Comet Assay

The Comet assay is a simple, sensitive, and versatile method for the detection of DNA damage in individual cells. The assay can be applied to cells collected from virtually any eukaryotic organism, and can be used to detect DNA damage resulting from exposure to a broad spectrum of genotoxic and cytotoxic compounds in vitro, in vivo, and in situ. Many pathological conditions are initiated by an increased incidence of DNA damage. The most common example is when DNA damage results in mutations capable of initiating carcinogenesis.

Changes in the normal function of an organism resulting from contaminant exposure are initiated at the cellular and molecular levels. DNA damage may be manifest in the form of base alterations, adduct formation, strand breaks, and cross linkages. Of these the most prevalent type of genetic damage is the DNA single strand break.

Strand breaks may be introduced directly by genotoxic compounds, through the induction of apoptosis or necrosis, secondarily through the interaction with oxygen radicals or other reactive intermediates, or as a consequence of excision repair enzymes. In addition to a linkage with cancer, studies have demonstrated that increases in cellular DNA damage precedes or corresponds with higher order cellular effects such as cell cycle arrest, or the induction of apoptosis, and in whole test organisms, reduced growth, abnormal development, and reduced survival.

The photograph at right shows the appearance of fluorescently-stained nuclear DNA on a Comet slide. The upper comet is of somatic cell DNA, and the lower comet a sperm cell. Relaxed or damaged DNA is the "comet tail" trailing behind the main bulk of the nuclear DNA or "comet head".