Production Of Chromosomal Aberrations Research Articles

Molecular mechanisms involved in the production of chromosomal aberrations: I. Utilization of neurospora endonuclease for the study of aberration production in G2 state of the cell cycle

Chinese hamster ovary cells (CHO) were X-irradiated in G2 state of the cell cycle and immediately treated, in the presence of inactivated Sendai virus, with Neurospora endonuclease (E.C. 3.1.4.), an enzyme which is specific for cleaving single-stranded DNA. With this treatment, the frequencies of all types of chromosome aberrations increased when compared to X-irradiated controls. These results are interpreted as due to the conversion of some of the X-ray induced singe-stranded DNA breaks into double-strand breaks by this enzyme. Similar enhancement due to this enzyme was found following treatment with methyl methanesulfonate (MMS) and bleomycin, but not following UV and mitomycin C. Addition of Micrococcus endonuclease and Neurospora endonuclease to the cells did not alter the frequencies of aberrations induced by UV. The introduction of enzymes with specific DNA-repair function offers possibilities to probe into the molecular events involved in the formation of structural chromosome aberrations induced by different classes of physical and chemical mutagens.

Mutagenicity tests with phenylbutazone in mammals

The ability of phenylbutazone to induce chromosome aberrations in mammals has been tested in the somatic and germ cells of male BALB/c mice. Induction of chromosomal aberrations was studied in bone marrow cells, 1, 2, 4 and 8 days after i.p. dosing of 400 mg kg phenylbutazone and polychromatic erythrocytes were examined for the presence of micronuclei 30 h after injection. The production of chromosome aberrations in germ cells was tested by the dominant lethality produced in the postmeiotic germ cell stages and the reciprocal translocations induced in the premeiotic one. All the tests yielded negative results. The in vitro observations reported in the literature as well some in vivo studies performed on humans suggest, however, that administration of this compound during long periods of time could result in the induction of chromosome anomalies.

The effect of the mode of administration of nitrogen mustard and cytosine arabinoside on the production of chromosomal aberrations in mouse bone marrow and ascites tumour cells

The cytogenetic effects of intraperitoneally (i.p.) and subcutaneously (s.c.) administered nitrogen mustard (HN2) and cytosine arabinoside (ara-C) on bone-marrow and ascites tumour cells of mice were studied. Ehrlich ascites tumour-bearing mice were treated with the mutagens, and cytological preparations were made from ascites tumour and bone-marrow cells of the same animal. The following parameters were investigated: frequencies of mitotic and chromosomal aberrations, time of aberration maxima and aberration spectra. HN2 (0.68 mg/kg b.w.), when given i.p., induced in ascites tumour cells a strong inhibition of mitotic frequency and very high aberration rates, whereas in bone marrow no aberrant chromosomes were observed. On the other hand, after s.c. administration, the same dose induced more aberrant metaphases in bone marrow than in tumour cells. Ara-C (315 mg/kg b.w.) resulted, after s.c. administration, in higher aberration frequencies both in ascites and bone-marrow cells compared with i.p. treatment. All ascites tumour cells showed higher aberration frequencies than bone-marrow cells. In bone marrow the aberration maximum occurred as soon as 6 h after treatment. Furthermore, clear differences with respect to the types of aberration found in the two systems were evident. The differences caused by the different modes of administration in two different types of cell are discussed in terms of metabolic inactivation and differences of the two tissues with respect to karyotype, cell cycle time and repair capacity.

The production of chromosome aberrations in various mammalian cells by triethylenemelamine.

The cytogenetic effects of triethylenemelamine (TEM) were studied using five different mammalian tissues. Treatments of 0.1 and 0.2 mg/kg TEM on differentiating mouse spermatogonia and bone marrow cells showed no significant differences in the frequency of chromosomal aberrations produced in these two tissues. At higher doses, however, the sensitivites of the two tissues appear to be different. The frequency of aberrations varies with time after treatment, with the greatest amount occurring at the latter fixation times. Results of an experiment on primary spermatocytes indicated a correlation between the frequency of chromosome aberrations and DNA replication. Human peripheral leukocytes were utilized in an attempt to clarify the cell-stage specificity of TEM-induced chromosome aberrations. Cultures were treated with TEM prior to PHA stimulation (G0), as well as various time intervals after stimulation (late G,1 S, and G2). The most sensitive stages of the cell cycle to aberration induction were later G1 and S, with chromatid aberrations the predominant type. A very low yield of chromosome damage was observed with the G0 and G1 treated stages. The experiments described tend to support the view that TEM is most effective at inducing aberrations when an intervening round of DNA replication has occurred.

UNUSUALLY HIGH INCIDENCE OF SPONTANEOUS CHROMOSOMAL ABERRATIONS IN MOUSE PRIMARY CELL CULTURE

Fibroblast cultures established from mouse embryos showed an abnormally high incidence of spontaneous chromosomal aberrations at early passages. The aberration frequency reached a peak (39.5%) at the 4th passage (13 days after initiation of the cultures), and then declined gradually. Culture media collected from the mouse cultures were found to be capable of inducing chromosomal aberrations in Chinese hamster cells. This indicates that some chromosome-damaging substances had evolved in the mouse primary cultures and were secreted into the culture medium. These substances seemed to affect cells very rapidly, since the production of chromosomal aberrations was detected as early as 2h after Chinese hamster cells were exposed to the conditioned medium derived from the mouse cultures. The substances appeared to be heat-labile, as the mouse conditioned medium lost its chromosome-damaging effect when it was prewarmed at 37°C for 24h. The nature of these toxic substances is, however, yet unknown. Preliminary studies on the primary cultures derived from other mammals imply that the phenomenon reported here is specific to certain groups of mammals except primates.

Mechanisms for sister chromatid exchanges and their relation to the production of chromosomal aberrations.

By taking advantage of the fact that fluorescent light (FL) induces strand breaks only in bromodeoxyuridine(BrdUy-substituted DNA, and that those breaks eventually lead to the formation of sister chromatid exchanges (SCEs), the response of SCEs to FL was studied carefully in Chinese hamster chromosomes in which, out of four DNA strands, BrdU-substitution had occurred either in one or three strands. The FL-induced SCE frequency did not differ greatly between these two types of chromosomes. However, when they were submitted to caffeine treatment, a drastic increase in the frequency was detected in the trifilarly-substituted chromosomes while a significant decrease occurred in the unifilarly-substituted chromosomes. Based on these results, a working hypothesis was developed that the SCE can arise by at least two different mechanisms, one operating at replicating points probably utilizing the machinery of DNA replication, and the other acting only in the post-replicational DNA portion, probably in a similar fashion as assumed in a general model of crossing over in the eukaryote. These dual mechansims may account for the discrepancy encountered in the explanations of the induction of SCEs by various exogenous agents as well as spontaneous SCEs. The present study also showed that some, but clearly not all, of chromatid deletions are the outcome of the failure to complete SCEs arising through these mechanisms.

Critical periods of the mitotic cycle: Influence of aminopterin and thymidine on production of chromosomal aberrations by radiation in Crepis capillaris

The influence of aminopterin (AP), tritiated thymidine ([ 3H] TdR) and “cold” thymidine (TdR) on production of chromosomal aberrations in meristematic cells of Crepis capillaris irradiated in different stages of the mitotic cycle with 300 rad of 60Co gamma-rays was studied. All the chemical treatments increased most of all the frequency of aberrations induced during two “critical periods” localized before the stage of DNA synthesis (fixation 9 h after irradiation) and before that of mitosis (4 h). Treatments with TdR and [ 3H] TdR increased most of all the frequency of chromatid aberrations when irradiation was performed in G 1, and the frequency of gaps when irradiated in G 2. Treatment with AP increased the yield of different types of aberration more uniformly. The modifying effect of the chemicals tested appeared to be independent of replicative synthesis. The “critical periods” are suggested to be the stages when regular “proof reading” and correction of spontaneous errors takes place [9,13]. In addition to this regular mechanism, radiation induces an “emergency” mechanism of repair. AP inhibits the mechanism of regular repair; in addition TdR and [ 3H] TdR suppress the lateral spread of primary injuries across the chromosome.

The effect of methylated oxypurines on the size of newlysynthesized DNA and on the production of chromosome aberrations after UV irradiation in Chinese hamster cells

The effect of methylated oxypurines on the size of newlysynthesized DNA and on the production of chromosome aberrations after UV irradiation in Chinese hamster cells

Does repair or stage sensitivity determine the shape of time-effect curves in radiation mutagenesis?

Seedlings of Crepis capillaris were irradiated after pulse-labelling with tritiated thymidine ([ 3 H]TdR), and both chromosomal aberrations and presence of silver grains were recorded in the same metaphase cells at various intervals throughout the whole mitotic cycle. The following results were obtained: ( a ) irradiated roots were homogeneous with respect to the number of aberrations, and heterogenous with respect to labelling index (LI); ( b ) time-effect curves for labelled (L) and unlabelled (U) cells showed no significant difference from one another; ( c ) no significant quantitative difference of aberration spectra produced in S and G 2 stages was found. These results support the view that the major factor which determines both quantitative and qualitative variation in the production of chromosomal aberrations by radiation is the time lapse between irradiation and fixation rather than relation of the time of irradiation to the time of DNA synthesis. In addition, it was found that labelling with [ 3 H]TdR modifies the effect of radiation on chromosomes.

Does repair or stage sensitivity determine the shape of time-effect curves in radiation mutagenesis?

Seedlings of Crepis capillaris were irradiated after pulse-labelling with tritiated thymidine ([3H]TdR), and both chromosomal aberrations and presence of silver grains were recorded in the same metaphase cells at various intervals throughout the whole mitotic cycle. The following results were obtained: (a) irradiated roots were homogeneous with respect to the number of aberrations, and heterogenous with respect to labelling index (LI); (b) time-effect curves for labelled (L) and unlabelled (U) cells showed no significant difference from one another; (c) no significant quantitative difference of aberration spectra produced in S and G2 stages was found. These results support the view that the major factor which determines both quantitative and qualitative variation in the production of chromosomal aberrations by radiation is the time lapse between irradiation and fixation rather than relation of the time of irradiation to the time of DNA synthesis. In addition, it was found that labelling with [3H]TdR modifies the effect of radiation on chromosomes.

X-ray and UV-induced chromatid aberrations: Evidence for polynemic chromosomes?

Ikushima and Wolff have recently interpreted both their observation of chromatid aberrations in second and third mitoses following X-irradiation and the production of chromatid type chromosomal aberrations by UV light administered during the G1 phase of the cell cycle in terms of a polyneme model of eukaryote chromosome structure. They were led to do so, however, largely because of their X-ray data, which they interpreted as evidence for the induction of sub-chromosomal lesions (by G1 irradiation; sub-chromatid for G2 irradiation) which appear as chromatid type aberrations only in later divisions. We here report data from similar X-ray experiments in which synchronized Chinese hamster tissue culture cells were irradiated in either G1 or G2 and then scored for chromatid aberrations in their first, second and third post-irradiation mitoses. Our results do not show the effect reported by Ikushima and Wolff. We conclude that all of the data available of aberration production is compatible with a simple mononeme model of eukaryote chromosome structure.

On the mechanism of production of chromosomal aberrations by ultraviolet radiation

On the mechanism of production of chromosomal aberrations by ultraviolet radiation

On the mechanism of production of chromosomal aberrations by ultraviolet radiation

On the mechanism of production of chromosomal aberrations by ultraviolet radiation

Genetic Effects of Radiation

The effects of radiation on biologic systems as manifested through genetic changes have been reviewed. The use of x-radiation by the health professions represents the largest contribution of radiation dose to the people of the United States. It is apparent that the genetic effect of radiation results in the production of chromosomal aberrations and gene mutations. Recognizing this, it becomes mandatory that appropriate measures are instituted to reduce to an absolute minimum the total amount of radiation that patients receive. Strict utilization of all known protective measures and adherence to protective guidelines promulgated by the ICRP and NCRP is imperative. Every attempt must be made to obtain maximal diagnostic yield from all radiation exposures used for diagnostic purposes, thereby assuring maximal benefit for our patients with minimal risk to our ancestors.

The effect of methylated oxypurines on the size of newly-synthesized DNA and on the production of chromosome aberrations after UV irradiation in chinese hamster cells

A comparison has been made, in Chinese hamster cells, of the ability of various methylated oxypurines to inhibit post-replication repair of DNA after UV irradiation and to potentiate UV-induced chromosome aberrations. DNA synthesized in UV-irradiated cells contains gaps, which are subsequently sealed by a process termed post-replication repair. In rodent cells this process is inhibited by caffeine and its analogues. This has been quantitated by measuring the molecular weight of the DNA synthesized in UV-irradiated cells during a 4-h pulse-labelling period in the presence or absence of inhibitors--the lower molecular weight the greater the inhibition. Eight methylated oxypurines were tested; caffeine and chlorocaffeine were always the most potent inhibitors, tetramethyluric acid was inactive, and the other five derivatives (methoxycaffeine, ethoxycaffeine, paraxanthine, theobromine and theophylline) had intermediate effects. Measurements of the potentiation of UV-induced chromosome aberrations showed that treatments with caffeine or chlorocaffeine again had the greatest effects, tetramethyluric acid and also theophylline had no potentiating activity, and methoxycaffeine was intermediate. This correlation between effects at the molecular and cytological levels is consistent with the hypothesis that the inhibition of post-replication repair by methylated oxypurines gives rise to the increased production of chromosome aberrations.

The effect of methylated oxypurines on the size of newly-synthesized DNA and on the production of chromosome aberrations after UV irradiation in chinese hamster cells☆

A comparison has been made, in Chinese hamster cells, of the ability of various methylated oxypurines to inhibit post-replication repair of DNA after UV irradiation and to potentiate UV-induced chromosome aberrations. DNA synthesized in UV-irradiated cells contains gaps, which are subsequently sealed by a process termed post-replication repair. In rodent cells this process is inhibited by caffeine and its analogues. This has been quantitated by measuring the molecular weight of the DNA synthesized in UV-irradiated cells during a 4-h pulse-labelling period in the presence or absence of inhibitors—the lower molecular weight the greater the inhibition. Eight methylated oxypurines were tested; caffeine and chlorocaffeine were always the most potent inhibitors, tetramethyluric acid was inactive, and the other five derivatives (methoxycaffeine, ethoxycaffeine, paraxanthine, theobromine and theophylline) had intermediate effects. Measurements of the potentiation of UV-induced chromosome aberrations showed that treatments with caffeine or chlorocaffeine again had the greatest effects, tetramethyluric acid and also theophylline had no potentiating activity, and methoxycaffeine was intermediate. This correlation between effects at the molecular and cytological levels is consistent with the hypothesis that the inhibition of post-replication repair by methylated oxypurines gives rise to the increased production of chromosome aberrations.

Biological effects of ultrasound

When ultrasound is absorbed by tissue, heat is produced which may be destructive or, if controlled, can be therapeutic. In addition, ultrasound produces biological effects which cannot be explained on the basis of heating alone. Under certain exposure conditions production of ultrasonic lesions in brain tissue can be explained on a purely thermal basis. Examples of nonthermal effects of ultrasound include changes in growth, mitotic index and the production of chromosomal aberrations in plant roots.

Mechanisms of chromosomal aberration production, III. Chemicals and ionizing radiation , , Mutation Res., 23 (1974) 197–212

Mechanisms of chromosomal aberration production, III. Chemicals and ionizing radiation , , Mutation Res., 23 (1974) 197–212

The significance of radiation-induced chromosome abnormalities in radiological protection.

A brief review is given of the production and analysis of chromosome aberrations induced by ionizing radiation. The various tissues in which it is possible to demonstrate aberrations are noted and particular emphasis is laid on the culture of peripheral blood lymphocytes. Some examples of recent applications of the technique are described. These are in the determination of suspected overdoses to radiation workers, in estimating doses to radiotherapy patients, and investigating the depth/biological profile for a negative π meson beam.

Mechanisms of chromosomal aberration production III. Chemicals and ionizing radiation

• A general model for the production of aberrations in eukaryote chromosomes is proposed. The basic assumptions of this model are: • (1) The chromosome is mononeme, containing but a single DNA double helix before replication; (2) Aberrations result only from lesions in DNA; (3) The primary lesions may be either polynucleotide strand breaks or altered bases which are converted to strand breaks either through the operation of enzymatic repair mechanisms or as a consequence of normal semiconservative DNA replication; (4) Final expression of polynucleotide strand breaks as chromosomal aberrations of various types is the consequence of the operation of repair mechanisms, DNA replication, and a single strand DNAase. • It is shown that this model is consitent with the available data on chromosomal aberration production by a variety of chemical agents as well as by ionizing radiation. In particular, it accounts for the observed differences in the types of aberrations produced by these two classes of aberration producing agents at different points in the cell cycle.