Comparative studies on the ultrastructure of nucleoli in human lymphosarcoma cells and leukemic lymphocytes.

various cultured cells by actinomycin D or chromomycin A3 (1 1, 12, 23). In all these cell types, the nucleolar shape seems to reflect a low rate of nucleolar RNA synthesis. Although the ultrastructural morphology of undifferen tiated and well-differentiated cells of lymphosarcomas (poorly and well-differentiated malignant lymphomas) is very similar to leukemic lymphocytes in various stages of their development and maturation (4, 5), the present studies are the first to compare the ultrastructure of the various types of nucleoli in lymphosarcoma cells to those of leukemic lymphocytes (8) and to show the presence of ring-shaped nucleoli in lymphosarcoma cells. The distribution of granular and fibrillar components of ring-shaped nucleoli of these cells also was analyzed. The ultrastructure of ring-shaped nucleoli in lympho sarcoma cells did not differ from that in leukemic lympho cytes. There was a decrease of granular components noted in ring-shaped nucleoli of both leukemic lymphocytes and differentiated lymphosarcoma cells. In addition, micro spherules were observed in some nucleoli of lymphosarcoma cells.