located deeper inside of the kidney. Arrows, differentiating nephrons; arrowheads, nephron progenitors. Scale bar, 40 μm. (L–Q) Dual immunostaining for Sall1 and Six2 at E13.5. Sall1 expression (red) is reduced in some of the nephron progenitors (arrowheads) and differentiating nephrons (arrows). Most of the Six2-positive cells (green) are negative for Sall1 in the mutant. *Stroma. Scale bar, 40 μm. (R–U) Immunostaining for Sall1 and Six2 at E14.5. Scale bar, 100 μm. (V and W) Immunostaining for Six2 at E15.5. Note that the differentiating nephrons (renal vesicles; arrows) were aberrantly large considering the reduced progenitors (arrowheads) in the Sall1 mutant. Six2 was slightly overstained, and therefore, the nascent nephrons expressing Six2 weakly were detectable. Scale bar, 40 μm. V′ and W′ show higher magnification. (X and Y) Immunostaining for Lef1 (Wnt activity) at E15.5. Lef1 is expressed in the differentiating nephrons (arrows) and excluded from the progenitors (arrowheads; dotted regions) in both Sall1^+/flox and Sall1^CreER/flox kidneys. Scale bar, 40 μm. ub, ureteric bud.