Immunolocalization of lamins in the thick nuclear lamina of human synovial cells

While in the great majority of cells the nuclear lamina is not resolved as a distinct structure separating the chromatin from the nuclear envelope, a demonstrable nuclear lamina ("fibrous lamina") of 30 to 300 nm thickness, interposed between the inner nuclear membrane and the peripheral chromatin, is characteristic for certain types of cells of vertebrates and invertebrates. We have examined whether the thick (50-70 nm) fibrous lamina of human synovial cells from patients suffering from rheumatoid arthritis indeed contains the lamins found in the indiscernible lamina structures present in most normal cells. We have observed, by electron microscopic immunolocalization, that both the A and the B type lamins occur throughout the entire nuclear lamina of these cells and that this structure is also resistant to treatments with nucleases and high salt buffers. This shows that the thick fibrous lamina only seen in certain vertebrate cells is compositionally related to the "masked" nuclear lamina of most other cells which usually is identified only upon removal of the adjacent nuclear structures.