Characterization of an endothelial protein in the developing rabbit kidney

A new protein (EnPo 1 antigen) abundant on endothelial cells and glomerular podocytes has been characterized by means of the mouse monoclonal antibody EnPo 1. Following electrophoretical separation of rabbit kidney homogenates EnPo 1 recognized a protein with a molecular weight of 110 kDa and an isoelectric point of 5.9 in Western blots. Using immunohistological techniques, the EnPo 1 antigen has been localized in high concentrations on glomerular podocytes of different developmental stages. Furthermore, the EnPo 1 antigen was expressed on endothelial cells of all adult rabbit organs tested so far. Detailed analysis of neonatal rabbit kidney revealed the abundance of EnPo 1 antigen on both differentiated vessels as well as on immature endothelial cells and endothelium of the microvasculature. Thus, for the first time a marker for in situ investigations of angiogenic processes within the mammalian kidney is available. Analysis of kidney cryosections by confocal laser scan microscopy revealed a direct connection between mature and differentiating vessels in the outer kidney cortex. Furthermore, two differentially organized cell populations discriminated by their EnPo 1 binding pattern were localized in the embryonic renal cortex. Morphologically, these cells were not distinguishable from other mesenchymal cells.