Cytochemical localization of terminal N-acetyl-D-galactosamine residues in cellular compartments of intestinal goblet cells: implications for the topology of O-glycosylation

Post-embedding cytochemistry with gold-labelled reagents: a review

The detection of antigens and glycoconjugates with the protein A-gold and the lectin-gold techniques, respectively, is reviewed. Special attention is directed to the necessary conditions for fixation and embedding as well as to the staining procedures of tissue sections for light and electron microscopy.

Lectin-binding sites in normal, hyperplastic, adenomatous and carcinomatous human colorectal mucosa

The carbohydrate structures of cellular glycoconjugates in normal, hyperplastic, adenomatous and carcinomatous human colorectal mucosa were analysed with six fluorescein isothiocyanate-conjugated lectins. In normal, hyperplastic and adenomatous colorectal mucosa showing mild or moderate dysplasia Concanavalin A (Con A), Lens culinaris (LCA), and wheat germ (WGA) agglutinins stained goblet cell glycoconjugates (actual mucin goblet itself) while peanut (PNA), Vicia villosa (VVA), and Griffonia simplicifolia-II (GSA-II) agglutinins showed a supranuclear staining of goblet cell glycoconjugates. After neuraminidase treatment of tissue sections PNA and VVA stained mucin goblets of mature cells in normal mucosa, while less differentiated cells in the lower crypt displayed a supranuclear staining with VVA. The mucin goblets in adenomatous mucosa with mild or moderate dysplasia did not stain with PNA and VVA, neither before nor after neuraminidase treatment. Areas of in situ cancer in adenomas and carcinomas displayed a strong and direct binding of Con A, LCA, WGA and PNA in an apical linear distribution, while the binding of VVA and GSA-II was heterogeneous. We conclude that there are alterations in the carbohydrate structures of cellular glycoconjugates, which can be related to goblet cell differentiation in normal colorectal mucosa and to the degree of dysplasia in adenomas. Heterogeneous and incompletely glycosylated glycoconjugates appear to be synthesized by the majority of colorectal carcinomas.

A post-embedding avidin-biotin peroxidase system to demonstrate the light and electron microscopic localization of lectin binding sites in rat kidney tubules

A post-embedding method for the light and electron microscopic demonstration of lectin binding sites in rat kidney tubules is described. The use of biotinylated lectins, followed by treatment with avidin peroxidase and the DAB-H2O2 sequence, produced intense staining of acrylic sections at the electron microscope level: brush borders and associated structures, cytoplasmic granules, basal infoldings and basement membrane-plasmalemmal interfaces of proximal tubules bound erythrophytohaemagglutinin, while distal tubules were mainly unstained. At the light microscope level, epoxy resin sections showed a similar staining pattern after etching, as did acrylic resin sections after intensification of the final reaction product. The binding of wheatgerm agglutinin to cytoplasmic granules and brush border structures in the proximal tubules was abolished, at both the light and electron microscope levels, by the competing sugar tri-N-acetylchitotriose. Epoxy resin ultrathin sections required etching before staining was achieved in the electron microscope, and results were far inferior to those obtained with acrylic resin. This method allows rapid and inexpensive screening of large numbers of lectins, if required, at both the light and electron microscope levels, using reagents that are stable for long periods of time.

Changes in the distribution of endothelial surface glycoconjugates associated with altered permeability of brain micro-blood vessels

Lectin-binding sites located on the endothelial cell (EC) surfaces in unaltered, leaking and resorbing micro-blood vessels (MBVs) in cryo-injured cat brain were studied. Lectin or glycoprotein-gold complexes and brain samples embedded in hydrophilic resin Lowicryl K4M were used. The lectins tested recognize the following residues: beta-D-galactosyl (Ricinus communis agglutinin 120, RCA and peanut agglutinin, PNA), sialyl (Limax flavus agglutinin), N-acetyl-D-galactosaminyl (Helix pomatia agglutinin and soybean agglutinin, SBA), alpha-D-glucosyl and alpha-D-mannosyl (concanavalin A). The luminal front was labeled with SBA, and both fronts of the EC were labeled with PNA only after neuraminidase digestion. The most abundant and regularly distributed on both fronts of the EC were beta-D-galactosyl residues (RCA). These residues were also most affected in altered MBVs. The labeling of sialic acid residues was less pronounced on both sides of the EC. Following alteration of the function of the blood-brain barrier by cold-lesion injury, in leaking MBVs which represent increased luminal transport, we observed a conspicuous diminution of the labeling of the luminal surface of the EC with some lectins. On the other hand, in resorbing blood vessels located in the area of edema, where a presumably reverse (abluminal) transport occurs, major changes in the distribution of lectin-binding sites occurred on the abluminal front of the EC and in the basement membrane. The results reported here indicate that luminal and abluminal fronts of the EC change their properties in various functional conditions of MBVs, and that these changes can also be a reflection of functional polarity of brain endothelium.

What's new in light and electron microscopic immunocytochemistry? Application of the protein A-gold technique to routinely processed tissue

The protein A-gold technique, a simple and reliable two-step postembedding immunocytochemical method, allows the light and electron microscopic detection of antigens in routinely fixed and embedded tissue. At the light microscopic level a permanent, nonfading stain is obtained. High resolution studies on intracellular antigens can be performed since the particulate nature of the colloidal gold permits accurate determination of the labeled cellular structures. The applicability of the protein A-gold technique for the localization of various peptide and protein antigens by light and electron microscopy is demonstrated.

Proteoglycan biosynthesis in chondrocytes: protein A-gold localization of proteoglycan protein core and chondroitin sulfate within Golgi subcompartments

The intracellular pathway of cartilage proteoglycan biosynthesis was investigated in isolated chondrocytes using a protein A-gold electron microscopy immunolocalization procedure. Proteoglycans contain a protein core to which chondroitin sulfate and keratan sulfate chains and oligosaccharides are added in posttranslational processing. Specific antibodies have been used in this study to determine separately the distribution of the protein core and chondroitin sulfate components. In normal chondrocytes, proteoglycan protein core was readily localized only in smooth-membraned vesicles which co-labeled with ricin, indicating them to be galactose-rich medial/trans-Golgi cisternae, whereas there was only a low level of labeling in the rough endoplasmic reticulum. Chondroitin sulfate was also localized in medial/trans-Golgi cisternae of control chondrocytes but was not detected in other cellular compartments. In cells treated with monensin (up to 1.0 microM), which strongly inhibits proteoglycan secretion (Burditt, L.J., A. Ratcliffe, P. R. Fryer, and T. Hardingham, 1985, Biochim. Biophys. Acta., 844:247-255), there was greatly increased intracellular localization of proteoglycan protein core in both ricin-positive vesicles, and in ricin-negative vesicles (derived from cis-Golgi stacks) and in the distended rough endoplasmic reticulum. Chondroitin sulfate also increased in abundance after monensin treatment, but continued to be localized only in ricin-positive vesicles. The results suggested that the synthesis of chondroitin sulfate on proteoglycan only occurs in medial/trans-Golgi cisternae as a late event in proteoglycan biosynthesis. This also suggests that glycosaminoglycan synthesis on proteoglycans takes place in a compartment in common with events in the biosynthesis of both O-linked and N-linked oligosaccharides on other secretory glycoproteins.

Post-embedding localization of glycoconjugates by means of lectins on thin sections of tissues embedded in LR white

A simple post-embedding technique for the electron microscopical detection of lectin-binding sites using thin sections of tissues embedded in the resin LR White is described. With this technique, no prior etching of the sections is necessary. The cellular fine structure is well preserved and permits close correlation of the labelling to distinct cellular compartments. After mild aldehyde fixation (4% formaldehyde and 0.5% glutaraldehyde for 30 min), enterocyte brush border, vesicles and lysosomes as well as goblet cell Golgi apparatus and mucin are intensely stained after 30-60 min. The hydrophilia and penetrability of LR White is shown by the formation of oxidized diaminobenzidine reaction product arising from horseradish peroxidase-conjugated lectins. The precipitate not only covers the surface of the sections but is also formed within the resin, as is revealed on cross-sections through thin and semithin sections. The addition of 0.2 M solutions of the appropriate inhibitory sugars prevented staining, which indicates a specific binding. Examples are given of the binding of gold-, ferritin- and peroxidase-conjugated lectins for the purpose of detecting glycoconjugates in various intracellular compartments.

Sialoglycoproteins with a high amount of O-glycosidically linked carbohydrate moieties stain yellow with silver in sodium dodecyl sulfate-polyacrylamide gels

Several sialoglycoproteins and human salivary proteins were analyzed in sodium dodecyl sulfate-polyacrylamide gels using the silver/Coomassie-staining protocol (J. K. Dzandu, M. E. Deh, D. L. Barratt, and G. E. Wise, 1984, Proc. Natl. Acad. Sci. USA 81, 1733-1737) to determine the extent to which yellow Ag staining originally reported for human red blood cell glycophorins can be applied to other sialoglycoproteins. Results showed that not all sialoglycoproteins elicit a positive yellow color in the silver stain reaction. Some of the sialoglycoproteins stained as brown or negative images in the Ag-staining cycle. Alkaline beta elimination of O-glycosidically linked carbohydrate chains of glycophorin resulted in the loss of yellow color development in the Ag-staining protocol. Analysis of acidic salivary proteins showed several yellow Ag-stained bands at Mr X 10(-3) = 150, 82, 70, 51, 46, and 42. These results suggest that the carbohydrate moieties of glycophorin removable by alkaline beta elimination are responsible for the characteristic yellow color in the Ag stain reaction. In addition, under our staining conditions sialoglycoproteins with a high amount of O-glycosidically linked carbohydrate chains give a characteristic yellow silver stain.

Discoidin I, an endogenous lectin, is externalized from Dictyostelium discoideum in multilamellar bodies

Discoidin I, a soluble lectin synthesized by aggregating Dictyostelium discoideum and implicated in their adhesion to the substratum, is localized in multilamellar bodies both intracellularly and upon externalization. These structures also contain a glycoconjugate that binds discoidin I. The multilamellar bodies apparently serve to package the lectin for externalization, and may then gradually release it to function extracellularly.

The carbohydrate moiety of aminopeptidase N of rabbit intestinal brush-border membrane

Endoglycosidase F was used to eliminate the N-linked complex glycans from intestinal aminopeptidase N. The glycans which were probably O-linked remaining after the endoglycosidase F treatment exhibited the human blood group A and H determinants expressed in enzymes from A+ or A- rabbits, respectively. The molecular mass estimation of the two types of glycans by SDS-polyacrylamide gel electrophoresis and the sugar composition of aminopeptidase from A+ and A- rabbits strongly suggested the presence of eight N-linked complex glycans and two O-linked oligosaccharides bearing the human group antigenicity.

Attachment of terminal N-acetylglucosamine to asparagine-linked oligosaccharides occurs in central cisternae of the Golgi stack

Using monoclonal antibodies and electron microscopy, we have localized N-acetylglucosamine transferase I within the Golgi apparatus. This enzyme initiates the conversion of asparagine-linked oligosaccharides to the complex type. We have found that the enzyme is concentrated in the central (or medial) cisternae of the Golgi stack. Cisternae at the cis and trans ends of the Golgi complex appear to lack this protein. These experiments establish a function for the medial portion of the Golgi and imply that the Golgi is partitioned into at least three biochemically and morphologically distinct cisternal compartments.

Glycoconjugate cytochemistry of the rat fundic gland using lectin/colloidal-gold conjugates and Lowicryl K4M. Helix pomatia lectin is a specific marker for mucous neck cells in fundic glands of the rat gastric mucosa

The fundic gland of the rat stomach was studied using the low-temperature embedding resin Lowicryl K4M and postembedding staining with lectin/colloidal-gold (CG) conjugates. Intense labeling with Ricinus communis agglutinin I was observed not only in mucous-producing cells but also in parietal cells. In contrast, Helix pomatia agglutinin (HPA) only labeled mucous neck cells and intermediate cells between mucous neck cells and chief cells. The other epithelial cells present in the rat fundic gland showed virtually no reaction with this lectin. Our results indicate that HPA might be a marker lectin of mucous neck cells and their derivatives. The combination of embedding in the hydrophilic resin Lowicryl K4M and postembedding staining with lectin-CG conjugates provided satisfactory staining results, and made it possible to visualize the precise distribution of terminal glycoconjugates in intracellular components as well as on the plasma membrane.

Two enzymes involved in the synthesis of O-linked oligosaccharides are localized on membranes of different densities in mouse lymphoma BW5147 cells

Microsomal membranes from mouse lymphoma BW5147 cells were fractionated on a continuous sucrose gradient and assayed for two enzymes involved in the synthesis of O-linked oligosaccharides. Both enzymes were recovered in membranes that were less dense than the membranes containing the endoplasmic reticulum marker enzymes, glucosidase I and II. UDP-Gal:N-acetylgalactosamine-beta 1, 3-galactosyltransferase had a distribution that coincided with that of the galactosyltransferase that acts on asparagine-linked oligosaccharides. This latter enzyme has been immunolocalized to the trans Golgi elements. The UDP-GalNAc:polypeptide N-acetylgalactosaminyl-transferase was recovered in a membrane fraction of intermediate density, between the endoplasmic reticulum and trans Golgi markers. These findings are consistent with the assembly of O-linked oligosaccharides occurring in at least two different Golgi compartments.