Genetic changes induced in human cells in space shuttle experiment (STS-95)

Background; Results of past space experiments suggest that the biological e ffect of space radiation could be enhanced under microgravity. To assess th e radiation risk for humans during long-term spaceflight, it is very import ant to clarify whether human cells exhibit a synergistic effect of radiatio n and microgravity. Hypothesis. If significant synergism occurs in human ce lls, genetic changes induced during spaceflight may be detected by using hu man tumor HCT-116 cells which are hypermutable due to a defect in the DNA m ismatch repair system. Methods; Cultured HCT-116 cells were loaded on the S pace Shuttle Discovery (STS-95) and grown during the 9-d mission. After lan ding, many single-cell clones were isolated, microsatellite repetitive sequ ences in each clone were amplified by PCR, and mutations in the microsatell ite loci were detected as changes in the length of PCR fragments. Mutation frequencies of ouabain-resistant phenotype were also analyzed. Results. The frequencies of microsatellite mutations as well as ouabain-resistant mutat ions in the flight sample were similar to those of the ground control sampl es. Some cells were treated in space with bleomycin which mimics the action of radiation, but the frequencies of microsatellite mutations were not sig nificantly different between the flight and the ground control samples. Con clusion: Under the present flight conditions, neither space radiation (abou t 20 mSv during this mission) nor microgravity caused excess mutations in h uman cells.