SEARCH · PubMed Health

Results for “actin polymerization”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 361 records · Page 20Linked to original sources

PubMed1999

Water in actin polymerization.

We have addressed the question whether water is part of the G- to F-actin polymerization reaction. Under osmotic stress, the critical concentration for G-Ca-ATP actin was reduced for six different osmolytes. These results are interpreted as showing that reducing water activity favored the polymerized state. The magnitude of the effect correlated, then saturated, with increasing MW of the osmolyte and suggested that up to 10-12 fewer water molecules were associated with actin when it polymerized. By contrast, osmotic effects were insignificant for Mg-ATP actin. The nucleotide binding site of the Mg conformation is more closed than the Ca and more closely resembles the closed actin conformation in the polymerized state. These results suggest that the water may come from the cleft of the nucleotide binding site.

Actins↗

PubMed2006

Transcriptional regulation of artemin is related to neurite outgrowth and actin polymerization in mature DRG neurons.

Artemin is a member of the glial cell line-derived neurotrophic factor (GDNF) family of ligands that helps to ensure the survival of sensory neurons. We used an in vitro isolated dorsal root ganglia model to study the effects of artemin on the adult rat neuronal system and investigate differentially regulated genes. We found that 285 genes were differentially transcribed by artemin after 3 h of treatment, including genes related to cell adhesion and actin polymerization. A series of genes involved in the regulation of actin dynamics, including coronin, Myr 5, Wiskott-Aldrich syndrome protein interacting protein, cofilin, drebrin and dynamin were down-regulated by artemin, suggesting that it plays a previously undefined role in the regulation of actin polymerization and synaptic vesicle movement. Artemin also down-regulated the expression of genes related to cell adhesion and matrix assembly, including biglycan, plectin, nestin, neuronatin and the neuron-glia-CAM-related cell adhesion molecule, which is functionally relevant to neurite elongation in DRG neurons. Artemin resulted in increases in total neurite length and branching of the DRG neurons. Also artemin caused an increase of synaptic vesicle clustering. Our results showed that the inhibition of DNA methylation suppressed the artemin-dependent neurite growth, suggesting that the genetic regulation could be relevant to neurite elongation in mature DRG.

Actins↗

PubMed1995

Relationship between light scattering in flow cytometry and changes in shape, volume, and actin polymerization in human polymorphonuclear leukocytes.

Using two different cytometers, an Epics Profile II and a FACScan, we determined the extent to which changes in forward and right angle scatter are a reliable measure for changes in polymorphonuclear leukocyte (PMN) shape, volume, and actin polymerization and whether distinct types of shape changes in PMNs can be recognized. PMN stimulation can substantially change the positions of PMNs in the scatter diagram of the FACScan but not of the Epics Profile II. Within the limits of the experiments, it has been possible to determine whether or not a shape change has taken place using the FACScan but not using the Epics Profile II. However, using either cytometer, it has not been possible to determine which type of shape change (e.g., spherical vs. polarized vs. nonpolar cells) has taken place. Furthermore, forward or right angle scatter changes are not a reliable measure for changes in cell volume or actin polymerization of human PMNs.

Actin Cytoskeleton↗

PubMed1979

Actin polymerization induced by a motility-related high-affinity cytochalasin binding complex from human erythrocyte membrane.

A high molecular weight complex (sedimentation coefficient approximately 27 S) containing high-affinity binding site(s) for [(3)H]dihydrocytochalasin B has been isolated from a low ionic strength extract of human erythrocyte membranes by sucrose density gradient centrifugation. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis showed that actin, spectrin, and other minor components, including two polypeptides with the electrophoretic mobility of band 4.1, were present in the complex-containing fraction. Addition of this complex to a solution of muscle monomeric actin (G-actin) in a low ionic strength medium resulted in a rapid increase in viscosity to a level comparable to that of a solution of filamentous actin (F-actin). Electron microscopy showed that the viscosity increase reflected actin filament formation. The rate of induced actin polymerization was dependent on the amount of complex added to the G-actin; in less than 1 hr, less than 1 mug of protein from the complex-containing fraction induced the conversion of 0.4 mg of G-actin to the "F" from. Binding studies indicated that, upon polymerization of the actin, the cytochalasin binding complex became associated with the actin filaments. Low concentrations of cytochalasins D and E and dihydrocytochalasin B inhibited actin polymerization induced by the complex; the relative potencies of the drugs in inhibiting this process corresponded to their relative affinities for the complex, as well as their relative potencies in affecting cell motility. These results suggest that the cytochalasin binding complex functions as a regulatory site for cell motility by controlling formation and membrane attachment of actin-containing microfilaments in the cell.

Actins↗

PubMed1998

Defective actin polymerization in EBV-transformed B-cell lines from patients with the Wiskott-Aldrich syndrome.

The Wiskott-Aldrich syndrome (WAS) is a rare X-linked recessive disorder characterized by eczema, thrombocytopenia, and immunodeficiency. An allelic variant of the disease is characterized by isolated thrombocytopenia (XLT). The gene responsible for WAS/XLT (WASP) encodes for a 502 amino acid protein (WASP) that is possibly involved in actin binding and cytoskeleton organization. The expression of WASP and the distribution of F-actin and alpha-actinin (which binds to and stabilizes actin filaments) have been analysed in lymphoblastoid cell lines from six patients with WAS and one with XLT. Western blot and immunocytochemistry did not reveal WASP expression in four WAS patients, whereas two WAS patients (with a moderate clinical course) expressed trace amounts of mutant WASP. In contrast, the XLT patient expressed normal amounts of WASP. Furthermore, cell lines from WAS and XLT patients also markedly differed in F-actin polymerization and alpha-actinin distribution. In particular, severe defects of cytoplasmic F-actin expression and of F-actin-positive microvillus formation, and impaired capping of alpha-actinin, were observed in all patients who lacked WASP. As a whole, the degree of impairment of WASP protein expression in WAS/XLT seems to correlate with anomalies of cytoskeletal organization, strongly supporting a role for WASP in the regulation of F-actin polymerization.

Actinin↗

PubMed1989

Subtilisin-cleaved actin: polymerization and interaction with myosin subfragment 1.

Homogeneous preparations of actin cleaved into two fragments, the N-terminal 9- and C-terminal 36-kDa peptides, were achieved by proteolysis of G-actin with subtilisin at 23 degrees C at a 1:1000 (w/w) ratio of enzyme to actin. The subtilisin cleavage site was identified by sequence analysis to be between Met-47 and Gly-48. Although under nondenaturing conditions the two fragments remained associated to one another, the cleavage affected macromolecular interactions of actin. The rates of cleaved actin polymerization by MgCl2, KCl, and myosin subfragment 1 (S-1) were slower and the critical concentrations for this process were higher than in intact protein. Intact and cleaved actin formed morphologically indistinguishable filaments and copolymerized in the presence of MgCl2. The affinity of actin for S-1 was decreased by about 10-fold due to subtilisin cleavage, but the S-1 ATPase activity was activated to the same Vmax value by both intact and cleaved actins. DNase I inhibition measurements revealed lower affinity of cleaved actin for DNase I than that of intact protein. These results are discussed in terms of actin's structure.

Actins↗

PubMed1993

Directional actin polymerization associated with spotted fever group Rickettsia infection of Vero cells.

Members of the spotted fever group (SFG) of rickettsiae spread rapidly from cell to cell by an unknown mechanism(s). Staining of Rickettsia rickettsii-infected Vero cells with rhodamine phalloidin demonstrated unique actin filaments associated with one pole of intracellular rickettsiae. F-actin tails greater than 70 microns in length were seen extending from rickettsiae. Treatment of infected cells with chloramphenicol eliminated rickettsia-associated F-actin tails, suggesting that de novo protein synthesis of one or more rickettsial proteins is required for tail formation. Rickettsiae were coated with F-actin as early as 15 min postinfection, and tail formation was detected by 30 min. A survey of virulent and avirulent species within the SFG rickettsiae demonstrated that all formed actin tails. Typhus group rickettsiae, which do not spread directly from cell to cell, lacked F-actin tails entirely or exhibited only very short tails. Transmission electron microscopy demonstrated fibrillar material in close association with R. rickettsii but not Rickettsia prowazekii. Biochemical evidence that actin polymerization plays a role in movement was provided by showing that transit of R. rickettsii from infected cells into the cell culture medium was inhibited by treatment of host cells with cytochalasin D. These data suggest that the cell-to-cell transmission of SFG rickettsiae may be aided by induction of actin polymerization in a fashion similar to that described for Shigella flexneri and Listeria monocytogenes.

Actin Cytoskeleton↗

PubMed2001

Smooth muscle differentiation marker gene expression is regulated by RhoA-mediated actin polymerization.

Smooth muscle cell (SMC) differentiation is regulated by a complex array of local environmental cues, but the intracellular signaling pathways and the transcription mechanisms that regulate this process are largely unknown. We and others have shown that serum response factor (SRF) contributes to SMC-specific gene transcription, and because the small GTPase RhoA has been shown to regulate SRF, the goal of the present study was to test the hypothesis that RhoA signaling is a critical mechanism for regulating SMC differentiation. Coexpression of constitutively active RhoA in rat aortic SMC cultures significantly increased the activity of the SMC-specific promoters, SM22 and SM alpha-actin, whereas coexpression of C3 transferase abolished the activity of these promoters. Inhibition of either stress fiber formation with the Rho kinase inhibitor Y-27632 (10 microm) or actin polymerization with latrunculin B (0.5 microm) significantly decreased the activity of SM22 and SM alpha-actin promoters. In contrast, increasing actin polymerization with jasplakinolide (0.5 microm) increased SM22 and SM alpha-actin promoter activity by 22-fold and 13-fold, respectively. The above interventions had little or no effect on the transcription of an SRF-dependent c-fos promoter or on a minimal thymidine kinase promoter that is not SRF-dependent. Taken together, the results of these studies indicate that in SMC, RhoA-dependent regulation of the actin cytoskeleton selectively regulates SMC differentiation marker gene expression by modulating SRF-dependent transcription. The results also suggest that RhoA signaling may serve as a convergence point for the multiple signaling pathways that regulate SMC differentiation.

Actins↗

PubMed1987

Actin polymerization and ATP hydrolysis.

F-actin is the major component of muscle thin filaments and, more generally, of the microfilaments of the dynamic, multifunctional cytoskeletal systems of nonmuscle eukaryotic cells. Polymeric F-actin is formed by reversible noncovalent self-association of monomeric G-actin. To understand the dynamics of microfilament systems in cells, the dynamics of polymerization of pure actin must be understood. The following model has emerged from recent work. During the polymerization process, adenosine 5'-triphosphate (ATP) that is bound to G-actin is hydrolyzed to adenosine 5'-diphosphate (ADP) that is bound to F-actin. The hydrolysis reaction occurs on the F-actin subsequent to the polymerization reaction in two steps: cleavage of ATP followed by the slower release of inorganic phosphate (Pi). As a result, at high rates of filament growth a transient cap of ATP-actin subunits exists at the ends of elongating filaments, and at steady state a stabilizing cap of ADP.Pi-actin subunits exists at the barbed ends of filaments. Cleavage of ATP results in a highly stable filament with bound ADP.Pi, and release of Pi destabilizes the filament. Thus these two steps of the hydrolytic reaction provide potential mechanisms for regulating the monomer-polymer transition.

Actin Cytoskeleton↗

PubMed2002

Nucleotides induce chemotaxis and actin polymerization in immature but not mature human dendritic cells via activation of pertussis toxin-sensitive P2y receptors.

Dendritic cells (DCs) are considered the principal initiators of immune response because of their ability to migrate into peripheral tissues and lymphoid organs, process antigens, and activate naive T cells. There is evidence that extracellular nucleotides regulate certain functions of DCs via G-protein-coupled P2Y receptors (P2YR) and ion-channel-gated P2X receptors (P2XR). Here we investigated the chemotactic activity and analyzed the migration-associated intracellular signaling events such as actin reorganization and Ca(++) transients induced by common P2R agonists such as adenosine 5'-triphosphate (ATP) and 2-methylthioadenosine triphosphate, the P2YR agonists UTP and adenosine 5'-diphosphate (ADP), or the P2XR agonists alphabeta-methylenadenosine-5'-triphosphate and 2',3'-(4-benzoyl)benzoyl-ATP. The common P2R agonists and the selective P2YR agonists turned out to be potent chemotactic stimuli for immature DCs, but not for mature DCs. In contrast, P2XR agonists had only marginal chemotactic activity in both DC types. Chemotaxis was paralleled by a rise in the intracellular Ca(++) concentration and by actin polymerization. Studies with pertussis toxin implicated that intracellular signaling events such as actin polymerization, mobilization of intracellular Ca(++), and migration induced by nucleotides was mediated via G(i/o) protein-coupled P2YR. Moreover, functional studies revealed selective down-regulation of this G(i/o) protein-coupled chemotactic P2YR responsiveness during maturation, although immature and mature DCs expressed similar amounts of mRNA for the P2R subtypes (P2Y(2)R, P2Y(4)R, P2Y(5)R, P2Y(7)R, P2Y(11)R and P2X(1)R, P2X(4)R, P2X(7)R), and no major differences in respect to the mRNA expression of these receptors could be observed by semiquantitative reverse transcription and polymerase chain reaction (RT-PCR). In summary, our data describe a differential chemotactic response of immature and mature DCs to nucleotides, and lend further support to the hypothesis that P2R are a novel class of immunomodulatory plasma membrane receptors suitable for pharmacological intervention.

Actins↗

PubMed2003

An Arabidopsis ACT2 dominant-negative mutation, which disturbs F-actin polymerization, reveals its distinctive function in root development.

Eight functional actin genes are present in Arabidopsis: The functional characterization of these genes in loss-of-function mutants is difficult, because highly conserved isovariants are generally expressed in the same tissue. We isolated a novel semi-dominant mutant allele (act2-2D) of an actin gene, ACT2, with a missense mutation which causes an amino acid substitution at the surface of the ACT2 protein. ACT2 promoter::ACT2-2D transgenic plants showed the same phenotype as act2-2D, indicating that act2-2D is a dominant-negative mutant. act2-2D exhibited defects in the initiation and elongation of root hairs, the elongation of root epidermal cells, and growth in aerial portions. Specifically, radial cell expansion was reduced and occasional cell death occurred in trichoblasts but not in atrichoblasts of the root epidermis. In contrast, cell division patterns in the root meristem were not affected. act2-3, a loss-of-function ACT2 mutant, did not develop most of these morphological abnormalities. Actin filament (F-actin) bundles in root epidermal cells of act2-2D were shorter than in the wild type and in the loss-of-function mutant. We conclude that defective F-actin polymerization caused the aberrant cell morphology in a dominant-negative manner, and that ACT2 functions in cell elongation and root hair formation.

Actins↗

PubMed2003

Mechanism of actin polymerization in cellular ATP depletion.

Cellular ATP depletion in diverse cell types results in the net conversion of monomeric G-actin to polymeric F-actin and is an important aspect of cellular injury in tissue ischemia. We propose that this conversion results from altering the ratio of ATP-G-actin and ADP-G-actin, causing a net decrease in the concentration of thymosinactin complexes as a consequence of the differential affinity of thymosin beta4 for ATP- and ADP-G-actin. To test this hypothesis we examined the effect of ATP depletion induced by antimycin A and substrate depletion on actin polymerization, the nucleotide state of the monomer pool, and the association of actin monomers with thymosin and profilin in the kidney epithelial cell line LLC-PK1. ATP depletion for 30 min increased F-actin content to 145% of the levels under physiological conditions, accompanied by a corresponding decrease in G-actin content. Cytochalasin D treatment did not reduce F-actin formation during ATP depletion, indicating that it was predominantly not because of barbed end monomer addition. ATP-G-actin levels decreased rapidly during depletion, but there was no change in the concentration of ADP-G-actin monomers. The decrease in ATP-G-actin levels could be accounted for by dissociation of the thymosin-G-actin binary complex, resulting in a rise in the concentration of free thymosin beta4 from 4 to 11 microm. Increased detection of profilin-actin complexes during depletion indicated that profilin may participate in catalyzing nucleotide exchange during depletion. This mechanism provides a biochemical basis for the accumulation of F-actin aggregates in ischemic cells.

Actins↗

PubMedDate not supplied

Inhibition of actin polymerization by cytochalasin B induces polyploidization and increases the number of nucleolar organizer regions in human megakaryocyte cell lines.

Megakaryocyte polyploidization is an advantageous and regulated mechanism which leads to an increase in platelet production. In megakaryocyte cell lines, polyploidization can be obtained by using cytochalasin B, an inhibitor of the actin polymerization. The Nucleolar Organizer Regions (AgNORs) are parts of nucleolar DNA transcribed into ribosomal RNA. They are detected by silver staining technique and their number is proportional to protein synthesis. In order to estimate protein synthesis in polyploidizing megakaryocytes, AgNORs were measured in three cell lines with megakaryocyte properties (DAMI, HEL and K562) after a 4-day culture in the presence or absence of cytochalasin B, an inhibitor of the actin polymerization. The mean number of AgNORs per cell was 16.4 +/- 4.3 (m +/- SEM); 24.4 +/- 2.5 and 13.6 +/- 3.1 for DAMI, HEL and K-562 cell lines, respectively. The addition of cytochalasin B (2 micrograms/ml) increased significantly the number of AgNORs per cell (DAMI: 437%, HEL: 384% and K-562: 345% of controls, p < 0.05 by t-test). Moreover, the numbers of nucleoles per cell after addition of cytochalasin B were augmented significantly (DAMI: 258%, HEL: 271% and K-562: 264% of controls, p < 0.05 by t-test). The total protein content estimated by Bradford's method increased significantly to 938%, 326% and 388% of controls in DAMI, HEL and K562, respectively (p < 0.05 by t-test) in cells where actin was inhibited by cytochalasin B. In the presence of cytochalasin B, the endomitotic index (EI) [mean of (log2 DNA content expressed in N) 1] measured by flow cytometry increased to 368%, 207% and 538%, for DAMI, HEL and K-562 cell lines, respectively (p < 0.05 by t-test) after treatment with cytochalasin B. In contrast, the number of AgNORs per unit of DNA (EI) and the total protein content per unit of DNA did not change for DAMI, HEL and K-562 cell lines (p < 0.05 by t-test) after treatment with cytochalasin B. In conclusion, the increase in the number of the Nucleolar Organizer Regions by an agent known to stimulate polyploidization of megakaryocytic cell lines suggests that polyploidization occurs by enhanced protein production proportionally to DNA synthesis.

Actins↗

PubMed1981

Ca2+ control of actin filament length. Effects of macrophage gelsolin on actin polymerization.

Gelsolin complexes with calcium (gelsolin-Ca2+) binds to the ends of actin filaments to which monomers add preferentially during elongation. It forms a stable complex with actin in a low ionic strength solution which does not normally favor the polymerization of actin. Gelsolin-Ca2+ increases the rate of nucleation of actin which precedes polymerization, but decreases the rate of elongation of the filaments. The final average length of filaments formed in the presence of gelsolin-Ca2+ is shorter and the equilibrium monomer concentration increases relative to actin polymerized in the absence of gelsolin-Ca2+. Gelsolin-Ca2+ also increases the number of actin filaments because the magnitude of the increase in monomer concentration is disproportionately small compared with the reduction in polymer length. In these respects, the population of actin filaments formed during polymerization in the presence of gelsolin-Ca2+ is similar to that resulting from the action of gelsolin on previously assembled actin filaments (Yin, H. L., Zaner, K. S., and Stossel, T. P. (1980) J. Biol. Chem. 255, 9494-9500). The calcium-dependent shortening of ects, the population of actin filaments formed during polymerization in the presence of gelsolin-Ca2+ is similar to that resulting from the action of gelsolin on previously assembled actin filaments (Yin, H. L., Zaner, K. S., and Stossel, T. P. (1980) J. Biol. Chem. 255, 9494-9500). The calcium-dependent shortening of ects, the population of actin filaments formed during polymerization in the presence of gelsolin-Ca2+ is similar to that resulting from the action of gelsolin on previously assembled actin filaments (Yin, H. L., Zaner, K. S., and Stossel, T. P. (1980) J. Biol. Chem. 255, 9494-9500). The calcium-dependent shortening of actin filaments is the primary mechanism for the dissolution of an actin gel by gelsolin. Therefore, the ability of gelsolin to produce short filaments irrespective of the initial state of assembly of the actin offers flexibility for controlling the network structure of the cytoplasm in which either the monomeric or polymeric form of actin molecules might predominate at different times.

Actins↗

PubMed1988

Relationship of pseudopod extension to chemotactic hormone-induced actin polymerization in amoeboid cells.

Aggregation-competent amoeboid cells of Dictyostelium discoideum are chemotactic toward cAMP. Video microscopy and scanning electron microscopy were used to quantitate changes in cell morphology and locomotion during uniform upshifts in the concentration of cAMP. These studies demonstrate that morphological and motile responses to cAMP are sufficiently synchronous within a cell population to allow relevant biochemical analyses to be performed on large numbers of cells. Changes in cell behavior were correlated with F-actin content by using an NBD-phallacidin binding assay. These studies demonstrate that actin polymerization occurs in two stages in response to stimulation of cells with extracellular cAMP and involves the addition of monomers to the cytochalasin D-sensitive (barbed) ends of actin filaments. The second stage of actin assembly, which peaks at 60 sec following an upshift in cAMP concentration, is temporally correlated with the growth of new pseudopods. The F-actin assembled by 60 sec is localized in these new pseudopods. These results indicate that actin polymerization may constitute one of the driving forces for pseudopod extension in amoeboid cells and that nucleation sites regulating polymerization are under the control of chemotaxis receptors.

Actins↗

PubMed2002

Hydrolysis of ATP by polymerized actin depends on the bound divalent cation but not profilin.

Growing evidence suggests that the nucleotide bound to actin filaments serves as a timer to control actin filament turnover during cell motility (Pollard, T. D., Blanchoin, L., and Mullins, R. D. (2000) Annu. Rev. Biophys. Biomol. Struct. 29, 545-576). We re-examined the hydrolysis of ATP by polymerized actin using mechanical quenched-flow methods to improve temporal resolution. The rate constant for ATP hydrolysis by polymerized Mg actin is 0.3 s(-1), 3-fold faster than that measured manually. The ATP hydrolysis rate is similar when Mg ATP actin elongates either the pointed end or the barbed end of filaments. Polymerized Ca actin hydrolyzes ATP at 0.05 s(-1). Mg ATP actin saturated with profilin can elongate barbed ends at >60 s(-1), 2 orders of magnitude faster than ATP hydrolysis (0.3 s(-1)). Given that profilin binds to a surface on actin that is buried in the Holmes model of the actin filament, we expect that profilin will block subunit addition at the barbed end of a filament. Profilin must move from this site at rates much faster than it dissociates from monomers (4 s(-1)). ATP hydrolysis is not required for this movement.

Actins↗

PubMed2006

Aspirin-triggered Lipoxin A4 inhibition of VEGF-induced endothelial cell migration involves actin polymerization and focal adhesion assembly.

Angiogenesis, the growth of new capillaries from pre-existing ones, occurs through dynamic functions of the endothelial cells (EC), including migration, which is essential to achieve an organized formation of the vessel sprout. We demonstrated previously that an aspirin-triggered lipoxin analog, 15-epi-16-(para-fluoro)-phenoxy-lipoxin A4 (ATL-1), inhibits vascular endothelial growth factor (VEGF)-induced EC migration. In the present study, we investigated the effects of ATL-1 in the actin cytoskeleton reorganization of EC stimulated with VEGF. Pretreatment of EC with ATL-1 caused a reduction in VEGF-induced stress fibers and therefore reduced the intracellular content of filamentous actin. A concomitant impairment in stress-activated protein kinase (SAPK2/p38) phosphorylation suggests that ATL inhibition of VEGF-stimulated actin polymerization involves the SAPK2/p38 pathway. Moreover, ATL-1 treatment inhibited focal adhesion clustering due to inhibition of focal adhesion kinase (FAK) phosphorylation and the subsequent association of FAK with the actin cytoskeleton. This final event, which ultimately allows cell migration, was reverted by an LX receptor antagonist, but not by a cys-LT1R antagonist, indicating an effect via the G-protein-linked LXA4 receptor. Together our results provide evidence that ATL-1 inhibits EC migration via the concerted inhibition of actin polymerization and proper assembly of focal adhesions, supporting a role for these novel lipid mediators as angiogenesis modulators.

Actins↗

PubMed2002

Bovine liver chromatin fraction contains actin polymerization activity inducing micronuclei formation when injected into prometaphase cultured cells.

We previously reported that exogenous histone H1, when injected into mitotic cells, disrupts the synchronous progression of mitotic events by delaying chromosome decondensation. This strategy was utilized to determine whether any other interphase proteins are also able to disrupt normal mitotic processes, when introduced into the mitotic phase. We found that a chromatin subfraction from bovine liver nuclei induced postmitotic micronuclei formation in a dose-dependent manner when injected into the prometaphase of rat kangaroo kidney epithelial (PtK(2)) cells. Close observation showed that, in the case of injected mitotic cells, the mitotic spindles were disrupted, chromosomes became scattered throughout the cytoplasm, and actin filaments were organized ectopically. In addition, when the fraction was injected into interphase cells, extra actin filaments were formed and microtubule organization was affected. In order to determine whether the micronuclei formation resulted from the ectopic formation of actin filaments, we examined the effect of the actin polymerization inhibitor, cytochalasin D. The results showed that the drug inhibited micronuclei formation. From these findings, we concluded that this chromatin subfraction contains actin polymerization activity, thus causing the disruption of mitotic spindles.

Actin Cytoskeleton↗