Absence of translocation induction in mouse stem cell spermatogonia by chemical mutagens probably due to selective elimination

In order to discriminate between different mechanisms put forward to explain the low observed yields of reciprocal translocation configurations at diakinesis-metaphase I spermatocytes following treatment of mouse stem cell spermatogonia with chemical clastogens, the physiological states of stem cells at the moment of treatment were modified. The cell cycle was shortened by pretreatment with 2 Gy of X-rays and/or the DNA repair capacity inhibited by pretreatment with 3-aminobenzamide. Using these conditions the induction of translocations by ethyl methanesulfonate, N-ethyl-N-nitrosourea, methyl methanesulfonate and Adriamycin was studied. The results indicate that selective elimination of aberration carrying cells is probably to a large extent responsible for the low induction rate of translocations in stem cells by chemical clastogens. The high ratio of simple chromosome breaks versus chromosome exchange type aberrations induced by chemical mutagens might be the main cause of the selective elimination.