Figure 4.

Collecting duct number is reduced in E18.5 Alk3^UB−/− kidneys. (A and B) E18.5 Alk3^UB−/− kidneys exhibit a paucity of medullary tissue compared with Wt, which suggests a reduction in tubular elements. (C through F) RNA in situ hybridization shows reduced Pax2 expression in Alk3^UB−/− collecting ducts. Pax2 mRNA expression is observed in the outer nephrogenic zone (boxed areas) and in tubules extending from the inner medulla to the cortex in Wt kidneys. (C and D) Pax2 mRNA expression is decreased in Alk3^UB−/− kidneys. (E and F) Higher power images of the nephrogenic zone demarcated in C and D demonstrate similar levels of Pax2 expression in Wt and Alk3^UB−/− kidneys. (G and H) Calbindin_28K antibody staining shows marked reduction in collecting duct number (arrows) in Alk3^UB−/− kidneys. (I) Collecting duct number is reduced 39% (P = 0.0001) in Alk3^UB−/− kidneys. Scale bars: (A through D) 500 μm, (G and H) 100 μm.