Probability of self-renewing divisions of spermatogonial stem cells in colonies, formed after fission neutron irradiation.

Repopulating spermatogenic colonies, found in the seminiferous epithelium after irradiation with fast-fission neutrons, were studied to determine the chance that a stem cell Asingle (As) spermatogonium would complete a self-renewing division (P). Mathematical formulas originally derived for such studies in haemopoietic colonies were employed, and a method specifically aimed at spermatogenic colonies was developed. The results showed that during the first division after irradiation, P is close to 1.0. P decreases in later generations, but remains 0.7 or higher up to the 4th or 5th divisions. The mean value for P was over 0.8, which is higher than the value of 0.6-0.7 found for stem cells in haemopoietic colonies.