STAGE-SPECIFIC AND SEGMENT-SPECIFIC EXPRESSION OF CELL-ADHESION MOLECULES N-CAM, A-CAM, AND L-CAM IN THE KIDNEY

CAM expression was investigated immunohistochemically in tissue sectio ns and in pure cultures of human proximal and distal tubular cells. In the fetal kidney, N-CAM immunoreactivity was detected in the non-indu ced and condensing metanephrogenic mesenchyme, and in all stages until the S-shaped bodies. A-CAM (N-cadherin) first appeared in the non-ind uced mesenchyme and remained present thereafter. Its expression became exclusively associated with the lower limb of the S-shaped bodies and the developing proximal tubule. In contrast, L-CAM (E-cadherin; uvomo rulin) staining was observed in the fetal collecting duct, the upper l imb of the S-shaped bodies, and the developing distal tubule. This seg ment-specific expression of A-CAM and L-CAM in the early developing ne phron was maintained in the adult kidney: A-CAM staining was restricte d to adherens junctions in the proximal tubule and thin limb, whereas L-CAM was expressed in Bowman's capsule and in all tubular segments ex cept the proximal convoluted and straight tubule. Also after in vitro culture, A-CAM expression was an exclusive property of proximal tubula r cells, while L-CAM was confined to distal tubular cells. In conclusi on, each major subdivision of the fetal and adult nephron displays a c haracteristic combination of L-CAM and Al-CAM, suggesting that they ma y be the basis of segmental differentiation and border formation betwe en adjacent nephron segments.