In-situ polymerase chain reaction. An overview of methods, applications and limitations of a new molecular technique.

The in-situ polymerase chain reaction (in-situ PCR) is a novel molecular technique that combines the extreme sensitivity of the PCR with the anatomical localization provided by in-situ hybridization. A number of groups have recently reported studies using in-situ PCR for the detection of specifically amplified single-copy nucleic acid sequences in single cell preparations or low copy DNA sequences in tissue sections. In this overview, we describe the principles of in-situ PCR, review the applications of this technique and discuss future aspects of in-situ PCR. We critically compare the different in-situ PCR protocols described in the literature. Emphasis is placed on the absolute requirement for controls to allow accurate interpretation of results and the possible problems and pitfalls of the in-situ PCR methods, including artefacts related to diffusion of PCR products and non-specific incorporation of labelled nucleotides into fragmented DNA undergoing repair. It is concluded that this technique will eventually play an important role in specialized diagnostic laboratories in the evaluation of viral diseases, haematological and other malignancies which have unique genetic markers.