Nucleolus and apoptosis.

The nucleolus represents a highly dynamic nuclear compartment of the interphase nucleus. It plays a key role in ribosome biogenesis. The number of nucleoli, their size, and their activity increase in exponentially growing cells; therefore these parameters reflect the proliferating activity of the cells. A variety of staining techniques have been employed to vizualize nucleolar changes in malignant cells. Staining of so-called nucleolar organizer regions (NORs), based upon a strong avidity of nucleolar proteins to bind silver ions, represents the technique most frequently used by pathologists. Nucleolar changes and pleomorphism associated with overt proliferation of tumor cells have also been documented by immunohistochemical and ultrastructural studies. Contrary to cell proliferation, cytostatics-induced changes of nucleolar phenotype in malignant cells point to a potential role of nucleolar components in the execution of active cell death. Recent studies have provided direct clues that so-called death domains and other apoptosis-related proteins are accumulated in nucleoli upon induction of active cell death. It can be concluded that the plurifunctionality of nucleoli regarding cell proliferation and apoptosis could open new vistas toward understanding dysregulation in malignant cells.