Role for Gremlin in Ureteric Branching Morphogenesis and Nephrogenesis in the Developing Mouse Kidney
Ureteric branching morphogenesis (UBM) is an important regulator of nephron endowment and renal architecture. Bone morphogenetic proteins (BMPs) are known to regulate UBM. Activity gradients of BMPs are often essential in ensuring normal development, with the action of BMPs on cells often dependent on the local concentration. These concentrations are tightly regulated by extracellular BMP antagonists such as Gremlin. We have examined UBM and nephrogenesis in mouse metanephroi cultured in the presence of exogenous Gremlin. Embryonic day 12.5 (E12.5) wildtype metanephroi were cultured for 48hrs in serum-free medium with or without 0.5, 1, 5, 10 or 20µg/ml rmGremlin. Whole metanephroi were double-immunostained with anti-CalbindinD28K and WT1 to specifically identify ureteric epithelium and developing glomeruli. UBM was reduced by approximately 25%, 80% and 90% in metanephroi cultured in the presence of 5, 10 and 20µg/ml rmGremlin (p<0.01, p<0.001 and p<0.001 respectively). Interestingly, glomerular number in metanephroi cultured in 0.5µg/ml rmGremlin was increased by approximately 40% in the absence of increased ureteric branching (p<0.001). Glomerular number was reduced by approximately 65% in metanephroi cultured in 10 and 20µg/ml rmGremlin (p<0.001 for both). At high concentrations, Gremlin dramatically altered ureteric tree and glomerular morphology with branches appearing short and dilated while glomeruli were abnormally shaped and ectopically located at the periphery of the metanephros, some distance away from any ureteric epithelium. These results indicate exogenous Gremlin inhibits kidney growth and ureteric branching in a dose-dependant manner and may be capable of inducing nephrogenesis.