Interphase cytogenetics using biotin and digoxigenin labelled probes II: Simultaneous differential detection of human and papilloma virus nucleic acids in individual nuclei

Determination of gene expression patterns by in situ hybridization in sections

In recent years, in situ RNA hybridization technique has found a widespread application in developmental biology. This method has frequently been used to determine gene expression patterns, which is a first step toward understanding of a gene function. Here, we provide a reliable and sensitive method for in situ RNA hybridization on frozen sections of mouse embryo using digoxigenin-labeled RNA probes. This technique can be used to study gene expression patterns at all stages of odontogenesis.

Detection of two different mRNAs in a single section by dual in situ hybridization: a comparison between colorimetric and fluorescent detection

We have compared the performance of two methods designed to simultaneously detect two different mRNAs within a single brain section by dual ISH. Specific mRNA riboprobes labeled with biotin and digoxigenin were simultaneously hybridized and visualized using either brightfield or fluorescence microscopy. For brightfield visualization, the biotin-labeled riboprobe was detected with a peroxidase chromogen, whereas, an alkaline phosphatase substrate was used for the detection of the digoxigenin-labeled riboprobe. Dual fluorescent ISH involved the detection of the biotin-labeled riboprobe with an Alexa((R))488-conjugated streptavidin followed by the visualization of the digoxigenin-labeled riboprobe with the red fluorescent substrate HNPP. The dual ISH protocols presented here offer sensitive methods to detect the expression of two mRNAs of interest, with both colorimetric and fluorescent ISH each having its strengths and limitations. For example, dual colorimetric ISH has proven to be particularly useful to study the distribution of two mRNAs in different brain nuclei, whereas, dual fluorescent ISH has provided better results when studying the co-localization of two different mRNAs in single neurons. The comprehensive step-by-step procedure is presented, together with a troubleshooting section in which the advantages and limitations of these procedures are reviewed in depth. Moreover, alternative protocols for dual ISH were also compared to those presented here.

Does human papilloma virus have a role in squamous cell carcinoma of the colon and upper rectum?

AIM

To determine if Human Papilloma Virus (HPV) has a role in the aetiology of adenosquamous and squamous cell carcinoma of the colon and upper rectum, and to describe the clinical features seen in our patients with this condition.

METHODS

Patients were identified with squamous cell carcinoma (SCC), adenosquamous carcinoma (Ad-SCC), or adenocarcinoma with squamous metaplasia (AA) of the colon and upper rectum over the 10 years from 1/1/1990 to 31/12/1999. Patients were identified from a prospective pathology database. All tumours were at least 5cm above the dentate line. Pathology blocks were stained using the Peroxidase labelled Streptavidin technique using mouse monoclonal antibody NCL-HPV-4C4, which identifies HPV 6, 11, 16 and 18. Age, gender and site matched controls (colorectal adenocarcinomas) were also stained. The clinical presentation and management was reviewed from the case notes.

RESULTS

Twenty patients were identified from a pathological database of 2351 colorectal cancers (0.85% of colorectal cancers). 0/20 of the study patients (SCC, Ad-SCC, AA) or adenocarcinoma controls stained positively for HPV 6, 11, 16, 18. The clinical presentation was similar to patients presenting with adenocarcinomas.

CONCLUSIONS

The peroxidase labelled streptavidin technique is an immunohistochemical technique with high specificity but lower sensitivity. There was no apparent association between HPV 6, 11, 16, 18 and squamous cell and adenosquamous carcinoma of the colon and rectum using this technique. Clinical features are similar in squamous and adenosquamous colorectal carcinomas to colorectal adenocarcinomas.

Endocrine tumors of the cervix: morphologic assessment, expression of human papillomavirus, and evaluation for loss of heterozygosity on 1p,3p, 11q, and 17p

BACKGROUND

Cervical endocrine tumors are rare lesions, with a varied diagnostic nomenclature. A recent consensus meeting proposed a standardized terminology. This study evaluated: 1) applicability of histopathologic guidelines; 2) evidence of loss of heterozygosity (LOH) at selected sites; and 3) the presence of human papillomavirus (HPV) detected by nonisotopic in situ hybridization (ISH).

METHODS

Thirty-eight cases (patient age range, 19-88 years; mean, 48 years) were retrieved. Outcome data were available for 32 patients. Classification was based on architectural and cytologic features. Tissue was available from 15 cases for LOH analysis with D3S1234(3p14), D3S1289(3p21), THRB(3p24), TP53(17p13), D1S468(1p36), and INT-2(11q13). In ten cases, tissue was analyzed by nonisotopic ISH with HPV probes for types 6/11, 16/18, and 31/33.

RESULTS

Tumors were divided into four groups: small cell carcinoma (SCC) (n=25); large cell neuroendocrine carcinoma (LCNC) (n=5); SCC with focal LCNC differentiation (n=3), and carcinoid tumor (n=5). Tumors defined as exclusively or predominantly SCC had a particularly poor prognosis, with 20 patients dead of disease (<6 years after diagnosis) and 6 alive with disease (after <3 years of follow-up). LOH at various 3p loci (3p14, 3p21, and 3p24) was observed in eight cases. One patient demonstrated LOH on 17p(TP53). Eight of ten cases assessed by ISH showed nuclear staining using a combined HPV-16/18 probe.

CONCLUSIONS

Cervical endocrine tumors are highly aggressive and can be subdivided into definable categories. LOH at 3p loci is a frequent finding, as is nuclear staining with a combined HPV-16/18 probe. LOH at 17p(TP53 locus) appears to be relatively uncommon, suggesting that p53 mutations may not be developmentally significant.

Cytochemical detection systems for in situ hybridization, and the combination with immunocytochemistry, 'who is still afraid of red, green and blue?'

An overview is given of the different non-radioactive cytochemical detection methodologies that are currently utilized to localize nucleic acid sequences in chromosomes, cells and tissue sections. Dependent on the reporter molecule (fluorochrome, enzyme or hapten) that is used to modify the appropriate nucleic acid probe, and the sensitivity that is required, the in situ hybridized sequences can be detected either directly after hybridization or indirectly, using cytochemical detection and amplification layers. These may then contain antibody and/or avidin molecules conjugated to fluorochromes, enzymes or colloidial gold particles. Since the choice of a suitable probe-labelling method in combination with a fluorescence, enzyme cytochemical or immunogold-silver detection procedure is often determined by the user's own practical experience and applications, the different detection methodologies are compared with each other in detail with respect to sensitivity, resolution, applicability for multiple probe detection, and signal evaluation. Furthermore, procedures are reviewed for the combination of in situ hybridization with immunocytochemical detection of proteins and/or incorporated bromodeoxyuridine, which allow the simultaneous visualization of genomic phenotypic and/or cell cycle parameters in the same sample. Possible improvements with respect to sensitivity, specificity and multiplicity of the detection methods, which may be interesting for one's own experimental design, are finally being discussed.

Correlation of numerical chromosome 11 and 17 imbalance with metastasis of primary breast cancer to lymph nodes

Abnormalities of chromosomes 11 and 17 have been widely reported in invasive carcinoma of the breast. Interphase cytogenetics using pericentromeric repeat probes allows the evaluation of numerical chromosomal aberrations in tumour cell populations. We have developed a method for interphase cytogenetics on fine needle aspirates taken from breast tumours and have applied it to the analysis of chromosomes 11 and 17 in 49 cases of invasive adenocarcinoma. Frequency distributions of signal number were generated for each case and no correlation was found between modal signal number and tumour size at presentation, nodal status or tumour differentiation. In 14 cases, two copies of each of chromosomes 11 and 17 were present, and in 14, the number of chromosomes 11 and 17 were equal but abnormal. In 14 cases, the chromosome 11 number was greater than chromosome 17 and in 7 cases, the chromosome 17 number was greater than chromosome 11. Chromosome inequality correlated with the presence of lymph node metastases or disseminated disease at presentation and the absence of in situ carcinoma. There was no relationship with the presence of vascular invasion. These data suggest that numerical chromosome 11 and 17 imbalance may indicate the ability of breast cancers to metastasize rather than invade vessels. The pattern of numerical chromosome abnormality described may define a subgroup of tumours with a greater tendency for metastasis.

Interphase cytogenetics: analysis of numerical chromosome aberrations in isolated cells

Probes which recognize pericentromeric repetitive sequences can be used to determine numerical chromosome aberrations in interphase nuclei. Under appropriate stringency conditions, these probes decorate only the chromosome from which they were derived. It has been assumed that abnormalities of signal number in interphase nuclei reflect aneuploidy rather than proliferation, but this has not been clearly demonstrated. In this paper, three alphoid probes (D3Z1, D11Z1, and DXZ1) were localized to the appropriate chromosomes and the factors governing the production of reproducible signal distributions from three aneuploid cervical carcinoma-derived epithelial cell lines were investigated. Abnormalities of signal number represent numerical chromosome aberrations rather than changes associated with proliferation. Using four simple rules of interpretation, reproducible results can be obtained with minimal technical variation and selection bias. These results demonstrate that pericentromeric repetitive probes can be used reproducibly to determine numerical chromosome aberrations independent of cell proliferation in interphase nuclei, a necessary prerequisite for the application of this approach to the analysis of human tumours.

Discrimination of closely homologous human genomic and viral sequences in cells and tissues: further characterization of Tmt

The experimentally derived parameter Tmt (tissue Tm) was defined previously to describe the end-point used for evaluation of the stringency of non-isotopic in situ hybridization and was found to differ from the theoretical melting temperature (Tm) for several HPV types. In this paper, the reasons for this discrepancy were investigated by performing a series of experiments with a variety of probes for both human genomic and integrated viral sequences in isolated and cultured normal and abnormal cells in addition to paraffin-embedded material. Tmt was shown to be dependent on several parameters of probe and target, and on the sensitivity of the detection system used but was not affected by aldehyde fixation or paraffin wax embedding under optimal conditions of nucleic acid unmasking. These data support the hypothesis that differences between Tmt and Tm may be due to the use of a different end-point for in situ hybridization analysis rather than biochemical alteration of DNA-DNA interactions in intact cells. Appropriate stringency conditions should therefore be determined by experiment rather than calculated theoretically for gene evaluation in cells and tissues.

Expression of the type I collagen gene in rat periodontal ligament during tooth movement as revealed by in situ hybridization

The in situ hybridization technique used digoxigenin-labelled oligodeoxynucleotide. In untreated molars, cells expressing a positive signal for type I collagen mRNA were distributed uniformly in the periodontal ligament space. After experimental tooth movement, the density of cells expressing a positive signal appeared to be much greater in the tension side than the pressure side. In both sides the distribution of the positively hybridizing cells was uniform along the principal fibres of the ligament. This characteristic distribution appeared at 12 h after the initiation of tooth movement, reached a maximum at 1-3 days, and persisted for about 14 days during the treatment. These results indicate that the remodelling of collagen fibres in periodontal ligament occurs in an orderly manner throughout the principal fibres, mainly on the tension side, and that the recovery of gene expression for type I collagen occurs within the first 14 days in response to experimental tooth movement.

Regulation of tumor necrosis factor-alpha-mRNA synthesis and distribution of tumor necrosis factor-alpha-mRNA synthesizing cells in rat liver during experimental endotoxemia

Stimulated liver macrophages (Kupffer cells) are known to release a variety of inflammation-related substances, e.g. cytokines, prostanoids, and reactive oxygen intermediates. For instance, exposure of Kupffer cells in vitro to lipopolysaccharide (endotoxin) leads to a strongly enhanced synthesis of the mRNA for tumor necrosis factor-alpha, the release of the mature protein into culture media. These events are influenced by prostanoids and corticoid hormones. Kupffer cells are thought to be the only source of tumor necrosis factor-alpha within the hepatic sinusoid, but neither this cell specificity nor the regulatory influence of glucocorticoids or prostanoids has been confirmed in the intact organ. Using non-radioactive in situ hybridization, it was possible to obtain specific signals for tumor necrosis factor-alpha-mRNA in individual Kupffer cells uniformly distributed (as compared to Kupffer cells detected by immunohistochemistry) throughout the liver. Kupffer cells were the only cells in the hepatic sinusoids of lipopolysaccharide-perfused livers to express mRNA for tumor necrosis factor-alpha. Simultaneous addition of endotoxin plus dexamethasone and endotoxin and prostaglandin E2 completely suppressed the synthesis of this mRNA. Unexpectedly, the presence of mRNA for tumor necrosis factor-alpha was also detected in the intrahepatic bile duct epithelium of lipopolysaccharide-perfused livers. It is known that biologically active endotoxin is secreted via the bile ducts. These results seem to indicate that bile duct epithelium responds to inflammatory agents with synthesis of tumor necrosis factor-alpha-mRNA. One must also consider new functional aspects of bile duct epithelium in chronic inflammatory diseases, e.g. primary biliary cirrhosis, chronic sclerosing cholangitis or graft-versus-host disease.

A polymerase chain reaction-sequence-specific oligonucleotide procedure for HLA class II typing using biotin- and digoxigenin-labeled probes simultaneously in hybridization

To simplify PCR-SSO HLA-DRB generic typing, we labeled eight of 15 oligonucleotide probes with DIG and the others with biotin, and hybridized each dot blot with both a biotin-labeled probe and a DIG-labeled probe simultaneously. We chose oligonucleotide pairs which require the same hybridization and stringent washing conditions and do not compete with each other during hybridization. After incubation with a mixture of anti-DIG Fab fragment-alkaline phosphatase and streptavidin-peroxidase conjugates, specific binding of the DIG-labeled probe was revealed by a chemiluminescent substrate (CSPD) and specific binding of the biotin-labeled probe was subsequently visualized by a chromogenic substrate (TMB). The sensitivity of both probes was similar and gave comparable hybridization signals. Using this simplified procedure, the number of hybridizations or dot blots can be reduced to half the usual amount and the labor involved in PCR-SSO typing significantly reduced.

Y chromosome loss in esophageal carcinoma: an in situ hybridization study

Carcinoma of the esophagus shows a strong male predominance and other epidemiologic differences from cancers arising at other sites. In this study, the prevalence of Y chromosome loss in 29 carcinomas of the esophagus and 53 carcinomas arising elsewhere in the aerodigestive tract was assessed by in situ hybridization of formalin-fixed paraffin-embedded tissue sections. Absence of the Y chromosome was defined as (1) negative staining for Y in neoplastic cells with positive staining for Y in immediately adjacent nonneoplastic epithelial and stromal cells, (2) positive staining of neoplastic cells with control probes for chromosomes X and 17, and (3) similar results at different stringencies and levels of protein digestion. According to these criteria, absence of the Y chromosome was observed in 13 of 14 (93%) adenocarcinomas of the esophagus, 8 of 13 (62%) squamous cell carcinomas of the esophagus, and 5 of 53 (9%) carcinomas arising in other sites. For the neoplasms examined, Y chromosome deletion was strongly and selectively associated with carcinomas, particularly adenocarcinomas, of the esophagus (P < .0001). These findings suggest that Y chromosome loss may be pathogenetically significant in these neoplasms.

The discrimination of high-risk HPV types by in situ hybridization and the polymerase chain reaction

The parameter Tmt has been defined by non-isotopic in situ hybridization and describes the tissue melting temperature (Tmt) of human papillomavirus (HPV) DNA sequences. In this study, multiple in situ hybridization signals for HPV types 16, 31 and 33 in individual archival biopsies hybridized with genomic probes are shown by polymerase chain reactions to be due to cross-hybridization of probe sequences to a single tissue target. Tmt is independent of viral type but depends on the homology between probe and target when using nick-translated whole genomic probes. The difference between Tm and Tmt is not due to the presence of viral capsid protein. Multiple HPV signals in archival material should not therefore be interpreted as indicative of multiple HPV infection unless adequate stringency conditions have been employed or they are present in morphologically distinct areas of the biopsy. Furthermore, extrapolation of calculated DNA homologies to non-isotopic in situ hybridization analysis may not be appropriate. A hybridization signal does not imply probe and target identity: this has implications for HPV typing in clinical material.

In situ hybridization of immunoglobulin light chain mRNA on bone marrow trephines using biotinylated probes and the APAAP method

A non-radioactive in situ hybridization method has been established for the detection of mRNA for the constant region of light chain immunoglobulin genes in routinely processed bone marrow trephines. The method utilizes a cocktail of biotinylated synthetic oligonucleotide probes to kappa or lambda mRNA. The method entails dewaxing of the paraffin-embedded sections, proteinase K treatment and overnight hybridization with the biotinylated probe. Detection of probe hybridization was performed by 2 immunocytochemical detection methods, utilizing either streptavidin-alkaline phosphatase or monoclonal anti-biotin followed by the alkaline phosphatase: anti-alkaline phosphatase (APAAP) labelling system. The new fuchsin/naphthol phosphate substrate yielded the strongest signal with specific localization of the hybridization signal to positive cells. Morphological preservation was excellent enabling both polyclonal and monoclonal plasma cells to be detected in bone marrow trephines. We conclude that this in situ hybridization method is no more difficult than standard immunohistochemical techniques and can be used in routine diagnostic laboratories.

Interphase cytogenetics on paraffin sections of malignant pleural mesothelioma. A comparison to conventional karyotyping and flow cytometric studies

We performed in situ hybridization (ISH) studies of malignant pleural mesotheliomas to detect numerical aberrations of chromosomes 1 and 7 in interphase nuclei of paraffin sections of 13 cases that had been analyzed previously by conventional karyotyping and flow cytometry. The hybridizations were performed with the biotin-labeled probes recognizing repetitive DNA sequences in the (peri)centromeric regions of chromosomes 1 (1q12) and 7(7cen). Application of histologic sections allowed us to analyze the tumor cells only. Comparison of the karyotype and ISH studies showed that the same chromosome copy numbers were detectable by both methods in 13 (chromosome 1) and in 12 (chromosome 7) cases evaluable by ISH. DNA indexes determined in the paraffin-embedded tumor material corresponded with the ISH findings. As compared with karyotype analysis, ISH showed a larger heterogeneity in chromosome copy numbers. The results can be divided into three groups: 1) Monosomy or disomy of chromosomes 1 and 7 was detected by both methods in two cases; 2) in four cases, disomy of both chromosome 1 and 7 was observed in most of the cells by ISH analysis, and karyotype analysis had shown clear polyploidization in three of these cases; 3) in seven cases, supernumerary copies of chromosomes 1 and/or 7 were present in an evident fraction (27-80%) of the cells analyzed by ISH, and karyotype analysis confirmed the aberrant copy numbers in five of these cases. On the other hand, ISH showed copy numbers not detected by karyotype analysis in six of the seven cases. Thus, by combining karyotype and interphase cytogenetic studies, complementary information about chromosomal aberrations in mesothelioma is obtained.

Hapten-tagged plasma proteins as immunocytochemical probes for the study of vascular permeability

Bovine serum albumin and transferrin were covalently coupled with fluorescein isothiocyanate and digoxigenin, respectively, and intravenously co-injected in equal amounts in mouse. The derivation of the two proteins induces minor alterations of their physicochemical properties as well as of their physiological functions. The two tracers were revealed within vascular and extravascular compartments of diaphragm by quantitative postembedding immunocytochemistry, using antibodies against each of the haptens in conjunction with the protein AG-gold complexes. The influence of different fixatives and embedding protocols on the immunodetectability of the hapten-tagged proteins was assessed. Both resist reasonably well to osmication and embedding in Epon. None of the haptens reacted with the heterologous antibody. At 30 minutes after injection, the tracers were detected in blood plasma, interstitium, and endothelial plasmalemmal vesicles. The presence of both proteins within the interendothelial clefts was inconspicuous. The ratios between the labeling densities found over endothelium, interstitial space, and vascular lumen were similar for both tracers. This suggests that the endothelium of mouse diaphragm capillaries might exhibit comparable permeabilities towards serum albumin and transferrin which are similar in size and charge. The study shows that hapten-tagged polypeptides are close to the corresponding native macromolecules, and represent interesting tools for the morphological study of dynamic processes such as transcytosis.

Nonradioactive in situ hybridization using digoxigenin-labeled oligonucleotides. Applications to musculoskeletal tissues

We have optimized a technique for in situ localization of specific mRNAs using digoxigenin-11-dUTP-labeled oligonucleotide probes. DNA probes were synthesized for type I and type II collagen as well as transforming growth factor-beta 1 and 2 (TGF beta 1 and TGF beta 2). Control experiments, such as competitive inhibition, nonsense sequence hybridization, and RNAse digestion all indicated that the technique was highly sensitive and specific. In sections of growth plate, type II collagen mRNA was predominantly expressed in the lower proliferative and upper hypertrophic zone, whereas chondrocytes in articular cartilage stained equally. These techniques then were applied to sections cut from archival pathology specimens of musculoskeletal tissues. Primitive chondrocytes in a chondrosarcoma expressed type I and type II collagen mRNA, but did not stain with the nonsense probe. Sections from an osteosarcoma, an aneurysmal bone cyst, and a neurofibroma also were investigated. The ability to use chemically synthesized oligonucleotide probes, the high resolution, and the short development times possible with this in situ procedure makes this technique appealing for applied research into the gene expression of normal and pathologic cellular events.

Detection of high risk human papillomavirus in routine cervical smears: strategy for screening

AIM

To develop a methodology for direct detection of high risk human papillomavirus (HPV) infection in routine cervical smears by non-isotopic in situ hybridisation (NISH) which can be compared with cytopathological assessment of the same cells.

METHODS

The methodology was established using cultured cells and routine cervical smears hybridised with digoxigenin labelled probes for HPV, 16, 18, 31, and 33. The technique was applied to the analysis of 53 patients from a sexually transmitted disease clinic.

RESULTS

The optimal sensitivity achieved for single HPV detection in cultured cells was 1-2 copies of HPV 16 per cell and that for detection of a cocktail of HPV types in routine cervical smears was 2.5-12 copies per cell. Of parallel smears taken from patients with a normal Papinacolau-stained smear 33.3% (24) contained a HPV 16, 18, 31, and 33 signal indicating an occult HPV infection. The prevalence of these HPV types was similar in women in whom a cytopathological diagnosis of wart virus infection was made (64.7%, 17) and in patients with mild dyskaryosis (75%, 12).

CONCLUSIONS

The methodology evolved localises HPV sequences directly to epithelial cell nuclei, which can be morphologically assessed by haematoxylin counterstaining. Sample contamination with exogenous viral sequences can be distinguished from true infection. In this study, a HPV signal was not found in morphologically normal epithelial cells. The methods described will permit the detection of HPV sequences in routinely collected cervical smears and the evaluation of the natural history and potential clinical relevance of HPV infection without changes in clinical practice.

Screening for high- and low-risk human papillomavirus types in single routine cervical smears by non-isotopic in situ hybridization

Routine cervical smears (n = 262) from a Sexually Transmitted Diseases clinic were screened by non-isotopic in situ hybridization (NISH) stratifying human papillomavirus (HPV) infections into HPV6/11 (low risk) and HPV16/18/33 (high risk) categories. Of 188 patients with cytologically normal smears, HPV sequences were demonstrated in 41%. Of the 128 cases analysed by dual NISH, 16% contained low risk, 20% high risk and 5% both groups. In patients with cytological evidence of wart virus infection (WVI) only, 54% (n = 50) contained high-risk and 22% low-risk HPV types. The comparable incidences in CIN1/2 plus WVI (n = 24) were not significantly different: 54% and 17%, respectively. Cytological criteria underestimate the prevalence of HPV infection in patients with cytologically normal smears. This represents either 'occult' or 'latent' infection. The identical prevalence of HPVB16/18/33 in WVI only, and CIN1/2 plus WVI, suggests that the cytopathic effect induced by these HPVs may represent one end of a spectrum of morphological change which progresses to cervical intraepithelial neoplasia (CIN).

Detection of rabies virus mRNA in mouse brain by using in situ hybridization with digoxigenin-labelled RNA probes

A non-isotopic method of in situ hybridization (ISH) was developed for the detection of rabies virus RNA in paraffin-embedded tissues. Digoxigenin-labelled RNA probes for rabies virus glycoprotein mRNA were used. The method had good sensitivity and low backgrounds, and there was excellent cellular localization of signals. ISH wih digoxigenin-labelled probes was compared with ISH with 3H-labelled probes. This non-isotopic method of ISH is more convenient than the radiolabelled method, and it is quicker because a long autoradiographic exposure is not required.

Rapid detection of hepatitis B virus DNA in liver tissue by in situ hybridisation and its combination with immunohistochemistry for simultaneous detection of HBV antigens

A rapid technique using a non-radioactive receptor molecule (digoxigenin) for intrahepatic hepatitis B virus (HBV) DNA detection using in situ hybridisation was developed. It can be adapted for use in combination with standard immunohistochemistry for simultaneous detection of both HBV DNA and HBV antigens. The total time required for dual detection of HBV antigens and HBV DNA starting from paraffin wax liver sections was two working days. A good signal to background ratio for the detection of HBV DNA was always obtained using this labelling. This technique is cheap, safe, and relatively simple which makes it an ideal tool for the detection of intrahepatic HBV DNA for both routine diagnostic purposes and in research.

Model system for optimising mRNA non-isotopic in situ hybridisation: riboprobe detection of lysozyme mRNA in archival gut biopsy specimens

The aim of this study was to optimise conditions for mRNA detection by nonisotopic in situ hybridisation (NISH) using biotinylated and digoxigenin labelled riboprobes. Because lysozyme gene transcripts are present at high concentrations in Paneth and other alimentary cells, archival gut biopsy specimens were chosen as a model system for these experiments. Most of the variables in NISH, from unmasking of mRNA, to its ultimate detection by peroxidase or alkaline phosphatase based detection systems, were examined in detail. The most important findings were that simultaneous heating of tissue targets and riboprobes at 95 degrees C for 15 minutes before hybridisation at 50 degrees C for two hours gave the most intense signal for lysozyme mRNA in Paneth cells, Brunner's glands, and lamina propria macrophages; digoxigenin labelled riboprobes gave a higher signal to noise ratio than their biotinylated counterparts, and probes 600 base pairs long were superior to shorter probes. It is concluded that the mRNA NISH method may be generally useful for detecting gene transcription in archival clinical biopsy specimens.

Application of molecular techniques in the rapid diagnosis of EBV-associated oral hairy leukoplakia

A rapid method for the detection of EBV-DNA in paraffin sections of lesions of oral hairy leukoplakia (OHL) is described. The method makes use of advances in molecular technology, including the use of synthetic oligonucleotides with digoxigenin labelling in an in situ hybridisation (ISH) reaction, which can be completed in 24 h. Using this method, sections from 15 of 17 patients clinically diagnosed as having OHL contained readily detectable EBV-DNA in small foci along the upper layers of the stratum spinosum. The sections examined from the two remaining patients appeared to be EBV-DNA negative but both patients were on AZT therapy and one was in addition receiving acyclovir.

The digoxigenin:anti-digoxigenin (DIG) technology--a survey on the concept and realization of a novel bioanalytical indicator system

A review is given on the novel non-radioactive digoxigenin:anti-digoxigenin (DIG) bioanalytical indicator system. After a general introduction on direct and indirect indicator systems based on previous non-radioactive indicator reactions as well as in vitro and in vivo amplification procedures the principle of the new digoxigenin:anti-digoxigenin technology is demonstrated. The novel system is based on the specific high-affinity interaction between the cardenolide digoxigenin from Digitalis plants and a digoxigenin-specific antibody coupled with a reporter group. A variety of methods for digoxigenin modification of nucleic acids, proteins and glycans are presented. In addition, various applications of the novel non-radioactive indicator system in a variety of direct or indirect detection approaches with either insoluble or soluble substrates are described. It is also shown that with these applications alternative reaction formats are used which are partly characterized by additional amplification steps.

In situ hybridisation in perspective

In the introduction to this review two questions were posed: is the technology associated with ISH ready for general use, and will the method become an important investigative tool? With the exception of the demonstration of some single and low copy sequences, non-radioactive ISH is now sufficiently developed and simplified to make it a routine technique. It is also clear that ISH will continue to have an important research role. In diagnostic pathology the technique is already providing valuable information and the present decade should see the development of many more diagnostic applications.

Detection of mRNA and hnRNA using a digoxigenin labelled cDNA probe by in situ hybridization on frozen tissue sections

A full-length cDNA clone encoding the constant region of T cell receptor beta chain was labelled by random priming DNA with digoxigenin-dUTP. The probe was used to estimate the relative amount of the receptor beta chain mRNA by in situ hybridization on frozen sections from human thymus and lymph nodes. The hybridization was visualized in blue using an anti-digoxigenin antibody conjugated with alkaline phosphatase and a subsequent enzyme-catalysed colour reaction. The distributions of the signal in tissue sections were as expected. Moreover, labelled cells showed hybrids both in the cytoplasm and in the nucleus, and strongly and weakly stained cells were clearly distinguishable. The results indicate that this method of in situ hybridization should be useful in the detection of specific mRNA in frozen sections.

Interphase cytogenetics using biotin and digoxigenin labelled probes: III. Increased sensitivity and flexibility for detecting HPV in cervical biopsy specimens and cell lines

A monoclonal antibody to digoxin enabled sandwich techniques to be used for the detection of hybridised digoxigenin labelled probes in cultured cells and paraffin wax sections. This system has greater flexibility than alkaline phosphatase conjugated polyclonal antidigoxigenin antibody and permits the use of alternative detector enzymes, such as horseradish peroxidase and fluorescence labels. The APAAP detection system that does not require the use of biotin can also be used in situations where endogenous biotin is a problem. The low level of background staining combined with precise substrate deposition of the amplified peroxidase system gives higher sensitivity and resolution. This permits localisation of closely adjacent chromosomal loci in interphase nuclei. The most sensitive peroxidase based digoxigenin detection system visualises two and a half to 12 copies of human papillomavirus (HPV) per nucleus. This system is also suitable for the analysis of low copy number HPV infection of cervical tissues.

In situ hybridisation with digoxigenin-labelled DNA probes for detection of viral genomes

The applicability of a recently developed non-radioactive DNA labelling and detection method, which uses the digoxigenin (DIG) enzyme linked immunosorbent assay (ELISA) system, for the detection of viral infections in pathology specimens by in situ hybridisation, was examined. Its efficacy was compared with that of biotin and radioisotope labelling methods. Three cases of progressive multifocal leucoencephalopathy, two of verruca vulgaris, and seven cases of laryngeal papilloma were studied. The sensitivity of the DIG labelled probe was almost the same as that of a 35S-labelled probe in the dot-blot hybridisation test. Using in situ hybridisation with 35S-labelled and DIG labelled probes, the levels of the hybridised signals detected were similar. The biotin labelled probe was less sensitive, particularly in the cases of laryngeal papilloma. The DIG labelling and detection method was highly sensitive and applicable to the detection of viral infection by ISH, and is preferable to a radiolabelled probe, especially when in situ hybridisation is done in the pathology laboratory.

Discrimination of closely homologous HPV types by nonisotopic in situ hybridization: definition and derivation of tissue melting temperatures

It is generally assumed that nucleic acid association during in situ hybridization reactions is similar to that of nucleic acid association in solution. This assumption has been investigated by detecting closely homologous human papillomavirus types 6 and 11 by in situ hybridization as a model for the evaluation of stringency conditions in clinical biopsies. By examining matched and mismatched, labelled and target sequences under various stringency conditions, empirical DNA-DNA stability curves and their derivative equations for tissue melting temperatures (Tmt) were derived. The corresponding values for Tmt are 10-20 degrees C higher than their solution equivalents. These data, supported by polymerase chain reaction experiments, demonstrate that closely homologous viral DNAs cross linked in tissue by formaldehyde fixation do not interact with the corresponding labelled probes as predicted from solution kinetic equations. This not only has theoretical implications but is also relevant to the accuracy of clinical diagnostic testing.

Non-radioactive labeling and detection of nucleic acids. III. Applications of the digoxigenin system

The digoxigenin-based non-radioactive DNA labeling and detection system was applied in various hybridization protocols using digoxigenin-labeled probes obtained by enzymatic incorporation of Dig-[11]-dUTP. In genomic blots single-copy genes (human tissue-type plasminogen activator, constant part of immunoglobulin kappa light chain) can be detected with only 0.5 to 5 micrograms human DNA depending on the type of probe and the length of the hybridizing region. Due to its high sensitivity and specificity, the digoxigenin system is also appropriate for colony-, plaque-, and in situ hybridizations with metaphase chromosome spreads and fixed cells. Especially in the latter applications it is of great advantage, that with the digoxigenin system any significant background or unspecific side reactions with biological materials are avoided.

Detection of messenger RNA using a digoxigenin end labelled oligodeoxynucleotide probe

A synthetic oligodeoxynucleotide sequence complementary to the mRNA for the adrenocorticotrophin (ACTH) precursor pro-opiomelanocortin (POMC) was end labelled using digoxigenin. The probe was used to detect POMC mRNA both on nitrocellulose filters and by non-isotopic in situ hybridisation (NISH) in tissue sections. Digoxigenin was identified using anti-digoxigenin alkaline phosphatase. The model system examined was the rat pituitary gland. Removal of both adrenal glands and dexamethasone administration were used to change the concentrations of POMC mRNA in the rat anterior lobe. The labelled probe reacted with a single band of appropriate molecular weight in Northern blot analysis. The distribution of signal in tissue sections and the changes induced by experimental manipulation were as predicted. The results indicate that this method of NISH will prove useful in the detection of specific messenger RNAs in tissue sections of buffered, formalin fixed, paraffin wax embedded material.

Interphase cytogenetics using biotin and digoxigenin labelled probes I: relative sensitivity of both reporter molecules for detection of HPV16 in CaSki cells

This study was undertaken to develop technology for the detection of nucleic acid using two different DNA probe reporter molecules, the ultimate aim being to differentially label two nucleic acids within the same nucleus. Digoxigenin and biotin were used to label DNA probes. The absolute and relative sensitivity of digoxigenin and biotin labelled DNA probes for detecting integrated human papilloma virus 16 (HPV16) was investigated in CaSki cells by non-isotopic in situ hybridisation (NISH). Several methods for the detection of labelled probes were also investigated. The optimal sensitivity of digoxigenin labelled probe was equivalent to that of biotin when alkaline phosphatase was used as the final detector. The median number of discrete viral signals discernible in each cell with the most sensitive detection system was seven to eight with both labelled probes. The average number of HPV16 genomes in each CaSki cell, derived by dot blot hybridisation, was about 270. The calculated absolute sensitivity of NISH for viral detection in this system is complex because of variation of signal size and number. Nevertheless, one signal per nucleus equates to as little as 30 to 40 viral copies, and probably much less. The ability to distinguish up to 15 discrete signals with both digoxigenin and biotin labelled probes in the nuclei of CaSki cells indicates that these methods will be useful in interphase cytogenetics in material routinely fixed in aldehyde.