Micronucleus

About: Micronucleus is a research topic. Over the lifetime, 2569 publications have been published within this topic receiving 74135 citations. The topic is also known as: Micronuclei, Chromosome-Defective.

Measurement of micronuclei in lymphocytes.

Abstract: The micronucleus technique has been proposed as a method for measurement of chromosomal damage in mitogen-stimulated human lymphocytes. Micronuclei require one cell division to be expressed and, consequently, the conventional micronucleus technique is very imprecise since the cells which have undergone only one division, and the micronuclei in them, cannot be identified separately from the total population of lymphocytes. To overcome this problem, two methods were developed to identify cells which have undergone their first mitosis. Using an autoradiographic technique, lymphocytes were pulse-labelled with [3H]thymidine at 48 h of culture, allowed to proceed through mitosis, identified by autoradiography between 72 and 84 h and micronuclei were scored in them. It was not possible to select a concentration of radiolabel which did not itself produce micronuclei and consequently the method was of no value for measuring pre-existing chromosomal damage present in vivo. However, it was capable of quantitating micronuclei produced by irradiation of lymphocytes in vitro. In the second method, cytokinesis was blocked using cytochalasin B. Micronuclei were scored in cytokinesis-blocked cells. These were easily recognisable owing to their binucleate appearance and a large number could be accumulated by adding 3.0 micrograms/ml cytochalasin B at 44 h and scoring at 72 h. Cytochalasin B did not itself produce micronuclei. The cytokinesis-block method was simple to perform; the 'in vivo' micronucleus frequency in normal individuals was 4.4 +/- 2.6 micronuclei/500 cytokinesis-blocked cells; and for lymphocytes irradiated in vitro there was a linear relationship between dose of radiation and number of induced micronuclei. The cytokinesis-block method appears to be the procedure of choice for quantitating micronuclei in lymphocytes.

Cytokinesis-block micronucleus cytome assay

Abstract: The cytokinesis-block micronucleus cytome assay is a comprehensive system for measuring DNA damage, cytostasis and cytotoxicity. DNA damage events are scored specifically in once-divided binucleated (BN) cells and include (a) micronuclei (MNi), a biomarker of chromosome breakage and/or whole chromosome loss, (b) nucleoplasmic bridges (NPBs), a biomarker of DNA misrepair and/or telomere end-fusions, and (c) nuclear buds (NBUDs), a biomarker of elimination of amplified DNA and/or DNA repair complexes. Cytostatic effects are measured via the proportion of mono-, bi- and multinucleated cells and cytotoxicity via necrotic and/or apoptotic cell ratios. Further information regarding mechanisms leading to MNi, NPBs and NBUDs formation is obtained using centromere and/or telomere probes. The assay is being applied successfully for biomonitoring of in vivo genotoxin exposure, in vitro genotoxicity testing and in diverse research fields such as nutrigenomics and pharmacogenomics as well as a predictor of normal tissue and tumor radiation sensitivity and cancer risk. The procedure can take up to 5 days to complete.

The cytokinesis-block micronucleus technique: A detailed description of the method and its application to genotoxicity studies in human populations

Abstract: The development of the cytokinesis-block (CB) technique has transformed the human-lymphocyte micronucleus assay (MN) into a reliable and precise method for assessing chromosome damage. Recent studies in our laboratory have confirmed that this method is a sensitive indicator of in vivo radiation exposure in (a) patients undergoing fractionated partial-body radiotherapy and (b) rodents exposed to uniform whole-body irradiation, thus supporting the application of the cytokinesis-block micronucleus (CBMN) assay for biological dosimetry. To further define the use of this assay in biomonitoring we performed extensive studies to determine the spontaneous level of MN in normal human populations and its relationship to various life-style factors. We have also developed a new variation to the CBMN assay that permits the conversion of excision-repairable lesions to MN within one cell-cycle using cytosine arabinoside. With this method the slope of the in vitro dose-response curves was increased by a factor of 1.8 for X-rays, 10.3 for ultraviolet (UV, 254 nm) radiation and approximately 40-fold for methylnitrosourea. Consequently the CBMN assay can now be used to measure not only whole chromosome loss or chromosome breaks but also excision-repair events. The versatility and simplicity of the CBMN assay together with new developments in automation should ensure its successful application in monitoring exposed populations as well as in identifying mutagen-sensitive individuals within a population.

The production of micronuclei from chromosome aberrations in irradiated cultures of human lymphocytes.

Abstract: A rapid assay for chromosomal damage would greatly speed studies of the mechanism by which chromosomal aberrations are formed The characteristics of such an assay--micronuclei produced in cultured human lymphocytes--are given here, together with the evidence that the assay accurately measures X-ray-induced chromosomal damage Micronuclei arise from chromosomal fragments that are not incorporated into daughter nuclei at mitosis because they lack a centromere In our experiments the response of lymphocytes from different donors was very uniform and agreed well with what was expected from metaphase analysis of aberrations: (1) the increase in micronucleus frequency begins at the time of the first mitoses, 48 hours after the cultures are started, (2) the exponent of the dose response equation (y=kDn) was 12 for micronuclei For one-hit aberrations n=1 whereas for two-hit aberrations n=2 Since two-hit aberrations predominate in these cultures, a value of n= approximately 18 was expected if no increase in mitotic delay or cell death occurred at higher doses, and n less than 18 if an increase occurred, (3) the frequency of micronuclei was decreased by a factor of about two when the dose was fractionated, as expected when most of the aberrations are two-hit The rejoining time for four or five donors was between 30 and 60 minutes, (4) the X-ray-induced micronucleus frequency in cells from people with Down's syndrome (trisomy-21) was twice that of control donors as expected from metaphase analysis [22,23] Since the micronucleus assay reflects the aberration frequencies so well and is so fast, it is suitable for a rapid assessment of chromosomal damage