Frequency of sister chromatid exchanges in cigarette smokers

Summary The effect of cigarette smoking on the frequency of sister chromatid exchanges (SCEs) was investigated in a group of adult men. It was observed that there was a significant increase in the mean SCE frequency per cell in smokers. Both the duration of smoking and the number of cigarettes smoked per day appeared to influence SCE frequency.     

Frequency of sister chromatid exchanges in severe protein calorie malnutrition.

Nine children with severe protein calorie malnutrition were studied regarding the frequency of sister chromatid exchanges (SCE's) in peripheral blood lymphocytes. The results showed that there was no significant difference between the number of SCE's in the malnourished children as compared to an adequate control group. An interesting finding was that the proportion of 3rd or subsequent division metaphases found in the malnourished children, was higher and significantly different from that seen in the control group.     

Frequency and sites of sister chromatid exchanges in rat kangaroo chromosomes

The frequency of sister chromatid exchanges in the chromosomes of a cell line from the Tasmanian rat kangaroo was determined to be 0.79 exchanges per chromosome for two cell cycles. Twenty-five percent of these exchanges occurred at the kinetochore. The mean frequency of exchanges per chromosomal arm was roughly proportional to the length of the chromosome, with the exception of a mean frequency of 0.20 exchanges per chromosome found at the kinetochore of all chromosomes, regardless of length. Thus, the kinetochore is a highly preferential site for sister chromatid exchanges. Compared to the main portion of the chromosomal arms the exchange frequency was somewhat lower adjacent to the kinetochore and at chromosome ends. The number of exchanges per unit length also tended to be lower for the short arm of chromosome 1. No correlation was found between the frequency of exchanges and late-replicating DNA.     

Statistical evaluation of sister chromatid exchanges

Summary Log-linear models are fitted to sister chromatid exchange (SCE) scores in order to test the significance of the differences in SCE scores observed between individuals or between experimental treatments. The analysis is performed at the level of chromosome groups. In each single test all measurements from all chromosome groups, both from the control and from the experimental sets, are utilized. By proceeding in this way full use is made of all the available information on the SCE scores at the level of chromosome groups and the shortcomings of the classical Student-t and chi-square tests are avoided.This work was supported by a grant Geconcerteerde Acties from the Belgian Government.     

Frequency of sister chromatid exchanges in oncological patients during treatment with cyclophosphane

The sister chromatid exchange (SCE) level in patients with cancer of lungs before treatment did not differ from the mean number of SCE in healthy donors. In the process of a cyclophosphane treatment the SCE frequency in the patient lymphocyte culture increased with the drug doses of 4 and 5 g. Analysis of the ratio of cells in mitoses I, II and III revealed no differences in the cell cycle rate for groups of healthy donors, patients before the treatment, and treated patients.     

Sister chromatid exchanges in balanced translocation carriers and in patients with unbalanced karyotypes

Summary Sister chromatid exchanges (SCEs) were studied in peripheral human leukocytes from 16 patients with balanced translocations or with unbalanced karyotypes, and from 4 controls. No difference was seen between these two groups of people in the mean number of SCEs per cell, or in the total number of SCEs observed for each pair of autosomes involved in the translocations studied. With this last number no difference from the expected number of SCEs, if one supposes that SCEs follow a random distribution, was seen.     

Frequency of mutagen-induced sister chromatid exchanges in the course of 3 cell cycles

The induction of SCE by fotrine (0.125 and 0.250 microgram/ml) and thiophosphamide (5 micrograms/ml) during the first three cell cycles was studied in the Chinese hamster cells. No increase in the SCE number was observed after treatment with thiophosphamide and fotrine at the G2 stage (the first stage from the moment of fixation) as compared with the control variants. The maximal sensitivity of the cells to the SCE induction by the mutagens is marked at the G1 stage of the first cell cycle before the moment of fixation. The level of SCE remains approximately the same in the second cell cycle before the moment of fixation (20-32 h) and decreased down to the control level at the G1 stage of the third cell cycle (48-52 h).     

Frequency of sister chromatid exchanges in human lymphocytes at different times of day

Analysis of the frequency of sister chromatid exchanges in the human blood taken from normal female donors was made at 9 a. m. and 9 p. m. The morning rate of exchange is shown to be less than the evening one. The influence of physiological state of the organism on the sister chromatid exchange is suggested.     

Effects of temperature on sister chromatid exchanges

Summary The influence of temperature on sister chromatid exchanges was investigated, and the results are discussed in connection with factors possibly involved in temperature-induced SCE-formation.Whereas the SCE frequency increased with increasing growth temperature in a cell line of Xenopus laevis (EAX), which permits the examination of great temperature differences, a Chinese hamster cell line (V-79) revealed a U-shaped temperature-response curve. In addition, it was found that cold treatment at 4°C caused an induction of SCEs in the V-79 cell line.Different BrdU concentrations had no effect on the temperature-induced SCE frequencies and mitomycin C led to an induction of SCEs parallel to the base-line values at different temperatures.     

Demonstration of spontaneous sister chromatid exchanges in vivo

The frequency of sister chromatid exchanges (SCEs) was examined as a function of bromodeoxyuridine (BUdR) concentration in vivo. Oneyear-old Wistar rats were continuously infused with BUdR through the tail vein for 24 h, sacrificed, and mitotic preparations prepared from femur bone marrow. It was observed that from the minimum concentration of BUdR which permitted accurate scoring (1.9 μg/g wt/h) to a BUdR concentration of 7 μg/g wt/h, SCE frequency remained constant. Above 7 μg BUdR/g wt/h SCE frequency increased, saturating at higher BUdR concentrations. The stability of SCE frequency at low BUdR concentrations is interpreted to indicate the existence of spontaneous SCEs in vivo.     

In vivo sister chromatid differentiation and baseline sister chromatid exchanges in a mouse ascites tumour model.

Induction of differentially stained sister chromatids at G2/M and determination of baseline sister chromatid exchanges (SCEs) in ascites form of mouse sarcoma 180 cell line have been done by in vivo incorporation of 5-bromodeoxyuridine (BrdU) for two consecutive DNA replication cycles. The baseline SCE frequency is 6.24 at log phase of tumour growth.     

Recombinational DNA repair and sister chromatid exchanges

We show that a recombinational repair mechanism for DNA lesions can be expected to produce exactly the types of exceptions to the usually observed semiconservative segregation of newly synthetized DNA that have been reported in the literature. This removes the obstacles their occurrence appearance to present to the interpretation that the eukaryote chromosome is mononeme, containing but a single DNA double helix prior to replication. We further note that such a recombinational repair system would generate single sister chromatid exchange (SCE) events but not twin SCE events. This, along with other factors, complicates the interpretation of single: twin ratios in terms of any particular model of eukaryote chromosome structure.     

In vivo sister chromatid differentiation and base line sister chromatid exchanges in Channa punctatus.

An in vivo system for differentially stained sister chromatids by incorporating 5' Bromo 2' deoxyuridine at two consecutive round of DNA replication has been developed in C. punctatus. The base line developed frequency of sister chromatid exchanges (SCEs) was found to be 0.038 SCE/chromosome. This low baseline frequency of SCEs could be useful in detecting genotoxicity of pollutants in aquatic medium.     

Non-uniform distribution of sister chromatid exchanges in human lymphocytes

To test whether sister chromatid exchange (SCE) scores on human chromosomes have a uniform distribution, simulated SCE scores were generated and compared with observed scores using log-linear models. The analysis was performed at the level of the chromosome groups. Using this method we first tested whether the number of SCEs was distributed uniformly, i.e. proportional to the relative length of the chromosomes. Refinements of this hypothesis were made by considering a variable region around a first SCE to be inert for other SCEs and by making the occurrence of an SCE on a chromosome dependent on the occurrence of another SCE on the same chromosome. In further analyses it was tested whether the number of SCEs was proportional to the number of G bands on a chromosome, or to the DNA content of the chromosomes. None of the tested hypotheses fitted the observed data, establishing the non-uniform distribution of these events.     

Ultrasonic induction of sister chromatid exchanges in human lymphocytes

Summary We analyzed sister chromatid exchange (SCE) frequencies as an indicator of DNA damage induced in human lymphocytes by real-time ultrasound. A range of exposure times and intensities was tested in a series of blind, randomized, in vitro experiments under spatial and sonographic conditions simulating exposure of a gravid abdomen and uterus. Our studies showed small but consistent effects of ultrasound on SCE frequencies, for each experiment. Differences between matched control and exposed means were significantly different from zero. X ² tests for homogeneity indicated no significant differences among either the means or the total distributions of the controls, nor among each of the separate dose levels. Consequently, experiments were pooled, and X ² analysis indicated significant differences both among distributions and among means of SCE frequencies for controls versus exposed cells (P(0.001). The pooled control mean was also significantly different from each of the pooled dose means. Correcting for multiple comparisons gave identical results for the paired comparisons of means except for the 20-min level which was borderline (0.025P(0.01). We conclude that the well-established value of clinical ultrasonography warrants its continued use; however, minimizing the numbers and lengths of exposure per patient would seem prudent, pending further information on clinical implications of our results.Supported in part by NIH-HD82855 and HD 11021 and a National Foundation Summer Science Research Grant for Medical Students, 8-80-22     

Enhancement of X-ray-induced sister chromatid exchanges in hypoxic cells

In these studies we have used wild-type Chinese hamster ovary cells (AA8) and a mutant cell line (UV-41) deficient in excision repair to compare sister chromatid exchange (SCE) induction after X irradiation under oxic and hypoxic conditions. X irradiation of AA8 cells under oxic conditions induced only a slight increase in SCEs, whereas at each dose tested a significantly greater number of SCEs were induced in hypoxic cells. When AA8 cells were X-irradiated and the addition of bromodeoxyuridine (BrdU) was delayed for 20 h to allow DNA lesions to be repaired, the levels of SCEs detected in both oxic and hypoxic cells returned to background levels. X irradiation of UV-41 cells also induced only a slight increase of SCEs in oxic cells, whereas a significant number of SCEs were induced in hypoxic cells. However, in contrast to results with AA8 cells, when hypoxic UV-41 cells were X-irradiated and the addition of BrdU was delayed for 20 h, the number of SCEs remained significantly above background levels. In combination with previous alkaline elution data, these results are consistent with the possibility that DNA-protein crosslinks are responsible for the SCEs induced by X irradiation of hypoxic cells. Irrespective of the mechanism(s) involved, the data presented suggest that the SCE assay may potentially aid in the detection of hypoxic tumor cells.     

UV-light induced sister chromatid exchanges in xeroderma pigmentosum lymphocytes

Summary Cultured lymphocytes from 9 patients with clinically different types of xeroderma pigmentosum were exposed to ultraviolet light at 24 h. An increased rate of sister chromatid exchanges was observed in 6 patients (128–148% increase in three, 34–51% in three), but not in three patients with deSanctis-Cacchione syndrome (xeroderma pigmentosum with mental defect), compared to simultaneously cultured controls. A positive result could be useful as preliminary cytogenetic diagnostic test. The results are interpreted as an expression of UV-light induced chromosomal instability due to impaired DNA repair.