Journal of Cytology
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Year : 2020  |  Volume : 37  |  Issue : 3  |  Page : 157
Micronucleus assay: Pitfalls and challenges

Department of Oral and Maxillofacial Pathology, Faculty of Dentistry, Shahed University, Tehran, Iran

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Date of Submission15-Mar-2020
Date of Decision09-May-2020
Date of Acceptance09-Jun-2020
Date of Web Publication09-Jul-2020

How to cite this article:
Naderi NJ. Micronucleus assay: Pitfalls and challenges. J Cytol 2020;37:157

How to cite this URL:
Naderi NJ. Micronucleus assay: Pitfalls and challenges. J Cytol [serial online] 2020 [cited 2021 Sep 21];37:157. Available from:


Genetic damage due to a genotoxic agent can produces acentric chromatid which is called micronucleus. Micronuclei are formed from aneugenic and clastogenic processes. In the 1980s, micronucleus test was introduced as a simple bio-monitoring method to assess the increased risk of cancer and cancer intervention. Micronucleus test is now accepted as a simple, non-invasive and inexpensive method to evaluate the effect of genotoxic and carcinogenic factors. Although the micronuclei test of human buccal mucosa cells seems simple and useful, there are a few points to be considered in the evaluation and enumeration of these bodies. Ignoring these facts can lead to erroneous results.

Staining technique is one of the most important factors to take into consideration. Some researchers used DNA-specific stains such as Feulgen, 4′, 6-diamidino-2-phenylindole dihydrochloride (DAPI) and Acridine orange. Others used DNA non-specific stains, Papanicolaou stain being the favorite in micronucleus study. DNA non-specific stains can be associated with false positive and false negative results due to under- or over-estimation of micronucleus count.[1],[2] A non-specific stain can lead to confusing outcome.

Micronucleus is a fragment of chromosome or whole part of it which separate from the nucleus during the cell division. In the interphase stage of cell cycle, a true micronucleus is round to oval-shaped object, 1/3 to 1/5 size of nucleus which located adjacent to the nucleus. A round object at a distance from the nucleus is not basically a micronucleus. It should be noted that the counting of micronuclei must be performed by a skilled, calibrated person. An untrained person may mistake the micronucleus with scattered droplets of stain. Small droplets of stain, particularly in slides stained by a non-specific stain for DNA is a challenge. The most important vulnerability of these droplets is the excessive count/overestimation of the micronuclei.

By some researchers, a concept of repair index has been added to the study literature of micronucleus assay. With repair index, in addition to micronucleus (MN), other nuclear changes comprising broken egg (BE), karyorrhexis (KR) and karyolysis (KL) evaluated simultaneously under RI = (KL + KR)/(MN + BE) formula.[3],[4],[5],[6] It seems repair index has more reliable results about tissue dynamics than micronucleus count. Since repair index considers the other nuclear anomalies, it may be a substitute for micronucleus assay. The relevance of repair index to the micronucleus count should be further investigated in comparative studies.

In spite of worthy results with micronucleus test, the method has not yet been confirmed on some aspects such as confirm of micronuclei under fluorescent light, age and the effect of life style on micronucleus count. Given the importance of reliable results, the contribution of researchers is critical to overcome the challenges in interpretation of micronucleus assay.

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Conflicts of interest

There are no conflicts of interest.

   References Top

Nersesyan A, Kundi M, Atefie K, Schulte-Hermann R, Knasmüller S. Effect of staining procedures on the results of micronucleus assays with exfoliated oral mucosa cells. Cancer Epidemiol Biomarkers Prev 2006;15:1835-40.  Back to cited text no. 1
Grover S, Mujib A, Jahagirdar A, Telagi N, Kulkarni P. A comparative study for selectivity of micronuclei in oral exfoliated epithelial cells. J Cytol 2012;29:230-5.  Back to cited text no. 2
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Ramirez A, Saldanha PH. Micronucleus investigation of alcoholic patients with oral carcinomas. Genet Mol Res 2002;1:246-60.  Back to cited text no. 3
Diler SB, Çelik A. Cytogenetic biomonitoring of carpet fabric workers using micronucleus frequency, nuclear changes, and the calculation of risk assessment by repair index in exfoliated mucosa cells. DNA Cell Biol 2011;30:821-7.  Back to cited text no. 4
Çelik A, Yildirim S, Ekinci SY, Taşdelen B. Bio-monitoring for the genotoxic assessment in road construction workers as determined by the buccal micronucleus cytome assay. Ecotoxicol Environ Saf 2013;92:265-70.  Back to cited text no. 5
Celik A, Diler SB, Eke D. Assessment of genetic damage in buccal epithelium cells of painters: Micronucleus, nuclear changes, and repair index. DNA Cell Biol 2010;29:277-84.  Back to cited text no. 6

Correspondence Address:
Dr. Noushin Jalayer Naderi
Department of Oral and Maxillofacial Pathology, Faculty of Dentistry, Shahed University, Tehran
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/JOC.JOC_29_20

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