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Comparison of radiosensitivity among different silkworm strains with respect to the killing effect on the embryos

1969; Elsevier BV; Volume: 8; Issue: 2 Linguagem: Inglês

10.1016/0027-5107(69)90013-x

1873-135X

Akio Murakami,

Animal Behavior and Reproduction

In a previous paper, marked differences in radiosensitivity to X-rays were reported among different silkworm strains with respect to the killing of hibernating embryos. In the relatively sensitive strains, Ascoli and Kojiki have an LD50 amounting to one-tenth of the value of the relatively resistant strains, Tenmon and Kansen. It has been known, however, that the radiosensitivity of silkworm embryos was markedly different according to the developmental stage of the embryos. The present study was conducted in order to eliminate such variance. By taking advantage of synchronous division of cells, at early cleavage stages of eggs, the sensitivity was compared withinne cell cycle for two representative strains, Kansen and Kojiki. As was already reported by the present author, the more sensitive phase to killing effects of X-rays in early cleavage cells in the silkworm was the dividing phase, while the more resistant phase was the interphase. The eggs grom inbred strains of Kansen were 7–8 times as resistant as Kojiki, and the difference between those strains was more pronounced in the cells in the phase resistant to radiation killing. This finding is in agreement with those in hibernating eggs. It can be concluded from the findings that the strain differences observed in the radiosensitivity of hibernating eggs may be of an intrinsic nature. In the reciprocal crosses, it has been shown that the sensitivity was under the control of the sensitivity of the maternal strains regardless of that of the parental strains. When females from different sensitivity strains were crossed to males of a fixed strain (pe:re), the sensitivity was markedly damaged depending on the sensitivity of each female. When fixed females were used, the difference in sensitivity was almost nil regardless of the sensitivity of the male parent. These findings suggest that the cytoplasmic effect may be operating for the differential sensitivity for different strains at an early developmental stage of embryos. However, it was demonstrated that no cytoplasmic effects in sensitivity have been observed at the late stage of embryos. This indicated that the cytoplasmic effect on the differential strain sensitivity may be limited to the cells during the early cleavage stage.