ABSTRACT
Simultaneous detection and localization of DNA or RNA by in situ hybridization have been demonstrated in recent years.1-3 As described in Chapters 12 and 13, the power of in situ hybridization allows the DNA or RNA of interest to be detected in intact cells or speci„c tissues. Unfortunately, this technique has a sensitivity limitation. In fact, it merely works well for analysis of high abundance nucleic acids, but can hardly detect low copy gene/DNA or low abundance RNA. In general, traditional Southern or northern blot hybridization also does not detect low abundance nucleic acids. To overcome this limitation, in situ polymerase chain reaction (PCR) and in situ reverse transcription (RT)-PCR methods have been developed for the detection of low copy genes/DNAs and low abundance mRNAs, respectively.4-6 These technologies are a virtual combination of PCR and in situ hybridization, which have become very powerful tools and are widely used in many disciplines.3-12
Clearly, there is a major difference between in situ PCR and regular solution PCR, even though the basic mechanism of DNA ampli„cation is similar. Solution PCR is carried out in a tube and requires extraction of DNA/RNA from cells or tissues to be tested. As a result, one cannot correlate PCR data with the histological or pathological features of the sample being examined. In contrast, in situ PCR can directly amplify target DNA sequences within intact cells or specimens, which enables one to know exactly what particular cell-or tissue type contains the ampli„ed DNA or cDNA. With in situ PCR hybridization techniques, a virus infection or a few copies of mRNA can be rapidly detected and localized.
