Gold Probes Research Articles

Visualization on cells by scanning laser confocal reflectance microscopy of silver-enhanced reaction products from protein- and immuno-colloidal gold probes

Visualization on cells by scanning laser confocal reflectance microscopy of silver-enhanced reaction products from protein- and immuno-colloidal gold probes

Silver enhancement of gold antibody probes in pre-embedding electron microscopic immunocytochemistry.

In pre-embedding EM immunocytochemistry with gold probes, the gold must be small enough to penetrate through cell membranes treated with mild detergents. Antibodies labeled with small gold probes (1-1.4 nm) are too small to be resolved in thin sections but can be seen if they are silver-enhanced after the gold has bound to the antigens in the cells. We investigated several aspects of gum arabic-silver lactate-hydroquinone enhancement solution (Danscher solution) by examining gold-conjugated antibodies embedded in agar, sectioned on a vibrotome, and enhanced with different solutions. The rate of silver enhancement was optimized in 50% gum arabic and 200 mM HEPES buffer, pH 5.8. We also examined chemicals used as developers and found that N-propyl gallate (NPG) gave a more uniform development than the routinely used hydroquinone (HQ). The diameter of the silver-enhanced particles after incubation in osmium tetratoxide (OSO4) decreased somewhat with longer incubation time and higher percentages, but the density (number per unit area) of silver-enhanced particles was little changed. The loss of silver-enhanced particle diameter was reduced by lowering the concentration of OSO4 to 0.1%. Comparison of commercial small gold probes showed that NPG enhancement of Nanogold gave more uniform particle size and a better correlation between enhancement time and particle density. When this procedure was applied to cell cultures with monoclonal antibodies, the silver-enhanced particles were similar to those in the agar sections. When free-floating tissue sections were used, longer silver enhancement times were needed to obtain similarly sized particles. This new NPG-silver-enhancement procedure offers a reliable and easy method to localize proteins in cultured cells and tissue sections by pre-embedding electron microscopic immunocytochemistry.

Site-specific cluster labels

This article discusses the development and use of various heavy-atom clusters (Hg 4, Ir 4, W 11, Au 11, 1.4 nm Au) that can be covalently attached to specific groups (e.g., -SH, -NH 2, -COOH) on biomolecules to produce high-resolution labels visible in the electron microscope. A number of applications are given, including labeling of proteins, carbohydrates, lipids in membranes and nucleic acids. Imrpoved immunolabeling with clusters over colloidal gold probes is discussed as well as the expanded utility of some of these clusters in TEM thin sections. With silver enhancement, the 1.4 nm gold cluster provides one of the most sensitive probes known for use in EM, light and confocal microscopy and in immunblotting.

B-50/GAP43 localization in polarized hippocampal neurons in vitro: An ultrastructural quantitative study

Hippocampal pyramidal neurons cultured in vitro gradually develop morphologically and biochemically distinct axons and dendrites, resulting in functional neuronal polarization [Dotti C.G. et al. (1988) J. Neurosci. 8, 1454–1468]. We have studied the distribution of the growth-associated protein B-50 in hippocampal neurons of the rat at stage 3 of development by means of light and electron microscopic immunocytochemistry. Hippocampal neurons grown for two to three days in vitro were aldehyde fixed and immunolabelled using polyclonal rabbit antibodies to B-50 and goat anti-rabbit immunoglobulins tagged with 1 nm gold particles. In order to permit visualization by both light and electron microscopy, the gold probes were silver intensified. Light microscopy demonstrated the absence of B-50 immunostaining in living neurons and the presence after permeabilization by fixation and subsequent treatment of the neurons with sodium borohydride, indicating that B-50 is located intracellularly. Both immunofluorescence and immunogold-silver labelling revealed that B-50 immunoreactivity outlined all neurites of the morphologically polarized neurons. For quantitative electron microscopy, six morphologically polarized neurons (developmental stage 3) were carefully selected from immunolabelled Epon-embedded neurons and processed completely to ultrathin sections. In this way the ultrastructural localization of B-50 has been studied in the cell body, the neurites and their growth cones. For each sectioned neuron, the relative distribution of the gold-silver deposits (representing B-50) over the plasma membrane of various cellular compartments was quantitated. B-50 is located at the plasma membrane of the neuronal cell body and all neurites including their growth cones. The density of B-50 on the plasma membrane of growth cones is not different from that of the neuritic shaft. In addition, B-50 is present on the cytosolic side of the membrane of small electron-lucent vesicles (average diameter 102.7 ± 2.5 nm) resembling transport vesicles. These vesicles are present in the cell body and the neurites. A two-fold concentration is found in the central region of the growth cones, suggesting a role of these vesicles in axonal transport, membrane insertion and (or) recycling. Since, at the onset of neuronal polarization, B-50 is present at the plasma membrane in all compartments of the hippocampal neuron, we suggest that at this stage of development B-50 does not participate directly in the processes leading to morphological polarization. The findings of a lack of B-50 enrichment on the plasma membrane of growth cones and the presence of B-50 on putative transport vesicles may indicate that B-50 plays a general role, not selective for the growth cone, at the neuronal plasma membrane during neuritogenesis.

The use of silver-enhanced 1-nm gold probes for light and electron microscopic localization of intra- and extracellular antigens in skin.

We used colloidal gold (1-nm diameter) with silver enhancement, in conjunction with a low-temperature post-embedding immunolabeling technique, to localize several antigens in normal skin at both the light and the electron microscopic level within the same tissue blocks. Normal skin subjected to cyrofixation and cryosubstitution and embedded in Lowicryl K11M was used as a substrate. Semi-thin sections (1 micron) were incubated in primary antibody (against epidermal basement membrane zone associated antigens and two keratin sub-types), biotinylated secondary antibodies, and then in 1-nm gold-conjugated streptavidin. Finally, the 1-nm gold label was enhanced using silver staining. Labeling of both basement membrane and keratin antigens was well demonstrated, and the area in the semi-thin sections showing the best structural preservation and the greatest intensity of immunolabeling was used to identify the part of the block to be used for ultra-thin sectioning. Ultra-thin sections were treated using a similar procedure to that employed for semi-thin sections. The labeling with silver-enhanced 1-nm gold probes was intense and readily visible by electron microscopy, even at low magnification. We have found this technique to have a high degree of specificity and sensitivity for labeling both intra- and extracellular antigens in skin, with the added advantage of providing the means for studies at both light microscopic and electron microscopic level.

Structure and growth of infection threads in the legume symbiosis with Rhizobium leguminosarum

SummarySpecific antibodies and enzyme–gold probes were used to study the structure and development of infection threads in nodules induced by Rhizobium leguminosarum on the roots of Vicia, Pisum and Phaseolus. In Pisum nodules, the tubular infection thread wall contains polysaccharides antigenically similar to those of the cell wall, including cellulose, xyloglucan, methyl‐esterified pectin and non‐esterified pectin, but none of these wall components is present around the infection droplet structures from which bacteria are internalized by plant plasma membrane. As reported previously for pea nodules, the luminal matrix of infection threads and infection droplets contains a plant glycoprotein; this glycoprotein is also secreted by infected and uninfected cortical cells of a Vicia root at the earliest stages of nodule initiation. Synthesis of a transcellular infection thread apparently involves reorganized deposition of components normally targeted to the cell wall, and infection thread growth is orientated anticlinally through the outer cortex in the same plane observed for the deposition of new cell walls following mitosis. Both the development of infection threads in the outer cortex and the initiation of cell division in the inner cortex are preceded by a similar process of cell reactivation involving centralization of nuclei and the development of anticlinal transvacuolar strands. It is therefore suggested that the two Rhizobium‐induced processes of infection thread growth and cortical cell division may both be consequences of a similar plant cell response in the inner and outer root cortex, respectively. Phaseolus nodules contained only short intracellular infection structures which terminated within individual cells and contained no luminal matrix material. The differences in infection thread structure between Pisum and Phaseolus nodules may reflect differences in ontogeny between “indeterminate” and “determinate” nodule meristems.

The role of the fat body, midgut and ovary in vitellogenin production and vitellogenesis in the female tick, Dermacentor variabilis

Polyclonal antibodies directed against D. variabilis vitellin were utilized for immunocytochemistry at the ultrastructural level. We localized vitelligenin (Vg) in rough endoplasmic reticulum cisternae, secretory granules and secreted products of fat body trophocytes and midgut vitellogenic cells from feeding and ovipositing females. Vg was localized in the oocyte Golgi bodies and in the yolk bodies of both feeding and ovipositing females. Uptake of exogenous Vg was indicated by the presence of immunospecific gold probe in coated pits and coated vesicles at the apical plasma membrane of oocytes from females in rapid engorgement and oviposition. In unmated females little detectable evidence of Vg uptake by developing oocytes suggests that mating and host detachment signal the beginning of vitellogenesis. We conclude that fat body trophocytes, midgut vitellogenic cells and oocytes are involved in the synthesis and/or processing of Vg and that feeding is the signal associated with the initiation of Vg synthesis and/or processing.

Unfixed tissue for electron immunocytochemistry: a simple preparation method for colloidal gold localization of sensitive epitopes using ethanediol dehydration

A quick, simple protocol is described for the preparation of tissue for electron immunocytochemistry without the use of fixatives or deleterious solvents. Fresh, normal human colon was rapidly dehydrated in ethanediol (ethylene glycol) then embedded directly in low-acid glycol methacrylate. Using both mono- and polyclonal antibodies, in conjunction with colloidal gold probes, a range of intra- and extracellular epitopes were localized; these epitopes included lysozyme, chromogranin, desmin and collagen IV. Overall, the tissue compared well with material fixed in glutaraldehyde, partially dehydrated and embedded in LR White acrylic resin. Ultrastructural detail was good and was further enhanced, without affecting probe density and epitope localization, by the addition of 1% tannic acid or 1% uranyl acetate to the dehydrant. The technique is applicable to a wide range of tissues, allowing excellent antigen retention which might prove useful for the immunolocalization of sensitive epitopes.

A novel methodology for double protein A-gold immunolabeling utilizing the monovalent fragment of protein A.

A method for sequential protein A-gold immunolabeling is described whereby the binding of second gold probe to the first antibody-protein A-gold complex is reduced to acceptably minimal levels. Immunolabeling of thin sections of embedded pituitary tissue was used as a model system. After an initial immunolabeling for prolactin, sections were incubated in normal serum (rabbit) followed by a monovalent fragment of protein A. These latter two incubations reduced artifactual second gold probe label over prolactin-labeled secretory granules to minimal levels (much less than 1 particle per granule) when sections were subsequently immunolabeled with normal serum. The combination of normal serum and protein A fragment incubations saturates IgG and protein A binding sites on the first antibody-gold probe complex. The latter is thereafter unable to bind further IgG (and thus gold probe) because of the monovalent nature of the protein A fragment. It is suggested that this methodology may be extended to multiple immunolabeling procedures for electron microscopy. In addition, when used before single labeling this method may be an effective way to minimize nonspecific IgG binding in cases where the tissue or antibody under study may be a problem.

B-50/GAP43 localization on membranes of putative transport vesicle in the cell body, neurites and growth cones of cultured hippocampal neurons

We conducted an electron microscopic immunocytochemical study to locate B-50/GAP43 in various cellular elements of hippocampal neurons grown in dissociated cell culture. B-50 was detected with pre- and post-embedding immunoincubation, using affinity-purified B-50 antibodies and secondary antibodies coated on gold probes. For the first time ultrastructural evidence is presented for the location of B-50 on the membranes of electron-lucent transport vesicles with a diameter of 99.4 ± 2.9 nm, present in the trans region of the Golgi apparatus, in neurites and in growth cones of cultured hippocampal neurons.

A 1.4-nm gold cluster covalently attached to antibodies improves immunolabeling.

A large gold cluster (Au1.4nm) was covalently coupled to IgG and Fab' fragments. Its gold core is 1.4 nm in diameter and the Fab'-Au1.4nm immunoconjugate is the smallest gold immunoprobe that can be seen directly in the conventional electron microscope. It is useful in high-resolution immunolabeling, providing a resolution of 7.0 nm. The cluster's visibility can be enhanced with silver development for use in EM or light microscopy for histological purposes, or to detect less than or equal to 0.2 pg of antigen in immunoblots. By using a gold compound with covalent attachment, a number of advantages over colloidal gold probes are realized, including better resolution, stability, uniformity, sensitivity, and complete absence of aggregation; its small size should also improve penetration and more quantitative labeling of antigenic sites.

Colloidal Gold and Its Application in Cell Biology

Publisher Summary This chapter discusses the scope and variety of applications of the colloidal gold method. The advantages of colloidal gold as a marker in electron microscopy (EM) immunocytochemistry include the particulate nature of colloidal gold, which allows a fine localization of marked sites, and the size range, which guarantees high flexibility in lateral resolution. Gold particles are negatively charged and can be complexed by noncovalent electrostatic adsorption with various macromolecules forming stable and bioactive gold-ligand complexes termed “gold probes,” and the characteristic X-ray signals emitted by gold could be used to image and quantify cell-bound gold markers by the application of X-ray microanalytical techniques and appropriate computer programs. The introduction of ultrasmall gold particles with increased penetration capabilities has enlarged the potential of colloidal gold reagents, particularly in the field of light microscopy. The addition of polymers is a well-established method for controlling the stability of colloidal dispersions. Nonionic macromolecules—such as polyethylene glycol and polysaccharides—as well as charged macromolecules can be adsorbed onto a metal surface. The adsorption of macromolecules onto colloidal gold depends on a number of factors, such as (1) the stability of the colloid itself, (2) the concentration, shape, configuration, and isoelectric point of macromolecules, and (3) the ionic strength, pH, and temperature of a suspending medium.

On the molecular profiling of cell surfaces by SEM.

Cell surfaces interface with a variety of environments and, as a consequence, cell surface properties are of considerable functional importance to the biological organism. SEM immunocytochemistry (SEM-IC) is one of a range of techniques used to analyse cell surface properties. A major goal of SEM-IC centres on extended survey or high-magnification morphological analysis of cell and tissue surfaces combined with molecular profiles of these surfaces as established by gold-labelling. The properties of colloidal gold make it the marker of choice for SEM-IC and a representative gold-labelling protocol is outlined. The SEM-IC gold-labelling technique has been applied advantageously to the analysis both of cell surfaces and cytoskeletal and extracellular matrix elements: a tabulation of the main SEM-IC biomedical applications is given. Illustrated examples demonstrate how SEM-IC provides a highly effective approach for analysis both of cell and tissue differentiation-maturation sequences, and of pathological change involving not only the entire tissue or cell surface but also minute changes in microdomain characteristics of the individual cell surface. Steps in exploiting the technique of colloidal gold SEM-IC have been several-fold and include: use of backscattered electron imaging; accurate localization of gold particles by superimposition on topographical maps of the cell surface; and use of small (1-10 nm) gold probes followed by silver enhancement in order to minimize steric hindrance. Factors under assessment include: use of low voltage SEM; BE imaging of samples coated with ultrathin metal films; and use of gold-labelled SEM-IC for direct quantification of the numbers of target molecules exposed on cell surfaces by automated image analysis of the digitized BE image.

Three-dimensional immunogold labeling of nuclear matrix proteins in permeabilized cells

A preembedment labeling procedure is described for the three-dimensional (3D) labeling of nuclear matrix proteins in permeabilized cells. The procedure is based on the use of ultra-small (1 nm) gold particles as a marker system. This marker penetrates the nucleus more efficiently than the conventionally used 5-10 nm colloidal gold probes. Dehydration is performed by freeze-substitution to preserve the ultrastructure of the cell as optimally as possible. During freeze-substitution the samples are stained by uranyl ions to stain the cellular material throughout the resin section. The 3D gold-labeled and uranyl-stained specimen is embedded in Epon resin and semi-thin (0.2-0.5 microns) sections are made for stereo electron microscopy. The applicability of this method is illustrated by the localization of nuclear matrix-associated nuclear bodies in permeabilized interphase and mitotic HeLa cells.

Visualization of Trichoderma reesei Cellobiohydrolase I and Endoglucanase I on Aspen Cellulose by Using Monoclonal Antibody-Colloidal Gold Conjugates

Monoclonal antibodies (MAbs) specific for cellobiohydrolase I (CBH I) and endoglucanase I (EG I) were conjugated to 10- and 15-nm colloidal gold particles, respectively. The binding of CBH I and EG I was visualized by utilizing the MAb-colloidal gold probes. The visualization procedure involved immobilization of cellulose microfibrils on copper electron microscopy grids, incubation of the cellulose-coated grids with cellulase(s), binding of MAb-colloidal gold conjugates to cellulase(s), and visualization via transmission electron microscopy. CBH I was seen bound to apparent crystalline cellulose as well as apparent amorphous cellulose. EG I was seen bound extensively to apparent amorphous cellulose with minimal binding to crystalline cellulose.

Ultrastructural localization of nuclear matrix proteins in HeLa cells using silver-enhanced ultra-small gold probes.

We describe a method for immunogold staining of nuclear matrix proteins using ultra-small gold particles. The nuclear matrix of HeLa cells is obtained by two fractionation steps: (a) cell permeabilization with Triton X-100 to isolate the cytoskeleton, and (b) nuclease digestion followed by an incubation in 0.25 M ammonium sulfate to isolate the nuclear matrix. To prevent redistribution of internal matrix proteins during nuclear matrix preparation, pre-fixation with 0.1% acrolein was performed. Under this condition up to 80% of protein and 90% of DNA and RNA could be removed on nuclear matrix isolation, without redistribution of internal nuclear matrix proteins. For immunogold labeling, 1-nm gold probes appeared to be required to obtain optimal penetration into the nucleus. These particles can be visualized after silver enhancement. After gold labeling the matrices are stained, embedded in Epon, and ultra-thin sections are prepared for examination in the electron microscope. The applicability of this method is examplified by the localization of a 125 KD internal nuclear matrix protein and the lamins A and C in nuclear matrix preparations of HeLa cells.

Video microscopic studies of membrane dynamics

The application of several imaging technologies and photobleaching to problems in membrane dynamics will be presented. These techniques emphasize different aspects of the measurement of translational transport: (1) tracing the trajectories of individual molecules undergoing a two dimensional random walk, and (2) investigating bulk changes in the distribution of membrane components in the plane of the membrane in single, locomoting cells.Nanovid microscopy, which uses 30-40 nm colloidal gold probes combined with video-enhanced contrast, allows investigation of random and directed movements of individual molecules in artificial membranes or in the plasma membrane of living cells. The movements of lipid molecules were followed in a supported, planar bilayer containing fluorescein-phosphatidylethanolamine (Fl-PE) labelled with 30 ran gold anti-fluorescein (anti-Fl) to validate the technique in a model system. The membrane-bound gold particles moved in random patterns which were indistinguishable from those produced by computer simulations of two dimensional random motion.

Direct observation of brownian motion of lipids in a membrane.

Nanovid microscopy, which uses 30- to 40-nm colloidal gold probes combined with video-enhanced contrast, can be used to examine random and directed movements of individual molecules in the plasma membrane of living cells. To validate the technique in a model system, the movements of lipid molecules were followed in a supported, planar bilayer containing fluorescein-conjugated phosphatidylethanolamine (Fl-PtdEtn) labeled with 30-nm gold anti-fluorescein (anti-Fl). Multivalent gold probes were prepared by conjugating only anti-Fl to the gold. Paucivalent probes were prepared by mixing an irrelevant antibody with the anti-Fl prior to conjugation. The membrane-bound gold particles moved in random patterns that were indistinguishable from those produced by computer simulations of two-dimensional random motion. The multivalent gold probes had an average lateral diffusion coefficient (D) of 0.26 x 10(-8) cm2/sec, and paucivalent probes had an average D of 0.73 x 10(-8) cm2/sec. Sixteen percent of the multivalent and 50% of the paucivalent probes had values for D in excess of 0.6 x 10(-8) cm2/sec, which, after allowance for stochastic variation, are consistent with the D of 1.3 x 10(-8) cm2/sec measured by fluorescence recovery after photobleaching of Fl-PtdEtn in the planar bilayer. The effect of valency on diffusion suggests that the multivalent gold binds several lipids forming a disk up to 30-40 nm in diameter, resulting in reduced diffusion with respect to the paucivalent gold, which binds one or a very few lipids. Provided the valency of the gold probe is considered in the interpretation of the results. Nanovid microscopy is a valid method for analyzing the movements of single or small groups of molecules within membranes.

Nanovid microscopy

By combining small colloidal gold probes with video-enhanced quantitative microscopy, the intracellular dynamics of specific proteins in living cells can now be studied.

An application for a color image analyzer for gold labellig in immunoelectrion microscopy to achieve enhanced demmonstration of small gold probes

An application for a color image analyzer for gold labellig in immunoelectrion microscopy to achieve enhanced demmonstration of small gold probes