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PubMed2005

Actin polymerization in the equatorial and postacrosomal regions of guinea pig spermatozoa during the acrosome reaction is regulated by G proteins.

The acrosome reaction (AR) is an exocytotic process of spermatozoa, and an absolute requirement for fertilization. During AR, actin polymerization is necessary in the equatorial and postacrosomal regions of guinea pig sperm for spermatozoa incorporation deep into the egg cytoplasm, but not for plasma membrane (PM) fusion nor the early steps of egg activation. To identify the mechanisms involved in this sperm actin polymerization, we searched for the protein members, known to be involved in a highly conserved model, that may apply to any cellular process in which de novo actin polymerization occurs from G protein activation. WASP, Arp 2/3, profilins I and II, and Cdc42, RhoA and RhoB GTPases were localized by indirect immunofluorescence (IIF) in guinea pig spermatozoa and their presence corroborated by Western blotting. WASP and profilin II were translocated to the postacrosomal region (Arp2/3 already were there) in long-term capacitated and acrosome-reacted spermatozoa, at the same time as actin polymerization occurred. These events were inhibited by GDP-beta-S and promoted by lysophosphatidic acid (LPA) and GTP-gamma-S, a small GTPase inhibitor and two activators, respectively. By immunoprecipitation, Cdc42-WASp association was identified in capacitated but not in noncapacitated gametes. Polymerized actin in the postacrosomal region is apparently anchored both to the postacrosomal perinuclear theca region and the overlying PM. Results suggest that GTPases are involved in sperm actin polymerization, in the postacrosomal region and the mechanism for polymerization might fit a previously proposed model (Mullins, 2000: Curr Opin Cell Biol 12:91-96).

Acrosome↗

PubMed2003

Phosphatidic acid induces actin polymerization by activating protein kinases in soybean cells.

Phosphatidic acid (PA) levels rise in response to wounding, stress and elicitors, suggesting that it mediates defense responses in plants. During such responses, actin filaments are altered. Since PA induces actin polymerization in animal cells we examined its effect on actin structures in suspension-cultured soybean cells. PA caused a three to four fold increase in cells containing filamentous actin. Immunoblotting with anti-actin antibody showed that actin polymerized within 30 min of treatment. The effect of PA on actin polymerization appears to be mediated by protein kinases because: 1) the effect was suppressed by staurosporin, a general protein kinase inhibitor, and by the protein kinase C-specific inhibitor, calphostin, 2) calyculin A, an inhibitor of protein phosphatase 1 and 2A, mimicked the effect of PA on actin polymerization, and 3) PA activated protein kinases in soybean cells. We suggest that a 54 kDa Ca2+-dependent protein kinase may transduce the PA signal because EGTA inhibited the 54 kDa kinase and the PA-induced actin polymerization, and similar protein kinases have been reported to co-localize with and regulate actin filaments. Our results support the role of PA as a signal mediator and identify actin as a downstream target of PA.

Actin Cytoskeleton↗

PubMed1993

Activation of actin polymerization by phosphatidic acid derived from phosphatidylcholine in IIC9 fibroblasts.

alpha-Thrombin induced a change in the cell morphology of IIC9 fibroblasts from a semiround to an elongated form, accompanied by an increase in stress fibers. Incubation of the cells with phospholipase D (PLD) from Streptomyces chromofuscus and exogenous phosphatidic acid (PA) caused similar morphological changes, whereas platelet-derived growth factor (PDGF) and phorbol 12-myristate 13-acetate (PMA) induced different changes, e.g., disruption of stress fibers and cell rounding. alpha-Thrombin, PDGF, and exogenous PLD increased PA by 20-40%, and PMA produced a smaller increase. alpha-Thrombin and exogenous PLD produced rapid increases in the amount of filamentous actin (F-actin) that were sustained for at least 60 min. However, PDGF produced a transient increase of F-actin at 1 min and PMA caused no significant change. Dioctanoylglycerol was ineffective except at 50 micrograms/ml. Phospholipase C from Bacillus cereus, which increased diacylglycerol (DAG) but not PA, did not change F-actin content. Down-regulation of protein kinase C (PKC) did not block actin polymerization induced by alpha-thrombin. H-7 was also ineffective. Exogenous PA activated actin polymerization with a significant effect at 0.01 microgram/ml and a maximal increase at 1 microgram/ml. No other phospholipids tested, including polyphosphoinositides, significantly activated actin polymerization. PDGF partially inhibited PA-induced actin polymerization after an initial increase at 1 min. PMA completely or largely blocked actin polymerization induced by PA or PLD. These results show that PC-derived PA, but not DAG or PKC, activates actin polymerization in IIC9 fibroblasts, and indicate that PDGF and PMA have inhibitory effects on PA-induced actin polymerization.

Actins↗

PubMed1999

Introduction of NAD decreases fMLP-induced actin polymerization in chicken polymorphonuclear leukocytes--the role of intracellular ADP-ribosylation of actin for cytoskeletal organization.

We reported previously that the arginine-specific ADP-ribosyltransferase in chicken polymorphonuclear leukocytes specifically modified actin, thereby inhibiting actin polymerization in vitro. In the present study, we investigated the effect of ADP-ribosylation on actin polymerization in situ. In the leukocytes, the introduction of NAD inhibited the increase in filamentous actin contents induced by a chemotactic peptide formyl-methionyl-leucyl-phenylalanine, while introduction of NAD together with novobiocin, a specific inhibitor for ADP-ribosyltransferase, did not. These results suggest that ADP-ribosylation regulates the formation of filamentous actin by the covalent modification of the protein in vivo.

Actins↗

PubMed1981

A new protein factor that modulates both microtubule assembly and actin polymerization.

A 94,000-dalton protein that has been shown to modulate microtubule assembly in a Mg2+- or Ca2+-dependent manner (Nishida & Sakai (1980) J. Biochem. 88, 1577-1586) was here shown to inhibit actin polymerization. The protein factor inhibited the rate and the extent of actin polymerization under nearly physiological conditions (for example, in 3 mM MgCl2 plus 90 mM KCl at pH 6.8). The inhibitory effect was dependent on divalent cation concentration; the lower the Mg2+ concentration was, the weaker the inhibitory effect. The inhibition was stoichiometric; addition of the protein factor caused a linear decrease in the extent of actin polymerization as measured by the viscosity increase, and under optimal conditions for inhibition about an equimolar amount of the protein factor was sufficient to inhibit the actin polymerization completely. Furthermore, inclusion of the protein factor increased the critical concentration of actin required for polymerization by a concentration nearly equivalent to that of the added factor. These results suggest the formation of a 1 : 1 complex between actin and the protein factor, which does not polymerize at all. Another assay for actin polymerization, pelleting of actin filaments by ultracentrifugation, confirmed the inhibitory effect of the protein factor. In addition to the inhibitory effect on polymerization, the protein factor had the ability to depolymerize actin filaments. We have temporarily called this protein factor PI factor. It may play an important role in cell structure and function through its interactions with actin and microtubules.

Actins↗

PubMed1993

The heat shock cognate protein from Dictyostelium affects actin polymerization through interaction with the actin-binding protein cap32/34.

During isolation of the F-actin capping protein cap32/34 from Dictyostelium discoideum, a 70 kDa protein was copurified which by cloning and sequencing was identified as a heat shock cognate protein (hsc70). This protein exhibited a specific and MgATP-dependent interaction with the heterodimeric capping protein. To investigate the protein-protein interaction in vitro, we expressed all three polypeptides separately in Escherichia coli and performed reconstitution experiments of complete or truncated hsc70 with the 32 and 34 kDa subunits of the capping protein. Viscosity measurements and studies on the polymerization kinetics of pyrene-labeled actin showed that hsc70 increased the capping activity of cap32/34 up to 10-fold, whereas hsc70 alone had no effect on actin polymerization. In addition, hsc70 acted as a molecular chaperone by stimulating the refolding of the denatured 32 and 34 kDa subunits of the capping protein. To study the interaction of the two domains of hsc70 with cap32/34, the N-terminal 42 kDa ATPase region and the C-terminal 30 kDa tail of hsc70 were expressed separately in E. coli. The 32 and 34 kDa subunits were capable of associating with both domains of hsc70. The ATPase domain of hsc70, which is structurally related to actin, proved to be responsible for the increased capping activity of cap32/34, whereas the C-terminal tail of hsc70 was involved in folding of the subunits of cap32/34. Our data indicate a novel linkage between 70 kDa heat shock proteins and the actin cytoskeleton.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗

PubMed1987

Botulinum C2 toxin potentiates activation of the neutrophil oxidase. Further evidence of a role for actin polymerization.

Botulinum C2 toxin was employed as a specific inhibitor of actin polymerization in rat neutrophils to determine its role in oxidase activation. This toxin was shown to inhibit actin polymerization and the microfilament-dependent function, phagocytosis. Oxidase activation in response to the chemotactic peptide, f-Met-Leu-Phe (FMLP) was enhanced approx. 3-fold. The enhancement by C2 toxin did not occur in cells pretreated with cytochalasin B. C2 toxin had no significant effect on the FMLP-induced intracellular Ca2+ rise. These data are consistent with an inhibitory role for actin polymerization in oxidase activation.

Actins↗

PubMed2001

A role for Wiskott-Aldrich syndrome protein in T-cell receptor-mediated transcriptional activation independent of actin polymerization.

Wiskott-Aldrich syndrome protein (WASP) plays a key role in cytoskeletal rearrangement and transcriptional activation in T-cells. Recent evidence links WASP and related proteins to actin polymerization by the Arp2/3 complex. To study whether the role of WASP in actin polymerization is coupled to T-cell receptor (TCR)-mediated transcriptional activation, we made a series of WASP deletion mutants and tested them for actin co-localization, actin polymerization, and transcriptional activation of NFAT. A WASP mutant with a deletion in the C-terminal region (WASPDeltaC) that is defective in actin polymerization potentiated NFAT transcription following TCR activation by anti-CD3 and anti-CD3/CD28 antibodies, but not by phorbol 12-myristate 13-acetate/ionomycin. Furthermore, cotransfection of a dominant-active mutant (WASP-WH2-C) for Arp2/3 polymerization did not inhibit NFAT activation. Finally, by analyzing a series of WASP double-domain deletion mutants, we determined that the WASP homology-1 domain is responsible for NFAT transcriptional activation. Our results suggest that WASP activates transcription following TCR stimulation in a manner that is independent of its role in Arp2/3-directed actin polymerization.

Actins↗

PubMed1996

Dexamethasone alters rapidly actin polymerization dynamics in human endometrial cells: evidence for nongenomic actions involving cAMP turnover.

Glucocorticoids, in addition to their well characterized effects on the genome, may affect cell function in a manner not involving genomic pathways. The mechanisms by which the latter is achieved are not yet clear. A possible means for this action may involve the actin cytoskeleton, since the dynamic equilibrium of actin polymerization changes rapidly following exposure to several stimuli, including hormones. The aim of the present work was to find out if glucocorticoids exert rapid, nongenomic effects on actin polymerization in Ishikawa human endometrial cells, which represent a well characterized in vitro cell model expressing functional glucocorticoid receptors. Short term exposure of the cells to the synthetic glucocorticoid dexamethasone resulted in an overall decrease of the G/total-actin ratio in a time- and dose-dependent manner. Specifically, in untreated Ishikawa cells the G/total-actin ratio was 0.48 +/- 0.01 (n = 26). It became 0.35 +/- 0.01 (n = 13, P < 0.01) following exposure to 10(-7) M dexamethasone for 15 min. This was induced by a significant decrease of the cellular G-actin level, without affecting the total actin content, indicating a rapid actin polymerization. This conclusion was fully confirmed by direct fluorimetry measurements, that showed a significant increase of the F-actin content by 44% (n = 6, P < 0.001) in cells treated with dexamethasone (10(-7)M, 15 min). The rapid dexamethasone-induced alterations of the state of actin polymerization were further supported by fluorescence microscopy. The latter studies showed that the microfilaments of cells pretreated with 10(-7)M dexamethasone for 15 min were more resistant to various concentrations of the antimicrofilament drug cytochalasin B, compared to untreated cells, implying microfilament stabilization. The action of dexamethasone on actin polymerization seems to be mediated via specific glucocorticoid binding sites, since the addition of the glucocorticoid antagonist RU486 completely abolished its effect. Moreover, it appears to act via non-transcriptional pathways, since actinomycin D did not block the dexamethasone-induced actin polymerization. In addition, cell treatment with 10(-7)M dexamethasone for 15 min fully reversed the forskolin-, but not the 8-bromo-cAMP-induced actin depolymerization. In line with these findings, the cAMP content of Ishikawa cells was decreased by 29.2% after a 15 min treatment with 10(-7)M dexamethasone (n = 4, P < 0.01). In conclusion, our results showed that dexamethasone induces rapid, time-, and dose-dependent changes in actin polymerization dynamics in Ishikawa cells. This action seems to be mediated via cAMP, involving probably nongenomic pathways. The above findings offer new perspectives for the understanding of the early cellular responses to glucocorticoids.

Actin Cytoskeleton↗

PubMed1985

The interaction between ATP-actin and ADP-actin. A tentative model for actin polymerization.

The involvement of interactions between ATP-actin and ADP-actin in actin polymerization has been studied. It has been found that ATP-actin and ADP-actin can copolymerize and that the rate of nucleation is enhanced when both ATP-actin and ADP-actin are present in solution. The fact that the heterologous interaction between ATP-actin (T) and ADP-actin (D) is stronger than either of the homologous reactions, T-T and D-D, agrees with the kinetic data in the accompanying paper (Carlier, M.-F., Pantaloni, D., and Korn, E.D. (1985) J. Biol. Chem. 260, 6565-6571) which show that filament ends having the DT conformation are more stable than those having the TT conformation. These data are incorporated into a model for actin polymerization in ATP in which the kinetic parameters for polymerization depend on the nature of the nucleotide (ADP or ATP) bound to the three terminal subunits of the actin filament.

4-Chloro-7-nitrobenzofurazan↗

PubMed1998

The Arp2/3 complex mediates actin polymerization induced by the small GTP-binding protein Cdc42.

The small GTP-binding protein Cdc42 is thought to induce filopodium formation by regulating actin polymerization at the cell cortex. Although several Cdc42-binding proteins have been identified and some of them have been implicated in filopodium formation, the precise role of Cdc42 in modulating actin polymerization has not been defined. To understand the biochemical pathways that link Cdc42 to the actin cytoskeleton, we have reconstituted Cdc42-induced actin polymerization in Xenopus egg extracts. Using this cell-free system, we have developed a rapid and specific assay that has allowed us to fractionate the extract and isolate factors involved in this activity. We report here that at least two biochemically distinct components are required, based on their chromatographic behavior and affinity for Cdc42. One component is purified to homogeneity and is identified as the Arp2/3 complex, a protein complex that has been shown to nucleate actin polymerization. However, the purified complex alone is not sufficient to mediate the activity; a second component that binds Cdc42 directly and mediates the interaction between Cdc42 and the complex also is required. These results establish an important link between a signaling molecule, Cdc42, and a complex that can directly modulate actin networks in vitro. We propose that activation of the Arp2/3 complex by Cdc42 and other signaling molecules plays a central role in stimulating actin polymerization at the cell surface.

Actin-Related Protein 2↗

PubMed2006

8-Chloro-adenosine inhibits growth at least partly by interfering with actin polymerization in cultured human lung cancer cells.

A key feature of actin is its ability to bind and hydrolyze ATP. 8-Chloro-adenosine (8-Cl-Ado), which can be phosphorylated to the moiety of 8-Cl-ATP in living cells, inhibits tumor cell proliferation. Therefore we tested the hypothesis that 8-Cl-Ado can interfere with the dynamic state of actin polymerization. We found that 8-Cl-Ado inhibited the growth of human lung cancer cell line A549 and H1299 in culture, and arrested the target cells in G2/M phase evidenced by fluorescence-activated cell sorting (FACS). Immunocytochemistry showed that the normal organization of microfilaments was disrupted in 8-Cl-Ado-exposed cells, which is accompanied by the decrease of cell size and the alteration of cell shape, and by aberrant mitosis and apoptosis in targeted cells. Furthermore, in vitro light scattering assays revealed that 8-Cl-ATP could directly inhibit the transition of G-actin to F-actin. DNase I inhibition assays showed that the G/F-actin ratio, a surrogate marker of actin polymerization status in living cells, was significantly increased in 8-Cl-Ado-exposed A549 and H1299 cells, compared to the G/F-actin ratio in unexposed cells. Taken together, these results indicate that 8-Cl-Ado exposure can alter the dynamic properties of actin polymerization, disrupt the dynamic instability or the rearrangement ability of actin filaments. Therefore, our data suggest that 8-Cl-Ado may exert its cytotoxicity at least partly by interfering with the dynamic instability of microfilaments, which may correlate with its inhibitory effects on cell proliferation and cell death.

2-Chloroadenosine↗

PubMed1997

Regulation of actin polymerization in cell-free systems by GTPgammaS and Cdc42.

We have established a cell-free system to investigate pathways that regulate actin polymerization. Addition of GTPgammaS to lysates of polymorphonuclear leukocytes (PMNs) or Dictyostelium discoideum amoeba induced formation of filamentous actin. The GTPgammaS appeared to act via a small G-protein, since it was active in lysates ofD. discoideum mutants missing either the alpha2- or beta-subunit of the heterotrimeric G-protein required for chemoattractant-induced actin polymerization in living cells. Furthermore, recombinant Cdc42, but not Rho or Rac, induced polymerization in the cell-free system. The Cdc42-induced increase in filamentous actin required GTPgammaS binding and was inhibited by a fragment of the enzyme PAK1 that binds Cdc42. In a high speed supernatant, GTPgammaS alone was ineffective, but GTPgammaS-loaded Cdc42 induced actin polymerization, suggesting that the response was limited by guanine nucleotide exchange. Stimulating exchange by chelating magnesium, by adding acidic phospholipids, or by adding the exchange factors Cdc24 or Dbl restored the ability of GTPgammaS to induce polymerization. The stimulation of actin polymerization did not correlate with PIP2 synthesis.

Actins↗

PubMed1983

The regulation of actin polymerization by the 88K protein/actin complex and cytochalasin B.

The action of the 88K protein/actin complex (88K/A) and cytochalasin B on various aspects of actin polymerization kinetics was investigated, and the results were interpreted in terms of the condensation polymerization and treadmilling mechanism for actin polymerization. A substoichiometric concentration of 88K/A promotes actin nucleation under physiological salt conditions, especially in the presence of Ca2+. In addition, it reduces both the elongation rate and the depolymerization rate by up to 70% and inhibits annealing of the actin filaments. As a consequence, the average length of actin filaments polymerized with 88K/A becomes less than that of a control. These data indicate that 88K/A caps one end of actin filaments or actin oligomers where in the absence of 88K/A the rates for both association and dissociation of monomers are faster than at the other end. In a KCl/MgCl2 medium, 88K/A increases the steady state monomer concentration (the critical concentration) to a limited extent. This is explained by assuming that 88K/A caps the lengthening end (in treadmilling) of actin filaments, where the critical concentration is lower than at the other end (the shortening end). Moreover, cytochalasin B which has been shown to bind to the barbed end of actin filaments does not affect the 88K/A-nucleated actin polymerization. Therefore, it is strongly suggested that 88K/A caps the barbed end of actin filaments and that the barbed end is the lengthening end as well as the rapidly growing and rapidly depolymerizing end. The result obtained in the study on the action of cytochalasin B was consistent with this suggestion.

Actins↗

PubMed1990

Lipopolysaccharide modulates chemotactic peptide-induced actin polymerization in neutrophils.

To study the effect of endotoxin (LPS) on the basal and chemotactic peptide, formyl-methionyl-leucyl-phenylalanine (fMLP)-induced alterations in neutrophil cytoskeleton, we purified (greater than 98%) LPS-free neutrophils (LPS- less than 10 pg/ml LPS), compared their cytoskeletal organization to that of circulating neutrophils, and examined the effect of LPS exposure on the basal and fMLP-induced change in the cytoskeleton as reflected by F-actin content and distribution. Shape, F-actin content and distribution were monitored by FACS analysis and fluorescence microscopy of NBDphallicidin-stained cells. The F-actin content of basal and fMLP-activated, purified LPS- cells is similar to that of circulating neutrophils (defined as cells drawn in LPS- buffers at 37 degrees C and analyzed after less than 10 seconds of ex vivo manipulation). LPS- cells are round with a diffuse F-actin distribution. Exposure of LPS- cells to LPS causes cell polarization and F-actin redistribution without net gain in F-actin content. Peptide activation of the LPS- cell causes actin polymerization, which is preceded by a brief lag time. Exposure of LPS- cells to LPS (LPS+) enhances fMLP-induced actin polymerization by: 1) increasing the maximal extent of polymerization; 2) shortening the lag time preceding polymerization and increasing the rate of polymerization; and 3) lowering fMLP dose required for half maximal F-actin response. The enhancement depends on LPS dose, duration of exposure, and temperature. To examine the mechanism whereby LPS enhances fMLP-induced actin polymerization, we determined the predominant end for filament growth in LPS- and LPS+ cells, the number of actin nuclei generated in LPS- and LPS+ by fMLP activation, and the number and affinity of fMLP receptors on LPS- and LPS+ cells by 3[H]fMLP binding. Actin polymerization in both LPS- and LPS+ occurs predominantly by monomer addition to the barbed ends of nuclei, and the number of actin nuclei in basal and fMLP-activated LPS- and LPS+ cells is similar. LPS+ cells express three times more fMLP receptors than LPS- cells. The results show that LPS- cells are similar in cytoskeletal organization to circulating neutrophils, LPS causes shape change without change in F-actin content, and LPS enhances fMLP-induced actin polymerization response in neutrophils. The results suggest that LPS enhancement of actin polymerization response is associated with an increase in the number of fMLP receptors expressed on the cell surface.

Actins↗

PubMed2000

Recruitment of the Arp2/3 complex and mena for the stimulation of actin polymerization in growth cones by nerve growth factor.

The growth of axons and dendrites during development and regeneration is regulated by cues in the environment. Many of these cues regulate the actin cytoskeleton of the protrusive structures (like filopodia) of the growth cone that are essential for detecting and responding to cues. Nerve growth factor, which promotes the formation of protrusive structures, stimulated actin polymerization in rat sympathetic growth cones, resulting within 1-2 min in accumulations of F-actin at the distal edge and in splotches of F-actin farther back. We examined the potential involvement of a protein machinery important in at least certain types of actin polymerization in non-neuronal cells. Members of the Arp2/3 complex, p34-Arc and p21-Arc, heavily concentrated in the early accumulations of F-actin, as did one member of the Ena/VASP family (Mena) but not another (VASP). Retention of Arc proteins at preferred sites of actin polymerization did not require polymerization itself. Growth cones of differentiated PC12 cells were similar to sympathetic growth cones in their response to NGF. Introduction into these cells of a peptide that should block the binding of Ena/VASP family proteins to the protein complex at sites of actin polymerization reduced the formation of splotches and filopodia in response to NGF. These results point to the early involvement of the Arp2/3 complex and the Ena/VASP family in growth factor-stimulated actin polymerization that gives rise to protrusive structures at the growth cone.

Actin-Related Protein 2↗

PubMed1984

Modulation of actin polymerization by the spectrin-band 4.1 complex.

The effect of human erythrocyte spectrin dimer and band 4.1 on the polymerization of actin was studied by two independent methods: by following the increase in fluorescence of actin covalently conjugated to N-pyrenyl-iodoacetamide (pyrenylactin) and by following the increase in light scattered by actin polymers. Both techniques indicated that the complex of spectrin dimer and band 4.1, but neither spectrin nor band 4.1 alone, stimulates the rate of nucleation (decreases the lag phase of polymerization) and stabilizes oligomers of F-actin. While the band 4.1-spectrin complex, but not spectrin alone, had no immediate effect on the rate of polymerization after the lag phase, it eventually decreases the rate of actin filament growth when the molecular ratio of actin-spectrin-band 4.1 approaches the physiological range. The complex has no detectable effect on the critical actin concentration and does not significantly alter the apparent order of the nucleation reaction.

Actins↗

PubMed2006

Actin polymerization regulates clathrin coat maturation during early stages of synaptic vesicle recycling at lamprey synapses.

Although it is established that presynaptic actin participates in synaptic vesicle recycling at several synapses, the earliest stages at which actin polymerization is employed during this process are still unclear. To address this, we prevented actin polymerization at lamprey synapses by applying latrunculin B or swinholide A. Latrunculin and swinholide depolymerize actin by sequestering actin monomers and, in addition, swinholide can sever existing actin filaments. When injected into individual presynaptic axons of the intact spinal cord, fluorescently labeled monomeric actin rapidly incorporated in a calcium-dependent manner into a stable, filamentous actin network concentrated at endocytic zones. This pool of actin was disrupted completely by latrunculin. At stimulated synapses, specific disruption of actin polymerization with latrunculin and swinholide induced a selective increase in unconstricted clathrin-coated pits and, in the case of swinholide, an additional increase in the size of plasma membrane evaginations. These results indicate that actin polymerization participates initially in the maturation of clathrin-coated pits during early stages of synaptic vesicle recycling.

Actin Cytoskeleton↗