Chromosomes micronucleus analysis

Rats and mice are generally used for in vivo studies, with the mouse being employed for bone marrow micronucleus analysis and the rat for metaphase analysis, but both can be used for either. Mice are cheaper and easier to handle than rats, and only a qualitative difference in response has been found between the species (Albanese et al., 1987). Chinese hamsters are also widely used for metaphase analysis because of their low diploid chromosome number of 22. However, there are few other historical toxicological data for this species. 

Damage induced in whole animals can be detected in in vivo chromosome assays in either somatic or germinal cells by examination of metaphases or the formation of micronuclei. The micronucleus test can also detect whole chromosome loss or aneuploidy in the absence of clastogenic activity and is considered comparable in sensitivity to chromosome analysis (Tsuchimoto and Matter, 1979). 

The test is used for the detection of cytogenetic damage to the chromosomes or the mitotic apparatus of erythroblasts by analysis of erythrocytes for formation of micronuclei (small nuclei, separate from and additional to the main nuclei of cells, produced during the telophase of mitosis (meiosis) by lagging chromosome fragments or whole chromosomes). When a bone marrow erythroblast develops into a polychromatic erythrocyte (immature erythrocyte), the main nucleus is extruded any micronucleus that has been formed may remain behind in the otherwise anucleated cytoplasm. 

Positive results from the in vitro micronucleus test indicate that the test substance induces chromosome damage and/or damage to the cell division apparams, in cultured mammahan somatic cells. Immunochemical labehng (FISH fluorescence in sim hybridization) of kinetochores, or hybridization with general or chromosome specific centromeric/telomeric probes can provide useful information on the mechanism of micronucleus formation. Use of cytokinesis block facilitates the acquisition of the additional mechanistic information (e.g., chromosome nondisjunction) that can be obtained by FISH techniques. The micronucleus assay has a number of advantages over metaphase analysis performed to measure chromosome aberrations (see OECD TG 487 draft). 

Developmental none Prenatal and postnatal development none Genetic toxicology Ames test, unscheduled DNA synthesis, chromosome analysis, mouse lymphoma and micronucleus tests... 

The principle techniques of the micronucleus assay can be applied at the end of a subacute/sub chronic study in the bone marrow of rodents (princliples are described in the section on genotoxicity elsewhere in this book). Usually, only bone marrow from one femur is used for histopathology, thus, the marrow from the second femur can be used for the micronucleus assay. It is not recommended to perform chromosomal analysis in animals from short-term or sub-chronic studies because this technique requires the in vivo treatment with antimitotic agents to arrest the mitotic stage of cell division. 

Purpose. The purpose of the in vivo micronucleus test is to evaluate the potential of the test substance to cause chromosomal damage (clastogenicity) or damage to the mitotic apparatus (aneugenicity) by the analysis of micronuclei in erythrocytes sampled in bone marrow and/or in peripheral blood of experimental animals (usually rodents) (Schmid 1975 Heddle 1973 Heddle and Salamone 1981). 

Tiirkez H, Aydin E, Sisman T et al. (2012d) Role of Peltigerarufescens (Weis) Humb. (a lichen) on imazalil-induced genotoxicity analysis of micronucleus and chromosome aberrations in vitro. Toxicol Ind Health 28(6) 492 98. 

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