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What is the fate of micronucleus DNA?

What is the fate of micronucleus DNA?


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Micronuclei are cellular structures that are formed as a by-product of, usually, defective mitosis. The piece of chromosome in a micronucleus may, or may not contain a centromere and the DNA is wrapped in a double lipid membrane.

I have tried to find information, but I failed to find out what the fate of these structures is within the cell once formed? And is the DNA within it lost for the cell?


Emergence of Micronuclei and Their Effects on the Fate of Cells under Replication Stress (2010) explores how micronuclei behave and determine cell fate. It found that micronuclei is pretty closely related to apoptosis. If the cells with micronuclei didn't go through apoptosis, there were instances where the micronuclei would literally just disappear. They were unable to determine if it was expelled by the cell or reabsorbed into the main nucleus. However, there were also cases where there would be an increase in the number of micronuclei.

They concluded that there is a number of ways for the cell to get rid of the micronuclei and they were unable to determine which is the most likely.

I was unable to find any more recent in-depth studies (that I could understand).


So, according to this paper there are several answers…

  • Case 1: It is reabsorbed into the nucleus and most likely the information within is saved.
  • Case 2: It is expelled from the cell and the information within is lost.
  • Case 3: The cell undergoes apoptosis and all information is lost.

The fate of micronucleated cells post X-irradiation detected by live cell imaging

Micronuclei are closely related to DNA damage. The presence of micronuclei in mammalian cells is a common phenomenon post ionizing radiation. The level of micronucleation in tumor cells has been used to predict prognosis after radiotherapy in many cancers. In order to understand how irradiation-induced micronuclei affect cell fate, we performed extensive long-term live cell imaging on X-irradiated nasopharyngeal carcinoma (NPC) cells. To visualize the dynamics of micronuclei more clearly, chromosomes were stably labeled with red fluorescent protein (RFP) by targeting to human histone H2B. Initially, significantly more micronuclei were observed in radiosensitive cells than in radioresistant cells post irradiation. Additionally, cells with micronuclei were found to be more likely to die or undergo cell cycle arrest when compared with micronucleus-free cells after irradiation, and the more micronuclei the cells contained the more likely they would die or undergo arrest. Moreover, micronucleated cells showed predisposition to produce daughter cells with micronuclei through chromosome lagging. Fluorescence in situ hybridization using human pan-centromeric probes revealed that about 70% of these micronuclei and lagging chromosomes did not contain centromeric signals. Finally, DNA damage was more severe and p38 stress kinase activity was higher in micronucleated cells than in micronucleus-free cells as shown by phospho-H2AX and phospho-p38 immunofluorescence staining. Altogether, our observations indicated that the presence of micronuclei coupled with activated DNA damage response could compromise the proliferation capacity of irradiated cells, providing the evidence and justification for using micronucleus index as a valuable biomarker of radiosensitivity.


The fate of micronucleated cells post X-irradiation detected by live cell imaging

Micronuclei are closely related to DNA damage. The presence of micronuclei in mammalian cells is a common phenomenon post ionizing radiation. The level of micronucleation in tumor cells has been used to predict prognosis after radiotherapy in many cancers. In order to understand how irradiation-induced micronuclei affect cell fate, we performed extensive long-term live cell imaging on X-irradiated nasopharyngeal carcinoma (NPC) cells. To visualize the dynamics of micronuclei more clearly, chromosomes were stably labeled with red fluorescent protein (RFP) by targeting to human histone H2B. Initially, significantly more micronuclei were observed in radiosensitive cells than in radioresistant cells post irradiation. Additionally, cells with micronuclei were found to be more likely to die or undergo cell cycle arrest when compared with micronucleus-free cells after irradiation, and the more micronuclei the cells contained the more likely they would die or undergo arrest. Moreover, micronucleated cells showed predisposition to produce daughter cells with micronuclei through chromosome lagging. Fluorescence in situ hybridization using human pan-centromeric probes revealed that about 70% of these micronuclei and lagging chromosomes did not contain centromeric signals. Finally, DNA damage was more severe and p38 stress kinase activity was higher in micronucleated cells than in micronucleus-free cells as shown by phospho-H2AX and phospho-p38 immunofluorescence staining. Altogether, our observations indicated that the presence of micronuclei coupled with activated DNA damage response could compromise the proliferation capacity of irradiated cells, providing the evidence and justification for using micronucleus index as a valuable biomarker of radiosensitivity.


The fate of micronucleated cells post X-irradiation detected by live cell imaging

Micronuclei are closely related to DNA damage. The presence of micronuclei in mammalian cells is a common phenomenon post ionizing radiation. The level of micronucleation in tumor cells has been used to predict prognosis after radiotherapy in many cancers. In order to understand how irradiation-induced micronuclei affect cell fate, we performed extensive long-term live cell imaging on X-irradiated nasopharyngeal carcinoma (NPC) cells. To visualize the dynamics of micronuclei more clearly, chromosomes were stably labeled with red fluorescent protein (RFP) by targeting to human histone H2B. Initially, significantly more micronuclei were observed in radiosensitive cells than in radioresistant cells post irradiation. Additionally, cells with micronuclei were found to be more likely to die or undergo cell cycle arrest when compared with micronucleus-free cells after irradiation, and the more micronuclei the cells contained the more likely they would die or undergo arrest. Moreover, micronucleated cells showed predisposition to produce daughter cells with micronuclei through chromosome lagging. Fluorescence in situ hybridization using human pan-centromeric probes revealed that about 70% of these micronuclei and lagging chromosomes did not contain centromeric signals. Finally, DNA damage was more severe and p38 stress kinase activity was higher in micronucleated cells than in micronucleus-free cells as shown by phospho-H2AX and phospho-p38 immunofluorescence staining. Altogether, our observations indicated that the presence of micronuclei coupled with activated DNA damage response could compromise the proliferation capacity of irradiated cells, providing the evidence and justification for using micronucleus index as a valuable biomarker of radiosensitivity.


Genomic Organization and Developmental Fate of Adjacent Repeated Sequences in a Foldback DNA Clone of Tetrahymena thermophila

DNA sequence elimination and rearrangement occurs during the development of somatic cell lineages of eukaryotes and was first discovered over a century ago. However, the significance and mechanism of chromatin elimination are not understood. DNA elimination also occurs during the development of the somatic macronucleus from the germinal micronucleus in unicellular ciliated protozoa such as Tetrahymena thermophila. In this study foldback DNA from the micronucleus was used as a probe to isolate ten clones. All of those tested (4/4) contained sequences that were repetitive in the micronucleus and rearranged in the macronucleus. The presence of inverted repeated sequences was clearly demonstrated in one of them by electron microscopy. DNA sequence analysis showed that the left portion of this clone contains three tandem, directly repeated copies of a 340-bp sequence, a 120-bp portion of which appears in inverted orientation at a 1.6-kb distance. This clone, pTtFB1, was subjected to a detailed analysis of its developmental fate. Subregions were subcloned and used as probes against Southern blots of micronuclear and macronuclear DNA. We found that all subregions defined repeated sequence families in the micronuclear genome. A minimum of four different families was defined, two of which are retained in the macronucleus and two of which are completely eliminated. The inverted repeat family is retained with little rearrangement. Two of the families, defined by subregions that do not contain parts of the inverted repeat, one in the "loop" and one in the "right flanking region," are totally eliminated during macronuclear development𠅊nd contain open reading frames. A fourth family occurs in the "loop" region and is rearranged extensively during development. The two gene families that are eliminated are stable in the micronuclear genome but are not clustered together as evidenced by experiments in which DNAs from nullisomic strains are used to map family members to specific micronuclear chromosomes. The inverted repeat family is also stable in the micronuclear genome and is dispersed among several chromosomes. The significance of retained inverted repeats to the process of elimination is discussed.


What is the Difference Between Micronucleus and Macronucleus?

Ciliates have two nuclei as micronucleus and macronucleus. Micronucleus is the smaller nucleus and the reproductive nucleus. In contrast, macronucleus is the larger one and the non-reproductive nucleus. So, this is the key difference between micronucleus and macronucleus. Micronucleus genome is diploid while macronucleus genome is polyploidy. Moreover, micronucleus contains a small amount of DNA, while macronucleus contains a large amount of DNA. Therefore, this is also a difference between micronucleus and macronucleus.

The following infographic summarizes the difference between micronucleus and macronucleus.


4. Different Types of Micronucleus Assays

Although all types of MN are based on the analysis of micronuclei frequency, they vary in terms of used cells and protocols. The summary is given in Table 3 , followed by a more detailed description.

Table 3

Types of micronucleus assays.

in vitro or in vivo genotoxicity

biological experiments where cytogenetic damage is assessed.

in vivo genotoxicity of chemicals, drugs or harmful condition

impact of nutrition lifestyle habits, such as smoking and drinking alcohol

risk of accelerated aging, certain types of cancer and neurodegenerative diseases.

prognosis of certain cancers.

4.1. Cytokinesis-Block Micronucleus Assay (CBMN)

The most popular version of MN is the cytokinesis-block micronucleus assay (CBMN) [6,30] ( Figure 1 ). Because Mn is visible only after cell division, the cytochalasin B that inhibits actin filaments polymerization and formation of contractile microfilaments is used to stop cytokinesis [42,43]. However, cytochalasin B does not stop karyokinesis, thus binucleated cells are formed with Mn present in their cytoplasm. The influence of cytochalasin B on cell proliferation and induction of Mn was discussed in the past [6,44]. The conclusion reached indicates that in most cases, the usage of cytochalasin B does not induce additional Mn, hence, the use of cytochalasin B is recommended [5,6,30,45,46,47,48]. This is of special importance when human lymphocytes are used, as their cell cycle may vary among individuals [4]. According to the mathematical model described by Fenech, MN with cytochalasin B applied to block cytokinesis is superior over MN without cytochalasin B because there are less false-negative results when MN using cytokinesis block is used [49].

A principle of cytokinesis-block micronucleus assay. 1. Nucleus with damaged DNA. 2. Inhibition of cytokinesis by the addition of cytochalasin B. 3. The Mn frequency is scored in binucleated cells only. Upper part𠅌ontrol binucleated cells without Mn, lower part—two binucleated cells with 1 or 6 Mn visible in the cytoplasm.

The CBMN is prevalently performed on human peripheral blood lymphocytes to study in vivo formation of Mn for biomonitoring or biological dosimetry, however, can be performed on different lymphocytes of other species, e.g., rodents, fish, dogs, rabbits, monkey and apes or other cells of different origin [50,51,52]. The CBMN is also very often used on blood samples in vitro to study genotoxic effects of chemicals. [6,53,54,55,56,57]. The information about in vitro genotoxicity testing by MN is gathered, revised and systematized in the Organization for Economic Co-operation and Development (OECD) 487 Guideline [4].

The CBMN provides a comprehensive basis for in vitro investigating of the chromosome damaging potential of chemicals, noteworthy, both aneugenic (changes in the chromosome number in the cell caused by e.g., tobacco smoking, pesticides) and clastogenic changes (structural aberration caused e.g., by ionizing radiation acridine yellow, benzene, ethylene oxide, arsene, phosphine) can be detected. According to the OECD guideline, cells should be are treated with chemical compounds in three different ways: cultured with cytochalasin B, cultured without cytochalasin B and cultured in the presence of exogenous metabolic activation system, usually prepared from the liver of rodents (S9 fraction). It is impossible to enumerate all applications of the CBMN. The most important applications of CBMN have already been described, but several more are mentioned in Table 4 .

Table 4

basic research on DNA damage and repair [58,59]
radiosensitivity studies of various groups, whether healthy or with genetic disorders [24,60,61,62]
attempts to link the radiosensitivity with the radiation reaction of normal tissues in persons undergoing radiotherapy [63,64]
predictive tests of neoplastic disease [60,65,66]
characterizations of cytogenetic damage during chemo- and radiotherapy [67,68]
biomonitoring of the environment or occupational exposure [32,69,70,71].

CBMN disorders characterization-occupational exposure, although in the basic version of the assay only Mn are scored, the assay can be extended by scoring other biomarkers, as nucleoplasmic bridges, nuclear buds, nuclear blebs, necrotic and/or apoptotic cells [32]. This type of the assay, called CBMN cytome assay, gives additional information about DNA damage and its repair, cytostasis and cytotoxicity [72].

4.2. Erythrocyte Micronucleus Assay–the Most Popular In Vivo MN

Erythrocyte micronucleus assay (EMn) was initially performed on immature erythrocytes from bone marrow of young mice and rats [73]. The disadvantage of the assay is that bone marrow examination entails sacrificing rodent life. In addition, potentially confounding factors, such as other nucleated cells (must cells, granulocytes or different types of lymphocytes), are present in the bone marrow [74]. EMn was also performed on cellular material taken from human bone marrow to determine cytogenetic damage after radio- and chemotherapy [75,76,77,78].

Due to the high invasiveness of the method, an alternative approach was developed, based on assessing the frequency of Mn in immature erythrocytes in peripheral blood [1,79]. During maturation, erythrocyte precursor cells lose their nuclei, however, retain Mn formed during the nucleated stage [2]. Immature erythrocytes (also called reticulocytes or polychromatic erythrocytes) can be easily recognized from the mature erythrocytes because they still contain RNA in their cytoplasm [1]. In bone marrow, immature erythrocytes constitute about 50% of all erythrocytes [80,81].

Human erythrocyte precursor cells present in the long bone marrow of control specimens contain nuclei, likely as a result of environmental or occupational exposure or genetic factors ( Figure 2 ). Immature erythrocytes arising from the precursor cells also contain Mn, however, they represent only a few percent of all erythrocytes in peripheral blood [81]. Though frequency of Mn in immature erythrocytes is significantly higher than in mature erythrocytes [1], splenic selection, a process that effectively removes micronucleated erythrocytes from peripheral blood, significantly reduces the frequency of Mn. Splenic selection occurs in rats and humans, also in mice, but to a lesser extent [74,82]. Therefore, in humans, the MN in immature erythrocytes is carried out only on individuals with the spleen removed [13,83]. To increase the assay reliability, the MN in immature erythrocytes in peripheral blood has been automated and is carried out by flow cytometry. With this technique, hundreds of thousands of cells can be analyzed in a reliable time, which allowed overcoming problems with low number of cells available for analysis and Mn splenic selection. Flow cytometry aided scoring of Mn in erythrocytes was validated both in rodents and humans [82,84,85].

Mammalian erythrocyte micronucleus assay. (1). Immature erythrocyte in bone marrow contains nucleus and RNA in its cytoplasm. When DNA damage is induced in vivo, micronucleus can arise in the nucleated erythrocyte. When nucleus is excluded during erythrocyte maturation the micronucleus stays in the cytoplasm. (2). In bone marrow, immature erythrocytes consist of around 50% of all erythrocytes. Occasionally these immature erythrocytes may contain Mn. (3). Sometimes the immature erythrocytes are released to peripheral blood, where they constitute less than 5% of all erythrocytes. The immature erythrocytes in blood can be recognized due to their specific surface receptors or RNA content. Flow cytometry technique makes the EMn feasible in peripheral blood of rodents and humans.

4.3. Buccal MN (BMm)–Mature but Underused Assay

Although BMm has been used for about 40 years, it seems that only in recent years it gains more interest. The first publications describing this test appeared in the 1980s [86,87]. However, the first publication of the operational protocol in Nature Protocols falls within the last 10 years, after harmonization of the assay by the international HUMNxl group [88,89]. Mn arise in dividing basal cells of oral epithelium but are observed in differentiated cells in the keratinized layer at the buccal surface [90,91]. In addition to Mn, several other cytogenetic biomarkers, including those related to cell death, can be analyzed, which gives more information of the origin of DNA damage, cytostasis and cytotoxicity, somehow analogous to the CBMN cytome assay mentioned earlier [88,91]. This approach was also called the buccal micronucleus cytome (BMCyt) assay [88,91,92].

Mn in the buccal cells are formed in the organism, in rapidly dividing buccal epithelial tissue ( Figure 3 ). Although cells from the oral cavity are exposed to genotoxic or cytotoxic factors by inhalation and food intake to a greater extent than peripheral blood lymphocytes, the background frequency of Mn in buccal cells is very low [93,94]. On the other side, patients undergoing head and neck radiotherapy may serve as a positive control, although some ethical issues must be considered, as in their case the collection of material is more problematic due to lesions and inflammation of the oral mucosa [88,95]. The BMm was used to investigate the impact of nutrition, lifestyle factors (as smoking, drinking alcohol or betel chewing), genotoxin and cytotoxin exposure. Interestingly, correlation was found between the frequency of Mn in buccal cells and increased risk of accelerated aging, certain types of cancer and neurodegenerative diseases [92,96].

Buccal micronucleus assay. (1) Mn are induced in vivo by genotoxic agents in rapidly dividing buccal epithelial tissue. Epithelial cells differentiate and move towards outer layer of oral mucosa. (2) Mn frequency can be estimated in smears of exfoliated buccal cells.

BMn seems to be advantageous over other types of MN to study how genotoxic factors affect organisms by inhalation. It is the only method capable to show genotoxic effects of moderate concentrations of radon, as those that are met in unventilated rooms, basements or caves [14,97]. Moreover, the sensitivity of BMn allowed also to show genotoxic effects of work in healthcare, where staff was exposed to very low doses of radiation [98]. BMn is gaining popularity and probably will become a standard cytogenetic test, especially since it is minimally invasive, easy to perform, and cell samples are taken from the oral cavity.

4.4. Other Types of MN

Occasionally, the MN is also performed on cells other than lymphocytes, fibroblasts and buccal cells, such as nasal mucosa cells or urine-derived cells [99,100,101]. Both the test objectives and the method of performance remain similar to CBMN or BMn, but these tests have not gained much popularity, so far.


Micronucleus formation, proliferative status, cell death and DNA damage in ethosuximide-treated human lymphocytes

Ethosuximide is a T-type Ca 2+ channel blocker that has been used as an anticonvulsant to treat absence seizures. Because no data have yet been reported on the cytotoxicity, genotoxicity and cell death effects of this drug, we have investigated ethosuximide-treated human lymphocytes with Fenech's CBMN (cytochalasin-blocked micronucleus cytome) assay and single-cell gel electrophoresis (comet assay). The tests allowed us to examine micronucleus formation, the proliferative status of the viable cells, nuclear blebbing, nucleoplasmic bridge formation, cell death (CBMN assay) and DNA damage (comet assay). The lymphocytes were treated for 24 h with 25, 50 or 100 μg/ml ethosuximide. The cells used for the CBMN assay were examined either immediately or 24 h after the cytochalasin blockade. For the comet assay, cells were examined immediately or 22 h after 2 h ethosuximide treatment. The results indicate that 25 and 50 μg/ml ethosuximide did not induce micronucleus formation, nuclear abnormalities, cell death or DNA damage, nor did they affect cell proliferation, suggesting no cytotoxic or genotoxic effects under such experimental conditions. However, under treatment with 100 μg/ml ethosuximide, an increase in micronucleus formation and nuclear abnormalities, but a decrease in cell proliferation and in DNA damage, and no change in the cell death ratio, were detected. Although apparently contradictory, the data obtained with the 100 μg/ml concentration may indicate that induction of cytotoxicity and genotoxicity are not to be disregarded when considering this drug concentration. The mechanisms underlying the cellular response to ethosuximide remain to be explored.


MATERIALS AND METHODS

Cell culture, cell lines and reagents

To construct cell lines stably expressing H2B-Dendra2, HEK293T cells were transfected with LV.CNV.puro.H2B-Dendra2 construct (a gift from Jacco van Rheenen, Molecular Pathology, The Netherlands Cancer Institute, The Netherlands) using X-tremeGENE (Roche) according to manufacturer's protocol. After 2 days, virus-containing medium was added to RPE-1 p53kd cells (a gift from Johan Kuiken and Roderick Beijersbergen, Department of Cellular and Molecular Medicine, The Netherlands Cancer Institute), and Dendra2-positive cells were sorted on green fluorescence at 2 weeks post-infection. RPE-1 cells expressing PCNA–mCherry and H2B–eGFP were kindly provided by Arshad Desai (Ludwig Institute for Cancer Research, USA). To make RPE-1 JNK-KTR cells, HEK293T cells were transfected with pLenti PGK Puro DEST JNKKTRClover (Addgene plasmid #59151, deposited by Markus Covert Regot et al., 2014) using X-tremeGENE (Roche) according to manufacturer's protocol. The obtained virus was added to RPE-1 and drug selection was performed (puromycin 1 μg/μl) at 24 h post-infection. All cells described above were cultured at 37°C at 5% CO2 in advanced Dulbecco's modified Eagle's medium with nutrient mixture F-12 (DMEM-F12) with Glutamax (GIBCO), supplemented with 10% fetal calf serum (Clontech), 100 U/ml penicillin (Invitrogen), 100 μg/ml streptomycin (Invitrogen) and 2 mM UltraGlutamin (Lonza). For cell cycle synchronization, cells were treated with 2.5 mM thymidine (Sigma) for 22 h and released by washing twice with phosphate-buffered saline (PBS). Inhibitors were all dissolved in DMSO and were used at the following concentrations: proTAME, 20 μM GSK923295, 50 nM NMS-P715, 480 nM Anisomicyn, 50 μM (1 h) and JNK inhibitor VIII, 10 μM. All cell lines described above have been shown to be free of mycoplasma contamination.

Time-lapse imaging

For live-cell imaging, cells were grown in Lab-Tek II chambered coverglass (Thermo Science). Images were acquired every 5, 10 or 15 min using a DeltaVision Elite (Applied Precision) microscope maintained at 37°C, 5% CO2 using a 20×0.75 NA lens (Olympus) and a Coolsnap HQ2 camera (Photometrics) with 2 times binning. Image analysis was performed with ImageJ software. For micronuclei tracking experiments, pre-converted micronuclei were identified by green fluorescence and photoconverted by using a brief (0.05 s) pulse of a 405 nm laser on a Deltavision Elite microscope equipped with a X4 laser module (Applied Precision). Subsequent live-cell imaging was performed as stated above. A Lionheart FX automated microscope was used for nuclear import assays (microscope maintained at 37°C, 5% CO2 using a 20× NA lens and a Sony CCD, 1.25 megapixel camera with 2 times binning BioTek).

SiRNA transfection

ON-TARGETplus SMARTpool siRNA targeting p53 (Thermo Scientific) was transfected using RNAiMAX (Life Technologies) according to the manufacturer's protocol at a final concentration of 20 nM, 24 h before the start of the experiment.

Immunofluorescence

Cells were grown on 10-mm glass coverslips and fixed in 3.7% formaldehyde with 0.5% Triton X-100 in PBS for 15 min at room temperature. Primary antibodies were incubated at 4°C overnight and secondary antibodies were incubated for 2 h at room temperature, both dissolved in PBS 0.1% Tween. The following antibodies were used: Mad1 (1:500, sc-65494, Santa Cruz Biotechnology), Crest (1:5000, CS1058, Cortex Biochem), CENP-A (1:300, ab13939, Abcam), CENP-C (1:600, PD030, MBL), CENP-T (1:1000, D286-3, MBL), H4K20me1 (1:2000, Hori et al., 2014). Secondary antibodies conjugated to Alexa Fluor 488, Alexa Fluor 568 and Alexa Fluor 647 (Molecular Probes) were used for immunofluorescence. DAPI was added to all samples before mounting using Vectashield mounting fluid (Vector Laboratories). Replication levels were determined for cells cultured in medium containing EdU for the indicated time. After fixation, EdU incorporation was visualized by staining with buffer (100 mM Tris-HCl pH 8.5, with 1 mM CuSO4) and Alexa Fluor 488–azide (Life Technologies) according to the manufacturer's protocol. Images were acquired on a DeltaVision Elite microscope (Applied Precision), taking 200-nm z-stacks with a PlanApo N 60× NA 1.42 objective (Olympus) and a Coolsnap HQ2 camera (Photometrics). Images were analysed after deconvolution using SoftWoRx (Applied Precision). Figures are maximum intensity projections of entire cells. Brightness and contrast were adjusted with Photoshop 6.0 (Adobe). For kinetochore stainings, since all proteins tested seemed to have lower levels in micronuclei, including centromeric proteins, all measurements were normalized to the average of 10 centromeres (CREST) in the primary nucleus (Fig. 4A,C).


Chromosomes trapped in micronuclei are liable to segregation errors

DNA in micronuclei is likely to get damaged. When shattered DNA from micronuclei gets reincorporated into the primary nucleus, aberrant rearrangements can take place, a phenomenon referred to as chromothripsis. Here, we investigated how chromatids from micronuclei act in subsequent divisions and how this affects their fate. We observed that the majority of chromatids derived from micronuclei fail to establish a proper kinetochore in mitosis, which is associated with problems in chromosome alignment, segregation and spindle assembly checkpoint activation. Remarkably, we found that, upon their formation, micronuclei already display decreased levels of important kinetochore assembly factors. Importantly, these defects favour the exclusion of the micronucleus over the reintegration into the primary nucleus over several divisions. Interestingly, the defects observed in micronuclei are likely overcome once micronuclei are reincorporated into the primary nuclei, as they further propagate normally. We conclude that the formation of a separate small nuclear entity represents a mechanism for the cell to delay the stable propagation of excess chromosome(s) and/or damaged DNA, by inducing kinetochore defects.

Keywords: Aneuploidy Chromosome segregation Micronucleus.

© 2018. Published by The Company of Biologists Ltd.

Conflict of interest statement

Competing interestsThe authors declare no competing or financial interests.


Watch the video: Micronucleus Assay. In Vitro Micronucleus Assay. In Vivo Micronucleus Assay (October 2022).