Use of avidin-biotin-peroxidase complex (ABC) in immunoperoxidase techniques: a comparison between ABC and unlabeled antibody (PAP) procedures

The use of avidin-biotin interaction in immunoenzymatic techniques provides a simple and sensitive method to localize antigens in formalin-fixed tissues. Among the several staining procedures available, the ABC method, which involves an application of biotin-labeled secondary antibody followed by the addition of avidin-biotin-peroxidase complex, gives a superior result when compared to the unlabeled antibody method. The availability of biotin-binding sites in the complex is created by the incubation of a relative excess of avidin with biotin-labeled peroxidase. During formation of the complex, avidin acts as a bridge between biotin-labeled peroxidase molecules; and biotin-labeled peroxidase molecules, which contains several biotin moieties, serve as a link between the avidin molecules. Consequently, a "lattice" complex containing several peroxidase molecules is likely formed. Binding of this complex to the biotin moieties associated with secondary antibody results in a high staining intensity.

Tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis for the separation of proteins in the range from 1 to 100 kDa

A discontinuous sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) system for the separation of proteins in the range from 1 to 100 kDa is described. Tricine, used as the trailing ion, allows a resolution of small proteins at lower acrylamide concentrations than in glycine-SDS-PAGE systems. A superior resolution of proteins, especially in the range between 5 and 20 kDa, is achieved without the necessity to use urea. Proteins above 30 kDa are already destacked within the sample gel. Thus a smooth passage of these proteins from sample to separating gel is warranted and overloading effects are reduced. This is of special importance when large amounts of protein are to be loaded onto preparative gels. The omission of glycine and urea prevents disturbances which might occur in the course of subsequent amino acid sequencing.

Global quantification of mammalian gene expression control

Gene expression is a multistep process that involves the transcription, translation and turnover of messenger RNAs and proteins. Although it is one of the most fundamental processes of life, the entire cascade has never been quantified on a genome-wide scale. Here we simultaneously measured absolute mRNA and protein abundance and turnover by parallel metabolic pulse labelling for more than 5,000 genes in mammalian cells. Whereas mRNA and protein levels correlated better than previously thought, corresponding half-lives showed no correlation. Using a quantitative model we have obtained the first genome-scale prediction of synthesis rates of mRNAs and proteins. We find that the cellular abundance of proteins is predominantly controlled at the level of translation. Genes with similar combinations of mRNA and protein stability shared functional properties, indicating that half-lives evolved under energetic and dynamic constraints. Quantitative information about all stages of gene expression provides a rich resource and helps to provide a greater understanding of the underlying design principles.

The unlabeled antibody enzyme method of immunohistochemistry: preparation and properties of soluble antigen-antibody complex (horseradish peroxidase-antihorseradish peroxidase) and its use in identification of spirochetes

Antigen was identified histochemically without the use of labeled antibodies by the sequential application of (a) specific rabbit antiserum, (b) sheep antiserum to rabbit immunoglobulin G, (c) specifically purified, soluble horseradish peroxidase-anti-horseradish peroxidase complex (PAP), (d) 3,3'-diaminobenzidine and hydrogen peroxide and (e) osmium tetroxide. A simple method for preparation of high yields of PAP consisted of precipitation of antibody from specific rabbit antiserum with horseradish peroxidase (PO) at equivalence, solubilization of the washed precipitate with excess PO at pH 2.3, 1°C, followed by immediate neutralization and separation of PAP from PO by half-saturation with ammonium sulfate. The ratio of PO to anti-PO in PAP was 3:2 irrespective of the source of antiserum. PAP was heterogeneous on electrophoresis, homogeneous on sedimentation, diffusion and electron microscopy and consisted of pentagons with diameters of 205 Å. s20, w, 11.98 x 10–13; d20, w, 2.48 x 10–7; molecular weight by sedimentation velocity, 429,000, and equilibrium, 413,000. Sensitivity and specificity of immunohistochemical staining of spirochetes was about 100- to 1000-fold that of immunofluorescence. The unexpected ratio of PO to anti-PO is presumed to be due to stabilization by the pentagonal shape in which three corners are suspected to be PO and two antibody fragment Fc.

A rapid and simple method for measuring thymocyte apoptosis by propidium iodide staining and flow cytometry

Corticosteroids, calcium ionophores and anti-CD3 monoclonal antibodies kill mouse thymocytes incubated in vitro. Cell death is preceded by extensive DNA fragmentation into oligonucleosomal subunits. This type of cell death (apoptosis), which physiologically occurs in the intrathymic process of immune cell selection, is usually evaluated by either electrophoretic or colorimetric methods which measure DNA fragmentation in the nuclear extracts. These techniques are unable to determine the percentage of apoptotic nuclei or recognize the apoptotic cells in a heterogeneous cell population. We have developed a flow cytometric method for measuring the percentage of apoptotic nuclei after propidium iodide staining in hypotonic buffer and have compared it with the classical colorimetric and electrophoretic techniques using dexamethasone (DEX)-treated mouse thymocytes. Apoptotic nuclei appeared as a broad hypodiploid DNA peak which was easily discriminable from the narrow peak of thymocytes with normal (diploid) DNA content in the red fluorescence channels. When the DEX-induced apoptosis was inhibited by either low-temperature (4 degrees C) incubation or cycloheximide treatment, no hypodiploid DNA peak appeared. Similarly, thymocyte death induced by sodium azide, a substance with cell-killing activity through non-apoptotic mechanisms, did not result in any variation in the normal DNA peak. The flow cytometric data showed an excellent correlation with the results obtained with both electrophoretic and colorimetric methods. This new rapid, simple and reproducible method should prove useful for assessing apoptosis of specific cell populations in heterogeneous tissues such as bone marrow, thymus and lymph nodes.

In vitro scratch assay: a convenient and inexpensive method for analysis of cell migration in vitro

The in vitro scratch assay is an easy, low-cost and well-developed method to measure cell migration in vitro. The basic steps involve creating a "scratch" in a cell monolayer, capturing the images at the beginning and at regular intervals during cell migration to close the scratch, and comparing the images to quantify the migration rate of the cells. Compared to other methods, the in vitro scratch assay is particularly suitable for studies on the effects of cell-matrix and cell-cell interactions on cell migration, mimic cell migration during wound healing in vivo and are compatible with imaging of live cells during migration to monitor intracellular events if desired. Besides monitoring migration of homogenous cell populations, this method has also been adopted to measure migration of individual cells in the leading edge of the scratch. Not taking into account the time for transfection of cells, in vitro scratch assay per se usually takes from several hours to overnight.

Staining of tissue sections for electron microscopy with heavy metals

Heavy metals may be incorporated from solution into tissue sections for electron microscopy. The resulting increase in density of the tissue provides greatly enhanced contrast with minimal distortion. Relative densities of various structures are found to depend on the heavy metal ions present and on the conditions of staining. Certain hitherto unobserved details are revealed and some sort of specificity exists, although the factors involved are not yet understood.

A simple method for organotypic cultures of nervous tissue

Hippocampal slices prepared from 2-23-day-old neonates were maintained in culture at the interface between air and a culture medium. They were placed on a sterile, transparent and porous membrane and kept in petri dishes in an incubator. No plasma clot or roller drum were used. This method yields thin slices which remain 1-4 cell layers thick and are characterized by a well preserved organotypic organization. Pyramidal neurons labelled by extra- and intracellular application of horse radish peroxidase resemble by the organization and complexity of their dendritic processes those observed in situ at a comparable developmental stage. Excitatory and inhibitory synaptic potentials can easily be analysed using extra- or intracellular recording techniques. After a few days in culture, long-term potentiation of synaptic responses can reproducibly be induced. Evidence for a sprouting response during the first days in culture or following sections is illustrated. This technique may represent an interesting alternative to roller tube cultures for studies of the developmental changes occurring during the first days or weeks in culture.

Bioorthogonal chemistry: fishing for selectivity in a sea of functionality

The study of biomolecules in their native environments is a challenging task because of the vast complexity of cellular systems. Technologies developed in the last few years for the selective modification of biological species in living systems have yielded new insights into cellular processes. Key to these new techniques are bioorthogonal chemical reactions, whose components must react rapidly and selectively with each other under physiological conditions in the presence of the plethora of functionality necessary to sustain life. Herein we describe the bioorthogonal chemical reactions developed to date and how they can be used to study biomolecules.

Immunoenzymatic labeling of monoclonal antibodies using immune complexes of alkaline phosphatase and monoclonal anti-alkaline phosphatase (APAAP complexes)

A murine monoclonal antibody specific for calf intestinal alkaline phosphatase has been prepared and used in an unlabeled antibody bridge technique for labeling monoclonal antibodies. This procedure--the alkaline phosphatase monoclonal anti-alkaline phosphatase (APAAP) method--gives excellent immunocytochemical labeling of tissue sections and cell smears, comparable in clarity and intensity to that achieved with immunoperoxidase labeling. If the enzyme label is developed with a naphthol salt as a coupling agent and Fast Red or hexazotized new fuchsin as a capture agent, a vivid red reaction product is obtained which is very easily detected by the human eye. For this reason the APAAP technique was found particularly suitable for labeling cell smears (for both cytoplasmic and surface-membrane antigens) and for detecting low numbers of antigen-bearing cells in a specimen (e.g., carcinoma cells in a malignant effusion). It was found possible to enhance the intensity of the APAAP labeling reaction substantially by repeating the second and third incubation steps (i.e., the unlabelled "bridge" antibody and APAAP complexes). The APAAP technique was superior to immunoperoxidase labeling for staining tissues rich in endogenous peroxidase, and could be used in conjunction with immunoperoxidase methods for double immunoenzymatic staining. The method was also applicable to the detection of antigenic molecules following their electrophoretic transfer from SDS-polyacrylamide gels to nitrocellulose sheets ("immunoblotting").

Ultrasensitive stain for proteins in polyacrylamide gels shows regional variation in cerebrospinal fluid proteins

A new silver stain for electrophoretically separated polypeptides can be rapidly and easily used and can detect as little as 0.01 nanogram of protein per square millimeter. When employed with two-dimensional electrophoresis, it should permit qualitative and quantitative characterization of protein distributions in body fluids and tissues. It has been used to demonstrate regional variations in cerebrospinal fluid proteins.

Isolation and functional properties of murine hematopoietic stem cells that are replicating in vivo

Hematopoietic stem cells (HSC) are multipotent cells that reside in the bone marrow and replenish all adult hematopoietic lineages throughout the lifetime of the animal. While experimenting with staining of murine bone marrow cells with the vital dye, Hoechst 33342, we discovered that display of Hoechst fluorescence simultaneously at two emission wavelengths revealed a small and distinct subset of whole bone marrow cells that had phenotypic markers of multipotential HSC. These cells were shown in competitive repopulation experiments to contain the vast majority of HSC activity from murine bone marrow and to be enriched at least 1,000-fold for in vivo reconstitution activity. Further, these Hoechst-stained side population (SP) cells were shown to protect recipients from lethal irradiation at low cell doses, and to contribute to both lymphoid and myeloid lineages. The formation of the Hoechst SP profile was blocked when staining was performed in the presence of verapamil, indicating that the distinctly low staining pattern of the SP cells is due to a multidrug resistance protein (mdr) or mdr-like mediated efflux of the dye from HSC. The ability to block the Hoechst efflux activity also allowed us to use Hoechst to determine the DNA content of the SP cells. Between 1 and 3% of the HSC were shown to be in S-G2M. This also enabled the purification of the G0-G1 and S-G2M HSC had a reconstitution capacity equivalent to quiescent stem cells. These findings have implications for models of hematopoietic cell development and for the development of genetic therapies for diseases involving hematopoietic cells.

Improved staining of proteins in polyacrylamide gels including isoelectric focusing gels with clear background at nanogram sensitivity using Coomassie Brilliant Blue G-250 and R-250

An improved procedure for staining of proteins following separation in polyacrylamide gels is described which utilizes the colloidal properties of Coomassie Brilliant Blue G-250 and R-250. The new method is based on addition of 20% v/v methanol and higher concentrations of ammonium sulfate to the staining solution previously described. The method combines the advantage of much shorter staining time with high sensitivity, a clear background not requiring destaining, stepwise staining, and stable fixation after staining. The method has been applied to staining of polyacrylamide gels after sodium dodecyl sulfate-electrophoresis and isoelectric focusing in carrier ampholyte-generated pH gradients.