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A system of filaments found in the cytoplasm of cells and responsible for the maintenance of and changes in cell shape, cell locomotion, movement of various elements in the cytoplasm, integration of the major cytoplasmic organelles, cell division, chromosome organization and movement, and the adhesion of a cell to a surface or to other cells.

Three major classes of filaments have been resolved on the basis of their diameter and cytoplasmic distribution: actin filaments (or microfilaments) each with an average diameter of 6 nanometers, microtubules with an average diameter of 25 nm, and intermediate filaments whose diameter of 10 nm is intermediate to that of the other two classes. The presence of this system of filaments in all cells, as well as their diversity in structure and cytoplasmic distribution, has been recognized only in the modern period of biology.

A technique that has greatly facilitated the visualization of these filaments, as well as the analysis of their chemical composition, is immunofluorescence applied to cells grown in tissue culture. See Immunofluorescence

Actin is the main structural component of actin filaments in all cell types, both muscle and nonmuscle. Actin filaments assume a variety of configurations depending on the type of cell and the state it is in. They extend a considerable distance through the cytoplasm in the form of bundles, also known as stress fibers since they are important in determining the elongated shape of the cell and in enabling the cell to adhere to the substrate and spread out on it. Actin filaments can exist in forms other than straight bundles. In rounded cells that do not adhere strongly to the substrate (such as dividing cells and cancer cells), the filaments form an amorphous meshwork that is quite distinct from the highly organized bundles. The two filamentous states, actin filament bundles and actin filament meshworks, are interconvertible polymeric states of the same molecule. Bundles give the cell its tensile strength, adhesive capability, and structural support, while meshworks provide elastic support and force for cell locomotion.

Microtubules are slender cylindrical structures that exhibit a cytoplasmic distribution distinct from actin filaments. Microtubules originate in structures that are closely associated with the outside surface of the nucleus known as centrioles. The major structural protein of these filaments is known as tubulin. Unlike the other two classes of filaments, microtubules are highly unstable structures and appear to be in a constant state of polymerization-depolymerization. See Centriole

Intermediate filaments function as the true cytoskeleton. Unlike microtubules and actin filaments, intermediate filaments are very stable structures. They have a cytoplasmic distribution independent of actin filaments and microtubules. In the intact cell, they anchor the nucleus, positioning it within the cytoplasmic space. During mitosis, they form a filamentous cage around the mitotic spindle which holds the spindle in a fixed place during chromosome movement.


(cell and molecular biology)
Protein fibers composing the structural framework of a cell.
References in periodicals archive ?
The drip loss in fresh meat is believed to be influenced by the genetics, rate of post mortem pH decline and stress [2], and structurally originates from the shrinkage of myofibrils, the permeability change of the cell membrane and the cytoskeletal protein degradation [1].
Then we measured the expression of cytoskeletal proteins ([alpha]-SMA and vimentin) by TGF-[beta]1 stimulation.
2006): "A keratin cytoskeletal protein regulates protein synthesis and epithelial cell growth", en Nature 441: 362-365.
While there has been tremendous interest in aberrant phosphorylation of cytoskeletal proteins in central nervous system disorders such as Alzheimer's disease and amyotrophic lateral sclerosis and its relation to degenerative changes, (48-50) the alterations, if any, in NF phosphorylation of peripheral nerves from these disorders is not completely understood.
Furthermore, the brains of alcohol-fed animals had higher levels of the degradation products of a cytoskeletal protein called spectrin, which is degraded by calpains.
All cytoskeletal proteins displayed strong immunoreactivity (Table).
Adhesion phase occurring at long term contact involves various biological molecules like extracellular matrix proteins, cell membrane proteins and cytoskeletal proteins which interact together to induce signal transduction, promoting the action of transcription factors and consequently regulating gene expression (2).
Because PC12 cells are particularly rich in cytoskeletal proteins (16) and because SLE patients may present serum antibodies against these proteins (17), it is likely that the positivity of the two SLE serum samples was caused by the recognition by antibodies of non-AChR proteins, probably cytoskeletal proteins.
In addition to making specific kinds of receptors, the neuron may also need new types of cytoskeletal proteins in order to regrow.
Examples of these are virus assembly systems, repressor-DNA interactions, cytoskeletal proteins, multienzyme complexes, muscle protein assemblies, immunio-complexes, blood clotting proteins, ribosomes, and RNA-protein complexes.
Eighth-place winner Yves Jude Jeanty of Stuyvesant identified telltale changes in cytoskeletal proteins that may indicate the ability of cells to move away after one collides with another.
These genes are involved in energy metabolism (glycolysis and electron transport), oxidative stress and production of cytoskeletal proteins, all of which could be involved in the growth of new skin during wound healing.