STRUCTURAL RELATIONSHIP BETWEEN THE NUCLEOLUS AND THE NUCLEAR-ENVELOPE

A quantitative ultrastructural analysis of the relationship between the invaginations formed by the inner and outer membrane of the nuclear envelope and the nucleoli was performed in a variety of established cell lines [human epidermoid carcinoma KB cells, human oviduct tumor TG cells and rabbit kidney RK13 cells] and in a human liver primary line grown in vitro. Statistical evidence is provided that such invaginations are significantly associated with nucleoli. This anatomical relationship reflects the existence of a junction with a remarkably stable ultrastructure between the nucleolus and the nuclear envelope. Functionally, this association may be related to nucleolocytoplasmic exchanges and/or may represent the mode of mechanical attachment of the nucleolus. The usefulness and limits of such a quantitative analysis to investigate relationships of this sort between 2 organelles are discussed.