Effect of actinomycin D on the structure of the chromatoid body in the rat spermatids.

The effect of actinomycin D on the chromadoid body of rat spermatids has been studied by light and electron microscopy, high resolution autoradiography and biochemical methods. Actinomycin D caused structural changes in the chromatoid body of young round nucleated spermatids. The normal irregularily lobulated chromatoid body acquired a ring-like configuration 12 h after an intratesticular injection of 2 microgram of the drug. The labelling of the chromatoid body with 3H-uridine which can normally be seen after 12 h was also abolished by actinomycin D. These observations lead to the suggestion that the chromatoid body contains a store of long-lived mRNA molecules that are activated later during spermiogenesis when transcription in the spermatid nucleus has ceased but a high level of protein synthesis still persists.