Abstract
Lethal effects of ionizing radiation are different in its extent depending on its dose-rate. At a cellular level, it is known that ATM gene is involved in this dose-rate effect. In order to study the dose-rate effect at an individual level, we irradiated third instar larvae of wild-type Drosophila and measured their viability. When they were irradiated with gamma-rays at dose-rate higher than 36Gy/h, LD50 was constant at 36.1±1.5 Gy and independent on the dose-rate. At dose-rate lower than 36Gy/h, LD50 became larger, according to an approximate equation LD50=35.7×log60{irradiation period(min)}-4.5Gy. Although an irradiation with 55Gy caused 100% lethality when the irradiation period was less than 3h, a part of irradiated larvae survived when irradiation period was longer than 5h. When mei-41, a Drosophila homolog to human ATM was used instead of wild-type flies, the dose rate effect disappeared. In mei-9 which is homologous to XPF, on the other hand, the dose-rate effect was evident though radiation sensitivity was higher than wild-type. These results suggest that the double strand break repair function under control of mei-41 gene is involved in the expression of dose-rate effect.
