Direct visualization of renal vascular morphogenesis inFlk1 heterozygous mutant mice

Flk1, a receptor tyrosine kinase for vascular endothelial growth factor (VEGF), is the earliest known marker for endothelial precursors (angioblasts). We examined heterozygous mice in which the Flk1gene was partially replaced by a promoter-lessLacZ insert and used β-galactosidase histochemistry to view cells transcribingFlk1. In day 10 (E10) embryos, a Flk1-positive network surrounded the metanephric blastema, and, atE11, a vessel entered the metanephros from its ventral aspect alongside the ingrowing ureteric bud. However, aortic branches did not engage embryonic kidneys at these time points. In newborns, β-galactosidase was localized exclusively and intensely to endothelial cells of all vessels and glomeruli. In contrast, whenE12 kidneys grown in organ culture for 6 days were examined, only scattered Flk1-positive cells were seen, glomeruli were unlabeled, and vessels were absent. When organ-cultured kidneys were then grafted into wild-type anterior eye chambers, numerous Flk1-positive endothelial cells...