Sunday 13 July 2003
In higher eukaryotes, the nuclear envelope breaks down during mitosis and nuclear pore complexes disassemble.
The outer-most part of the nucleus is the nuclear envelope. This consists of a double lipid bilayer. The nuclear envelope completely surrounds the nucleoplasm.
The double-membrane acts as a barrier to water-soluble substances. Clusters of membrane bound proteins form a basket-like apparatus called nuclear pore complex (NCP). These apparati allow the passage of RNA and proteins to flow in and out of the nucleus. The structural strength of the nucleus comes from a layer of nuclear lamina that lies just inside of the nuclear membrane.
The nuclear envelope is composed of the nuclear lamina, the nuclear pore complexes, and the nuclear membranes.
The nuclear lamina is a discontinuous structure that occupies only a fraction of the nuclear periphery, and at some points, the inner nuclear membrane may interact directly with the chromatin.
The nuclear membranes can be divided into 3 morphologically distinct but interconnected domains: the outer nuclear membrane, the inner nuclear membrane, and the nuclear pore membrane.
- The inner nuclear membrane is adjacent to the nuclear lamina, a meshwork of intermediate filament proteins termed lamins.
- Several integral proteins of the nuclear envelope inner membrane that may be associated with the lamina and the chromatin have been identified. The first was a protein called lamin B receptor (LBR) that binds in vitro to lamin B.
Regulation of transcription
Cells have evolved sophisticated multi-protein complexes that can regulate gene activity at various steps of the transcription process. Recent advances highlight the role of nuclear positioning in the control of gene expression and have put nuclear envelope components at centre stage. On the inner face of the nuclear envelope, active genes localize to nuclear-pore structures whereas silent chromatin localizes to non-pore sites. Nuclear-pore components seem to not only recruit the RNA-processing and RNA-export machinery, but contribute a level of regulation that might enhance gene expression in a heritable manner.
nuclear membrane proteins (nuclear envelope proteins)
nuclear pore complexes (NPCs)
- pathology of lamins
- pathology of lamin receptors
Pathology (nuclear envelopathies)
emerin deficiency results in X-linked Emery-Dreifuss muscular dystrophy (EDMD).
lamin A/C mutations cause
- autosomal-dominant form of EDMD
- limb-girdle muscular dystrophy with atrioventricular conduction disturbances (type 1B)
- hypertrophic cardiomyopathy and Dunnigan-type familial partial lipodystrophy
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