Survival and Renewal of Murine Stem Spermatogonia Following 60 Co g Radiation

Abstract

Spermatogonia, with the exception of the few that are either isolated or paired, exist in clones of varying size, and even though the spermatogonium has been the object of much study, our understanding of the radioresponse of the components of this triumvirate is incomplete. Isolated, paired, and clonal spermatogonia are distinguished most reliably when viewed in segments of seminiferous tubules mounted in toto. Tubular segments were isolated from the testes of 80- to 90-day-old BALB/c mice following irradiation doses of 25 to 800 rad and intervals of 1 to 14 days. Neither isolated nor paired spermatogonia were apparently affected by doses up to 200 rad. In contrast the population of A/sub 1/-spermatogonial clones was markedly reduced by a dose of 25 rad. The D/sub 0/ and n for the clone were 217 rad and 0.5, respectively. In the apparent absence of a significant elevation in necrosis at doses of 20 rad and less, the loss of A/sub 1/ clones was attributed to mitotic inhibition. The comparative unresponsiveness of the isolated spermatogonium to irradiation, its low mitotic rate when contrasted with the clone's high radiosensitivity and mitotic activity, and its apparent ability to excise an abnormal cell and otherwise fragment tomore » give rise to additional clones led to the tentative conclusion that the clone, and not the isolated spermatogonium, is the stem cell.« less