Radiosensitivity variation during the cell cycle in pronuclear mouse embryos in vitro

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Abstract
Radiosensitivity of pronuclear mouse (B6D2 F1 .times. ICR) embryos was measured in vitro as a function of time during the cell cycle. This was done by measuring the dose of X-rays (LD50) required to prevent development of 50% of the pronuclear embryos to the blastocyst stage in 5 days of culture. LD50 varied from 1-2 Gy [gray] during the period from G1 to the 1st cleavage. The cell cycle of the pronuclear embryo was analyzed by [3H]thymidine autoradiography. Compared to earlier studies on 2-cell mouse embryo radiosensitivity, the pronuclear embryos appear to be more sensitive to radiation than the 2-cell embryos. As judged by the radiation sensitivity on a blastomere basis, the pronuclear embryos are not different in their radiation sensitivity from the 2-cell embryos. During early cleavage stages of mice, radiosensitivity is mainly governed by the content of cells of various cell cycle ages in the embryo.
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