Stage- 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 sections and in pure cultures of human proximal and distal tubular cells. In the fetal kidney, N-CAM immunoreactivity was detected in the non-induced and condensing metanephrogenic mesenchyme, and in all stages until the S-shaped bodies. A-CAM (N-cadherin) first appeared in the non-induced 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; uvomorulin) staining was observed in the fetal collecting duct, the upper limb of the S-shaped bodies, and the developing distal tubule. This segment-specific expression of A-CAM and L-CAM in the early developing nephron was maintained in the adult kidney: A-CAM staining was restricted to adherens junctions in the proximal tubule and thin limb, whereas L-CAM was expressed in Bowman's capsule and in all tubular segments except the proximal convoluted and straight tubule. Also after in vitro culture, A-CAM expression was an exclusive property of proximal tubular cells, while L-CAM was confined to distal tubular cells. In conclusion, each major subdivision of the fetal and adult nephron displays a characteristic combination of L-CAM and A-CAM, suggesting that they may be the basis of segmental differentiation and border formation between adjacent nephron segments.