Abstract
We have previously found that in A-survivors who were exposed in utero, only a small increase in the translocation frequency was observed in T lymphocytes (examined at age 40). To clarify the underlying mechanisms, we conducted studies in mice. Pregnant mice (15.5th day p.c.) or mice of various ages were irradiated with 2 Gy of X-rays. When the mice reached the age of 20 weeks, translocation frequencies (FG) were measured with FISH in blood T cells, spleen T cells, and bone marrow (BM) cells. To test the possible involvement of apoptotic elimination of chromosomally damaged cells, fetal mice of p53-/- or p53+/- were also irradiated and examined. FG at 20 weeks of age was very low if mice were irradiated in utero or soon after birth as we have seen in A-survivors, but it gradually increased with the increase of age at the time of exposure, and finally reached the same level of adults after 6 weeks of the age. p53 gene status did not affect the low FG in irradiated fetuses. We also examined acute radiation effect 4 to 48 hrs after the exposure in spleen cells from 4-day old mice, and found many chromatid-type aberrations as we usually find in BM cells from adults. We interpreted the results as indicating that progeny cells from survived stem cells after irradiation, which are aberration free by some reasons in fetuses or neonates, washed out the aberration-bearing lymphoid cells during the growth period. The apparent radioresistant nature of the stem cells is not related to p53 gene status but the underlying mechanisms are not clear as yet.
