Fig. 5
MAPK/ERK-deficient UB tips prematurely differentiate into UB stalk-like cells. A Comparison of differentially expressed genes in UBdko to a published dataset of genes with enriched expression in either the UB tip or UB stalk (Rutledge et al.) revealed that of the previously identified UB tip-enriched genes that are differentially expressed in the UBdko, all (39/39 genes) are downregulated (blue). Of the UB stalk-enriched genes differentially expressed in the UBdko, 95% (78/82 genes) are upregulated (red). B Schematic representation of the gene expression changes between the UBs of wildtype (control) and HoxB7Cre-GFP;Mek1fl/fl;Mek2−/− (dko) kidneys at E12.5. It is known that the control kidney has distinct gene expression signatures in the UB tips (blue) compared to the UB stalks (red). Additionally, the control kidney exhibits a stereotypic branching pattern. We have shown previously that in the absence of MAPK/ERK activation, the UB has a noticeable branching defect. Our analysis here revealed that MAPK/ERK-deficient UB epithelium loses the expression of tip specific genes and instead shows upregulation of stalk-enriched genes (n = 4 kidneys/genotype). C–H’ Immunofluorescent staining of the E16.5 kidney paraffin sections. Calbindin-1 (CALB1) labels UB epithelium (green), and arrows indicate CALB1-positive cortical UB epithelium. C-D’ Na/K-ATPase (red), a marker of principal cells in the mature collecting duct, is absent in the cortical UB tips of C, C’ control kidneys but is detected in CALB1-positive cortical UB epithelium in D, D’ UBdko. Similarly, V-ATPase-B1/2 (red), a marker of intercalated cells in the mature collecting duct, is absent in the cortical epithelium of E, E’ control kidneys but localized to cortical epithelium of F, F’ UBdko. G, G’ Aquaporin-2 (AQP2), another marker of intercalated cells, is also absent from control but H, H’ detected in UBdko cortical epithelium. Scale bar, 100 μm