Expression of transforming growth factor-β type II receptor mRNA in embryonic and adult rat kidney

Summary: The transforming growth factor-β (TGF-β) family of growth factors regulates cell proliferation, differentiation, extracellular matrix synthesis and angiogenesis in many developing tissues. Transforming growth factor-β1 was recently shown to affect the branching of ureteric epithelium and nephron formation in cultured rat metanephroi. As the TGF-β type II receptor is specific for the TGF-β family, the present study used in situ hybridization to localize mRNA for this receptor in metanephroi from Sprague-Dawley rat embryos. Transforming growth factor-β type II receptor mRNA was located in ureteric duct epithelium, undifferentiated mesenchymal cells in the nephrogenic zone, vesicles, comma-shaped bodies and S-shaped bodies. In some S-shaped bodies, TGF-β type II receptor mRNA was not expressed in the lower limb, which subsequently forms the renal corpuscle. Expression was not observed in capillary loop stage glomeruli and maturing glomeruli, or in proximal tubules and interstitial cells. In adult rat kidney, TGF-β type II receptor mRNA was expressed in cortical collecting ducts and distal tubules but not in glomeruli or proximal tubules. These findings demonstrate that the prominent expression of TGF-β type II receptor mRNA decreases as glomeruli and tubules develop. Expression then remains undetectable in adult glomeruli and proximal tubules. the developmentally-regulated expression of this receptor suggests a key role in glomerular and nephron development.     

Immunolocalization of fibroblast growth factor-1 and -2 in the embryonic rat kidney

Summary: Fibroblast growth factors (FGF) regulate cell proliferation, migration, differentiation and angiogenesis during morphogenesis in many different tissues. Recent evidence indicates that exogenous FGF-2 stimulates mesenchymal condensation in cultured rat metanephroi, a crucial epithelial-mesenchymal induction event in the developing nephron. the aim of the present investigation was to determine the in vivo distribution of FGF-1 and FGF-2 in developing rat metanephroi at embryonic days 14, 15, 16, 18 and 20. Avidin-biotin enhanced indirect immunohistochemistry was used to demonstrate that both FGF-1 and FGF-2 were co-localized in metanephroi at all ages studied. High levels of FGF-1 and FGF-2 were present in ureteric bud branches and in developing distal tubules. Fibroblast growth factor-1 and FGF-2 were colocalized in developing nephron elements, from vesicles to S-shaped bodies, and in the mesangium of capillary loop and maturing stage glomeruli. Both growth factors were present in the mesenchyme of the nephrogenic zone and in the interstitium of the developing cortex. However, immunostaining for FGF was not evident in mesenchymal condensates, endothelial cells, medullary interstitial cells, or in the thin undifferentiated epithelium of the immature loop of Henle. These findings indicate that the expression of both FGF-1 and FGF-2 is tightly regulated in the embryonic kidney and suggest a role for these molecules in kidney development.