Figure 4

BMP pathway activation in the developing kidney. A. At E10.5, strong reporter activation is seen in mesonephric tubules within the intermediate mesoderm. B. Weak reporter activation is seen in the Wolffian duct at E10.5. C. At E12.5, the reporter is active in the trunk of the collecting duct, and islands of vascular activation can be seen throughout the mesenchyme. D. Collecting duct tips show no reporter activation. Likewise, nephrogenic mesenchyme shows little or no reporter activation. E. Nuclear pSMAD1/5/8 staining is seen in the center of the E12.5 kidney, with renal vesicles and collecting duct trunks showing the most intense staining. F. Very few cells interspersed within the nephrogenic mesenchyme display nuclear pSMAD1/5/8 staining. Cells of the renal vesicle, however display extensive nuclear pSMAD1/5/8 accumulation. G. Numerous cells within the collecting duct trunk display nuclear pSMAD1/5/8 staining (arrows). H. Little pSMAD1/5/8 staining is seen in collecting duct tips. I. Reporter activation is seen in tubules and glomeruli throughout the E17.5 kidney from the subcortical layer to the nascent papilla. J. Enlargement of the boxed region in panel D. Reporter activation is seen in tubules and glomeruli, but is largely absent from the nephrogenic zone. K. Nuclear pSMAD1/5/8 staining is seen in cells of the glomerulus, tubules and nascent nephrons. Nuclear pSmad1/5/8 staining is sparse in the nephrogenic zone. L. Enlargements of pSmad1/5/8 stained nephrogenic zone, collecting ducts trunks, nephron tubules, and glomerulus showing localization of nuclear pSmad1/5/8 accumulation (arrows). M. Costaining with DBA lectin shows reporter activation in collecting duct trunks. N. No activation can be seen in DBA staining collecting duct tips. O. In the nephrogenic zone, activation can be seen only in nascent nephron structures, and individual cells adjacent to the nephrogenic mesenchyme (arrowheads). P. Reporter activation can be seen throughout the early comma shaped body with the exception of the proximal podocytes. Q. At later stages in the comma shaped body, signaling is concentrated to the presumptive proximal tubule and Bowman's capsule. R. In the s shaped body, pathway activation is seen in the proximal tubule and Bowman's capsule. S. Costaining with lotus lectin shows that the pathway remains active in more mature convoluted proximal tubules of the medulla. T. Distal tubules characteristically located at the vascular pole of the glomerulus display little pathway activation. Cells of Bowman's display pathway activation, but podocytes do not. U, V. Adjacent sections from E17.5 BRE-lacZ embryos stained for reporter activation (U) and the endothelial marker CD31 (V) show pathway activation in the glomerular capillary. Mesangial cells display little activation. Abbreviations: BC: Bowman's capsule, Caps: Capsule, CD tip: Collecting duct tip, CD trunk: collecting duct trunk, DT: distal tubule, G: glomerulus, GC: glomerular capillary, MD: mesonephric (Wolffian) duct, M: medulla, Ma: mesangium, MT: mesonephric tubule, NM: nephrogenic mesenchyme, NZ: nephrogenic zone, P: podocyte, PT: proximal tubule, RV: renal vesicle, T: tubules, US: urinary space, V: vasculature.