Premature onset of mitosis and potentiation of chromosome damage induced by poly-D-lysine in plant cells: evidence for G2 repair

Poly-D-lysine has been reported to induce a triggering of mitosis in plant cells due to a selective stimulatory effect on cells arrested in G2. Root-tip cells of Allium cepa L. were first exposed to maleic hydrazide (MH) early in the cell cycle and posttreated with different concentrations of the polycationic agent while in G2. The result was a dose-dependent potentiation of chromosome damage observed at metaphase without any apparent effect induced by poly-D-lysine itself. The enhancement of the yield of chromosomal aberrations was concomitant with an increase in the frequency of mitosis. In order to test further the stimulatory effect of poly-D-lysine on mitosis, as well as the consequences of a shortening of the time available for repair, cells synchronized by protracted treatment with 5-aminouracil (5-AU), which also induces chromosome damage, were allowed to recover in the presence of the polycationic compound. Our data show that a premature arrival at mitosis resulted in an increase in the frequency of damaged cells observed.     

Suppressing effect of antimutagenic flavorings on chromosome aberrations induced by UV-light or X-rays in cultured Chinese hamster cells

Chromosome aberrations induced by UV-light or X-rays were suppressed by the post-treatment with antimutagenic flavorings, such as anisaldehyde, cinnamaldehyde, coumarin, and vanillin. UV- or X-ray-irradiated surviving cells increased in the presence of each flavoring. X-ray-induced breakage-type and exchange-type chromosome aberrations were suppressed by the vanillin treatment in the G1 phase of the cell cycle and a greater decrease in the number of X-ray-induced chromosome aberrations during G1 holding was observed in the presence of vanillin. Furthermore, a greater decrease in the number of X-ray-induced DNA single-strand breaks was observed in the presence of vanillin. Treatment with vanillin in the G2 phase suppressed UV- and X-ray-induced breakage-type but not exchange-type chromosome aberrations. The suppression of breakage-type aberrations was assumed to be due to a modification of the capability of the post-replicational repair of DNA double-strand breaks. These G1- and G2-dependent anticlastogenic effects were not observed in the presence of 2',3'-dideoxythymidine, an inhibitor of DNA polymerase beta. Based on these results, the anticlastogenic effect of vanillin was considered to be due to the promotion of the DNA rejoining process in which DNA polymerase beta acts.     

Inhibition of chromosome repair by caffeine or isonicotinic acid hydrazide on chromosome damage induced by mitomycin C in human lymphocytes

The frequency of interchromatic exchanges induced by mitomycin C in cultured human lymphocytes was markedly lowered in the presence of caffeine or isonicotinic acid hydrazide (INH) during a post-treatment period. The autoradiographic experiment showed that the decrease in the exchange frequency did not result from delaying or cell-killing effects by the post-treatment with caffeine or INH. Therefore, it may deduced that the exchange formation closely related to a process sensitive to caffeine or INH.     

Body-weight and chromosome aberrations induced by X-rays in somatic cells of Drosophila melanogaster

Summary Variations in suppression efficiency were observed among nonsense mutations at different locations within the lysozyme gene (e) of T4 phage. The present experiments using three amber mutants in lysozyme gene indicate such variations presumably depend upon the base sequences neighboring to the nonsense mutations.Part of this work is the thesis work of one of the authors (E.A.) and was reported at the Annual Meeting (1968) of Genetic Society of Japan     

A comparative study of the effect of RNA and DNA treatment on somatic nuclei in plant cells

Summary The effect of different concentrations of ribonucleic acid (RNA) and desoxyribonucleic acid (DNA) has been studied on meristematic somatic cells ofAllium cepa. The principal effects noted with both are polyploidy and reductional separation of chromosomes.It has been assumed that RNA causes viscosity change in the plasma, which is responsible for polyploidy. DNA, though entering in a minute quantity due to its high molecular weight, gets ultimately converted into RNA precursors and finally causes the same effect. Somatic reduction is caused by an increase in the DNA content of the plasma and as such, application of this chemical causes reductional separation of chromosomes. RNA, on the other hand, needs gradual conversion into DNA precursors to cause the effect. The concurrent nature of the two processes allows the simultaneous occurrence of polyploidy and somatic reduction after a brief interval following artificial treatment.With 8 Figures in the Text     

Relationships between chromosome damage, cell cycle delay and cell killing induced by bleomycin or X-rays

The extent of mitotic delay and chromosome aberration induction by X-rays and bleomycin has been compared in normal human foetal fibroblasts at doses giving approximately equal levels of cell killing, assayed as colony-forming ability. Bleomycin induced much less G2 delay and chromosome damage than X-rays. We conclude that the major mechanism of cell killing by bleomycin does not involve chromosome damage but the cells pass through a number of division cycles before dying and a common DNA lesion is involved in G2 delay and chromosome damage.     

The effect of 1,10-phenanthroline on the chromosome damage and sister-chromatid exchanges induced by streptozotocin in mammalian and insect cells

The effect of the metal chelating agent 1,10-Phenanthroline (PNT) on the streptozotocin (STZ)-induced chromosomal aberrations (CAs) and sister-chromatid exchanges (SCEs) in Chinese hamster ovary (CHO) and mosquito (Aedes albopictus) cells was investigated. Treatment of CHO and mosquito cells with STZ produced a significant and dose-response increase in the yield of CAs as well as SCEs (p<0.05). The addition of PNT prevented the induction of CAs by STZ in both types of cells, causing a significant decrease in the frequency of STZ-induced CAs (46.5-72.5%) (p<0.05). This fact indicates that intracellular transition metals are implicated in STZ-induced CAs and that the Fenton reaction (Fe(2+)+H(2)O(2)-->OH degrees +OH(-)+ Fe(3+)) is partly responsible for the production of CAs by this compound. On the other hand, the addition of PNT to CHO and mosquito cell cultures did not prevent the induction of SCEs by STZ. Therefore, it is valid to assume that the induction of CAs and SCEs by STZ occurs by different mechanisms.     

Hyperthermic enhancement of chromosome damage and lack of effect on sister-chromatid exchanges induced by bleomycin in Chinese hamster cells in vitro.

Chinese hamster cells, M-3, were treated with BLM (1--4 micrograms/ml) for 30 min to 1 h at 37 degrees or 43 degrees C. After treatment, the cells were reincubated at 37 degrees until recovery. The material treated at 43 degrees showed increased damage expressed as chromosome and chromatid-type breaks and exchanges. Since the amount of BLM entering the cell at 37 degrees is supposedly similar to that which enters the cell at 43 degrees, the enhanced damage is the result of true synergism, and not the facilitation of the drug's entry into the cell.     

Potentiation by caffeine of ultraviolet-light damage in cultured human cells.

Five cultured human cell lines (T-1 kidney, Chang liver, H.Ep. No. 2, HeLa-S3 and HeLa-O) were irradiated with ultraviolet light and immediately exposed to 1.0 and 3.0 mM caffeine for 44 h thereafter. This caffeine treatment reduced the surviving fraction (assayed by colony formation) of the irradiated population, but did not significantly reduce the colony-forming ability of unirradiated control cells. These findings suggest that many cultured human cell lines exhibit post-UV potentiation of potentially lethal damage by caffeine.     

Effects of age, sex and diagnostic X-rays on chromosome damage

The frequency of micronuclei assayed in lymphocytes obtained from 73 young adults increases significantly with the age, but not the sex, of the donor. The dose of medical X-rays absorbed by the lymphocytes in the 2 years before the examination has no significant effect on micronucleus frequency, provided the data are adjusted for age. However, a small significant increase in frequency is associated with X-ray examinations that involve the injection of contrast media into the blood.     

X-ray-related potentially lethal damage expressed by chromosome condensation and the influence of caffeine

Caffeine has been reported to induce premature chromosome condensation (PCC) in S-phase cells in the presence of an inhibitor of DNA synthesis. We found that when S-phase cells are treated with caffeine and hydroxyurea after X irradiation, substantially more potentially lethal damage (PLD) is expressed, but the addition of cycloheximide, which inhibits PCC induction in S-phase cells, in the presence of caffeine and hydroxyurea reduces the expression of PLD to the same level as seen with caffeine alone. This can be interpreted to mean that the expression of PLD seen with caffeine in the absence of an inhibitor of DNA synthesis is not associated with chromosome condensation. Evidence that PCC induction in S-phase cells and the influence of caffeine on PLD expression were suppressed by incubation at 40 degrees C of tsBN75 cells with a ts defect in ubiquitin-activating enzyme indicates the involvement of ubiquitin in these two processes. These observations as well as previous findings on ubiquitin suggest to us that caffeine induces changes in DNA-chromatin conformation, which are caused by induction of PCC or ubiquitination of chromosomal protein. Such changes occurring postirradiation would favor expression of PLD.     

Distribution of breakpoints induced by etoposide and X-rays along the CHO X chromosome

SORB (selected observed residual breakpoints) induced by ionizing radiation or endonucleases are often non-randomly distributed in mammalian chromosomes. However, the role played by chromatin structure in the localization of chromosome SORB is not well understood. Anti-topoisomerase drugs such as etoposide are potent clastogens and unlike endonucleases or ionizing radiation, induce DNA double-strand breaks (DSB) by an indirect mechanism. Topoisomerase II (Topo II) is a main component of the nuclear matrix and the chromosome scaffold. Since etoposide leads to DSB by influencing the activity of Topo II, this compound may be a useful tool to study the influence of the chromatin organization on the distribution of induced SORB in mammalian chromosomes. In the present work, we compared the distribution of SORB induced during S-phase by etoposide or X-rays in the short euchromatic and long heterochromatic arms of the CHO9 X chromosome. The S-phase stage (early, mid or late) at which CHO9 cells were exposed to etoposide or X-rays was marked by incorporation of BrdU during treatments and later determined by immunolabeling of metaphase chromosomes with an anti-BrdU FITC-coupled antibody. The majority of treated cells were in late S-phase during treatment either with etoposide or X-rays. SORB induced by etoposide mapped preferentially to Xq but random localization was observed for SORB produced by X-rays. Possible explanations for the uneven distribution of etoposide-induced breakpoints along Xq are discussed.     

Relationship of chromosomal damage induced by caffeine to growth temperature and ATP level in proliferating cells

Caffeine is known to induce chromosomal aberrations in proliferating cells when they are incubated during G2 and mitotic prophase. In the present paper, this caffeine effect has been analyzed in Allium cepa root meristems growing at different culture temperatures under steady-state kinetics. Caffeine (1-10 mM) induces chromosomal aberrations in a dose-dependent manner, and the treatment efficiency correlates linearly with the square of caffeine concentration. The efficiency of caffeine incubations, within the range 5-25 degrees C during equivalent cycle time periods has also been studied. It has been found that the lower the culture temperature, the higher the level of chromosomal aberrations. Moreover, at different temperatures, the level of chromosomal aberrations is a simple function of caffeine concentration and the ATP level. Therefore, the efficiency of caffeine treatment appears to be determined by some interaction between caffeine concentration and cellular ATP level. Our present results demonstrate that the influence of growth temperature on the chromosome-breaking effect of caffeine can be, at least partially, explained by the ATP levels during the incubation periods. In short, under different kinetics of plant cell proliferation, the ATP level, and/or something correlating with it, could explain the efficiency of caffeine in inducing chromosomal aberrations: the lower the ATP level, the higher the caffeine efficiency.