Abstract
We have previously reported that in mice irradiated in utero or soon after birth, the frequency of translocations did not persist when examined at the age of 20 weeks. One might suspect that this observation is due to longer interval between fetal or neonatal irradiation and chromosome test than that in adult exposures for elimination of aberrant cells. To test the possibility, fetal (day 15.5 p.c.) and adult mice were irradiated with 2 Gy of X-rays, and translocation yields were measured in bone marrow cells at 2-10 weeks after fetal irradiation and at 24-120 hours and 5-11weeks after adult irradiation. Thus, post irradiation time in fetuses is almost the same as in adults. Chromosomes 1 (yellow) and 3 (red) were painted with FISH for detection of translocations. Mean frequency of translocations involving the painted chromosomes was 0.7% at 2-10 weeks after fetal exposures. This value was almost the same as that observed in our previous study (0.5%) when mice were examined at 19-22 weeks after fetal exposures. On the other hand, the higher frequency was clearly observed in adults, i.e., about 3.4% at 24-120 hours and 5-11 weeks after irradiation. These results indicated that the lower frequency of translocations after fetal exposure was not affected by the longer post irradiation time, but a majority of aberrations disappeared from bone marrow in 2 weeks after irradiation of fetuses. We speculated that descendants from survived stem cells in fetuses, which were fortunately free from aberrations, diluted the aberration-bearing cells during the subsequent, normal growth period.
