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PubMed2003

Regulation of p120-catenin nucleocytoplasmic shuttling activity.

P120-catenin is the prototypic member of a subfamily of Armadillo repeat domain (Arm domain) proteins involved in cell-cell adhesion. Interestingly, all members of the p120 subfamily have also been observed in the nucleus, suggesting that they have additional roles that have yet to be determined. Here, we have developed a novel model system for studying the nucleocytoplasmic shuttling capabilities of p120. We show that simultaneous deletion of both of the conventional nuclear localization sequences (NLSs) in p120 had little effect on its nuclear localization. Instead, the Armadillo repeat domain was essential, and deletion of Arm repeat 3 or Arm repeat 5 eliminated nuclear entry despite the presence of both NLSs. In addition, deletion of Arm repeat 8 resulted in constitutive nuclear localization of p120-3A in both E-cadherin-positive and -negative cell lines. Thus, the core shuttling functions are dependent on the Arm domain. We have also identified two regions within the N-terminus of p120 that modulate nuclear shuttling dynamics of p120. In cadherin-deficient cells, normal epithelial morphology could be restored by both WT-E-cadherin and p120 uncoupled E-cadherin mutants, but only WT-E-cadherin strongly reduced nuclear localization of p120. Moreover, structural changes in p120 that reduced its affinity for E-cadherin increased p120 nuclear localization. Thus, reduced shuttling in the presence of E-cadherin is principally due to sequestration, a condition that is probably dynamic under normal circumstances but completely lost in metastatic cells that have downregulated E-cadherin. Notably, Arm repeats 3 and 5 are necessary for both E-cadherin binding and nuclear translocation, indicating that these repeats have dual roles. Surprisingly, in the absence of E-cadherin there was significant colocalization of cytoplasmic p120 with elements of the tubulin cytoskeleton, particularly in perinuclear locations. Depolymerizing microtubules with nocodazole increased nuclear p120, whereas stabilizing tubulin with taxol reduced nuclear p120 and strongly increased p120 association with microtubules. Thus, p120 has intrinsic nucleocytoplasmic shuttling activity that is modulated, in part, by extrinsic factors such as cadherin binding and interactions with the microtubule network.

Cadherins↗
PubMed2005

Pharmacological and clinical basis of treatment of Familial Mediterranean Fever (FMF) with colchicine or analogues: an update.

Familial Mediterranean Fever (FMF), an autosomal recessive disorder, is characterised by recurrent attacks of fever and serositis, lasting 24-72 hours. Since 1972 colchicine has become the drug of choice for prophylaxis against FMF attacks and amyloidosis FMF-associated. Colchicine, an alkaloid neutral, is absorbed in the jejunum and ileum. It metabolised by liver and only small amounts are recovered unchanged in the urine. Really plasma half-life is prolonged in patients with liver or renal failure. Colchicine is able to prevent activation of neutrophils, binding beta-tubulin and making beta-tubulin-colchicine complexes; this way inhibits assembly of microtubules and mitotic spindle formation; moreover its mode of action includes modulation of chemokines, prostanoids production, inhibition of neutrophil and endothelial cell adhesion molecules. The minimal daily dose in adults is 1.0 mg/die, but in children there is not a definite dose. Since in vitro high dosages of colchicine stop mitosis, this drug might interfere with male and female fertility and with children growth, but, according to current guidelines and because of rare side effects of the drug, FMF patients are recommended to take colchicine. Since colchicine treatment is often complicated by frequent gastrointestinal side effects, by our experience, in order to improve colchicine tolerance we recommend: lactose-free diet and treatment of intestinal bacterial overgrowth and/or Hp-infection, assessed by breath tests. Since our data showed that 10-15% of FMF patients seem are non-responders or intolerant to colchicine, today we are working in the design of colchicine analogues which may have lesser toxicities and a larger therapeutic window.

Adult↗
PubMed1991

Cloning, expression, and protein interaction of human nebulin fragments composed of varying numbers of sequence modules.

Nebulin, a family of giant myofibrillar proteins of 600-900 kDa, contains a large number of highly conserved sequence repeats of 31-38 amino acids. To investigate the significance of this repeat, human skeletal muscle nebulin cDNA fragments encoding two, six, seven, eight, or fifteen repeat modules were expressed in high yield as nonfusion proteins in Escherichia coli with the pET3d plasmid vector. F-actin cosedimentation and solid phase binding assays demonstrated that all nebulin fragments, except the smallest two-module 67-mer, bound to muscle actin with high affinity under physiological ionic conditions. Solid phase binding assays also revealed that a six-module fragment, NB5, binds to myosin and C-terminal protein but fails to bind to tropomyosin, troponin, and tubulin. Furthermore, the binding of NB5 to actin was inhibited by both tropomyosin and troponin. Immunoelectron microscopic localization of NB5 indicated that this N-terminal region fragment is situated near the distal end of thin filaments in the sarcomere. These results indicate that nebulin is a giant protein with an unprecedently large number of actin-binding sites along its length and is anchored at the C terminus to the Z line in the sarcomere. Nebulin may function as a multifunctional template protein that regulates the length of thin filaments and participates in muscle activities by interacting with actin and myosin filaments in the sarcomere of skeletal muscles.

Actins↗
PubMed1998

Microtubule dynamics in a cytosolic extract of fetal rat brain.

Brain microtubule dynamics were studied by video-enhanced differential interference contrast microscopy in a cytosolic extract from fetal rat brain, prepared under conditions designed to produce minimal alterations in microtubule stability. With urchin sperm axoneme fragments as nucleation seeds, the extract was shown to support cellular-like microtubule dynamics. Microtubules elongated from one end of the axonemes, and did not spontaneously self-assemble in the absence of axonemes. The following microtubule kinetic parameters were measured in the extract: velocity of elongation (8.1 mm/min), velocity of rapid shortening (5.8 mm/min), catastrophe frequency (0.17 min(-1)), and rescue frequency (1 min(-1)). These parameters were in close agreement with reported values for growth cones of living neurons. Microtubule properties in the fetal brain extract were shown to be affected by agents with known effects on the cytoskeleton. pp60c-src, a tyrosine kinase important in cell adhesion molecule-dependent axon growth, caused small increases in the frequency of microtubule catastrophe (0.31 min(-1)) and rescue (2 min(-1)) without changing the velocities of elongation or rapid-shortening. Although pp60c-src phosphorylated purified porcine brain tubulin in vitro, it did not elicit significant changes in its polymerization properties, suggesting that other cytoskeletal proteins in the brain extract are involved in modulating microtubule dynamics. The cytosolic extract of fetal rat brain provides a useful system for studying regulation of microtubule assembly in neuronal growth cones.

Animals↗
PubMed1976

Protein kinase associated with tubulin: affinity chromatography and properties.

Rat brain tubulin purified by colchicine-agarose affinity chromatography contains protein kinase activity. The kinase activity can be separated completely from tubulin by chromatography on casein columns and is not subsequently retained by colchicine affinity columns. Protein kinase activity associated with purified tubulin does not correlate with the total content of protein kinase activity in brain homogenates, since microtubules isolated from 48 000g fetal brain supernatants contain twice as much protein kinase activity than adult microtubules, although the total protein kinase activity is twice as high in the 48 000g adult supernatant. The protein kinase of tubulin preparations, while corresponding to a different molecule than tubulin, is probably not simply the result of contamination. These observations are interpreted in terms of specific associations between protein kinase and tubulin complexes. The protein kinase-tubulin association may be an important determinant in the regulation of tubulin function. Fetal tubulin polymerizes twice as well as adult tubulin in the absence of glycerol at the same tubulin concentration. The preferred substrate for the protein kinase either in vivo or in vitro (pH 7.4, 37 degrees C) is a specific high-molecular-weight protein, distinct from tubulin, which copurifies with tubulin through different kinds of isolation procedures (i.e., colchicine affinity chromatography and ammonium sulfate precipitation followed by diethylaminoethyl-cellulose chromatography). The tubulin-associated protein kinase is completely dependent on cyclic adenosine monophosphate (Km=10(-7)M), as demonstrated by the complete suppression of activity upon addition of the protein kinase modulator, a well-known specific inhibitor of cAMP-dependent protein kinases

Aging↗
PubMed1989

Phenylazoxycyanide damages microtubular protein more than its reference antibiotic, calvatic acid.

The effect of phenylazoxycyanide and calvatic acid, its reference antibiotic, on some functions of tubulin obtained from different sources has been studied. Our purpose was to establish a possible correlation between the antitumour activity of these drugs and their antimicrotubular action. Microtubules are subcellular structures involved in proliferation and maintenance of the cell shape and probably in malignant transformation; indeed most antimitotic drugs influence the stability of microtubules through the interaction with tubulin, their main protein. In this work we found phenylazoxycyanide impairs, more than calvatic acid, polymerization of purified tubulin from calf brain. It also damages, in a dose-dependent manner, colchicine-binding ability of tubulin derived from rat liver and AH-130 Yoshida ascite hepatoma cells. Compounds displaying an azoxycyano group may represent new antimicrotubular agents and their effect could be modulated by the different polarity and structural characteristic of the molecule.

Animals↗
PubMed1996

Synaptic membrane G proteins are complexed with tubulin in situ.

The G proteins G S and Gi1 appear to be capable of binding to tubulin specifically, and it has been suggested that such binding results in G protein activation via direct transfer of GTP. This study was undertaken to demonstrate that consequences of G protein activation by tubulin, i.e., stimulation or inhibition of adenyl cyclase, were dependent on the G proteins expressed as well as unique aspects of the membrane or cytoskeleton in a given cell type. Membranes from rat C6 glioma cells, which express G s alpha but not G i alpha 1, responded to the addition of tubulin with a stable activation of adenyl cyclase. Conversely, membranes from rat cerebral cortex, which contain both G s and G i 1, responded to exogenous tubulin with a stable inhibition of adenyl cyclase. Unlike C6 membranes, cerebral cortex membranes are richly endowed with tubulin, and antitubulin antibodies immunoprecipitated complexes of tubulin and G i 1 and G s from detergent extracts of these membranes. Nearly 90% of the G s alpha from Triton X-114 extracts coimmunoprecipitated with tubulin, suggesting that these proteins exist as a complex in the synaptic membrane. Such complexes may provide the framework for a G protein-cytoskeleton link that participates in the modulation of cellular signal transduction.

Adenylyl Cyclase Inhibitors↗
PubMed2000

Retinoic acid differentiation of HL-60 cells promotes cytoskeletal polarization.

Retinoic acid (RA) treatment of HL-60 cells in vitro induces granulocytic differentiation, involving reorganization of the nucleus and cytoplasm, development of chemoattractant-directed migration, and eventual apoptosis. The present studies with HL-60/S4 cells document that major elements of the cytoskeleton are changed: actin increases by 50%; vimentin decreases by more than 95%. The cellular content of alpha-tubulin does not significantly change; but the centrosomal-microtubule (MT) array moves away from the lobulating nucleus. Cytoskeletal-modifying chemicals modulate this polarized reorganization: Taxol and cytochalasin D enhance centrosome movement; nocodazole reverses it. Cytoskeletal-modifying chemicals do not appear to affect nuclear lobulation or the integrity of envelope-limited chromatin sheets (ELCS). Employing bcl-2-overexpressing HL-60 cells permitted demonstration of nuclear lobulation, ELCS formation, and centrosome-MT movement concomitantly during RA-induced differentiation, implying independence between the cellular reorganization and apoptotic programs. RA appears to promote an inherent potential in HL-60 cells for cytoskeletal polarization, likely to be important for chemoattractant-directed cell migration, an established characteristic of mature granulocytes.

Actins↗
PubMed2003

Differential regulation of microtubule dynamics by three- and four-repeat tau: implications for the onset of neurodegenerative disease.

The microtubule (MT)-associated protein tau is important in neuronal development and in Alzheimer's and other neurodegenerative diseases. Genetic analyses have established a cause-and-effect relationship between tau dysfunction/misregulation and neuronal cell death and dementia in frontotemporal dementia and parkinsonism associated with chromosome 17; several mutations causing this dementia lead to increased ratios of four-repeat (4R) to three-repeat (3R) wild-type tau, and an attractive hypothesis is that the abnormally high ratio of 4R to 3R tau might lead to neuronal cell death by altering normal tau functions in adult neurons. Thus, we tested whether 3R and 4R tau might differentially modulate the dynamic instability of MTs in vitro using video microscopy. Although both isoforms promoted MT polymerization and decreased the tubulin critical subunit concentration to approximately similar extents, 4R tau stabilized MTs significantly more strongly that 3R tau. For example, 4R tau suppressed the shortening rate, whereas 3R tau had little or no detectable effect. Similarly, 3R tau had no effect on the length shortened during a shortening event, whereas 4R tau strongly reduced this parameter. Further, when MTs were diluted into buffer containing 4R tau, the MTs were stabilized and shortened slowly. In contrast, when diluted into 3R tau, the MTs were unstable and shortened rapidly. Thus, 4R tau stabilizes MTs differently and significantly more strongly than 3R tau. We suggest a "dosage effect" or haploinsufficiency model in which both tau alleles must be active and properly regulated to produce appropriate amounts of each tau isoform to maintain MT dynamics within a tolerable window of activity.

Alleles↗
PubMed2001

Stathmin/Op18 phosphorylation is regulated by microtubule assembly.

Stathmin/Op 18 is a microtubule (MT) dynamics-regulating protein that has been shown to have both catastrophe-promoting and tubulin-sequestering activities. The level of stathmin/Op18 phosphorylation was proved both in vitro and in vivo to be important in modulating its MT-destabilizing activity. To understand the in vivo regulation of stathmin/Op18 activity, we investigated whether MT assembly itself could control phosphorylation of stathmin/Op18 and thus its MT-destabilizing activity. We found that MT nucleation by centrosomes from Xenopus sperm or somatic cells and MT assembly promoted by dimethyl sulfoxide or paclitaxel induced stathmin/Op18 hyperphosphorylation in Xenopus egg extracts, leading to new stathmin/Op18 isoforms phosphorylated on Ser 16. The MT-dependent phosphorylation of stathmin/Op18 took place in interphase extracts as well, and was also observed in somatic cells. We show that the MT-dependent phosphorylation of stathmin/Op18 on Ser 16 is mediated by an activity associated to the MTs, and that it is responsible for the stathmin/Op18 hyperphosphorylation reported to be induced by the addition of "mitotic chromatin." Our results suggest the existence of a positive feedback loop, which could represent a novel mechanism contributing to MT network control.

Animals↗
PubMed1994

Modulation of cytoskeletal organization of podocytes during the course of aminonucleoside nephrosis in rats.

By immunoelectron microscopy the modulation of cytoskeletal organization of podocytes during the course of puromycin aminonucleoside-induced nephrosis was examined. In control rats, tubulin and vimentin were present, limited to the podocyte cell body and the major processes. Their distribution in the foot processes was virtually negative. Myosin exhibited the same distribution pattern, albeit much more scattered, with no relation to any podocyte organelles or cell structures. Actin was scattered over the fibrillar zones of the cell body and its processes, including the foot processes. In proteinuric rats, loss of foot processes occurred and the glomerular basement membrane was covered by broad cytoplasmic sheets of podocytes, which contained these four subunits of cytoplasmic filaments. Accompanied by the disappearance of proteinuria, the structural organization of the foot processes was completely restored, in which tubulin, vimentin, and myosin were scarcely observed. Our results confirmed that the loss of foot processes is caused by their retraction, and indicated that the specific localization of the podocytic cytoskeleton contributes to the maintenance of the particular cell shape. Its reorganization may account for the structural modification of podocytes.

Actins↗
PubMedDate not supplied

Tubulin synthesis, structure, and function: what are the relationships?

In most eukaryotes, families of tubulin genes give rise to multiple isoforms of tubulin, which may be modified post-translationally. The synthesis of isotubulins is spatially and temporally regulated, leading to the presence of different tubulins within an organism. The cellular localization of tubulin is also nonrandom with discrete isoforms residing in specific regions of some cells. Much work, dependent upon interrelated molecular and immunological technologies, has gone into determining why cells produce multiple isotubulins. One proposal would have us believe that isotubulins are functionally discrete and that the isotubulin composition of a microtubule determines its function. A second idea is that tubulin multigene families arose by gene duplication and subsequent genetic drift. The duplicated genes survive in modified form, as they provide the cell with the ability to effectively regulate tubulin synthesis at the transcriptional level while yielding multifunctional tubulins. Analysis of mutant tubulin genes is revealing functionally important regions of tubulin, prompting a return to the consideration of those properties of the molecule that are fundamental to microtubule formation rather than function per se. A model for autoregulation of tubulin synthesis has been developed, but little is yet known of other molecular signals or mechanisms involved in regulation of tubulin production. Further study of flagella formation promises to change this situation. Complementing the genetic studies is the examination of tubulin posttranslational modifications including detyrosination/tyrosination, acetylation/deacetylation, and phosphorylation. Enzymatic mechanisms mediating tubulin posttranslational changes are partially elucidated, as are the influences of the modifications on microtubule properties. Potential functions of the posttranslational changes are the modulation of microtubule-associated protein binding to microtubules, the provision of a mechanism to indicate microtubule age, or as mediators of cellular morphogenesis, a role which could be dependent upon the first two functions. Despite the progress that has been made, the physiological significance of having several isotubulins within a single cell and the molecular details of microtubule function remain obscure.

Animals↗
PubMed2006

Glutamate acting on AMPA but not NMDA receptors modulates the migration of hippocampal interneurons.

Paracrine GABA and glutamate acting, respectively, on GABAA and NMDA receptors modulate the migration of hippocampal pyramidal cells. Using corticohippocampal organotypic explants from glutamic acid decarboxylase (GAD) 67-enhanced green fluorescent protein (EGFP) knock-in embryos, we now report that, in contrast to pyramidal neurons, the blockade of AMPA but not NMDA receptors exerts important actions on the migration of GABAergic interneurons. In addition, the blockade of GABAA receptors fails to modify the migration rates of GABAergic interneurons. Immunohistochemical analyses of GAD67-EGFP embryos (from embryonic day 14 to birth) reveal that interneurons colonize the hippocampal primordium by embryonic day 15. At that stage, the hippocampal primordium is already composed of pioneer glutamatergic neurons, including (1) Cajal-Retzius cells, immunopositive to calretinin and reelin, and (2) other presumptive pioneer pyramidal cells that are immunopositive to betaIII-tubulin and vesicular glutamate transporter 3 and immunonegative to GABA or GAD67. Therefore, the migrations of pyramidal neurons and GABAergic interneurons are cross-modulated: glutamate released from pioneer glutamatergic neurons facilitates the migration of GABAergic interneurons, which in turn would release GABA, facilitating the migration of glutamatergic neuroblasts. This general sequence may provide a retroactive positive loop needed to construct the hippocampal network. It might constitute a primitive homeostatic mechanism in the developing brain that acts to balance GABA-glutamate contributions to network construction and activity.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed2006

Allosteric inhibition of kinesin-5 modulates its processive directional motility.

Small-molecule inhibitors of kinesin-5 (refs. 1-3), a protein essential for eukaryotic cell division, represent alternatives to antimitotic agents that target tubulin. While tubulin is needed for multiple intracellular processes, the known functions of kinesin-5 are limited to dividing cells, making it likely that kinesin-5 inhibitors would have fewer side effects than do tubulin-targeting drugs. Kinesin-5 inhibitors, such as monastrol, act through poorly understood allosteric mechanisms, not competing with ATP binding. Moreover, the microscopic mechanism of full-length kinesin-5 motility is not known. Here we characterize the motile properties and allosteric inhibition of Eg5, a vertebrate kinesin-5, using a GFP fusion protein in single-molecule fluorescence assays. We find that Eg5 is a processive kinesin whose motility includes, in addition to ATP-dependent directional motion, a diffusive component not requiring ATP hydrolysis. Monastrol suppresses the directional processive motility of microtubule-bound Eg5. These data on Eg5's allosteric inhibition will impact these inhibitors' use as probes and development as chemotherapeutic agents.

Allosteric Regulation↗
PubMed2003

Autonomous and phosphorylation-responsive microtubule-regulating activities of the N-terminus of Op18/stathmin.

Op18 is the prototypical member of a family of phosphorylation-responsive regulators of microtubule (MT) dynamics. Previous dissection of Op18 has suggested that it has a functional dichotomy in which an intact N-terminus is required for catastrophe promotion (i.e. transition from growing to shrinking MTs), whereas an intact C-terminus is required for efficient ternary Op18-tubulin complex formation and the resultant tubulin-sequestering activity. Here we have expressed and functionally analyzed the properties of the N-terminus of Op18. The data show that the N-terminal 57 residues are sufficient for low-affinity tubulin interactions, as shown by inhibition of basal GTP hydrolysis of soluble heterodimers. In addition, high concentrations of the Op18 N-terminal portion increased the catastrophe rate during MT assembly in vitro. Overexpression of the N-terminus in a human cell line results in MT destabilization in interphase and phosphorylation-modulated accumulation of metaphase-arrested cells with dense short MTs. These results demonstrate that the N-terminus of Op18 has autonomous activity. Evidently, this activity is enhanced by the increase in tubulin affinity that is provided by the extended alpha-helical portion of native Op18.

Amino Acid Sequence↗
PubMed2002

Roles for the tubulin- and PTP-PEST-binding paxillin LIM domains in cell adhesion and motility.

Cell dynamics mediated through cell-extracellular matrix contacts, such as adhesion and motility involve the precise regulation of large complexes of structural and signaling molecules called focal adhesions (FAs). Paxillin is a multi-domain FA adaptor protein containing five amino-terminal paxillin leucine-aspartate repeat (LD) motifs and four carboxyl-terminal Lin-11 Isl-1 and Mec-3 (LIM) domains. The LD motifs support paxillin binding to actopaxin, integrin linked kinase (ILK), FA kinase (FAK), paxillin kinase linker (PKL) and vinculin. Of the LIM domains, LIM2 and 3 comprise the paxillin FA-targeting motif, with phosphorylation of these domains modulating paxillin targeting and cell adhesion to fibronectin (Fn). The identity of the paxillin FA targeting partner remains to be determined; however, the LIM domains mediate interactions with tubulin and the protein-tyrosine phosphatase (PTP)-PEST. PTP-PEST binding requires both LIM3 and 4, whereas, the precise LIM target of tubulin binding is not known. In this report, we demonstrate that the individual paxillin LIM2 and 3 domains support specific binding to tubulin and suggest a potential role for this interaction in the regulation of paxillin sub-cellular compartmentalization. In addition, expression of paxillin molecules with mutations in the tubulin- and PTP-PEST-binding LIM domains differentially impaired Chinese hamster ovary K1 (CHO.K1) cell adhesion and migration to Fn. Perturbation of LIM3 or 4 inhibited adhesion while mutation of LIM2 or 4 decreased cell motility. Interestingly, expression of tandem LIM2-3 inhibited cell adhesion and spreading while LIM3-4 stimulated a well-spread polarized phenotype. These data offer further support for a critical role for paxillin in cell adhesion and motility.

Animals↗
PubMed2006

Caveolin-1 interacts with the chaperone complex TCP-1 and modulates its protein folding activity.

We report that caveolin-1, one of the major structural protein of caveolae, interacts with TCP-1, a hetero-oligomeric chaperone complex present in all eukaryotic cells that contributes mainly to the folding of actin and tubulin. The caveolin-TCP-1 interaction entails the first 32 amino acids of the N-terminal segment of caveolin. Our data show that caveolin-1 expression is needed for the induction of TCP-1 actin folding function in response to insulin stimulation. Caveolin-1 phosphorylation at tyrosine residue 14 induces the dissociation of caveolin-1 from TCP-1 and activates actin folding. We show that the mechanism by which caveolin-1 modulates TCP-1 activity is indirect and involves the cytoskeleton linker filamin. Filamin is known to bind caveolin-1 and to function as a negative regulator of insulin-mediated signaling. Our data support the notion that the caveolin-filamin interaction contributes to restore insulin-mediated phosphorylation of caveolin, thus allowing the release of active TCP-1.

Amino Acid Sequence↗
PubMed1998

Ganglioside GM1 alters neuronal morphology by modulating the association of MAP2 with microtubules and actin filaments.

In previous studies, we demonstrated that the exogenous ganglioside GM1 increased the complexity of the microtubular network and level of tubulin, selectively changed the distribution of microtubule associated protein-2 (MAP2) immunoreactivity from the perikarya to distal neuritic processes and increased immunogold label of MAP2 in the subplasmalemmal cytoplasm, neuritic filopodia and growth cones of Neuro-2a neuroblastoma cells. Since these areas are rich in actin filaments, our data suggested that MAP2 may be associated with microfilaments in the early stages of ganglioside-induced neuritogenesis. To determine if GM1 alters neuronal morphology by facilitating the interaction of actin and MAP2, we examined the immunolocalization of these two proteins with confocal and electron microscopy. We found that along with the redistribution of MAP2 from perikaryal to neuritic regions, there was parallel redistribution of actin. The uniform subplasmalemmal actin meshwork was disrupted in areas of processes and filopodia with a redistribution of actin to these areas in close association with MAP2. Our present results suggest that gangliosides enhance neuritogenesis by redistributing actin as well as MAP2 to processes and filopodia thereby facilitating their interaction. The association of MAP2 with actin filaments is likely to be an early step in ganglioside-mediated filopodia formation.

Actins↗