In situ hybridization: a new tool in molecular medicine

In situ hybridization (ISH) is a molecular technique that been used over three decades to detect specific nucleic acid sequences of gene expression at the cellular level. It is a morphologic method of localizing specific DNA or RNA sequences in the individual cell. The technique can be applied to cells frozen or fixed tissues or whole organisms and cytologic preparations; various types of probes can be utilized and the reaction can be visualized by autoradiography using isotopic markers or by colorimetric methods using fluorochromes or enzymes. It has been used primarily for localization of DNA sequences and applied recently to the localization of viral DNA sequences which provides insight into the pathology of viral infection and is enabling the diagnosis of viral infection. Analysis of gene expression by in situ hybridization messenger RNA (mRNA) is a crucial step towards understanding gene function and biology at molecular level. Nowadays, ISH is applied in three major categories: 1) infectious disease 2.) cytogenetics and 3.) gene expression. This technique has undoubtedly become a powerful new tool for molecular diagnostic techniques and is increasingly important in several areas of molecular medicine.