Origin of intranuclear inclusions in myeloma cells.

The mechanism of inclusion of the cytoplasmic dense bodies into the nucleus of myeloma cells was studied by transmission electron microscopy. The findings in different cells suggest that the inclusion of the electron-dense bodies is a result of an interaction between the nuclear envelope and the endoplasmic reticulum. The ability of the nuclear membrane to form an extension into the cytoplasm and the connection with the cisternae of endoplasmic reticulum enables the movement of the dense bodies towards the nucleus. The proposed mechanism does not support the concept of a simple invagination of the bodies into the nucleus or that they are produced in the nucleus itself.