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Irregularly shaped nuclear envelopes are seen in many of the progeria fibroblasts. The nuclear lamina is a dense (~30 to 100 nm thick) fibrillar network inside the nucleus of eukaryote cells. It is composed of intermediate filaments and membrane associated proteins.
The nuclear envelope is made up of two lipid bilayer membranes, an inner nuclear membrane and an outer nuclear membrane. These membranes are connected to each other by nuclear pores. Two sets of intermediate filaments provide support for the nuclear envelope. An internal network forms the nuclear lamina on the inner nuclear membrane. [7]
The nuclear pore complex (NPC), is a large protein complex giving rise to the nuclear pore. Nuclear pores are found in the nuclear envelope that surrounds the cell nucleus in eukaryotic cells . The nuclear envelope is studded by a great number of nuclear pores that give access to various molecules, to and from the nucleoplasm and the cytoplasm.
During mitosis, lamins are phosphorylated by Mitosis-Promoting Factor (MPF), which drives the disassembly of the lamina and the nuclear envelope. This allows chromatin to condense and the DNA to be replicated. After chromosome segregation, dephosphorylation of nuclear lamins by a phosphatase promotes reassembly of the nuclear envelope.
The nuclear envelope consists of two membranes, an inner and an outer nuclear membrane, perforated by nuclear pores. [ 10 ] : 649 Together, these membranes serve to separate the cell's genetic material from the rest of the cell contents, and allow the nucleus to maintain an environment distinct from the rest of the cell.
The nuclear envelope's structure is determined by a network of intermediate filaments (protein filaments). This network is organized into a mesh-like lining called the nuclear lamina , which binds to chromatin , integral membrane proteins, and other nuclear components along the inner surface of the nucleus.
Smaller molecules are able to pass freely through the nuclear pore to get into and out of the nucleoplasm, while larger proteins need the help of receptors on the surface of the nuclear envelope. [9] The nuclear matrix is also believed to be contained in the nucleoplasm where it functions to maintain the size and shape of the nucleus, in a role ...
Depolymerization of the nuclear lamins leads to disintegration of the nuclear envelope. Transfection experiments demonstrate that phosphorylation of human lamin A is required for lamin depolymerization, and thus for disassembly of the nuclear envelope, which normally occurs early in mitosis.