The number of nucleolar silver-stained granules of active nucleolus organizer regions in mitotic and interphase cells of rat Yoshida and Zajdela ascitic tumors.

To provide more information on the number of silver-stained granules (SSGs) of active mitotic nucleolus organizer regions (NORs) as well as interphase nucleoli, rat Yoshida ascitic sarcoma and Zajdela ascitic hepatoma cells were studied by means of standardized one-step and two-step silver-staining procedures. The number of SSGs of mitotic active NORs was relatively constant and corresponded to the number of active NORs of animals bearing the tumors investigated. Some anaphases and telophases were "asymmetric", i.e. chromosomal figures (future nuclei) in one and the same cell contained different number of SSGs (active NORs). The incidence of such asymetric anaphases and telophases was higher in aneuploid (hypoploid) Zajdela hepatoma than in euploid (diploid) Yoshida sarcoma cells. In the interphase, the number of SSGs was low in small or large cells with distinct chromocenters or chromosomes condensation presumably representing postmitotic and premitotic cells. In contrast, the highest number of SSGs was noted in nucleoli of large cells which were usually characterized by a fine chromatin structure.