Early and Late Chromosome Damage after Exposure to X Rays and Neutrons and Its Biological Implications for Prenatal Development of a Mouse Strain

摘要

The preimplantation embryo of mammals is a very valuable and convenient biological system for studying radiation effects and their biological implications. The development during this prenatal stage is very similar in all mammals. Therefore, extrapolation from mice to humans and vice versa is comparatively easy. During the preimplantation period, the embryo is very radiosensitive, the cell cycle phases are very well defined, and at least during the first cell cycles a high degree of synchrony exists. The first cell divisions can be followed very easily. It can be observed whether the cells have divided once, twice or three times after a radiation exposure which took place during the zygote stage (one cell). The zygote of a mammal is the stem cell par excellence, as from this cell a whole organism develops. Therefore, the integrity of such a cell system can be judged by the prenatal development. Changes in radiosensitivity during the various phases of the cell cycle, cell proliferation and cell differentiation can be investigated by observation of this cell system. As all cells are proliferating and all cells are in the same stages of differentiation during the first cell cycles, the biological system is comparatively homogeneous. Most of the data which are reported in this contribution have been obtained using a mouse strain (Heiligenberger mouse strain, HLG) with a genetic predisposition for a specific malformation, gastroschisis; some experiments were done with mice which were crossbred with C57BL mice. The mice were irradiated after a short mating period (3 h) with X rays (250 kV) or cyclotron neutrons (average 6 MeV). During the irradiation period the zygote was in the stage 1 h postconception (p.c.).