LECTIN-BINDING SITES DURING POSTNATAL DIFFERENTIATION OF NORMAL AND CYSTIC RABBIT RENAL CORPUSCLES

Fluorochrome-labeled lectins were used to study the expression of glyc oconjugates during the postnatal differentiation of normal and cystic rabbit renal corpuscles. Glomerular cysts (GC) are induced in the rabb it by a single injection of corticoids. The Bowman's capsule of these cysts is exclusively formed of podocytes (parietal podocytes). During normal development, the cell coat of the podocytes is intensely positi ve for wheat germ agglutinin (WGA) and Maclura pomifera agglutinin (MP A). This reaction decreases considerably during maturation, in paralle l with an increase in the number of binding sites masked by terminal s ialylation. Throughout the stages studied, the podocyte coat is peanut agglutinin (PNA)-negative, but it becomes intensely positive after ne uraminidase treatment. Visceral and parietal podocytes in the glomerul ar cysts show the same pattern of glycosylation as the normal podocyte s. In contrast, normal parietal cells only transiently expressed a wea k reactivity to WGA and MPA during the first stages of differentiation , and did not express cryptic binding sites at any stage. The glomerul ar basement membrane (GBM) is positive to WGA, to succinylated WGA, an d to MPA, in all the stages studied. Maturation of the GBM is characte rized by expression of cryptic MPA-binding sites, and by a considerabl e increase in the number of cryptic PNA-binding sites. The basement me mbrane of the parietal layer of the cystic Bowman's capsule shows the same pattern of glycosylation, despite the fact that this epithelial l ayer is solely formed of podocytes and lacks endothelial cells. In con trast, the normal parietal basement membrane does not express PNA or M PA cryptic sites at any stage. On the whole, the only difference obser ved between normal and experimental kidneys is that the cysts show an advance in the temporal expression of glyconjugates with respect to th e normal renal corpuscles. This suggests that the corticoids stimulate the terminal differentiation of the cellular components of the renal corpuscle.