Nephrology zyxwvutsrqp 1996; zyxwvutsrqp 2, 167-174 Original Article Immunolocalization of fibroblast growth factor01 and 02 in the embryonic rat kidney BELINDA CANCILLA, JENNIFER CAUCHI, BRIAN KEY, VICTOR NURCOMBE, DAINE ALCORN AND JOHN BERTRAM Department of Anatomy zyxwvuts and Cell Biology, University of Melbourne, Parkvilk, Victoriu, Australia Summary: Fibroblast growth factors (FGF) regulate cell proliferation, migration, differentiation and angio- genesis during morphogenesis in many different tissues. Recent evidence indicates that exogenous FGF-2 stimulates mesenchymal condensation in cultured rat metanephroi, a crucial epithelial-mesenchymal induc- tion event in the developing nephron. The aim of the present investigation was to determine the in zy 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 co- localized in developing nephron elements, from vesicles to S-shaped bodies, and in the mesangium of capil- lary 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 undif- ferentiated 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 kid- ney development. Key words: development, fibroblast growth factor, glomerulus, immunohistochemistry,kidney, metanephros. INTRODUCTION The metanephros, or permanent kidney, is of mesodermal origin; the epithelial cells of the nephron, including the epithelial cells of the renal corpuscle are derived from metanephric mesenchyme, while the ureteric bud forms the ureter, renal pelvis, calyces and collecting tubules. The epithelial ureteric bud grows into the metanephric mes- enchyme and is induced by this tissue to branch dichoto- mously. Mesenchyme condenses at the tips of the ureteric branches; these mesenchymalcondensates then convert to an epithelium and form a vesicle. The vesicle subsequently invaginates to form a cleft, resulting in a comma-shaped body. This body invaginates a second time to form an S-shaped body. At this stage, all future nephron compo- nents are present: the glomerular anlage (the lower limb of the S-shaped body which contains podocytes and Bow- man's capsule), the proximal tubule, loop of Henle and dis- tal straight tubule anlagen (middle limb of the S-shaped Correspondence: John F. Bertram, Department of Anatomy and Cell Received 9 November 1995; accepted 20 March 1996. Biology, University of Melbourne, Parkville, Victoria 3052, Australia. body), the future macula densa is already in place (the cells in the first bend of the S-shaped body adjacent to the end of the lower limb), and the distal convoluted tubule anlage (upper limb of the S-shaped body). The developing vascu- lature of the kidney is closely associated with the early nephron elements and capillaries that have invaded the cleft of comma- and S-shaped bodies begin to loop and anastomose to form the glomerular tuft of capillaries.' The developing mesangium is present at the capillary loop stage of glomerular development. The free end of the upper limb of the S-shaped body fuses with the ureteric bud causing their lumina to become continuous. The proximal and dis- tal portions of the S-shaped body then begin to elongate and fold to form the tubule system of the maturing nephron.2 The loop of Henle develops through three dis- tinct stages: (i) the primitive loop of Henle; proximal and distal tubule anlagen containing thick undifferentiated epithelium; (ii) the immature loop of Henle; the proximal tubule anlage lengthens and differentiates to form proxi- mal straight tubule epithelium and thin undifferentiated epithelium, and the distal tubule anlage differentiates into distal straight tubule epithelium. The boundary between thin undifferentiated epithelium and distal tubule occurs