Micronucleus test
Encyclopedia
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.
Genotoxic
In genetics, genotoxicity describes a deleterious action on a cell's genetic material affecting its integrity. This includes both certain chemical compounds and certain types of radiation....
compounds. There are two major versions of this test, one in vivo
In vivo
In vivo is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research...
and the other In vitro
In vitro
In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...
. 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
Flow cytometry
Flow cytometry is a technique for counting and examining microscopic particles, such as cells and chromosomes, by suspending them in a stream of fluid and passing them by an electronic detection apparatus. It allows simultaneous multiparametric analysis of the physical and/or chemical...
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
Cell culture
Cell culture is the complex process by which cells are grown under controlled conditions. In practice, the term "cell culture" has come to refer to the culturing of cells derived from singlecellular eukaryotes, especially animal cells. However, there are also cultures of plants, fungi and microbes,...
.
A micronucleus is the erratic (third) nucleus that is formed during the anaphase
Anaphase
Anaphase, from the ancient Greek ἀνά and φάσις , is the stage of mitosis or meiosis when chromosomes move to opposite poles of the cell....
of mitosis
Mitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
or meiosis
Meiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
.
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
Fluorescent in situ hybridization
FISH is a cytogenetic technique developed by biomedical researchers in the early 1980s that is used to detect and localize the presence or absence of specific DNA sequences on chromosomes. FISH uses fluorescent probes that bind to only those parts of the chromosome with which they show a high...
(FISH) with probes targeted to the centromere
Centromere
A centromere is a region of DNA typically found near the middle of a chromosome where two identical sister chromatids come closest in contact. It is involved in cell division as the point of mitotic spindle attachment...
region, it can be determined if a whole chromosome, or only a fragment is lost.