Distribution of emerin during the cell cycle

Human emerin is a nuclear membrane protein that is lost or altered in patie nts with Emery-Dreifuss muscular dystrophy (EMD). While the protein is expr essed in the majority of human tissues analyzed, the pathology predominates in cardiac and skeletal muscles of patients with EMD. Our results show that emerin can be detected by immunocytochemistry and imm unoblotting in the nuclear envelope of all vertebrates studied from man to Xenopus. Immunolocalizations and nuclear envelope extraction experiments co nfirm that emerin possesses properties characteristic for integral membrane proteins of the inner nuclear membrane. Some nuclear envelope proteins are localized also in annulate lamellae (AL) , i.e. cytoplasmic flattened membrane cisternae penetrated by pore complexe s. To verify whether emerin is contained in these membrane stacks, we have induced the formation of AL by exposure of rat cells (line RV-SMC) to suble thal doses of the antimitotic drug vinblastine sulfate and found that emeri n is present in the nuclear envelope, but is absent from AL. In contrast to the homogeneous distribution of emerin in the nuclear envelo pe of interphase cells, this protein shows a focal accumulation in the nucl ear membranes of late telophase cells. During early reassembly of the nucle ar envelope at this mitotic stage emerin colocalizes with lamin A/C but not with lamin B and LAP2 proteins, Confocal! laser scanning microscopy after double-labeling experiments with emerin and tubulin shows that emerin is co ncentrated in areas of the mitotic spindle and in the midbody of mitotic ce lls suggesting a close interaction of these proteins. Our data suggest that emerin participates in the reorganisation of the nuclear envelope at the e nd of mitosis.