The behaviour and structure of the leading lamella during fibroblast locomotion: Centripetal movements of arc-shaped microfilament bundles beneath the dorsal cell surface

Heath, Julian P.

doi:10.1016/0309-1651(81)90079-5

Cited by 56 publications

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“…The dynamics of actin in these lamella are particularly interesting since the isotropic actin gel is transformed over time into an increasingly bundled gel and is concomitantly infiltrated with myosin (DeBiasio et al, 1988) . In the fibroblast, a progression of cytoskeletal arrangements is seen from the newly polymerized actin network at the leading edge (Wang, 1985), to the production of "arcs" (Heath, 1983) composed of small bundles of filaments which are continually swept towards the nucleus where an arrangement oflarger perinuclear actin bundles known as the cellular geodome is found . As actophorin-like proteins (Mabuchi, 1983;Bamburg et al, 1980) and gelsolin (another actin filament severing protein), have been isolated from a number of vertebrate sources, it is possible that severing activity in concert with crosslinking proteins also found in protruding lamella (Geiger et al, 1984) form an increasingly anisotropic gel by a mechanism similar to that postulated here.…”

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The actin filament severing protein actophorin promotes the formation of rigid bundles of actin filaments crosslinked with alpha-actinin.

Maciver

Wachsstock

Schwarz

et al. 1991

The Journal of Cell Biology

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Abstract. The actin filament severing protein, Acanthamoeba actophorin, decreases the viscosity of actin filaments, but increases the stiffness and viscosity of mixtures of actin filaments and the crosslinking protein a-actinin . The explanation of this paradox is that in the presence of both the severing protein and crosslinker the actin filaments aggregate into an interlocking meshwork of bundles large enough to be visualized by light microscopy. The size of these bundles depends on the size of the containing vessel . The actin filaments in these bundles are tightly packed in some areas while in others they are more disperse. The bundles form a continuous reticulum that fills the container, since the filaments from a particular bundle S NCE the first descriptions of ameboid locomotion a century and a half ago, the concept of a reversible transformation between "sol" and "gel" has been central to hypothesis attempting to explain the phenomenon. Although it was proposed that the protoplasm is a contractile three-dimensional reticulum as early as 1873 (De Bruyn, 1947), only in comparatively recent times has this reticulum been shown to be mainly an actin-based system (Pollard and Ito, 1970) . Subsequent research has revealed that cytoplasmic actin filaments are associated with myosin (reviewed by Korn and Hammer, 1988) and a number of other proteins that regulate actin filament assembly and crosslinking (reviewed by Stossel et al., 1985, andPollard and . Because there are multiple crosslinking proteins in these cytoplasmic actin gels, the physiological function of the individual crosslinking proteins by mutation or gene disruption is difficult to demonstrate (Wallraff et al ., 1986;Schleicher et al., 1988). Consequently most of our knowledge about cytoplasmic actin gels has come from in vitro reconstitution with actin and purified individual crosslinkers such as a-actinin.Alpha-actinin is a major actin crosslinking protein in skeletal muscle and nonmuscle cells . Skeletal muscle a-actinins are calcium-insensitive crosslinking proteins. Some, but not all, a-actinins from smooth muscle and nonmuscle cells are inhibited by calcium . Acanthamoeba a-actinin is calcium insensitive but is otherwise a typical a-actinin (Pollard, 1981;

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Section: Physiological Relevance Of These Findingsmentioning

confidence: 99%

The actin filament severing protein actophorin promotes the formation of rigid bundles of actin filaments crosslinked with alpha-actinin.

Maciver

Wachsstock

Schwarz

et al. 1991

The Journal of Cell Biology

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“…At least one end of the stress fiber is usually attached to the membrane, opposite to the site of adhesion plaque on the external surface (10, 12). Besides stress fibers, actin bundles have also been identified in the "arcs" of spreading cells (9,20) and in microvilli (26).Although these different types of bundles probably represent different structures and probably serve different functions, they share a common characteristic: the ability to reorganize. For example, "arcs" form near the leading edge of the cell, then move toward the nucleus and disappear (9,20).…”

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“…Besides stress fibers, actin bundles have also been identified in the "arcs" of spreading cells (9,20) and in microvilli (26).…”

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“…For example, "arcs" form near the leading edge of the cell, then move toward the nucleus and disappear (9,20). Stress fibers exhibit a drastic reorientation when cells are placed in an electric field (16).…”

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Reorganization of actin filament bundles in living fibroblasts.

Wang¹

1984

The Journal of Cell Biology

141

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We investigated how actin bundles assemble, disassemble, and reorganize during cell movement. Living chick embryonic fibroblasts were microinjected with actin molecules that had been fluorescently labeled with tetramethylrhodamine. We found that the fluorescent analogue of actin can be used successfully by both existing and newly formed cellular structures. Using time-lapse photography coupled to image-intensified fluorescence microscopy, we were able to detect various patterns of reorganization in motile cells~ Assembly of stress fibers occurred near both the leading and the trailing ends of the cell. The initial structure appeared as discrete spots that subsequently extended into stress fibers. The extension occurred unidirectionally. The site of initiation near the leading edge remained stationary relative to the substrate during subsequent cell advancement. However, the orientation of the fiber could change according to the direction of cell movement. In addition, existing stress fibers could merge or fragment. The shortening of stress fibers can occur from either end of the fiber. Shortening from the proximal end (centrifugal shortening) was accompanied by a decrease in fluorescence intensity, as if the bundle were disassembling, and usually led to the total disappearance of the bundle. Shortening from the distal end (centripetal shortening), on the other hand, is usually accompanied by an increase in fluorescence intensity at the distal end of the bundle, as if this end had pulled loose from its attachment and retracted toward the center of the cell. Besides stress fibers, arc-like actin bundles have also been detected in spreading cells. These observations can explain how the organization of actin bundles coordinates with cell movement, and how stress fibers reach a highly regular pattern in static cells.Light and electron microscopic studies have clearly demonstrated the presence of actin bundles in nonmuscle cells (2). The most prominent class, stress fibers, contain a number of accessory proteins such as alpha-actinin, tropomyosin, and myosin, arranged in a regular pattern somewhat similar to that in myofibrils (7,14,18). At least one end of the stress fiber is usually attached to the membrane, opposite to the site of adhesion plaque on the external surface (10, 12). Besides stress fibers, actin bundles have also been identified in the "arcs" of spreading cells (9,20) and in microvilli (26).Although these different types of bundles probably represent different structures and probably serve different functions, they share a common characteristic: the ability to reorganize. For example, "arcs" form near the leading edge of the cell, then move toward the nucleus and disappear (9,20). Stress fibers exhibit a drastic reorientation when cells are placed in an electric field (16). Even in relatively static cells, changes in the organization of actin bundles have been detected (29). This is not surprising in view of the highly dynamic nature of the actin filaments, which are capable of polymerization-...

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Effects of electroporation on the tubulin cytoskeleton and directed migration of corneal fibroblasts cultured within collagen matrices

Harkin

Hay

1996

Cell Motil. Cytoskeleton

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The behaviour and structure of the leading lamella during fibroblast locomotion: Centripetal movements of arc-shaped microfilament bundles beneath the dorsal cell surface

Cited by 56 publications

References 0 publications

The actin filament severing protein actophorin promotes the formation of rigid bundles of actin filaments crosslinked with alpha-actinin.

The actin filament severing protein actophorin promotes the formation of rigid bundles of actin filaments crosslinked with alpha-actinin.

Reorganization of actin filament bundles in living fibroblasts.

Effects of electroporation on the tubulin cytoskeleton and directed migration of corneal fibroblasts cultured within collagen matrices

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