Effect of Actinomycin-D on the Ultrastructure of Molting in a Parasitic Nematode, Nippostrongylus Brasiliensis

Abstract

The effect of actinomycin_D on the fine structure of the hypodermis of Nippostrongylus brasiliensis was studied during the second molt. The drug inhibited cuticle formation to approximately 90% of control levels, and several ultrastructural alterations were observed in response to treatment with the antibiotic. The morphology of the hypodermis in treated larvae did not progress beyond that state seen in early second stage (L_2) worms. The appearance of large ribosome-bound vesicles derived from the RER in the hypodermis of L_2 treated with 50ug/ml actinomycin-D was diminished, and subsequent cuticle deposition was inhibited. Nucleolar alterations suggestive of segration, capping and fragmentation were observed in worms exposed to the drug for more than 12-18 hr. Configurational changes of RER such as concentric ring formation and aggregation of cisternae near the nuclear envelope were reported. Both actinomycin-D and ? –amanitin induced the formation of nuclear and cytoplasmic crystalline inclusions after 12-18 hr of treatment. The inclusions were not limited by a membrane, and consisted of an aggregation of electron dense particles having an approximate diameter of 100A. The results were correlated with known biochemical and ultrastructural effects of actinomycin-D.