The micronucleus test: A method used in mutagenicity testing

Micronucleus is a cytoplasmic round body which contains chromatin mass (DNA). Micronuclei arise when replicating cell populations are subjected to chromosomal breakage by clastogens (agents causing chromosomal breakage) or to chromosome loss by mitotic spindle dysfunction. The micronucleus test is a rapid method to test the mutagenicity of various agents. This test can also be used to assess the cytogenetic damage caused by exposures to genotoxic agents, and is proven to be as sensitive as the laborious cytogenetic analysis. This paper discuss the discovery of micronuclei, the cause of micronuclei formation and the various aspects of the micronucleus test. Micronuclei can be analyzed in various cells, in vivo using various individuals (human, animals, and plants), or in vitro using cultured cells. The most frequently screened cells in in vivo micronucleus test are the erythrocytes, and in in vitro micronucleus test are the lymphocytes. The use of fluorescent stain in micronucleus test gives a more reliable result, but the use is limited, due to the limited fluorescent time. In the future, this can be overcome using Flow-cytometric enumeration. The Feulgen based staining of micronuclei gives a less well pronounced image, thus difficult to score manually, though the result is reliable. In the future this can be overcome using automated enumeration method.