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G Obe

Publications and source records attributed to G Obe.

At least 55 records · Page 3Linked to original sources
PubMed1997

Computerized image analysis of sister chromatid exchanges in Chinese hamster ovary cells.

In this paper we show that sister chromatid exchanges (SCE) can be analysed by computer-supported determination of areas and shapes of darkly stained chromatid sections. In combination with appropriate statistical analyses, our method leads to measurements of SCE frequencies in neocarzinostatin-treated Chinese hamster ovary cells which are nearly as precise as the ones obtained by classical microscopical analyses. We discuss our data as an approach to the development of a fully automated SCE scoring system.

Animals↗
PubMed1997

Ultrasound permeabilizes CHO cells for the endonucleases AluI and benzon nuclease.

Ultrasound permeabilizes Chinese hamster ovary (CHO) cells for the endonucleases AluI and benzon nuclease which leads to the induction of chromosomal aberrations by these enzymes. A few aberrant cells were observed when trypsinized cells or adherent cells were exposed to the enzymes in the absence of ultrasound. Our data show that sonication can be used to introduce endonucleases into CHO cells. We further demonstrate that few cells can internalize endonucleases without previous permeabilization.

Animals↗
PubMed1997

Frequencies of polycentric chromosomes following combinational treatments of Chinese hamster ovary cells with restriction endonucleases and X-rays, bleomycin or DNase I.

Chinese hamster ovary cells were treated with combinations of the restriction endonucleases AluI, EcoRI or PstI and bleomycin, DNase I or X-rays. With few exceptions the frequencies of polycentric chromosomes calculated as dicentric chromosomes (DIC) were additive or less than additive after combinational treatments when compared with the effects of treatments with the single compounds. Less than additivity was found when the frequencies of DIC were higher than 150 DIC per 100 cells indicating a saturation effect. The data suggest that DNA double-strand breaks (DSB) with different end-structures produce polycentric chromosomes to the same extent as DSB with the same end-structures.

Animals↗
PubMed1997

Localization of chromosome breakpoints induced by DNase I in Chinese hamster ovary (CHO) cells.

DNase I was electroporated into S-phase CHO cells and induced chromosome breakpoints were localized in G-banded metaphases. More than 75% of breakpoints mapped to Giemsa-light bands, 18% to Giemsa-dark bands and about 7% to band junctions. Chromosome breakpoint clusters produced by DNase I colocalized with chromosome breakpoints induced by the restriction endonucleases AluI and BamHI in the G1- and S-phases of the cell cycle in CHO cells. Digestion of metaphase spreads with AluI, BamHI and DNase I produced G-bands, indicating that G-light bands are more sensitive to endonuclease action. The possible role of nuclease-sensitive sites in active chromatin as selective targets for the induction of chromosome breakpoints by these endonucleases is discussed.

Animals↗
PubMed1997

Chromosomal aberrations in blood lymphocytes of astronauts after long-term space flights.

PURPOSE: To analyse lymphocyte chromosomes from astronauts of MIR and EUROMIR missions. MATERIALS AND METHODS: Peripheral lymphocytes from seven astronauts before and after space flights were cultured and analysed for structural chromosomal aberrations. RESULTS: Chromosome-type but not chromatid-type aberrations were significantly elevated after space flights when compared to pre-flight values. In one astronaut two rogue cells were found. CONCLUSIONS: Overall the frequencies of aberrations were found to be correlated with estimated absorbed cosmic radiation doses.

Astronauts↗
PubMed1996

Intrachromosomal localization of breakpoints induced by the restriction endonucleases AluI and BamHI in Chinese hamster ovary cells treated in S phase of the cell cycle.

The restriction endonucleases (REs) AluI and BamHI were electroporated into Chinese hamster ovary (CHO) cells during S phase of the cell cycle and breakpoints in G-banded metaphases were mapped to Giemsa-light or -dark bands or to band junctions. The majority of AluI- and BamHI-induced breakpoints were located in Giemsa-light bands. Both REs induced similar distributions of breakpoint clusters. The localization pattern of S phase-induced breakpoints in CHO cells is similar to the pattern of G1-induced breakpoints reported earlier. These data show that breakpoint localization for both REs is independent of the cell cycle stage (G1 or S) in which aberrations are induced and give further support to the hypothesis that nuclease hypersensitive regions (NHRs) associated with active genes play an important role in the distribution of breakpoints.

Animals↗
PubMed1996

DNA damage induced by UV light affects restriction endonuclease recognition sites: correlation between effects at chromosomal level and naked DNA.

Cytogenetic and molecular analyses were performed in G1 Chinese hamster ovary cells treated with 254 nm UV light, to test the hypothesis that UV may affect the recognition site of specific restriction endonucleases (RE). Since short-wavelength UV light induces mainly cyclobutane dimers (CPD) at TT and CT sequences, RE were selected according to the presence or absence of thymine at the recognition site (DraI TTT/AAA, AluI AG/CT and HaeIII GG/CC). A drastic reduction of DraI-and AluI-induced chromosome-type aberrations was found in cells pretreated with UV. Conversely, such a reduction was not observed with HaeIII. To better understand this phenomenon, a molecular analysis was carried out at both the genome level and at the hypoxanthine phosphoribosyl transferase gene level, showing that the cutting pattern of DraI on isolated DNA from UV-irradiated cells was strongly reduced compared with an untreated sample, whereas HaeIII was not able to modify the cutting pattern of irradiated cells. Our data demonstrate a good correlation between the results obtained with cytogenetic and molecular approaches, suggesting that cyclobutane dimers are the main lesions responsible for the observed reduction of the cleaving activities of RE, at both the chromatin and naked DNA levels.

Animals↗
PubMed1996

Do DNA double-strand breaks induced by Alu I lead to development of novel aberrations in the second and third post-treatment mitoses?

Several authors have reported that ionizing radiation can give rise to novel aberrations several mitotic divisions after the exposure. At our institute this phenomenon has been observed in mouse preimplantation embryos. This cell system is uniquely well suited for such investigations because the first three cell divisions show a high degree of synchrony. Thus the expression of chromosomal aberrations at the first, second and third mitosis after irradiation can be scored unambiguously. To investigate whether DNA double-strand breaks may be the lesions responsible for the delayed expression of chromosomal aberrations, we have studied the frequencies of aberrations in the first, second and third mitosis after treatment of one-cell mouse embryos with the restriction enzyme Alu I. Embryos were permeabilized with Streptolysin-O. The results indicate that the induction of double-strand breaks does not lead to novel aberrations in the third post-treatment mitosis. Several embryos scored at the second mitosis showed very high numbers of aberrations, indicating that Alu I may remain active in the cells for a period of one cell cycle. After treatment with Streptolysin-O alone, enhanced aberration frequencies were observed in the third post-treatment mitosis, suggesting that membrane damage has a delayed effect on the cellular integrity.

Animals↗
PubMed1995

Chromosomal aberrations induced in human whole blood cultures by pipetting cell pellets in the presence of AluI.

A physical method is described to permeabilize human peripheral lymphocytes in culture for the restriction endonuclease AluI. Blood cultures are incubated for 20 h, pelleted, strongly pipetted with different types of Pasteur pipettes in the presence of AluI and recovered for up to 54 h in the presence of 5-bromodeoxyuridine. Up to 20% of aberrant first posttreatment (M1) metaphases with chromosome-type aberrations are found. The method works with whole blood cultures and is therefore easy to perform.

Bromodeoxyuridine↗
PubMed1995

Cytological effects of 50 Hz electromagnetic fields on human lymphocytes in vitro.

Incubation of human peripheral blood cultures in the presence of an electromagnetic field (EMF) of 50 Hz and 5 mT leads to stimulation of the cell cycle of dividing lymphocytes but has no influence on the frequencies of sister-chromatid exchanges. Comparative studies with two different exposure systems and with different culture temperatures indicate that the effect on the cell cycle results from the EMF and is not a thermal effect. These data support the assumption that with respect to their suspected carcinogenic effects EMFs have no initiating but probably promoting effects.

Carcinogens↗
PubMed1995

Localization of chromosome breakpoints induced by AluI and BamHI in Chinese hamster ovary cells treated in the G1 phase of the cell cycle.

Intact Chinese hamster ovary cells were exposed to the restriction endonucleases (REs) AluI or BamHI. In metaphase spreads from these cells, 300 breakpoints per RE were localized in G-banded chromosome type aberrations (dicentrics, translocations, rings, terminal and interstitial deletions). The majority of breakpoints induced by both REs were localized in G-light bands and showed a similar distribution of breakpoint clusters. RE digestion of metaphase spreads with AluI induced C-banding, and with BamHI G-banding. The data indicate that nuclease sensitive sites associated with active genes are mainly responsible for the distribution of breakpoints.

Animals↗
PubMed1995

Neocarzinostatin induces chromosomal aberrations and sister chromatid exchanges in Chinese hamster ovary cells.

Chinese hamster ovary (CHO) cells were treated with neocarzinostatin (NCS) and analyzed for chromosomal aberrations and sister chromatid exchanges (SCE). After treatment the cells were recovered for 9, 20, 26 or 30 h. NCS induces chromosomal aberrations and SCE. SCE were much more frequent in cells with chromosome type aberrations at 20 h recovery time than in those with chromatid type aberrations at 9 h recovery time. In second post-treatment cells at 26 or 30 h recovery time NCS induced chromosomal aberrations but only few SCE.

Animals↗
PubMed1994

Are rogue cells an indicator of cancer risk due to the action of bacterial restriction endonucleases?

Cytogenetic surveys in normal individuals have occasionally shown the occurrence of cells with multiple chromosome-type aberrations in some of the subjects. These cells, which are rare, have been termed as rogue cells. Rogue cells, which have been observed worldwide, have a mysterious nature. It has been suggested that they may give rise to cancer. Various mechanisms have been considered for the causation of the rouge-cell phenomenon in the past but none of them appears to be fully justified. In this paper we propose their occurrence due to the action of bacterial restriction endonucleases.

Animals↗
PubMed1994

Combination treatments of Chinese hamster ovary cells with various restriction endonucleases result in chromosomal aberrations whose frequencies are additive or less than additive.

Chinese hamster ovary cells were treated with combinations of different restriction endonucleases (RE). The frequencies of chromosomal aberrations after combination treatments were additive or less than additive when compared with the effects of the single RE. These data indicate that DNA double-strand breaks (DSB) induced by different types of RE in combination treatments lead to chromosomal aberrations in the same way as DSB induced by single RE.

Animals↗
PubMed1994

Induction of sister-chromatid exchanges by AluI, DNase I, benzon nuclease and bleomycin in Chinese hamster ovary (CHO) cells.

Various endonucleases (AluI, DNase I, benzon nuclease) and bleomycin induce sister-chromatid exchanges (SCE) in Chinese hamster ovary (CHO) cells. The frequencies of SCE are elevated in cells with chromosome-type aberrations, only slightly elevated in cells with chromatid exchanges, and in the control range in cells without chromosomal aberrations. These data indicate that SCE are produced when DNA breaks induced in G1 are either not repaired or misrepaired.

Animals↗