Comet Assay

Abstract

The “comet assay” was designed by Ostling and Johanson in 1984. Its name was derived from the shape of the nuclear DNA after some steps of manipulation. The comet assay can be applied to all cells, tissues and organs as long as it is possible to generate single cells. The concept of the assay is comparatively simple. In order to study DNA damage either directly after exposure to an agent or after repair has taken place, single cells are placed in a matrix on a microscope slide, all non-DNA material is removed, and an electrophoresis run in a weak electrical field is carried out. Depending on the experimental conditions, various types of DNA damage result in negatively charged loops and fragments which are drawn in the direction of the anode and either form the tail of the “comet” or, in the case of small fragments, migrate into the anode material. The comet assay in its various modifications definitely is a valuable tool for the assessment of DNA damage and is now used in many fields of research. A major problem is that many researchers underestimate the difficulties involved with the proper execution of this assay. The greatest danger for any seemingly “simple” assay is an uncritical use of the method resulting in a lot of contradictory results with the final result of abandoning the assay, because it is “unreliable”. Hopefully, the comet assay will not meet that fate.