Effect of actinomycin-D on the progesterone induced cytodifferentiation of the chick oviduct epithelium.

The effect of actinomycin D on the ultrastructural changes induced by 5 mg of progesterone in the immature chick oviduct epithelium was studied at 0-24h after injection. The height of the epithelium increased during the experimental period. When actinomycin D was given half an hour before progesterone, it inhibited the formation of secretory granules, whereas it could not prevent the formation of the organelles involved in protein synthesis (polysomes, rough endoplasmic reticulum, Golgi apparatus) and the increase in the amount of mitochondria. On the other hand, actinomycin D enhanced the formation of progesterone induced secretory granules if it was administered after the steroid. Apical vacuoles were present within 2h after a combined treatment with progesterone and actinomycin D. Actinomycin D did not affect the changes in the plasma membrane caused by progesterone. The formation of microvilli and cilia began 7 and 12h, respectively, after progesterone. The epithelial cell plasma membranes developed a marked interdigitation, first observable 2h after progesterone administration. The intercellular spaces were markedly wider after actinomycin D, but not after progesterone only. There were significant changes in nuclear morphology after actinomycin D and progesterone injections. There was marked nuclear shrinkage as well as a significant decrease in the amount of nuclear pores by 2h after actinomycin D, administered either before or after progesterone. The amount of perichromatin granules (35-45 nm) increased following actinomycin D administration. There were no changes in the other nuclear granules. With prior actinomycin D administration, the amount of nucleoli per nucleus was decreased 7h after progesterone, whereas their amount increased within 2h if the actinomycin D treatment followed progesterone injection. Actinomycin D and progesterone treatment increased the incidence of nucleolonemata. Detachment of heterochromatin from the nuclear membrane was slightly delayed by actinomycin D, when given before progesterone. The results can be explained on the basis of transcriptional and post-transcriptional effects of actinomycin D. [ABSTRACT FROM AUTHOR]