Microkernel (cytology)

Micronuclei are formed in the process of cell division from: lagging acentric fragments arising from chromosome breaks (the so-called clastogenic effect); lagging chromosomes (the so-called aneugenic effect). Basically, there are three types of violations of the normal process of core formation:

• The micronuclei of the “standard” type, small in size, are well formed and are located close to the main nucleus or at some distance from it, sometimes even at the periphery of the cell.
• Microkernels of the “main” type, not differing in size from the main core, often in close proximity to each other.
• In rare cases, an unformed chromosome material, which is the arrangement of chromosomes in the metaphase of mitosis.

At the moment, specific factors for the formation of micronuclei from unformed chromosome material are not thoroughly known. The very causes that determine violations in the fission process, leading to the formation of micronuclei, can be associated with factors that have a statokinetic effect (delaying and causing disturbances in the phases of mitosis associated with the formation of the spindle and the divergence of chromosomes). Various studies by Ilyinsky and other authors have shown that such violations can be associated with a wide range of factors, ranging from exposure to heavy metals, the effects of ionizing radiation and ending with viral infections.

Micronuclei arise from fragments of chromosomes that are devoid of centromeres and therefore excluded from cell nuclei at the time of cell division. In other words, they are acentric fragments resulting from structural chromosome abnormalities and not falling into the newly formed nucleus during cell division. In addition, they can form from chromosomes remaining in anaphase.

Microkernel Test (ME Test)

The development of a micronucleus test is usually associated with the name of Schmidt, who was proposed by him in 1970, although this test was proposed simultaneously in 1970-1973. several groups of researchers. It was shown that the micronuclear test (MY test) is not inferior in sensitivity to the test for the study of chromosomal aberrations in the cells of the bone marrow of animals, while being much less time-consuming.

The micronucleus test is a relatively new, but generally accepted cytogenetic method for assessing the mutagenic effect of agents of various nature. Using this method, a large number of chemical, physical and biological agents were tested for mutagenic activity; the test is already used at the first stage of testing potential mutagens and carcinogens.

The advantages of the micronuclear test include speed, regardless of the study of the karyotype of the species, often containing a large number of small poorly distinguishable chromosomes, reliability, and the fact that testing can be carried out in tissues with low mitotic activity. Micronuclear analysis is carried out in nuclear-free erythrocytes, in embryo cells, in spermatids, ootides, which is especially important in predicting possible consequences for the heredity of offspring. In environmental genetics, this test is used to assess the mutagenic effect of environmental factors during various industrial accidents, environmental disasters associated with powerful emissions of pollutants into the environment, as well as when examining workers associated with hazardous industries.

In particular, long-term studies of the effects of radiation exposure from tests at the Semipalatinsk test site, the Tomsk radioactive trail, and the accident at the Chernobyl nuclear power plant can serve as an example. Studies have shown an increased frequency of MJ in the cells of the peripheral blood and oral mucosa (buccal epithelium) in individuals exposed to radiation. The use of the micronuclear test in experiments on animals, in particular, on brown frogs under conditions of chronic radiation exposure in the vicinity of the Chernobyl nuclear power plant, allows us to consider this criterion as one of the indicators of the ecological conditions of the living environment of organisms. This is also confirmed by the data on the increased level of cytogenetic damage, based on the MJ test, in immature bone marrow erythrocytes of the European red-backed vole, whose natural populations have been living in radiation-contaminated territories for more than 20 generations after the Chernobyl accident. In addition to assessing the mutagenic effect of ionizing radiation of MN, the test is sensitive to the genotoxic effect of a number of chemical compounds, which often act as components of environmental pollution. So, it was shown that in people working in the production of chlorophenoxy herbicides, the frequency of micronuclei in the cells of epithelial and mucous tissues was significantly increased. Also, drugs can be tested with an ME test.

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