Spatiotemporal expression patterns of sialoglycoconjugates during nephron morphogenesis and their regional and cell type-specific distribution in adult rat kidney
The expression of α2,6- and α2,3-linked sialic acids on N-glycans was studied in embryonic, postnatal, and adult rat kidney. Histochemistry and blotting using Polyporus squamosus and Sambucus nigra lectins for α2,6-linked sialic acids and the Maackia amurensis lectin for α2,3-linked sialic acids were performed and sialyltransferase activity was assayed. N-glycans with α2,6- and α2,3-linked sialic acid were differently expressed in the two embryonic anlagen and early stages of nephron. Metanephrogenic mesenchyme was positive for α2,3-linked sialic acid but not for the α2,6-linked one, which became detectable initially in the proximal part of S-shaped bodies. Collecting ducts were positive for α2,6-linked sialic acid, whereas α2,3-linked sialic acid was restricted to their ampullae. Although positive in embryonic kidney, S1 and S2 of proximal tubules became unreactive for α2,3-linked sialic acid in postnatal and adult kidneys. In adult kidney, intercalated but not principal cells of collecting ducts were reactive for α2,3-linked sialic acid. In contrast, α2,6-linked sialic acids were detected in all cells of adult kidney nephron. Blot analysis revealed a different but steady pattern of bands reactive for α2,6- and α2,3-linked sialic acid in embryonic, postnatal, and adult kidney. Activity of α2,6 and α2,3 sialyltransferases was highest in embryonic kidney and decreased over postnatal to adult kidney with the activity of α2,6 sialyltransferase always being three to fourfold that of α2,3 sialyltransferase. Thus, α2,6- and α2,3-linked sialic acids are differently expressed in embryonic anlagen and mesenchyme-derived early stages of nephron and show regional and cell type-specific differences in adult kidne
