Fluorescence in situ Hybridization (FISH)

Fluorescence in situ hybridization (FISH) is a methodology that is a product of combining the disciplines of cytogenetics and molecular genetics. FISH is, therefore, sometimes referred to as molecular cytogenetics. Due to its robust nature, FISH may be performed on a variety of specimen types, from blood and bone marrow preparations to paraffin-embedded tissue preparations.

FISH is widely used for diagnostic and prognostic purposes. Due to its flexibility in providing clinical information that may be otherwise diffi cult or impossible to obtain, several assays are currently available that are used in the characterization of carcinomas, lymphoma/leukemias, and sarcomas. Innovative applications of this powerful methodology continue to be developed.

FISH employs a methodology that preserves morphology while allowing accurate and reliable localization and measurement of DNA probe signals in situ. The technique uses DNA probes that hybridize to specific regions of chromosomes or to unique sequences. The target DNA of the chromatin is first denatured and then permitted to reanneal in the presence of a high concentration of denatured probe DNA. Optimum temperature, salt concentrations, and formamide enable the annealing of the probe DNA to its exact complementary sequence on the target in situ DNA. A series of stringency washes removes any unbound and nonspecifically bound DNA probe(s). The chromatin is then counterstained to be visualized under fluorescence conditions.