bluuebunny/crossref_metadata_2025_split huggingface dataset:
Organization of cortical microfilaments in dividing root cells
Authors: Liu Bo , Palevitz Barry A. 
Published: February 2005

AbstractIn order to assess the possible role of microfilaments (Mfs) in events preceding plant cell division, actin was localized in root cells of Allium cepa and Tradescantia virginiana by immunofluorescence microscopy. The distribution of Mfs was compared to that of microtubules (Mts) by means of dual localizations employing both antiactin and antitubulin. Cycling interphase cells contain Mfs that extend into all regions of the cytoplasm in random fashion. Prior to the rearrangement of the cortical Mt array into the initial broad preprophase band (PPB), the number of Mfs in the cytoplasm decreases, while a new population appears in the cortex. The cortical Mfs, which usually occupy the entire cell surface, are aligned parallel to the cortical Mts. When the initial PPB appears, these Mfs still cover the cortex or are arranged as a broad band encompassing the PPB. As the PPB narrows, the Mfs are also confined to an increasingly restricted zone usually wider than the PPB.than the PPB. When the PPB reaches its narrowest, densest configuration, aligned Mfs are excluded from the band proper, while others appear in flanking regions of the cortex. From prometaphase through anaphase, cortical Mfs are largely restricted to the ends of the cell overlying the spindle poles; they also tend to become more randomly oriented. Little or no actin is present in the spindle. During telophase, the two zones of aligned cortical Mfs over the ends of the cell gradually disappear and are replaced by new interphase networks. These changes provide additional data on the possible control of PPB organization by actin, and in addition indicate that the cortex may be the origin of the actin that aggregates at the spindle poles during cytochalasin treatment. © 1992 Wiley‐Liss, Inc.
Action of tolytoxin on cell morphology, cytoskeletal organization, and actin polymerization
Authors: Patterson Gregory M. L. , Smith Charles D. , Kimura Lucille H. , Britton Bruce A. , Carmeli Shmuel 
Published: February 2005

AbstractTolytoxin, a cytostatic, antifungal macrolide produced by blue‐green algae of the genus Scytonema, is a potent, reversible inhibitor of cytokinesis in cultured mammalian cells. Treatment of KB cells with 2–16 nM tolytoxin results in profound morphological changes, beginning with the formation of zeiotic processes and culminating in nuclear protrusion. In L1210 cells, cytokinesis is inhibited by as little as 2 nM tolytoxin, while karyokinesis proceeds normally, resulting in polynucleation. Tolytoxin specifically disrupts microfilament organization in A10 cells, while having no apparent effect on microtubules or intermediate filaments. Tolytoxin inhibited actin polymerization in vitro and also caused the depolymerization or fragmentation of F‐actin in vitro. Tolytoxin exhibits effects that closely resemble those of cytochalasin B but is effective at concentrations 1/50−1/1,000 that of cytochalasin B. © 1993 Wiley‐Liss, Inc.
Protein kinases are required for embryonic neural crest cell galvanotaxis
Authors: Nuccitelli Richard , Smart Tanya , Ferguson James 
Published: February 2005

AbstractEmbryonic quail neural crest cells migrate towards the negative pole of an imposed dc electric field as small as 7 mV/mm (0.4 mV per average cell length). The involvement of protein kinases in the mechanism utilized by these cells to detect and respond to such imposed fields was tested through the use of several kinase inhibitors. Evidence for the involvement of protein kinase C (PKC) included: (1) inhibition of the directed motility by 1 μM sphingosine that was reversed by the addition of the phorbol ester, PMA; (2) stimulation of a faster response to the imposed field by PMA; and (3) inhibition of the directed translocation by 5 μM H‐7. However, another PKC inhibitor, staurosporin, did not inhibit the directed translocation (1 nM‐1 μM). We also found evidence for the involvement of either cAMP‐ or cGMP‐dependent protein kinase. The galvanotactic response was partially inhibited by the addition of 10 μM H‐9 and the response was enhanced in the presence of the phosphodiesterase inhibitor, IBMX. However, the adenylate cyclase stimulant, forskolin, had no significant influence on the directed motility, although it reduced the average cell velocity. While these experiments suggest that cAMP‐ or cGMP‐dependent protein kinase or PKC may be involved in the galvanotaxis response, two other protein kinases appeared not to be required. The myosin light chain kinase inhibitor, ML‐7, had no effect on the directed motility in an imposed field, so myosin light chain kinase may not be required for galvanotaxis. Similarly, 5 μM W‐7 had no significant effect on the directed translocation, suggesting that calmodulin‐dependent protein kinase is not involved.Interestingly, the continuous activity of a protein kinase is apparently not required for the directed translocation response. The addition of the PKC and cAMP‐dependent protein kinase inhibitor, H‐7, after the cells had been exposed to the field for 1 hour, had no effect on the subsequent directed translocation. Thus, for these inhibitors to block the directed translocation, they must be present at the same time as the initial field application. This implies that an integral step in the cellular response mechanism for galvanotaxis involves the stimulation of a protein kinase whose effect is long lasting. © 1993 Wiley‐Liss, Inc.
Morphology of nexin links in relation to interdoublet sliding in the sperm flagellum
Authors: Hakan Bozkurt H. , Woolley David M. 
Published: February 2005

AbstractIn this work, we examine whether the “nexin” linkages of the flagellum can extend in length to accommodate interdoublet sliding. Flagellar bends of large angle were induced in bull spermatozoa by hypotonic treatment. It is argued that this produces large interdoublet displacements that are, nevertheless, still within physiological limits. Such flagella were examined by the rapid‐freeze, deep‐etch techique and the nexin linkages identified by their position in relation to the inner dynein arms and by their straplike, bipartite, morphology. They were found to bridge perpendicularly (or occasionally at an angle) between the A‐ and B‐tubules of adjacent doublets. The nexin linkages were no more than ∼20 nm in length, even in regions in which ∼200 nm of sliding could be inferred. Variable registration between adjacent nexin rows gave some further support to the assumption that sliding had indeed taken place. From this, it is concluded that elastic deformation of the links, such as would accommodate interdoublet sliding, does not occur; some form of displacement must occur between nexin and the adjacent B‐tubule. © 1993 Wiley‐Liss, Inc.
Dynamics of microfilaments are similar, but distinct from microtubules during cytokinesis in living, dividing plant cells
Authors: Zhang Dahong , Wadsworth Patricia , Hepler Peter K. 
Published: February 2005

AbstractThe development and dynamics of the phragmoplast cytoskeleton have been analyzed in living stamen hair cells of Tradescantia. Microtubules and actin microfilaments have been identified by microinjecting either carboxyfluorescein labeled brain tubulin or rhodamine phalloidin. Examination with the confocal laser scanning microscope has permitted sequential imaging of the fluorescent cytoskeletal elements in single living cells progressing through division. Phragmoplast microtubules initially emerge through the lateral coalescence of preexisting interzone microtubules. As cytokinesis progresses, these tightly clustered microtubules shorten in length and expand centrifugally toward the cell periphery. By contrast, the phragmoplast microfilaments appear to arise de novo in late anaphase in close association with the proximal surfaces of the reconstituting daughter nuclei. The microfilaments are oriented parallel to the microtubules but conspicuously do not occupy the equatorial region where microtubules interdigitate and where the cell plate vesicles aggregate and fuse. As development proceeds the microfilaments shorten in length and expand in girth, similar to microtubules, although they remain excluded from the cell plate region. In terminal phases of cell plate formation, microtubules degrade first in the central regions of the phragmoplast and later toward the edges, whereas microfilaments break down more uniformly throughout the phragmoplast. © 1993 Wiley‐Liss, Inc.
Control of profilin and actin expression in muscle and nonmuscle cells
Authors: Babcock Gary , Rubenstein Peter A. 
Published: February 2005

AbstractProfilin is a small G‐actin binding protein implicated in sequestering actin monomers in vivo. We have quantitated profilin and actin expression in human hepatoma HepG‐2 cells and in two mouse myogenic cell lines, BC3H1 and C2C12, to determine whether the expression of profilin and the expression of nonmuscle isoactin or total actin are co‐regulated. During differentiation of both muscle cell types, profilin and nonmuscle actin expression decrease in a coordinate manner as shown by measurements of steady state mRNA and newly synthesized protein. In human hepatoma HepG‐2 cells, the twofold increase in actin synthesis observed after 24 hours of exposure to cytochalasin D did not result in an increase in profilin synthesis. Thus, profilin and actin expression are not coregulated in all cells. To determine if there is sufficient profilin to sequester a large portion of cellular G‐actin, we measured total profilin and G‐actin levels in the three cell types. In each case, profilin accounted for less than 10% of the total G‐actin on a molar basis. Thus, profilin is not responsible for total G‐actin sequestration in these cells. Finally, using poly‐L‐proline affinity chromatography, we showed that, in the cell types tested, less than 20% of the poly‐L‐proline purified profilin existed as a complex with G‐actin. The profilin in these cells may be interacting with cellular components other than actin. © 1993 Wiley‐Liss, Inc.
Interaction of brain mitochondria with microtubules reconstituted from brain tubulin and MAP2 or TAU
Authors: Jung D. , Filliol D. , Miehe M. , Rendon A. 
Published: February 2005

AbstractTo explore the behaviour of microtubule‐associated proteins, MAP2 and TAU in the interactions of mitochondria with microtubules, an homologous acellular system has been reconstituted with organelles isolated from rat brain. We have established a quantitative in vitro binding assay based on the cosedimentation of 125I‐labeled microtubules with mitochondria. We found that binding of microtubules to mitochondria was concentration dependent and saturable. Binding was insensitive to ATP. A comparison of taxol‐stabilized microtubules prepared from MAP‐free tubulin or tubulin coated with TAU or MAP2 showed that the microtubule‐associated proteins diminished, or reduced to background levels, the formation of complexes with mitochondria. In contrast, the amount of MAP‐free taxol microtubules that cosedimented with mitochondria increased two‐ and six‐fold when mitochondria were coated with MAP2 or TAU. These studies suggest that the two major brain MAPs could have a crosslinking or a spacing role, depending on their organelle localization. © 1993 Wiley‐Liss, Inc.
Actin in the merozoite of the malaria parasite, Plasmodium falciparum
Authors: Field S. J. , Pinder Jennifer C. , Clough Barbara , Dluzewski A. R. , Wilson R. J. M. , Gratzer W. B. 
Published: February 2005

AbstractMerozoites of the human malaria parasite, Plasmodium falciparum, when treated with cytochalasin B, will attach irreversibly to red cells with formation of a vestigial internal (parasitophorous) vacuole, but they are inhibited from moving into the cell. The existence of an actin‐based motile mechanism is implied. Immunoblotting, peptide mapping and the DNase inhibition assay have been used to show that the merozoite contains actin. It makes up an estimated 0.3% of the total parasite protein and is partitioned in the ratio of about 1:2 between the cytosolic and particulate protein fractions. In the former it is unpolymerised and in the latter filamentous. Most of the anti‐actin‐reactive protein in the soluble fraction and about 20% of that in the pellet has an apparent molecular weight of 55,000 and reacts with an anti‐ubiquitin antibody; it is thus evidently ubiquitinyl actin, or arthrin, which has so far been detected only in insect flight muscle. © 1993 Wiley‐Liss, Inc.
Microtubule rearrangement and bending during assembly of large curved microtubule bundles in mouse cochlear epithelial cells
Authors: Tucker John B. , Paton Calum C. , Henderson Craig G. , Mogensen Mette M. 
Published: February 2005

AbstractMature inner pillar cells in the mammalian organ of Corti are curved through about 60°, where they arch over adjacent epithelial cells and the apex of an intercellular space called the tunnel of Corti. This report deals with changes in microtubule organization that are associated with cell bending and tunnel formation during morphogenesis of the mouse organ of Corti.A large bundle of up to 3,000 microtubules assembles in each inner pillar cell. Microtubule rearrangement occurs about 5 days after bundle assembly begins. The lumen of each initially straight hollow tube‐shaped microtubule bundle is occluded as the bundle becomes more compact and elliptical in cross section. This event anticipates the once‐only bending which subsequently occurs between particular levels (abut 9–19 μm) below the top of a bundle as it curves into its final shape about 2 days later. Microtubule rearrangement presumably facilitates bending which is effected in the plane of lest mechanical resistance parallel to the short axis of a bundle's elliptical cross‐sectional profile.Precocious bending of bundles has been induced about 1.5 days in advance of the natural event. Abnormal positioning of these prematurely curved bundles indicates that bending is effected by a contractile mechanism located within bundles rather than being a response to externally applied forces. The potential importance of such microtubule‐associated contractions for active modulation of the vibratory response in the cochlea during hearing is considered. © 1993 Wiley‐Liss, Inc.
Cellular automaton model of the actin cytoskeleton
Authors: Dufort Paul A. , Lumsden Charles J. 
Published: February 2005

AbstractWe describe a cellular automaton model of the actin cytoskeleton. The model incorporates spatial and temporal behavior at the macomolecular level and is relevant to the viscous nonequilibrium conditions suspected to occur in vivo. The model include cation and nucleotide binding to actin monomers, actin nucleation and polymerization into filaments, coss‐linking with α‐actinin, monomer sequestration with pfilin, filament severing, capping and nucleation with gelsolin, binding of profilin and gelsolin to membrane‐bound phosphatidylinositide biphosphate (PIP2), and regulation of coss‐linking and severing by changing calcium levels. We derive (1) equations for the molecular trnslation and rotation probabilities required for the cellular automaton simulation in terms of molecular size, shape, cytoplasmic viscosity, and temperature; and (2) equations for the binding probabilities of adjacent molecules in terms of experimentally determined reaction rate constants. The model accurately captures the known characteristics of actin polymerization and subsequent ATP hydrolysis under different cation and nucleotide conditions. An examination of gelation and sol‐gel transitions resulting from calcium regulation of α‐actinin and gelsolin predicts an inhomogeneous distribution of bound α‐actinin and F‐actin. The double‐bound α‐actinin (both ends bound to F‐actin) is tightly bunched, while single‐bound α‐actinin is moderately bunched and unbound α‐actinin is homogeneously distributed. The spatial organization of the α‐actinin is quantified using estimates of fractal dimension. The simulation results also suggest that actin/α‐actinin gels may shift from an isotropic to an amorphous phase after shortening of filaments. The gel‐sol transition of the model shows excellent agreement with the present theory of polymer gels. The close correspondence of the model's predictions with previous experimental and theoretical results suggests that the model may be pertinent to better understanding the spatial and temporal properties of complex cytoskeletal processes. © 1993 Wiley‐Liss, Inc.
Rises of intracellular Ca2+ and pH mediate the initiation of sperm motility by hyperosmolality in marine teleosts
Authors: Oda Shoji , Morisawa Masaaki 
Published: February 2005

AbstractSpermatozoa of marine teleosts, puffers and flounder, wee completely quiescent when they were washed to remove electrolytic components of the seminal plasma and then diluted in nonelectrolyte solutions isotonic to the seminal plasma. Sperm motility was initiated upon dilution in hypertonic nonelectrolyte solutions. These observations suggest that sperm motility is suppressed by seminal osmolality and motility is triggered solely by the increase in external osmolality which occurs at natural spawning in hypertonic seawater. Extracellular Ca2+ had no influence on the osmolality‐dependent initiation of sperm motility. However, sperm motility was initiated even in isotonic solution when Ca2+ was introduced into the sperm cells by Ca2+ ionophore. Intracellular Ca2+ increased at the osmolality‐dependent initiation of sperm motility under Ca2+ ‐free conditions. These results suggest that the release of Ca2+ from intracellular storage in response to the increase in external osmolality has a key role in the initiation of sperm motility. A transient increase in intracellular pH was also observed at the hyperosmolality‐dependent initiation of sperm motility. Furthermore, initiation of sperm motility was induced even in isotonic solutions when intracellular pH increased by the treatment with ammonium salts. These results suggest that an increase in intracellular pH, as well as the rise in intracellular Ca2+, has an important role in the initiation of sperm motility in marine teleosts. © 1993 Wiley‐Liss, Inc.
Sulphonate buffers affect the recovery of microtubule‐associated proteins MAP1 and MAP2: Evidence that MAP1A promotes microtubule assembly
Authors: Pedrotti Barbara , Soffientini Adolfo , Islam Khalid 
Published: February 2005

AbstractThe influence of two commonly used sulphonate buffers, PIPES and MES, on the in vitro assembly of bovine brain microtubule protein was examined. Microtubule assembly was monitored by turbimetry and, after centrifugation, the polymerised protein was analysed by SDS‐PAGE and western blotting. Assembly in MES when compared with PIPES resulted in a higher recovery of microtubule proteins at both pH 6.4 and pH 6.9 and in an altered protein composition. The buffer pH affected the total amount of protein polymerized but did not significantly affect the protein composition. At both pH conditions the recovery of HMW‐MAPs was markedly increased in MES buffer and this increase was mostly due to an increase in the amount of MAP1. © 1993 Wiley‐Liss, Inc.
Perspectives on tubulin isotype function and evolution based on the observation that Tetrahymena thermophila microtubules contain a single α‐ and β‐tubulin
Authors: Gaertig Jacek , Thatcher Thomas H. , McGrath Kathleen E. , Callahan Rosemary C. , Gorovsky Martin A. 
Published: February 2005

AbstractWe have cloned and sequenced the two β‐tubulin genes of the ciliated protozoan Tetrahymena thermophila. The two genes encode identical 443 amino acid peptides which are 99.7% identical to the β‐tubulin proteins of T. pyriformis and 95% identical to human β1 tubulin. T. thermophila contains only one β‐tubulin gene (Callahan et al., 1984: Cell 36:441–445). Thus, all of the extremely diverse microtubule structures in this unicellular organism can be formed from a single α‐ and a single β‐tubulin peptide. We have also carried out a phylogenetic analysis of 84 complete β‐tubulin peptide sequences. This analysis supports two hypotheses regarding β‐tubulin evolution and function: (1) Multifunctional β‐tubulins are under greater evolutionary constraint than β‐tubulins present in specialized cells or in cells with very few microtubule related functions, which can evolve rapidly; and (2) Cells which form axonemes maintain a homogeneous population of tubulins. © 1993 Wiley‐Liss, Inc.
Myosin heavy chain dephosphorylation during cytokinesis in dividing sea urchin embryos
Authors: Larochelle Denis A. , Epel David 
Published: February 2005

AbstractMyosin heavy chain (MHC) phosphorylation was examined throughout the period of first cleavage in developing sea urchin embryos. MHC was found to be phosphorylated in these cells and, furthermore, the relative state of myosin phosphorylation was found to decrease as cells progressed through cytokinesis. Following the completion of cytokinesis, the relative state of MHC phosphorylation returned to levels observed in precytokinesis cells. The above results were obtained with myosin immunoprecipitated from whole cell lysates. In order to specifically examine the phosphorylation, state of MHC in the cleavage furrow, a protocol was developed for the isolation of intact contractile rings from dividing sea urchin embryos. MHC was immunoprecipitated from isolated contractile rings and the relative phosphorylation state of this MHC was compared with that of MHC isolated from whole cell lysates prepared at the same time. MHC from isolated contractile rings was found to be significantly less phosphorylated than total cellular MHC, suggesting a role for MHC dephosphorylation during cytokinesis. © 1993 Wiley‐Liss, Inc.