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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 ?
Then we measured the expression of cytoskeletal proteins ([alpha]-SMA and vimentin) by TGF-[beta]1 stimulation.
All cytoskeletal proteins displayed strong immunoreactivity (Table).
Antibodies to T- and L-isoforms of the cytoskeletal protein, fimbrin, in patients with systemic lupus erythematosus.
Phosphorylation of membrane-associated cytoskeletal proteins affects red blood cell shape, and a disruption of the normal pattern of phosphorylation may contribute to the formation of acanthocytes.
Several host cytoskeletal proteins are involved in tail formation, including [Alpha]-actinin (48), filamin (59), fimbrin (59), vasodilator-stimulated phosphoprotein (VASP) (60), vinculin (49,61), and neural-Wiskott-Aldrich syndrome protein (N-WASP) (63).
2004), suggesting that a rearrangement of cytoskeletal proteins has a role in the intracellular accumulation of lipid droplets (Luegmayr et al.
In addition to providing valuable insight to advance drug discovery and development efforts, the small molecule compounds identified using these assays may prove useful as tools in elucidating the identity, roles and regulation of cytoskeletal proteins involved in various processes, such as actin and microtubule dynamics in pathogens including various Candida species, E.
Microcystin-LR is a strong inhibitor of protein phosphatase 1 and 2A and eventually causes hyperphosphorylation of cytosolic and cytoskeletal proteins (14).
However, Cdk5 is also found in differentiated neurons, where it seems to be involved in stopping the neurons dividing and in regulating synaptic plasticity and cytoskeletal proteins such as tau, a pathological form of which characterises some forms of neurodegeneration (Karl Herrup, Case Western Reserve University, Cleveland, USA).
expression of certain genes, or actions of cytoskeletal proteins.
For drug discovery, PCA has been applied to numerous receptor-activated pathways (GPCRs, cytokine and growth factor receptors and nuclear hormone receptors), signal transduction pathways (kinases, phosphatases and ligases), transcription factors, cytoskeletal proteins, and biosynthetic pathways.