The genetic effects induced by an irradiation in low doses at Drosophila melanogaster

This article generalizes the results received by authors in researches of genetic effects of an irradiation for Drosophila. It is supposed, that the main effect of low intensity irradiation is connected with the induced genetic instability on which background the realization of effects of a different direction is possible.     

Chlorophyll mutations after low doses of chronic irradiation of barley

The chlorophyll mutation rate on a large number of plants after the dose rates 0·004–16·800 R/day during the whole vegetation cycle was examined. The mutation frequency increases as early as after the dose rate 4 mR/day. The dose rate of approximately 8 mR/day is necessary to double the mutation frequency.     

Proteolytic processes in lung tissue of rat posterity after whole-body chronic irradiation with low doses

Intensification of proteolytic processes accompanied by inhibited antiprotease activity in lung tissue of first generation posterity of rats irradiated with a total dose of 0.25 Gy (0.01 Gy per day) before gestation was shown. The obtained data satisfied to imbalance in functioning of regulation systems, tension of adaptation mechanisms with possible rapider reduction of adaptation resistance of broncho-lung system of irradiated parents' posterity. Vector changes in correlation of indexes in the proteinase-antiproteinase system were analogous in all experimental series (irradiated male x irradiated female, irradiated male x intact female, intact male x irradiated female) with maximal expression in the group obtained from parents both irradiated before gestation. It could be possible to propose a presence of non-stable genome in posterity of irradiated parents, that satisfied to role of genetic aspects in development of the late functional disorders.     

Stimulating effect of very low doses of chronic gamma irradiation on the development of chick embryos

A study was made of the influence of chronic gamma-irradiation, with very low doses, of chick embryos during incubation on the dynamics of changes in the parameters characterizing the proliferative activity of cells. The original method is proposed for the analysis of these parameters and the results obtained by this method are discussed.     

The systemic response of antioxidant enzymes to the oxidative stress induced by irradiation at low doses

As a result of total chronic gamma irradiation of mice (137Cs, 0.6 cGy/day, 9 days) the functioning of superoxide generation and utilisation systems in liver were disturbed. The regulatory links between the activities of superoxide dismutase and glutathione peroxidase are found to be maintained. Postradiation effects were more expressed for a total dose of 1.2 cGy than for a dose of 5.4 cGy, providing support for the hypothesis of delayed reparation as a reason of harmful action of low-dose irradiation.     

Increased radiosensitivity after irradiation of lymphocytes low adaptive doses

The variability of blood lymphocyte reaction on the adaptive irradiation (0.05 Gy at first, then 1.0 Gy 5 h later) was investigated by micronuclei assay. Blood samples were obtained from 700 children. It was shown that in all groups studied there were children with enhanced radiosensitivity ("radiosensitivity syndrome"-RS) after exposure to adaptive low dose of radiation. The radiosensitivity syndrome occurred more often in groups of ill children; part of them was characterized by the enhanced blood content of immunoglobulin E, enhanced level of T helpers and T suppressors. A high spontaneous level of lymphocytes with micronucleus is a factor of radiosensitivity formation. The possible factors resulted in radiosensitivity syndrome are discussed.     

In phantom assessment of superficial doses under TomoTherapy irradiation

PurposeAim of this work is the assessment of build-up and superficial doses of different clinical Head&Neck plans delivered with Helical TomoTherapy (HT) (Accuray, Sunnyvale, CA). Depth dose profiles and superficial dose points were measured in order to evaluate the Treatment Planning System (TPS) capability of an accurate dose modeling in regions of disequilibrium. Geometries and scattering conditions were investigated, similar to the ones generally encountered in clinical treatments.MethodsMeasurements were performed with two dosimeters: Gafchromic® EBT3 films (Ashland Inc., Wayne, NJ) and a synthetic single crystal diamond detector (PTW-Frieburg microDiamond, MD). A modified version of the Alderson RANDO phantom was employed to house the detectors. A comparison with TPS data was carried out in terms of dose difference (DD) and distance-to-agreement (DTA).ResultsDD between calculated data and MD measurements are within 4% even in points with high spatial dose variation. For depth profiles, EBT3 data show a DDmax of 3.3% and DTAmax of 2.2 mm, in low and high gradient regions, respectively, and compare well with MD data. EBT3 superficial points always results in measured doses lower than TPS evaluated ones, with a maximum DTA value of 1.5 mm.ConclusionsDoses measured with the two devices are in good agreement and compare well with calculated data. The deviations found in the present work are within the reference tolerance level, suggesting that the HT TPS is capable of a precise dose estimation both in superficial regions and in correspondence with interfaces between air and PMMA.     

A model of chromosome aberration induction and chronic myeloid leukaemia incidence at low doses

Some chromosome aberration types, generally translocations, are correlated with specific cancers. An example is provided by chronic myeloid leukemia (CML) cells, most of which carry a translocation involving the ABL gene on chromosome 9 and the BCR gene on chromosome 22. The hypothesis of a causal relationship between CML and the chimeric protein product of the BCR-ABL translocation has recently received strong support. In this framework, a mechanistic model and Monte-Carlo code simulating radiation-induced chromosome aberrations in human lymphocytes will be presented. The current version of the model can predict dose-response curves for the main aberration types following acute irradiation with gamma rays and light ions of different energies. The model is based on the assumption that only clustered DNA lesions can lead to aberrations and that only lesion free ends in neighbouring chromosome territories can join and form exchanges. Such lesions are distributed within the cell nucleus according to the radiation track structure, i.e. randomly for low-LET radiation and along straight lines for high-LET light ions. Interphase chromosome territories are explicitly simulated and background aberrations are taken into account. Very good agreement was found with experimental data taken from the literature that provided a further validation of the model. As an application, yields of BCR-ABL translocations were calculated. Preliminary results led to a CML induction dose-response that is approximately quadratic below 0.1 Gy and essentially linear at higher doses up to 1 Gy. The numerical values obtained for the probability of CML induction are consistent with values obtained by other groups with different approaches.Dedicated to Herwig Paretzke on the occasion of his 60th birthday.     

Genetic aspects of the irradiation in small doses of laboratory lines and experimental populations Drosophila melanogaster

One of explanations of revealed effects of small doses of an irradiation is induced genetic instability on which background there is a realization of the various radiobiological reactions resulting as to stimulation, and significant oppression of the vital functions of a cell or an organism. In work the given estimations of consequences of an irradiation in small doses of mutant lines of the drosophila are submitted. Paramount value in definition of their size and an orientation of reaction of a genotype is supposed, that, have processes leaders to change of activity of mobile genetic elements and programmed destruction of a cell.     

Evaluation of effects of gamma-irradiation at low doses on repair and meiotic recombination mutants of Drosophila melanogaster

A comparative study of the effects of gene mutations mus209, mus309, mei-41 and rad54 of Drosophila melanogaster on the sensitivity to low-level exposure of different duration was carried out. Taken into account was the survival rate at different stages of ontogeny, female fecundity, the frequency of dominant lethal mutations (DLM) and the DNA damage. mei-41 and rad-54 mutants were most sensitive to the action of low dose radiation (80 mGy) in terms of survival and DLM. However, at the level of DNA damage, an increased radiosensitivity is observed only at larger doses of low intensity irradiation. Based on these observations, we can conclude about the importance of repair and its genes in the formation of the effect of low level doses of ionizing radiation in Drosophila.     

Reduction of background mutations by low-dose X irradiation of Drosophila spermatocytes at a low dose rate

A sex-linked recessive lethal mutation assay was performed in Drosophila melanogaster using immature spermatocytes and spermatogonia irradiated with X rays at a high or low dose rate. The mutation frequency in the sperm irradiated with a low dose at a low dose rate was significantly lower than that in the sham-irradiated group, whereas irradiation with a high dose resulted in a significant increase in the mutation frequency. It was obvious that the dose-response relationship was not linear, but rather was U-shaped. When mutant germ cells defective in DNA excision repair were used instead of wild-type cells, low-dose irradiation at a low dose rate did not reduce the mutation frequency. These observations suggest that error-free DNA repair functions were activated by low dose of low-dose-rate radiation and that this repaired spontaneous DNA damage rather than the X-ray-induced damage, thus producing a practical threshold.