Nonradioactive In Situ Hybridization: Recent Techniques and Applications

Quantitation of microRNA-92a in colorectal adenocarcinoma and its precancerous lesions: Co-utilization of in situ hybridization and spectral imaging

The expression level of microRNA (miR)-92a has been proven to increase during the development of colorectal adenocarcinoma (CA) and has been verified at the cellular, plasma and fecal levels by various quantitative methods. However, a method to quantitate the expression level using tissue sections has not been established. To do this, in situ hybridization (ISH) and multispectral imaging microscopy (MSI) were introduced to quantitate miR-92a expression on the microscopic level. ISH of miR-92a was first performed on 34 tissue samples of CA and adenomas with high-grade and low-grade intraepithelial neoplasms, while 31 paralesional normal tissue samples were defined as the control. Subsequently, a MSI technique was applied to quantitate the hybridization signal in terms of optical density (OD) at the visible wavelength. A t-test with unequal variance was used to examine the statistical significance between the groups. Despite all 34 tissue sections demonstrating at least partial positivity of miR-92a expression following ISH, visual grading was inconclusive. As such, the signal of ISH was transformed in terms of OD and further analyzed by employing the MSI system. A statistically significant difference was observed between the expression levels of miR-92a in CA and the paralesional normal controls. By contrast, a poor correlation was revealed between visual and spectral grading. The co-utilization of ISH and MSI generated a legible observation in the expression level of miR-92a, revealing the dynamic change in miR-92a expression in the progression of the disease and providing important information for further functional investigation.

Double and triple in situ hybridization for coexpression studies: combined fluorescent and chromogenic detection of neuropeptide Y (NPY) and serotonin receptor subtype mRNAs expressed at different abundance levels

Multiple fluorescence in situ hybridization is the method of choice for studies aimed at determining simultaneous production of signal transduction molecules and neuromodulators in neurons. In our analyses of the monoamine receptor mRNA expression of peptidergic neurons in the rat telencephalon, double tyramide-signal-amplified fluorescence in situ hybridization delivered satisfactory results for coexpression analysis of neuropeptide Y (NPY) and serotonin receptor 2C (5-HT2C) mRNA, a receptor subtype expressed at high-to-moderate abundance in the regions analyzed. However, expression of 5-HT1A mRNA, which is expressed at comparatively low abundance in many telencephalic areas, could not be unequivocally identified in NPY mRNA-reactive neurons due to high background and poor signal-to-noise ratio in fluorescent receptor mRNA detections. Parallel chromogenic in situ hybridization provided clear labeling for 5-HT1A mRNA and additionally offered the possibility to monitor the chromogen deposition at regular time intervals to determine the optimal signal-to-noise ratio. We first developed a double labeling protocol combining fluorescence and chromogenic in situ hybridization and subsequently expanded this variation to combine double fluorescence and chromogenic in situ hybridization for triple labelings. With this method, we documented expression of 5-HT2C and/or 5-HT1A in subpopulations of telencephalic NPY-producing neurons. The method developed in the present study appears suitable for conventional light and fluorescence microscopy, combines advantages of fluorescence and chromogenic in situ hybridization protocols and thus provides a reliable non-radioactive alternative to previously published multiple labeling methods for coexpression analyses in which one mRNA species requires highly sensitive detection.

Present and future of rapid and/or high-throughput methods for nucleic acid testing

BACKGROUND

Behind the success of 'completing' the human genome project was a more than 30-year history of technical innovations for nucleic acid testing.

METHODS

Discovery of specific restriction endonucleases and reverse transcriptase was followed shortly by the development of the first diagnostic nucleic acid tests in the early 1970s. Introduction of Southern, Northern and dot blotting and DNA sequencing later in the 1970s considerably advanced the diagnostic capabilities. Nevertheless, it was the discovery of the polymerase chain reaction (PCR) in 1985 that led to an exponential growth in molecular biology and the introduction of practicable nucleic acid tests in the routine laboratory. The past two decades witnessed a continuing explosion of technological innovations in molecular diagnostics. In addition to classic PCR and reverse transcriptase PCR, numerous variations of PCR and alternative amplification techniques along with an ever-increasing variety of detection chemistries, closed tube (homogeneous) assays, and automated systems were developed. Discovery of real-time quantitative PCR and the development of oligonucleotide microarrays, the 'DNA chip', in the 1990s heralded the beginning of another revolution in molecular biology and diagnostics that is still in progress.

In situ hybridization in the pathology laboratory: General principles, automation, and emerging research applications for tissue-based studies of gene expression

Diagnostic anatomic pathologists play an important role in the care of patients through their careful evaluation of morphological features in routinely prepared histological sections stained with Hematoxylin and Eosin. Morphological assessment of tissue sections, backed by over one hundred years of experience is powerful and allows for the accurate classification and diagnosis of the majority of disease states within pathologically altered tissues. However, the appearance of cells and their architectural arrangement within a morphologically complex tissue represents only a fraction of the information, which is contained within a histological section. These tissues also contain all of the cellular proteins and expressed genes, which help to ultimately determine the biological behavior of cells, as well as provide clues to the origins and pathogenesis of disease states. Technical and theoretical advances in our understanding of cellular biology have provided pathologists with powerful tools to probe beyond pure morphology into the abnormalities in both protein and gene expression that underlie human disease. These tools, which include immunohistochemistry and in situ hybridization, are playing an increasingly important role in diagnostic pathology, as well as in translational research. This review will focus on the emerging role of in situ hybridization within clinical and research laboratories, and will highlight a number of technical advances that have expanded the application of this technology.