Radioautographic studies using tritiated phenylalanine have been performed on ovarian oocyte nuclei of Triturus vulgaris meridionalis. In a first experiment, the tritium-labeled aminoacid was intracoelomically injected in females; then pieces of ovary were repeatedly excised at variable time intervals (3. hours to 13 days) after injections. In a second experiment, clusters of oocytes were incubated in H3 phenylalanine and their nuclei were isolated after 2 to 10 1/2 hr of incubation. The results turned out alike in both experiments: nucleoli were labeled after 3 hr and lampbrush chromosomes after 6 hr from the beginning of exposure to tritiated phenylalanine. Furthermore, by incubating isolated nuclei—repeatedly washed and freed from cytoplasm or the nuclear content alone (in this case the nuclear membrane had been previously removed), nucleoli and lampbrush chromosomes were labeled shortly after the beginning of incubation. These last experiments show that protein synthesis may be carried out in oocyte nuclei isolated from cytoplasm: nucleoli and lampbrush chromosomes incorporate H3 phenylalanine and therefore they could be thought to represent nuclear sites of protein synthesis. The lateral structures of lampbrush chromosomes-including those which do not incorporate H3 uridine, such as spheres and globules-are labeled after treatment with H3 phenylalanine. In this respect, spheres and globules are similar to the so-called "Binnenkörper" found in oocyte nuclei of panoistic and meroistic ovaries of Insects.
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Con il contributo del Ministero per i Beni e le Attività Culturali