451
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Fant X, Merdes A, Haren L. Cell and molecular biology of spindle poles and NuMA. INTERNATIONAL REVIEW OF CYTOLOGY 2004; 238:1-57. [PMID: 15364196 DOI: 10.1016/s0074-7696(04)38001-0] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
Mitotic and meiotic cells contain a bipolar spindle apparatus of microtubules and associated proteins. To arrange microtubules into focused spindle poles, different mechanisms are used by various organisms. Principally, two major pathways have been characterized: nucleation and anchorage of microtubules at preexisting centers such as centrosomes or spindle pole bodies, or microtubule growth off the surface of chromosomes, followed by sorting and focusing into spindle poles. These two mechanisms can even be found in cells of the same organism: whereas most somatic animal cells utilize the centrosome as an organizing center for spindle microtubules, female meiotic cells build an acentriolar spindle apparatus. Most interestingly, the molecular components that drive acentriolar spindle pole formation are also present in cells containing centrosomes. They include microtubule-dependent motor proteins and a variety of structural proteins that regulate microtubule orientation, anchoring, and stability. The first of these spindle pole proteins, NuMA, had already been identified more than 20 years ago. In addition, several new proteins have been characterized more recently. This review discusses their role during spindle formation and their regulation in the cell cycle.
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Affiliation(s)
- Xavier Fant
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, King's Buildings, Edinburgh EH9 3JR, United Kingdom
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452
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Affiliation(s)
- Andrew R Parker
- Department of Zoology, University of Oxford, Oxford OX1 3PS, UK.
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453
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Denton MJ, Dearden PK, Sowerby SJ. Physical law not natural selection as the major determinant of biological complexity in the subcellular realm: new support for the pre-Darwinian conception of evolution by natural law. Biosystems 2003; 71:297-303. [PMID: 14563569 DOI: 10.1016/s0303-2647(03)00100-x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Before Darwin many biologists considered organic forms to be immutable natural forms or types which like inorganic forms such as atoms or crystals are part of a changeless world order and determined by physical law. Adaptations were viewed as secondary modifications of these 'crystal like' abstract afunctional 'givens of physics.' We argue here that much of the emerging picture of biological order in the subcellular realm resembles closely the pre-Darwinian conception of nature. We point out that in the subcellular realm, between nano and micrometers, physical law necessarily plays a far more significant role in organizing matter than in the familiar 'Darwinian world' between millimeters and meters (where matter can be arranged into almost any contingent artifactual arrangement we choose, as witness Lego toys, watches or jumbo jets). Consequently, when deploying matter into complex structures in the subcellular realm the cell must necessarily make extensive use of natural forms-such as the protein and RNA folds, microtubular forms and tensegrity structures-which like atoms or crystals self-organize under the direction of physical law into what are essentially 'pre-Darwinian' afunctional abstract molecular architectures in which adaptations are trivial secondary modifications of what are evidently primary givens of physics.
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Affiliation(s)
- Michael J Denton
- Biochemistry Department, University of Otago, PO Box 56, Dunedin, New Zealand.
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454
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Abstract
The Drosophila egg contains all the components required to properly execute the early mitotic divisions but is unable to assemble a functional centrosome without a sperm-provided basal body. We show that 65% of unfertilized eggs obtained from a laboratory strain of Drosophila mercatorum can spontaneously assemble a number of cytoplasmic asters after activation, most of them duplicating in a cell cycle-dependent manner. Such asters are formed by a polarized array of microtubules that have their Asp-associated minus-ends converging at a main focus, where centrioles and typical centrosomal antigens are found. Aster assembly is spatially restricted to the anterior region of the oocyte. When fertilized, the parthenogenetic egg forms the poles of the gonomeric spindle by using the sperm-provided basal body, despite the presence within the same cytoplasm of maternal centrosomes. Thirty-five percent of parthenogenetic eggs and all unfertilized and fertilized eggs from the sibling bisexually reproducing D. mercatorum strain do not contain cytoplasmic asters. Thus, the Drosophila eggs have the potential for de novo formation of functional centrosomes independent of preexisting centrioles, but some control mechanisms preventing their spontaneous assembly must exist. We speculate that the release of the block preventing centrosome self-assembly could be a landmark for ensuring parthenogenetic reproduction.
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455
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Abstract
Microtubules are intrinsically polar structures. A consequence of this polarity is that the two ends of the microtubule polymer exhibit different properties. The more dynamic plus ends and the mechanisms that regulate their behavior have been the focus of much recent attention. Here, we concentrate on the dynamics and regulation of minus ends, which play distinct but equally critical roles in microtubule function. In the first part of this review, we compare the in vitro and in vivo behavior of microtubules from a minus end perspective. This comparison suggests that cells possess conserved mechanisms to specifically inhibit minus end polymerization, and perhaps also to actively promote depolymerization. In the second part, we focus on the spatial positioning of minus ends, which is achieved by localized microtubule nucleation, minus end capping and minus end anchoring as well as by motor-dependent sorting. These mechanisms are used in different biological contexts to generate the diversity of organized microtubule arrays in cells.
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Affiliation(s)
- Alexander Dammermann
- Ludwig Institute for Cancer Research, Department of Cellular and Molecular Medicine, University of California, San Diego, CMM-East, Rm 3080, 9500 Gilman Drive, La Jolla, CA 92093, USA
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456
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Theraulaz G, Gautrais J, Camazine S, Deneubourg JL. The formation of spatial patterns in social insects: from simple behaviours to complex structures. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2003; 361:1263-1282. [PMID: 12816611 DOI: 10.1098/rsta.2003.1198] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Many of the collective activities performed by social insects result in the formation of complex spatio-temporal patterns. Without centralized control, workers are able to work together and collectively tackle tasks far beyond the abilities of any one individual. The resulting patterns produced by a colony are not explicitly coded at the individual level, but rather emerge from nonlinear interactions between individuals or between individuals and their environment. We present a few selected examples to illustrate some of the basic mechanisms used by social insects, such as templates, stigmergy and self-organization. These mechanisms can be used in combination to organize pattern formation at the colony level.
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Affiliation(s)
- Guy Theraulaz
- CNR-FRE 2382, Centre de Recherches sur la Cognition Animale, Université Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex 4, France
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457
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Kruse K, Jülicher F. Self-organization and mechanical properties of active filament bundles. PHYSICAL REVIEW E 2003; 67:051913. [PMID: 12786184 DOI: 10.1103/physreve.67.051913] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2002] [Revised: 01/21/2003] [Indexed: 11/07/2022]
Abstract
A general framework for the description of active bundles of polar filaments is presented. The activity of the bundle results from mobile cross-links that induce relative displacements between the aligned filaments. Our generic description is based on momentum conservation within the bundle. By specifying the internal forces, a simple minimal model for the bundle dynamics can be derived, capturing a rich variety of dynamic behaviors. In particular, contracted states as well as solitary and oscillatory waves appear through dynamic instabilities. We present the full bifurcation diagram of this model and study the effects of a dynamic motor distribution on the bundle dynamics. Furthermore, we discuss the mechanical properties of the bundle in the presence of externally applied forces. Our description is motivated by dynamic phenomena in the cytoskeleton and could apply to in vitro experiments as well as to stress fibers and to self-organization phenomena during cell locomotion.
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Affiliation(s)
- Karsten Kruse
- Max-Planck-Institut für Physik komplexer Systeme, Nöthnitzer Strasse 38, 01187 Dresden, Germany.
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458
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Liverpool TB, Marchetti MC. Instabilities of isotropic solutions of active polar filaments. PHYSICAL REVIEW LETTERS 2003; 90:138102. [PMID: 12689327 DOI: 10.1103/physrevlett.90.138102] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2002] [Indexed: 05/24/2023]
Abstract
We study the dynamics of an isotropic solution of polar filaments coupled by molecular motors which generate relative motion of the filaments in two and three dimensions. We investigate the stability of the homogeneous state for constant motor concentration taking into account excluded volume and an estimate of entanglement. At low filament density the system develops a density instability, while at high density entanglement drives the instability of orientational fluctuations.
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459
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Affiliation(s)
- Roland Wedlich-Soldner
- Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA
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460
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Marcus AI, Li W, Ma H, Cyr RJ. A kinesin mutant with an atypical bipolar spindle undergoes normal mitosis. Mol Biol Cell 2003; 14:1717-26. [PMID: 12686621 PMCID: PMC153134 DOI: 10.1091/mbc.e02-09-0586] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Motor proteins have been implicated in various aspects of mitosis, including spindle assembly and chromosome segregation. Here, we show that acentrosomal Arabidopsis cells that are mutant for the kinesin, ATK1, lack microtubule accumulation at the predicted spindle poles during prophase and have reduced spindle bipolarity during prometaphase. Nonetheless, all abnormalities are rectified by anaphase and chromosome segregation appears normal. We conclude that ATK1 is required for normal microtubule accumulation at the spindle poles during prophase and possibly functions in spindle assembly during prometaphase. Because aberrant spindle morphology in these mutants is resolved by anaphase, we postulate that mitotic plant cells contain an error-correcting mechanism. Moreover, ATK1 function seems to be dosage-dependent, because cells containing one wild-type allele take significantly longer to proceed to anaphase as compared with cells containing two wild-type alleles.
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Affiliation(s)
- A I Marcus
- The Pennsylvania State University, Department of Biology, 208 Mueller Laboratory, University Park, Pennsylvania 16801, USA
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461
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Liverpool TB. Anomalous fluctuations of active polar filaments. PHYSICAL REVIEW E 2003; 67:031909. [PMID: 12689103 DOI: 10.1103/physreve.67.031909] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2001] [Revised: 08/05/2002] [Indexed: 11/06/2022]
Abstract
Using a simple model, we study the fluctuating dynamics of inextensible, semiflexible polar filaments interacting with active and directed force generating centers such as molecular motors. Taking into account the fact that the activity occurs on time scales comparable to the filament relaxation time, we obtain some unexpected differences between both the steady-state and dynamical behaviors of active as compared to passive filaments. For the statics, the filaments have a length-scale-dependent rigidity. Dynamically, we find strongly enhanced anomalous diffusion.
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Affiliation(s)
- Tanniemola B Liverpool
- Condensed Matter Theory Group, Blackett Laboratory, Imperial College, London SW7 2BZ, United Kingdom.
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462
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Hammele M, Zimmermann W. Modeling oscillatory microtubule polymerization. PHYSICAL REVIEW E 2003; 67:021903. [PMID: 12636711 DOI: 10.1103/physreve.67.021903] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2002] [Indexed: 11/07/2022]
Abstract
Polymerization of microtubules is ubiquitous in biological cells and under certain conditions it becomes oscillatory in time. Here, simple reaction models are analyzed that capture such oscillations as well as the length distribution of microtubules. We assume reaction conditions that are stationary over many oscillation periods, and it is a Hopf bifurcation that leads to a persistent oscillatory microtubule polymerization in these models. Analytical expressions are derived for the threshold of the bifurcation and the oscillation frequency in terms of reaction rates, and typical trends of their parameter dependence are presented. Both, a catastrophe rate that depends on the density of guanosine triphosphate liganded tubulin dimers and a delay reaction, such as the depolymerization of shrinking microtubules or the decay of oligomers, support oscillations. For a tubulin dimer concentration below the threshold, oscillatory microtubule polymerization occurs transiently on the route to a stationary state, as shown by numerical solutions of the model equations. Close to threshold, a so-called amplitude equation is derived and it is shown that the bifurcation to microtubule oscillations is supercritical.
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Affiliation(s)
- Martin Hammele
- Theoretical Physics, University of Saarland, D-66041 Saarbrücken, Germany
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463
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Forgacs G, Newman SA, Hinner B, Maier CW, Sackmann E. Assembly of collagen matrices as a phase transition revealed by structural and rheologic studies. Biophys J 2003; 84:1272-80. [PMID: 12547807 PMCID: PMC1302703 DOI: 10.1016/s0006-3495(03)74942-x] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
We have studied the structural and viscoelastic properties of assembling networks of the extracellular matrix protein type-I collagen by means of phase contrast microscopy and rotating disk rheometry. The initial stage of the assembly is a nucleation process of collagen monomers associating to randomly distributed branched clusters with extensions of several microns. Eventually a sol-gel transition takes place, which is due to the interconnection of these clusters. We analyzed this transition in terms of percolation theory. The viscoelastic parameters (storage modulus G' and loss modulus G") were measured as a function of time for five different frequencies ranging from omega = 0.2 rad/s to 6.9 rad/s. We found that at the gel point both G' and G" obey a scaling law, with the critical exponent Delta = 0.7 and a critical loss angle being independent of frequency as predicted by percolation theory. Gelation of collagen thus represents a second order phase transition.
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Affiliation(s)
- Gabor Forgacs
- Department of Physics and Biology, University of Missouri, Columbia, Missouri 65211, USA.
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464
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Denton MJ, Marshall CJ, Legge M. The protein folds as platonic forms: new support for the pre-Darwinian conception of evolution by natural law. J Theor Biol 2002; 219:325-42. [PMID: 12419661 DOI: 10.1006/jtbi.2002.3128] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Before the Darwinian revolution many biologists considered organic forms to be determined by natural law like atoms or crystals and therefore necessary, intrinsic and immutable features of the world order, which will occur throughout the cosmos wherever there is life. The search for the natural determinants of organic form-the celebrated "Laws of Form"-was seen as one of the major tasks of biology. After Darwin, this Platonic conception of form was abandoned and natural selection, not natural law, was increasingly seen to be the main, if not the exclusive, determinant of organic form. However, in the case of one class of very important organic forms-the basic protein folds-advances in protein chemistry since the early 1970s have revealed that they represent a finite set of natural forms, determined by a number of generative constructional rules, like those which govern the formation of atoms or crystals, in which functional adaptations are clearly secondary modifications of primary "givens of physics." The folds are evidently determined by natural law, not natural selection, and are "lawful forms" in the Platonic and pre-Darwinian sense of the word, which are bound to occur everywhere in the universe where the same 20 amino acids are used for their construction. We argue that this is a major discovery which has many important implications regarding the origin of proteins, the origin of life and the fundamental nature of organic form. We speculate that it is unlikely that the folds will prove to be the only case in nature where a set of complex organic forms is determined by natural law, and suggest that natural law may have played a far greater role in the origin and evolution of life than is currently assumed.
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Affiliation(s)
- Michael J Denton
- Department of Biochemistry, University of Otago, PO Box 56, Dunedin, New Zealand.
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465
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466
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Cook PR. Predicting three-dimensional genome structure from transcriptional activity. Nat Genet 2002; 32:347-52. [PMID: 12410231 DOI: 10.1038/ng1102-347] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2002] [Accepted: 09/10/2002] [Indexed: 11/09/2022]
Affiliation(s)
- Peter R Cook
- Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK.
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467
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Gruber J, Harborth J, Schnabel J, Weber K, Hatzfeld M. The mitotic-spindle-associated protein astrin is essential for progression through mitosis. J Cell Sci 2002; 115:4053-9. [PMID: 12356910 DOI: 10.1242/jcs.00088] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Astrin is a mitotic-spindle-associated protein expressed in most human cell lines and tissues. However, its functions in spindle organization and mitosis have not yet been determined. Sequence analysis revealed that astrin has an N-terminal globular domain and an extended coiled-coil domain. Recombinant astrin was purified and characterized by CD spectroscopy and electron microscopy. Astrin showed parallel dimers with head-stalk structures reminiscent of motor proteins, although no sequence similarities to known motor proteins were found. In physiological buffers, astrin dimers oligomerized via their globular head domains and formed aster-like structures. Silencing of astrin in HeLa cells by RNA interference resulted in growth arrest, with formation of multipolar and highly disordered spindles. Chromosomes did not congress to the spindle equator and remained dispersed. Cells depleted of astrin were normal during interphase but were unable to progress through mitosis and finally ended in apoptotic cell death. Possible functions of astrin in mitotic spindle organization are discussed.
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Affiliation(s)
- Jens Gruber
- Max Planck Institute for Biophysical Chemistry, Department of Biochemistry, Am Fassberg 11 37070 Göttingen, Germany
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468
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Abstract
Antiparallel overlap of microtubules is central to the morphogenesis of bipolar mitotic spindles. How does this overlap arise, and how is it maintained? A recent theoretical study uses computer simulations to investigate whether motor protein complexes can achieve this task. The "virtual" results reveal that a mixed polarity motor complex is needed to do the job.
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Affiliation(s)
- Arshad Desai
- Max Planck Institute of Cell Biology and Genetics, Dresden, Germany
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469
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Abstract
Microtubules and microfilaments play important roles in cell morphogenesis. The picture emerging from drug studies and molecular-genetic analyses of mutant higher plants defective in cell morphogenesis shows that the roles played by them remain the same in both tip-growing and diffuse-growing cells. Microtubules are important for establishing and maintaining growth polarity whereas actin microfilaments deliver the materials required for growth to specified sites. The recent cloning of several cell morphogenesis genes has revealed that conserved mechanisms as well as novel signal transduction pathways spatially organize the plant cytoskeleton.
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Affiliation(s)
- Jaideep Mathur
- Botanical Institute III, University of Köln, Gyrhofstrasse 15, 50931, Köln, Germany
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470
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Nédélec F. Computer simulations reveal motor properties generating stable antiparallel microtubule interactions. J Cell Biol 2002; 158:1005-15. [PMID: 12235120 PMCID: PMC2173220 DOI: 10.1083/jcb.200202051] [Citation(s) in RCA: 136] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
An aster of microtubules is a set of flexible polar filaments with dynamic plus ends that irradiate from a common location at which the minus ends of the filaments are found. Processive soluble oligomeric motor complexes can bind simultaneously to two microtubules, and thus exert forces between two asters. Using computer simulations, I have explored systematically the possible steady-state regimes reached by two asters under the action of various kinds of oligomeric motors. As expected, motor complexes can induce the asters to fuse, for example when the complexes consist only of minus end-directed motors, or to fully separate, when the motors are plus end directed. More surprisingly, complexes made of two motors of opposite directionalities can also lead to antiparallel interactions between overlapping microtubules that are stable and sustained, like those seen in mitotic spindle structures. This suggests that such heterocomplexes could have a significant biological role, if they exist in the cell.
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Affiliation(s)
- François Nédélec
- Cell Biology and Biophysics Program, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany.
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471
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Kruse K, Sekimoto K. Growth of fingerlike protrusions driven by molecular motors. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2002; 66:031904. [PMID: 12366149 DOI: 10.1103/physreve.66.031904] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2002] [Revised: 05/23/2002] [Indexed: 05/23/2023]
Abstract
The actin cortex is an important part of the motile machinery of a eucaryotic cell. The cortex is steadily reorganized, for example, through the action of molecular motors forming active crosslinks between pairs of actin filaments. Here, the effect of correlations between molecular motors on the induced relative motion of two aligned filaments is investigated. It is found that the average relative velocity between filaments depends nonmonotonically on the motor concentration. Depending on the properties of the filaments' ends, the active interaction between filaments of the same orientation may lead either to a complete overlap or to separation. In addition to pure actin polymerization the active separation of filaments might be involved in the growth of long fingerlike protrusions (filopods).
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Affiliation(s)
- K Kruse
- Institut Curie, Physicochimie, UMR CNRS/IC 168, 26 rue d'Ulm, 75248 Paris Cedex 05, France
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472
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Yvon AMC, Walker JW, Danowski B, Fagerstrom C, Khodjakov A, Wadsworth P. Centrosome reorientation in wound-edge cells is cell type specific. Mol Biol Cell 2002; 13:1871-80. [PMID: 12058055 PMCID: PMC117610 DOI: 10.1091/mbc.01-11-0539] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The reorientation of the microtubule organizing center during cell migration into a wound in the monolayer was directly observed in living wound-edge cells expressing gamma-tubulin tagged with green fluorescent protein. Our results demonstrate that in CHO cells, the centrosome reorients to a position in front of the nucleus, toward the wound edge, whereas in PtK cells, the centrosome lags behind the nucleus during migration into the wound. In CHO cells, the average rate of centrosome motion was faster than that of the nucleus; the converse was true in PtK cells. In both cell lines, centrosome motion was stochastic, with periods of rapid motion interspersed with periods of slower motion. Centrosome reorientation in CHO cells required dynamic microtubules and cytoplasmic dynein/dynactin activity and could be prevented by altering cell-to-cell or cell-to-substrate adhesion. Microtubule marking experiments using photoactivation of caged tubulin demonstrate that microtubules are transported in the direction of cell motility in both cell lines but that in PtK cells, microtubules move individually, whereas their movement is more coherent in CHO cells. Our data demonstrate that centrosome reorientation is not required for directed migration and that diverse cells use distinct mechanisms for remodeling the microtubule array during directed migration.
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Affiliation(s)
- Anne-Marie C Yvon
- Department of Biology and Program in Molecular and Cellular Biology, University of Massachusetts, Amherst, MA 01002, USA
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473
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Humphrey D, Duggan C, Saha D, Smith D, Käs J. Active fluidization of polymer networks through molecular motors. Nature 2002; 416:413-6. [PMID: 11919627 DOI: 10.1038/416413a] [Citation(s) in RCA: 186] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Entangled polymer solutions and melts exhibit elastic, solid-like resistance to quick deformations and a viscous, fluid-like response to slow deformations. This viscoelastic behaviour reflects the dynamics of individual polymer chains driven by brownian motion: since individual chains can only move in a snake-like fashion through the mesh of surrounding polymer molecules, their diffusive transport, described by reptation, is so slow that the relaxation of suddenly imposed stress is delayed. Entangled polymer solutions and melts therefore elastically resist deforming motions that occur faster than the stress relaxation time. Here we show that the protein myosin II permits active control over the viscoelastic behaviour of actin filament solutions. We find that when each actin filament in a polymerized actin solution interacts with at least one myosin minifilament, the stress relaxation time of the polymer solution is significantly shortened. We attribute this effect to myosin's action as a 'molecular motor', which allows it to interact with randomly oriented actin filaments and push them through the solution, thus enhancing longitudinal filament motion. By superseding reptation with sliding motion, the molecular motors thus overcome a fundamental principle of complex fluids: that only depolymerization makes an entangled, isotropic polymer solution fluid for quick deformations.
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Affiliation(s)
- D Humphrey
- Center for Nonlinear Dynamics, University of Texas at Austin, Texas 78712, USA
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474
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Compton DA. In vitro approaches for the study of molecular motors in aster formation. Methods Cell Biol 2002; 67:225-39. [PMID: 11550471 DOI: 10.1016/s0091-679x(01)67016-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/21/2023]
Affiliation(s)
- D A Compton
- Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755, USA
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475
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Debec A, Grammont M, Berson G, Dastugue B, Sullivan W, Couderc JL. Toucan protein is essential for the assembly of syncytial mitotic spindles in Drosophila melanogaster. Genesis 2001; 31:167-75. [PMID: 11783007 DOI: 10.1002/gene.10019] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The toc gene of Drosophila melanogaster encodes a 235-kD polypeptide with a coiled-coil domain, which is highly expressed during oogenesis (Grammont et al., 1997, 2000). We now report the localization of the Toucan protein during early embryonic development. The Toucan protein is present only during the syncytial stages and is associated with the nuclear envelope and the cytoskeletal structures of the syncytial embryo. In anaphase A, Toucan is concentrated at the spindle poles near the minus end of microtubules. This microtubule association is very dynamic during the nuclear cell cycle. Mutant embryos lacking the Toucan protein are blocked in a metaphase-like state. They display abnormal and nonfunctional spindles, characterized by broad poles, detachment of the centrosomes, and failure of migration of the chromosomes. These results strongly suggest that Toucan represents a factor essential for the assembly and the function of the syncytial mitotic spindles.
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Affiliation(s)
- A Debec
- Observatoire Océanologique, Laboratoire de Biologie du Développement, Université Pierre et Marie Curie/CNRS, Villefranche-sur-Mer, France
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476
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Lee HY, Kardar M. Macroscopic equations for pattern formation in mixtures of microtubules and molecular motors. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2001; 64:056113. [PMID: 11736020 DOI: 10.1103/physreve.64.056113] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2001] [Indexed: 05/23/2023]
Abstract
Inspired by patterns observed in mixtures of microtubules and molecular motors, we propose continuum equations for the evolution of motor density and microtubule orientation. The chief ingredients are the transport of motors along tubules, and the alignment of tubules in the process. The macroscopic equations lead to aster and vortex patterns in qualitative agreement with experiments. While the early stages of evolution of tubules are similar to coarsening of spins following a quench, the rearrangement of motors leads to arrested coarsening at low densities. Even in one dimension, the equations exhibit a variety of interesting behaviors, such as symmetry breaking, moving fronts, and motor localization.
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Affiliation(s)
- H Y Lee
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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477
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Abstract
In vivo microscopy has recently revealed the dynamic nature of many cellular organelles. The dynamic properties of several cellular structures are consistent with a role for self-organization in their formation, maintenance, and function; therefore, self-organization might be a general principle in cellular organization.
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Affiliation(s)
- T Misteli
- National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
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478
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Kruse K, Camalet S, Jülicher F. Self-propagating patterns in active filament bundles. PHYSICAL REVIEW LETTERS 2001; 87:138101. [PMID: 11580629 DOI: 10.1103/physrevlett.87.138101] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2000] [Indexed: 05/23/2023]
Abstract
Bundles of polar filaments which interact via active elements can exhibit complex dynamic behaviors. By using a simple and general description for the bundle dynamics, we find regimes for which density profiles propagate as solitary waves with a characteristic velocity along the bundle. These behaviors emerge from an interplay of local contractions in the bundle and relative sliding of oppositely oriented filaments. By introducing filament binding to and detachment from a substrate, the system is able to generate net motion as a self-organization phenomenon.
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Affiliation(s)
- K Kruse
- Institut Curie, Physicochimie, UMR CNRS/IC 168, 26 rue d'Ulm, 75248 Paris Cedex 05, France
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479
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Lipowsky R, Klumpp S, Nieuwenhuizen TM. Random walks of cytoskeletal motors in open and closed compartments. PHYSICAL REVIEW LETTERS 2001; 87:108101. [PMID: 11531504 DOI: 10.1103/physrevlett.87.108101] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2000] [Indexed: 05/23/2023]
Abstract
Random walks of molecular motors, which bind to and unbind from cytoskeletal filaments, are studied theoretically. The bound and unbound motors undergo directed and nondirected motion, respectively. Motors in open compartments exhibit anomalous drift velocities. Motors in closed compartments generate stationary nonequilibrium states with spatially varying densities of the motor concentrations and currents. "Traffic jams" on the filaments lead to a maximum of the motor current at an optimal motor concentration. Quantitative estimates based on experimental data for bound motors indicate that these transport phenomena are accessible to experiments.
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Affiliation(s)
- R Lipowsky
- Max-Planck-Institut für Kolloid und Grenzflächenforschung, 14424 Potsdam, Germany
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480
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Vorobjev I, Malikov V, Rodionov V. Self-organization of a radial microtubule array by dynein-dependent nucleation of microtubules. Proc Natl Acad Sci U S A 2001; 98:10160-5. [PMID: 11504928 PMCID: PMC56932 DOI: 10.1073/pnas.181354198] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2001] [Accepted: 07/11/2001] [Indexed: 11/18/2022] Open
Abstract
Polarized radial arrays of cytoplasmic microtubules (MTs) with minus ends clustered at the cell center define the organization of the cytoplasm through interaction with microtubule motors bound to membrane organelles or chromosomes. It is generally assumed that the radial organization results from nucleation of MTs at the centrosome. However, radial MT array can also be attained through self-organization that requires the activity of a minus-end-directed MT motor, cytoplasmic dynein. In this study we examine the role of cytoplasmic dynein in the self-organization of a radial MT array in cytoplasmic fragments of fish melanophores lacking the centrosome. After activation of dynein motors bound to membrane-bound organelles, pigment granules, the fragments rapidly form polarized radial arrays of MTs and position pigment aggregates at their centers. We show that rearrangement of MTs in the cytoplasm is achieved through dynein-dependent MT nucleation. The radial pattern is generated by continuous disassembly and reassembly of MTs and concurrent minus-end-directed transport of pigment granules bearing the nucleation sites.
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Affiliation(s)
- I Vorobjev
- Department of Physiology and Center for Biomedical Imaging Technology, University of Connecticut Health Center, Farmington, CT 06032-1507, USA
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481
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482
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Surrey T, Nedelec F, Leibler S, Karsenti E. Physical properties determining self-organization of motors and microtubules. Science 2001; 292:1167-71. [PMID: 11349149 DOI: 10.1126/science.1059758] [Citation(s) in RCA: 355] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
In eukaryotic cells, microtubules and their associated motor proteins can be organized into various large-scale patterns. Using a simplified experimental system combined with computer simulations, we examined how the concentrations and kinetic parameters of the motors contribute to their collective behavior. We observed self-organization of generic steady-state structures such as asters, vortices, and a network of interconnected poles. We identified parameter combinations that determine the generation of each of these structures. In general, this approach may become useful for correlating the morphogenetic phenomena taking place in a biological system with the biophysical characteristics of its constituents.
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Affiliation(s)
- T Surrey
- Cell Biology and Biophysics Program, European Molecular Biology Laboratory, 69117 Heidelberg, Germany
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483
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Abstract
Molecular motors that hydrolyze ATP and use the derived energy to generate force are involved in a variety of diverse cellular functions. Genetic, biochemical, and cellular localization data have implicated motors in a variety of functions such as vesicle and organelle transport, cytoskeleton dynamics, morphogenesis, polarized growth, cell movements, spindle formation, chromosome movement, nuclear fusion, and signal transduction. In non-plant systems three families of molecular motors (kinesins, dyneins, and myosins) have been well characterized. These motors use microtubules (in the case of kinesines and dyneins) or actin filaments (in the case of myosins) as tracks to transport cargo materials intracellularly. During the last decade tremendous progress has been made in understanding the structure and function of various motors in animals. These studies are yielding interesting insights into the functions of molecular motors and the origin of different families of motors. Furthermore, the paradigm that motors bind cargo and move along cytoskeletal tracks does not explain the functions of some of the motors. Relatively little is known about the molecular motors and their roles in plants. In recent years, by using biochemical, cell biological, molecular, and genetic approaches a few molecular motors have been isolated and characterized from plants. These studies indicate that some of the motors in plants have novel features and regulatory mechanisms. The role of molecular motors in plant cell division, cell expansion, cytoplasmic streaming, cell-to-cell communication, membrane trafficking, and morphogenesis is beginning to be understood. Analyses of the Arabidopsis genome sequence database (51% of genome) with conserved motor domains of kinesin and myosin families indicates the presence of a large number (about 40) of molecular motors and the functions of many of these motors remain to be discovered. It is likely that many more motors with novel regulatory mechanisms that perform plant-specific functions are yet to be discovered. Although the identification of motors in plants, especially in Arabidopsis, is progressing at a rapid pace because of the ongoing plant genome sequencing projects, only a few plant motors have been characterized in any detail. Elucidation of function and regulation of this multitude of motors in a given species is going to be a challenging and exciting area of research in plant cell biology. Structural features of some plant motors suggest calcium, through calmodulin, is likely to play a key role in regulating the function of both microtubule- and actin-based motors in plants.
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Affiliation(s)
- A S Reddy
- Department of Biology and Program in Cell and Molecular Biology, Colorado State University, Fort Collins 80523, USA
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484
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Liverpool TB, Maggs AC, Ajdari A. Viscoelasticity of solutions of motile polymers. PHYSICAL REVIEW LETTERS 2001; 86:4171-4174. [PMID: 11328123 DOI: 10.1103/physrevlett.86.4171] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2000] [Indexed: 05/23/2023]
Abstract
We explore the linear viscoelastic response of an entangled, isotropic solution of polar semiflexible polymers with active, motile centers which generate longitudinal motion. Because of the activity of these centers, the short-time modulus displays two novel power-law regimes: Initially G(t) proportional to t(-1/8), then the response is "Rouse-like" with G(t) proportional to t(-1/2). At longer times we find accelerated relaxation due to directed reptation, resulting in a reduced low frequency viscosity.
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Affiliation(s)
- T B Liverpool
- Physico-Chimie Theorique, ESA CNRS 7083, E.S.P.C.I., 75231 Paris Cedex 05, France
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485
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Nédélec F, Surrey T, Maggs AC. Dynamic concentration of motors in microtubule arrays. PHYSICAL REVIEW LETTERS 2001; 86:3192-3195. [PMID: 11290140 DOI: 10.1103/physrevlett.86.3192] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2000] [Indexed: 05/23/2023]
Abstract
We present experimental and theoretical studies of the dynamics of molecular motors in microtubule arrays and asters. By solving a convection-diffusion equation we find that the density profile of motors in a two-dimensional aster is characterized by continuously varying exponents. Simulations are used to verify the assumptions of the continuum model. We observe the concentration profiles of kinesin moving in quasi-two-dimensional artificial asters by fluorescent microscopy and compare with our theoretical results.
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Affiliation(s)
- F Nédélec
- EMBL, Cell Biology, Heidelberg, Germany
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486
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Abstract
Endostatin is a potent endogenous angiogenesis inhibitor that induces regression of tumors in mice. Neither an extracellular receptor for endostatin nor intracellular signals that result in the regression of tumor vascular beds have been identified. We demonstrate that endostatin, but not angiostatin, at comparable concentrations to those used in in vivo animal trials, rapidly down-regulates many genes in exponentially growing endothelial cells. These include immediate early response genes, cell cycle-related genes, and genes regulating apoptosis inhibitors, mitogen-activated protein kinases, focal adhesion kinase, G-protein-coupled receptors mediating endothelial growth, a mitogenic factor, adhesion molecules, and cell structure components. Suppression of both apoptosis inhibitors and cell proliferation genes may have a limited contribution to the antiangiogenesis process because endostatin induces neither apoptosis nor growth inhibition, unless studied under reduced serum conditions. In contrast, the antimigratory effect of endostatin was rapid and potent even under serum-supplemented conditions. Endostatin caused gene suppression and migration arrest exclusively in endothelial cells, most profoundly in microvascular endothelial cells. The c-myc null fibroblasts obtained by targeted homologous recombination showed an attenuated migration rate compared with isogenic parental cells, whereas the introduction of the c-myc gene into endothelial cells abrogated the antimigratory effect of endostatin. Inhibition of E-box-driven transcription by overexpressing max or mad suppressed endothelial migration. Thus, rapid down-regulation of genes by endostatin neither restores proliferating endothelial cells to their resting states nor induces apoptosis; rather, it potently inhibits endothelial cell migration partly via suppression of c-myc expression.
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Affiliation(s)
- M Shichiri
- Department of Clinical and Molecular Endocrinology, Tokyo Medical and Dental University Graduate School, Tokyo, Japan.
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487
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Affiliation(s)
- Masayoshi Shichiri
- Department of Clinical and Molecular Endocrinology Tokyo Medical and Dental University Graduate School Tokyo Japan
| | - Yukio Hirata
- Department of Clinical and Molecular Endocrinology Tokyo Medical and Dental University Graduate School Tokyo Japan
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488
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Affiliation(s)
- A W Murray
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA.
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489
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Helfer E, Harlepp S, Bourdieu L, Robert J, MacKintosh FC, Chatenay D. Viscoelastic properties of actin-coated membranes. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2001; 63:021904. [PMID: 11308515 DOI: 10.1103/physreve.63.021904] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2000] [Indexed: 05/23/2023]
Abstract
In living cells, cytoskeletal filaments interact with the plasma membrane to form structures that play a key role in cell shape and mechanical properties. To study the interaction between these basic components, we designed an in vitro self-assembled network of actin filaments attached to the outer surface of giant unilamellar vesicles. Optical tweezers and single-particle tracking experiments are used to study the rich dynamics of these actin-coated membranes (ACM). We show that microrheology studies can be carried out on such an individual microscopic object. The principle of the experiment consists in measuring the thermally excited position fluctuations of a probe bead attached biochemically to the membrane. We propose a model that relates the power spectrum of these thermal fluctuations to the viscoelastic properties of the membrane. The presence of the actin network modifies strongly the membrane dynamics with respect to a fluid, lipid bilayer one. It induces first a finite (omega=0) two-dimensional (2D) shear modulus G(0)(2D) approximately 0.5 to 5 microN/m in the membrane plane. Moreover, the frequency dependence at high frequency of the shear modulus [G(')(2D)(f ) approximately f(0.85+/-0.07)] and of the bending modulus (kappa(ACM)(f) approximately f(0.55+/-0.21)) demonstrate the viscoelastic behavior of the composite membrane. These results are consistent with a common exponent of 0.75 for both moduli as expected from our model and from prior measurements on actin solutions.
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Affiliation(s)
- E Helfer
- Laboratoire de Dynamique des Fluides Complexes, U.M.R. 7506, 3 rue de l'Université, 67084 Strasbourg Cedex, France
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490
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491
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Abstract
In all eukaryotes, a microtubule-based structure known as the spindle is responsible for accurate chromosome segregation during cell division. Spindle assembly and function require localized regulation of microtubule dynamics and the activity of a variety of microtubule-based motor proteins. Recent work has begun to uncover the molecular mechanisms that underpin this process. Here we describe the structural and dynamic properties of the spindle, and introduce the current concepts regarding how a bipolar spindle is assembled and how it functions to segregate chromosomes.
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Affiliation(s)
- T Wittmann
- Department of Cell Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA.
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492
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Weiss M, Nilsson T. Protein sorting in the Golgi apparatus: a consequence of maturation and triggered sorting. FEBS Lett 2000; 486:2-9. [PMID: 11108832 DOI: 10.1016/s0014-5793(00)02155-4] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
To explain how resident proteins distribute in peak-like patterns at various positions in the secretory pathway, Glick and co-workers postulated that resident proteins comprise different populations (termed kin populations) and that these compete with each other for entering retrograde transport carriers [Glick et al. (1997) FEBS Lett. 414, 177-181]. Using modelling and computer simulation, they could demonstrate that differences in competitiveness sufficed to generate overlapping but distinct peak-like steady state distributions of the different kin populations across the Golgi stack. In this study, we have tested the robustness of the competition model and find that over-expression or changes in the number of kin populations affect their overall steady state distributions. To increase the robustness of the system, we have introduced a milieu-induced trigger for recycling. This allows for a decrease in the coupling between kin populations permitting both over-expression as well as changes in the number of kin populations. We have also extended the model to include a Golgi to endoplasmic reticulum (ER) recycling pathway and find that only a small amount of resident proteins may recycle at any time without upsetting their observed distributions in the Golgi stack. The biological relevance of a trigger-induced sorting mechanism and ER recycling is discussed.
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Affiliation(s)
- M Weiss
- MPI for FLuid Dynamics, Department of Nonlinear Dynamics, Göttingen, Germany.
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493
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Abstract
Self-organization of living cells results from the tangle of positive and negative feedback developed to ensure their homeostasis and/or their differentiation. There are three major means cellular regulation operates: the genetic, the epigenetic, and the metabolic ones. The regulation type in each of them has been overviewed. Further examination of relations between complexity and developmental stability points out sui generis properties of feedback loops, which are redundancy and pleiotropy. Prototypical schemes for positive and negative regulation with redundant and pleiotropic (including multifunctional) proteins are presented. They stress a theoretical shift from the analytical to the systemic framework. The systemic paradigm appears to be of increasing interest and importance in the study of concepts for the representation of genetic and epigenetic regulations.
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Affiliation(s)
- M Roux-Rouquie
- Institut Pasteur, 25-28, rue du Docteur Roux, Paris Cedex 15, 75724, France
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494
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Kruse K, Jülicher F. Actively contracting bundles of polar filaments. PHYSICAL REVIEW LETTERS 2000; 85:1778-1781. [PMID: 10970612 DOI: 10.1103/physrevlett.85.1778] [Citation(s) in RCA: 115] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2000] [Indexed: 05/23/2023]
Abstract
We introduce a phenomenological model to study the properties of bundles of polar filaments which interact via active elements. The stability of the homogeneous state, the attractors of the dynamics in the unstable regime, and the tensile stress generated in the bundle are discussed. We find that the interaction of parallel filaments can induce unstable behavior and is responsible for active contraction and tension in the bundle. The interaction between antiparallel filaments leads to filament sorting. Our model could apply to simple contractile structures in cells such as stress fibers.
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Affiliation(s)
- K Kruse
- Institut Curie, Physicochimie, UMR CNRS/IC 168, 26 rue d'Ulm, 75248 Paris Cedex 05, France
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495
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Smirnova EA, Reddy AS, Bowser J, Bajer AS. Minus end-directed kinesin-like motor protein, Kcbp, localizes to anaphase spindle poles in Haemanthus endosperm. CELL MOTILITY AND THE CYTOSKELETON 2000; 41:271-80. [PMID: 9829781 DOI: 10.1002/(sici)1097-0169(1998)41:3<271::aid-cm8>3.0.co;2-w] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Microtubule-based motor proteins assemble and reorganize acentrosomal mitotic and meiotic spindles in animal cells. The functions of motor proteins in acentrosomal plant spindles are unknown. The cellulosic cell wall and relative small size of most plant cells precludes accurate detection of the spatial distribution of motors in mitosis. Large cell size and absence of a cellulosic cell wall in Haemanthus endosperm make these cells ideally suited for studies of the spatial distribution of motor proteins during cell division. Immunolocalization of a kinesin-like calmodulin-binding protein (KCBP) in Haemanthus endosperm revealed its mitotic distribution. KCBP appears first in association with the prophase spindle. Highly concentrated within the cores of individual kinetochore fibers, KCBP decorates microtubules of kinetochore-fibers through metaphase. By mid-anaphase (when a barrel-shaped spindle becomes convergent), the protein redistributes and accumulates at the spindle polar regions. In telophase, KCBP relocates toward the phragmoplast and cell plate. These data suggest a role for KCBP in anaphase spindle microtubule convergence, which assures coherence of kinetochore-fibers within each sister chromosome group. Increasing coherence of kinetochore-fibers prevents splitting within each sister chromosome group and formation of multinucleated cells.
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Affiliation(s)
- E A Smirnova
- Biology Faculty, Moscow State University, Moscow, Russia
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496
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Blangy A, Chaussepied P, Nigg EA. Rigor-type mutation in the kinesin-related protein HsEg5 changes its subcellular localization and induces microtubule bundling. CELL MOTILITY AND THE CYTOSKELETON 2000; 40:174-82. [PMID: 9634214 DOI: 10.1002/(sici)1097-0169(1998)40:2<174::aid-cm6>3.0.co;2-f] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
HsEg5 is a human kinesin-related motor protein essential for the formation of a bipolar mitotic spindle. It interacts with the mitotic centrosomes in a phosphorylation-dependent manner. To investigate further the mechanisms involved in targetting HsEg5 to the spindle apparatus, we expressed various mutants of HsEg5 in HeLa cells. All these mutants share a mutation of Thr-112 in the N-terminal motor domain, resulting in the inactivation of the ATP binding domain. In vitro, the HsEg5-T112N mutant motor domain showed a nucleotide-independent microtubule association, typical of a kinesin protein binding to microtubules in a rigor state. In vivo, overexpression of the HsEg5 rigor mutant in HeLa cells induced, in interphase, microtubule bundling, and, in mitosis, the formation of monopolar mitotic spindles similar to those observed after microinjection of anti-HsEg5 antibodies. Localization of the HsEg5 rigor mutant on cytoplasmic microtubules did not require the C-terminal tail domain but was lost when the stalk domain was also deleted. Sucrose gradient centrifugation experiments showed that microtubule bundling was most likely caused by the binding of HsEg5 mutants in a dimeric state. These results demonstrate that the precise subcellular localization of HsEg5 in vivo is regulated not only by the phosphorylation of the tail domain but also by the oligomeric state of the protein.
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Affiliation(s)
- A Blangy
- Swiss Institute for Experimental Cancer Research, Epalinges.
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497
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Abstract
The interplay between microtubules and the motor enzyme, cytoplasmic dynein, is essential for organisation of the cytoplasm, organelle transport, and cell division in eukaryotic cells. During mitosis, cytoplasmic dynein organises microtubules into two spindle pole asters, as well as the comparable multiple cytoplasmic asters induced by the microtubule-stabilising agent taxol. The mechanisms behind this cell cycle-regulated organisation are, however, not fully understood. We report here that the unidirectional dynein-dependent pigment organelle aggregation in taxol-treated melanophores from Atlantic cod, induces multiple microtubule asters. Usually, the pigment aggregates to a central pigment mass in the cell center, but pigment aggregation in taxol-treated cells induces formation of several peripheral pigment clusters that each localise to the center of a microtubule aster formation. When a cell with previously formed peripheral pigment clusters redisperse pigment, the asters disappear. Upon a subsequent reaggregation of the pigment, the aster formations reappear. The results indicate that the pigment aggregation process organises the microtubules into these formations. Immuno-electron microscopy of isolated pigment organelles indicates the presence of several dynein molecules on each pigment organelle, making it possible for each organelle to interact with several microtubules and thereby focusing microtubule minus ends. The possibility of unidirectional dynein-dependent organelle movement for organising microtubules into asters during cell division, and similarities in signal transduction between mitosis and pigment movement, are discussed.
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Affiliation(s)
- H Nilsson
- Göteborg University, Department of Zoology, Zoophysiology, Sweden.
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498
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Smirnova EA, Bajer AS. Early stages of spindle formation and independence of chromosome and microtubule cycles in Haemanthus endosperm. CELL MOTILITY AND THE CYTOSKELETON 2000; 40:22-37. [PMID: 9605969 DOI: 10.1002/(sici)1097-0169(1998)40:1<22::aid-cm3>3.0.co;2-h] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
We analyzed transformation of the interphase microtubular cytoskeleton into the prophase spindle and followed the pattern of spindle axis determination. Microtubules in endosperm of the higher plant Haemanthus (Scadoxus) were stained by the immunogold and immunogold silver-enhanced methods. Basic structural units involved in spindle morphogenesis were "microtubule converging centers." We emphasized the importance of relative independence of chromosomal and microtubular cycles, and the influence of these cycles on the progress of mitosis. Cells with moderately desynchronized cycles were functional, but extreme desynchronization led to aberrant mitosis. There were three distinct phases of spindle development. The first one comprised interphase and early to mid-prophase. During this phase, the interphase microtubule meshwork radiating from the nuclear surface into the cytoplasm rearranged and formed a dense microtubule cage around the nucleus. The second phase comprised mid to late prophase, and resulted in the formation of normal (bipolar) or transitory aberrant (apolar or multipolar) prophase spindles. The third phase comprised late prophase with prometaphase. The onset of prometaphase was accompanied by a rapid association of microtubule converging centers with kinetochores. In this stage aberrant spindles transformed invariably into bipolar ones. Lateral association of a few bipolar kinetochore fibers at early prometaphase established the core of the bipolar spindle and its alignment. We concluded that (1) spindle formation is a largely independent microtubular process modified by the chromosomal/kinetochore cycle; and (2) the initial polarity of the spindle is established by microtubule converging centers, which are a functional substitute of the centrosome/MTOC. We believe that the dynamics of microtubule converging centers is an expression of microtubule self-organization driven by motor proteins as proposed by Mitchison [1992: Philos. Trans. R. Soc. Lond. B. 336:99].
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Affiliation(s)
- E A Smirnova
- Biology Faculty, Moscow State University, Russia
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499
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Zong ZP, Fujikawa-Yamamoto K, Li AL, Yamaguchi N, Chang YG, Murakami M, Ishikawa Y. Involvement of protein kinase C in taxol-induced polyploidization in a cultured sarcoma cell line. Eur J Pharmacol 2000; 394:181-7. [PMID: 10771283 DOI: 10.1016/s0014-2999(00)00155-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Taxol was found to inhibit the proliferation and to induce the polyploidization of cultured methylcholanthrene-induced sarcoma cells (Meth-A cells). To investigate whether protein kinase C is involved in taxol-induced polyploidization, phorbol 12-myristate 13-acetate (PMA), which regulates the activity of protein kinase C, was used along with taxol to treat the cells. We found that PMA did not interfere with the proliferation and did not induce polyploidization by itself. However, at low concentration, taxol, which by itself did not induce polyploidization, clearly induced polyploidization in the presence of PMA. To explore the mechanism by which PMA potentiates polyploidization, the levels of the G1 checkpoint-related proteins cyclin E and cdk2, and those of the G2 checkpoint-related proteins cyclin B and cdc2 were determined by flow cytometry. We found that both G1 and G2 checkpoint-related proteins increased during the induction of polyploidization. To verify the relationship between protein kinase C and tubulin polymerization, flow cytometry was used to determine the total content of tubulin protein, and morphological observation was used to examine spindle organization. PMA did not affect the taxol-induced increase in tubulin protein, but markedly potentiated taxol-induced spindle disorganization. These findings suggest that protein kinase C plays an important role in regulating the induction of polyploidization in Meth-A cells.
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Affiliation(s)
- Z P Zong
- Division of Basic Science, Medical Research Institute, Kanazawa Medical University, Uchinada, Japan.
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500
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Fouquet J, Kann M, Souès S, Melki R. ARP1 in Golgi organisation and attachment of manchette microtubules to the nucleus during mammalian spermatogenesis. J Cell Sci 2000; 113 ( Pt 5):877-86. [PMID: 10671377 DOI: 10.1242/jcs.113.5.877] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Actin related protein of vertebrate, Arp1, is a major component of the dynactin complex. To characterise and localise Arp1 during mammalian spermatogenesis, polyclonal antibodies were raised against a human recombinant Arp1. Anti-Arp1 antibodies were used for western-immunoblotting, indirect immunofluorescence and immunoelectron microscopy. In round spermatids, Arp1 was detected at the centrosome and at the Golgi apparatus. In elongated spermatids, Arp1 was predominantly found along microtubules of the manchette and at their site of attachment to the nuclear envelope. In maturing spermatids, Arp1 was still present in the pericentriolar material, but in testicular spermatozoa it was not detectable. These various localisations of Arp1 and their changes during spermatid differentiation suggest that the dynactin complex in association with dynein might contribute to several activities: the functional organisation of the centrosome and of the Golgi apparatus and the shaping of the nucleus by manchette microtubules.
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Affiliation(s)
- J Fouquet
- Laboratoire de Biologie Cellulaire, Centre Universitaire des Saints-Pères, Université René Descartes, Paris V, France.
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