カイコ発生初期卵に対する紫外線の影響その生物学的意義
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概要
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To analyze the relationship between UV sensitivity and embryonic development, the present experiment was carried out using synchronized cell population during early embryogenesis of the silkworm. Embryos (or eggs) were obtained from crosses between C108 strain wild type females and pe and re marker strain males. This mating procedure has the advantage of permitting the estimation of both cell killing in terms of lowered hatchability and the measurement of the mutational incidence of the egg-color-specific loci of pe and re. The UV source was a germicidal lamp, and the source of the visible light for photoreactivation was a fluorescence lamp. The eggs were subjected to UV treatment with relevant time intervals from immediately after the oviposition up to 15 hours after the oviposition. A marked change of UV sensitivity was observed with the progress of embryonic development. Sensitivity to UV was relatively low in the first 10 hours after oviposition, and then it gradually increased with the age of the eggs. From 10 hours on after the oviposition, an extremely high sensitivity was observed. In the silkworm, there is a well known fact that cleavage nuclei first migrate somewhat into the inner part of the egg and move to the upper surface of the egg at the blastula stage. Thus it can be concluded that these highly sensitive stages correspond to the stage of blasstula, while the stages with low sensitivity correspond to the age of the egg from meiotic oocyte to blastula. It is of interest to note that photoreactivation to UV damage was more effective for eggs in UV sensitive stages than for those in resistant stages. In addition, no cyclic change of UV sensitivity in eggs during early cleavage stages (from 200 to 400 min after oviposition) was observed in accordance with the division cycly, in spite of a cyclical change in sensitivity to ionizing radiation during cleavage of the silkworm as reported by Myrakami (1969). This suggests that injury the nuclei in early stages are not responsive to UV killing of the embryos because the nuclei are protected by the cytoplasm. Although the cytoplasm per se was not so sensitive to UV, the death of cleaving eggs may be attributable, in part, to the cytoplasmic injury caused by its direct exposure to UV. This suggestion might be relevant to the observation that the cytoplasm is able to repair its damage induced by ionizing radiation. In any case, the present study indicated that the lethal effect of UV to the embryos is related to the event occurring within or governed by both nucleus and cytoplasm in the silkworm egg.
- 社団法人日本動物学会の論文
- 1972-01-15
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関連論文
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- カイコ発生初期卵に対する紫外線の影響その生物学的意義