RESUMO
The influence of microgravity on induction and repair of double-strand breaks was studied in the yeast mutant rad54-3, which is temperature-conditional for the repair of DNA double-strand breaks. The experiment was performed on the shuttle Atlantis flight STS-84. Cell samples were kept at 0-4 degrees C until they reached orbit, where they were transferred to 22 (permissive temperature for repair) and 37 degrees C (restrictive temperature). They were exposed to graded doses of beta particles from an in-built (63)Ni source during the repair period. After 152 h in microgravity, the radiation exposure was stopped, and the samples were returned to low-temperature conditions, where they remained until final evaluation in the home laboratory. The amount of double-strand breaks remaining was estimated from the differences in survival after plating and incubation at the restrictive temperature. The results show that there is no significant difference for both the induction and the repair of double-strand breaks between microgravity and terrestrial conditions.
Assuntos
Dano ao DNA , Reparo do DNA , DNA Fúngico/efeitos da radiação , Ausência de Peso , Saccharomyces cerevisiae/genética , Voo Espacial , TemperaturaRESUMO
The influence of microgravity on the repair of x-ray-induced DNA double-strand breaks was studied in the temperature-conditional repair mutant rad54-3 of diploid yeast Saccharomyces cerevisiae. Cells were exposed on the ground and kept at a low temperature until microgravity conditions were achieved. In orbit, they were incubated at the permissive temperature to allow repair. Before re-entry they were again cooled down and kept at a low temperature until final analysis. The experiment, which was flown on the shuttle Atlantis on flight STS-76 (SMM-03), showed that repair of pre-formed DNA double-strand breaks in yeast is not impaired by microgravity.
Assuntos
Medicina Aeroespacial , Reparo do DNA , DNA Bacteriano/fisiologia , Saccharomyces/genética , Ausência de Peso , DNA Bacteriano/efeitos da radiação , Relação Dose-Resposta à Radiação , Humanos , Modelos Estruturais , Doses de Radiação , Saccharomyces/efeitos da radiação , Raios XRESUMO
Humans in space are exposed both to space radiation and microgravity. The question whether radiation effects are modified by microgravity is an important aspect in risk estimation. No interaction is expected at the molecular level since the influence of gravity is much smaller than that of thermal motion. Influences might be expected, however, at the cellular and organ level. For example, changes in immune competence could modify the development of radiogenic cancers. There are no data so far in this area. The problem of whether intracellular repair of radiation-induced DNA lesions is changed under microgravity conditions was recently addressed in a number of space experiments. The results are reviewed; they show that repair processes are not modified by microgravity.
Assuntos
Cocarcinogênese , Reparo do DNA , Meio Ambiente Extraterreno , Hipogravidade , Efeitos da Radiação , Proteínas de Saccharomyces cerevisiae , Voo Espacial , Partículas beta/efeitos adversos , DNA/efeitos da radiação , Dano ao DNA , DNA Helicases , Enzimas Reparadoras do DNA , Proteínas Fúngicas/genética , Humanos , Sistema Imunitário/efeitos da radiação , Neoplasias Induzidas por Radiação/epidemiologia , Neoplasias Induzidas por Radiação/etiologia , Neoplasias Induzidas por Radiação/genética , Doenças Profissionais/epidemiologia , Doenças Profissionais/etiologia , Doenças Profissionais/genética , Radiometria , Medição de Risco , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/efeitos da radiação , Raios X/efeitos adversosRESUMO
The mechanisms of biological effect of charged particles in space was studied through the inactivation effect of very low-density charged particles on very low-density cells at different impact parameters. A small type of microbeam facility with alpha-radioactive source and CN track detector were used. A diploid wild type Saccharomyces cerevisiae served as experimental eukaryotic cell. The correlation between cell inactivation and impact parameter of alpha-particles on cells was obtained through a CCD-camera system. The results showed that inactivation range of 1.13 MeV/u alpha-particles on cell-agarose mixture was about 5.5 micrometers, larger than the sum (about 3.l micrometers) of ion track-penumbra radius and yeast cell radius. The cell inactivation rate was 0.36-0.33. It suggests that multi-hit on a cell is necessary for killing it. However, in case of miss, the inactivation rate may not be zero at certain impact parameters.
Assuntos
Partículas alfa , Saccharomyces cerevisiae/efeitos da radiação , Aceleradores de Partículas , Doses de Radiação , Monitoramento de Radiação/instrumentação , Radiometria , Saccharomyces cerevisiae/citologiaRESUMO
The influence of microgravity on the repair of radiation induced genetic damage in a temperature-conditional repair mutant of the yeast Saccharomyces cerevisiae (rad 54-3) was investigated onboard the IML-1 mission (January 22nd-30th 1992, STS-42). Cells were irradiated before the flight, incubated under microgravity at the permissive (22 degrees C) and restrictive (36 degrees C) temperature and afterwards tested for survival. The results suggest that repair may be reduced under microgravity.