What's new in "in situ hybridization".

In situ hybridization (ISH) represents a technique which allows the visualization of cellular DNA or RNA in tissue sections, single cell or chromosome preparations. In addition to the originally used nick-translated DNA probes, synthetic oligodeoxyribonucleotides and single stranded cDNA probes are applied to ISH. With the more recent introduction of single stranded antisense RNA probes a highly specific and more sensitive technique became available. Besides the labeling of probes by the incorporation of radionucleotides non-radioactive labeling, particularly with biotin, is gaining increasing importance. Today, the most significant application for ISH in diagnostic pathology is the morphological analysis of viral infections because of the restricted availability of specific antibodies for immunohistochemistry. Furthermore, the visualization of mRNAs by ISH has proved to be useful for the visualization of specific gene expression of tumor cells, particularly, for the localization of mRNAs encoded by oncogenes and neuroendocrine genes. ISH was shown to be a more reliable tool to characterize the expression of a specific gene than conventional immunocytochemical procedures, because ISH demonstrates the actual amount of specific mRNA, whereas immunocytochemistry reflects the actual amount of immunoreactive peptide and is, therefore, dependent on peptide secretion, intracellular peptide degradation, peptide transport, and post-translational peptide processing. With the steadily increasing number of cloned nucleotide sequences the number of potentially useful probes and, consequently, the field of applications for ISH and its impact in research and diagnostic pathology is growing rapidly.