IN-SITU HYBRIDIZATION AND ITS DIAGNOSTIC APPLICATIONS IN PATHOLOGY

In situ hybridization (ISH) is a technique by which specific nucleotid e sequences are identified in cells or tissue sections. These may be e ndogenous, bacterial or viral, DNA or RNA. On the basis of research ap plications, the technique is now being translated into diagnostic prac tice, mainly in the areas of gene expression, infection and interphase cytogenetics, Diagnostic applications are most often based on short n ucleotide sequences (oligomers) labelled with non-isotopic reporter mo lecules, and sites of binding may be localized by histochemical or imm unohistochemical methods. The technique can be applied to routinely fi xed and processed tissues; with some targets, it is even possible to o btain hybridization in autopsy material. ISH has been used to detect m essenger RNA (mRNA) as a marker of gene expression, where levels of pr otein storage are low; for example, to confirm an endocrine tumour as the source of excess hormone production. Its application in infectious diseases has to date been mainly in viral infections, such as the typ ing of human papillomavirus (HPV) or the detection of Epstein-Barr vir us by the presence of small nuclear RNAs (EBERs). The expression of mR NAs for histone proteins has been used to detect cells in S phase, and related methods may be applied to detect apoptotic cells. Using probe s to chromosome-specific sequences, it is possible to detect aneuploid y, and to document changes in specific chromosomes, which may have pro gnostic significance in some tumours, such as B-cell chronic lymphatic leukaemia. Using sequence-specific probes, translocations can be iden tified, such as the t(11;12) of Ewing's sarcoma. This review presents an outline of the technique of in sits hybridization and discusses are as of current and potential diagnostic application. (C) 1997 by John W iley Br Sons, Ltd.