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Nuclear Envelope and Lamins: Organization and Dynamics

The nuclear envelope (NE) separates the nucleus and the cytoplasm and plays an important role in the maintenance of nuclear structure. The NE undergoes a complex cycle of assembly and disassembly during cell divisions to allow proper segregation of the chromosomes. Recent advances in basic and clinical research, especially in light of a number of human diseases that are collectively called laminopathies (diseases caused by mutations in A-type lamins or lamin-binding proteins), suggest that the NE not only acts as a structural barrier separating the nuclear genome and transcriptional machinery from the cytoplasm, but also serves as a node that integrates the different structural and signalling networks between the nucleus and the cytoplasm. 
 
 
 
Key concepts 
 
 
 
There are three structural components of the nuclear envelope: the outer and inner nuclear membranes, the nuclear pore complexes and the nuclear lamina. 
 
 
 
 
The nuclear lamina is mainly composed of type V intermediate filament proteins called lamins, which contain a C-terminal CAAX motif and undergo extensive post-translational processing. 
 
 
 
 
Lamins are grouped into A- and B-types based on their sequence homologies, biochemical properties and behaviors during mitosis. 
 
 
 
 
Mutations in LMNA, which encodes the A-type lamins, cause multiple distinct diseases that are collectively called laminopathies in humans, including diseases of striated muscle, peripheral neuropathy, lipodystrophy syndromes and premature aging or progeroid syndromes. 
 
 
 
 
Lamins exert multiple functions via interacting with various lamin-binding proteins, including an increasing number of proteins located at the inner nuclear membrane that are retained there because of their interactions with lamin. 
 
 
 
 
The lamin-binding inner nuclear membrane proteins also function to modulate the output of cell–cell signalling via interacting with transcription factors of different signalling pathways and integrate nuclear and cytoplasmic architecture via the LINC complex (linker of nucleoskeleton and cytoskeleton). 
 
 
 
 
The nuclear pore complexes are large protein assemblies that are organized into structures with eightfold rotational symmetry and serve as gated channels that mediate nucleocytoplasmic transport across the nuclear envelope. 
 
 
 
 
The nuclear envelope undergoes ordered disassembly and assembly during mitosis. 
 
 
 
 
Disassembly of the nuclear envelope during mitosis is caused by the mitotic phosphorylation of nuclear envelope components. 
 
 
 
 
Even during interphase, the nuclear envelope is not static. 
 
 
 
 
 
 
Keywords: 
 
nuclear envelope; 
nuclear lamina; 
lamin; 
nuclear membrane; 
nuclear pore complex; 
nucleoporin