A critical stage in spermatogenesis for radiation-induced cell death in the medaka fish, Oryzias latipes.

To ensure the high-fidelity transmission by reproductive cells of genetic information from generation to generation, cells have evolved surveillance systems to eliminate genomic lesions by inducing cell suicide and/or DNA repair. In this report, gamma-ray-induced cell death was investigated using the medaka fish, Oryzias latipes, because of the ease with which the differentiation stages of its spermatogenic cells can be identified. After 4.75 Gy gamma irradiation, the maximum rate of death of spermatogonial stem cells was observed at 18 h, and that of differentiating spermatogonia was at 12 h, followed by a peak in the extent of DNA fragmentation detected by the TUNEL assay. Dose-response curves for the death rate showed an obvious increase in the death rate for early-differentiating spermatogonia even after 0.11 Gy irradiation, whereas there were no such increases for spermatogonial stem cells and late-differentiating spermatogonia. In the male germ cells of this fish, the stage during spermatogenesis most sensitive to radiation-induced cell death is in early-differentiating spermatogonia, the immediate descendants of the stem cells. These spermatogonia may have a rigorous surveillance system for genomic lesions induced in spermatogonial stem cells. (C) 2002 by Radiation Research Society.