Studies on the ultrastructure of nucleoli in human smooth muscle cells

Abstract

Nucleoli were studied in smooth muscle cells in the stroma of nontumorous portions of prostate glands from patients with prostatic cancer without previous antitumor therapy to provide more information on the presence and ultrastructure of ring-shaped nucleoli in human cells, The results have shown that smooth muscle cells contain nucleoli with varying amounts of nucleolonemas as well as ring-shaped nucleoli which were not previously reported in these cells. Large nucleoli with or without well defined nucleolonemas were usually observed in less mature forms of smooth muscle cells which were rich in ribosomes. In contrast, ring-shaped nucleoli were mostly present in highly differentiated and mature smooth muscle cells characterized by a large number of myofilaments and a low concentration of ribosomes in their cytoplasm. The ultrastructural morphology of ring-shaped nucleoli in these cells did not differ from that in mature lymphocytes, differentiated lymphosarcoma cells, plasmacytes, monocytes, myeloblasts and promyelocytes. In addition, ring-shaped nucleoli were also noted in some endothelial cells of small capillaries and fibrocytes. The finding of ring-shaped nucleoli in these different cell types apparently indicates that the presence and formation of such nucleoli represents a general phenomenon that reflects a reduced but continuing synthesis of ribosome precursors in the nucleolus.