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

Abstract

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 80-90 day old BALB/c mice following irradiation doses of 25-800 rad and intervals of 1-14 days. Neither isolated nor paired spermatogonia were apparently affected by doses up to 200 rad, and the isolated spermatogonium was characterized by D0 of 288 rad and an n of 3.8. In contrast the population of A1-spermatogonial clones was markedly reduced by a dose of 25 rad. The D0 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 200 rad and less, the loss of A1 clones was attributed to mitotic inhibition. Return of the clonal population to the preirradiation level was marked by an increase in asynchronous interclonal differentiation and an increase in mitotic activity within the three spermatogonial classes, this being especially so with respect to the clone. 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 to give rise to additional clones led to the tentative conclusion that the clone, and not the isolated spermatogonium, is the stem cell.