Abstract
Inhibition by actinomycin D has been used to show some of the processes which characterize the oocytes growth. 1. 1. The incorporation of radioactive precursors ( 3H-orotic acid and 3H-arginine) reveals an increased nuclear metabolism at the end of oogenesis. This fact is confirmed by experiments with actinomycin D which, by inhibiting the release and migration of RNA and of basic proteins, causes an accumulation of these substances in the nucleus. 3H-orotic acid is incorporated preferentially in chromatin. 2. 2. Microscopical examinations show that most of the cellular elements (nuclear and cytoplasmic) are affected by the antibiotic. Apparition of aberrant cytoplasmic structures is a manifestation of this fact: they are fibrillar formations in the cytoplasm of young oocytes and twisted lamellae around the nuclear membrane of older ones. All cellular components reacting to the action of the actinomycin D are characterized by the presence of RNA. 3. 3. In mature oocytes, actinomycin particularly affects basophilic particles called “heavy bodies”. As a result, after fertilization, embryonic growth is stopped without alteration of the mitotic mechanism. The “heavy bodies” are rather similar in appearance to the micronucleoli and might contain RNA-m liberated in the cytoplasm during the transformation of the voluminous nucleus of the oocyte in the small female pronucleus.
Published Version
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