Fluorescence In Situ Hybridization, commonly known as FISH testing, is a laboratory technique used to visualize genetic material within cells. It allows scientists to detect specific DNA or RNA sequences on chromosomes. This method provides a direct way to observe chromosomal structures and genetic alterations, offering insights into cellular health and disease.
Understanding FISH Testing
FISH testing uses “probes” that glow under a microscope. These probes are pieces of DNA or RNA tagged with a fluorescent dye. They are complementary to specific genetic sequences, acting like a molecular key on the cell’s genetic material.
When these probes encounter their matching sequence, they bind, or “hybridize,” to it. This binding process allows researchers to “see” the targeted genetic material directly, highlighting its presence or absence. This direct visualization provides precise information about the location and quantity of specific genetic elements.
How FISH Testing is Performed
FISH testing begins by preparing a cell sample, which can be sourced from materials like blood, tissue, or bone marrow. The cells are then processed and fixed onto a glass slide, preserving their structure for analysis. This ensures the genetic material is accessible for subsequent steps.
Next, fluorescently tagged probes are applied to the cell sample. The sample and probes are heated to separate their double-stranded DNA into single strands (denaturation), allowing probes to access target sequences. Following denaturation, probes bind specifically to their complementary DNA or RNA sequences (hybridization).
After hybridization, unbound probes are washed away, and the slide is examined using a fluorescence microscope. This microscope emits light that excites the fluorescent dye on bound probes, causing them to glow. The glowing signals indicate the exact location and presence of targeted genetic sequences, allowing researchers to observe chromosomal abnormalities or specific gene patterns.
Key Uses of FISH Testing
FISH testing is applied in medical and research fields to identify specific genetic alterations. One primary use is detecting chromosomal abnormalities linked to genetic disorders, such as extra or missing chromosomes in Down syndrome. It can also pinpoint smaller changes, including microdeletions or translocations.
The technique also plays a role in cancer diagnosis and prognosis. FISH can identify specific gene rearrangements or amplifications in cancer cells, guiding treatment decisions. For instance, it can detect HER2 gene amplification in breast cancer, indicating the cancer may respond to targeted therapies like trastuzumab. Similarly, it helps identify specific translocations in leukemias and lymphomas, aiding disease classification and predicting patient outcomes.