[Ultrastructure of the fibrillar center in oocyte nucleoli at the diplonema stage in the golden hamster].

Topography of the fibrillar centre and other nucleolar components has been studied during the oocyte large growth in golden hamster. The fibrillar centre was found to show a tendency to marginal distribution, which is characteristic of the initial period of large growth and its final stages. Localization of the fibrillar centre correlates with the amount of granular component and the general level of the nucleus transcription activity. A possible role of the marginal localization of the nucleolus fibrillar centre in maturating oocytes is discussed as a distinguishing trait of chromosomes that enter into meiosis.