Nephrin is specifically located at the slit diaphragm of glomerular podocytes

We describe here the size and location of nephrin, the first protein to be identified at the glomerular podocyte slit diaphragm. In Western blots, nep hrin antibodies generated against the two terminal extracellular Ig domains of recombinant human nephrin recognized a 180-kDa protein in lysates of hu man glomeruli and a 150-kDa protein in transfected COS-7 cell lysates. In i mmunofluorescence, antibodies to this transmembrane protein revealed reacti vity in the glomerular basement membrane region, whereas the podocyte cell bodies remained negative. In immunogold-stained thin sections, nephrin labe l was found at the slit between podocyte foot processes. The congenital nep hrotic syndrome of the Finnish type (NPHS1), a disease in which the nephrin gene is mutated, is characterized by massive proteinuria already in utero and lack of slit: diaphragm and foot processes. These features, together wi th the now demonstrated localization of nephrin to the slit diaphragm area, suggests an essential role for this protein in the normal glomerular filtr ation barrier. A zipper-like model for nephrin assembly in the slit diaphra gm is discussed, based oh the present and previous data.