[The nucleolus in oocytes of multylayer mouse follicles: topography of fibrillarin, RNA polymerase I and coilin].

By electron microscopy, conventional fluorescence and confocal microscopy, some features of structural and molecular organization of the nucleolus in oocyte nucleus from mouse multilayer follicles were examined. The examined nucleolus lacks almost all characteristic nucleolar components, such as fibrillar centers, dense fibrillar and granular components. This nucleolus consists exclusively of a homogenous filamentous material and is penetrated by numerous interstices. Besides, a striking association of the nucleolus with coilin, a marker of Cajal bodies, was observed. We could map the coilin accumulation in three different areas: around, in the periphery, or inside the nucleolus. Additionally, we examined a topological relationship between coilin and two key proteins of nucleolar transcription-processing machinery, RNA polymerase I and fibrillarin. RNA polymerase I rather than fibrillarin was found to be colocalized with coilin. Finally, we propose that data on dynamics of coilin relation with the nucleolus may elucidate a possible role of coilin in functional relationship between the nucleolus and Cajal bodies.