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.
Koana
Takao
T
Low Dose Radiation Research Center, Central Research Institute of Electric Power Industry, Iwado-Kita 2-11-1, Komae, Tokyo 201-8511, Japan. koana@criepi.denken.or.jp
Okada
Mikie O
MO
Ogura
Keiji
K
Tsujimura
Hidenobu
H
Sakai
Kazuo
K
D000818:Animals; D002874:Chromosome Mapping; D003433:Crosses, Genetic; D004249:DNA Damage; D004260:DNA Repair; D004307:Dose-Response Relationship, Radiation; D004330:Drosophila / Q000235:genetics* / Q000528:radiation effects*; D005260:Female; D005808:Genes, Recessive; D008297:Male; D009154:Mutation; D013090:Spermatocytes / Q000528:radiation effects*; D013094:Spermatozoa / Q000528:radiation effects*; D014965:X-Rays