Dicentric Formation Research Articles

Comparative analysis of the yields of dicentrics and chromosomal translocations

Purpose Chromosomal dicentrics and translocations are commonly employed as biomarkers to estimate radiation doses. The main goal of this article is to perform a comparative analysis of yields of both types of aberrations. The objective is to determine if there are relevant distinctions between both yields, allowing for a comprehensive assessment of their respective suitability and accuracy in the estimation of radiation doses. Materials and methods The analysis involved data from a partial-radiation simulation study with the calibration data obtained through two scoring methods: conventional and PAINT modified. Subsequently, a Bayesian bivariate zero-inflated Poisson model was employed to compare the posterior marginal density of the mean of dicentrics and translocations and assess the differences between them. Results When employing the conventional method of scoring, the findings indicate that there is no notable disparity between the yield of observed translocations and dicentrics. However, when utilizing the PAINT modified method, a notable discrepancy is observed for higher doses, indicating a relevant difference in the mean number of the two types of aberrations. Conclusions The choice of scoring method significantly influences the analysis of radiation-induced aberrations, especially when distinguishing between complex and simple chromosomal formations. Further research and analysis are necessary to gain a deeper understanding of the factors and mechanisms impacting the formation of dicentrics and translocations.

Postirradiation temperature influences DSB repair and dicentric chromosome formation-potential impact for dicentric chromosome analysis in interlaboratory comparisons.

The objective was to investigate the influence of different pre-storage temperatures in the dicentric chromosome analysis (DCA) protocol (22°C vs. 37°C) by using γ-H2AX+53BP1 foci as a marker for deoxyribonucleic acid (DNA) double-strand break (DSB) damage induction and repair and the formation of dicentric chromosomes as a result of mis-repair. Repair of γ-H2AX+53BP1 DSB foci was absent in samples that were incubated for 2h at 22°C after exposure of 0.5 and 1.2Gy. When 0.5- and 1.2-Gy-exposed samples were incubated at 37°C for 2h, there was an average decline of 31 and 52% of DSB foci, respectively. This indicated that DNA repair occurred. There was a 27% decrease in dicentric chromosome yield at 1.2Gy and a 15% decrease at 3.5Gy after post-irradiation incubation for 2 h at 37°C relative to the observed dicentric frequencies at 22°C. Recommended to re-phase: our data suggested that there were more open DSBs after a 2-h incubation at 22°C, which contributed to more mis-repair and dicentric formation from the start of culture. Our findings are corroborated by publications showing that lesion interaction based on enzymatic activity is suppressed below 21°C. As such temperature variations can be a source of variation in DCA during interlaboratory comparison studies, we propose to establish a common guide for the standardisation of pre-culture conditions in cytogenetic dosimetry proficiency testing.

Relative Biological Effectiveness and Non-Poissonian Distribution of Dicentric Chromosome Aberrations after Californium-252 Neutron Exposures of Human Peripheral Blood Lymphocytes.

Cells exposed to fast neutrons often exhibit a non-Poisson distribution of chromosome aberrations due to the high ionization density of the secondary reaction products. However, it is unknown whether lymphocytes exposed to californium-252 (252Cf) spectrum neutrons, of mean energy 2.1 MeV, demonstrate this same dispersion effect at low doses. Furthermore, there is no consensus regarding the relative biological effectiveness (RBE) of 252Cf neutrons. Dicentric and ring chromosome formation was assessed in human peripheral blood lymphocytes irradiated at doses of 12-135 mGy. The number of aberrations observed were tested for adherence to a Poisson distribution and the maximum low-dose relative biological effectiveness (RBEM) was also assessed. When 252Cf-irradiated lymphocytes were examined along with previously published cesium-137 (137Cs) data, RBEM values of 15.0 ± 2.2 and 25.7 ± 3.8 were found for the neutron-plus-photon and neutron-only dose components, respectively. Four of the five dose points were found to exhibit the expected, or close to the expected non-Poisson over-dispersion of aberrations. Thus, even at low doses of 252Cf fast neutrons, when enough lymphocyte nuclei are scored, chromosome aberration clustering can be observed.

O40. The cytogenetic response of human T-lymphocytes to low doses of p(66)/Be neutrons and heterogeneous exposures to 60Co [formula omitted]-rays

Introduction Radiological health concerns for individuals exposed to ionizing radiation are governed by both the extent of exposure, as well as the microscopic dose distribution of the radiation modality. Several quantitative biological endpoints have been developed for radiation dose estimation and are employed worldwide. For real world biodosimetry applications, qualitative aspects such as the radiation type and homogeneity of exposure are vital in the decision making process with respect to suitable medical interventions. Materials and methods Whole blood samples collected from two consenting adults were exposed to 60 Co γ -rays to doses ranging from 1–6 Gy and 0–2 Gy p(66)/Be neutrons. The samples exposed to 60 Co γ -rays were subsequently diluted with un-irradiated blood to yield a series of equivalent total body doses (ETBD) from 0 up to 4 Gy. Dicentric formation frequencies in T-lymphocyte metaphase spreads were enumerated with the aid of a semi-automated image analysis microscopy system. Results Dicentric formation induction frequencies were used to estimate whole body doses for each sample respectively. Estimated whole body doses where compared to the equivalent total body dose (ETBD) and found to be in agreement (Pearson’s ρ 0.97 p ( σ 2 / y ¯ ≥ 1.2 ) and high LET neutron samples ( σ 2 / y ¯ ≈ 1.2 ) were found to be over-dispersed assuming a Poisson distribution applies to the induction of dicentric formations in cells. Conclusion The dispersion parameter proves to be a useful addition to the dicentric chromosome assay to ascertain qualitative aspects of the exposure conditions required for effective population triage for samples analysed with the high throughput automated image analysis system.

O.4 - A comparative study of the cytogenetic responses for homo- and heterogeneous exposures of human T-lymphocytes

Introduction: Biological dosimetry is central in the assessment and mitigation of large scale radiation accidents and occupational over-exposures. Several biological endpoints have been successfully employed to estimate doses for both in vitro and in vivo exposures. Comprehensive statistical analysis of the dose–response parameters can yield more information than mere quantitative dose estimates. Qualitative aspects of the radiation type and dose distribution can be predicted, which is important for real world biodosimetry applications. Materials and Methods: Equivalent total body dose estimates were prepared for blood samples exposed to 60Co gamma-rays at doses ranging from 1 to 6Gy. The samples were subsequently dilutedwith sham irradiated blood to yield a range of total body dose equivalents between 0 and 4 Gy. Dicentric formation frequency in lymphocyte metaphase spreads was quantified using a semi-automated image analysis system. Results: Cytogenetic aberration frequencies for each irradiation and dilution condition were translated to whole body dose values using dose– response curves established in the laboratory. The measured values were in agreement with the calculated estimates (P-value > 0.05). The overdistribution of chromosomal aberrations correlated with the non-uniformity of the radiation applied; which is reflected by the indices of dispersion (σ2/ μ > 1.2) for heterogeneously exposed samples. Conclusion: The degree of non-uniformity of exposures can be predicted on the basis of over-dispersion parameters calculated using advanced statistical analysis of dicentric frequency distributions.

Antigenotoxic potential of rutin and quercetin in Swiss mice exposed to gamma radiation.

Ionizing radiation induces a variety of genetic damages through the formation free radicals such as reactive oxygen species (ROS). Appropriate antioxidant intervention may inhibit or reduce free radical toxicity and thus offer protection against radiation. Rutin (RUT) and quercetin (QRT) are flavonoids known to be potent dietary antioxidants. The present study tested the antigenotoxic effect of RUT and QRT in vivo against radiation- induced chromosomal damage. Swiss albino mice were administered orally with RUT and QRT (10 and 20 mg/kg b.wt.) once daily for five consecutive days. One hour after the last administration of RUT and QRT on the fifth day, the animals were whole body exposed to 3 Gy gamma radiation. The anti-genotoxic potential was assessed in terms of chromosomal aberrations, micronucleus test, and alkaline comet assay. Significant decline in dicentric formation was observed in RUT and QRT treated group. Further, the antigenotoxic potential of RUT and QRT caused a significant (p < 0.001) reduction in micronucleated polychromatic, normochromatic erythrocytes; increased PCE/NCE ratio was observed in the RUT and QRT treated group. Administration of RUT and QRT before irradiation resulted in a significant (p < 0.01) decrease in the DNA damage at the post-irradiation time when compared with irradiation alone group. Present findings demonstrate the potential of RUT and QRT in mitigating radiation-induced mortality and cytogenetic damage, which may be attributed to scavenging of radiation-induced free radicals.

Track structure based modelling of chromosome aberrations after photon and alpha-particle irradiation

A computational model of radiation-induced chromosome aberrations in human cells within the PARTRAC Monte Carlo simulation framework is presented. The model starts from radiation-induced DNA damage assessed by overlapping radiation track structures with multi-scale DNA and chromatin models, ranging from DNA double-helix in atomic resolution to chromatin fibre loops, heterochromatic and euchromatic regions, and chromosome territories. The repair of DNA double-strand breaks via non-homologous end-joining is followed. Initial spatial distribution and complexity, diffusive motion, enzymatic processing, synapsis and ligation of individual DNA ends from the breaks are simulated. To enable scoring of different chromosome aberration types resulting from improper joining of DNA fragments, the repair module has been complemented by tracking the chromosome origin of the ligated fragments and the positions of centromeres. The modelled motion of DNA ends has sub-diffusive characteristics and corresponds to measured chromatin mobility within time-scales of a few hours. The calculated formation of dicentrics after photon and α-particle irradiation in human fibroblasts is compared to experimental data (Cornforth et al., 2002, Radiat Res 158, 43). The predicted yields of dicentrics overestimate the measurements by factors of five for γ-rays and two for α-particle irradiation. Nevertheless, the observed relative dependence on radiation dose is correctly reproduced. Calculated yields and size distributions of other aberration types are discussed. The present work represents a first mechanistic approach to chromosome aberrations and their kinetics, combining full track structure simulations with detailed models of chromatin and accounting for the kinetics of DNA repair.

A simple and rapid fluorescence in situ hybridization microwave protocol for reliable dicentric chromosome analysis

Fluorescence in situhybridization (FISH) is an extremely effective and sensitive approach to analyzing chromosome aberrations. Until recently, this procedure has taken multiple days to complete. The introduction of telomeric and centromeric peptide nucleic acid (PNA) probes has reduced the procedure's duration to several hours, but the protocols still call for a high temperature (80–90°C) step followed by 1–3 h of hybridization. The newest method to speed up the FISH protocol is the use of a microwave to shorten the heating element to less than a minute; however this protocol still calls for a 1-h hybridization period. We have utilized PNA centromere/telomere probes in conjunction with a microwave oven to show telomere and centromere staining in as little as 30 s. We have optimized the hybridization conditions to increase the sensitivity and effectiveness of the new protocol and can effectively stain chromosomes in 2 min and 30 s of incubation. We have found that our new approach to FISH produces extremely clear and distinct signals. Radiation-induced dicentric formation in mouse and human fibroblast cells was analyzed by two individual scorers and the observed dicentrics matched very well.

Concentration‐Dependent Protection by Ethanol Extract of Propolis against γ‐Ray‐Induced Chromosome Damage in Human Blood Lymphocytes

Radioprotection with natural products may be relevant to the mitigation of ionizing radiation-induced damage in mammalian systems; in this sense, propolis extracts have shown effects such as antioxidant, antitumoral, anti-inflammatory, and immunostimulant. We report for the first time a cytogenetic study to evaluate the radioprotective effect, in vitro, of propolis against radiation-induced chromosomal damage. Lymphocytes were cultured with increasing concentrations of ethanol extract of propolis (EEP), including 20, 40, 120, 250, 500, 750, 1000, and 2000 μg mL−1 and then exposed to 2 Gy γ-rays. A significant and concentration-dependent decrease is observed in the frequency of chromosome aberrations in samples treated with EEP. The protection against the formation of dicentrics was concentration-dependent, with a maximum protection at 120 μg mL−1 of EEP. The observed frequency of dicentrics is described as negative exponential function, indicating that the maximum protectible fraction of dicentrics is approximately 44%. Free radical scavenging and antioxidant activities are the mechanisms that these substances use to protect cells from ionizing radiation.

Telomere Disruption Results in Non-Random Formation of De Novo Dicentric Chromosomes Involving Acrocentric Human Chromosomes

Genome rearrangement often produces chromosomes with two centromeres (dicentrics) that are inherently unstable because of bridge formation and breakage during cell division. However, mammalian dicentrics, and particularly those in humans, can be quite stable, usually because one centromere is functionally silenced. Molecular mechanisms of centromere inactivation are poorly understood since there are few systems to experimentally create dicentric human chromosomes. Here, we describe a human cell culture model that enriches for de novo dicentrics. We demonstrate that transient disruption of human telomere structure non-randomly produces dicentric fusions involving acrocentric chromosomes. The induced dicentrics vary in structure near fusion breakpoints and like naturally-occurring dicentrics, exhibit various inter-centromeric distances. Many functional dicentrics persist for months after formation. Even those with distantly spaced centromeres remain functionally dicentric for 20 cell generations. Other dicentrics within the population reflect centromere inactivation. In some cases, centromere inactivation occurs by an apparently epigenetic mechanism. In other dicentrics, the size of the α-satellite DNA array associated with CENP-A is reduced compared to the same array before dicentric formation. Extra-chromosomal fragments that contained CENP-A often appear in the same cells as dicentrics. Some of these fragments are derived from the same α-satellite DNA array as inactivated centromeres. Our results indicate that dicentric human chromosomes undergo alternative fates after formation. Many retain two active centromeres and are stable through multiple cell divisions. Others undergo centromere inactivation. This event occurs within a broad temporal window and can involve deletion of chromatin that marks the locus as a site for CENP-A maintenance/replenishment.

Relationship between heterochromatic interstitial telomeric sequences and chromosome damage induced by the radiomimetic compound streptonigrin in Chinese hamster ovary cells

The relationship between (heterochromatic) interstitial telomeric sequences (ITSs) and the chromosome damage induced by the radiomimetic compound streptonigrin (SN) was investigated in Chinese hamster ovary (CHO) cells by using PNA- and Q-FISH techniques with a pantelomeric probe. CHO cells were exposed to increasing concentrations of SN and chromosomal aberrations were analyzed in the first mitosis after treatment. Cytogenetic analysis revealed that 16.9% and 11.7% of the total aberrations induced by SN in cells harvested 18 h and 3 h after treatment, respectively, exhibited one or more FISH-detectable telomeric signals. Although there was a significant induction by SN of chromosome breaks at centromeric regions containing ITSs, about 70% of the chromosome breaks exhibiting telomeric signals observed in SN-treated cells occurred outside the centromeric regions of chromosomes. This observation, along with the finding of entirely labeled acentric fragments in both untreated and SN-treated cells show that, although this antibiotic induces breakage at centromeric regions containing ITSs, these chromosome regions are not the preferential target for the clastogenic action of SN. In addition, our results show that heterochromatic ITSs are involved more than expected in the formation of chromatid breaks and exchanges induced by SN, and that these sequences are not preferentially involved in the formation of dicentrics, multicentrics, centric rings, chromosome breaks, acentric fragments and chromatid deletions induced by this antibiotic. These findings indicate that the involvement of heterochromatic ITSs in the chromosome damage induced by SN is not random. Moreover, our results show that SN induces telomeric repeats translocations, although this effect depends on the concentration of the drug, and that this antibiotic increases the size of ITSs, this latter effect not being related to the chromosomal sensitivity of the exposed cells to this compound. The mechanism by which SN induces amplification of heterochromatic ITSs remains to be elucidated.

Effect of bleomycin on interstitial telomeric sequences of immortalized Chinese hamster ovary cells

The effect of the radiomimetic compound bleomycin (BLM) on interstitial telomeric sequences (ITSs) was investigated in Chinese hamster ovary (CHO) cells by using PNA-FISH with a pantelomeric probe. CHO cells were exposed to increasing concentrations of BLM and chromosomal aberrations were analyzed in the first mitosis after treatment. Cytogenetic analysis revealed that 18.1% and 9.5% of the total aberrations observed in cells exposed to BLM and harvested 18 h and 3 h after treatment, respectively, exhibited one or more FISH-detectable telomeric signals. Most of the chromosome breaks exhibiting telomeric signals observed in BLM-treated cells occurred in the centromeric regions of chromosomes. This observation, along with the finding of entirely labeled acentric fragments in BLM-exposed cells but not in untreated cells, shows that this antibiotic induces breakage at chromosomal sites containing ITSs. In addition, our results show that heterochromatic ITSs are involved more than expected in the formation of chromosome/chromatid breaks – and perhaps chromatid exchanges – induced by BLM, taking into account the percentage of the genome covered by telomeric sequences. On the contrary, our data strongly suggest that ITSs are not preferentially involved in the formation of dicentrics, multicentrics, centric rings, acentric fragments or chromatid deletions induced by BLM. Moreover, our results show that BLM is capable of inducing amplification and translocation of telomeric repeats, and suggest that this antibiotic produces breakage within centromeric ITSs, although chromosome regions containing these sequences are not the preferential target for BLM clastogenic action. On the other hand, our results show that BLM treatment increases the size of ITSs and that this effect is not related to the chromosomal sensitivity of the exposed cells to this compound.

Relative Biological Effectiveness (RBE) and Dose Rate Dependent Ratio of Translocation to Dicentric Chromosome Yield in 252 Cf Neutrons

The relative biological effectiveness (RBE) of 252 Cf neutrons at different dose rates (2, 0.2&0.02 cGy/min) was assessed in human lymphocyte and bone marrow cells using cytogenetic end points (by Giemsa staining). The RBE values for 1 Gy of 252 Cf neutrons for chromosomal aberration yield in lymphocyte at the dose rates of 2 and 0.02 cGy/min were 3.3 and 12.0, respectively, in comparison to that of 60 Co γ - or 137 Cs γ -rays. RBE values of Cf(n) in human bone marrow were determined for the first time in the present study, and were 6.5 for chromatid-type and 4.4 for chromosome-type aberrations at the dose rate of 2 cGy/min. These values were higher than those of lymphocytes obtained in the present study. As studied by FISH method, the exposure of 252 Cf neutrons and 60 Co γ - and 137 Cs γ -rays at different dose rates also revealed the fact that the ratio of the dicentric chromosome yield to the translocation yield was influenced by LET and dose rates. No dose rate effect was found for the induction of dicentric chromosome aberrations. But an increase in the incidence of translocation was observed in the 252 Cf neutrons exposure at a dose rate of 0.02 cGy/min. These results suggest that the formation of dicentrics and translocations differed with source of radiation and dose rate.

Relative biological effectiveness (RBE) and dose rate dependent ratio of translocation to dicentric chromosome yield in 252Cf neutrons

The relative biological effectiveness (RBE) of 252 Cf neutrons at different dose rates (2, 0.2&0.02 cGy/min) was assessed in human lymphocyte and bone marrow cells using cytogenetic end points (by Giemsa staining). The RBE values for 1 Gy of 252 Cf neutrons for chromosomal aberration yield in lymphocyte at the dose rates of 2 and 0.02 cGy/min were 3.3 and 12.0, respectively, in comparison to that of 60 Co γ - or 137 Cs γ -rays. RBE values of Cf(n) in human bone marrow were determined for the first time in the present study, and were 6.5 for chromatid-type and 4.4 for chromosome-type aberrations at the dose rate of 2 cGy/min. These values were higher than those of lymphocytes obtained in the present study. As studied by FISH method, the exposure of 252 Cf neutrons and 60 Co γ - and 137 Cs γ -rays at different dose rates also revealed the fact that the ratio of the dicentric chromosome yield to the translocation yield was influenced by LET and dose rates. No dose rate effect was found for the induction of dicentric chromosome aberrations. But an increase in the incidence of translocation was observed in the 252 Cf neutrons exposure at a dose rate of 0.02 cGy/min. These results suggest that the formation of dicentrics and translocations differed with source of radiation and dose rate.

Effect of immobilized laminin on karyotypic variability in two karyotypically different variants of the indian muntjac skin fibroblast cell line

The numerical and structural karyotypic variability has been investigated in the Indian muntjac skin fibroblasts "markerless" cell line MT and in its karyotypic variant MT(d) cultivated on the laminin 2/4 coated surface. In cell line MT preincubated in serum free medium for 2.5 and 1 h and then cultivated on the laminin-coated surface in the serum-containing medium for 1, 2 and 3 days, the character of cell distribution for the chromosome number has changed. These changes involve a significant decrease in frequency of cells with modal number of chromosomes, and an increase in frequency of cells with lower chromosomal number. Some new additional structural variants of the karyotype (SVK) appeared. The observed alterations seem to be due to disturbances of chromosome segregation and establishing a new advantageous balance karyotypic structure. The karyotypic variant MT(d) distinguished from MT by the increased number of dicentrics (telomeric associations) and cultivated under the same conditions showed no change in the character of cell distribution for the chromosome number. In cell line MT, the frequency of chromosomal aberrations did not change relative to control variants. In karyotypic variant MT(d) under the same conditions. the frequency of chromosomal aberrations significantly increases in 3 days mainly due to formation of dicentrics. These results confirm the conclusion that, similarly to aneuploidy, formation of dicentrics in "markerless" cell lines appears to be the way for cell population to adapt to unfavourable factors of the environment. Possible reasons for differences in the character of the numerical and structural karyotypic variability between cell line MT and its karyotypic variant MT(d) are discussed.

Novel mechanisms of gene disruption at the medulloblastoma isodicentric 17p11 breakpoint

Isodicentric 17q is the most commonly reported chromosomal abnormality in medulloblastomas. Its frequency suggests that genes disrupted in medulloblastoma formation may play a role in tumorigenesis. We have previously identified two chromosome 17 breakpoint at a 1 Mb resolution. Our aims were to accurately map the position of these breakpoints and to identify mechanisms of gene disruption at this site. CGH with a custom tiling path genomic BAC array of chromosome 17 enriched with fosmids at the breakpoint regions was used to analyze a series of 45 medulloblastomas and three medulloblastoma-derived cell lines. In total, 17 of 45 medulloblastomas had an isodicentric 17q. Two breakpoint regions were identified and their positions were mapped. The array identified a more complex arrangement at the breakpoint than has been reported previously using lower resolution BAC arrays. The patterns observed indicated that dicentric chromosome formation occurs both via nonallelic homologous recombination between palindromically arranged low copy repeats (the previously accepted mechanism) and by recombination between nonidentical sequences. In addition, novel alternative structural alterations, a homozygous deletion and a duplication, were identified within the chromosome breakpoint region in two cases. At the resolution of the array, these structural alterations spanned the same genes as cases with dicentric 17q formation, implying that the disruption of genes at the chromosome breakpoint itself may be of greater biological significance than has previously been suspected.

Maternal paracentric inversion of chromosome 9 and recurrent pregnancy loss: Identification by Preimplantation Genetic Diagnosis (PGD) of a putative dicentric chromosome 9 in blastomeres from 6–8 cell cleaving embryos

Paracentric chromosome inversions occur when a single chromosome undergoes two breaks and recombines with the segment between the two breaks inverted. Paracentric inversions do not include the centromere. Inversion carriers are most often phenotypically normal, however they are at risk of producing genetically unbalanced gametes due to recombination within inverted segments. The traditional model for the meiotic behavior of a pair of chromosomes heterozygous for a paracentric inversion assumes occasional crossing over within the inverted region. When this occurs, a dicentric and an acentric are formed. When the dicentric’s two centromeres subsequently separate toward opposite poles, it breaks into two monocentrics. Resulting cells will have deficiencies, and may have duplications, of genetic material. Crossing over need not occur within the inversion; therefore chromosomally balanced gametes predominate. As unbalanced gametes are relatively rare and most of these would result in early pregnancy loss, paracentric inversions are rarely found to be involved in reproductive failure. Two recent cases of unbalanced live-born progeny with intact dicentrics have been described. It appears that, in these cases, one of the two centromeres inactivated immediately after dicentric formation with subsequent migration of an intact dicentric into the secondary oocyte or ootid. Therefore, we will determine the cytogenetic status of embryos from a female paracentric inversion carrier. Analysis of embryonic cells apparently with a derived dicentric chromosome. Case report. In vitro fertilization (IVF) and PGD was performed on a couple due to three pregnancy losses. The husband has normal semen parameters. The 36 year old female is a carrier of a paracentric inversion of chromosome 9[46, XX, inv(9)(q21.2q22.3)]. PGD-aneuploidy was first performed for chromosomes 9, 14, 15, 22, X and Y. We next performed PGD for teleomeric sequences of chromosome 9. Routine protocols were followed. Microscopy was performed using an epi-fluorescent microscope and multiple fluorescent signal detection was accomplished using a Spectral Cube imaging system. Eleven of 13 embryos were aneuploid. Seven of the 11 showed three chromosome 9 centromeres. As the standard model of paracentric behavior does not predict trisomic progeny, 9p and 9q telomere sequences were analyzed to determine whether entire chromosome 9s were present within the blastomeres. Five of 7 trisomy 9 blastomeres showed three 9p and one 9q sequence. The other two showed two 9p and two 9q sequences. Each of the remaining (n = 6) diploid chromosome 9 embryos tested showed the correct number of 9 telomeric sequences expected from two entire chromosome 9s. Dicentrics whose centromeres are joined by their q arms will have two p-arm and no q-arm telomeric sequences. Cells with a dicentric and a normal chromosome will therefore have a total of 3 p-arm and one q-arm telomeres. This was found in 5 of 7 embryos with three chromosome 9 centromeres. The apparent presence of a dicentric chromosome in a high percentage of embryos suggests the possibility that the recombinational event took place during a mitotic division in the maternal germ line. To our knowledge, this is the first report of a dicentic chromosome in embryos from couples undergoing IVF-PGD and the first suggesting mitotic recombination as a mechanism for the generation of a dicentric chromosome.

Telomeric fusion as a mechanism for the loss of 1p in meningioma

Characteristic cytogenetic aberrations are found in the various histopathological designations of meningioma. These aberrations range from the loss of 22q in histologically benign tumors to complex hypodiploid karyotypes in atypical and malignant tumors. This progression is characterized by increasing chromosome loss and instability, with a critical step being the loss of 1p. We report a detailed cytogenetic investigation of chromosome aberrations in a series of 88 meningiomas using Giemsa banding and multicolor spectral karyotyping (SKY). Clonal chromosome aberrations were identified in 46 (52%) tumors by G banding. Thirty-five tumors showing complex chromosome aberrations not fully characterized by G banding were subsequently reanalyzed by SKY. The SKY technique refined the G-band findings in 18 (51%) of the tumors on which it was applied. The most common features of cytogenetic progression in the complex karyotypes were chromosome arm–specific losses relating to the formation of deletions and dicentric chromosomes involving 1p. Part or all of 1p was lost in 19 tumors. Five tumors showed evidence for the loss of 1p in a progressive step-wise series of telomeric fusions involving the formation of unstable intermediates. Five recurring dicentric chromosomes were identified, including dic (1;11)(p11;p11), dic(1;12)(p12∼p13;p11), dic(1;22)(p11;q12∼q13), dic(7;19)(p11;p11), and dic(19;22)(p11∼p13;q11∼q13). These findings provide evidence that telomeric fusions play a role in the formation of clonal deletions, dicentrics, and unbalanced translocations of 1p. The loss of 1p has possible diagnostic and prognostic implications in the management of meningioma.

Post-treatment effects of DNA topoisomerase inhibitors on UVB- and X-ray-induced chromosomal aberration formations

Post-treatments with nogalamycin, an inhibitor of DNA topoisomerase I, for last 3 h of the culture (during the G 2 phase) drastically enhanced the yield of ultraviolet light B (UVB)-induced exchange-type chromatid aberrations, while showing little effect on the formation of breakage-type aberrations in Chinese hamster V79 cells. These results are very similar to those obtained with ICRF-193, an inhibitor of topoisomerase II, with respect to the effect on UVB-induced chromatid aberrations. Thus, both types of topoisomerases may suppress the formation of exchange-type chromatid aberrations in the G 2 phase which is suggested to be the principal stage of the cell cycle for chromatid aberration formation. In human lymphocytes irradiated with X-rays before phytohaemagglutinin (PHA) stimulation, post-treatments with nogalamycin through the whole cell cycle enhanced only the yield of dicentrics, while showing little effect on the yields of any other chromosome-type aberrations. Nogalamycin added 6 h after PHA stimulation to irradiated cells also showed almost the same effects, whereas, addition of nogalamycin 24 h after PHA stimulation showed no effect on X-ray-induced chromosome-type aberrations. These results suggest that X-ray-induced DNA damage lead to chromosome-type aberrations before the start of S phase and topoisomerase I may suppress the formation of dicentrics, exchange-type chromosome aberrations. Post-treatments with ICRF-193 showed no effect on the formation of X-ray-induced chromosome-type aberrations, suggesting nonparticipation of topoisomerase II in this process.

Drinking beer reduces radiation-induced chromosome aberrations in human lymphocytes.

We here investigated and reported the effects of beer drinking on radiation-induced chromosome aberrations in blood lymphocytes. Human blood that was collected either before or after drinking a 700 ml beer was in vitro irradiated with 200 kVp X rays or 50 keV/microm carbon ions. The relation between the radiation dose and the aberration frequencies (fragments and dicentrics) was significantly (p < 0.05) lower for lymphocytes collected 3 h after beer drinking than those before drinking. Fitting the dose response to a linear quadratic model showed that the alpha term of carbon ions was significantly (p < 0.05) decreased by beer drinking. A decrease of dicentric formation was detected as early as 0.5 h after beer drinking, and lasted not shorter than 4.5 h. The mitotic index of lymphocytes was higher after beer drinking than before, indicating that a division delay would not be responsible for the low aberrations induced by beer drinking. An in vitro treatment of normal lymphocytes with 0.1 M ethanol, which corresponded to a concentration of 6-times higher than the maximum ethanol concentration in the blood after beer drinking, reduced the dicentric formation caused by X-ray irradiation, but not by carbonion irradiation. The beer-induced reduction of dicentric formation was not affected by serum. It is concluded that beer could contain non-ethanol elements that reduce the chromosome damage of lymphocytes induced by high-LET radiation.