Clonal analysis of radiation-induced translocations in stem-cell spermatogonia of normal and T70H translocation heterozygous mice

7 T(1;13)70H/+ and 13 +/+ male mice were given 2 doses of 250 rad acute X-rays separated by 24 h. The +/+ mice were analysed in 2 groups during the first meiotic division for induced translocations, on average 177 and 233 days after irradiation, and the T70H/+ mice were analysed in parallel with the second group of +/+ males. One testis was treated with normal air-drying procedures yielding a random sample of cells. The other testis was processed according to a new technique, which enabled separate analysis of the various locations along the seminiferous epithelium where groups of cells are synchronously in the diakinesis-metaphase I stage of meiosis. The number of cells in such groups was estimated. Both capita epididymes were used for a sperm count. In agreement with an earlier finding, fewer induced translocations were recovered from the T70H/+ mice than from +/+ mice (10.6 versus 19.2%, air-drying technique).Estimates of the group sizes in combination with the occurrence of induced translocations yielded the following information. A synchronously moving group of diakinesis-metaphase I cells originates from, on average, 1.25 stem cells (Appendix). We found an indication for a reduction in group size by 33% when a clone originated from a stem cell carrying an induced translocation compared with a wild-type clone (see Appendix). Both, the data on group size and the sperm counts indicate that, 7 months after the irradiation, the seminiferous epithelium has not totally recovered. Final recovery seems to be slower or absent in the T70H/+ males. The data obtained from the T70H/+ heterozygotes indicate the stem-cell spermatogonia to be responsible for the reduction of the rate of translocation induction with this karyotype, either due to a reduced formation rate or due to a diminished capacity of some of the induced translocation-carrying stem cells to proliferate into a clone reaching the meiotic divisions.