Actin and the coordination of protrusion, attachment and retraction in cell crawling

1996 ◽  
Vol 16 (5) ◽  
pp. 351-368 ◽  
Author(s):  
J. Victor Small ◽  
Kurt Anderson ◽  
Klemens Rottner
Keyword(s):  
Actin Cytoskeleton ◽  
Actin Filament ◽  
Actin Filaments ◽  
Actin Polymerization ◽  
The Other ◽  
Coordination Mechanism ◽  
Over Expression ◽  
Cell Crawling ◽  
Cell Front ◽  
A Cell

To crawl over a substrate a cell must first protrude in front, establish new attachments to the substrate and then retract its rear. Protrusion and retraction utilise different subcompartments of the actin cytoskeleton and operate by different mechanisms, one involving actin polymerization and the other myosin-based contraction. Using as examples the rapidly locomoting keratocyte and the slowly moving fibroblast we illustrate how over expression of one or the other actin subcompartments leads to the observed differences in motility. We also propose, that despite these differences there is a common coordination mechanism underlying the genesis of the actin cytoskeleton that involves the nucleation of actin filaments at the protruding cell front, in the lamellipodium, and the relocation of these filaments, via polymerization and flow, to the more posterior actin filament compartments.

scholarly journals Mechanisms of actin disassembly

2013 ◽  
Vol 24 (15) ◽  
pp. 2299-2302 ◽  
Author(s):  
William Brieher
Keyword(s):  
Actin Cytoskeleton ◽  
Cell Motility ◽  
Actin Filament ◽  
Actin Filaments ◽  
Actin Polymerization ◽  
Actin Depolymerization ◽  
Filament Dynamics ◽  
Physiological Demands ◽  
In Cells

The actin cytoskeleton is constantly assembling and disassembling. Cells harness the energy of these turnover dynamics to drive cell motility and organize cytoplasm. Although much is known about how cells control actin polymerization, we do not understand how actin filaments depolymerize inside cells. I briefly describe how the combination of imaging actin filament dynamics in cells and using in vitro biochemistry progressively altered our views of actin depolymerization. I describe why I do not think that the prevailing model of actin filament turnover—cofilin-mediated actin filament severing—can account for actin filament disassembly detected in cells. Finally, I speculate that cells might be able to tune the mechanism of actin depolymerization to meet physiological demands and selectively control the stabilities of different actin arrays.

scholarly journals A Modified Actin (Gly65Val Substitution) Expressed in Cotton Disrupts Polymerization of Actin Filaments Leading to the Phenotype of Ligon Lintless-1 (Li1) Mutant

2021 ◽  
Vol 22 (6) ◽  
pp. 3000
Author(s):  
Yuefen Cao ◽  
Hui Huang ◽  
Yanjun Yu ◽  
Huaqin Dai ◽  
Huanfeng Hao ◽  
...  
Keyword(s):  
Actin Cytoskeleton ◽  
Actin Filaments ◽  
Textile Industry ◽  
Actin Polymerization ◽  
Natural Fibers ◽  
Wild Type ◽  
Over Expression ◽  
High Resolution Mapping ◽  
In The Wild ◽  
Resolution Mapping

Dynamic remodeling of the actin cytoskeleton plays a central role in the elongation of cotton fibers, which are the most important natural fibers in the global textile industry. Here, a high-resolution mapping approach combined with comparative sequencing and a transgenic method revealed that a G65V substitution in the cotton actin Gh_D04G0865 (GhACT17D in the wild-type) is responsible for the Gossypium hirsutum Ligon lintless-1 (Li1) mutant (GhACT17DM). In the mutant GhACT17DM from Li1 plant, Gly65 is substituted with valine on the lip of the nucleotide-binding domain of GhACT17D, which probably affects the polymerization of F-actin. Over-expression of GhACT17DM, but not GhACT17D, driven by either a CaMV35 promoter or a fiber-specific promoter in cotton produced a Li1-like phenotype. Compared with the wild-type control, actin filaments in Li1 fibers showed higher growth and shrinkage rates, decreased filament skewness and parallelness, and increased filament density. Taken together, our results indicate that the incorporation of GhACT17DM during actin polymerization disrupts the establishment and dynamics of the actin cytoskeleton, resulting in defective fiber elongation and the overall dwarf and twisted phenotype of the Li1 mutant.

scholarly journals Dissection of two parallel pathways for formin-mediated actin filament elongation

2018 ◽  
Vol 293 (46) ◽  
pp. 17917-17928 ◽  
Author(s):  
Laura A. Sherer ◽  
Mark E. Zweifel ◽  
Naomi Courtemanche
Keyword(s):  
Actin Filament ◽  
Actin Filaments ◽  
Total Internal Reflection ◽  
Actin Polymerization ◽  
Internal Reflection ◽  
Total Internal Reflection Fluorescence ◽  
The Other ◽  
Tirf Microscopy ◽  
Parallel Pathways

Formins direct the elongation of unbranched actin filaments that are incorporated into a diverse set of cytoskeletal structures. Elongation of formin-bound filaments occurs along two parallel pathways. The formin homology 2 (FH2) pathway allows actin monomers to bind directly to barbed ends bound by dimeric FH2 domains. The formin homology 1 (FH1) pathway involves transfer of profilin-bound actin to the barbed end from polyproline tracts located in the disordered FH1 domains. Here, we used a total internal reflection fluorescence (TIRF) microscopy-based fluorescence approach to determine the fraction of actin subunits incorporated via the FH1 and FH2 pathways during filament elongation mediated by two formins. We found that the fraction of filament elongation that occurs via each pathway directly depends on the efficiency of the other pathway, indicating that these two pathways compete with each other for subunit addition by formins. We conclude that this competition allows formins to compensate for changes in the efficiency of one pathway by adjusting the frequency of subunit addition via the other, thus increasing the overall robustness of formin-mediated actin polymerization.

scholarly journals Tropomyosin inhibits ADF/cofilin-dependent actin filament dynamics

2002 ◽  
Vol 156 (6) ◽  
pp. 1065-1076 ◽  
Author(s):  
Shoichiro Ono ◽  
Kanako Ono
Keyword(s):  
Actin Filament ◽  
Actin Filaments ◽  
Actin Polymerization ◽  
Biological Properties ◽  
Actin Dynamics ◽  
Background Suppression ◽  
Thin Filaments ◽  
Actin Organization ◽  
C Elegans ◽  
Filament Dynamics

Tropomyosin binds to actin filaments and is implicated in stabilization of actin cytoskeleton. We examined biochemical and cell biological properties of Caenorhabditis elegans tropomyosin (CeTM) and obtained evidence that CeTM is antagonistic to ADF/cofilin-dependent actin filament dynamics. We purified CeTM, actin, and UNC-60B (a muscle-specific ADF/cofilin isoform), all of which are derived from C. elegans, and showed that CeTM and UNC-60B bound to F-actin in a mutually exclusive manner. CeTM inhibited UNC-60B–induced actin depolymerization and enhancement of actin polymerization. Within isolated native thin filaments, actin and CeTM were detected as major components, whereas UNC-60B was present at a trace amount. Purified UNC-60B was unable to interact with the native thin filaments unless CeTM and other associated proteins were removed by high-salt extraction. Purified CeTM was sufficient to restore the resistance of the salt-extracted filaments from UNC-60B. In muscle cells, CeTM and UNC-60B were localized in different patterns. Suppression of CeTM by RNA interference resulted in disorganized actin filaments and paralyzed worms in wild-type background. However, in an ADF/cofilin mutant background, suppression of CeTM did not worsen actin organization and worm motility. These results suggest that tropomyosin is a physiological inhibitor of ADF/cofilin-dependent actin dynamics.

scholarly journals Coordinated regulation of platelet actin filament barbed ends by gelsolin and capping protein.

1996 ◽  
Vol 134 (2) ◽  
pp. 389-399 ◽  
Author(s):  
K Barkalow ◽  
W Witke ◽  
D J Kwiatkowski ◽  
J H Hartwig
Keyword(s):  
Actin Cytoskeleton ◽  
Actin Filament ◽  
Actin Polymerization ◽  
Residual Activity ◽  
Human Platelets ◽  
Actin Assembly ◽  
Capping Protein ◽  
Capping Proteins ◽  
End Capping ◽  
Human And Mouse

Exposure of cryptic actin filament fast growing ends (barbed ends) initiates actin polymerization in stimulated human and mouse platelets. Gelsolin amplifies platelet actin assembly by severing F-actin and increasing the number of barbed ends. Actin filaments in stimulated platelets from transgenic gelsolin-null mice elongate their actin without severing. F-actin barbed end capping activity persists in human platelet extracts, depleted of gelsolin, and the heterodimeric capping protein (CP) accounts for this residual activity. 35% of the approximately 5 microM CP is associated with the insoluble actin cytoskeleton of the resting platelet. Since resting platelets have an F-actin barbed end concentration of approximately 0.5 microM, sufficient CP is bound to cap these ends. CP is released from OG-permeabilized platelets by treatment with phosphatidylinositol 4,5-bisphosphate or through activation of the thrombin receptor. However, the fraction of CP bound to the actin cytoskeleton of thrombin-stimulated mouse and human platelets increases rapidly to approximately 60% within 30 s. In resting platelets from transgenic mice lacking gelsolin, which have 33% more F-actin than gelsolin-positive cells, there is a corresponding increase in the amount of CP associated with the resting cytoskeleton but no change with stimulation. These findings demonstrate an interaction between the two major F-actin barbed end capping proteins of the platelet: gelsolin-dependent severing produces barbed ends that are capped by CP. Phosphatidylinositol 4,5-bisphosphate release of gelsolin and CP from platelet cytoskeleton provides a mechanism for mediating barbed end exposure. After actin assembly, CP reassociates with the new actin cytoskeleton.

scholarly journals Insights into the evolution of regulated actin dynamics via characterization of primitive gelsolin/cofilin proteins from Asgard archaea

2020 ◽  
Vol 117 (33) ◽  
pp. 19904-19913 ◽  
Author(s):  
Caner Akıl ◽  
Linh T. Tran ◽  
Magali Orhant-Prioux ◽  
Yohendran Baskaran ◽  
Edward Manser ◽  
...  
Keyword(s):  
Actin Cytoskeleton ◽  
Actin Filament ◽  
Calcium Binding ◽  
Mammalian Cells ◽  
Actin Polymerization ◽  
Calcium Release ◽  
Duplication Event ◽  
Cellular Level ◽  
Actin Dynamics

Asgard archaea genomes contain potential eukaryotic-like genes that provide intriguing insight for the evolution of eukaryotes. The eukaryotic actin polymerization/depolymerization cycle is critical for providing force and structure in many processes, including membrane remodeling. In general, Asgard genomes encode two classes of actin-regulating proteins from sequence analysis, profilins and gelsolins. Asgard profilins were demonstrated to regulate actin filament nucleation. Here, we identify actin filament severing, capping, annealing and bundling, and monomer sequestration activities by gelsolin proteins from Thorarchaeota (Thor), which complete a eukaryotic-like actin depolymerization cycle, and indicate complex actin cytoskeleton regulation in Asgard organisms. Thor gelsolins have homologs in other Asgard archaea and comprise one or two copies of the prototypical gelsolin domain. This appears to be a record of an initial preeukaryotic gene duplication event, since eukaryotic gelsolins are generally comprise three to six domains. X-ray structures of these proteins in complex with mammalian actin revealed similar interactions to the first domain of human gelsolin or cofilin with actin. Asgard two-domain, but not one-domain, gelsolins contain calcium-binding sites, which is manifested in calcium-controlled activities. Expression of two-domain gelsolins in mammalian cells enhanced actin filament disassembly on ionomycin-triggered calcium release. This functional demonstration, at the cellular level, provides evidence for a calcium-controlled Asgard actin cytoskeleton, indicating that the calcium-regulated actin cytoskeleton predates eukaryotes. In eukaryotes, dynamic bundled actin filaments are responsible for shaping filopodia and microvilli. By correlation, we hypothesize that the formation of the protrusions observed from Lokiarchaeota cell bodies may involve the gelsolin-regulated actin structures.

scholarly journals Unidirectional sliding of myosin filaments along the bundle of F-actin filaments spontaneously formed during superprecipitation.

1985 ◽  
Vol 101 (6) ◽  
pp. 2335-2344 ◽  
Author(s):  
S Higashi-Fujime
Keyword(s):  
Actin Filament ◽  
Actin Filaments ◽  
Room Temperature ◽  
The Other ◽  
Reverse Direction ◽  
Myosin Filament ◽  
Bipolar Structure ◽  
Myosin Filaments ◽  
Direction Of Movement ◽  
Cold Spring

I reported previously (Higashi-Fujime, S., 1982, Cold Spring Harbor Symp. Quant. Biol., 46:69-75) that active movements of fibrils composed of F-actin and myosin filaments occurred after superprecipitation in the presence of ATP at low ionic strengths. When the concentration of MgCl2 in the medium used in the above experiment was raised to 20-26 mM, bundles of F-actin filaments, in addition to large precipitates, were formed spontaneously both during and after superprecipitation. Along these bundles, many myosin filaments were observed to slide unidirectionally and successively through the bundle, from one end to the other. The sliding of myosin filaments continued for approximately 1 h at room temperature at a mean rate of 6.0 micron/s, as long as ATP remained in the medium. By electron microscopy, it was found that most F-actin filaments decorated with heavy meromyosin pointed to the same direction in the bundle. Myosin filaments moved actively not only along the F-actin bundle but also in the medium. Such movement probably occurred along F-actin filaments that did not form the bundle but were dispersed in the medium, although dispersed F-actin filaments were not visible under the microscope. In this case, myosin filament could have moved in a reverse direction, changing from one F-actin filament to the other. These results suggested that the direction of movement of myosin filament, which has a bipolar structure and the potentiality to move in both directions, was determined by the polarity of F-actin filament in action.

scholarly journals Actin filament content and organization in unstimulated platelets.

1984 ◽  
Vol 98 (6) ◽  
pp. 1985-1991 ◽  
Author(s):  
J E Fox ◽  
J K Boyles ◽  
C C Reynolds ◽  
D R Phillips
Keyword(s):  
Actin Filament ◽  
Actin Filaments ◽  
Actin Polymerization ◽  
Gel Filtration ◽  
Structural Reorganization ◽  
Filamentous Form ◽  
Thin Sections ◽  
Cell Extracts ◽  
Triton X ◽  
Filament Content

The extent of actin polymerization in unstimulated, discoid platelets was measured by DNase I inhibition assay in Triton X-100 lysates of platelets washed at 37 degrees C by gel filtration, or in Triton X-100 lysates of platelets washed at ambient temperatures by centrifugation in the presence of prostacyclin. About 40% of the actin in the discoid platelets obtained by either method existed as filaments. These filaments could be visualized by electron microscopy of thin sections. Similar results were obtained when the actin filament content of discoid platelets was measured by sedimentation of filaments from Triton X-100 lysates at high g forces (145,000 g for 45 min). However, few of these filaments sedimented at the lower g forces often used to isolate networks of actin filaments from cell extracts. These results indicate that actin filaments in discoid cells are not highly crosslinked. Platelets isolated by centrifugation in the absence of prostacyclin were not discoid, but were instead irregular with one or more pseudopodia. These platelets also contained approximately 40-50% of their actin in a filamentous form; many of these filaments sedimented at low g forces, however, indicating that they were organized into networks. The discoid shape of these centrifuged platelets could be restored by incubating them for 1-3 h at 37 degrees C, which resulted in the reversal of filament organization. High g forces were then required for the sedimentation of the actin. Approximately 80-90% of the actin in platelets washed at 4 degrees C was filamentous; this high actin filament content could be attributed to actin polymerization during the preparation of the platelets at low temperatures. These studies show that platelet activation involves mechanisms for the structural reorganization of existing filaments, in addition to those previously described for mediating actin polymerization.

scholarly journals The actin filament-severing domain of plasma gelsolin.

1986 ◽  
Vol 103 (4) ◽  
pp. 1473-1481 ◽  
Author(s):  
C Chaponnier ◽  
P A Janmey ◽  
H L Yin
Keyword(s):  
Binding Site ◽  
Human Plasma ◽  
Actin Filament ◽  
Binding Sites ◽  
Actin Filaments ◽  
The Other ◽  
Actin Binding ◽  
Plasma Gelsolin ◽  
Chymotryptic Peptide ◽  
Native Plasma

Gelsolin, a multifunctional actin-modulating protein, has two actin-binding sites which may interact cooperatively. Native gelsolin requires micromolar Ca2+ for optimal binding of actin to both sites, and for expression of its actin filament-severing function. Recent work has shown that an NH2-terminal chymotryptic 17-kD fragment of human plasma gelsolin contains one of the actin-binding sites, and that this fragment binds to and severs actin filaments weakly irrespective of whether Ca2+ is present. The other binding site is Ca2+ sensitive, and is found in a chymotryptic peptide derived from the COOH-terminal two-thirds of plasma gelsolin; this fragment does not sever F-actin or accelerate the polymerization of actin. This paper documents that larger thermolysin-derived fragments encompassing the NH2-terminal half of gelsolin sever actin filaments as effectively as native plasma gelsolin, although in a Ca2+-insensitive manner. This result indicates that the NH2-terminal half of gelsolin is the actin-severing domain. The stringent Ca2+ requirement for actin severing found in intact gelsolin is not due to a direct effect of Ca2+ on the severing domain, but indirectly through an effect on domains in the COOH-terminal half of the molecule to allow exposure of both actin-binding sites.

scholarly journals Actin filaments function as a tension sensor by tension-dependent binding of cofilin to the filament

2011 ◽  
Vol 195 (5) ◽  
pp. 721-727 ◽  
Author(s):  
Kimihide Hayakawa ◽  
Hitoshi Tatsumi ◽  
Masahiro Sokabe
Keyword(s):  
Actin Cytoskeleton ◽  
Optical Tweezers ◽  
Actin Filament ◽  
Actin Filaments ◽  
Stress Fiber ◽  
Mechanical Forces ◽  
Actin Bundle ◽  
Structure And Dynamics ◽  
Binding Rate ◽  
Tension Sensor

Intracellular and extracellular mechanical forces affect the structure and dynamics of the actin cytoskeleton. However, the underlying molecular and biophysical mechanisms, including how mechanical forces are sensed, are largely unknown. Actin-depolymerizing factor/cofilin proteins are actin-modulating proteins that are ubiquitously distributed in eukaryotes, and they are the most likely candidate as proteins to drive stress fiber disassembly in response to changes in tension in the fiber. In this study, we propose a novel hypothesis that tension in an actin filament prevents the filament from being severed by cofilin. To test this, we placed single actin filaments under tension using optical tweezers. When a fiber was tensed, it was severed after the application of cofilin with a significantly larger delay in comparison with control filaments suspended in solution. The binding rate of cofilin to an actin bundle decreased when the bundle was tensed. These results suggest that tension in an actin filament reduces the cofilin binding, resulting in a decrease in its effective severing activity.

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