Polarity of actin at the leading edge of cultured cells

Small, J. Victor; Isenberg, G.; Celis, Julio E.

doi:10.1038/272638a0

Cited by 254 publications

(159 citation statements)

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“…The general organization of the actin cytoskeleton in carcinoma cells resembles closely what has been described previously for chemotactic amoeboid cells such as macrophages (51), leukocytes (55) and Dictyostelium discoideum (52,56,57). Although the extreme edge of the cell has some features comparable to what has been described for constitutively moving cells such as keratocytes (58), the general organization of the actin cytoskeleton in rat adenocarcinoma cells is different.…”

Section: Organization Of the Leading Edge Of Cells After Stimulationsupporting

confidence: 57%

“…In unstimulated cells, the cytoskeleton at the edge of the cell is arranged as a network of long filaments, occasionally in bundles parallel to the edge. When such cells do have a leading edge, the filaments in that particular area are arranged in a 1-1.5 urn wide high density orthogonal network at the edge, very similar to the leading edge of unstimulated fibroblasts (52,54,58,59). The density of the filaments then rapidly decreases a few microns away from the edge.…”

Section: Organization Of the Leading Edge Of Cells After Stimulationmentioning

confidence: 99%

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Molecular Analysis of Motility in Metastatic Mammary Adenocarcinoma Cells

Segall¹

1998

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Section: Organization Of the Leading Edge Of Cells After Stimulationsupporting

confidence: 57%

Section: Organization Of the Leading Edge Of Cells After Stimulationmentioning

confidence: 99%

Molecular Analysis of Motility in Metastatic Mammary Adenocarcinoma Cells

Segall¹

1998

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“…In addition, since a clear increase in fluorescence intensity is detected along the length of the fiber, polymerization or association of additional filaments probably occurs during elongation. This would explain why filaments near the membrane have a uniform polarity (19), whereas filaments in the central region of stress fibers exhibit mixed polarities (1).…”

Section: Discussionmentioning

confidence: 99%

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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“…Early electron micrographs of thin sections showed microfilaments (subsequently confirmed to be actin) in the cytoplasm next to the leading edge (1). Even better, electron micrographs of negatively stained specimens showed dense arrays of filaments at angles to the plasma membrane (2). Drugs that interfere with actin polymerization stop the protrusion of the leading edge (3), and two elegant fluorescence microscopy experiments established that actin polymerizes near the leading edge.…”

mentioning

confidence: 99%

“…As the cell moved forward, the spot of fluorescent actin was stationary relative to the substrate and turned over on a time scale of tens of seconds. Electron microscopy (2) showed that these leading edge actin filaments are mostly oriented with their faster growing ''barbed ends'' (6) toward the leading edge of motile cells.…”

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confidence: 99%

Theory from the Oster Laboratory Leaps Ahead of Experiment in Understanding Actin-Based Cellular Motility

Pollard

2016

Biophysical Journal

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By the early 1990s, most biophysicists and cell biologists agreed that polymerization of actin filaments at the leading edge of a motile cell pushes the plasma membrane forward, creating a protrusion that extends the border of the cell (Fig. 1). For cells on a flat substrate, like a microscope slide, this leading edge is a relatively flat lamella less than 1 mm thick. To balance protrusion at the front end, contractility of the cytoplasm was believed to pull the rear of the cell forward toward attachments that form continuously behind the leading edge.Multiple lines of evidence supported the idea that actin polymerization drives cellular movements. Early electron micrographs of thin sections showed microfilaments (subsequently confirmed to be actin) in the cytoplasm next to the leading edge (1). Even better, electron micrographs of negatively stained specimens showed dense arrays of filaments at angles to the plasma membrane (2). Drugs that interfere with actin polymerization stop the protrusion of the leading edge (3), and two elegant fluorescence microscopy experiments established that actin polymerizes near the leading edge. First, Yu-Li Wang injected live cells with fluorescent actin, which incorporated into cellular actin structures (4). When he bleached a spot in the fluorescent leading lamella of the stationary cell, the spot moved away from the leading edge as new fluorescent actin was incorporated next to the plasma membrane. Over time, the fluorescence recovered, showing that the filaments turned over. Julie Theriot and Tim Mitchison used photoactivation to learn more (5). They injected motile cells with actin coupled to a ''caged'' fluorescent dye. After the tagged actin molecules incorporated into cellular actin structures, they uncaged the fluorescent dye with a light pulse near the leading edge. As the cell moved forward, the spot of fluorescent actin was stationary relative to the substrate and turned over on a time scale of tens of seconds. Electron microscopy (2) showed that these leading edge actin filaments are mostly oriented with their faster growing ''barbed ends'' (6) toward the leading edge of motile cells.Many of these ideas were reinforced by parallel experiments on the movements of certain bacteria through the cytoplasm of host animal cells (7). Actin polymerization next to the bacterium assembles a comet tail of actin filaments that propels the bacterium through the cytoplasm (8,9). This work culminated in reconstitution of bacterial motility from purified actin and a few other proteins (10).Knowing the equilibrium constant for subunit addition to actin filaments, Hill and Kirschner made solid thermodynamic arguments for how polymerization might produce the force to push the membrane forward (11). However, Peskin, Odell, and Oster (12) pointed out ''such arguments provide no mechanistic explanation of how the free energy of polymerization is actually transduced into directed mechanical force.'' A series of three classic papers in Biophysical Journal by George Oster with Charles Peskin...

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Polarity of actin at the leading edge of cultured cells

Cited by 254 publications

References 12 publications

Molecular Analysis of Motility in Metastatic Mammary Adenocarcinoma Cells

Molecular Analysis of Motility in Metastatic Mammary Adenocarcinoma Cells

Reorganization of actin filament bundles in living fibroblasts.

Theory from the Oster Laboratory Leaps Ahead of Experiment in Understanding Actin-Based Cellular Motility

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