Cell surface labelling with gold colloid particulates: the use of avidin and staphylococcal protein A-coated gold in conjunction with biotin and fc-bearing ligands

The silver anniversary of gold: 25 years of the colloidal gold marker system for immunocytochemistry and histochemistry

Since 1971, when W.P. Faulk and G.M. Taylor published "An immunocolloid method for the electron microscope", colloidal gold has become a very widely used marker in microscopy. It has been used to detect a huge range of cellular and extracellular constituents by in situ hybridization, immunogold, lectin-gold, and enzyme-gold labeling. Besides its use in light microscopic immunogold and lectin-gold silver staining, colloidal gold remains the label of choice for transmission electron microscopy studying thin sections, freeze-etch, and surface replicas, as well as for scanning electron microscopy. The year 1996 is the 25th anniversary of the introduction of colloidal gold as a marker in immunoelectron microscopy and this overview outlines some of the major milestones in the development of the colloidal gold marker system.

Optimization of conditions for specific binding of antibody-coated beads to cells

It has previously been demonstrated that cells can bind antibody-coated beads; this effect can be used to enhance the fractionation of cells using magnetic fields or by centrifugation on isopycnic, isotonic density gradients. As a general rule, the higher the expression of surface antigens the more beads bind to cells. However, we have also noted that other factors also affect the number of beads found bound to cells. Experiments have been carried out to determine what factors affect binding of antibody-coated beads to cells. The optimum conditions for binding of antibody-coated beads to MOLT-4 T cells were found to be, namely, a 20:1 bead to cell ratio in a 1 ml incubation volume, with continuous end-over-end mixing for 1 h at 25 degrees C. Furthermore, the optimum centrifugation conditions at which the samples were separated on isopycnic, isotonic density gradients were determined as 220 x gmax for 90 min, at 20 degrees C. The results indicate the preferred conditions that are necessary to achieve optimum bead binding by cells and their subsequent fractionation. Different antibody-coated beads were examined including Dynabeads M-450, used as a known standard. In addition we describe, as a possible alternative to Dynabeads, dense polystyrene beads, for the separation of cells on the basis of the immunological identity of the surface of cells using density perturbation methods.

Freeze-fracture cytochemistry: a simplified guide and update on developments

A wide variety of methods by which cytochemistry and freeze-fracture can be successfully combined have recently become available. All these techniques are designed to provide information on the chemical nature of structural components revealed by freeze-fracture, but differ in how this is achieved, in precisely what type of information is obtained, and in which types of specimen can be studied. Colloidal gold labelling is the most widely used cytochemical technique in freeze-fracture cytochemistry, and for many of the methods it is indispensable. In principle, there are four points in which the cytochemical labelling step may be integrated into the standard freeze-fracture procedure: (i) before the specimen has been frozen, (ii) after it has been fractured and thawed, (iii) after platinum shadowing or (iv) after completion of the full replication sequence. Retention of the gold label so that it can be viewed with replicas can be achieved by depositing platinum and/or carbon upon the labelled surface, thereby partially entrapping the marker particles within the replica, or by retaining, attached to the replica, fragments of fractured membrane (or other cellular components) that would normally have been lost during the replica cleaning step. Another approach to visualizing the label is to use sections, either with portions of a replica included face-on, or for examining the fracture path through the sample (without replica). Recent developments have centered on the use of replicas to stabilize half-membrane leaflets; not only may these and associated attached components be retained for labelling just before mounting, but they provide a means for manipulating the specimen--specifically, turning it over during processing--so that additional structural information can be obtained. This article aims to explain how modern freeze-fracture cytochemistry works, and how the various techniques differ in what they can tell us about membranes and other cellular structures. With the effectiveness of many of the techniques now demonstrated, freeze-fracture cytochemistry is firmly established, alongside a range of related labelling techniques, for increasing application in cell and membrane biology in the 1990s.

Tissue and species conservation of the vertebrate and arthropod forms of the low molecular weight (16-18000) proteins of gap junctions

Gap junctions have been isolated from four murine tissues, from rat and Xenopus laevis liver, and from Nephrops norvegicus (Norway lobster) hepatopancreas. The preparations of gap junctions from each vertebrate tissue contain a single major protein, Mr 16,000, and those from Nephrops hepatopancreas a protein, Mr 18,000. Immunocytochemical studies using affinity-purified antibodies raised against gap junctions from Nephrops show the junctional origin of the 18k protein. Immunological studies using Western blotting and biochemical studies using tryptic peptide mapping show no significant differences between the 16k junctional proteins of mouse and hence provide no evidence of tissue variation. These studies also suggest that the mouse, rat, and Xenopus 16k proteins and the Nephrops 18k protein share some common structural features.

Immunochemistry of the outer retina

The immunochemistry of the outer retina is discussed with particular reference to photoreceptor cells, the retinal pigment epithelium and the interphotoreceptor space. The antigens identified and the techniques utilised are summarised.

Platinum-shadowed, whole-mounts for transmission electron microscopy of cells cultured on plastic

A simple and convenient method is described whereby cells cultured on polystyrene plastic substrata may be critical point-dried, rotary-shadowed with platinum/carbon and finally released by means of propylene oxide for examination whole in the transmission electron microscope. The technique is particularly useful for the localization of colloidal gold probes, both intra- and extra-cellularly. The problem of premature melting of polystyrene at about 307 K after prolonged exposure to carbon dioxide is solved by limiting the residence time in the critical point-drier to 1 h. Details for cleaning and mounting the released films of cells on specimen grids are given. The technique expands the application of the 'whole-mount' approach of Hopkins and co-workers (Hopkins et al., 1981; Hopkins, 1985) to cells cultured directly on polystyrene substrata, that is, in conventional plastic culture vessels.

The surface distribution of low density lipoprotein receptors on cultured fibroblasts and endothelial cells. Ultrastructural evidence for dispersed receptors

The distribution of low density lipoprotein (LDL) receptors marked with colloidal gold-conjugated low density lipoproteins has been mapped on the surfaces of cultured human skin fibroblasts and bovine aortic endothelial cells viewed whole in the transmission electron microscope. A dispersed or scattered population of LDL receptors, in addition to and clearly distinct from clustered receptors was detected on the surfaces of both fibroblasts and dividing endothelial cells. No LDL receptors could be detected on contact-inhibited endothelial cells. Clustered receptors imaged in whole-mount preparations were often arranged in rings with an approximate diameter of 250 nm. In ultra-thin sections of marked cells, clustered receptors were localised in coated pits while the few dispersed receptors seen were restricted to non-coated membrane regions. Clustered receptors often appeared localised on the rims of coated pits whose central areas were not marked. The dispersed population of receptors was usually distributed diffusely amongst the clusters on dividing endothelial cells and normal fibroblasts. Only the dispersed population appeared on LDL receptor internalisation-defective mutant fibroblasts. The marginal zones of both fibroblasts and dividing endothelial cells were populated by dispersed receptors. Clusters appeared further "inland" and were rarely seen near the cell margins. These results indicate that LDL receptors on dividing endothelial cells and fibroblasts may be dispersed on the cell surface upon or soon after their insertion during recycling.

Localisation of the protein and glycoprotein components of bovine nasal epithelial desmosomes by immunoelectron microscopy

Desmosomal proteins (dp1-4) and glycoproteins (dg1-3) have been localised within desmosomes of bovine nasal epithelium by immunogold labelling of ultrathin frozen sections. Beginning in the extracellular space and proceeding through the plaque to the tonofilaments, the following localisations were found. Labelling for the 130,000 and 115,000 Mr glycoproteins (dg2 and dg3) was predominantly in the extracellular space, a location consistent with their proposed adhesive function. The glycoproteins of 175,000-164,000 Mr (dg1) were also found in the extracellular space and in addition had cytoplasmic domains extending throughout the cytoplasmic plaque. The 83,000 Mr protein (dp3) was located along the cytoplasmic face of the membrane and extended into the plaque, whereas an antibody which recognises both the 83,000 Mr protein (dp3) and the 75,000 Mr protein (dp4) gave labelling both in and beyond the plaque. Labelling for the high mol. wt proteins of Mr 250,000 and 215,000 (dp1 and dp2) was largely excluded from the plaque, and was located distally, adjacent to the tonofilaments. Hemidesmosomes could not be labelled with antibodies to dg1-3 or dp3 and 4, but some labelling was obtained with antibody to dp1 and 2.

Morphological features of established cultures of human squamous lung carcinoma cells and the cellular distribution of tumor-specific glycoproteins

Phenotypic characteristics of a cloned cell line, RH-SLC-L11, established from a human squamous lung carcinoma, were studied. The line has maintained its morphologically characteristic growth pattern for over 3 years. Settling cells exhibited extensive surface blebbing during spreading and established small cell islands that eventually expanded by mitosis to confluent cultures. Cell islands and confluent cultures presented three cell types: (i) small, polygonal cells, (ii) polygonal cells of intermediary size and (iii) very large, extremely flattened, degenerating cells. Mitotic activity was present predominantly in type (i) and the sequence (i)--(iii) is presumed to represent the lines' cycle. Previous work has demonstrated that the SLC-L11 line releases tumor-associated glycoproteins and glycolipids. These could be identified with a murine Mab (43-9F). The specific epitope was determined by carbohydrate residues and was shown to have growth factor-like properties. Mab 43-9F bound heterogeneously to the surface of SLC-L11 cells: Most large cells were unreactive while both type (i) and (ii) cells showed conspicuous differences in immunostaining intensity. Immunocytochemical analysis also indicated redistribution, shedding and internalization of antigen-Mab complexes, which may have significant impact on the use of the epitope as tumor marker in diagnosis and therapy. No definite clue was obtained as to the release of the antigenic carbohydrate epitope itself.

Problems in the production and use of 5 nm avidin-gold colloids

Over the past 5 years we have encountered several problems in the production and use of 5 nm avidin-gold colloids for markers in electron microscopy. These problems include flocculation of colloids during reduction of chloroauric acid, insoluble gold pellets following ultracentrifugation, and non-specific binding of avidin-gold colloids to biological membranes. We are able to avoid these problems by: avoiding the use of crystalline chloroauric acid; succinoylating egg white avidin prior to adsorption on the gold sols; resuspending the pellets following ultracentrifugation in 5 mM phosphate buffer, pH 7.5; and using the avidin-gold colloids within 4 weeks of production.

The appearance and internalization of transferrin receptors at the margins of spreading human tumor cells

Using gold complexes stabilized with a monoclonal antibody specific for the human transferrin receptor, the distribution of transferrin receptors on the surfaces of human epidermoid carcinoma A431 cells has been mapped at high resolution. On prefixed cells and cells incubated at 5 degrees C, the receptors are predominantly within and around clathrin-coated microdomains near the free cell margin. By preincubating the cells with saturating concentrations of free antibody at 5 degrees C and warming them to 37 degrees C in the presence of the gold complexes, the appearance of new receptors in the membrane has been followed. The majority first appear near the free cell margin and then move centripetally. At first, they are monodisperse, but as they move toward the site of internalization they form loose aggregates. Within the immediate vicinity of the clathrin-coated microdomains the migrating receptors form closely packed, ordered aggregates. These observations indicate recycling transferrin receptors move to their site of internalization without cross-linking.

Synthesis and effects of basement membrane components in cultured rat Schwann cells

Schwann cells, the myelin-forming cells of the peripheral nervous system, are surrounded by a basement membrane. Whether cultured rat Schwann cells synthesize the basement membrane-specific components, laminin and collagen type IV, and whether these components influence the adhesion, morphology, and growth of these cells have been investigated. Both laminin and collagen type IV were detected in the cytoplasm of Schwann cells by immunofluorescence. After ascorbate treatment, laminin and collagen type IV were both found in an extracellular fibrillar matrix bound to the Schwann cell surface. Laminin was further localized on the Schwann cell surface by electron microscopy using gold immunolabeling. Anti-laminin IgG-labeled gold particles were scattered over the cell surface, and linear rows of particles and small aggregates were found along the cell edges and at points of contact with other cells. When added to the culture medium, laminin acted as a potent adhesion factor, stimulating Schwann cell adhesion as much as eightfold above control levels on type IV collagen. In the presence of laminin, the cells became stellate and by 24 hr had extended long, thin processes. Laminin also stimulated cell growth in a dose-dependent manner and anti-laminin IgG completely inhibited cell attachment and growth in the absence of exogenous laminin. Thus, cultured Schwann cells synthesize laminin and collagen type IV, two major components of basement membrane, and laminin may trigger Schwann cell differentiation in vivo during early stages of axon-Schwann cell interaction before myelination.

Labelling of colloidal gold with protein. A quantitative study using beta-lactoglobulin

Markers prepared by labelling colloidal gold with macromolecules such as lectins, antibodies and protein A are gaining wide acceptance both in transmission and scanning electron microscopy. However detailed information on the process and extent of adsorption of macromolecules onto gold particles are still lacking. The adsorption isotherm of protein onto gold particles was studied quantitatively using goat beta-lactoglobulin (beta L) tritiated in vivo. When this protein was modified chemically by iodination with 125I, the adsorption isotherm was not significantly different (Langmuir type for monolayer). In the presence of saturating amount of beta L, a maximum of 13-14 molecules was adsorbed per particle of 12 nm in diameter for a theoretical maximum of 20 (compact monolayer). Ellipsometric measurements on nickel-coated slides indicated that betas L was adsorbed onto metallic surfaces as a compact monolayer. The molecules were irreversibly adsorbed on gold particles, kept to a large extent their capacity to bind anti-beta L antibodies and could not be displaced by polyethylene glycol, a stabilizer commonly used in the preparation of gold markers. Only markers labelled with more than 5 beta L molecules per particle could be completely bound by immobilized anti-beta L antibodies. Preliminary data indicated that the energetics of adsorption of beta L onto colloidal gold was in agreement with that expected from the mutual interaction of surface and adsorbate.

Polypeptides immunologically related to band 3 are present in nucleated somatic cells

Band 3, the major transmembrane polypeptide of erythrocytes, mediates the exchange of anions (chloride and bicarbonate) across the membrane. We suspected that band 3 was present on nucleated somatic cells as well as erythrocytes because the senescent cell antigen that is immunologically related to band 3 is present on lymphocytes, platelets, adult liver cells, and embryonic kidney cells; and antibodies prepared against the senescent cell antigen isolated from leukocytes react with erythrocyte band 3. For this reason, we examined human fibroblasts, lung cells, neutrophils, mononuclear leukocytes, squamous epithelial (mouth) cells, lung squamous epithelial carcinoma, mouse neuroblastoma cells, and rat hepatocytes for immunoreactive forms of band 3 by using monospecific antibodies to erythrocyte band 3. The results demonstrated that polypeptides sharing common antigenic determinants with erythrocyte band 3 are present in nucleated somatic cells as determined by immunofluorescence, immunoelectron microscopy, and immunoautoradiography. Peptide mapping revealed substantial sequence homology between erythrocyte band 3 and the band 3-like protein of leukocytes. Immunofluorescence studies indicate that the band 3-like proteins in nucleated cells participate in antibody-induced cell surface capping.

Internalization and processing of transferrin and the transferrin receptor in human carcinoma A431 cells

The binding and subsequent intracellular processing of transferrin and transferrin receptors was studied in A431 cells using 125I-transferrin and a monoclonal antibody to the receptor (ATR) labeled with 125I and gold colloid. Using 125I-transferrin we have shown that, whereas at 37 degrees C uptake proceeded linearly for up to 60 min, most of the ligand that was bound was internalized and then rapidly returned to the incubation medium undegraded. At 37 degrees C, the intracellular half-life of the most rapidly recycled transferrin was 7.5 min. 125I-ATR displayed the same kinetics of uptake but following its internalization at 37 degrees C, it was partially degraded. At 22 degrees C and below, the intracellular degradation of 125I-ATR was selectively inhibited and as a result it accumulated intracellularly. Electron microscopy of conventional thin sections and of whole-cell mounts was used to follow the uptake and processing of transferrin receptors labeled with ATR-gold colloid complexes. Using a pulse-chase protocol, the intracellular pathway followed by internalized ATR gold-receptor complexes was outlined in detail. Within 5 min at 22 degrees C the internalized complexes were transferred from coated pits on the cell surface to a system of narrow, branching cisternae within the peripheral cytoplasm. By 15 min they reached larger, more dilated elements that, in thin section, appeared as irregular profiles containing small (30-50-nm diam) vesicles. By 30 min, the gold complexes were located predominantly within typical spherical multivesicular bodies lying in the peripheral cytoplasm, and by 40-60 min, they reached a system of cisternal and multivesicular body elements in the juxtanuclear area. At 22 degrees C, no other compartments became labeled but if they were warmed to 37 degrees C the gold complexes were transferred to lysosome-like elements. Extracting ATR-gold complexes with Triton X after a 30-min chase at 22 degrees C and purifying them on Sepharose-transferrin indicated that the internalized complexes remained bound to the transferrin receptor during their intracellular processing.

Examination of whole cell mounts by transmission electron microscopy using cultures grown on carbon coated coverslips

Cultures of porcine granulosa cells have been grown on serum coated carbon films deposited on glass coverslips. Intact and detergent-treated cultures were critical point dried, chromium shadowed and removed from the coverslips by dilute hydrofluoric acid. Whole cell mounts were examined by conventional transmission electron microscopy. The advantage of this system over other methods includes the ability to: (1) examine cells with a highly rounded morphology, (2) use high cell densities, (3) study cell projections extending onto the substratum, (4) maintain cultures for long periods, (5) examine large samples easily, (6) readily use the same cultures for transmitted light and fluorescent microscopy, scanning and transmission electron microscopy (SEM and TEM).