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Characterization and representative structures of N-oligosaccharides bound to apolipoprotein H.

We studied the structure of N-linked carbohydrates bound to apolipoprotein H by a combination of two methods which make use of lectins. Digoxigenin-labelled lectins are used for the structural characterization of carbohydrate chains of glycoproteins. Concanavalin A lectin affinity chromatography was used to analyse apolipoprotein H according to the characteristics of its carbohydrate chain inner to sialic acid residues. Our results from digoxigenin-labelled lectins analysis showed that apolipoprotein H gave positive bands to SNA, DSA, GNA, PNA and AAA lectins. Apolipoprotein H gave a negative band when reacted with MAA lectin. When we applied apolipoprotein H onto the Concanavalin A lectin column no detectable amounts of protein were eluted with Concanavalin A buffer. After adding a buffer with low sugar concentration (10 mM glucoside) a large amount of apolipoprotein H was recovered. These molecules of apolipoprotein H weakly bound to the lectin. When a higher sugar concentration (500 mM mannoside) was added most of the sample applied was eluted. These molecules of apolipoprotein H firmly bound to the column having high affinity for the lectin. These results combined with those coming from the digoxigen-labeled lectins method enable us to understand the inner structure of carbohydrate chains with their outer branches. Molecules of apolipoprotein H which weakly bind to Concanavalin A could bear complex N-glycans organized in biantennary or truncated hybrid structures. Firmly bound apolipoprotein H referred to molecules rich in N-glycan hybrid structures. They have an outer branch belonging to the high mannose carbohydrate chains which explain the ability to bind to the column and an other main branch bearing the sequence galactose beta-(1-4)-N-acetylglucosamine beta-(1-2) mannose. Galactose could be the terminal sugar or, alternatively, be masked with sialic acid alpha-(2-6) terminally linked.

Amino Acid Sequence↗

Efficient synthesis of 3-aminodigoxigenin and 3-aminodigitoxigenin probes.

Oxidation of digoxigenin and digitoxigenin to the 3-ketones followed by reductive amination produced a mixture of amine epimers. The inability to separate the epimeric mixtures of chemiluminescent digoxigenin probes derived by conjugation to the acridinium label prompted us to develop an HPLC method to separate the amines. Labeling of the pure amines resulted in good yields of the isomerically pure probes.

Cardiotonic Agents↗

On-line continuous-flow, multi-protein biochemical assays for the characterization of bioaffinity compounds using electrospray quadrupole time-of-flight mass spectrometry.

The applicability of a homogeneous on-line continuous-flow, multi-protein biochemical assay was demonstrated for the interaction between fluorescein-biotin and streptavidin and for digoxin and anti-digoxigenin using electrospray quadrupole time-of-flight mass spectrometry (Q-TOF MS). In the on-line continuous-flow biochemical MS-based system several receptors (e.g., streptavidin and anti-digoxigenin, respectively) were allowed to react with corresponding reporter ligands (e.g.,fluorescein-biotin and digoxin, respectively). The methodology presented allows the simultaneous measurement of affinity and molecular mass of an active compound. By using automated MS and MS-MS switching functions of the Q-TOF, structure information is obtained allowing the characterization of bioactive compounds. No cross-reactivities were observed between the two model systems fluorescein-biotin/streptavidin and digoxin/anti-digoxigenin.

Algorithms↗

Epidermal cell kinetics by combining in situ hybridization and immunohistochemistry.

Double labelling can serve as a useful tool for providing information about cell kinetics in normal and hyperproliferative tissues in general, and skin in particular. We have developed a double-labelling method that combines immunohistochemistry using the monoclonal antibody MIB1 and non-isotopic in situ hybridization using either a digoxigenin-labelled RNA probe specific for histone 3 mRNA sequences or a Fluorescein-labelled oligonucleotide probe specific for histone 2b, 3, 4 mRNA sequences. Double labelling was performed on normal, tape-stripped normal skin and psoriatic skin. The three proliferation markers were also examined by single labelling. The ratio of cells in the S-phase (Ns) and the growth fraction (Ncy) was determined. In normal skin, psoriatic skin and tape-stripped normal skin after 24 h and after 48 h, we calculated that 15%, 16%, 3% and 12% of growth fraction consisted of cells in the S-phase respectively. The S-phase lasts approximately 10 h, so the cell cycle time in normal and psoriatic skin is approximately 62.5 h. At present, the MIB1/H3 digoxigenin or MIB1/H2b-H3-H4 Fluorescein double-labelling technique cannot be used routinely. Therefore, in order to understand the cell kinetic processes better, experiments are recommended to optimize these methods. From a practical point of view and for reasons of specificity and sensitivity, we prefer the Fluorescein-labelled oligonucleotide probe method.

Cell Division↗

Detection of tissue kallikrein and kinin B1 and B2 receptor mRNAs in human brain by in situ RT-PCR.

Tissue kallikrein (TK) and kinin receptors have been immuno-localized in various areas of the human nervous system, suggesting that the kallikrein-kinin system (KKS) may be functionally active in the brain. The aim of this study was to determine the cellular expression of TK and kinin B1 and B2 receptor mRNAs in specific regions of the human brain by in situ reverse transcriptase polymerase chain reaction. Autopsy samples of the brain, spinal cord, kidney and salivary gland were embedded in paraffin. Sections (5 microm), adhered onto silane coated glass slides, were treated with Proteinase K and DNase, followed by reverse transcription polymerase chain reaction with specific KKS primers and digoxigenin-dUTP. Detection of the digoxigenin-label demonstrated localization of TK, B1 and B2 mRNAs in the cytoplasm of some neuronal cell bodies in the hypothalamus, thalamus, frontal cortex and spinal cord. TK mRNA was also observed in the ependymal cells lining the cerebral ventricles and epithelial cells of the choroid plexus. In the choroid plexus, only B1 gene expression was observed in some choroidal epithelial cells while no B2 labeling was detected. The identification of mRNAs to TK, B1 and B2 kinin receptors in human nervous tissue supports previous evidence for the presence of the KKS in the brain and confirms localized protein synthesis.

Adolescent↗

Comparison of different approaches for the incorporation of non-radioactive labels into polymerase chain reaction products.

Different methods for labelling polymerase chain reaction (PCR) products with non-radioactive labels for their detection by hybridization with immobilized DNA probes were compared. The use of digoxigenin (DIG) as a label provided greater sensitivity than biotin in a PCR system targeting the invA gene from Salmonella typhimurium. Incorporation of digoxigenin into amplicons in the form of 5'-DIG-labelled oligonucleotide primers resulted in better assay signals and was more economical than DIG-labelled dUTP.

Bacterial Proteins↗

Rapid enumeration of Escherichia coli in oysters by a quantitative PCR-ELISA.

Direct enumeration of Escherichia coli from oysters was achieved using a polymerase chain reaction (PCR) amplification of the lamB gene coupled with an enzyme-linked immunosorbent assay (ELISA). Amplified PCR products generated using a digoxigenin-labelled primer were heat denatured before being quantified by an ELISA. A biotinylated probe immobilized onto streptavidin-coated microplates was used to capture the digoxigenin-labelled fragments that were detected with a peroxidase antidigoxigenin conjugate. Subsequent enzymic conversion of substrate gave distinct absorbance differences when assaying oyster samples containing E. coli in the range 10-10(5) cfu g-1.

Animals↗

Use of an alkaline phosphatase-labelled probe for the detection of Mycoplasma synoviae in chickens.

Short nucleotides directly labelled to alkaline phosphatase (SNAP probes) are an interesting alternative to digoxigenin-labelled probes (DIG probes), because they reduce the number of steps necessary in dot blots for the detection of DNA or amplificate. This study examined the questions whether a SNAP probe might not only save time, but also increase the sensitivity of another PCR-based DNA probe test using a digoxigenin probe. Amplificates obtained by multispecies polymerase chain reaction (PCR), with either purified genomic DNA or DNA extracted from tracheal swabs taken in chicken flocks, were detected by both methods. The results for the clinical specimens were compared to culture. Under stringent conditions, the specificity and sensitivity obtained with the SNAP probe were comparable to the results obtained with the DIG probe. The quantities 10 fg (SNAP probe) and 100 fg (DIG probe) of purified Mycoplasma synoviae DNA were detected after amplification, but more positive clinical specimens were detected with the DIG probe. Under non-stringent conditions sensitivity with purified DNA did no change, but the coloration of the dots improved markedly, and more positive specimens could be detected with the SNAP probe than with the DIG probe, truly positives as confirmed by culture. Because cross-reaction with Mycoplasma gallisepticum and Mycoplasma imitans, two species with DNA that was also recognized by the multispecies primers, occurred under non-stringent conditions, it was concluded that, to take the full advantage of SNAP probes, their use in combination with species-specific primer pairs is recommended. PCR as a method for mycoplasma detection is however, always accompanied with serological and cultural methods. When a M. synoviae mono-infection is likely by serological results, non-stringent dot blot conditions and use of the SNAP probe will ease and improve the detection of mycoplasma.

Alkaline Phosphatase↗

Histone H1-mediated transfection: role of calcium in the cellular uptake and intracellular fate of H1-DNA complexes.

Previously, we have shown that the transgene expression in the endothelial cell line ECV 304 strongly depends on the presence of low concentrations of Ca2+. However, it remained unclear, which transfection steps are controlled by Ca2+ ions. In the present study, we constructed transfection complexes of digoxigenin-labelled DNA and FITC-labelled histone H1. We monitored the pathway of these complexes with the use of anti-digoxigenin and anti-cathepsin B antibodies and immunofluorescence microscopy. Double labelling of DNA and cathepsin B permitted the localization of transfection complexes into endosomes/lysosomes which suggests an uptake of transfection complexes via endocytosis. It was also found that the uptake of transfection complexes by the cells was independent of the presence or absence of Ca2+ ions in the transfection medium. On the other hand, the presence of Ca2+ in the transfection medium dramatically changed the composition of the transfection complexes inside the endosome/lysosome compartment, which resulted in a strong reduction of H1 binding to DNA. Presence of Ca2+ in the postincubation medium for 24 h resulted in release of the transfection complexes with reduced H1 content from the endosomes/lysosomes into the cytosol. In the absence of Ca2+ the transfection complexes practically disappeared. These results allow us to come to the following conclusions: Ca2+ ions control the reorganization of the transfection complexes in endosomes/lysosomes and their release into the cytosol, which is an important prerequisite for transgene expression, whereas uptake of transfection complexes by the cells is not dependent on Ca2+.

Animals↗

Microtiter format gene quantification by covalent capture of competitive PCR products: application to HIV-1 detection.

We have developed a simple gene quantification system using the competitive polymerase chain reaction (CPCR) followed by microtiter format analysis. CPCR is carried out using a mutant competitor with the same size as the target DNA product, and a minimal base exchange to insure the same amplification kinetics. One primer is aminated at the 5' end to produce PCR products that are captured onto carboxylated wells of microtiter plates through peptide bond formation. The non-aminated DNA strands are stripped off from the wells by alkali washing, and the remaining aminated strands are hybridized with either a digoxigenin-labeled wild type-specific oligonucleotide probe or a competitor-specific probe. To standardize the hybridization conditions of the probes, a DNA construct containing wild type and mutant competitor sequences in tandem is captured at different concentrations, hybridized with the probes, and used to generate a standard curve. Bound probes are detected by anti-digoxigenin antibody conjugated with peroxidase and chromogen. Optical densities are recorded with a conventional microtiter plate reader and converted to concentrations according to the standard curves. The ratios of wild type DNA to mutant competitor are used to determine the initial amounts of wild type DNA in the samples. This method was used successfully to quantify human immunodeficiency virus type 1 (HIV-1) env gene in human lymphocytes. It only requires a thermal cycler and a conventional microtiter plate reader, and can be readily done on a large scale. Potential applications include detection of other pathogens, diagnosis of genetic disorders and studies of gene expression.

Base Sequence↗

Endocrine-dependent accumulation of IGF-I by hypothalamic glia.

Tanycytes are specialized glial cells of the hypothalamus and median eminence. Immunoreactive insulin-like growth factor I (IGF-I) levels fluctuate in tanycytes with the natural variations in sex steroids associated with the ovarian cycle. To determine whether these changes are as a result of differences in IGF-I accumulation, the peptide was labelled with digoxigenin and injected into the lateral cerebral ventricle. Tanycyte-like cells specifically accumulated digoxigenin-labelled IGF-I. This accumulation was mediated by IGF-I receptors and showed marked differences during the oestrous cycle, being low in the afternoon of pro-oestrus and high in the afternoon of oestrus. These results indicate that the accumulation by tanycytes of IGF-I or IGF-I fragments capable of receptor-mediated internalization is under endocrine control, suggesting that hypothalamic glia may be involved in neuroendocrine regulation.

Animals↗

Microwave treatment enhances detection of RNA and DNA by in situ hybridization.

The use of oligonucleotide probes with nonisotopic detection systems has made in situ hybridization (ISH) more accessible for use in diagnostic pathology; however, ISH using formalin-fixed, paraffin-embedded tissues remains much more sensitive when performed with radioactively labeled probes compared with nonisotopic reporter systems, especially using oligonucleotide probes. We investigated the effects of microwave pretreatment on the detection of RNA and DNA in formalin-fixed, paraffin-embedded tissues in an attempt to improve the sensitivity of ISH with digoxigenin-labeled probes. Titration of normal tissues with oligonucleotide probe cocktails for albumin, prolactin, chromogranin (Cg) A and B mRNAs and a cDNA probe for JC virus showed a significant increase in sensitivity with the use of microwave treatment step rather than heating at 70 degrees C in 2 x SSC for 30 min. Analysis of various solutions used for microwaving showed that 10 mM citrate buffer was more effective than 2 x SSC, phosphate-buffered saline, tissue unmasking fluid, or water. A 15- to 20-min period of microwaving in an 800-W oven produced optimum results. Analysis of a group of tumors for albumin and CgA and B mRNAs and infected brain biopsies for JC virus DNA showed increased sensitivity of the microwave technique using digoxigenin-labeled probes. These results show that microwave treatment can enhance the detection of mRNA and DNA in formalin-fixed, paraffin-embedded tissues.

DNA↗

Characterization of a cloned pR72H probe for Vibrio parahaemolyticus detection and development of a nonisotopic colony hybridization assay.

Vibrio parahaemolyticus is a halophilic bacterium often found in shellfish and is an important causative agent of food poisoning in Taiwan. A rapid and efficient detection method is required to identify this foodborne pathogen. A 0.76-Kb HindIII DNA fragment was cloned from the chromosomal DNA of V. parahaemolyticus strain no. 93, designated as pR72H fragment, was used as a polynucleotide probe. It was labeled with digoxigenin-11-dUTP (DIG) by the random primer-labeling method. The sensitivity and specificity of the digoxigenin-labeled 0.76-Kb DNA probe was determined by colony hybridization assay. Under stringent hybridization conditions, 122 of 124 isolates of V. parahaemolyticus showed positive hybridization reaction with DIG-0.76-Kb DNA probe; the negative strains were attributed to slow growth. The DIG-0.76-Kb probe did not hybridize with 86 isolates of other vibrios and a number of other enterics as well as nonenteric microorganisms. The sensitivity and specificity of this DIG probe are 98% and 100%, respectively. This nonisotopic colony hybridization assay can be very useful for routine monitoring of V. parahaemolyticus in the food industry, environmental analysis and clinical laboratories.

Chromosomes, Bacterial↗

Measurement of HIV-1 reverse transcriptase by a nonradioactive assay system.

Reverse transcriptase activity was measured by incorporation of dUMP linked to digoxigenin into a suitable template-primer molecule. Incorporation was monitored by using peroxidase-conjugated Fab fragments directed against digoxigenin. The standard assay measuring incorporation of radiolabeled nucleotides into acid-precipitable material was compared with this new immunochemical assay with regard to its usefulness for testing inhibitors of reverse transcriptase.

Digoxigenin↗

Analysis of immunoglobulin VH gene repertoire by an anchored PCR-ELISA.

We developed a novel technique to analyze the relative concentration of the expressed immunoglobulin (Ig) VH genes using an enzyme-linked immunosorbent assay (ELISA). Expressed Ig cDNA are amplified via anchored PCR and then subjected to a "nested PCR" reaction that attaches biotin to the 5' end of the antisense strand. This allows us to tether the antisense strand of PCR products onto avidin-coated ELISA plates. Digoxigenin-labeled oligonucleotides specific for the leader sequence sense strand of each major Ig VH gene subgroup are used to probe the plate-tethered, alkaline-denatured, and single-stranded antisense cDNA. Bound probes then are detected with alkaline-phosphatase-conjugated anti-digoxigenin antibodies. Using this method, we assessed the distribution of Ig VH genes used by IgM-expressing blood B cells of normal adults. We found the predominant subgroup is VH3, representing approximately half (range 41-59%) of the expressed IgM repertoire. The next largest subgroups used are VH4 (19-23%), VH1 (15-17%), and VH5 (7-11%). The VH2, VH6, and VH7 subgroups each constitute less than 3% of the expressed IgM repertoire. These results agree with those obtained using traditional and more laborious methods that analyze the distribution of Ig clones in cDNA libraries. In addition, we find that this method compares favorably in sensitivity and specificity to more conventional techniques for assessing the clonality of blood or tissue B-cell populations. This rapid and nonradioactive method should have utility for assessing the Ig repertoires expressed by normal, autoimmune, or neoplastic B-cell populations.

Adult↗

Non-radioactive direct sequencing of PCR products amplified from neuropathological specimens.

We have developed a simple, rapid and relatively inexpensive protocol for direct non-isotopic cycle sequencing of DNA amplified using the polymerase chain reaction (PCR). PCR is performed on routine and archival neuropathological tissue. For sequencing, a 5'-digoxigenin end-labelled oligonucleotide primer is annealed and extended during thermal cycling, sequencing reactions are separated on a standard sequencing gel and the gel is contact-blotted to a nylon membrane. Sequenced DNA is visualized using immunological detection of digoxigenin.

Base Sequence↗

In situ reverse transcription-PCR for monitoring gene expression in individual Methanosarcina mazei S-6 cells.

An in situ reverse transcription-PCR protocol for detecting specific mRNA in Methanosarcina mazei S-6 is described. This method allowed us to detect heat shock-induced increases in the intracellular levels of the transcript of the universal stress gene dnaK. The cell walls of paraformaldehyde-fixed cells were permeabilized by a thermal cycling procedure or by lysozyme treatment, and the cellular DNA was removed with DNase. The cells were subjected to a seminested reverse transcription-PCR protocol in which a digoxigenin-labeled primer was used. Detection of the reporter molecule was based on the 2-hydroxy-3-naphtoic acid-2'-phenylanilide phosphate-Fast Red detection system and binding of anti-digoxigenin-alkaline phosphatase conjugate. Fluorescence in permeabilized cells increased after a heat shock compared to fluorescence in non-heat-shocked cells, and the increase corresponded to an increase in the level of the dnaK transcript.

Cell Wall↗

Chemiluminescence dot blot hybridization assay for detection of B19 parvovirus DNA in human sera.

A chemiluminescence dot blot hybridization assay was used for the detection of B19 parvovirus DNA in human sera by using digoxigenin-labeled probes. The probes were revealed immunoenzymatically by use of anti-digoxigenin Fab fragments conjugated with alkaline phosphatase. The chemiluminescence signal was obtained by reacting the labeled probe-target complex with an enzyme-triggerable dioxetane substrate. The emitted photons were detected with instant photographic films. In the search for B19 parvovirus DNA, 2,808 serum samples were analyzed.

DNA Probes↗