The radiosensitivity of spermatogonial stem cells in C3H/101 F1 hybrid mice.

The radiosensitivity of spermatogonial stem cells of C3H/HeH x 101/H F1 hybrid mice was determined by counting undifferentiated spermatogonia at 10 days after X-irradiation. During the spermatogenic cycle, differences in radiosensitivity were found, which were correlated with the proliferative activity of the spermatogonial stem cells. In stage VIIirr, during quiescence, the spermatogonial stem cells were most radiosensitive with a D0 of 1.4 Gy. In stages XIirr-Virr, when the cells were proliferatively active, the D0 was about 2.6 Gy. Based on the D0 values for sensitive and resistant spermatogonia and on the D0 for the total population, a ratio of 45:55% of sensitive to resistant spermatogonial stem cells was estimated for cell killing. When the present data were compared with data on translocation induction obtained in mice of the same genotype, a close fit was obtained when the translocation yield (Y; in % abnormal cells) after a radiation dose D was described by Y = e tau D, with tau = 1 for the sensitive and tau = 0.1 for the resistant spermatogonial stem cells, with a maximal e tau D of 100.