Intranuclear undulating membranous structures in cells of a human parosteal osteosarcoma

Large numbers of paracrystalline undulating membranous structures (UMS) were observed in the nuclei of dense cells in a human parosteal osteosarcoma. The electron-dense walls of the structures were 15-20 nm thick, and circular profiles had an outer diameter of 60-70 nm and an inner diameter of 25-30 nm. The UMS-containing cell nuclei displayed a number of other characteristic features, including vermicellar bodies, large numbers of interchromatin granules, and prominent perichromatin granules. The possible significance of these features is discussed.