Influence of pulsing electromagnetic field on the frequency of sister-chromatid exchanges in cultured mammalian cells

Summary Exposure of Chinese hamster cells to pulsing electromagnetic field (PEMF) with 0.18–2.5 mT did not influence the baseline frequency of sister-chromatid exchanges (SCE). The results suggest that PEMF with the magnetic intensity examined does not interfere with DNA replication nor produce DNA lesions, thereby leading to an increased frequency of SCE.     

Genotype-specific reduction in methyl nitrosourea (MNU) induced sister chromatid exchanges (SCE) in vivo during aging

We studied mice from five strains (BALB/c, C3H/HeSnJ, C57BL/6J, Csb and 129/ReJ) at two ages (young, 10 +/- 1 weeks; and old, 67 +/- 3 weeks) for the induction of sister chromatid exchanges (SCEs) in vivo by methyl nitrosourea (MNU). The SCE frequency is genotype-specific. The F1 phenotype resembles the 'low' responding parent. SCE induction is significantly lower in the older animals of each strain than their younger counterparts, and the reduction of SCE/cell with old age is strain-specific. A general explanation for these results must include strain differences in relative mutagenic sensitivity, genotype-specific pattern of reduction in DNA repair and other such factors affecting SCE formation, with old age.     

Genotype-specific reduction in methyl nitrosourea (MNU) induced sister chromatid exchanges (SCE) in vivo during aging

Summary We studied mice from five strains (BALB/c, C3H/HeSnJ, C57BL/6J, Cs^b and 129/ReJ) at two ages (young, 10±1 weeks; and old, 67±3 weeks) for the induction of sister chromatid exchanges (SCEs) in vivo by methyl nitrosourea (MNU). The SCE frequency is genotype-specific. The F₁ phenotype resembles the low responding parent. SCE induction is significantly lower in the older animals of each strain than their younger counterparts, and the reduction of SCE/cell with old age is strain-specific. A general explanation for these results must include strain differences in relative mutagenic sensitivity, genotype-specific pattern of reduction in DNA repair and other such factors affecting SCE formation, with old age.     

Sister chromatid exchanges in lymphocytes of normal and alcoholic subjects.

The effects of alcohol consumption, cigarette smoking and age on sister chromatid exchange (SCE) frequency in human lymphocytes were assessed by means of multiple linear regression. An increase in SCE rates was associated with alcohol consumption (p = 0.0001), smoking (p = 0.0231), and, to a small extent (p = 0.057), age. These three confounding factors explain 48% of the inter-personal variation in SCE rates among subjects studied.     

Enhancement by caffeine of sister-chromatid exchange frequency induced by antineoplastic agents in human lymphocytes.

The SCE frequency induced by Thiotepa and the effect of this antineoplastic drug in combination with caffeine have been studied in cultures of human peripheral blood. Caffeine was found to enchance SCE and breakage frequencies induced by Thiotepa in human lymphocytes.     

Sister chromatid exchanges in lymphocytes of normal and alcoholic subjects

The effects of alcohol consumption, cigarette smoking and age on sister chromatid exchangen (SCE) frequency in human lymphocytes were assessed by means of multiple linear regression. An increase in SCE rates was associated with alcohol consumption (p=0.0001), smoking (p=0.0231), and, to a small extent (p=0.057), age. These three confounding factors explain 48% of the inter-personal variation in SCE rates among subjects studied.We are grateful to Dr D. Krapavickaité for performing, the statistical analysis, and to Mrs V. Navickiené for technical assistance. We also wish to thank Dr B. Lambert (Stockholm, Sweden) for his valuable suggestions.     

Bone marrow genotoxicity of N-methyl, N-nitrosourea (NMU): n-alkanols as sister chromatid exchange (SCE) anti-inducers

The in vivo SCE test was used to demonstrate significant inhibition of NMU bone marrow genotoxicity by pretreatment of Chinese hamsters with n-alkanols. Our findings exclude a loss of intracellular DNA alkylation potential through a competitive direct reaction of NMU with the weakly nucleophilic polar end of the n-alkanols, but not through methylations of nucleophilic membrane sites possibly liberated by structural modifications which the membrane-active amphiphilics induce.     

Enhancement by caffeine of sister-chromatid exchange frequency induced by antineoplastic agents in human lymphocytes

Summary The SCE frequency induced by Thiotepa and the effect of this antineoplastic drug in combination with caffeine have been studied in cultures of human peripheral blood. Caffeine was found to enhance SCE and breakage frequencies induced by Thiotepa in human lymphocytes.Acknowledgment. I am deeply grateful to Dr M.J.W. Faed, for stimulating discussions, guidance and constructive criticism. This paper is a part of my Ph.D. thesis submitted to Dundee University.     

Distribution of sister chromatid exchanges in different types of chromatin in the X chromosome ofMicrotus cabrerae

We used the X chromosomes ofMicrotus cabrerae as a model to analyze the distribution of sister chromatid exchanges (SCEs) on different types of chromatin, because of the marked heterogeneity of the heterochromatin in the entire short arm and a portion of the long arm of this chromosome. Computer-simulated distributions, according to an algorithm that makes it possible to modify the distribution on the basis of any possible hypothesis, were compared with real distributions by log-linear models. We found that the frequency of SCEs in different types of heterochromatin was higher than that expected for a random distribution, and located an SCE hot-spot at the junction between euchromatin and heterochromatin. The possible relationship between the distribution of SCEs and base composition or chromatin accessibility are discussed.     

Possible mutagenic activity of saccharin

Summary A mutagenic effect of saccharin in Chinese hamsters, using the in vivo SCE test, was observed when massive overdoses were administered; cyclamate was not mutagenic.     

Possible mutagenic activity of saccharin.

A mutagenic effect of saccharin in Chinese hamsters, using the in vivo SCE test, was observed when massive overdoses were administered; cyclamate was not mutagenic.     

Steroid hormones enhanced sister-chromatid exchange in cultured CHO cells

The influence of steroid hormones on the induction of sister-chromatid exchange (SCE) in cultured CHO cells was studied. It was observed that estradiol-17 beta, estriol, estrone and ethynyl estradiol treatments enhanced SCE rates compared to the controls. Overall, these compounds produced a dose response effect. The importance of a detailed study on the long-term genetic effects of steroids on mammalian cells is emphasized.     

Effect of pulsing electromagnetic fields on DNA synthesis in mammalian cells in culture

DNA synthesis in Chinese hamster V79 cells was significantly enhanced when they were exposed to weak, pulsing electromagnetic fields generated by specific combinations of the pulse width (25 microseconds), frequency (10, 100 Hz) and magnetic intensity (2 X 10(-5), 8 X 10(-5) T). Conversely the DNA synthesis of cells in the fields at 4 X 10(-4) T was repressed to 80% of that in controls not exposed to the fields.     

Metabolic requirements for entry of DNA in Branhamella catarrhalis.

Although requirements for transformation in Branhamella catarrhalis are quite complex, DNA synthesis does not appear to be one of these needs, as indicated by the inability of nalidixic acid to interefere with transformation. Exogenous sources of energy, such as cAMP and cGMP also failed to enhance frequency, suggesting cells may actively engage in energy production to achieve uptake of DNA, or lack a transport mechanism for these compounds.     

Metabolic requirements for entry of DNA inBranhamella catarrhalis

Summary Although requirements for transformation inBranhamella catarrhalis are quite complex, DNA synthesis does not appear to be one of these needs, as indicated by the inability of nalidixic acid to interefere with transformation. Exogeneous sources of energy, such as cAMP and cGMP, also failed to enhance frequency, suggesting cells may actively engage in energy production to achieve uptake of DNA, or lack a transport mechanism for these compounds.     

Regulation of macronuclear DNA content during the cell cycle of the ciliate Tetrahymena paravorax (microstome form)]

Results of autoradiographic studies of 3H-thymidine incorporation support a model of macronuclear DNA content regulation involving an action upon the extremes of DNA content: elimination of S phase in cells with large DNA content, additional S phase in cells with DNA content. The frequency of each of these phenomena is about 20%: the inequality of frequencies obtained with the two types of sister cells (proters and opisthes) is relatable to the asymetry of cytodieresis observed in this ciliate.     

Steroid hormones enhanced sister-chromatid exchange in cultured CHO cells

Summary The influence of steroid hormones on the induction of sister-chromatid exchange (SCE) in cultured CHO cells was studied. It was observed that estradiol-17 , estriol, estrone and ethynyl estradiol treatments enhanced SCE rates compared to the controls. Overall, these compounds produced a dose response effect. The importance of a detailed study on the long-term genetic effects of steroids on mammalian cells is emphasized.This work was supported by NIH-Minority Biomedical Research Support Program (MBRS), Grant No. RR 08124-11. The author is thankful for the technical assistance provided by NIH-MBRS student, Hoang Duong.     

Occurrence of sister chromatid exchanges at euchromatin-C band junctions inAllium cepa chromosomes

Summary Distribution of SCE in C band and non-C band regions ofAllium cepa chromosomes.     

Rate of sister chromatid exchanges in mammalian cells differing in diploid numbers

Summary The rate of sister chromatid exchanges (SCE) under identical experimental conditions is the same in various mammalian species irrespective of their diploid chromosome numbers.Supported in part by Research grants VC-21 from American Cancer Society and DEB-76-10580 from National Science Foundation.     

Custom-designed zinc finger nucleases: What is next?

Custom-designed zinc finger nucleases (ZFNs)--proteins designed to cut at specific DNA sequences--combine the non-specific cleavage domain (N) of Fok I restriction endonuclease with zinc finger proteins (ZFPs). Because the recognition specificities of the ZFPs can be easily manipulated experimentally, ZFNs offer a general way to deliver a targeted site-specific double-strand break (DSB) to the genome. They have become powerful tools for enhancing gene targeting--the process of replacing a gene within a genome of cells via homologous recombination (HR)--by several orders of magnitude. ZFN-mediated gene targeting thus confers molecular biologists with the ability to site-specifically and permanently alter not only plant and mammalian genomes but also many other organisms by stimulating HR via a targeted genomic DSB. Site-specific engineering of the plant and mammalian genome in cells so far has been hindered by the low frequency of HR. In ZFN-mediated gene targeting, this is circumvented by using designer ZFNs to cut at the desired chromosomal locus inside the cells. The DNA break is then patched up using the new investigator-provided genetic information and the cells' own repair machinery. The accuracy and high efficiency of the HR process combined with the ability to design ZFNs that target most DNA sequences (if not all) makes ZFN technology not only a powerful research tool for site-specific manipulation of the plant and mammalian genomes, but also potentially for human therapeutics in the future, in particular for targeted engineering of the human genome of clinically transplantable stem cells.