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Nonisotopic detection of microRNA using digoxigenin labeled RNA probes.

MicroRNAs (miRNAs) are an important class of endogenously derived, small approximately 22 nucleotide noncoding regulatory RNAs that have recently become implicated in development, cell regulation and cancers of various tissues. Here we report a nonisotopic Northern analysis method for miRNA detection using 3'-digoxigenin (DIG)-labeled RNA oligo probes. Northern blot analysis was performed using miRNA or total RNA fractions extracted from human leukemic cell lines, and blots were hybridized with either 32P- or DIG-labeled RNA probe for miR-181, miR-155 or miR-16. A labeled probe for U6 small nuclear RNA served as an internal control. The use of DIG-labeled RNA probes was equally sensitive compared to 32P-labeled probes in detecting miRNA quantities as low as 50 ng. The ability to use nonisotopic methods and yet obtain sensitive and reliable results offers an advantage to investigators who prefer to avoid isotopes.

Blotting, Northern↗

Detection of thioredoxin in human serum and biological samples using a sensitive sandwich ELISA with digoxigenin-labeled antibody.

Thioredoxin is a low molecular weight, redox active protein important in cellular proliferation, signal transduction and antioxidant function. Thioredoxin is secreted by normal as well as neoplastic cells and is potentially involved in paracrine cell communication as suggested by its co-cytokine activity. Thus, the thioredoxin level in biological fluids, cells and tissue homogenates could be an important indicator of physiological or pathophysiological conditions. Hence, an accurate and sensitive measurement is of paramount importance in studies involving thioredoxin. We present here an ultrasensitive enzyme linked immuno-absorbent assay (ELISA) for human thioredoxin using digoxigenin-labelled goat polyclonal anti-human thioredoxin. The assay could detect a minimum level of 15 pg/ml thioredoxin in human serum, cell culture media, and in cell and tissue samples. The assay was optimized for concentration of both antibodies, blocking agent, plates, incubation time and reaction volumes. Excellent linearity and reproducibility were obtained. The assay was applied to different baboon tissues and human serum samples. The intrassay coefficient of variation (CV) was between 6.0 to 14 and the interassay CV was from 1.6 to 11.1. Excellent parallelism of standards with serum samples, tissue homogenates or cell lysates was obtained. More than 90% recovery of human thioredoxin was observed in 10% human serum. The assay is easy to use, rapid, reproducible, but above all it is a quantitative, specific and sensitive way to measure thioredoxin in a variety of biological specimens.

Animals↗

Comparison of detection techniques for cytokine reverse transcriptase polymerase chain reaction; digoxigenin-labeled polymerase chain reaction permits sensitive detection of cytokine mRNA in rat heart allografts.

The polymerase chain reaction (PCR) is a sensitive method for the analysis of cytokine mRNA expression. The amount of specific mRNA in tissues involved in an inflammatory immune response can be low and therefore requires highly sensitive detection of the PCR products. In our study we have compared different detection techniques in order to replace the commonly used detection by means of radiolabeled probes. Besides the detection of DNA in agarose gels by ethidium bromide (EB), we used detection by digoxigenin (DIG)-labeled probes, as well as the direct incorporation of DIG-labeled nucleotides in the PCR, in comparison to detection by means of 32P-labeled probes. In vitro activated rat lymph node cells, lymph node tissue, and acutely or chronically rejected rat heart allografts were examined for expression of mRNA of the cytokines IL-2 and IFNgamma. The directly DIG-labeled PCR appeared to be the best alternative for detection of PCR products by means of radiolabeled probes. While IL-2 mRNA was not detected by means of EB and IFNgamma mRNA was only detected at the highest PCR cycle numbers in acutely and chronically rejected rat heart allografts, both cytokine mRNA's were readily detected by directly DIG-labeled PCR.

Animals↗

Synthesis and biological activity of some 3-amino compounds related to digoxigenin.

3 alpha-Amino 1a and 3 beta-amino 1b analogues of digoxigenin 14 and their 12 beta-acetate derivatives 2a and 2b were prepared and tested for inotropic activity in the isolated guinea-pig atrial preparation. The 3 alpha-amino compounds were inactive whereas the 3 beta-amino compounds showed comparable activity to their 3 beta-hydroxy counterparts. The replacement of the 17 beta-butenolide ring by other ring systems was investigated. Compounds with a 3'-furyl ring, 9b and 16 were found to possess appreciable activity. A compound with a 4'-pyridazinyl ring 13b exhibited weak activity, whereas the isomeric butenolide compound 11b proved inactive. N-monomethylation of the amine 2b reduced activity and N-dimethylation abolished activity. Acetylation of the 12 beta-hydroxyl function gave less active compounds.

Animals↗

Quantitation of cucurbit yellow stunting disorder virus in Bemisia tabaci (Genn.) using digoxigenin-labelled hybridisation probes.

A cost-efficient hybridisation assay was developed to estimate the amount of cucurbit yellow stunting disorder virus (CYSDV) in Bemisia tabaci (Gennadius) whiteflies infesting protected cucumber crops. cDNA from the coat protein (cp) gene and the hsp70 homologue protein gene from CYSDV were obtained by reverse transcriptase-PCR from viruliferous whiteflies and cloned into plasmids. Digoxigenin (DIG)-labelled cDNA probes reacted with extracts from these whiteflies applied on nylon membranes. Precision and linear ranges were established in a hybridisation analysis using known concentrations of unlabelled homologue cDNA. Extracts from non-viruliferous B. tabaci showed a concentration-dependent effect on the assay with cp-specific probes but not with hsp70-specific probes. The hsp70 probe was used to evaluate natural B. tabaci populations in commercial cucumber crops, and the estimated amounts of CYSDV per whitefly were found ranging from 5.6 fg to approximately 2.5 pg of corresponding hsp70-cDNA.

Animals↗

Detection of rabbit haemorrhagic disease virus (RHDV) by in situ hybridisation with a digoxigenin labelled RNA probe.

An in-situ hybridisation (ISH) technique for the detection of rabbit haemorrhagic disease virus (RHDV) was developed. Thirteen seronegative adult rabbits were infected oro-nasally using the BS89 RHDV strain. Liver and spleen samples were collected from 4 h post infection (p.i.) and repeated every 4 h till 44 h p.i. Each sample was tested immunohistochemically, by sandwich ELISA and by ISH. A 2.482-kb RNA probe, matching the genomic fragment coding for the VP60 structural protein of RHDV, was arranged. Two RNA probes (sense and antisense) were transcribed in vitro and UTP-digoxigenin-labelled. The antisense probe clearly detected positivity in the cytoplasm of the hepatocytes at 8 h p.i. Labelled hepatocytes were scattered throughout the sections until 24 h p.i. followed by a more diffuse perilobular positive reaction. A much weaker signal of similar distribution was detected up to 24 h p.i. using the sense RNA probe. All spleen samples tested negative for both probes. Liver samples were positive at 32 h p.i. using both ELISA and the immunoperoxidase test. Spleen samples were positive using only the ELISA at 32 h p.i. This study showed that RHDV replication occurred almost immediately after inoculation and that the liver appears to be the main site of replication.

Animals↗

Detection of field isolates of human and animal group C rotavirus by reverse transcription-polymerase chain reaction and digoxigenin-labeled oligonucleotide probes.

Rotaviruses (RV) are important etiological agents of acute gastroenteritis in infants and young children, as well as the young of a variety of animals worldwide. These viruses belong to Reoviridae family and contain a genome of 11 segments of double-stranded RNA (dsRNA). Two major proteins, VP4 and VP7, encoded by genome segments 4 and 7, 8 or 9, respectively, evoke a neutralizing antibody response and form the basis for the current classification of group (gp) A rotavirus into P (VP4) and G (VP7) serotypes. Although much recent progress has been made on the molecular biology of gp C RV, routine methods to detect and discriminate human, porcine, and bovine strains are not available widely. In this study, a multiplex reverse transcriptase-polymerase chain reaction (RT-PCR) and digoxigenin-labeled (dig) oligonucleotide probes using chemiluminescence has been developed to detect and discriminate VP7 genes from culture-adapted and field isolates of human, porcine and bovine gp C RV. The multiplex RT-PCR and dig-probes were specific for the VP7 genes of human, porcine and bovine gp C RV and allowed detection and characterization of single and mixed infections of porcine gp C RV with porcine gp A or gp B rotaviruses. Detection rates for gp C RV were more than 50% when compared with polyacrylamide gel electrophoresis. These new diagnostic assays may help determine the epidemiological importance of these viruses in human and animal infections.

Animals↗

A new procedure to differentiate citrus tristeza virus isolates by hybridisation with digoxigenin-labelled cDNA probes.

A non-isotopic hybridisation procedure was developed to differentiate isolates of citrus tristeza virus (CTV) using digoxigenin (DIG)-labelled cDNA probes and different kinds of target RNA. Hybridisation of DIG-probes with purified double-stranded RNA (dsRNA) or concentrated total RNA extracts spotted on nylon membranes allowed detection of CTV nucleic acid equivalent to as little as 0.1-1 mg infected tissue, when the reaction was developed with a chemiluminiscent substrate. This sensitivity was similar to or slightly better than that obtained by hybridisation with a 32P-labelled probe. CTV was also detectable by hybridisation of DIG-probes with tissue prints from freshly cut young citrus shoots. Hybridisation of tissue prints with DIG-probes under stringent conditions (60 degrees C and 50% formamide) could differentiate CTV isolates in citrus, whether grown in the greenhouse or in the field. This rapid and sensitive procedure can easily be applied to many samples, even under field conditions, and opens the way to monitoring spatio-temporal movement of specific CTV strains (or groups of strains) in epidemiological studies.

Antibodies, Monoclonal↗

Aromatic residues mediate the pressure-induced association of digoxigenin and antibody 26-10.

We have previously found that the complex between fluorescently labeled digoxigenin and the monoclonal antibody 26-10 forms with a decrease in volume of approximately 30 ml/mol, leading to increased association of these species under applied hydrostatic pressure. In the present study, we have utilized a panel of mutant antibodies and Fab fragments, previously characterized for their importance in the binding affinity of digoxin:26-10, to probe the molecular basis of pressure sensitivity in this complex, as measured by fluorescence polarization spectroscopy. Several mutations that result in marked decreases in affinity exerted little or no significant effect on the association volume. Mutation at any of several key aromatic residues of the 26-10 Fab heavy chain led to a decrease in the pressure-induced association, and two mutants with Trp-->Arg mutations at heavy chain residue 100 exhibited pressure-induced dissociation. The effect of charged groups was found to depend on their proximity to contacting aromatic groups. The ability to understand and control the pressure sensitivity of antigen-antibody complexes has numerous potential applications in immunoseparations and immunosensors.

Amino Acids↗

Non-isotopic in situ hybridization with digoxigenin and alkaline phosphatase labelled oligodeoxynucleotide probes. Applications in pituitary gland.

We report the application of digoxigenin labelled oligonucleotide probes for the detection of hormonal messenger RNAs (mRNAs) in human pituitary adenomas. Positive signal for the appropriate mRNA was detected in tumours associated with Cushing's disease, acromegaly and hyperprolactinaemia, where immunoreactivity for adrenocorticotrophin (ACTH) growth hormone and prolactin had also been confirmed. In addition, we report the detection of proopiomelanocortin (POMC) mRNA in the rat pituitary gland using an oligodeoxynucleotide probe directly linked to alkaline phosphatase.

Adenoma↗

Colorimetric detection of lagomorphs' calicivirus genomic sequences by polymerase chain reaction incorporating digoxigenin dUTP.

A method of reverse transcription followed by polymerase chain reaction (RT-PCR) has been implemented for the demonstration of the rabbit haemorrhagic disease virus (RHDV) genome in organ suspensions, leukocytes and excretions of infected rabbits. RT-PCR has been tested with 10 RHDV strains isolated at various geographic sites and times using a pair of primers coming from the gene region coding for the capsid protein VP60. The same primers were effective in the amplification of 4 of 5 European brown hare syndrome (EBHS) virus isolates. Non-radioactive labelling of PCR products with digoxigenin during the amplification and a system of colorimetric assessment of hybridization reactions between a biotin-labelled RHDV capture probe and the chains of labelled amplicons (PCR ELISA) were used for specific analyses of nucleic acid synthesis. The sensitivity of the alternative procedure of analysis of the dig-labelled PCR products with PCR ELISA was two logs10 higher than that of conventional electrophoresis in agarose gel stained with ethidium bromide. The results of the hybridization reactions, carried out under various stringency conditions, have confirmed the presumption that the genomic similarity between the amplified and the probed areas of the capsid protein VP60 gene was not uniform within all the tested caliciviruses. A higher degree of heterogeneity was observed between the isolates of EBHSV and RHDV.

Animals↗

Chemiluminescent analysis of Borrelia burgdorferi penicillin-binding proteins using ampicillin conjugated to digoxigenin.

Knowledge of the penicillin-binding proteins (PBPs) of Borrelia burgdorferi is important for understanding both the targets of beta-lactams used therapeutically for Lyme borreliosis and the complex membrane biology of the distinctive spirochetal pathogen which causes Lyme disease. In this study, the PBPs of a number of B. burgdorferi strains and variants were examined using a rapid and sensitive chemiluminescent assay which employs ampicillin conjugated to digoxigenin (dig-amp). The minimum inhibitory concentration of dig-amp for B. burgdorferi high-passage strain B31 (0.012 micrograms/ml) was essentially no different from that of free ampicillin (0.025 micrograms/ml). Dig-amp bound specifically to B. burgdorferi B31 PBPs with molecular masses of 92, 80, 65, 46, 40, 34, 31, 29, 22, 20 and 13 kDa; the 31 kDa and 34 kDa PBPs were proven to be OspA and OspB, respectively. All of the borrelial PBPs were present in the cytoplasmic membrane fraction of B. burgdorferi, findings consistent with their activities as PBPs but inconsistent with OspA and OspB as surface-exposed outer membrane lipoproteins. Furthermore, among the PBP profiles of other high- and low-passage variants of B. burgdorferi strains Sh-2-82, HB19, and N40, which differed somewhat from one another, OspD (28 kDa) but not OspC (22-25 kDa) also was strongly implicated as a PBP; however, OspC possessed a gel mobility easily misconstrued as that of a 26 kDa PBP often expressed reciprocally with OspB. The ramifications of classifying OspA, OspB, and OspD as PBPs are discussed. While the current inability to genetically manipulate B. burgdorferi hinders determining which of the borrelial PBPs are essential for spirochetal viability (i.e., are the lethal targets of beta-lactams), a priori knowledge of the borrelial PBPs will facilitate the production and purification of recombinant derivatives whose activities can be assessed further in vitro.

Ampicillin↗

Detection of African horse sickness viruses by dot-blot hybridization using a digoxigenin-labelled probe.

In order to develop a non-radioactive dot-blot hybridization assay, for the detection of African-horse sickness virus (AHSV), genome segment 7 from 9 serotypes was amplified by RT-PCR. The resulting PCR products were denatured, immobilized on nylon membranes and then hybridized to a non-radioactive digoxigenin-labelled probe. This probe (265 bp in length) was generated by nested-PCR using genome segment 7 of AHSV, serotype 4 as a template. The dot-blot was visualized by chemiluminescence. Positives were obtained from the PCR products amplified from all 9 AHSV serotypes, but not from any other equine virus or orbivirus isolates. The sensitivity and specificity of this probe, together with the simplicity and rapidity of this technique, suggest that a non-radioactive dot blot assay may be useful as a method for the routine and rapid diagnosis of viral infections.

Base Sequence↗

Effect of developmental lead exposure on the expression of specific NMDA receptor subunit mRNAs in the hippocampus of neonatal rats by digoxigenin-labeled in situ hybridization histochemistry.

The N-methyl-D-aspartate (NMDA) receptor has an important role in learning and memory. In this study, the effects of chronic Pb exposure on NMDA receptor subunit mRNAs expression in the developing rat hippocampus were examined by digoxigenin (DIG)-labeled in situ hybridization. In Pb-exposed rats, hippocampal NR1-2a mRNA levels were significantly increased in CA1, CA4 and DG subfields at 15 days of age and CA4 and DG subfields at 20 days of age. The lead (Pb) exposure resulted in a significant increase of NR2D mRNA levels in CA1, CA2, CA4 and DG hippocampal subfields at 20 days of age. Hippocampal NR2A mRNA levels were significantly decreased in CA1, CA2, CA3 and DG subfields from 15-day-old Pb-exposed rats and CA1, CA3 and DG subfields from 20-day-old Pb-exposed rats. Hippocampal NR3A mRNA levels were also significantly decreased in CA1, CA4 and DG subfields at 15 days of age and CA1 and DG subfields at 20 days of age in Pb-exposed rats. The Pb-induced subunit specific changes in hippocampal NMDA receptor subunit mRNA expression may lead to abnormality of natural NMDA stoichiometry and interfere with the physiological function of the NMDA receptor in the development of defined neuronal connections.

Age Factors↗

Analysis of brain mRNA by reverse transcription-polymerase chain reaction and hybridization with digoxigenin-labeled DNA probe.

The interleukin-1 family of polypeptides (IL-1 alpha, IL-1 beta and IL-1 receptor antagonist (RA)) induces various centrally mediated host defense responses to infectious pathogens. Considerable interest has focussed on IL-1 as a mediator in disease and in the production of systemic acute phase responses. We have recently studied the effects of a peripheral stimulation by intraperitoneal (i.p.) administration of lipopolysaccharide (LPS) on the mRNAs expressions of IL-1 (alpha, beta, RA) and their receptors (IL-1 receptor type I and type II (IL-1R1, IL-1R2)) in the central nervous system (CNS). The levels of these expressions being very low in the CNS, the reverse transcription-polymerase chain reaction (RT-PCR) techniques are required for these studies. RT-PCR is a developed method of identifying mRNAs in very small amount of nucleic acid. We have previously developed a method to choose specific PCR primers. The detection of specific PCR products is extremely important. Since amplifications with these specific PCR primers can be achieved under the same conditions (buffers and temperatures) reliable results can be obtained. Characterization of a PCR product requires the use of a specific DNA probe that hybridizes to the region of interest. In addition to providing specificity of detection, the use of labeled DNA probes provides increased sensitivity over ethidium bromide staining. We have previously described a method of synthesis of non-radioactive probe labeled with digoxigenin by nested PCR. Moreover the major advantage to the use of non-radioactive label is that it does not have a short half-life and can last for weeks or even months. A quantification of the PCR products can be obtained using a method based on the analysis of photographic negatives of agarose gels.

Animals↗

Production of digoxigenin-labelled RNA probes and the detection of cytokine mRNA in rat spleen and brain by in situ hybridization.

Non-radioactive in situ hybridization is a sensitive method for determining the site of production for secretory molecules such as cytokines. We report here on the central and peripheral induction of proinflammatory cytokines by endotoxin, and outline procedures for the generation and application of rat-specific digoxigenin (Dig)-labelled RNA probes for the localization of mRNA by in situ hybridization. Rats were injected either intravenously (i.v.) or intracerebroventricularly (i.c.v.) with vehicle or lipopolysaccharide (LPS) and sacrificed at various time intervals post-injection. Rats were then perfused with 4% paraformaldehyde and the spleens and brains were removed and cryoprotected in 30% sucrose. Dig-labelled, rat-specific, antisense and sense RNA probes were generated by in vitro transcription from PCR-derived templates. Positive staining with all the antisense probes was cytoplasmic, whereas the sense probes showed no staining. Numerous tumor necrosis factor alpha (TNF-alpha) and interleukin-1 beta (IL-1beta) mRNA positive cells were observed in the marginal zone and in the red pulp of the spleen after iv LPS injections, whereas sections from saline-treated animals showed minimal cytokine mRNA expression. Cells positive for TNF-alpha and IL-1beta mRNA were detectable in the brain after i.c.v. injections of LPS, but not after icv injection of vehicle. An antisense probe for c-fos was utilized in these studies as a positive control for our procedure due to its anatomically specific expression in the rat brain after LPS. In conclusion we have demonstrated that in situ hybridization with Dig-labelled RNA probes is an efficient, sensitive and reliable tool to localize cytokine mRNA production in rat tissue.

Actins↗

Altered subcellular localization patterns of ferritin and beta-actin mRNAs in muscle cultures, resulting from incomplete penetration of digoxigenin-labelled riboprobes.

Protocols for in situ hybridization (ISH) of cultured cells often include storage in alcohol at -20 degrees C between fixation of the cultures and the ISH procedure. In experiments aimed at localizing ferritin mRNA in C2 muscle cultures by ISH with digoxigenin-labelled riboprobes, we have noticed that omission of the ethanol storage dramatically changed the pattern of mRNA localization. In cultures stored in 50%, 70%, or 90% ethanol for at least 15 min, ferritin signal was stronger on myotubes than myoblasts but was uniformly distributed over both. In untreated cultures, the signal was patchy, concentrated on the extremities of the elongated myoblasts and very sparse in myotubes. Similar results were obtained with a probe to beta-actin used as a control, except that signal was higher in myoblasts in all conditions. When the probes were reduced in size to approximately 100 bases from 561 for ferritin and 1150 for actin, the pattern became uniform, regardless of prehybridization treatment. The patchy pattern disappeared when cells were treated with RNase A following hybridization, suggesting that it is non-specific, despite its absence in cultures hybridized with a sense probe. We conclude that incomplete access of RNA probes can result not only in a reduced ISH signal but also in artefactual patterns of mRNA localization.

Actins↗