- Micronucleus test
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A micronucleus test is a test used in toxicological screening for potential genotoxic compounds. There are two major versions of this test, one in vivo and the other In vitro. The in vivo test normally uses mouse bone marrow or mouse peripheral blood. Micronuclei were first used to quantify chromosomal damage by H.J. Evans et al., in roottips of the Broad Bean, Vicia faba. Subsequently the in vivo assay was developed independently by W. Schmid and by J.A. Heddle and their colleagues. The assay is now recognized as one of the most successful and reliable assays for genotoxic carcinogens, i.e., carcinogens that act by causing genetic damage. The mouse peripheral blood assay was developed by J.T. MacGregor and has now been adapted for measurement by flow cytometry by A. Tometsko and colleagues. The first use of micronuclei in cultured cells was by J.A. Heddle and colleagues in human lymphocytes. The assay has been improved by M. Fenech and colleagues for use in lymphocytes and other cells in culture cells.
A micronucleus is the erratic (third) nucleus that is formed during the anaphase of mitosis or meiosis. Micronucleus, the name itself indicates small nucleus, are cytoplasmic bodies having a portion of acentric chromosome or the whole chromosome which were not carried during the anaphase to the opposite poles, finally resulting in missing of part or whole chromosomes for the daughter cell. These chromosome fragments or whole chromosomes normally develop nuclear membrane and forms as micronuclei as a third nucleus. After cytokinesis one daughter cell is with one nucleus and the other is with one large and one small nucleus i.e., micronuclei. There is a chance of more than one micronuclei when more genetic damage was happened. Micronucleus test is used in genotoxicity asessment tool of various chemicals and easy to conduct rather than chromosomal Aberration test because of its easeness in conducting studies and evaluation. Using fluorescent in situ hybridization (FISH) with probes targeted to the centromere region, it can be determined if a whole chromosome, or only a fragment is lost.
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