Early expression of desmosomal components during kidney tubule morphogenesis in human and murine embryos

Developing kidneys of human and murine fetuses have been stained with monoclonal antibodies to desmosomal proteins 1 and 2 (desmoplakins) (dp 1&2), desmosomal glycoprotein 1 (desmoglein) and a polyclonal antiserum to desmosomal glycoproteins 2 and 3 (desmocollins). All three antibodies stain the mesenchymal condensates that represent the first stage in kidney tubule development, indicating that desmosomal antigens are expressed very early in tubule morphogenesis. Desmosomal antigens are continuously expressed throughout the developing tubule being concentrated at the apical and basal regions of the lateral membranes of cells. Staining is also present in both visceral and parietal membranes of the developing Bowman's capsule. In the mature tubule, desmosomal staining becomes restricted to a discontinuous apico-lateral ring around the cells. Staining is completely lost from the visceral membrane of the mature Bowman's capsule (the podocytes) but persists in the parietal membrane. At the condensate stage, staining for dp1&2 is much more intense than staining for simple epithelial keratin. Electron microscopy showed the presence of small (ca 0.1 microns) punctate junctions in the developing tubule. These may be immature desmosomes. No fully mature desmosomes such as are present in mature kidney were found. The results suggest that desmosomal proteins and glycoproteins are involved in the early development of adhesive contacts between cells of the kidney tubule. The changing pattern of antigen expression, the loss of desmosomal staining from the podocytes and the immaturity of junctions suggest that desmosomal adhesion is labile during tubule morphogenesis, perhaps in order to facilitate changes of cell-cell contact.