Domain-specific disassembly and reassembly of nuclear membranes during mitosis.

The nuclear envelope contains three distinct membrane domains, the outer membrane, the inner membrane, and the pore membrane, that reversibly vesiculate in mitosis. We previously suggested from single-labeling immunofluorescence microscopy analysis of mitotic cells in culture that mitotic vesiculation of the nuclear membranes may proceed in a domain-specific manner (Chaudhary and Courvalin, J. Cell. Biol. 122, 295-306, 1993). In the present study, we add biochemical support to this hypothesis by sorting domain-specific mitotic vesicles. Antibodies directed against the lamin B receptor, a marker of the inner membrane, and glycoprotein gp210, a marker of the pore membrane, were used to isolate by affinity two populations of mitotic vesicles that were selectively enriched in each of these markers. These two vesicle populations were of different size distribution; the pore membrane-derived vesicles were smaller (80% being < or = 200 nm) than the inner membrane-derived vesicles (80% > or = 200 nm). Double-labeling immunofluorescence microscopy analysis of mitotic cells in culture showed that the time course and topology of disassembly and reassembly of inner and pore membrane domains were different, confirming that domain-specific vesicles are generated during mitosis. In these studies, protein LAP2/thymopoietin beta, another marker of the inner nuclear membrane, was segregating as lamin B receptor, suggesting that both proteins were contained in the same mitotic vesicles.