How does Fluorescence in situ hybridization (FISH) work?

In FISH, fluorescently labeled DNA or RNA probes are designed to complementarity bind to target sequences of interest within the sample. These probes hybridize with their complementary sequences, forming stable probe-target complexes that can be visualized under a fluorescence microscope. The probes can be labeled directly by integrating a fluorophore or indirectly using a hapten. The labeled probe and target DNA are denatured before being combined to allow complementary DNA sequences to anneal. The labeled probe and target DNA are denatured before being combined to allow complementary DNA sequences to anneal. If the probe is indirectly labeled, an extra step is needed for visualization using an enzymatic or immunological detection system. The immunological detection system relies on antibodies binding to specific targets, and this binding is then visualized with fluorochromes under ultraviolet light or using a colored reaction visible under a light microscope. On the other hand, the enzymatic detection system uses a fluorescent dye that emits colored signals where the probe is bound to the target sequence. By tagging the probes with fluorescent dye, researchers can see where they are located on the chromosome.