Relation between X-Ray Sensitivity and Stages of the Cell Cycle in Spermatogonia of the Mouse

Abstract

Male mice were injected intraperitoneally with 15 mu C of H/sup 3/- thymidine per mouse, x-irradiated 1 hour later with 20, afterward. Autoradiograms of 5- mu sections of the testes were prepared, and counts were made of the numbers of normal and necrotic, unlabeled and labeled, type A, intermediate, and type B spermatogonia. Results indicate that damaged spermatogonia die as they reach a definite, critical stage in the cell cycle, regardless of the stage at which they were irradiated. Cell death occurs in late interphase or very early prophase for type A and intermediate spermatogonia and in anaphase or telophase for type B spermatogonia. Type B spermatogonia are remarkably resistant to cell killing for a period of about 5 to 7 hours after completion of DNA synthesis. This period corresponds approximately to the duration of prophase. Interphase is the sensitive stage. Since type A and intermediate spermatogonia die before division, the fate of the cells irradiated while in mitosis escapes detection. If the conclusion of a high radioresistance during early division stages drawn for type B spermatogonia also might be applied to type A and intermediate spermatogonia, a key might be provided for the interpretation of the radiation response ofmore » mouse spermatogonia. Thus, the much longer duration of the xray-sensitive period (interphase) and the much shorter duration of the x-ray-resistant period (prophase) of the cell cycle in intermediate and type B spermatogonia in comparison to type A spermatogonia may possibly account for the greater x-ray sensitivity of intermediate and type B cells. Accordingly, the existence in the type A population of four cell generations each having different durations of the x-ray-sensitive and of the x- ray-resistant periods of the cell cycle offers a possible explanation for the heterogeneity of the radiation survival curve of these cells. (auth)« less