Combined immuno- and non-radioactive hybridocytochemistry on cells and tissue sections: influence of fixation, enzyme pre-treatment, and choice of chromogen on detection of antigen and DNA sequences

Conditions for combination of DNA in situ hybridization, using biotinylated DNA probes, with immunohistochemistry were investigated on cryostat sections, cytological preparations, and paraffin sections. We found that cryostat sections and cytological preparations are suitable for in situ hybridization of target DNA after fixation in acetone, methanol, ethanol, or Carnoy without further proteinase pretreatment. Acetone is also very suitable for immunostaining of cell surface or cytoskeleton antigens. We therefore performed combined immunoenzyme and in situ hybridization staining using this fixative. The best results were obtained when immunoperoxidase staining with diaminobenzidine/H2O2 was followed directly by in situ hybridization. In addition to immunoperoxidase, alkaline phosphatase-antialkaline phosphatase (APAAP) staining with naphthol ASBI phosphate and New Fuchsin as a substrate could be used. In most instances, detection of the biotinylated hybrid with a streptavidin-biotinylated polyalkaline phosphatase method using nitroblue tetrazolium and 5-bromo-4-chloro-3-indolylphosphate as the substrate was preferable. The double stainings were studied on the following test models: (a) frozen tonsil sections: cell surface antigens (pan T) and ribosomal DNA; (b) frozen genital condyloma sections; cytokeratins and human papillomavirus type 6 + 11 (HPV-6/11) DNA; (c) CaSKi cells: cytokeratins and HPV-16 DNA; (d) infected fetal lung fibroblasts: vimentin and cytomegalovirus (CMV) DNA. An adapted procedure was followed on routinely formaldehye-fixed and paraffin-embedded condyloma tissue. Immunoperoxidase staining for papilloma virus capsid antigen could be combined with DNA in situ hybridization with HPV-6/11 DNA. In this model, however, the accessibility of the target DNA had to be improved by enzyme treatment after the immunostaining and before starting the in situ hybridization.     

High-resolution in situ hybridization and TUNEL staining with free-floating brain sections.

We applied in situ hybridization and the TUNEL technique to free-floating (vibratomed) sections of embryonic and postnatal mouse CNS. Full-length cDNAs specific for oligodendrocyte- or astrocyte-specific genes were labeled with digoxigenin using the random primer method. With paraformaldehyde-fixed sections, the nonradioactive in situ hybridization method provides detection of individual, very small glial progenitor cells in embryonic development. Small, isolated cells expressing oligodendrocyte specific messages can be detected in the neuroepithelium at embryonic and postnatal stages. The technique can be completed within 3 days and is as sensitive as the radioactive method. Likewise, the TUNEL method using DAB as the chromogen on free-floating sections provides excellent resolution. These DAB-stained sections can be embedded in plastic and thin-sectioned to visualize the ultrastructure of apoptotic cells. Both in situ hybridization and TUNEL methods can be applied to the same section, the tissue embedded in plastic, and semithin sections cut. The high resolution obtained with this combined procedure makes it possible to determine whether brain cells expressing glia-specific messages are undergoing apoptosis.     

An improved method for the simultaneous demonstration of mRNA and esterase activity at the human neuromuscular junction

The aim of this study was to develop a simple means of studying the distribution of mRNA coding for post-synaptic proteins at the human neuromuscular junction. A reliable method by which to identify the junctions in tissue sections after in situ hybridization was essential. A method is described for combining the histochemical demonstration of esterase activity at the neuromuscular junction with autoradiographic localization of mRNA by in situ hybridization in the same cryostat section of skeletal muscle. The indigogenic esterase method of Strum and Hall-Craggs (1982) was modified in such a way that it is able to survive the multiple steps involved in in situ hybridization and autoradiography. The protocol is simple and reproducible and has been used successfully on sections of both rat and human skeletal muscle. To demonstrate the method, sections were reacted to reveal esterase activity and were then processed for in situ hybridization using a 35S-labelled probe specific for the -s ubunit of the acetylcholine receptor. The reaction product was retained after the lengthy in situ hybridization and autoradiographic procedures. To our knowledge, this is the first demonstration of acetylcholine receptor mRNA by in situ hybridization at human neuromuscular junctions. © Chapman & Hall     

An efficient in situ hybridization protocol for multiple tissue sections and probes on miniaturized slides

To facilitate detection of gene activity in tissue sections we combined common protocols of in situ hybridization on tissue sections (TSISH) with the technique of whole-mount in situ hybridization (WMISH). Miniature glass slides for mounting tissue sections were cut from regular microscope slides and handled for in situ hybridization in laboratory-made 2-ml containers (baskets) similar to those originally used for WMISH on Drosophila embryos. A salient point of the method is the use of airtight reaction vessels placed in a dry thermostat for critical hybridization steps as this facilitates reproducible and stringent hybridization conditions which are difficult to achieve on tissue sections otherwise. The practicability of the method is illustrated on consecutive serial frozen sections of murine neonatal cerebellum hybridized for math1 and neuroD, two developmentally regulated genes with distinct expression patterns. For both genes excellent spatial resolution and a highly dynamic range of signal intensity was obtained. The approach enables simple processing of multiple probes, allows the efficient and economic use of small tissue samples and is amenable to automation.     

In situ RNA hybridization using Technovit resin in Arabidopsis thaliana

A protocol is described for RNA in situ hybridization using thin sections prepared by Technovit resin. Technovit is a widely used resin for histological examinations. Since it does not require time-consuming processes such as removal of the resin and can be performed without high temperature treatment, a high resolution of sections could be possible compared to other resins and paraffin. Thin sections (approximately 4 m) were made from inflorescences of Arabidopsis thaliana embedded in Technovit 8100 resin, and in situ hybridization was performed using the protocol described in this article. Hybridization signals were observed using LEAFY and other genes as probes, showing that this resin can be used for in situ analysis. In our experiments, the most important factor for a successful in situ hybridization pattern was to optimize the RNase A concentration after hybridization. We routinely used RNase A at a concentration of 2–5 ng/ml, a concentration much lower than that used for paraffin embedding method. Thus, the use of the Technovit resin for plant tissue embedding results in a faster protocol and greater quality than allowed by paraffin sections.     

Islet amyloid polypeptide (IAPP) is synthesized in the islets of Langerhans. Detection of IAPP polypeptide and IAPP mRNA by combined in situ hybridization and immunohistochemistry in rat pancreas.

We investigated the localization of IAPP mRNA by means of in situ hybridization in tissue sections of rat pancreas. A 35S-labeled, IAPP-specific DNA probe--hybridized specifically in the islets of Langerhans. This localization was confirmed by immunohistochemical localization of insulin and IAPP polypeptides on adjacent tissue sections. Moreover, combined in situ hybridization of IAPP mRNA and immunohistochemistry of insulin and IAPP polypeptide on the same section, using insulin as specific marker shows the presence of IAPP mRNA in the islets of Langerhans.     

Detection of calcitonin-encoding mRNA by radioactive and non-radioactive in situ hybridization: improved colorimetric detection and cellular localization of mRNA in thyroid sections

The localization of mRNA encoding calcitonin was studied by in situ hybridization using 35S-labeled RNA probes and biotin-labeled DNA probes. Radiolabeled probes were detected by autoradiography and biotin-labeled probes by streptavidin-biotin-peroxidase. To intensify the colorimetric signal, the indirect avidin-biotin complex (ABC) method was performed. However, the results were often variable. To improve the sensitivity, the peroxidase reaction signal was enhanced with a gold-silver deposit intensification reaction. To shorten the incubation times and to enhance the colorimetric reaction, several reaction steps were performed in a microwave oven. The localization of calcitonin mRNA in thyroid tissue, as detected with in situ hybridization, was confirmed by immunohistochemical localization of the calcitonin polypeptide. The results of in situ hybridization using biotinylated probes were compared to in situ hybridization using radioactive probes. Our data show that the results of in situ hybridization applied on frozen and paraffin-embedded sections using biotinylated DNA probes, detected with an indirect streptavidin-biotin-peroxidase reaction and intensified by silver-gold enhancement, were comparable to those obtained with radioactive probes. The localization of calcitonin encoding mRNA was in agreement with the localization of the calcitonin polypeptide.     

Comparative usefulness of tissue fixatives for in situ viral nucleic acid hybridization

Traditionally tissues for in situ hybridization of viral nucleic acid have been small pieces obtained from laboratory rodents, and fixatives that are designed for electron microscopy, such as periodate-lysine-paraformaldehyde (PLP) can handle them adequately. However, these fixatives have limited penetrating ability and may produce no appreciable hardening, so alternative fixation methods were evaluated. The intention was to determine whether fixatives adequate for bulky tissues such as whole or halved pig and cow brains would also be compatible with in situ hybridization. Various fixatives were evaluated using a system of intracranial inoculation of BALB/c mice with pseudorabies virus (PRV) followed by in situ hybridization of brain tissue sections with a 35S-labeled PRV DNA probe. Loss of tissue sections was a major problem, particularly with PLP and formalin, but positive results were obtained with five fixatives tested. Cellular morphology was especially good with PLP and with a modification of Carnoy's fluid, MOCA fixative. An incidental but important observation was that formalin is compatible with in situ hybridization. Retroactive studies of viral diseases using routinely processed blocks of tissue (formalin-fixed, paraffin-embedded) are therefore conceivable.     

Sensitive nonradioactive detection of mRNA in tissue sections: novel application of the whole-mount in situ hybridization protocol.

The relative insensitivity of nonradioactive mRNA detection in tissue sections compared to the sensitive nonradioactive detection of single-copy DNA sequences in chromosome spreads, or of mRNA sequences in whole-mount samples, has remained a puzzling issue. Because of the biological significance of sensitive in situ mRNA detection in conjunction with high spatial resolution, we developed a nonradioactive in situ hybridization (ISH) protocol for detection of mRNA sequences in sections. The procedure is essentially based on the whole-mount ISH procedure and is at least equally sensitive. Increase of the hybridization temperature to 70C while maintaining stringency of hybridization by adaptation of the salt concentration significantly improved the sensitivity and made the procedure more sensitive than the conventional radioactive procedure. Thicker sections, which were no improvement using conventional radioactive ISH protocols, further enhanced signal. Higher hybridization temperatures apparently permit better tissue penetration of the probe. Application of this highly reliable protocol permitted the identification and localization of the cells in the developing heart that express low-abundance mRNAs of different members of the Iroquois homeobox gene family that are supposedly involved in cardiac patterning. The radioactive ISH procedure scarcely permitted detection of these sequences, underscoring the value of this novel method.     

In situ detection of bacteria in calcified biofilms using FISH and CARD-FISH

Modified protocols of fluorescence in situ hybridization (FISH) and catalyze reporter deposition fluorescence in situ hybridization (CARD-FISH) were developed in order to detect bacteria in situ in calcified stromatolite biofilms. Smooth, well-preserved thin sections of calcified biofilms (~5 microm thin, vertical sectioning of ~1 cm deep) were obtained by cryo-sectioning using the adhesive tape-stabilization technique. A modified hybridization buffer was applied during hybridization to prevent calcite dissolution as well as false binding of oligonucleotide probes to the charged mineral surfaces. Particularly, bright and specific CARD-FISH signals allowed the detection of bacteria in intensively calcified biofilms even at low magnification, which is suitable for investigating millimeter- to centimeter-scale vertical distribution patterns of bacteria.     

Development of a genomic in situ hybridization method using Technovit 7100 sections of early wheat embryo.

It is difficult to observe the behavior of chromosomes in early wheat embryos because they are wrapped in several cell layers of the ovary. Here we conducted genomic in situ hybridization on sections of ovary embedded in Technovit 7100, a resinous compound suitable for in situ hybridization of mRNA in sectioned tissues. With this resin it is possible to make thin sections with high resolution, no autofluorescence, and good water permeability. These features enable histochemical study using fluorescence microscopy. We established the most suitable conditions for the denaturation of target DNA embedded in Technovit resin, and performed GISH on them. Using this method, we identified Leymus mollis chromosomes in the young ovary of F1 hybrids between wheat and L. mollis. Furthermore, we observed the behavior of maize chromosomes in early wheat x maize hybrid embryos.