Cytoskeleton actin microfilaments

The Locomotion of Amoeba The Locomotion of Fibroblastic Cell Types The Locomotion of Leukocytes The Behavior of Locomoting Cells The Role of the Cytoskeleton in Cell Locomotion The Microtubule-Based Cytoskeleton The Intermediate Filament-Based Cytoskeleton The Microfilament-Based Cytoskeleton The Organization of Microfilaments in Cells Microfilament Dynamics and Cell Locomotion Sites of Lamellar Protrusion May Be Determined by the Nucleation of Actin Polymerization... 

Actin microfilaments and the membrane cytoskeleton play critical roles in neuronal growth and secretion 129... 

Actin filaments are the thinnest of the cytoskeletal filaments, and therefore also called microfilaments. Polymerized actin monomers form long, thin fibers of about 8 nm in diameter. Along with the above-mentioned function of the cytoskeleton, actin interacts with myosin ( thick ) filaments in skeletal muscle fibers to provide the force of muscular contraction. Actin/Myosin interactions also help produce cytoplasmic streaming in most cells. 

An essential component of skeletal muscle (discussed further in Chapter 19) is filamentous actin (F-actin). It is composed of 375-residue globular subunits of a single type and with a highly conserved sequence.60 61 It is found not only in muscle but also in other cells where it is a component of the cytoskeleton. The actin microfilament has the geometry of a left-... 

The most abundant microfilaments are composed of fibrous actin (F-actin Fig. 7-10). The thin filaments of F-actin are also one of the two major components of the contractile fibers of skeletal muscle. There is actually a group of closely related actins encoded by a multigene family. At least four vertebrate actins are specific to various types of muscle, while two (P- and y-actins) are cytosolic.298 299 Actins are present in all animal cells and also in fungi and plants as part of the cytoskeleton. The microfilaments can associate to... 

In addition, several annexins have been shown to interact directly or indirectly with actin microfilaments and microtubules, thus annexins have the potential to form a structural link between the membrane and the underlying cortical cytoskeleton (reviewed in Gerke et al. 2005 Hayes et al., 2004). As well as lateral inter-annexin interactions (either homotypic or heterotypic with other types of annexin)... 

Eukaryotic cells have an internal scaffold, the cytoskeleton, that controls the shape and movement of the cell. The cytoskeleton is made up of actin microfilaments, intermediate filaments and microtubules. 

Together with actin microfilaments and microtubules, keratin filaments make up the cytoskeleton of vertebrate epithelial cells. Keratins belong to a family of intermediate filament proteins that form a-helical coiled-coil dimers that associate laterally and end to end to form 10 nm diameter filaments. Keratin and actin filaments and microtubules form an integrated cytoskeleton that preserves the shape and structural integrity of the ker-atinocyte as well as serves to transmit mechanical loads. Keratins account for about 30% of the total protein in basal cells. 

Disrupts actin cytoskeleton (cell adhesion inhibitor) [attractant feeding deterrent, antineoplastic, cytotoxic] Disrupts actin cytoskeleton blocks cell division by blocking actin microfilament formation [inhibits Glc transport, toxic]... 

Actin is one of the most highly conserved proteins and the monomeric subunit of microfilaments (Alberts et aL 2002 Perry and Cotterill 1965). Microfilaments belong to one of the three major components of the cytoskeleton. Actin is also a component of thin filaments managing contractility in muscle cells. Overall, actin serves in a variety of critical cellular mechanisms such as cell division, motility and shape, vesicle movement, signal transduction, and assembly and maintenance of cell junctions. 

Fig. 8 Confocal fluorescence microscopy of B50 neuroblastoma cells, (a, b) Immunolabeling of mtHSP70 green) in B50 cells in controls (a) and cisPt-treated cells (b). After cisPt, mitochondria are clustered around the nucleus and form dense masses in the cytoplasm (b). Nuclei are counterstained with Hoechst blue), (c, d) Double immunolabeling of filamentous actin red) and a-tubulin green) in B50 control cells (c) and in 48 h cisPt-treated cells (d). CisPt-induced cytoskeleton damage leads tubulin to reorganize into thick bundles (e) and to disruption of filamentous actin microfilaments and accumulation of depolymerized actin at cell periphery (f).

Microfilaments and Microtubules. There are two important classes of fibers found in the cytoplasm of many plant and animal ceUs that are characterized by nematic-like organization. These are the microfilaments and microtubules which play a central role in the determination of ceU shape, either as the dynamic element in the contractile mechanism or as the basic cytoskeleton. Microfilaments are proteinaceous bundles having diameters of 6—10 nm that are chemically similar to actin and myosin muscle ceUs. Microtubules also are formed from globular elements, but consist of hoUow tubes that are about 30 nm in diameter, uniform, and highly rigid. Both of these assemblages are found beneath the ceU membrane in a linear organization that is similar to the nematic Hquid crystal stmcture. 

The cytoskeleton also contains different accessory proteins, which, in accordance with their affinities and functions, are designated as microtubule-associated proteins (MAPs), actin-binding proteins (ABPs), intermediate-filament-associated proteins (IFAPs), and myosin-binding proteins. This chapter is focused on those parts of the cytoskeleton that are composed of microfilaments and microtubules and their associated proteins. The subject of intermediate filaments is dealt with in detail in Volume 2. 

The Cytoskeleton—Microtubules and Microfilaments Patterns of Arrangement of Actin Filaments in Animal Cells... 

Nonmuscle cells perform mechanical work, including self-propulsion, morphogenesis, cleavage, endocytosis, exocytosis, intracellular transport, and changing cell shape. These cellular functions are carried out by an extensive intracellular network of filamentous structures constimting the cytoskeleton. The cell cytoplasm is not a sac of fluid, as once thought. Essentially all eukaryotic cells contain three types of filamentous struc-mres actin filaments (7-9.5 nm in diameter also known as microfilaments), microtubules (25 nm), and intermediate filaments (10-12 nm). Each type of filament can be distinguished biochemically and by the electron microscope. 

Two major types of muscle fibers are found in humans white (anaerobic) and red (aerobic). The former are particularly used in sprints and the latter in prolonged aerobic exercise. During a sprint, muscle uses creatine phosphate and glycolysis as energy sources in the marathon, oxidation of fatty acids is of major importance during the later phases. Nonmuscle cells perform various types of mechanical work carried out by the structures constituting the cytoskeleton. These strucmres include actin filaments (microfilaments), micrombules (composed primarily of a- mbulin and p-mbulin), and intermediate filaments. The latter include keratins, vimentin-like proteins, neurofilaments, and lamins. 

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