Differential binding of tritiated actinomycin to the nuclei of mammalian spermatogenic cells in vivo.

Abstract

Summary. Chinese hamsters, Cricetulus griseus, were given a single injection of 2·0 μg [3H]actinomycin D directly into the left testis. For 24 hr after injection, the distribution of the radioisotope in the reproductive organs, blood plasma and liver was followed, using liquid scintillation counting techniques. After 24 hr, nearly 50% of the injected dose remained in the left testis while insignificant amounts of label were associated with the right testis. The left epididymis gradually accumulated radioisotope probably by intratubular transport from the left testis. The right epididymis possessed negligible amounts of label after 24 hr. Levels of the antibiotic in blood plasma and liver steadily decreased during the experimental period. Localization of [3H]actinomycin D within the spermatogenic cells of the seminiferous epithelium was determined by autoradiography. The results indicated that the antibiotic was differentially bound by various types of spermatogenic cells. Of the spermatocytes, Stage VIII leptotene nuclei (31·6 grains/nucleus) were much more heavily labelled compared to early Stage V pachytene nuclei (6·2 grains/nucleus). Actinomycin D was lightly bound to nuclei of Step 5 and Step 8 round spermatids (3·6 and 3·8 grains/nucleus, respectively). Elongating spermatid nuclei (Steps 9 to 14) were lightly labelled at best, whereas elongated spermatid nuclei (Steps 15 to 18) were very heavily grained. The label intensity decreased in Step-19 spermatids (spermiation step). Labelling variations among spermatogenic cells may be attributable to the physicochemical state of deoxyribonucleoprotein complexes in these cells.