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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 ?
Involvement of actin filaments in budding of measles virus: studies on cytoskeletons of infected cells.
Because there was no effect on the actin cytoskeleton in this case, the downstream target of Rho kinase is mostly likely myosin II.
As further evidence that conscious is related to microtubules, he notes that several dissimilar anaesthetics (and even Xenon, an inert gas) turn consciousness off and also immobilize paramecia, which themselves have cytoskeletons. Additionally, he brings in counterfactuality--the possible effect of the classical "wiring," even though the associated neurons do not actually fire.
The actin cytoskeleton forms the scaffold of cardiomyocytes, which is also required for regulating the signaling pathway and related gene expression under both physiological and pathological conditions [17-21].
Evidence accumulated from studies of our group in the last years point to a critical role of the endogenous phosphorylation of IF proteins in response to a variety of signals in both physiological and pathological conditions [116,148,149, 152, 175-177], highlighting the cytoskeleton as a preferential target of the signal transduction pathways.
They found that, in ground squirrel neurons, the microtubule cytoskeleton remains intact while it deteriorates in the neurons of humans and other nonhibernating animals, including rats.
It is associated with endoplasmic reticulum, ribosome, Golgi apparatus, lysosomes, mitochondria, multiple vesicles that are supposed to be arranged on the dynamic cytoskeleton. This is to ensure specific cell activity of DNA replication, repair and chromosome formation during interphase.
Actin is important to a number of vital cell functions, including maintenance of the cytoskeleton, which defines cell shape and structure.
In this context, in order to have standard culture conditions for the maintenance of stem cells and the possibility of testing the effect of any kind of biomaterial on these cells, it is mandatory to elucidate intracellular events produced by the involvement of the cytoskeleton and mechanotransduction, which is the transduction of mechanical stimulus into intracellular signaling, both chemical and biophysical.
In the article titled "Moderate Fluid Shear Stress Could Regulate the Cytoskeleton of Nucleus Pulposus and Surrounding Inflammatory Mediators by Activating the FAK-MEK5-ERK5-cFos-AP1 Signaling Pathway" [1], a grant number was missing.
Cell polarity is the asymmetric organisation of several cellular components, including its plasma membrane, cytoskeleton or organelles.
During the process of EMT, cell-cell and cell-extracellular matrix (ECM) adhesions are changed with the loss of epithelial markers (such as E-cadherin) and the gain of mesenchymal markers (such as vimentin), leading to reorganization of the actin cytoskeleton and acquisition of the capability of moving and invading ECM [18-21].