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Schäfer, K., H. Wang, A. Pich, M. Möller, C. Damm y S. Ernst. "Lumineszierende Kunststofffilme und -filamente für Warn- und Sicherheitssysteme". Chemie Ingenieur Technik 82, n.º 9 (27 de agosto de 2010): 1474–75. http://dx.doi.org/10.1002/cite.201050105.
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Deschauer, M. y T. Müller. "Okulopharyngeale Muskeldystrophie". Nervenheilkunde 23, n.º 08 (2004): 442–46. http://dx.doi.org/10.1055/s-0038-1626405.
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ZusammenfassungDie okulopharyngeale Muskeldystrophie (OPMD) ist eine autosomal-dominant vererbte Muskelerkrankung mit spätem Beginn, die klinisch durch eine Ptosis, Dysphagie und proximale Paresen gekennzeichnet ist. Die Erkrankung wird durch eine Trinukleotidvermehrung im Gen für das Poly-A-bindende Protein (PABPN1) verursacht. Hierdurch kommt es zu einer Verlängerung des Proteins um wenige Alanine, die zur Aggregation des Proteins führen. Diese Aggregate sind elektronenmikroskopisch als charakteristische intranukleäre Filamente nachweisbar. Der genaue pathogenetische Mechanismus, durch den es zum selektiven Befall der Muskelzellen und zur Ausbildung des typischen Phänotypes kommt, ist derzeit noch unklar.
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Pratt, Zachary L., Bingming Chen, Charles J. Czuprynski, Amy C. L. Wong y Charles W. Kaspar. "Characterization of Osmotically Induced Filaments of Salmonella enterica". Applied and Environmental Microbiology 78, n.º 18 (13 de julio de 2012): 6704–13. http://dx.doi.org/10.1128/aem.01784-12.
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ABSTRACTSalmonella entericaforms aseptate filaments with multiple nucleoids when cultured in hyperosmotic conditions. These osmotic-induced filaments are viable and form single colonies on agar plates even though they contain multiple genomes and have the potential to divide into multiple daughter cells. Introducing filaments that are formed during osmotic stress into culture conditions without additional humectants results in the formation of septa and their division into individual cells, which could present challenges to retrospective analyses of infectious dose and risk assessments. We sought to characterize the underlying mechanisms of osmotic-induced filament formation. The concentration of proteins and chromosomal DNA in filaments and control cells was similar when standardized by biomass. Furthermore, penicillin-binding proteins in the membrane of salmonellae were activein vitro. The activity of penicillin-binding protein 2 was greater in filaments than in control cells, suggesting that it may have a role in osmotic-induced filament formation. Filaments contained more ATP than did control cells in standardized cell suspensions, though the levels of two F0F1-ATP synthase subunits were reduced. Furthermore, filaments could septate and divide within 8 h in 0.2× Luria-Bertani broth at 23°C, while nonfilamentous control cells did not replicate. Based upon the ability of filaments to septate and divide in this diluted broth, a method was developed to enumerate by plate count the number of individual, viable cells within a population of filaments. This method could aid in retrospective analyses of infectious dose of filamented salmonellae.
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Chen, Che-Yu, Lee G. Mundy, Eve C. Ostriker, Shaye Storm y Arnab Dhabal. "Self-gravitating filament formation from shocked flows: velocity gradients across filaments". Monthly Notices of the Royal Astronomical Society 494, n.º 3 (10 de abril de 2020): 3675–85. http://dx.doi.org/10.1093/mnras/staa960.
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ABSTRACT In typical environments of star-forming clouds, converging supersonic turbulence generates shock-compressed regions, and can create strongly magnetized sheet-like layers. Numerical magnetohydrodynamic simulations show that within these post-shock layers, dense filaments and embedded self-gravitating cores form via gathering material along the magnetic field lines. As a result of the preferred-direction mass collection, a velocity gradient perpendicular to the filament major axis is a common feature seen in simulations. We show that this prediction is in good agreement with recent observations from the CARMA Large Area Star Formation Survey (CLASSy), from which we identified several filaments with prominent velocity gradients perpendicular to their major axes. Highlighting a filament from the north-west part of Serpens South, we provide both qualitative and quantitative comparisons between simulation results and observational data. In particular, we show that the dimensionless ratio Cv ≡ Δvh2/(GM/L), where Δvh is half of the observed perpendicular velocity difference across a filament, and M/L is the filament’s mass per unit length, can distinguish between filaments formed purely due to turbulent compression and those formed due to gravity-induced accretion. We conclude that the perpendicular velocity gradient observed in the Serpens South north-west filament can be caused by gravity-induced anisotropic accretion of material from a flattened layer. Using synthetic observations of our simulated filaments, we also propose that a density-selection effect may explain observed subfilaments (one filament breaking into two components in velocity space) as reported in recent observations.
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Fard, Mohammad Ansari, Sina Taamoli y Shant Baghram. "Cosmological filaments in the light of excursion set of saddle points". Monthly Notices of the Royal Astronomical Society 489, n.º 1 (9 de agosto de 2019): 900–909. http://dx.doi.org/10.1093/mnras/stz2210.
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ABSTRACT The universe in large scales is structured as a network known as cosmic web. Filaments are one of the structural components of this web, which can be introduced as a novel probe to study the formation and evolution of structures and as a probe to study the cosmological models and to address the missing baryon problem. The aim of this work is to introduce an analytical framework to study the statistics of filaments such as number density of them and also to obtain the length-mass relation. For this objective, we model filaments as collapsed objects which have an extension in one direction, accordingly we use the ellipsoidal collapse to study the evolution of an over-dense region via gravitational instability. We find that the non-linear density of filaments in the epoch of formation is almost mass independent and is in order of ∼30. By introducing filament’s extended condition, we find a fitting function for length-mass relation. For the statistics of filaments, we propose a novel framework named excursion set of saddle points. In this approach, we count the saddle points of the density field Hessian matrix, and relate it to the count of filaments. In addition, we addressed the filament in filament problem with up-crossing approximation.
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Sundin, L., G. E. Nilsson, M. Block y C. O. Lofman. "Control of gill filament blood flow by serotonin in the rainbow trout, Oncorhynchus mykiss". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 268, n.º 5 (1 de mayo de 1995): R1224—R1229. http://dx.doi.org/10.1152/ajpregu.1995.268.5.r1224.
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The effects of exogenously applied serotonin [5-hydroxytryptamine (5-HT)] on the distal arterial vasculature of gill filaments were observed using an epi-illumination microscope equipped with a water-immersion objective and connected to a video camera. In addition, ventral aortic flow (Q) and celiac artery pressure (PCA) were measured. Intra-arterial injection of serotonin (100 nmol/kg) completely stopped the blood flow in the distal part of the filaments and caused a rapid decrease of PCA. Repeatedly, the flow reduction was found to coincide with a constriction of the distal portion of the efferent filamental vasculature. Because there was no concomitant reduction in Q, it is concluded that a redistribution of blood to more proximal parts of the filaments occurred. After treatment with the serotonergic receptor antagonist methysergide, the vasoconstrictor effect of serotonin on the filamental vasculature was eliminated, while a decrease in PCA was still observed. The results demonstrate a specific site(s) for the serotonergic vasoconstriction in the distal portion of the filament.
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Fily, Yaouen, Priya Subramanian, Tobias M. Schneider, Raghunath Chelakkot y Arvind Gopinath. "Buckling instabilities and spatio-temporal dynamics of active elastic filaments". Journal of The Royal Society Interface 17, n.º 165 (abril de 2020): 20190794. http://dx.doi.org/10.1098/rsif.2019.0794.
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Biological filaments driven by molecular motors tend to experience tangential propulsive forces also known as active follower forces. When such a filament encounters an obstacle, it deforms, which reorients its follower forces and alters its entire motion. If the filament pushes a cargo, the friction on the cargo can be enough to deform the filament, thus affecting the transport properties of the cargo. Motivated by cytoskeletal filament motility assays, we study the dynamic buckling instabilities of a two-dimensional slender elastic filament driven through a dissipative medium by tangential propulsive forces in the presence of obstacles or cargo. We observe two distinct instabilities. When the filament’s head is pinned or experiences significant translational but little rotational drag from its cargo, it buckles into a steadily rotating coiled state. When it is clamped or experiences both significant translational and rotational drag from its cargo, it buckles into a periodically beating, overall translating state. Using minimal analytically tractable models, linear stability theory and fully nonlinear computations, we study the onset of each buckling instability, characterize each buckled state, and map out the phase diagram of the system. Finally, we use particle-based Brownian dynamics simulations to show our main results are robust to moderate noise and steric repulsion. Overall, our results provide a unified framework to understand the dynamics of tangentially propelled filaments and filament-cargo assemblies.
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Beisser, R., S. Werner, B. Heinrich y J. Pelzer. "Emissionen aus 3D-Tischdruckern – Nachstellende Untersuchungen – Teil 1/Emissions from desktop 3D printers – more closely examined – Part 1". Gefahrstoffe 80, n.º 01-02 (2020): 53–60. http://dx.doi.org/10.37544/0949-8036-2020-01-02-55.
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Um Aussagen über die Exposition am Arbeitsplatz gegenüber Emissionen von 3D-Tischdruckern treffen zu können, wurde das Emissionsverhalten eines exemplarischen 3D-Tischgerätes bei nachstellenden Untersuchungen in einer Prüfkammer genauer untersucht. Beim Druck des Testkörpers in Form eines Würfels wurden für sieben ausgewählte Filamente die Konzentrationen der flüchtigen organischen Verbindungen und der Aldehyde sowie die Partikelanzahl gemessen. Alle Konzentrationen lagen weit unter den jeweiligen Arbeitsplatzgrenzwerten und auch unter dem Leitwert 1 für total volatile organic compounds (TVOC) oder Innenraumarbeitsplatzrichtwerten (RW). Die Partikelmessungen zeigten, dass umso mehr Partikel emittiert wurden, je wärmer ein Kunststoff verarbeitet werden musste. Alle Werte lagen unter dem Prüfwert von 3,5 ∙ 1011 Partikel pro 10 Minuten, der in der Vergabegrundlage für den Blauen Engel nach dem Umweltzeichen RAL UZ 205 „Bürogeräte mit Druckfunktion“ festgelegt ist.
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Alina, D., I. Ristorcelli, L. Montier y M. Juvela. "Statistics on the relative orientation between magnetic fields and filaments hosting Planck Galactic Cold Clumps". Proceedings of the International Astronomical Union 14, A30 (agosto de 2018): 104. http://dx.doi.org/10.1017/s1743921319003594.
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AbstractWe present a statistical analysis of the relative orientation between the plane-of-sky magnetic field and the filaments associated with the Galactic Cold Clumps. We separated polarization parameters components of the filaments and their background using thin optical medium assumption, the filaments were detected using the Rolling Hough Transform algorithm and we separated the clump and the filament contributions in our maps. We found that in high column density environments the magnetic fields inside the filaments and in the background are less likely to be aligned with each other. This suggests a decoupling between the inner and background magnetic fields at some stage of filaments’ evolution. A preferential alignment between the filaments and their inferred magnetic fields is observed in the whole selection if the clumps’ contribution is subtracted. Interestingly, a bimodal distribution of relative orientation is observed between the filamentary structures of the clumps and the filaments’ magnetic field. Similar results are seen in a subsample of nearby filaments. The relative orientation clearly shows a transition from parallel to no preferential and perpendicular alignment depending on the volume densities of both clumps and filaments. Our results confirm a strong interplay between the magnetic field and filamentary structures during their formation and evolutionary process.
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Lombardo, Andrew T., Shane R. Nelson, Guy G. Kennedy, Kathleen M. Trybus, Sam Walcott y David M. Warshaw. "Myosin Va transport of liposomes in three-dimensional actin networks is modulated by actin filament density, position, and polarity". Proceedings of the National Academy of Sciences 116, n.º 17 (9 de abril de 2019): 8326–35. http://dx.doi.org/10.1073/pnas.1901176116.
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The cell’s dense 3D actin filament network presents numerous challenges to vesicular transport by teams of myosin Va (MyoVa) molecular motors. These teams must navigate their cargo through diverse actin structures ranging from Arp2/3-branched lamellipodial networks to the dense, unbranched cortical networks. To define how actin filament network organization affects MyoVa cargo transport, we created two different 3D actin networks in vitro. One network was comprised of randomly oriented, unbranched actin filaments; the other was comprised of Arp2/3-branched actin filaments, which effectively polarized the network by aligning the actin filament plus-ends. Within both networks, we defined each actin filament’s 3D spatial position using superresolution stochastic optical reconstruction microscopy (STORM) and its polarity by observing the movement of single fluorescent reporter MyoVa. We then characterized the 3D trajectories of fluorescent, 350-nm fluid-like liposomes transported by MyoVa teams (∼10 motors) moving within each of the two networks. Compared with the unbranched network, we observed more liposomes with directed and fewer with stationary motion on the Arp2/3-branched network. This suggests that the modes of liposome transport by MyoVa motors are influenced by changes in the local actin filament polarity alignment within the network. This mechanism was supported by an in silico 3D model that provides a broader platform to understand how cellular regulation of the actin cytoskeletal architecture may fine tune MyoVa-based intracellular cargo transport.
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Mudry, Ryan E., Cynthia N. Perry, Meredith Richards, Velia M. Fowler y Carol C. Gregorio. "The interaction of tropomodulin with tropomyosin stabilizes thin filaments in cardiac myocytes". Journal of Cell Biology 162, n.º 6 (15 de septiembre de 2003): 1057–68. http://dx.doi.org/10.1083/jcb.200305031.
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Actin (thin) filament length regulation and stability are essential for striated muscle function. To determine the role of the actin filament pointed end capping protein, tropomodulin1 (Tmod1), with tropomyosin, we generated monoclonal antibodies (mAb17 and mAb8) against Tmod1 that specifically disrupted its interaction with tropomyosin in vitro. Microinjection of mAb17 or mAb8 into chick cardiac myocytes caused a dramatic loss of the thin filaments, as revealed by immunofluorescence deconvolution microscopy. Real-time imaging of live myocytes expressing green fluorescent protein–α-tropomyosin and microinjected with mAb17 revealed that the thin filaments depolymerized from their pointed ends. In a thin filament reconstitution assay, stabilization of the filaments before the addition of mAb17 prevented the loss of thin filaments. These studies indicate that the interaction of Tmod1 with tropomyosin is critical for thin filament stability. These data, together with previous studies, indicate that Tmod1 is a multifunctional protein: its actin filament capping activity prevents thin filament elongation, whereas its interaction with tropomyosin prevents thin filament depolymerization.
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Cohen, Shenhav, Bo Zhai, Steven P. Gygi y Alfred L. Goldberg. "Ubiquitylation by Trim32 causes coupled loss of desmin, Z-bands, and thin filaments in muscle atrophy". Journal of Cell Biology 198, n.º 4 (20 de agosto de 2012): 575–89. http://dx.doi.org/10.1083/jcb.201110067.
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During muscle atrophy, myofibrillar proteins are degraded in an ordered process in which MuRF1 catalyzes ubiquitylation of thick filament components (Cohen et al. 2009. J. Cell Biol. http://dx.doi.org/10.1083/jcb.200901052). Here, we show that another ubiquitin ligase, Trim32, ubiquitylates thin filament (actin, tropomyosin, troponins) and Z-band (α-actinin) components and promotes their degradation. Down-regulation of Trim32 during fasting reduced fiber atrophy and the rapid loss of thin filaments. Desmin filaments were proposed to maintain the integrity of thin filaments. Accordingly, we find that the rapid destruction of thin filament proteins upon fasting was accompanied by increased phosphorylation of desmin filaments, which promoted desmin ubiquitylation by Trim32 and degradation. Reducing Trim32 levels prevented the loss of both desmin and thin filament proteins. Furthermore, overexpression of an inhibitor of desmin polymerization induced disassembly of desmin filaments and destruction of thin filament components. Thus, during fasting, desmin phosphorylation increases and enhances Trim32-mediated degradation of the desmin cytoskeleton, which appears to facilitate the breakdown of Z-bands and thin filaments.
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Virga, Epifanio G. "Dissipative shocks behind bacteria gliding". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 372, n.º 2029 (28 de noviembre de 2014): 20130360. http://dx.doi.org/10.1098/rsta.2013.0360.
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Gliding is a means of locomotion on rigid substrates used by a number of bacteria, including myxobacteria and cyanobacteria. One of the hypotheses advanced to explain this motility mechanism hinges on the role played by the slime filaments continuously extruded from gliding bacteria. This paper solves, in full, a non-linear mechanical theory that treats as dissipative shocks both the point where the extruded slime filament comes into contact with the substrate, called the filament’s foot , and the pore on the bacterium outer surface from where the filament is ejected. I prove that kinematic compatibility for shock propagation requires that the bacterium uniform gliding velocity (relative to the substrate) and the slime ejecting velocity (relative to the bacterium) must be equal, a coincidence that seems to have already been observed.
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Çolakoğlu, Gülsen y Anthony Brown. "Intermediate filaments exchange subunits along their length and elongate by end-to-end annealing". Journal of Cell Biology 185, n.º 5 (25 de mayo de 2009): 769–77. http://dx.doi.org/10.1083/jcb.200809166.
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Actin filaments and microtubules lengthen and shorten by addition and loss of subunits at their ends, but it is not known whether this is also true for intermediate filaments. In fact, several studies suggest that in vivo, intermediate filaments may lengthen by end-to-end annealing and that addition and loss of subunits is not confined to the filament ends. To test these hypotheses, we investigated the assembly dynamics of neurofilament and vimentin intermediate filament proteins in cultured cells using cell fusion, photobleaching, and photoactivation strategies in combination with conventional and photoactivatable fluorescent fusion proteins. We show that neurofilaments and vimentin filaments lengthen by end-to-end annealing of assembled filaments. We also show that neurofilaments and vimentin filaments incorporate subunits along their length by intercalation into the filament wall with no preferential addition of subunits to the filament ends, a process which we term intercalary subunit exchange.
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Tilney, L. G., D. J. DeRosier, A. Weber y M. S. Tilney. "How Listeria exploits host cell actin to form its own cytoskeleton. II. Nucleation, actin filament polarity, filament assembly, and evidence for a pointed end capper." Journal of Cell Biology 118, n.º 1 (1 de julio de 1992): 83–93. http://dx.doi.org/10.1083/jcb.118.1.83.
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After Listeria, a bacterium, is phagocytosed by a macrophage, it dissolves the phagosomal membrane and enters the cytoplasm. The Listeria than nucleates actin filaments from its surface. These newly assembled actin filaments show unidirectional polarity with their barbed ends associated with the surface of the Listeria. Using actin concentrations below the pointed end critical concentration we find that filament elongation must be occurring by monomers adding to the barbed ends, the ends associated with the Listerial surface. If Listeria with tails are incubated in G actin under polymerizing conditions, the Listeria is translocated away from its preformed tail by the elongation of filaments attached to the Listeria. This experiment and others tell us that in vivo filament assembly must be tightly coupled to filament capping and cross-bridging so that if one process outstrips another, chaos ensues. We also show that the actin filaments in the tail are capped on their pointed ends which inhibits further elongation and/or disassembly in vitro. From these results we suggest a simple picture of how Listeria competes effectively for host cell actin. When Listeria secretes a nucleator, the host's actin subunits polymerize into a filament. Host cell machinery terminate the assembly leaving a short filament. Listeria overcomes the host control by nucleating new filaments and thus many short filaments assemble. The newest filaments push existing ones into a growing tail. Thus the competition is between nucleation of filaments caused by Listeria and the filament terminators produced by the host.
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Ijpma, Gijs, Ahmed M. Al-Jumaily, Simeon P. Cairns y Gary C. Sieck. "Myosin filament polymerization and depolymerization in a model of partial length adaptation in airway smooth muscle". Journal of Applied Physiology 111, n.º 3 (septiembre de 2011): 735–42. http://dx.doi.org/10.1152/japplphysiol.00114.2011.
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Length adaptation in airway smooth muscle (ASM) is attributed to reorganization of the cytoskeleton, and in particular the contractile elements. However, a constantly changing lung volume with tidal breathing (hence changing ASM length) is likely to restrict full adaptation of ASM for force generation. There is likely to be continuous length adaptation of ASM between states of incomplete or partial length adaption. We propose a new model that assimilates findings on myosin filament polymerization/depolymerization, partial length adaptation, isometric force, and shortening velocity to describe this continuous length adaptation process. In this model, the ASM adapts to an optimal force-generating capacity in a repeating cycle of events. Initially the myosin filament, shortened by prior length changes, associates with two longer actin filaments. The actin filaments are located adjacent to the myosin filaments, such that all myosin heads overlap with actin to permit maximal cross-bridge cycling. Since in this model the actin filaments are usually longer than myosin filaments, the excess length of the actin filament is located randomly with respect to the myosin filament. Once activated, the myosin filament elongates by polymerization along the actin filaments, with the growth limited by the overlap of the actin filaments. During relaxation, the myosin filaments dissociate from the actin filaments, and then the cycle repeats. This process causes a gradual adaptation of force and instantaneous adaptation of shortening velocity. Good agreement is found between model simulations and the experimental data depicting the relationship between force development, myosin filament density, or shortening velocity and length.
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Goldsmith, K. J. A. y J. M. Pittard. "The isothermal evolution of a shock-filament interaction". Monthly Notices of the Royal Astronomical Society 491, n.º 4 (4 de diciembre de 2019): 4783–801. http://dx.doi.org/10.1093/mnras/stz3320.
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ABSTRACT Studies of filamentary structures that are prevalent throughout the interstellar medium are of great significance to a number of astrophysical fields. Here, we present 3D hydrodynamic simulations of shock-filament interactions where the equation of state has been softened to become almost isothermal. We investigate the effect of such an isothermal regime on the interaction (where both the shock and filament are isothermal), and we examine how the nature of the interaction changes when the orientation of the filament, the shock Mach number, and the filament density contrast are varied. We find that only sideways-oriented filaments with a density contrast of 102 form a three-rolled structure, dissimilar to the results of a previous study. Moreover, the angle of orientation of the filament plays a large role in the evolution of the filament morphology: the greater the angle of orientation, the longer and less turbulent the wake. Turbulent stripping of filament material leading to fragmentation of the core occurs in most filaments; however, filaments orientated at an angle of 85° to the shock front do not fragment and are longer lived. In addition, values of the drag time are influenced by the filament length, with longer filaments being accelerated faster than shorter ones. Furthermore, filaments in an isothermal regime exhibit faster acceleration than those struck by an adiabatic shock. Finally, we find that the drag and mixing times of the filament increase as the angle of orientation of the filament is increased.
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Guan, Chengyu, Jun Zou, Qingchang Chen, Mingming Shi y Bobo Yang. "Effect of Different Bonding Materials on Flip-Chip LED Filament Properties". Applied Sciences 10, n.º 1 (19 de diciembre de 2019): 47. http://dx.doi.org/10.3390/app10010047.
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This article researches the effect of Sn-based solder alloys on flip-chip light-emitting diode LED (FC-LED) filament properties. SEM images, shearing force, steady-state voltage, blue light luminous flux, and junction temperature were examined to demonstrate the difference between two types of FC-LED filaments welded with two solders. The microstructure surface of Sn90Sb10 filament solder joints was smoother and had fewer voids and cracks compared with that of SAC0307 filament solder joints, which indicates that the Sn90Sb10 filaments had a higher shearing force than the SAC0307 filaments; moreover, the average shearing force was beyond 200 gf (standard shearing force). The steady-state voltage and junction temperature of the Sn90Sb10 solder-welded FC-LED filament were lower, and the Sn90Sb10 filament had a relatively higher blue light luminous flux. If high reliability of the solder joints and better photoelectric properties of the filaments are required, this Sn90Sb10 solder is the best bonding material for FC-LED filament welding.
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Schepers, Anna V., Charlotta Lorenz, Peter Nietmann, Andreas Janshoff, Stefan Klumpp y Sarah Köster. "Multiscale mechanics and temporal evolution of vimentin intermediate filament networks". Proceedings of the National Academy of Sciences 118, n.º 27 (29 de junio de 2021): e2102026118. http://dx.doi.org/10.1073/pnas.2102026118.
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The cytoskeleton, an intricate network of protein filaments, motor proteins, and cross-linkers, largely determines the mechanical properties of cells. Among the three filamentous components, F-actin, microtubules, and intermediate filaments (IFs), the IF network is by far the most extensible and resilient to stress. We present a multiscale approach to disentangle the three main contributions to vimentin IF network mechanics—single-filament mechanics, filament length, and interactions between filaments—including their temporal evolution. Combining particle tracking, quadruple optical trapping, and computational modeling, we derive quantitative information on the strength and kinetics of filament interactions. Specifically, we find that hydrophobic contributions to network mechanics enter mostly via filament-elongation kinetics, whereas electrostatics have a direct influence on filament–filament interactions.
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Cesar, F., J.-O. Bovin, L. R. Wallenberg, G. Karlsson, L. K. L. Falk y T. Oku. "Synthesis and characterization of carbon filaments grown from Pd3P colloids". Journal of Materials Research 15, n.º 9 (septiembre de 2000): 1857–59. http://dx.doi.org/10.1557/jmr.2000.0267.
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Amorphous carbon filaments were synthesized by catalytic pyrolysis of propene over Pd3P colloids. The channel close to the center of the filaments usually contained particles, which were analyzed by analytical electron microscopy to be palladium. The palladium particles could be found anywhere along the filament. The carbon filaments were of two types and of different diameters, about 8–15 nm and about 40–80 nm. The thinner type of filament shows a channel diameter of about 5 nm. The type of filament produced depends on the reaction conditions. Increased reaction time results in a large number of filaments, whereas an increased propene gas flow results in more of the thicker type of filaments.
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Jiang, He, Jiming Sa, Cong Fan, Yiwen Zhou, Hanwen Gu, Xuezhou Yang, Xiaofeng Su y Zhushanying Zhang. "Thermal Performance of LED Filament in Flip-Chip Packaging Manufactured for Different Correlated Color Temperature". Applied Sciences 11, n.º 19 (23 de septiembre de 2021): 8844. http://dx.doi.org/10.3390/app11198844.
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The effect of correlated color temperature (CCT) on the thermal performance of light emitting diode (LED) filament in flip-chip packaging was investigated in detail. Two filaments with different lengths were selected as the research object, and the thermal resistance of filaments under three CCT (2200 K, 2400 K, 2700 K) were studied. The optical properties and thermal parameters of the two groups of filaments were measured, and the results were analyzed combined with the color coordinate. The experimental results show that thermal properties of LED filaments is closely related to CCT. Under constant current condition, junction temperature decreases with the increase of color difference. With the change of phosphor glue and phosphorus powder ratio, the color temperature of LED filament also changes. In the filaments with the same chip structure and packaging mechanism, the higher the proportion of red phosphorescent powder, the worse the heat dissipation performance of the filament. These results show that in the design and manufacture of LED filament, it is helpful to control the CCT of LED filament under the premise of meeting the use requirements.
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Perng, M. D., L. Cairns, P. van den IJssel, A. Prescott, A. M. Hutcheson y R. A. Quinlan. "Intermediate filament interactions can be altered by HSP27 and alphaB-crystallin". Journal of Cell Science 112, n.º 13 (1 de julio de 1999): 2099–112. http://dx.doi.org/10.1242/jcs.112.13.2099.
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HSP27 and alphaB-crystallin are both members of the small heat shock protein family. alphaB-crystalllin has been proposed to modulate intermediate filaments and recently a mutation in alphaB-crystallin has been identified as the genetic basis of desmin related myopathy. This disease is characterised in its pathology by aggregates of intermediate filaments associated with alphaB-crystallin. Here we report that HSP27 like alphaB-crystallin is associated with glial fibrillary acidic protein and vimentin intermediate filament networks in unstressed U373MG astrocytoma cells. HSP27 is also associated with keratin filaments in MCF7 cells, indicating that this association is not restricted to a particular intermediate filament type. The association of sHSPs with both the soluble and filamentous intermediate filament fractions of U373 cells was demonstrated biochemically. Heat shock or drug treatments induced a co-collapse of intermediate filaments and associated small heat shock proteins. These data show that the presence of HSP27 or alphaB-crystallin could not prevent filament collapse and suggest that the purpose of this association is more than just filament binding. Indeed, in U373MG cells the intermediate filament association with small heat shock proteins is similar to that observed for another protein chaperone, HSC70. In order to discern the effect of different chaperone classes on intermediate filament network formation and maintenance, several in vitro assays were assessed. Of these, falling ball viscometry revealed a specific activity of small heat shock proteins compared to HSC70 that was apparently inactive in this assay. Intermediate filaments form a gel in the absence of small heat shock proteins. In contrast, inclusion of alphaB-crystallin or HSP27 prevented gel formation but not filament assembly. The transient transfection of GFAP into MCF7 cells was used to show that the induction of a completely separate network of intermediate filaments resulted in the specific association of the endogenous HSP27 with these new GFAP filaments. These data lead us to propose that one of the major functions of the association of small heat shock proteins with intermediate filaments is to help manage the interactions that occur between filaments in their cellular networks. This is achieved by protecting filaments against those non-covalent interactions that result when they come into very close proximity as seen from the viscosity experiments and which have the potential to induce intermediate filament aggregation as seen in some disease pathologies.
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Lewis, A. K. y P. C. Bridgman. "Nerve growth cone lamellipodia contain two populations of actin filaments that differ in organization and polarity." Journal of Cell Biology 119, n.º 5 (1 de diciembre de 1992): 1219–43. http://dx.doi.org/10.1083/jcb.119.5.1219.
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The organization and polarity of actin filaments in neuronal growth cones was studied with negative stain and freeze-etch EM using a permeabilization protocol that caused little detectable change in morphology when cultured nerve growth cones were observed by video-enhanced differential interference contrast microscopy. The lamellipodial actin cytoskeleton was composed of two distinct subpopulations: a population of 40-100-nm-wide filament bundles radiated from the leading edge, and a second population of branching short filaments filled the volume between the dorsal and ventral membrane surfaces. Together, the two populations formed the three-dimensional structural network seen within expanding lamellipodia. Interaction of the actin filaments with the ventral membrane surface occurred along the length of the filaments via membrane associated proteins. The long bundled filament population was primarily involved in these interactions. The filament tips of either population appeared to interact with the membrane only at the leading edge; this interaction was mediated by a globular Triton-insoluble material. Actin filament polarity was determined by decoration with myosin S1 or heavy meromyosin. Previous reports have suggested that the polarity of the actin filaments in motile cells is uniform, with the barbed ends toward the leading edge. We observed that the actin filament polarity within growth cone lamellipodia is not uniform; although the predominant orientation was with the barbed end toward the leading edge (47-56%), 22-25% of the filaments had the opposite orientation with their pointed ends toward the leading edge, and 19-31% ran parallel to the leading edge. The two actin filament populations display distinct polarity profiles: the longer filaments appear to be oriented predominantly with their barbed ends toward the leading edge, whereas the short filaments appear to be randomly oriented. The different length, organization and polarity of the two filament populations suggest that they differ in stability and function. The population of bundled long filaments, which appeared to be more ventrally located and in contact with membrane proteins, may be more stable than the population of short branched filaments. The location, organization, and polarity of the long bundled filaments suggest that they may be necessary for the expansion of lamellipodia and for the production of tension mediated by receptors to substrate adhesion molecules.
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Rost, Agustín, Federico Stasyszyn, Luis Pereyra y Héctor J. Martínez. "A comparison of cosmological filaments catalogues". Monthly Notices of the Royal Astronomical Society 493, n.º 2 (5 de febrero de 2020): 1936–47. http://dx.doi.org/10.1093/mnras/staa320.
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ABSTRACT In this work, we compare three catalogues of cosmological filaments identified in the Sloan Digital Sky Survey by means of different algorithms by Tempel et al., Pereyra et al., and Martínez et al. We analyse how different identification techniques determine differences in the filament statistical properties: length, elongation, redshift distribution, and abundance. We find that the statistical properties of the filaments strongly depend on the identification algorithm. We use a volume-limited sample of galaxies to characterize other properties of filaments such as: galaxy overdensity, luminosity function of galaxies, mean galaxy luminosity, filament luminosity, and the overdensity profile of galaxies around filaments. In general, we find that these properties primarily depended on filament length. Shorter filaments have larger overdensities, are more populated by red galaxies, and have better defined galaxy overdensity profiles, than longer filaments. Concluding that galaxies belonging to filaments have characteristic signatures depending on the identification algorithm used.
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Riley, Danny A., James L. W. Bain, Joyce L. Thompson, Robert H. Fitts, Jeffrey J. Widrick, Scott W. Trappe, Todd A. Trappe y David L. Costill. "Decreased thin filament density and length in human atrophic soleus muscle fibers after spaceflight". Journal of Applied Physiology 88, n.º 2 (1 de febrero de 2000): 567–72. http://dx.doi.org/10.1152/jappl.2000.88.2.567.
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Soleus muscle fibers were examined electron microscopically from pre- and postflight biopsies of four astronauts orbited for 17 days during the Life and Microgravity Sciences Spacelab Mission (June 1996). Myofilament density and spacing were normalized to a 2.4-μm sarcomere length. Thick filament density (∼1,062 filaments/μm2) and spacing (∼32.5 nm) were unchanged by spaceflight. Preflight thin filament density (2,976/μm2) decreased significantly ( P < 0.01) to 2,215/μm2 in the overlap A band region as a result of a 17% filament loss and a 9% increase in short filaments. Normal fibers had 13% short thin filaments. The 26% decrease in thin filaments is consistent with preliminary findings of a 14% increase in the myosin-to-actin ratio. Lower thin filament density was calculated to increase thick-to-thin filament spacing in vivo from 17 to 23 nm. Decreased density is postulated to promote earlier cross-bridge detachment and faster contraction velocity. Atrophic fibers may be more susceptible to sarcomere reloading damage, because force per thin filament is estimated to increase by 23%.
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Dumitrache, Cristiana. "Evolution of Complex Filaments". International Astronomical Union Colloquium 167 (1998): 221–24. http://dx.doi.org/10.1017/s0252921100047631.
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AbstractThis study focusses on the less studied aspects of filaments evolution: the coupling of two or more filaments to form a complex filament and also the split of one such filament into many components. This phenomenon was first observed by d’Azambuja – we apply statistical mathematical methods to obtain evolutionary sequences and detect the complex filaments.
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Xia, Zhigang, Cancan Wang, Chiyu Fu, Jiang Wei y Weilin Xu. "Novel composite siro-spinning with forced migrations of filaments". Textile Research Journal 89, n.º 19-20 (19 de enero de 2019): 3927–36. http://dx.doi.org/10.1177/0040517518824850.
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In this study, a novel composite siro-spinning method with cyclically migrating filaments was developed as a simple and safe way to enhance filament-staple-fiber coherence. The novel composite siro-spinning method was theoretically demonstrated to produce a yarn with migrated filaments clasping both internal and external fibers. It was predicted that migrated filaments of the novel composite sirospun yarn were not straight enough to resist yarn tensile drawing as the filament parallelism with the yarn axis decreased. However, migrated filaments could clasp the staple fibers firmly to enhance filament-staple-fiber coherence, contributing an excellent frictional resistance of the novel composite yarn. Experiments were then conducted to validate the demonstration. Experimental results proved that the novel composite sirospun yarn had cyclic filament immersion and exposure appearance, resulting in medium hairiness and yarn imperfection after comparison with corefil sirospun and siro corefil yarns. The novel composite sirospun yarn with severe filament migrations had poor filament straightness, but filament deformations that were effective in clamping staple fibers. Therefore, the novel composite sirospun yarn had less strength, but greater frictional resistance than corefil sirospun and siro corefil yarns.
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Luther, P. K. "Three-dimensional reconstruction of a simple Z-band in fish muscle." Journal of Cell Biology 113, n.º 5 (1 de junio de 1991): 1043–55. http://dx.doi.org/10.1083/jcb.113.5.1043.
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The three-dimensional structure of the Z-band in fish white muscle has been investigated by electron microscopy. This Z-band is described as simple, since in longitudinal sections it has the appearance of a single zigzag pattern connecting the ends of actin filaments of opposite polarity from adjacent sarcomeres. The reconstruction shows two pairs of links, the Z-links, between one actin filament and the facing four actin filaments in the adjacent sarcomere. The members of each pair have nearly diametrically opposed origins. In relation to one actin filament, one pair of links appears to bind along the final 10 nm of the actin filament (proximal site) and the other pair binds along a region extending from 5 to 20 nm from the filament end (distal site). Between one pair and the other, there is a rotation of approximately 80 degrees round the filament axis. A Z-link with a proximal site at the end of one actin filament attaches at a distal site on the oppositely oriented actin filaments of the facing sarcomere and vice versa. The length of each Z-link is consistent with the length of an alpha-actinin molecule. An additional set of links located 10-15 nm from the center of the Z-band occurs between actin filaments of the same polarity. These polar links connect the actin filaments along the same direction on each side of the Z-band. The three-dimensional structure appears to have twofold screw symmetry about the central plane of the Z-band. Only approximate twofold rotational symmetry is observed in directions parallel to the actin filaments. Previous models of the Z-band in which four identical and rotationally symmetrical links emanate from the end of one actin filament and span across to the ends of four actin filaments in the adjacent sarcomere are therefore incorrect.
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Hookway, Caroline, Liya Ding, Michael W. Davidson, Joshua Z. Rappoport, Gaudenz Danuser y Vladimir I. Gelfand. "Microtubule-dependent transport and dynamics of vimentin intermediate filaments". Molecular Biology of the Cell 26, n.º 9 (mayo de 2015): 1675–86. http://dx.doi.org/10.1091/mbc.e14-09-1398.
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We studied two aspects of vimentin intermediate filament dynamics—transport of filaments and subunit exchange. We observed transport of long filaments in the periphery of cells using live-cell structured illumination microscopy. We studied filament transport elsewhere in cells using a photoconvertible-vimentin probe and total internal reflection microscopy. We found that filaments were rapidly transported along linear tracks in both anterograde and retrograde directions. Filament transport was microtubule dependent but independent of microtubule polymerization and/or an interaction with the plus end–binding protein APC. We also studied subunit exchange in filaments by long-term imaging after photoconversion. We found that converted vimentin remained in small clusters along the length of filaments rather than redistributing uniformly throughout the network, even in cells that divided after photoconversion. These data show that vimentin filaments do not depolymerize into individual subunits; they recompose by severing and reannealing. Together these results show that vimentin filaments are very dynamic and that their transport is required for network maintenance.
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Pappas, Christopher T., Paul A. Krieg y Carol C. Gregorio. "Nebulin regulates actin filament lengths by a stabilization mechanism". Journal of Cell Biology 189, n.º 5 (24 de mayo de 2010): 859–70. http://dx.doi.org/10.1083/jcb.201001043.
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Efficient muscle contraction requires regulation of actin filament lengths. In one highly cited model, the giant protein nebulin has been proposed to function as a molecular ruler specifying filament lengths. We directly challenged this hypothesis by constructing a unique, small version of nebulin (mini-nebulin). When endogenous nebulin was replaced with mini-nebulin in skeletal myocytes, thin filaments extended beyond the end of mini-nebulin, an observation which is inconsistent with a strict ruler function. However, under conditions that promote actin filament depolymerization, filaments associated with mini-nebulin were remarkably maintained at lengths either matching or longer than mini-nebulin. This indicates that mini-nebulin is able to stabilize portions of the filament it has no contact with. Knockdown of nebulin also resulted in more dynamic populations of thin filament components, whereas expression of mini-nebulin decreased the dynamics at both filament ends (i.e., recovered loss of endogenous nebulin). Thus, nebulin regulates thin filament architecture by a mechanism that includes stabilizing the filaments and preventing actin depolymerization.
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Schmieder, Brigitte, Guillaume Aulanier y Tibor Török. "Solar prominences". Proceedings of the International Astronomical Union 4, S257 (septiembre de 2008): 223–32. http://dx.doi.org/10.1017/s1743921309029330.
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AbstractSolar filaments (or prominences) are magnetic structures in the corona. They can be represented by twisted flux ropes in a bipolar magnetic environment. In such models, the dipped field lines of the flux rope carry the filament material and parasitic polarities in the filament channel are responsible for the existence of the lateral feet of prominences.Very simple laws do exist for the chirality of filaments, the so-called “filament chirality rules”: commonly dextral/sinistral filaments corresponding to left- (resp. right) hand magnetic twists are in the North/South hemisphere. Combining these rules with 3D weakly twisted flux tube models, the sign of the magnetic helicity in several filaments were identified. These rules were also applied to the 180° disambiguation of the direction of the photospheric transverse magnetic field around filaments using THEMIS vector magnetograph data (López Ariste et al. 2006). Consequently, an unprecedented evidence of horizontal magnetic support in filament feet has been observed, as predicted by former magnetostatic and recent MHD models.The second part of this review concerns the role of emerging flux in the vicinity of filament channels. It has been suggested that magnetic reconnection between the emerging flux and the pre-existing coronal field can trigger filament eruptions and CMEs. For a particular event, observed with Hinode/XRT, we observe signatures of such a reconnection, but no eruption of the filament. We present a 3D numerical simulation of emerging flux in the vicinity of a flux rope which was performed to reproduce this event and we briefly discuss, based on the simulation results, why the filament did not erupt.
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Kwiecinski, James A. y Robert A. Van Gorder. "Dynamics of nearly parallel interacting vortex filaments". Journal of Fluid Mechanics 835 (27 de noviembre de 2017): 575–623. http://dx.doi.org/10.1017/jfm.2017.792.
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The dynamics of interacting vortex filaments in an incompressible fluid, which are nearly parallel, have been approximated in the Klein–Majda–Damodaran model. The regime considers the deflection of each filament from a central axis; that is to say, the vortex filaments are assumed to be roughly parallel and centred along parallel lines. While this model has attracted a fair amount of mathematical interest in the recent literature, particularly concerning the existence of certain specific vortex filament structures, our aim is to generalise several known interesting filament solutions, found in the self-induced motion of a single vortex filament, to the case of pairwise interactions between multiple vortex filaments under the Klein–Majda–Damodaran model by means of asymptotic and numerical methods. In particular, we obtain asymptotic solutions for counter-rotating and co-rotating vortex filament pairs that are separated by a distance, so that the vortex filaments always remain sufficiently far apart, as well as intertwined vortex filaments that are in close proximity, exhibiting overlapping orbits. For each scenario, we consider both co- and counter-rotating pairwise interactions, and the specific kinds of solutions obtained for each case consist of planar filaments, for which motion is purely rotational, as well as travelling wave and self-similar solutions, both of which change their form as they evolve in time. We choose travelling waves, planar filaments and self-similar solutions for the initial filament configurations, as these are common vortex filament structures in the literature, and we use the dynamics under the Klein–Majda–Damodaran model to see how these structures are modified in time under pairwise interaction dynamics. Numerical simulations for each case demonstrate the validity of the asymptotic solutions. Furthermore, we develop equations to study a co-rotating hierarchy of many satellite vortices orbiting around a central filament. We numerically show that such configurations are unstable for plane-wave solutions, which lead to collapse of the hierarchy. We also consider more general travelling wave and self-similar solutions for co-rotating hierarchies, and these give what appears to be chaotic dynamics.
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Cunningham, Maria R., Claire-Elise Green, Paul A. Jones, Giles Novak y Laura Fissel. "The role of automated methods for filament finding in understanding the complex relationship between filaments, magnetic fields and star formation". Proceedings of the International Astronomical Union 14, S345 (agosto de 2018): 23–26. http://dx.doi.org/10.1017/s1743921319003132.
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AbstractThe discovery of the ubiquity of filaments in the interstellar medium in the last two decades has begged the question: “What role do filaments play in star formation?” Here we describe how our automated filament finding algorithms can combine with both magnetic field measurements and high-resolution observations of dense cores in these filaments, to provide a statistically large sample to investigate the effect of filaments on star formation. We find that filaments are likely actively accreting mass from the interstellar medium, explaining why some 60% of stars, and all massive stars, form “on-filament”.
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Ho, C. L., J. L. Martys, A. Mikhailov, G. G. Gundersen y R. K. Liem. "Novel features of intermediate filament dynamics revealed by green fluorescent protein chimeras". Journal of Cell Science 111, n.º 13 (1 de julio de 1998): 1767–78. http://dx.doi.org/10.1242/jcs.111.13.1767.
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In order to study the dynamic behavior of intermediate filament networks in living cells, we have prepared constructs fusing green fluorescent protein to intermediate filament proteins. Vimentin fused to green fluorescent protein labeled the endogenous intermediate filament network. We generated stable SW13 and NIH3T3 cell lines that express an enhanced green fluorescent protein fused to the N-terminus of full-length vimentin. We were able to observe the dynamic behavior of the intermediate filament network in these cells for periods as long as 4 hours (images acquired every 2 minutes). In both cell lines, the vimentin network constantly moves in a wavy manner. In the NIH3T3 cells, we observed extension of individual vimentin filaments at the edge of the cell. This movement is dependent on microtubules, since the addition of nocodazole stopped the extension of the intermediate filaments. Injection of anti-IFA causes the redistribution or ‘collapse’ of intermediate filaments. We injected anti-IFA antibodies into NIH3T3 cells stably expressing green fluorescent protein fused to vimentin and found that individual intermediate filaments move slowly towards the perinuclear area without obvious disassembly. These results demonstrate that individual intermediate filaments are translocated during the collapse, rather than undergoing disassembly-induced redistribution. Injections of tubulin antibodies disrupt the interactions between intermediate filaments and stable microtubules and cause the collapse of the vimentin network showing that these interactions play an important role in keeping the intermediate filament network extended. The nocodazole inhibition of intermediate filament extension and the anti-IFA microinjection experiments are consistent with a model in which intermediate filaments exhibit an extended distribution when tethered to microtubules, but are translocated to the perinuclear area when these connections are severed.
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Murphy, D. B., R. O. Gray, W. A. Grasser y T. D. Pollard. "Direct demonstration of actin filament annealing in vitro." Journal of Cell Biology 106, n.º 6 (1 de junio de 1988): 1947–54. http://dx.doi.org/10.1083/jcb.106.6.1947.
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Direct electron microscopic examination confirms that short actin filaments rapidly anneal end-to-end in vitro, leading over time to an increase in filament length at steady state. During annealing of mixtures of native unlabeled filaments and glutaraldehyde-fixed filaments labeled with myosin subfragment-1, the structural polarity within heteropolymers is conserved absolutely. Annealing does not appear to require either ATP hydrolysis or the presence of exogenous actin monomers, suggesting that joining occurs through the direct association of filament ends. During recovery from sonication the initial rate of annealing is consistent with a second-order reaction involving the collision of two filament ends with an apparent annealing rate constant of 10(7) M-1s-1. This rapid phase lasts less than 10 s and is followed by a slow phase lasting minutes to hours. Annealing is calculated to contribute minimally to filament elongation during the initial stages of self-assembly. However, the rapid rate of annealing of sonicated fixed filaments observed in vitro suggests that it may be an efficient mechanism for repairing breaks in filaments and that annealing together with polymer-severing mechanisms may contribute significantly to the dynamics and function of actin filaments in vivo.
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Jones, L. N. y F. M. Pope. "Isolation of intermediate filament assemblies from human hair follicles." Journal of Cell Biology 101, n.º 4 (1 de octubre de 1985): 1569–77. http://dx.doi.org/10.1083/jcb.101.4.1569.
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We used developing human hair follicle cells for the isolation of hard alpha-keratin structural components. Intracellular dispersions examined by electron microscopy contained both individual alpha-keratin filaments and the tactoid-like filament assemblies observed in situ organized along subfibrillar arms of macrofibrils. The assemblies of average width 47 nm were composed of closely packed alpha-keratin filaments and originated from the initial filament arrays observed in sections of developing mammalian hair follicles. We have distinguished two types of assemblies: the para-like or hexagonally packed and the ortho-like spiral or whorl type. Axial banding extended across the width of filament assemblies, which suggested that hard alpha-keratin filaments pack in lateral register and form a lattice that contains interfilamentous bridges. We observed axial banding patterns with periods ranging from 20 to 22 nm, consistent with the 22-nm periodic structure deduced from x-ray diffraction studies and present in models proposed for hard alpha-keratin and other intermediate filaments. Preliminary biochemical studies of filaments and filament assemblies indicate that they consist of the closely related group of proteins (low-sulfur proteins) ubiquitous among extracts of hard mammalian keratins. Isolated hard alpha-keratin filament assemblies provide a new and valuable structural entity for investigating the assembly mechanisms involved in the formation of the filament-matrix framework found in hard mammalian keratin appendages.
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Kennedy, Daniel T. y Robert A. Van Gorder. "Motion of open vortex-current filaments under the Biot–Savart model". Journal of Fluid Mechanics 836 (12 de diciembre de 2017): 532–59. http://dx.doi.org/10.1017/jfm.2017.826.
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Vortex-current filaments have been used to study phenomena such as coronal loops and solar flares as well as tokamaks, and recent experimental work has demonstrated dynamics akin to vortex-current filaments on a table-top plasma focus device. While MHD vortex dynamics and related applications to turbulence have attracted consideration in the literature due to a wide variety of applications, not much analytical progress has been made in this area, and the analysis of such vortex-current filament solutions under various geometries may motivate further experimental efforts. To this end, we consider the motion of open, isolated vortex-current filaments in the presence of magnetohydrodynamic (MHD) as well as the standard hydrodynamic effects. We begin with the vortex-current model of Yatsuyanagi, Hatori & Kato (J. Phys. Soc. Japan, vol. 65, 1996, pp. 745–759) giving the self-induced motion of a vortex-current filament. We give the ‘cutoff’ formulation of the Biot–Savart integrals used in this model, to avoid the singularity at the vortex core. We then study the motion of a variety of vortex-current filaments, including helical, planar and self-similar filament structures. In the case where MHD effects are weak relative to hydrodynamic effects, the filaments behave as expected from the pure hydrodynamic theory. However, when MHD effects are strong enough to dominate, then we observe structural changes to the filaments in all cases considered. The most common finding is reversal of vortex-current filament orientation for strong enough MHD effects. Kelvin waves along a vortex filament (as seen for helical and self-similar structures) will reverse their translational and rotational motion under strong MHD effects. Our findings support the view that vortex-current filaments can be studied in a manner similar to classical hydrodynamic vortex filaments, with the primary role of MHD effects being to change the filament motion, while preserving the overall geometric structure of such filaments.
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Qi, D., R. W. Mitchell, T. Burdyga, L. E. Ford, K. H. Kuo y C. Y. Seow. "Myosin light chain phosphorylation facilitates in vivo myosin filament reassembly after mechanical perturbation". American Journal of Physiology-Cell Physiology 282, n.º 6 (1 de junio de 2002): C1298—C1305. http://dx.doi.org/10.1152/ajpcell.00554.2001.
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Phosphorylation of the 20-kDa regulatory myosin light chain (MLC) of smooth muscle is known to cause monomeric myosins in solution to self-assemble into thick filaments. The role of MLC phosphorylation in thick filament formation in intact muscle, however, is not clear. It is not known whether the phosphorylation is necessary to initiate thick filament assembly in vivo. Here we show, by using a potent inhibitor of MLC kinase (wortmannin), that the MLC phosphorylation and isometric force in trachealis muscle could be abolished without affecting calcium transients. By measuring cross-sectional densities of the thick filaments electron microscopically, we also show that inhibition of MLC phosphorylation alone did not cause disassembly of the filaments. The unphosphorylated thick filaments, however, partially dissolved when the muscle was subjected to oscillatory strains (which caused a 25% decrease in the thick filament density). The postoscillation filament density recovered to the preoscillation level only when wortmannin was removed and the muscle was stimulated. The data suggest that in vivo thick filament reassembly after mechanical perturbation is facilitated by the cyclic MLC phosphorylation associated with repeated stimulation.
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Aebi, U., R. Millonig y H. Salvo. "The 3-Dimensional Molecular Structure of the Actin Filament Revisited". Proceedings, annual meeting, Electron Microscopy Society of America 43 (agosto de 1985): 480–81. http://dx.doi.org/10.1017/s0424820100119223.
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To date, most 3-D reconstructions of undecorated actin filaments have been obtained from actin filament paracrystal data (for refs, see 1,2). However, due to the fact that (a) the paracrystals may be several filament layers thick, and (b) adjacent filaments may sustantially interdigitate, these reconstructions may be subject to significant artifacts. None of these reconstructions has permitted unambiguous tracing or orientation of the actin subunits within the filament. Furthermore, measured values for the maximal filament diameter both determined by EM and by X-ray diffraction analysis, vary between 6 and 10 nm. Obviously, the apparent diameter of the actin filament revealed in the EM will critically depend on specimen preparation, since it is a rather flexible supramolecular assembly which can easily be bent or distorted. To resolve some of these ambiguities, we have explored specimen preparation conditions which may preserve single filaments sufficiently straight and helically ordered to be suitable for single filament 3-D reconstructions, possibly revealing molecular detail.
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Taylor, Kenneth A., Dianne W. Taylor y Fred Schachat. "Isoforms of α-Actinin from Cardiac, Smooth, and Skeletal Muscle Form Polar Arrays of Actin Filaments". Journal of Cell Biology 149, n.º 3 (1 de mayo de 2000): 635–46. http://dx.doi.org/10.1083/jcb.149.3.635.
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We have used a positively charged lipid monolayer to form two-dimensional bundles of F-actin cross-linked by α-actinin to investigate the relative orientation of the actin filaments within them. This method prevents growth of the bundles perpendicular to the monolayer plane, thereby facilitating interpretation of the electron micrographs. Using α-actinin isoforms isolated from the three types of vertebrate muscle, i.e., cardiac, skeletal, and smooth, we have observed almost exclusively cross-linking between polar arrays of filaments, i.e., actin filaments with their plus ends oriented in the same direction. One type of bundle can be classified as an Archimedian spiral consisting of a single actin filament that spirals inward as the filament grows and the bundle is formed. These spirals have a consistent hand and grow to a limiting internal diameter of 0.4–0.7 μm, where the filaments appear to break and spiral formation ceases. These results, using isoforms usually characterized as cross-linkers of bipolar actin filament bundles, suggest that α-actinin is capable of cross-linking actin filaments in any orientation. Formation of specifically bipolar or polar filament arrays cross-linked by α-actinin may require additional factors that either determine the filament orientation or restrict the cross-linking capabilities of α-actinin.
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Moraczewska, Joanna. "Filamenty cienkie i mikrofilamenty – funkcjonalne kompleksy aktyny z tropomiozyną". Kosmos 67, n.º 1 (10 de julio de 2018): 31–41. http://dx.doi.org/10.36921/kos.2018_2366.
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Aktyna jest uniwersalnym białkiem o strukturze dobrze zachowanej w toku ewolucji. W komórkach aktyna istnieje w równowadze pomiędzy formą monomeryczną i filamentową. Pomimo zachowanej w toku ewolucji struktury, aktyna pełni zdumiewająco wiele różnorodnych funkcji. Jest to możliwe dzięki zdolności aktyny do oddziaływania z wieloma białkami, wśród których znajdują się motory miozynowe oraz białka regulujące dynamiczną polimeryzację i depolimeryzację aktyny. Nadrzędnymi regulatorami filamentów aktynowych są tropomiozyny, rodzina superhelikalnych białek, które polimeryzują wzdłuż filamentowej aktyny, dzięki czemu stabilizują filamenty zapobiegając ich depolimeryzacji oraz kontrolują dostęp i aktywność białek wiążących aktynę. Tropomiozyny działają jako „stróże” filamentu, którzy kontrolują oddziaływania aktyny, co prowadzi do segregacji białek wiążących aktynę do swoistych przedziałów komórkowych gdzie białka te realizują określone funkcje komórkowe. W artykule zostały omówione zależne od tropomiozyny mechanizmy regulacji oddziaływań aktyny z niektórymi miozynami oraz z Arp2/3 i kofiliną – białkami, które inicjują rozgałęzianie, polimeryzację i depolimeryzację filamentów aktynowych.
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Kampourakis, Thomas, Yin-Biao Sun y Malcolm Irving. "Myosin light chain phosphorylation enhances contraction of heart muscle via structural changes in both thick and thin filaments". Proceedings of the National Academy of Sciences 113, n.º 21 (9 de mayo de 2016): E3039—E3047. http://dx.doi.org/10.1073/pnas.1602776113.
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Contraction of heart muscle is triggered by calcium binding to the actin-containing thin filaments but modulated by structural changes in the myosin-containing thick filaments. We used phosphorylation of the myosin regulatory light chain (cRLC) by the cardiac isoform of its specific kinase to elucidate mechanisms of thick filament-mediated contractile regulation in demembranated trabeculae from the rat right ventricle. cRLC phosphorylation enhanced active force and its calcium sensitivity and altered thick filament structure as reported by bifunctional rhodamine probes on the cRLC: the myosin head domains became more perpendicular to the filament axis. The effects of cRLC phosphorylation on thick filament structure and its calcium sensitivity were mimicked by increasing sarcomere length or by deleting the N terminus of the cRLC. Changes in thick filament structure were highly cooperative with respect to either calcium concentration or extent of cRLC phosphorylation. Probes on unphosphorylated myosin heads reported similar structural changes when neighboring heads were phosphorylated, directly demonstrating signaling between myosin heads. Moreover probes on troponin showed that calcium sensitization by cRLC phosphorylation is mediated by the thin filament, revealing a signaling pathway between thick and thin filaments that is still present when active force is blocked by Blebbistatin. These results show that coordinated and cooperative structural changes in the thick and thin filaments are fundamental to the physiological regulation of contractility in the heart. This integrated dual-filament concept of contractile regulation may aid understanding of functional effects of mutations in the protein components of both filaments associated with heart disease.
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Dey, Arup, Isnala Nanjin Roan Eagle y Nita Yodo. "A Review on Filament Materials for Fused Filament Fabrication". Journal of Manufacturing and Materials Processing 5, n.º 3 (29 de junio de 2021): 69. http://dx.doi.org/10.3390/jmmp5030069.
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Fused filament fabrication (FFF) is one of the most popular additive manufacturing (AM) processes that utilize thermoplastic polymers to produce three-dimensional (3D) geometry products. The FFF filament materials have a significant role in determining the properties of the final part produced, such as mechanical properties, thermal conductivity, and electrical conductivity. This article intensively reviews the state-of-the-art materials for FFF filaments. To date, there are many different types of FFF filament materials that have been developed. The filament materials range from pure thermoplastics to composites, bioplastics, and composites of bioplastics. Different types of reinforcements such as particles, fibers, and nanoparticles are incorporated into the composite filaments to improve the FFF build part properties. The performance, limitations, and opportunities of a specific type of FFF filament will be discussed. Additionally, the challenges and requirements for filament production from different materials will be evaluated. In addition, to provide a concise review of fundamental knowledge about the FFF filament, this article will also highlight potential research directions to stimulate future filament development. Finally, the importance and scopes of using bioplastics and their composites for developing eco-friendly filaments will be introduced.
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Arzoumanian, D., Ph André, V. Könyves, P. Palmeirim, A. Roy, N. Schneider, M. Benedettini et al. "Characterizing the properties of nearby molecular filaments observed with Herschel". Astronomy & Astrophysics 621 (enero de 2019): A42. http://dx.doi.org/10.1051/0004-6361/201832725.
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Context. Molecular filaments have received special attention recently thanks to new observational results on their properties. In particular, our early analysis of filament properties from Herschel imaging data in three nearby molecular clouds revealed a narrow distribution of median inner widths centered at a characteristic value of about 0.1 pc. Aims. Here, we extend and complement our initial study with a detailed analysis of the filamentary structures identified with Herschel in eight nearby molecular clouds (at distances <500 pc). Our main goal is to establish statistical distributions of median properties averaged along the filament crests and to compare the results with our earlier work based on a smaller number of filaments. Aims. We use the column density (NH2) maps derived from Herschel data and the DisPerSE algorithm to trace a network of individual filaments in each cloud. We analyze the density structure along and across the main filament axes in detail. We build synthetic maps of filamentary clouds to assess the completeness limit of our extracted filament sample and validate our measurements of the filament properties. These tests also help us to select the best choice of parameters to be used for tracing filaments with DisPerSE and fitting their radial column density profiles. Methods. Our analysis yields an extended sample of 1310 filamentary structures and a selected sample of 599 filaments with aspect ratios larger than 3 and column density contrasts larger than 0.3. We show that our selected sample of filaments is more than 95% complete for column density contrasts larger than 1, with only ~ 5% spurious detections. On average, more than 15% of the total gas mass in the clouds, and more than 80% of the dense gas mass (at NH2 > 7 × 1021 cm−2), is found to be in the form of filaments. Analysis of the radial column density profiles of the 599 filaments in the selected sample indicates a narrow distribution of crest-averaged inner widths, with a median value of 0.10 pc and an interquartile range of 0.07 pc. In contrast, the extracted filaments span wide ranges in length, central column density, column density contrast, and mass per unit length. The characteristic filament width is well resolved by Herschel observations, and a median value of ~0.1 pc is consistently found using three distinct estimates based on (1) a direct measurement of the width at half power after background subtraction, as well as (2) Gaussian and (3) Plummer fits. The existence of a characteristic filament width is further supported by the presence of a tight correlation between mass per unit length and central column density for the observed filaments. Results. Our detailed analysis of a large filament sample confirms our earlier result that nearby molecular filaments share a common mean inner width of ~0.1 pc, with typical variations along and on either side of the filament crests of about ± 0.06 pc around the mean value. This observational result sets strong constraints on possible models for the formation and evolution of filaments in molecular clouds. It also provides important hints on the initial conditions of star formation.
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Hormoz, Sahand y Michael P. Brenner. "Absence of singular stretching of interacting vortex filaments". Journal of Fluid Mechanics 707 (10 de agosto de 2012): 191–204. http://dx.doi.org/10.1017/jfm.2012.270.
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AbstractA promising mechanism for generating a finite-time singularity in the incompressible Euler equations is the stretching of vortex filaments. Here, we argue that interacting vortex filaments cannot generate a singularity by analysing the asymptotic dynamics of their collapse. We use the separation of the dynamics of the filament shape, from that of its core, to derive constraints that must be satisfied for a singular solution to remain self-consistent uniformly in time. Our only assumption is that the length scales characterizing filament shape obey scaling laws set by the dimension of circulation as the singularity is approached. The core radius necessarily evolves on a different length scale. We show that a self-similar ansatz for the filament shapes cannot induce singular stretching, due to the logarithmic prefactor in the self-interaction term for the filaments. More generally, there is an antagonistic relationship between the stretching rate of the filaments and the requirement that the radius of curvature of filament shape obeys the dimensional scaling laws. This suggests that it is unlikely that solutions in which the core radii vanish sufficiently fast to maintain the filament approximation exist.
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Contant, Sheila, Liliane M. F. Lona y Verônica M. A. Calado. "Predição do comportamento térmico de tubos compósitos através de redes neurais". Polímeros 14, n.º 5 (diciembre de 2004): 295–300. http://dx.doi.org/10.1590/s0104-14282004000500004.
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Compósitos poliméricos (plásticos reforçados) são materiais formados a partir de um reforço (fase descontínua, normalmente uma fibra) e uma matriz polimérica. Esse tipo de material apresenta várias vantagens em relação aos materiais convencionais de engenharia. Entre os métodos de fabricação de compósitos poliméricos está o filament winding (filamento contínuo ou enrolamento filamentar), um processo empregado na fabricação de sólidos de revolução, como tubos e tanques. Neste trabalho, redes neurais artificiais, uma ferramenta computacional inspirada no funcionamento do cérebro humano, foram aplicadas ao processo de filament winding para predição do comportamento térmico de tubos compósitos durante a etapa de cura. Informações sobre o comportamento térmico das peças compósitas podem auxiliar na seleção do ciclo de cura, que é um dos desafios na obtenção de peças de qualidade e a um baixo custo. As redes neurais foram treinadas com dados obtidos através do modelo Lee-Springer. A metodologia foi validada com resultados experimentais da literatura.
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Fowler, V. M., M. A. Sussmann, P. G. Miller, B. E. Flucher y M. P. Daniels. "Tropomodulin is associated with the free (pointed) ends of the thin filaments in rat skeletal muscle." Journal of Cell Biology 120, n.º 2 (15 de enero de 1993): 411–20. http://dx.doi.org/10.1083/jcb.120.2.411.
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The length and spatial organization of thin filaments in skeletal muscle sarcomeres are precisely maintained and are essential for efficient muscle contraction. While the major structural components of skeletal muscle sarcomeres have been well characterized, the mechanisms that regulate thin filament length and spatial organization are not well understood. Tropomodulin is a new, 40.6-kD tropomyosin-binding protein from the human erythrocyte membrane skeleton that binds to one end of erythrocyte tropomyosin and blocks head-to-tail association of tropomyosin molecules along actin filaments. Here we show that rat psoas skeletal muscle contains tropomodulin based on immunoreactivity, identical apparent mobility on SDS gels, and ability to bind muscle tropomyosin. Results from immunofluorescence labeling of isolated myofibrils at resting and stretched lengths using anti-erythrocyte tropomodulin antibodies indicate that tropomodulin is localized at or near the free (pointed) ends of the thin filaments; this localization is not dependent on the presence of myosin thick filaments. Immunoblotting of supernatants and pellets obtained after extraction of myosin from myofibrils also indicates that tropomodulin remains associated with the thin filaments. 1.2-1.6 copies of muscle tropomodulin are present per thin filament in myofibrils, supporting the possibility that one or two tropomodulin molecules may be associated with the two terminal tropomyosin molecules at the pointed end of each thin filament. Although a number of proteins are associated with the barbed ends of the thin filaments at the Z disc, tropomodulin is the first protein to be specifically located at or near the pointed ends of the thin filaments. We propose that tropomodulin may cap the tropomyosin polymers at the pointed end of the thin filament and play a role in regulating thin filament length.
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Trombitas, K., P. H. Baatsen, M. S. Kellermayer y G. H. Pollack. "Nature and origin of gap filaments in striated muscle". Journal of Cell Science 100, n.º 4 (1 de diciembre de 1991): 809–14. http://dx.doi.org/10.1242/jcs.100.4.809.
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Immunoelectron microscopy was used to study the nature and origin of ‘gap’ filaments in frog semitendinosus muscle. Gap filaments are fine longitudinal filaments observable only in sarcomeres stretched beyond thick/thin filament overlap: they occupy the gap between the tips of thick and thin filaments. To test whether the gap filaments are part of the titin-filament system, we employed monoclonal antibodies to titin (T-11, Sigma) and observed the location of the epitope at a series of sarcomere lengths. At resting sarcomere length, the epitope was positioned in the I-band approximately 50 nm beyond the apparent ends of the thick filament. The location did not change perceptibly with increasing sarcomere length up to 3.6 microns. Above 3.6 microns, the span between the epitope and the end of the A-band abruptly increased, and above 4 microns, the antibodies could be seen to decorate the gap filaments. Between 5 and 6 microns, the epitope remained approximately in the middle of the gap. Even with this high degree of stretch, the label remained more or less aligned across the myofibril. The abrupt increase of span beyond 3.6 microns implies that the A-band domain of titin is pulled free of its anchor points along the thick filament, and moves toward the gap. Although this domain is functionally inextensible at physiological sarcomere length, the epitope movement in extremely stretched muscle shows that it is intrinsically elastic. Thus, the evidence confirms that gap filaments are clearly part of the titin-filament system. They are derived not only from the I-band domain of titin, but also from its A-band domain.
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Pospich, Sabrina, Esa-Pekka Kumpula, Julian von der Ecken, Juha Vahokoski, Inari Kursula y Stefan Raunser. "Near-atomic structure of jasplakinolide-stabilized malaria parasite F-actin reveals the structural basis of filament instability". Proceedings of the National Academy of Sciences 114, n.º 40 (18 de septiembre de 2017): 10636–41. http://dx.doi.org/10.1073/pnas.1707506114.
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During their life cycle, apicomplexan parasites, such as the malaria parasite Plasmodium falciparum, use actomyosin-driven gliding motility to move and invade host cells. For this process, actin filament length and stability are temporally and spatially controlled. In contrast to canonical actin, P. falciparum actin 1 (PfAct1) does not readily polymerize into long, stable filaments. The structural basis of filament instability, which plays a pivotal role in host cell invasion, and thus infectivity, is poorly understood, largely because high-resolution structures of PfAct1 filaments were missing. Here, we report the near-atomic structure of jasplakinolide (JAS)-stabilized PfAct1 filaments determined by electron cryomicroscopy. The general filament architecture is similar to that of mammalian F-actin. The high resolution of the structure allowed us to identify small but important differences at inter- and intrastrand contact sites, explaining the inherent instability of apicomplexan actin filaments. JAS binds at regular intervals inside the filament to three adjacent actin subunits, reinforcing filament stability by hydrophobic interactions. Our study reveals the high-resolution structure of a small molecule bound to F-actin, highlighting the potential of electron cryomicroscopy for structure-based drug design. Furthermore, our work serves as a strong foundation for understanding the structural design and evolution of actin filaments and their function in motility and host cell invasion of apicomplexan parasites.
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Higashi-Fujime, S. "Unidirectional sliding of myosin filaments along the bundle of F-actin filaments spontaneously formed during superprecipitation." Journal of Cell Biology 101, n.º 6 (1 de diciembre de 1985): 2335–44. http://dx.doi.org/10.1083/jcb.101.6.2335.
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I reported previously (Higashi-Fujime, S., 1982, Cold Spring Harbor Symp. Quant. Biol., 46:69-75) that active movements of fibrils composed of F-actin and myosin filaments occurred after superprecipitation in the presence of ATP at low ionic strengths. When the concentration of MgCl2 in the medium used in the above experiment was raised to 20-26 mM, bundles of F-actin filaments, in addition to large precipitates, were formed spontaneously both during and after superprecipitation. Along these bundles, many myosin filaments were observed to slide unidirectionally and successively through the bundle, from one end to the other. The sliding of myosin filaments continued for approximately 1 h at room temperature at a mean rate of 6.0 micron/s, as long as ATP remained in the medium. By electron microscopy, it was found that most F-actin filaments decorated with heavy meromyosin pointed to the same direction in the bundle. Myosin filaments moved actively not only along the F-actin bundle but also in the medium. Such movement probably occurred along F-actin filaments that did not form the bundle but were dispersed in the medium, although dispersed F-actin filaments were not visible under the microscope. In this case, myosin filament could have moved in a reverse direction, changing from one F-actin filament to the other. These results suggested that the direction of movement of myosin filament, which has a bipolar structure and the potentiality to move in both directions, was determined by the polarity of F-actin filament in action.