The induction of chromosomal damage and cell killing in mouse spermatogonial stem cells following combined treatments with hydroxyurea, 3-aminobenzamide and X-rays

To analyze in more detail the relation between the sensitivity of spermatogonial stem cells to killing and the induction of genetic damage, mature male mice received combined treatments with hydroxyurea (HU), 3-aminobenzamide (3-AB) and X-rays. Stem cell killing was determined using the repopulation index method and translocations were studied via spermatocyte analysis. HU was administered at 16 or at 48 h before further treatment in order to create stem cell populations with different sensitivities in whic the translocation induction and stem cell killing could be studied and compared. The sensitivities for cell death and genetic damage appeared to be strongly correlated: at 16 h after HU significantly higher values were found than at 48 h or in controls without HU pretreatment.By using 3-AB in the treatment schedules we were able to investigate whether the sensitization of stem cells towards cell death and genetic damage is the outcome of a radiation- or drug-induced G₁ delay. The effect of 3-AB was most pronounced at 16 h after HU. This confirms that at this interval a large fraction of stem cells is in G₁. Our data therefore indicate that all treatments that induce an enrichment of G₁ cells also result in a sensitization of stem cells to cell killing or the induction of mutagenic damage.