An in vitro system to study nuclear envelope breakdown.

During mitosis in vertebrate cells, the nuclear compartment is completely disintegrated in the process of nuclear envelope breakdown (NEBD). NEBD comprises the disassembly of nuclear pore complexes, disintegration of the nuclear lamina, and the retraction of nuclear membranes into the endoplasmic reticulum. Deciphering of the mechanisms that underlie these dynamic changes requires the identification of the involved molecular components and appropriate experimental tools to define their mode of action. Here, we describe an in vitro, imaging-based experimental system, which recapitulates NEBD. In our assay, we induce NEBD on nuclei of semi-permeabilized HeLa cells expressing fluorescently tagged nuclear envelope (NE) marker proteins by addition of mitotic cell extract that is supplemented with fluorescently labeled dextran. Time-lapse confocal microscopy is used to monitor the fate of the selected NE marker protein, and loss of the NE permeability barrier is deduced by influx of the fluorescent dextran into the nucleus. This in vitro system provides a powerful tool to follow NEBD and to characterize factors required for the reorganization of the NE during mitosis.