Journal articles on the topic 'Spindle'
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1
Li, Jiandong, Qiang Wang, Xurui Sun, Jue Qu, Ang Qiu, Wei Kang, and Shuaijun Ma. "Research on the Effect of Spindle Speed on the Softening and Hardening Characteristics of the Axial Operating Stiffness of Machine Tool Spindle." Lubricants 10, no. 7 (June 22, 2022): 132. http://dx.doi.org/10.3390/lubricants10070132.
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Spindle stiffness is one of the most critical indicators for evaluating and measuring the service performance of spindles. The traditional static stiffness indexes only involve static analysis and rarely focus on the study of spindle-carrying capacity under operating conditions. In this paper, the explicit solution approach is used to develop a mechanical model of the spindle’s axial operating stiffness. This model was then used to explore the influence of rotational speed on the softening and hardening features of the spindle axial operating stiffness, and experimental verification was carried out. According to studies, the speed of a fixed-position preload spindle can lead its operating stiffness to exhibit a “stiffness-hardening” feature. However, when the axial displacement of the spindle is small, the operating stiffness curve of the spindle displays a noticeable “fluctuation” phenomenon for low-speed spindles. Furthermore, the speed-induced preload has a significant impact on the test results when testing spindle axial operating stiffness.
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Brecher, C. Prof, S. Neus, H. M. Eckel, T. Motschke, and M. Fey. "Frequenzgangmessung an Spindeln unter Drehzahl*/FRF Measurement on rotating spindles." wt Werkstattstechnik online 107, no. 05 (2017): 318–22. http://dx.doi.org/10.37544/1436-4980-2017-05-14.
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Das statische und dynamische Verhalten von Hauptspindelsystemen ist über Nachgiebigkeitsfrequenzgänge beschreibbar. Dabei beeinflussen Drehzahleffekte die dynamischen Nachgiebigkeiten des Systems Werkzeug – Werkzeugschnittstelle – Spindel maßgeblich. Dieser Fachartikel beschreibt eine Methodik zur messtechnischen Ermittlung von Nachgiebigkeitsfrequenzgängen an rotierenden Spindeln mit absoluter sowie relativer Kraftanregung in Verbindung mit berührungsloser Verlagerungsmessung. The static and dynamic behavior of main spindles in machine tools can be described via Frequency Response Functions (FRFs). Dynamic compliances of the system tool-interface-spindle are decisively influenced by rotational speed effects. This technical article describes a methodology for FRF measurement of rotating spindles with absolute and relative force excitation in conjunction with non-contact displacement measurement.
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Lu, Y., Ying Xue Yao, and W. Z. Xie. "Finite Element Analysis of Dynamic Characteristics of High-Speed Motorized Spindle." Applied Mechanics and Materials 10-12 (December 2007): 900–904. http://dx.doi.org/10.4028/www.scientific.net/amm.10-12.900.
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High speed machining is a promising technology for significantly increasing productivity and reducing production costs. Development of high-speed spindle technology is strategically critical to the implementation of high speed machining. Compared to conventional spindles, and motorized spindles are equipped with built-in motors for better power transmission and balance to achieve high-speed operation. However, the built-in motor introduces additional mass to the spindle shaft, besides, since its very high working speed, some high-speed rotational effects, including centrifugal forces and gyroscopic moments on the spindle shaft can not be neglected in the analysis as is done in conventional spindle, thus complicating its mechanical-dynamic behaviors. In this paper, the FEM model of motorized spindle is set up to research on its dynamic characteristics in theory with an eye to high-speed rotational effects, including centrifugal forces and gyroscopic moments on the motorized spindle shaft. The motorized spindle’s natural frequencies and corresponding vibration shapes are got through the modal analysis, and the effect of the axial preload on the natural frequency is programmed to be seen clearly.
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Zulkipli, Ihsan, Joanna Clark, Madeleine Hart, Roshan L. Shrestha, Parveen Gul, David Dang, Tami Kasichiwin, Izabela Kujawiak, Nishanth Sastry, and Viji M. Draviam. "Spindle rotation in human cells is reliant on a MARK2-mediated equatorial spindle-centering mechanism." Journal of Cell Biology 217, no. 9 (June 25, 2018): 3057–70. http://dx.doi.org/10.1083/jcb.201804166.
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The plane of cell division is defined by the final position of the mitotic spindle. The spindle is pulled and rotated to the correct position by cortical dynein. However, it is unclear how the spindle’s rotational center is maintained and what the consequences of an equatorially off centered spindle are in human cells. We analyzed spindle movements in 100s of cells exposed to protein depletions or drug treatments and uncovered a novel role for MARK2 in maintaining the spindle at the cell’s geometric center. Following MARK2 depletion, spindles glide along the cell cortex, leading to a failure in identifying the correct division plane. Surprisingly, spindle off centering in MARK2-depleted cells is not caused by excessive pull by dynein. We show that MARK2 modulates mitotic microtubule growth and length and that codepleting mitotic centromere-associated protein (MCAK), a microtubule destabilizer, rescues spindle off centering in MARK2-depleted cells. Thus, we provide the first insight into a spindle-centering mechanism needed for proper spindle rotation and, in turn, the correct division plane in human cells.
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Kondo, Ryo, Daisuke Kono, and Atsushi Matsubara. "Evaluation of Machine Tool Spindle Using Carbon Fiber Composite." International Journal of Automation Technology 14, no. 2 (March 5, 2020): 294–303. http://dx.doi.org/10.20965/ijat.2020.p0294.
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Spindle is one of the most important component of machine tools because spindle’s performance including thermal property and dynamic property greatly influences the accuracy and productivity in machining process. This study investigates the effect of the application of carbon fiber reinforced plastic (CFRP) to the spindle shaft on the performance of machine tool spindles. CFRP and steel spindle shafts with the same geometry were developed for fair comparison. Thermal and dynamic properties of the developed shaft and spindle unit were evaluated and compared. The experimental and simulation results showed that the CFRP spindle shaft improved the axial thermal displacement and dynamic stiffness. The axial thermal displacement was decreased to 1/3 of that of the steel spindle. The compliance was also decreased to 1/2. The design of the thermal displacement distribution around the bearing should be an important issue in the CFRP spindle for the thermal stability of the dynamic property.
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Woolner, Sarah, Lori L. O'Brien, Christiane Wiese, and William M. Bement. "Myosin-10 and actin filaments are essential for mitotic spindle function." Journal of Cell Biology 182, no. 1 (July 7, 2008): 77–88. http://dx.doi.org/10.1083/jcb.200804062.
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Mitotic spindles are microtubule-based structures responsible for chromosome partitioning during cell division. Although the roles of microtubules and microtubule-based motors in mitotic spindles are well established, whether or not actin filaments (F-actin) and F-actin–based motors (myosins) are required components of mitotic spindles has long been controversial. Based on the demonstration that myosin-10 (Myo10) is important for assembly of meiotic spindles, we assessed the role of this unconventional myosin, as well as F-actin, in mitotic spindles. We find that Myo10 localizes to mitotic spindle poles and is essential for proper spindle anchoring, normal spindle length, spindle pole integrity, and progression through metaphase. Furthermore, we show that F-actin localizes to mitotic spindles in dynamic cables that surround the spindle and extend between the spindle and the cortex. Remarkably, although proper anchoring depends on both F-actin and Myo10, the requirement for Myo10 in spindle pole integrity is F-actin independent, whereas F-actin and Myo10 actually play antagonistic roles in maintenance of spindle length.
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Morales-Mulia, Sandra, and Jonathan M. Scholey. "Spindle Pole Organization in Drosophila S2 Cells by Dynein, Abnormal Spindle Protein (Asp), and KLP10A." Molecular Biology of the Cell 16, no. 7 (July 2005): 3176–86. http://dx.doi.org/10.1091/mbc.e04-12-1110.
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Dynein is a critical mitotic motor whose inhibition causes defects in spindle pole organization and separation, chromosome congression or segregation, and anaphase spindle elongation, but results differ in different systems. We evaluated the functions of the dynein–dynactin complex by using RNA interference (RNAi)-mediated depletion of distinct subunits in Drosophila S2 cells. We observed a striking detachment of centrosomes from spindles, an increase in spindle length, and a loss of spindle pole focus. RNAi depletion of Ncd, another minus-end motor, produced disorganized spindles consisting of multiple disconnected mini-spindles, a different phenotype consistent with distinct pathways of spindle pole organization. Two candidate dynein-dependent spindle pole organizers also were investigated. RNAi depletion of the abnormal spindle protein, Asp, which localizes to focused poles of control spindles, produced a severe loss of spindle pole focus, whereas depletion of the pole-associated microtubule depolymerase KLP10A increased spindle microtubule density. Depletion of either protein produced long spindles. After RNAi depletion of dynein–dynactin, we observed subtle but significant mislocalization of KLP10A and Asp, suggesting that dynein–dynactin, Asp, and KLP10A have complex interdependent functions in spindle pole focusing and centrosome attachment. These results extend recent findings from Xenopus extracts to Drosophila cultured cells and suggest that common pathways contribute to spindle pole organization and length determination.
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Larson, Matthew E., and William M. Bement. "Automated mitotic spindle tracking suggests a link between spindle dynamics, spindle orientation, and anaphase onset in epithelial cells." Molecular Biology of the Cell 28, no. 6 (March 15, 2017): 746–59. http://dx.doi.org/10.1091/mbc.e16-06-0355.
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Proper spindle positioning at anaphase onset is essential for normal tissue organization and function. Here we develop automated spindle-tracking software and apply it to characterize mitotic spindle dynamics in the Xenopus laevis embryonic epithelium. We find that metaphase spindles first undergo a sustained rotation that brings them on-axis with their final orientation. This sustained rotation is followed by a set of striking stereotyped rotational oscillations that bring the spindle into near contact with the cortex and then move it rapidly away from the cortex. These oscillations begin to subside soon before anaphase onset. Metrics extracted from the automatically tracked spindles indicate that final spindle position is determined largely by cell morphology and that spindles consistently center themselves in the XY-plane before anaphase onset. Finally, analysis of the relationship between spindle oscillations and spindle position relative to the cortex reveals an association between cortical contact and anaphase onset. We conclude that metaphase spindles in epithelia engage in a stereotyped “dance,” that this dance culminates in proper spindle positioning and orientation, and that completion of the dance is linked to anaphase onset.
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Walker, Diana L., Dong Wang, Ye Jin, Uttama Rath, Yanming Wang, Jørgen Johansen, and Kristen M. Johansen. "Skeletor, a Novel Chromosomal Protein That Redistributes during Mitosis Provides Evidence for the Formation of a Spindle Matrix." Journal of Cell Biology 151, no. 7 (December 25, 2000): 1401–12. http://dx.doi.org/10.1083/jcb.151.7.1401.
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A spindle matrix has been proposed to help organize and stabilize the microtubule spindle during mitosis, though molecular evidence corroborating its existence has been elusive. In Drosophila, we have cloned and characterized a novel nuclear protein, skeletor, that we propose is part of a macromolecular complex forming such a spindle matrix. Skeletor antibody staining shows that skeletor is associated with the chromosomes at interphase, but redistributes into a true fusiform spindle structure at prophase, which precedes microtubule spindle formation. During metaphase, the spindle, defined by skeletor antibody labeling, and the microtubule spindles are coaligned. We find that the skeletor-defined spindle maintains its fusiform spindle structure from end to end across the metaphase plate during anaphase when the chromosomes segregate. Consequently, the properties of the skeletor-defined spindle make it an ideal substrate for providing structural support stabilizing microtubules and counterbalancing force production. Furthermore, skeletor metaphase spindles persist in the absence of microtubule spindles, strongly implying that the existence of the skeletor-defined spindle does not require polymerized microtubules. Thus, the identification and characterization of skeletor represents the first direct molecular evidence for the existence of a complete spindle matrix that forms within the nucleus before microtubule spindle formation.
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Baskin, T. I., and W. Z. Cande. "Kinetic analysis of mitotic spindle elongation in vitro." Journal of Cell Science 97, no. 1 (September 1, 1990): 79–89. http://dx.doi.org/10.1242/jcs.97.1.79.
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Studies of mitotic spindle elongation in vitro using populations of diatom spindles visualized with immunofluorescence microscopy have shown that the two interdigitating half-spindles are driven apart by an ATP-dependent process that generates force in the zone of overlap between half-spindles. To characterize further the system responsible for spindle elongation, we observed spindle elongation directly with polarized light or phase-contrast video-microscopy. We report that the kinetics of spindle elongation versus time are linear. A constant rate of spindle elongation occurs despite the continuous decrease in length of the zone of overlap between half-spindles. The average rate of spindle elongation varies as a function of treatment, and rates measured match spindle elongation rates measured in vivo. When spindles elongated in the presence of polymerizing tubulin (from bovine brain), the extent of elongation was greater than the original zone of half-spindle overlap, but the rate of elongation was constant. No component of force due to tubulin polymerization was found. The total elongation observed in the presence of added tubulin could exceed a doubling of original spindle length, matching the elongation in the intact diatom. The linear rate of spindle elongation in vitro suggests that the force transducer for anaphase B is a mechanochemical ATPase, analogous to dynein or myosin, and that the force for spindle elongation does not arise from stored energy, e.g. in an elastic matrix in the midzone. Additionally, on the basis of observations described here, we conclude that the force-transduction system for spindle elongation must be able to remain in the zone of microtubule overlap during the sliding apart of half-spindles, and that the transducer can generate force between microtubules that are not strictly antiparallel.
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Yu, Che-Hang, Stefanie Redemann, Hai-Yin Wu, Robert Kiewisz, Tae Yeon Yoo, William Conway, Reza Farhadifar, Thomas Müller-Reichert, and Daniel Needleman. "Central-spindle microtubules are strongly coupled to chromosomes during both anaphase A and anaphase B." Molecular Biology of the Cell 30, no. 19 (September 1, 2019): 2503–14. http://dx.doi.org/10.1091/mbc.e19-01-0074.
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Spindle microtubules, whose dynamics vary over time and at different locations, cooperatively drive chromosome segregation. Measurements of microtubule dynamics and spindle ultrastructure can provide insight into the behaviors of microtubules, helping elucidate the mechanism of chromosome segregation. Much work has focused on the dynamics and organization of kinetochore microtubules, that is, on the region between chromosomes and poles. In comparison, microtubules in the central-spindle region, between segregating chromosomes, have been less thoroughly characterized. Here, we report measurements of the movement of central-spindle microtubules during chromosome segregation in human mitotic spindles and Caenorhabditis elegans mitotic and female meiotic spindles. We found that these central-spindle microtubules slide apart at the same speed as chromosomes, even as chromosomes move toward spindle poles. In these systems, damaging central-spindle microtubules by laser ablation caused an immediate and complete cessation of chromosome motion, suggesting a strong coupling between central-spindle microtubules and chromosomes. Electron tomographic reconstruction revealed that the analyzed anaphase spindles all contain microtubules with both ends between segregating chromosomes. Our results provide new dynamical, functional, and ultrastructural characterizations of central-spindle microtubules during chromosome segregation in diverse spindles and suggest that central-spindle microtubules and chromosomes are strongly coupled in anaphase.
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Harding, Christian, Breanna Holloway, Christopher Schmickl, Pamela DeYoung, Crystal Kwan, Sonia Ancoli-Israel, Sarah Banks, and Atul Malhotra. "0459 Restriction of Breathing in OSA Does Not Affect Sleep Spindle Density." SLEEP 47, Supplement_1 (April 20, 2024): A197—A198. http://dx.doi.org/10.1093/sleep/zsae067.0459.
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Abstract Introduction Obstructive sleep apnea (OSA) is associated with major neurocognitive sequalae including impaired memory. OSA patients are deficient in NREM sleep spindles (11 Hz to 16 Hz electroencephalography (EEG) sigma oscillations) which have been shown to promote memory. This finding is a result of less time spent in deeper sleep states in which most spindles occur but also a reduction in spindle density, particularly during the later portion of the night. We tested the hypothesis that spindle density deficiencies are driven by restriction of breathing preventing spindle generation. Methods 109 adults (ages 65-83, 53% female) with normal cognition underwent overnight polysomnography (PSG). Presence of sleep apnea was defined using AASM recommended criteria (apnea-hypopnea index >15, n=81[OSA] vs 28[controls]). The right occipital channel EEG was bandpass filtered between 0.3-35Hz. Following rejection of movement artifacts, spindles were detected in NREM sleep stages 2 and 3 (N2/N3) using complex demodulation to extract high sigma activity signals from background sigma noise. Spindles were classified depending on whether the patient was in eupnea or apnea-hypopnea. Results Overall spindle density in OSA patients did not differ from overall spindle density in controls (2.86 vs 3.17 spindles/minute, t(57.4)=0.49, p=0.14). Apnea-hypopnea spindle density in OSA patients did not differ from eupnea spindle density in controls (3.10 vs 3.17 spindles/minute, t(70.8)=0.31, p-value=0.76). Eupnea spindle density in OSA patients was significantly lower than eupnea spindle density in controls (2.57 vs 3.17 spindles/minute, t(54.4)=2.94, p-value< 0.01). Conclusion Contrary to our hypothesis, sleep spindle density was not reduced in OSA patients during apnea-hypopnea compared to healthy controls during eupnea, suggesting restriction of breathing does not affect spindle generation, but was reduced in OSA patients during eupnea. Whilst we did not observe an overall OSA-related spindle density deficit, our results suggest that previous findings of lower spindle density in OSA patients may in fact result from changes in spindle behaviour during eupnea. This observation raises the interesting possibility that using OSA interventions to prevent apnea-hypopnea occurring may not recover normal spindle density. Alternatively, our results could suggest that undetected N2/N3 sleep disruptions are occurring when OSA patients are breathing, skewing eupnea spindle density estimates. Support (if any) 1R01AG063925-01A1
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Lázaro-Diéguez, Francisco, Iaroslav Ispolatov, and Anne Müsch. "Cell shape impacts on the positioning of the mitotic spindle with respect to the substratum." Molecular Biology of the Cell 26, no. 7 (April 2015): 1286–95. http://dx.doi.org/10.1091/mbc.e14-08-1330.
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All known mechanisms of mitotic spindle orientation rely on astral microtubules. We report that even in the absence of astral microtubules, metaphase spindles in MDCK and HeLa cells are not randomly positioned along their x-z dimension, but preferentially adopt shallow β angles between spindle pole axis and substratum. The nonrandom spindle positioning is due to constraints imposed by the cell cortex in flat cells that drive spindles that are longer and/or wider than the cell's height into a tilted, quasidiagonal x-z position. In rounder cells, which are taller, fewer cortical constraints make the x-z spindle position more random. Reestablishment of astral microtubule–mediated forces align the spindle poles with cortical cues parallel to the substratum in all cells. However, in flat cells, they frequently cause spindle deformations. Similar deformations are apparent when confined spindles rotate from tilted to parallel positions while MDCK cells progress from prometaphase to metaphase. The spindle disruptions cause the engagement of the spindle assembly checkpoint. We propose that cell rounding serves to maintain spindle integrity during its positioning.
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Yukawa, Masashi, Tomoki Kawakami, Masaki Okazaki, Kazunori Kume, Ngang Heok Tang, and Takashi Toda. "A microtubule polymerase cooperates with the kinesin-6 motor and a microtubule cross-linker to promote bipolar spindle assembly in the absence of kinesin-5 and kinesin-14 in fission yeast." Molecular Biology of the Cell 28, no. 25 (December 2017): 3647–59. http://dx.doi.org/10.1091/mbc.e17-08-0497.
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Accurate chromosome segregation relies on the bipolar mitotic spindle. In many eukaryotes, spindle formation is driven by the plus-end–directed motor kinesin-5 that generates outward force to establish spindle bipolarity. Its inhibition leads to the emergence of monopolar spindles with mitotic arrest. Intriguingly, simultaneous inactivation of the minus-end–directed motor kinesin-14 restores spindle bipolarity in many systems. Here we show that in fission yeast, three independent pathways contribute to spindle bipolarity in the absence of kinesin-5/Cut7 and kinesin-14/Pkl1. One is kinesin-6/Klp9 that engages with spindle elongation once short bipolar spindles assemble. Klp9 also ensures the medial positioning of anaphase spindles to prevent unequal chromosome segregation. Another is the Alp7/TACC-Alp14/TOG microtubule polymerase complex. Temperature-sensitive alp7cut7pkl1 mutants are arrested with either monopolar or very short spindles. Forced targeting of Alp14 to the spindle pole body is sufficient to render alp7cut7pkl1 triply deleted cells viable and promote spindle assembly, indicating that Alp14-mediated microtubule polymerization from the nuclear face of the spindle pole body could generate outward force in place of Cut7 during early mitosis. The third pathway involves the Ase1/PRC1 microtubule cross-linker that stabilizes antiparallel microtubules. Our study, therefore, unveils multifaceted interplay among kinesin-dependent and -independent pathways leading to mitotic bipolar spindle assembly.
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Crowder, Marina E., Jonathan R. Flynn, Karen P. McNally, Daniel B. Cortes, Kari L. Price, Paul A. Kuehnert, Michelle T. Panzica, Armann Andaya, Julie A. Leary, and Francis J. McNally. "Dynactin-dependent cortical dynein and spherical spindle shape correlate temporally with meiotic spindle rotation in Caenorhabditis elegans." Molecular Biology of the Cell 26, no. 17 (September 2015): 3030–46. http://dx.doi.org/10.1091/mbc.e15-05-0290.
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Oocyte meiotic spindles orient with one pole juxtaposed to the cortex to facilitate extrusion of chromosomes into polar bodies. In Caenorhabditis elegans, these acentriolar spindles initially orient parallel to the cortex and then rotate to the perpendicular orientation. To understand the mechanism of spindle rotation, we characterized events that correlated temporally with rotation, including shortening of the spindle in the pole-to pole axis, which resulted in a nearly spherical spindle at rotation. By analyzing large spindles of polyploid C. elegans and a related nematode species, we found that spindle rotation initiated at a defined spherical shape rather than at a defined spindle length. In addition, dynein accumulated on the cortex just before rotation, and microtubules grew from the spindle with plus ends outward during rotation. Dynactin depletion prevented accumulation of dynein on the cortex and prevented spindle rotation independently of effects on spindle shape. These results support a cortical pulling model in which spindle shape might facilitate rotation because a sphere can rotate without deforming the adjacent elastic cytoplasm. We also present evidence that activation of spindle rotation is promoted by dephosphorylation of the basic domain of p150 dynactin.
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O'Toole, E. T., D. N. Mastronarde, T. H. Giddings, M. Winey, D. J. Burke, and J. R. McIntosh. "Three-dimensional analysis and ultrastructural design of mitotic spindles from the cdc20 mutant of Saccharomyces cerevisiae." Molecular Biology of the Cell 8, no. 1 (January 1997): 1–11. http://dx.doi.org/10.1091/mbc.8.1.1.
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The three-dimensional organization of mitotic microtubules in a mutant strain of Saccharomyces cerevisiae has been studied by computer-assisted serial reconstruction. At the nonpermissive temperature, cdc20 cells arrested with a spindle length of approximately 2.5 microns. These spindles contained a mean of 81 microtubules (range, 56-100) compared with 23 in wild-type spindles of comparable length. This increase in spindle microtubule number resulted in a total polymer length up to four times that of wild-type spindles. The spindle pole bodies in the cdc20 cells were approximately 2.3 times the size of wild-type, thereby accommodating the abnormally large number of spindle microtubules. The cdc20 spindles contained a large number of interpolar microtubules organized in a "core bundle." A neighbor density analysis of this bundle at the spindle midzone showed a preferred spacing of approximately 35 nm center-to-center between microtubules of opposite polarity. Although this is evidence of specific interaction between antiparallel microtubules, mutant spindles were less ordered than the spindle of wild-type cells. The number of noncore microtubules was significantly higher than that reported for wild-type, and these microtubules did not display a characteristic metaphase configuration. cdc20 spindles showed significantly more cross-bridges between spindle microtubules than were seen in the wild type. The cross-bridge density was highest between antiparallel microtubules. These data suggest that spindle microtubules are stabilized in cdc20 cells and that the CDC20 gene product may be involved in cell cycle processes that promote spindle microtubule disassembly.
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WERNER WOLF, KLAUS. "Mitotic and meiotic spindles from two insect orders, Lepidoptera and Diptera, differ in terms of microtubule and membrane content." Journal of Cell Science 97, no. 1 (September 1, 1990): 91–100. http://dx.doi.org/10.1242/jcs.97.1.91.
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Spindles from the gonads of five insect species were examined after conventional preparation for electron microscopy. The aim of the study was to determine (1) the range of variation of the spindle membranes between mitotic and meiotic cells and (2) the correlation of possible differences with the microtubule content of the spindles. The study involved four moth species, Ephestia kuehniella, Phragmatobia fuliginosa, Orgyia thyellina, Orgyia antiqua, and one fly, Megaselia scalaris. Somatic and gonial mitoses in all species examined showed a sparse spindle membrane inventory. In contrast, spermatocytes consistently had a multi- layered spindle envelope. In spermatocytes of all Lepidoptera species examined, but not in those of M. scalaris, diverse forms of intraspindle membranes existed in addition to the spindle envelope. Microtubule counts in serially cross-sectioned spindles of E. kuehniella revealed an about 6-fold increase in the mass of polymerized tubulin during the transition from spermatogonia to primary spermatocytes. The increase was 3.3-fold in O. thyellina and less than 3-fold in M. scalaris. The density of intraspindle membranes in E. kuehniella was higher than in O. thyelhna by factors of 1.8 to 3.0. The correlation between the amount of spindle membranes and the microtubule content of the spindle indicates a functional relationship. Spindle membranes are believed to influence microtubule stability via the regulation of the Ca2+ concentration within the spindle area. The high microtubule mass in spindles from Lepidoptera spermatocytes may result from the membrane-dependent lowering of the Ca2+ level within the spindles. Finally, an unconventional idea on the role of intraspindle membranes is offered. This concept is not intended to challenge the function of spindle-associated membranes as Ca2+-sequestrating compartments. Intraspindle membranes are considered as stuffing material in sheathed spindles. Membranous compartments reduce the free volume within the spindle. Thereby, monomeric tubulin is concentrated and the formation of microtubules is favoured.
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McClain, Ian J., Caroline Lustenberger, Peter Achermann, Jonathan M. Lassonde, Salome Kurth, and Monique K. LeBourgeois. "Developmental Changes in Sleep Spindle Characteristics and Sigma Power across Early Childhood." Neural Plasticity 2016 (2016): 1–9. http://dx.doi.org/10.1155/2016/3670951.
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Sleep spindles, a prominent feature of the non-rapid eye movement (NREM) sleep electroencephalogram (EEG), are linked to cognitive abilities. Early childhood is a time of rapid cognitive and neurophysiological maturation; however, little is known about developmental changes in sleep spindles. In this study, we longitudinally examined trajectories of multiple sleep spindle characteristics (i.e., spindle duration, frequency, integrated spindle amplitude, and density) and power in the sigma frequency range (10–16 Hz) across ages 2, 3, and 5 years (n=8; 3 males). At each time point, nocturnal sleep EEG was recorded in-home after 13-h of prior wakefulness. Spindle duration, integrated spindle amplitude, and sigma power increased with age across all EEG derivations (C3A2, C4A1, O2A1, and O1A2; allps < 0.05). We also found a developmental decrease in mean spindle frequency (p<0.05) but no change in spindle density with increasing age. Thus, sleep spindles increased in duration and amplitude but decreased in frequency across early childhood. Our data characterize early developmental changes in sleep spindles, which may advance understanding of thalamocortical brain connectivity and associated lifelong disease processes. These findings also provide unique insights into spindle ontogenesis in early childhood and may help identify electrophysiological features related to healthy and aberrant brain maturation.
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Uteng, Marianne, Christian Hentrich, Kota Miura, Peter Bieling, and Thomas Surrey. "Poleward transport of Eg5 by dynein–dynactin in Xenopus laevis egg extract spindles." Journal of Cell Biology 182, no. 4 (August 18, 2008): 715–26. http://dx.doi.org/10.1083/jcb.200801125.
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Molecular motors are required for spindle assembly and maintenance during cell division. How motors move and interact inside spindles is unknown. Using photoactivation and photobleaching, we measure mitotic motor movement inside a dynamic spindle. We find that dynein–dynactin transports the essential motor Eg5 toward the spindle poles in Xenopus laevis egg extract spindles, revealing a direct interplay between two motors of opposite directionality. This transport occurs throughout the spindle except at the very spindle center and at the spindle poles, where Eg5 remains stationary. The variation of Eg5 dynamics with its position in the spindle is indicative of position-dependent functions of this motor protein. Our results suggest that Eg5 drives microtubule flux by antiparallel microtubule sliding in the spindle center, whereas the dynein-dependent concentration of Eg5 outside the spindle center could contribute to parallel microtubule cross-linking. These results emphasize the importance of spatially differentiated functions of motor proteins and contribute to our understanding of spindle organization.
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Woodruff, Jeffrey B., David G. Drubin, and Georjana Barnes. "Mitotic spindle disassembly occurs via distinct subprocesses driven by the anaphase-promoting complex, Aurora B kinase, and kinesin-8." Journal of Cell Biology 191, no. 4 (November 15, 2010): 795–808. http://dx.doi.org/10.1083/jcb.201006028.
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The mitotic spindle is a complex and dynamic structure. Although much has been learned about how spindles assemble and mediate chromosome segregation, how spindles rapidly and irreversibly disassemble during telophase is less clear. We used synthetic lethal screens in budding yeast to identify mutants defective in spindle disassembly. Real-time, live cell imaging analysis of spindle disassembly was performed on nine mutants defective in this process. Results of this analysis suggest that spindle disassembly is achieved by mechanistically distinct but functionally overlapping subprocesses: disengagement of the spindle halves, arrest of spindle elongation, and initiation of interpolar microtubule depolymerization. These subprocesses are largely governed by the anaphase-promoting complex, Aurora B kinase, and kinesin-8. Combinatorial inhibition of these subprocesses yielded cells with hyperstable spindle remnants and dramatic defects in cell cycle progression, establishing that rapid spindle disassembly is crucial for cell proliferation.
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Shetty, M., A. Perera, M. Kadar, M. Davey, G. Nixon, L. Walter, and R. Horne. "O069 The effects of sleep disordered breathing on sleep spindle activity in children and the relationship with neurocognition." SLEEP Advances 3, Supplement_1 (October 1, 2022): A29. http://dx.doi.org/10.1093/sleepadvances/zpac029.068.
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Abstract Introduction Conventional sleep macro-architecture measures of sleep disruption have not been associated with the adverse neurocognitive sequelae of sleep disordered breathing (SDB). Sleep spindles protecting the sleeping brain from external sensory stimuli and can serve as markers of sleep integrity. We investigated the relationship between sleep spindles and sleep fragmentation and neurocognition across the spectrum of SDB in children. Methods Children 3-12y referred for clinical assessment of SDB and age matched control children from the community were recruited. Sleep spindles were identified manually during N2 and N3 sleep. Spindle activity was characterised as spindle number, spindle density (number of spindles/ h) and spindle intensity (spindle density x average spindle duration). The Stanford-Binet Intelligence Scales measured global intellectual ability and the NeuroPSYchological assessment (NEPSY-II) measured language, attention, visuospatial ability and sensorimotor skills. Results Children were grouped into control, Primary Snoring, Mild OSA and Moderate/severe OSA, N=10/ group. All measures of spindle activity were lower in the SDB groups compared to the Control children and this reached statistical significance for Mild OSA (p<0.05 for all). Spindle activity was not correlated with any measure of the Stanford-Binet. Overall, all measures of spindle activity were positively correlated with the Design Copy and the Inhibition Naming combined scale score and negatively correlated with Auditory Attention subscales of the NEPSY-II. Conclusion The reduced spindle activity observed in the children with SDB, particularly Mild OSA, indicates that sleep micro-architecture is disrupted and that this disruption may underpin the negative effects of SDB on attention, learning and memory.
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Gorgoni, Maurizio, Giulia Lauri, Ilaria Truglia, Susanna Cordone, Simone Sarasso, Serena Scarpelli, Anastasia Mangiaruga, et al. "Parietal Fast Sleep Spindle Density Decrease in Alzheimer’s Disease and Amnesic Mild Cognitive Impairment." Neural Plasticity 2016 (2016): 1–10. http://dx.doi.org/10.1155/2016/8376108.
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Several studies have identified two types of sleep spindles: fast (13–15 Hz) centroparietal and slow (11–13 Hz) frontal spindles. Alterations in spindle activity have been observed in Alzheimer’s disease (AD) and Mild Cognitive Impairment (MCI). Only few studies have separately assessed fast and slow spindles in these patients showing a reduction of fast spindle count, but the possible local specificity of this phenomenon and its relation to cognitive decline severity are not clear. Moreover, fast and slow spindle density have never been assessed in AD/MCI. We have assessed fast and slow spindles in 15 AD patients, 15 amnesic MCI patients, and 15 healthy elderly controls (HC). Participants underwent baseline polysomnographic recording (19 cortical derivations). Spindles during nonrapid eye movements sleep were automatically detected, and spindle densities of the three groups were compared in the derivations where fast and slow spindles exhibited their maximum expression (parietal and frontal, resp.). AD and MCI patients showed a significant parietal fast spindle density decrease, positively correlated with Minimental State Examination scores. Our results suggest that AD-related changes in spindle density are specific for frequency and location, are related to cognitive decline severity, and may have an early onset in the pathology development.
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Zou, Jianwei, Mark A. Hallen, Christine D. Yankel, and Sharyn A. Endow. "A microtubule-destabilizing kinesin motor regulates spindle length and anchoring in oocytes." Journal of Cell Biology 180, no. 3 (February 4, 2008): 459–66. http://dx.doi.org/10.1083/jcb.200711031.
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The kinesin-13 motor, KLP10A, destabilizes microtubules at their minus ends in mitosis and binds to polymerizing plus ends in interphase, regulating spindle and microtubule dynamics. Little is known about kinesin-13 motors in meiosis. In this study, we report that KLP10A localizes to the unusual pole bodies of anastral Drosophila melanogaster oocyte meiosis I spindles as well as spindle fibers, centromeres, and cortical microtubules. We frequently observe the pole bodies attached to cortical microtubules, indicating that KLP10A could mediate spindle anchoring to the cortex via cortical microtubules. Oocytes treated with drugs that suppress microtubule dynamics exhibit spindles that are reoriented more vertically to the cortex than untreated controls. A dominant-negative klp10A mutant shows both reoriented and shorter oocyte spindles, implying that, unexpectedly, KLP10A may stabilize rather than destabilize microtubules, regulating spindle length and positioning the oocyte spindle. By altering microtubule dynamics, KLP10A could promote spindle reorientation upon oocyte activation.
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Bird, Alexander W., and Anthony A. Hyman. "Building a spindle of the correct length in human cells requires the interaction between TPX2 and Aurora A." Journal of Cell Biology 182, no. 2 (July 28, 2008): 289–300. http://dx.doi.org/10.1083/jcb.200802005.
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To assemble mitotic spindles, cells nucleate microtubules from a variety of sources including chromosomes and centrosomes. We know little about how the regulation of microtubule nucleation contributes to spindle bipolarity and spindle size. The Aurora A kinase activator TPX2 is required for microtubule nucleation from chromosomes as well as for spindle bipolarity. We use bacterial artificial chromosome–based recombineering to introduce point mutants that block the interaction between TPX2 and Aurora A into human cells. TPX2 mutants have very short spindles but, surprisingly, are still bipolar and segregate chromosomes. Examination of microtubule nucleation during spindle assembly shows that microtubules fail to nucleate from chromosomes. Thus, chromosome nucleation is not essential for bipolarity during human cell mitosis when centrosomes are present. Rather, chromosome nucleation is involved in spindle pole separation and setting spindle length. A second Aurora A–independent function of TPX2 is required to bipolarize spindles.
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Nazarova, Elena, Eileen O'Toole, Susi Kaitna, Paul Francois, Mark Winey, and Jackie Vogel. "Distinct roles for antiparallel microtubule pairing and overlap during early spindle assembly." Molecular Biology of the Cell 24, no. 20 (October 15, 2013): 3238–50. http://dx.doi.org/10.1091/mbc.e13-05-0232.
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During spindle assembly, microtubules may attach to kinetochores or pair to form antiparallel pairs or interpolar microtubules, which span the two spindle poles and contribute to mitotic pole separation and chromosome segregation. Events in the specification of the interpolar microtubules are poorly understood. Using three-dimensional electron tomography and analysis of spindle dynamical behavior in living cells, we investigated the process of spindle assembly. Unexpectedly, we found that the phosphorylation state of an evolutionarily conserved Cdk1 site (S360) in γ-tubulin is correlated with the number and organization of interpolar microtubules. Mimicking S360 phosphorylation (S360D) results in bipolar spindles with a normal number of microtubules but lacking interpolar microtubules. Inhibiting S360 phosphorylation (S360A) results in spindles with interpolar microtubules and high-angle, antiparallel microtubule pairs. The latter are also detected in wild-type spindles <1 μm in length, suggesting that high-angle microtubule pairing represents an intermediate step in interpolar microtubule formation. Correlation of spindle architecture with dynamical behavior suggests that microtubule pairing is sufficient to separate the spindle poles, whereas interpolar microtubules maintain the velocity of pole displacement during early spindle assembly. Our findings suggest that the number of interpolar microtubules formed during spindle assembly is controlled in part through activities at the spindle poles.
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Jang, J. K., T. Rahman, and K. S. McKim. "The Kinesinlike Protein Subito Contributes to Central Spindle Assembly and Organization of the Meiotic Spindle in Drosophila Oocytes." Molecular Biology of the Cell 16, no. 10 (October 2005): 4684–94. http://dx.doi.org/10.1091/mbc.e04-11-0964.
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In the oocytes of many species, bipolar spindles form in the absence of centrosomes. Drosophila melanogaster oocyte chromosomes have a major role in nucleating microtubules, which precedes the bundling and assembly of these microtubules into a bipolar spindle. Here we present evidence that a region similar to the anaphase central spindle functions to organize acentrosomal spindles. Subito mutants are characterized by the formation of tripolar or monopolar spindles and nondisjunction of homologous chromosomes at meiosis I. Subito encodes a kinesinlike protein and associates with the meiotic central spindle, consistent with its classification in the Kinesin 6/MKLP1 family. This class of proteins is known to be required for cytokinesis, but our results suggest a new function in spindle formation. The meiotic central spindle appears during prometaphase and includes passenger complex proteins such as AurB and Incenp. Unlike mitotic cells, the passenger proteins do not associate with centromeres before anaphase. In the absence of Subito, central spindle formation is defective and AurB and Incenp fail to properly localize. We propose that Subito is required for establishing and/or maintaining the central spindle in Drosophila oocytes, and this substitutes for the role of centrosomes in organizing the bipolar spindle.
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McCoy, Kelsey M., Emily S. Tubman, Allison Claas, Damien Tank, Shelly Applen Clancy, Eileen T. O’Toole, Judith Berman, and David J. Odde. "Physical limits on kinesin-5–mediated chromosome congression in the smallest mitotic spindles." Molecular Biology of the Cell 26, no. 22 (November 5, 2015): 3999–4014. http://dx.doi.org/10.1091/mbc.e14-10-1454.
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A characteristic feature of mitotic spindles is the congression of chromosomes near the spindle equator, a process mediated by dynamic kinetochore microtubules. A major challenge is to understand how precise, submicrometer-scale control of kinetochore microtubule dynamics is achieved in the smallest mitotic spindles, where the noisiness of microtubule assembly/disassembly will potentially act to overwhelm the spatial information that controls microtubule plus end–tip positioning to mediate congression. To better understand this fundamental limit, we conducted an integrated live fluorescence, electron microscopy, and modeling analysis of the polymorphic fungal pathogen Candida albicans, which contains one of the smallest known mitotic spindles (<1 μm). Previously, ScCin8p (kinesin-5 in Saccharomyces cerevisiae) was shown to mediate chromosome congression by promoting catastrophe of long kinetochore microtubules (kMTs). Using C. albicans yeast and hyphal kinesin-5 (Kip1p) heterozygotes ( KIP1/kip1∆), we found that mutant spindles have longer kMTs than wild-type spindles, consistent with a less-organized spindle. By contrast, kinesin-8 heterozygous mutant ( KIP3/kip3∆) spindles exhibited the same spindle organization as wild type. Of interest, spindle organization in the yeast and hyphal states was indistinguishable, even though yeast and hyphal cell lengths differ by two- to fivefold, demonstrating that spindle length regulation and chromosome congression are intrinsic to the spindle and largely independent of cell size. Together these results are consistent with a kinesin-5–mediated, length-dependent depolymerase activity that organizes chromosomes at the spindle equator in C. albicans to overcome fundamental noisiness in microtubule self-assembly. More generally, we define a dimensionless number that sets a fundamental physical limit for maintaining congression in small spindles in the face of assembly noise and find that C. albicans operates very close to this limit, which may explain why it has the smallest known mitotic spindle that still manifests the classic congression architecture.
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Cande, W. Z., and K. McDonald. "Physiological and ultrastructural analysis of elongating mitotic spindles reactivated in vitro." Journal of Cell Biology 103, no. 2 (August 1, 1986): 593–604. http://dx.doi.org/10.1083/jcb.103.2.593.
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We have developed a simple procedure for isolating mitotic spindles from the diatom Stephanopyxis turris and have shown that they undergo anaphase spindle elongation in vitro upon addition of ATP. The isolated central spindle is a barrel-shaped structure with a prominent zone of microtubule overlap. After ATP addition greater than 75% of the spindle population undergoes distinct structural rearrangements: the spindles on average are longer and the two half-spindles are separated by a distinct gap traversed by only a small number of microtubules, the phase-dense material in the overlap zone is gone, and the peripheral microtubule arrays have depolymerized. At the ultrastructural level, we examined serial cross-sections of spindles after 1-, 5-, and 10-min incubations in reactivation medium. Microtubule depolymerization distal to the poles is confirmed by the increased number of incomplete, i.e., c-microtubule profiles specifically located in the region of overlap. After 10 min we see areas of reduced microtubule number which correspond to the gaps seen in the light microscope and an overall reduction in the number of half-spindle microtubules to about one-third the original number. The changes in spindle structure are highly specific for ATP, are dose-dependent, and do not occur with nonhydrolyzable nucleotide analogues. Spindle elongation and gap formation are blocked by 10 microM vanadate, equimolar mixtures of ATP and AMPPNP, and by sulfhydryl reagents. This process is not affected by nocodazole, erythro-9-[3-(2-hydroxynonyl)]adenine, cytochalasin D, and phalloidin. In the presence of taxol, the extent of spindle elongation is increased; however, distinct gaps still form between the two half-spindles. These results show that the response of isolated spindles to ATP is a complex process consisting of several discrete steps including initiation events, spindle elongation mechanochemistry, controlled central spindle microtubule plus-end depolymerization, and loss of peripheral microtubules. They also show that the microtubule overlap zone is an important site of ATP action and suggest that spindle elongation in vitro is best explained by a mechanism of microtubule-microtubule sliding. Spindle elongation in vitro cannot be accounted for by cytoplasmic forces pulling on the poles or by microtubule polymerization.
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Yamamoto, Takaharu G., Sonoko Watanabe, Anthony Essex, and Risa Kitagawa. "SPDL-1 functions as a kinetochore receptor for MDF-1 in Caenorhabditis elegans." Journal of Cell Biology 183, no. 2 (October 20, 2008): 187–94. http://dx.doi.org/10.1083/jcb.200805185.
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The spindle assembly checkpoint (SAC) ensures faithful chromosome segregation by delaying anaphase onset until all sister kinetochores are attached to bipolar spindles. An RNA interference screen for synthetic genetic interactors with a conserved SAC gene, san-1/MAD3, identified spdl-1, a Caenorhabditis elegans homologue of Spindly. SPDL-1 protein localizes to the kinetochore from prometaphase to metaphase, and this depends on KNL-1, a highly conserved kinetochore protein, and CZW-1/ZW10, a component of the ROD–ZW10–ZWILCH complex. In two-cell–stage embryos harboring abnormal monopolar spindles, SPDL-1 is required to induce the SAC-dependent mitotic delay and localizes the SAC protein MDF-1/MAD1 to the kinetochore facing away from the spindle pole. In addition, SPDL-1 coimmunoprecipitates with MDF-1/MAD1 in vivo. These results suggest that SPDL-1 functions in a kinetochore receptor of MDF-1/MAD1 to induce SAC function.
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Woodruff, Jeffrey B., David G. Drubin, and Georjana Barnes. "Spindle assembly requires complete disassembly of spindle remnants from the previous cell cycle." Molecular Biology of the Cell 23, no. 2 (January 15, 2012): 258–67. http://dx.doi.org/10.1091/mbc.e11-08-0701.
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Incomplete mitotic spindle disassembly causes lethality in budding yeast. To determine why spindle disassembly is required for cell viability, we used live-cell microscopy to analyze a double mutant strain containing a conditional mutant and a deletion mutant compromised for the kinesin-8 and anaphase-promoting complex-driven spindle-disassembly pathways (td-kip3 and doc1Δ, respectively). Under nonpermissive conditions, spindles in td-kip3 doc1Δ cells could break apart but could not disassemble completely. These cells could exit mitosis and undergo cell division. However, the daughter cells could not assemble functional, bipolar spindles in the ensuing mitosis. During the formation of these dysfunctional spindles, centrosome duplication and separation, as well as recruitment of key midzone-stabilizing proteins all appeared normal, but microtubule polymerization was nevertheless impaired and these spindles often collapsed. Introduction of free tubulin through episomal expression of α- and β-tubulin or introduction of a brief pulse of the microtubule-depolymerizing drug nocodazole allowed spindle assembly in these td-kip3 doc1Δ mutants. Therefore we propose that spindle disassembly is essential for regeneration of the intracellular pool of assembly-competent tubulin required for efficient spindle assembly during subsequent mitoses of daughter cells.
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Masuda, H., T. Hirano, M. Yanagida, and W. Z. Cande. "In vitro reactivation of spindle elongation in fission yeast nuc2 mutant cells." Journal of Cell Biology 110, no. 2 (February 1, 1990): 417–25. http://dx.doi.org/10.1083/jcb.110.2.417.
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To investigate the mechanisms of spindle elongation and chromosome separation in the fission yeast Schizosaccharomyces pombe, we have developed an in vitro assay using a temperature-sensitive mutant strain, nuc2. At the restrictive temperature, nuc2 cells are arrested at a metaphase-like stage with short spindles and condensed chromosomes. After permeabilization of spheroplasts of the arrested cells, spindle elongation was reactivated by addition of ATP and neurotubulin both at the restrictive and the permissive temperatures, but chromosome separation was not. This suggests that the nuc2 cells are impaired in function at a stage before sister chromatid disjunction. Spindle elongation required both ATP and exogenous tubulin and was inhibited by adenylyl imidodiphosphate (AMPPNP) or vanadate. The ends of yeast half-spindle microtubules pulse-labeled with biotinylated tubulin moved past each other during spindle elongation and a gap formed between the original half-spindles. These results suggest that the primary mechanochemical event responsible for spindle elongation is the sliding apart of antiparallel microtubules of the two half-spindles.
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McCullar, Katie, David Barker, John McGeary, Caroline Gredvig-Ardito, Jared Saletin, and Mary Carskadon. "0048 Investigating the Effects of Consecutive Nights of Pre-sleep Alcohol Use on Sleep Spindle Density and Distribution." SLEEP 47, Supplement_1 (April 20, 2024): A22. http://dx.doi.org/10.1093/sleep/zsae067.0048.
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Abstract Introduction We previously reported the impact of consecutive nights of alcohol on sleep macrostructure variables. Sleep spindle density and distribution, however, remain unexamined in response to alcohol. This report tests the hypothesis that sleep spindle density will be lower following pre-sleep alcohol and most affected early in the sleep period. Methods Thirty (15F; ages=22-57, mean=33) healthy adult participants took part in a crossover, within-subjects study with two 3-night in-lab conditions: a Mixer + Alcohol condition targeted a BrAC of 0.08 mg/L and a counter-balanced Mixer-only condition; conditions were separated by ≥ 3 days. All drinking ended 1 hour before lights out. Sleep EEG derivations C3-A2 and C4-A1 were submitted to a validated sleep spindle detection algorithm (Ferrarelli, et al., 2007). Sleep spindle density in NREM sleep (#/min; Stages 2-4) was averaged between channels and submitted to a series of linear mixed-effects models. A first, 2x3 model examined the factors beverage and night (Nights 1-3) on NREM spindle density. Next, data were stratified into thirds of the night, with the model repeated for each third. Results A main effect of alcohol on sleep spindle density across the whole night was identified (F(1,145)=5.33, p=.022). Sleep spindle density was lower on Mixer + Alcohol nights (1.6±0.7 spindles/min) vs Mixer-only (1.9±0.5 spindles/min). No effect of Night(1-3) or interaction of beverage and night was observed (p’s>.05). Next, we identified opposing effects of alcohol on sleep spindle density in early vs. late sleep. In the first third of the night sleep spindle density was lower on Mixer + Alcohol nights (0.4±0.3 spindles/min) compared to Mixer-only (0.9 ± 0.3 spindles/min; F(1,145)=8.33, p<.01)). In the final third of the night, spindle density was conversely higher in the Mixer + Alcohol nights (2.9±1.1 spindles/min) compared to Mixer-only (2.1±0.8 spindles/min; F(1,145)=4.1, p=.03)). No other effects were identified (p’s>.05). Conclusion Alcohol use prior to sleep resulted in reduced sleep spindle density early in the night and higher spindle density late in the night. No effects of consecutive nights were observed. These differences add to a growing discussion of the impact that alcohol has on sleep physiology across the night. Support (if any) R01AA025593
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Hara, Yuki, and Akatsuki Kimura. "An allometric relationship between mitotic spindle width, spindle length, and ploidy in Caenorhabditis elegans embryos." Molecular Biology of the Cell 24, no. 9 (May 2013): 1411–19. http://dx.doi.org/10.1091/mbc.e12-07-0528.
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The mitotic spindle is a diamond-shaped molecular apparatus crucial for chromosomal segregation. The regulation of spindle length is well studied, but little is known about spindle width. Previous studies suggested that the spindle can self-organize to maintain a constant aspect ratio between its length and width against physical perturbations. Here we determine the widths of metaphase spindles of various sizes observed during embryogenesis in Caenorhabditis elegans, including small spindles obtained by knocking down the tpxl-1 or spd-2 gene. The spindle width correlates well with the spindle length, but the aspect ratio between the spindle length and spindle width is not constant, indicating an allometric relationship between these parameters. We characterize how DNA quantity (ploidy) affects spindle shape by using haploid and polyploid embryos. We find that the length of the hypotenuse, which corresponds to the distance from the apex of the metaphase plate to the spindle pole, remains constant in each cell stage, regardless of ploidy. On the basis of the quantitative data, we deduce an allometric equation that describes the spindle width as a function of the length of the hypotenuse and ploidy. On the basis of this equation, we propose a force-balance model to determine the spindle width.
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Hogan, C. J., L. Stephens, T. Shimizu, and W. Z. Cande. "Physiological evidence for involvement of a kinesin-related protein during anaphase spindle elongation in diatom central spindles." Journal of Cell Biology 119, no. 5 (December 1, 1992): 1277–86. http://dx.doi.org/10.1083/jcb.119.5.1277.
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We have developed a new model system for studying spindle elongation in vitro using the pennate, marine diatom Cylindrotheca fusiformis. C. fusiformis can be grown in bulk to high densities while in log phase growth and synchronized by a simple light/dark regime. Isolated spindles can be attained in quantities sufficient for biochemical analysis and spindle tubulin is approximately 5% of the total protein present. The spindle isolation procedure results in a 10-fold enrichment of diatom tubulin and a calculated 40-fold increase in spindle protein. Isolated spindles or spindles in permeabilized cells can elongate in vitro by the same mechanism and with the same pharmacological sensitivities as described for other anaphase B models (Cande and McDonald, 1986; Masuda et al., 1990). Using this model, in vitro spindle elongation rate profiles were developed for a battery of nucleotide triphosphates and ATP analogs. The relative rates of spindle elongation produced by various nucleotide triphosphates parallel relative rates seen for kinesin-based motility in microtubule gliding assays. Likewise ATP analogs that allow discrimination between myosin-, dynein-, and kinesin-mediated motility produce relative spindle elongation rates characteristic of kinesin motility. Also, isolated spindle fractions are enriched for a kinesin related protein as identified by a peptide antibody against a conserved region of the kinesin superfamily. These data suggest that kinesin-like motility contributes to spindle elongation during anaphase B of mitosis.
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Yu, Hechun, Wenchao Li, Jin Wang, Suxiang Zhang, Xiucheng Cao, Renzong Wang, Guoqing Zhang, and Xiaolong Yin. "Research on the Effect of Tip Surface Coatings on High-Speed Spindles’ Noise." Coatings 12, no. 6 (June 6, 2022): 783. http://dx.doi.org/10.3390/coatings12060783.
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The contact interface between the stator and the rotor tip of the spindle could be destructed when the spindle is rotating continually at high speed, which will cause strong noise and severe vibration. In order to reduce the sound pressure level of the noise generated by the rotating spindle, three different coating materials, that is, Al-Ti-Cr-C, Ti-C and DLC, were applied to the rotor tip surface of the spindle. The effects of the coating materials on the sound pressure levels of the rotating spindles were studied by using the treated spindles and the untreated spindles. Results showed that compared with Coating Al-Ti-Cr-C, the Coating Ti-C containing only the two main elements of Ti and C produces the smallest sound pressure level in the experiment speed range; the surface roughness of Coating DLC is smaller, but the sound pressure level of the entire spindle becomes larger than Coating Ti-C; the sound pressure level of the spindles with surface coating treatment is obviously lower than that of the spindles without coating treatment. The research results can provide basic data for the design and production of noiseless spinning spindles.
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Xue, Zhihui, Changzhen Liu, Wenqing Shi, Yongjie Miao, Yi Shen, Ding Tang, Yafei Li, et al. "OsMTOPVIB is required for meiotic bipolar spindle assembly." Proceedings of the National Academy of Sciences 116, no. 32 (July 24, 2019): 15967–72. http://dx.doi.org/10.1073/pnas.1821315116.
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The organization of microtubules into a bipolar spindle is essential for chromosome segregation. Both centrosome and chromatin-dependent spindle assembly mechanisms are well studied in mouse, Drosophila melanogaster, and Xenopus oocytes; however, the mechanism of bipolar spindle assembly in plant meiosis remains elusive. According to our observations of microtubule assembly in Oryza sativa, Zea mays, Arabidopsis thaliana, and Solanum lycopersicum, we propose that a key step of plant bipolar spindle assembly is the correction of the multipolar spindle into a bipolar spindle at metaphase I. The multipolar spindles failed to transition into bipolar ones in OsmtopVIB with the defect in double-strand break (DSB) formation. However, bipolar spindles were normally assembled in several other mutants lacking DSB formation, such as Osspo11-1, pair2, and crc1, indicating that bipolar spindle assembly is independent of DSB formation. We further revealed that the mono-orientation of sister kinetochores was prevalent in OsmtopVIB, whereas biorientation of sister kinetochores was frequently observed in Osspo11-1, pair2, and crc1. In addition, mutations of the cohesion subunit OsREC8 resulted in biorientation of sister kinetochores as well as bipolar spindles even in the background of OsmtopVIB. Therefore, we propose that biorientation of the kinetochore is required for bipolar spindle assembly in the absence of homologous recombination.
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Sluder, G., E. A. Thompson, F. J. Miller, J. Hayes, and C. L. Rieder. "The checkpoint control for anaphase onset does not monitor excess numbers of spindle poles or bipolar spindle symmetry." Journal of Cell Science 110, no. 4 (February 15, 1997): 421–29. http://dx.doi.org/10.1242/jcs.110.4.421.
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Exit from mitosis in animal cells is substantially delayed when spindle assembly is inhibited, spindle bipolarity is disrupted, or when a monopolar spindle is formed. These observations have led to the proposal that animal cells have a ‘spindle assembly’ checkpoint for the metaphase-anaphase transition that monitors bipolar spindle organization. However, the existence of such a checkpoint is uncertain because perturbations in spindle organization can produce unattached kinetochores, which by themselves are known to delay anaphase onset. In this study we have tested if cells monitor bipolar spindle organization, independent of kinetochore attachment, by analyzing the duration of mitosis in sea urchin zygotes and vertebrate somatic cells containing multipolar spindles in which all kinetochores are attached to spindle poles. We found that sea urchin zygotes containing tripolar or tetrapolar spindles progressed from nuclear envelope breakdown to anaphase onset with normal timing. We also found that the presence of supernumerary, unpaired spindle poles did not greatly prolong mitosis. Observation of untreated PtK1 cells that formed tripolar or tetrapolar spindles revealed that they progressed through mitosis, on average, at the normal rate. More importantly, the interval between the bipolar attachment of the last monooriented chromosome and anaphase onset was normal. Thus, neither of these cell types can detect the presence of gross aberrations in spindle architecture that inevitably lead to aneuploidy. We conclude that animal cells do not have a checkpoint for the metaphase-anaphase transition that monitors defects in spindle architecture independent of the checkpoint that monitors kinetochore attachment to the spindle. For dividing cells in which spindle microtubule assembly is not experimentally compromised, we propose that the completion of kinetochore attachment is the event which limits the time of the metaphase-anaphase transition.
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Leslie, R. J. "Chromosomes attain a metaphase position on half-spindles in the absence of an opposing spindle pole." Journal of Cell Science 103, no. 1 (September 1, 1992): 125–30. http://dx.doi.org/10.1242/jcs.103.1.125.
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To examine the relative roles of chromosomes, spindle poles and microtubules in the formation of the metaphase spindle and metakinesis, I have experimentally placed an extra centrosome-free pronucleus close to a forming bipolar spindle in a living cell. The chromosomes from the extra nucleus induce the formation of an extra half-spindle from one pole of the otherwise normal bipolar spindle with chromosomes positioned at the putative metaphase plate. I conclude that chromosomes determine the location of half-spindles by sustaining a higher than normal density of microtubules. These results are surprising for two reasons: first, because previous in vivo experiments in tissue culture cells show that mono-oriented chromosomes with functional attachments to spindle microtubules do not support half-spindle formation but oscillate unstably or move to one spindle pole. Additionally, the generally accepted view is that chromosomes attain a metastable condition at the metaphase plate as a result of a balance between forces directed to opposite spindle poles. However, our observation that chromosomes on extra half-spindles attain a metastable position in the absence of an opposing spindle pole, suggests that Ostergren's model does not account for metakinesis in sea urchin embryos.
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Simon, Katharine, Neal Nakra, Sara Mednick, Paola Malerba, and Marni Nagel. "0191 Characteristics of sleep spindles across development in males with Duchenne/Becker Muscular Dystrophy Disorder." Sleep 45, Supplement_1 (May 25, 2022): A87—A88. http://dx.doi.org/10.1093/sleep/zsac079.189.
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Abstract Introduction Sleep supports cognition, in particular, the consolidation of memories. Sleeping brain rhythms, such as slow oscillations (1hz) and spindles (9-15 Hz), play a key role in facilitating this consolidation. Our prior research reported age-associated declines in slow oscillations in Duchenne and Becker Muscular Dystrophy (DMD/BMD) (Simon et al., 2020). Here, we characterize age-associated changes in sleep spindle characteristics across development in this group. Methods Following our 2020 analysis, we retrospectively analyzed the clinical sleep studies of 28 DMD/BMD males (Age span: 4 to 20 years). We applied our spindle detection algorithm to six electrodes (F3, F4, C3, C4, 01, O2). We assessed spindle density, frequency, and amplitude based on age (child, early adolescent, and late adolescent). Results We conducted rmANOVAs to evaluate each spindle characteristics using within-factors (Stage and Electrode) and between-factor (Age). We found significantly more spindles with longer durations in N2 than N3; greater spindle density at frontal compared to occipital regions; and higher amplitudes at central compared to frontal sites. We found no age-associated changes in these spindle metrics. We did find an age-associated change in the frequency of spindles, with significantly greater average spindle amplitude increasing significantly with age. Conclusion In line with prior research, we found more spindles in N2 than N3 and greater spindle density at frontal compared to posterior electrodes. In contrast to our previous research demonstrating age-associated declines in slow oscillations, our current analyses show minimal age-associated changes in spindle characteristics from 4 to 20 years. Further analysis is required to assess for age-associated changes in spindle-slow oscillation coupling occur across development. Our findings have implications for functional changes in sleep-dependent cognition mechanisms across development in BMD/DMD. Support (If Any)
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Savoian, Matthew S., and David M. Glover. "Differing requirements for Augmin in male meiotic and mitotic spindle formation in Drosophila." Open Biology 4, no. 5 (May 2014): 140047. http://dx.doi.org/10.1098/rsob.140047.
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Animal cells divide using a microtubule-based, bipolar spindle. Both somatic, mitotic cells and sperm-producing male meiotic spermatocytes use centrosome-dependent and acentrosomal spindle-forming mechanisms. Here, we characterize the largely undefined, centrosome-independent spindle formation pathway used during male meiosis. Our live and fixed cell analyses of Drosophila spermatocytes reveal that acentrosomal microtubules are nucleated at kinetochores and in the vicinity of chromatin and that together these assemble into functional spindles. Mutational studies indicate that γ-tubulin and its extra-centrosomal targeting complex, Augmin, are vital for this process. In addition, Augmin facilitates efficient spindle assembly in the presence of centrosomes. In contrast to the pronounced recruitment of Augmin on spindles in other cell types, the complex is absent from those of spermatocytes but does accumulate on kinetochores. Polo kinase facilitates this kinetochore recruitment while inhibiting Augmin's spindle association, and this in turn dictates γ-tubulin distribution and spindle density. Polo's negative regulation of Augmin in male meiosis contrasts with its requirement in loading Augmin along mitotic spindles in somatic Drosophila cells. Together our data identify a novel mechanism of acentrosomal spindle formation in spermatocytes and reveal its divergence from that used in mitotic cells.
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Sluder, G., and D. A. Begg. "Experimental analysis of the reproduction of spindle poles." Journal of Cell Science 76, no. 1 (June 1, 1985): 35–51. http://dx.doi.org/10.1242/jcs.76.1.35.
Full textAbstract:
We have investigated the functional properties of the mechanisms that control the reproduction of spindle poles in fertilized sea-urchin eggs. By prolonging mitosis by three independent means, we show that a spindle pole can split during mitosis into two functional poles of normal appearance. However, these poles have only half the normal reproductive capacity; each daughter cell that receives a split pole, always forms a monopolar spindle at the next division. Each monopolar spindle appears to be exactly half of a spindle because two of them can come together to form a functional bipolar spindle of normal appearance. The poles of such spindles show normal reproduction in subsequent divisions. By following the development of individual cells with monopolar spindles, we show that such a cell can stay in mitosis longer than normal, and the single pole splits into two asters, which move apart to give a functional bipolar spindle. The poles of such a spindle have only half the normal reproductive capacity, because the two daughters of the cell always form monopolar spindles at the next mitosis. This novel cycle of development is often repeated. The occurrence of such phenomena does not depend upon the method used to induce monopolar spindles. These results show that each normal pole has two polar determinants. The results also demonstrate that the reproduction of spindle poles consists of three distinct events: splitting of the polar determinants, physical separation of the two determinants, and duplication of the determinants to return the pole to a duplex state. Splitting and duplication are distinct events because they can be experimentally put out of phase with each other for several cell cycles.
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Lin, Chiou-Hong, Chi-Kuo Hu, and Hsiu-Ming Shih. "Clathrin heavy chain mediates TACC3 targeting to mitotic spindles to ensure spindle stability." Journal of Cell Biology 189, no. 7 (June 21, 2010): 1097–105. http://dx.doi.org/10.1083/jcb.200911120.
Full textAbstract:
Mitotic spindles play essential roles in chromosome congression and segregation during mitosis. Aurora A regulates spindle assembly in part via phosphorylating human TACC3 on S558, which triggers TACC3 relocalization to mitotic spindles and stabilizes microtubules (MTs). In this study, we identified clathrin heavy chain (CHC) as an adaptor protein to recruit S558-phosphorylated TACC3 onto the spindle during mitosis for MT stabilization. CHC binds phospho-S558 TACC3 via its linker domain and first CHC repeat. CHC depletion or mutation on phospho-TACC3 binding abrogates TACC3 spindle relocalization. Depletion of either or both CHC and TACC3 yields similar defective phenotypes: loss of ch-TOG on spindles, disorganized spindles, and chromosome misalignment with comparable mitotic delay. Our findings elucidate the association between aurora A phosphorylation and spindle apparatus and demonstrate that regulation from aurora A is mediated by CHC in recruiting phospho-TACC3 and subsequently ch-TOG to mitotic spindles.
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Helmke, Kara J., and Rebecca Heald. "TPX2 levels modulate meiotic spindle size and architecture in Xenopus egg extracts." Journal of Cell Biology 206, no. 3 (July 28, 2014): 385–93. http://dx.doi.org/10.1083/jcb.201401014.
Full textAbstract:
The spindle segregates chromosomes in dividing eukaryotic cells, and its assembly pathway and morphology vary across organisms and cell types. We investigated mechanisms underlying differences between meiotic spindles formed in egg extracts of two frog species. Small Xenopus tropicalis spindles resisted inhibition of two factors essential for assembly of the larger Xenopus laevis spindles: RanGTP, which functions in chromatin-driven spindle assembly, and the kinesin-5 motor Eg5, which drives antiparallel microtubule (MT) sliding. This suggested a role for the MT-associated protein TPX2 (targeting factor for Xenopus kinesin-like protein 2), which is regulated by Ran and binds Eg5. Indeed, TPX2 was threefold more abundant in X. tropicalis extracts, and elevated TPX2 levels in X. laevis extracts reduced spindle length and sensitivity to Ran and Eg5 inhibition. Higher TPX2 levels recruited Eg5 to the poles, where MT density increased. We propose that TPX2 levels modulate spindle architecture through Eg5, partitioning MTs between a tiled, antiparallel array that promotes spindle expansion and a cross-linked, parallel architecture that concentrates MTs at spindle poles.
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Endow, S. A., and D. J. Komma. "Use of GFP Fusions to a Microtubule Motor Protein to Analyze Spindle Dynamics in Live Oocytes and Embryos of Drosophila." Microscopy and Microanalysis 3, S2 (August 1997): 127–28. http://dx.doi.org/10.1017/s1431927600007522.
Full textAbstract:
Ncd is a kinesin-related microtubule motor protein of Drosophila that plays essential roles in spindle assembly and function during meiosis in oocytes and mitosis in early embryos. Antibody staining experiments have localized the Ned motor protein to spindle fibers and spindle poles throughout the meiotic and early mitotic divisions, demonstrating that Ncd is a spindle motor.We have made ncd-gfp gene fusions with wild-type and S65T gfp and expressed the chimaeric genes in Drosophila to target GFP to the spindle. Transgenic Drosophila carrying the ncd-gfp gene fusions in an ncd null mutant background are wild type with respect to chromosome segregation, indicating that the Ncd-GFP fusion proteins can replace the function of wild-type Ncd. The Ncd-GFP fusion proteins in transgenic Drosophila are expressed under the regulation of the native ncd promoter.Analysis of live Drosophila oocytes and early embryos shows green fluorescent spindles, demonstrating association of Ncd-GFP with meiotic and mitotic spindles. In mitotic spindles, Ncd-GFP localizes to centrosomes (Fig. 1a) and spindle fibers (Fig. 1b).
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Connolly, Amy A., Valerie Osterberg, Sara Christensen, Meredith Price, Chenggang Lu, Kathy Chicas-Cruz, Shawn Lockery, Paul E. Mains, and Bruce Bowerman. "Caenorhabditis elegansoocyte meiotic spindle pole assembly requires microtubule severing and the calponin homology domain protein ASPM-1." Molecular Biology of the Cell 25, no. 8 (April 15, 2014): 1298–311. http://dx.doi.org/10.1091/mbc.e13-11-0687.
Full textAbstract:
In many animals, including vertebrates, oocyte meiotic spindles are bipolar but assemble in the absence of centrosomes. Although meiotic spindle positioning in oocytes has been investigated extensively, much less is known about their assembly. In Caenorhabditis elegans, three genes previously shown to contribute to oocyte meiotic spindle assembly are the calponin homology domain protein encoded by aspm-1, the katanin family member mei-1, and the kinesin-12 family member klp-18. We isolated temperature-sensitive alleles of all three and investigated their requirements using live-cell imaging to reveal previously undocumented requirements for aspm-1 and mei-1. Our results indicate that bipolar but abnormal oocyte meiotic spindles assemble in aspm-1(-) embryos, whereas klp-18(-) and mei-1(-) mutants assemble monopolar and apolar spindles, respectively. Furthermore, two MEI-1 functions—ASPM-1 recruitment to the spindle and microtubule severing—both contribute to monopolar spindle assembly in klp-18(-) mutants. We conclude that microtubule severing and ASPM-1 both promote meiotic spindle pole assembly in C. elegans oocytes, whereas the kinesin 12 family member KLP-18 promotes spindle bipolarity.
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Cha, B., L. Cassimeris, and D. L. Gard. "XMAP230 is required for normal spindle assembly in vivo and in vitro." Journal of Cell Science 112, no. 23 (December 1, 1999): 4337–46. http://dx.doi.org/10.1242/jcs.112.23.4337.
Full textAbstract:
XMAP230 is a high molecular mass microtubule-associated protein isolated from Xenopus oocytes and eggs, and has been recently shown to be a homolog of mammalian MAP4. Confocal immunofluorescence microscopy revealed that XMAP230 is associated with microtubules throughout the cell cycle of early Xenopus embryos. During interphase XMAP230 is associated with the radial arrays of microtubules and midbodies remaining from the previous division. During mitosis, XMAP230 is associated with both astral microtubules and microtubules of the central spindle. Microinjection of affinity-purified anti-XMAP230 antibody into blastomeres severely disrupted the assembly of mitotic spindles during the rapid cleavage cycles of early development. Both monopolar half spindles and bipolar spindles were assembled from XMAP230-depleted extracts in vitro. However, spindles assembled in XMAP230-depleted extracts exhibited a reduction in spindle width, reduced microtubule density, chromosome loss, and reduced acetylation of spindle MTs. Similar defects were observed in the spindles assembled in XMAP230-depleted extracts that had been cycled through interphase. Depletion of XMAP230 had no effect on the pole-to-pole length of spindles, and depletion of XMAP230 from both interphase and M-phase extracts had no effect on the rate of microtubule elongation. From these results, we conclude that XMAP230 plays an important role in normal spindle assembly, primarily by acting to stabilize spindle microtubules, and that the observed defects in spindle assembly may result from enhanced microtubule dynamics in XMAP230-depleted extracts.
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Saunamäki, Tiia, Eero Huupponen, Juho Loponen, and Sari-Leena Himanen. "CPAP Treatment Partly Normalizes Sleep Spindle Features in Obstructive Sleep Apnea." Sleep Disorders 2017 (2017): 1–10. http://dx.doi.org/10.1155/2017/2962479.
Full textAbstract:
Objective. Obstructive sleep apnea (OSA) decreases sleep spindle density and frequency. We evaluated the effects of continuous positive airway pressure (CPAP) treatment on different features of sleep spindles.Methods. Twenty OSA patients underwent two night polysomnographies in a diagnostic phase and one night polysomnography after 6 months of CPAP treatment. The control group comprised 20 healthy controls. Sleep spindles were analyzed by a previously developed automated method. Unilateral and bilateral spindles were identified in central and frontopolar brain locations. Spindle density and frequency were determined for the first and last half of the NREM time.Results. The density of bilateral central spindles, which did not change in the untreated OSA patients, increased towards the morning hours during CPAP treatment and in the controls. Central spindles did not become faster with sleep in OSA patients and the central spindles remained slow in the left hemisphere even with CPAP.Conclusion. CPAP treatment normalized spindle features only partially. The changes may be associated with deficits in thalamocortical spindle generating loops.Significance. This study shows that some sleep spindle changes persist after CPAP treatment in OSA patients. The association of these changes to daytime symptoms in OSA patients needs to be further evaluated.
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Masuda, H., K. L. McDonald, and W. Z. Cande. "The mechanism of anaphase spindle elongation: uncoupling of tubulin incorporation and microtubule sliding during in vitro spindle reactivation." Journal of Cell Biology 107, no. 2 (August 1, 1988): 623–33. http://dx.doi.org/10.1083/jcb.107.2.623.
Full textAbstract:
To study tubulin polymerization and microtubule sliding during spindle elongation in vitro, we developed a method of uncoupling the two processes. When isolated diatom spindles were incubated with biotinylated tubulin (biot-tb) without ATP, biot-tb was incorporated into two regions flanking the zone of microtubule overlap, but the spindles did not elongate. After biot-tb was removed, spindle elongation was initiated by addition of ATP. The incorporated biot-tb was found in the midzone between the original half-spindles. The extent and rate of elongation were increased by preincubation in biot-tb. Serial section reconstruction of spindles elongating in tubulin and ATP showed that the average length of half-spindle microtubules increased due to growth of microtubules from the ends of native microtubules. The characteristic packing pattern between antiparallel microtubules was retained even in the "new" overlap region. Our results suggest that the forces required for spindle elongation are generated by enzymes in the overlap zone that mediate the sliding apart of antiparallel microtubules, and that tubulin polymerization does not contribute to force generation. Changes in the extent of microtubule overlap during spindle elongation were affected by tubulin and ATP concentration in the incubation medium. Spindles continued to elongate even after the overlap zone was composed entirely of newly polymerized microtubules, suggesting that the enzyme responsible for microtubule translocation either is bound to a matrix in the spindle midzone, or else can move on one microtubule toward the spindle midzone and push another microtubule of opposite polarity toward the pole.
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Tucker, J. B., S. A. Mathews, K. A. Hendry, J. B. Mackie, and D. L. Roche. "Spindle microtubule differentiation and deployment during micronuclear mitosis in Paramecium." Journal of Cell Biology 101, no. 5 (November 1, 1985): 1966–76. http://dx.doi.org/10.1083/jcb.101.5.1966.
Full textAbstract:
Spindles underwent a 12-fold elongation before anaphase B was completed during the closed mitoses of micronuclei in Paramecium tetraurelia. Two main classes of spindle microtubules have been identified. A peripheral sheath of microtubules with diameters of 27-32 nm was found to be associated with the nuclear envelope and confined to the midportion of each spindle. Most of the other microtubules had diameters of approximately 24 nm and were present along the entire lengths of spindles. Nearly all of the 24-nm microtubules were eliminated from spindle midportions (largely because of microtubule disassembly) at a relatively early stage of spindle elongation. Disassembly of some of these microtubules also occurred at the ends of spindles. About 60% of the total microtubule content of spindles was lost at this stage. Most, perhaps all, peripheral sheath microtubules remained intact. Many of them detached from the nuclear envelope and regrouped to form a compact microtubule bundle in the spindle midportion. There was little, if any, further polymerization of 24-nm microtubules after the disassembly phase. Polymerization of microtubules with diameters of 27-32 nm continued as spindle elongation progressed. Most microtubules in the midportions of well-elongated spindles were constructed from 14-16 protofilaments. A few 24-nm microtubules with 13 protofilaments were also present. The implications of these findings for spatial control of microtubule assembly, disassembly, positioning, and membrane association, that apparently discriminate between microtubules with different protofilament numbers have been explored. The possibility that microtubule sliding occurs during spindle elongation has also been considered.
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Brecher, C., M. Fey, J. Falker, and B. Möller. "Externe Dämpfung bei Hochgeschwindigkeitsspindeln*/External damping in high speed spindles - Comparative investigation of the influence of a damping bush on the stability behavior during milling." wt Werkstattstechnik online 105, no. 05 (2015): 257–62. http://dx.doi.org/10.37544/1436-4980-2015-05-9.
Full textAbstract:
Die dynamischen Eigenschaften der Maschinenstruktur sowie der Hauptspindel bestimmen maßgeblich das dynamische Prozessverhalten von Werkzeugmaschinen. Über eine gezielte Dämpfung an den Lagerstellen der Spindel soll die stabile Schnitttiefe erhöht werden. In diesem Fachbeitrag wird der Einfluss einer Dämpfungsbuchse am Loslagersitz auf das statische, dynamische und das Bearbeitungsverhalten durch die vergleichende Untersuchung zweier Hochgeschwindigkeitsspindeln betrachtet. The dynamic process behavior of machine tools depends on both the characteristics of the machine structure and the main spindle. By means of an additional damping of the bearing bushes, the stable cutting depth of the main spindle is to be increased. In this article, the influence of a damping bush at the floating bearing seat on the static, dynamic and stability behavior is investigated by comparing two high speed spindles.