Intranuclear Fibrillar Bodies in Actinomycin D-treated Oocytes

Earlier investigations have shown that actinomycin D, which inhibits DNA-dependent RNA synthesis (Reich et al., 1961) by binding to DNA (Kirk, 1960), has a profound effect on the nuclear structure of cells. Some of the most striking consequences are visible in the nucleoli which exhibit both a decrease in size and a variety of fine structural changes (Journey and Goldstein, 1961; Reynolds et al., 1964; Stevens, 1964; Schoefl, 1964; Jacob and Sirlin, 1964; J6z6quel and Bernhard, 1964; Boloukh&re Presburg, 1965; Stenram, 1965; De Man and Noorduyn, 1967). These alterations commonly involve segregation of nucleolar material into granular, fibrillar, and amorphous components, leading to degranulation of the nucleolar matrix and ultimately resulting in a disintegration of the nucleolar substance. In the present series of experiments, in addition to changes in nucleolar structure, fibrillar bodies have been observed in the nuclei of oocytes after inhibition of RNA synthesis with actinomycin D. Intranuclear fibrils have been previously reported after actinomycin D treatment in a study on cultured amphibian embryonic cells (Jones and Elsdale, 1964; Jones, 1967). The fibrillar bodies reported in this study, however, are very different from those found by Jones and Elsdale; they are composed of many more fibrils and appear more numerous. They are also much larger; in fact, they are sufficiently sizeable so to be readily visible by light microscopy which makes possible the application of cytochemical tests.