Abstract
The exposure of X-rays or heavy ion particles to diapause eggs of the black-striped strain (PS) silkworm, Bombyx mori, resulted in somatic mutations appearing as a white spot on the black integument during larval stage. This result indicates that the silkworm larvae from the eggs of the black-striped strain (PS) of the silkworm represent an appropriate model for estimating the biological effect of cosmic radiation, radiosensitivity of the eggs against X-rays and heavy ion particles (C and Ne beam) was examined as ground-based experiments. Ne beam irradiation of diapause eggs displayed dose- and linear energy transfer (LET)-dependent effects, causing a maximal rate of the mutation at 150 keV/㎛. Especially, a high incidence of somatic mutation (about 90%) was observed in the diapause-terminated eggs which received C, Ne, Fe beam on day 2 after the resumption of embryogenesis. In contrast, irradiation of Fe ion beam to the diapause terminated resulted in the occurrence of different type of somatic mutation, which showed the many tiny white spots on the black integument, from those in the same eggs irradiated with Ne beam. In the analysis of gene expression using RT-PCR-differential display method, a remarkable difference was observed in electrophoretic bands of amplified DNA derived from template RNAs of Ne beam irradiated eggs and non-irradiated eggs. This shows that the specific gene expression may be induced by irradiation of Ne beam to the diapause-terminated eggs.
