Radiation-induced DNA single-strand scission and its rejoining in spermatogonia and spermatozoa of mouse.

Gamma-ray-induced DNA single-strand scissions and the ability to repair the scissions in spermatogonia from young mice and in spermatozoa from adult mice were studied quantitatively by an alkaline sucrose density-gradient centrifugation method. The average size of DNAs in non-irradiated spermatogonia was 2.6--3.0 X 10(8) daltons, similar to those of a spermatid-rich population, and the size of DNA in non-irradiated spermatozoa was 1.2 X 10(8) daltons. In spermatogonia, the radiosensitivity of DNA was 0.42 single-strand breaks/10(12) daltons of DNA/rad in oxic conditions and only 0.24 under anoxic conditions. In spermatozoa the break efficiency of DNA was 0.22 single-strand breaks/10(12) daltons of DNA/rad under oxic conditions and altered little under anoxic irradiation. The DNA scissions were efficiently repaired in spermatogonia within 10 min, whereas the breaks in spermatozoa were not rejoined at all even after two days of post-irradiation time. The radiosensitivities of DNA, repair capability and non- and/or slow-reparable DNA scissions were compared in spermatogonium-rich, spermatid-rich and spermatozoan-rich populations.