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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 ?
Coverslips bearing fibrin-trapped cells were immersed in a cytoskeleton-stabilizing lysing medium containing Triton X100, with or without protease inhibitors (1, 3), to produce cytoskeletons within the clot.
In addition, the distribution of F-actin was examined with Texas Red phalloidin in cytoskeletons of molluscan (N.
One well-studied network is the membrane-associated cytoskeleton of the human red blood cell-a two-dimensional network whose elements are tetramers of the protein spectrin.
Although the cytoskeleton chains appear convoluted in the simulation, the chain junctions (the white disks in [ILLUSTRATION FOR FIGURE 1 OMITTED]) fluctuate only slightly around their mean positions.
Horwitz reported at the Keystone integrins meeting that he and his colleagues at the University of Illinois at Urbana-Champaign have isolated a set of proteins that may link integrins to actin, a major constituent of the cytoskeleton.
In this model, IFs provide the core while plectin forms peripheral linkers that connect to MTs, the actin-based cytoskeleton, and membrane structures.
Improved procedures for electron microscopic visualization of the cytoskeleton of cultured cells.
For transmission electron microscopy of cytoskeletons, fresh hemolymph obtained at 6 [degrees] C was diluted into Triton lysis medium containing 0.
In different experiments, erythrocyte cytoskeletons were prepared from hemolymph collected either at room temperature ([approximate]22 [degrees] C) or at cold-seep temperature (coldroom at [approximate]6 [degrees] C); the lysis media were also maintained either at [approximate]22 [degrees] C or [approximate]6 [degrees] C.
We have begun characterizing X with two objectives: first, finding a way to inhibit it that is more practical than the current method of extreme dilution; second, determining whether its mode of action is on the cytoskeleton.