Ultrastructural visualization of galactosyl residues in various alimentary epithelial cells with the peanut lectin-horseradish peroxidase procedure

Summary

A conjugate of peanut lectin with horseradish peroxidase (PL-HRP) has been employed for ultrastructural localization of glycoprotein with presumed terminal galactose residues in mouse alimentary epithelial cells. The PL-HRP conjugate imparted electron opacity in sites that stain at the light microscopic level, as for example, Golgi cisternae in surface epithelial cells of the stomach and in superficial and deep crypt cells and goblet cells of the large intestine. Ultrastructural staining revealed that Golgi cisternae intermediate between the trans and cis faces stained selectively in these sites. Secretion stored in secretory granules or Golgi vesicles in the cells lacked affinity for PL-HRP conjugate, however. Selective staining of intermediate Golgi cisternae in cells with unreactive secretory product is interpreted as indicating the site of galactosyl transferase activity and a location where glactose occurs transitorily as the terminal sugar in the glycoprotein side chains. The luminal aspect of the surface epithelial cells in the stomach and columnar cells in the colon also stained, but with some variability. Staining of these surfaces was considered possibly attributable to PL affinity of some of the secretory glycoprotein which, after absorbing to the cell surface, lost terminal sialic acid through action of luminal enzyme. PL-HRP conjugate stained granules in pancreatic zymogen cells near the block surface but not in other cells, presumably because of limited penetration of reagent. Secretion on the surface of pancreatic acinar cells or in the lumen also exhibited affinity for PL-HRP complex as did the luminal surface of gastric chief cells. Staining of secretion in the pancreatic zymogen cells and gastric chief cells for galactose appeared inconsistent with lack of evidence for presence of glycoprotein in these sites which failed to stain with the periodic acid-Schiff or periodic acid-thiocarbohydrazide-silver proteinate methods for demonstrating glycoprotein at the light and electron microscopic levels. This discrepancy points to possible selective binding of PL-HRP conjugate to a moiety other than terminal galactose of glycoprotein in a few histologic sites. These results demonstrate the applicability of the PL-HRP technique at the ultrastructural level and provide information concerning the chemical structure of epithelial cell glycoproteins and their biosynthesis.