scholarly journals Self-organization of kinetochore-fibers in human mitotic spindles

2021 ◽  
Author(s):  
William Conway ◽  
Robert Kiewisz ◽  
Gunar Fabig ◽  
Colm P Kelleher ◽  
Hai-Yin Wu ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
De Novo ◽  
Electron Tomography ◽  
Polarized Light ◽  
Eukaryotic Cell ◽  
The Self ◽  
Self Organization ◽  
Macromolecular Complex ◽  
Biophysical Modeling ◽  
Mitotic Spindles

During eukaryotic cell division, chromosomes are linked to microtubules (MTs) in the spindle by a macromolecular complex called the kinetochore. The bound kinetochore microtubules (KMTs) are crucial to ensuring accurate chromosome segregation. Recent electron tomography reconstructions (Kiewisz et al. 2021) captured the positions and configurations of every MT in human mitotic spindles, revealing that many KMTs in these spindles do not reach the pole. Here, we investigate the processes that give rise to this distribution of KMTs using a combination of analysis of the electron tomography reconstructions, photoconversion experiments, quantitative polarized light microscopy, and biophysical modeling. Our results indicate that in metaphase, KMTs grow away from the kinetochores along well-defined trajectories, continually decreasing in speed as they approach the poles. The locations of KMT minus ends, and the turnover and movements of tubulin in KMTs, are consistent with models in which KMTs predominately nucleate de novo at kinetochores and are inconsistent with substantial numbers of non-KMTs being recruited to the kinetochore in metaphase. Taken together, this work leads to a mathematical model of the self-organization of kinetochore-fibers in human mitotic spindles.

scholarly journals Katanin controls mitotic and meiotic spindle length

2006 ◽  
Vol 175 (6) ◽  
pp. 881-891 ◽  
Author(s):  
Karen McNally ◽  
Anjon Audhya ◽  
Karen Oegema ◽  
Francis J. McNally
Keyword(s):  
Chromosome Segregation ◽  
Eukaryotic Cell ◽  
Meiotic Spindle ◽  
Mitotic Spindles ◽  
Wild Type ◽  
Female Meiosis ◽  
C Elegans ◽  
Microtubule Severing ◽  
Spindle Poles ◽  
Type C

Accurate control of spindle length is a conserved feature of eukaryotic cell division. Lengthening of mitotic spindles contributes to chromosome segregation and cytokinesis during mitosis in animals and fungi. In contrast, spindle shortening may contribute to conservation of egg cytoplasm during female meiosis. Katanin is a microtubule-severing enzyme that is concentrated at mitotic and meiotic spindle poles in animals. We show that inhibition of katanin slows the rate of spindle shortening in nocodazole-treated mammalian fibroblasts and in untreated Caenorhabditis elegans meiotic embryos. Wild-type C. elegans meiotic spindle shortening proceeds through an early katanin-independent phase marked by increasing microtubule density and a second, katanin-dependent phase that occurs after microtubule density stops increasing. In addition, double-mutant analysis indicated that γ-tubulin–dependent nucleation and microtubule severing may provide redundant mechanisms for increasing microtubule number during the early stages of meiotic spindle assembly.

scholarly journals Three-dimensional structure of the kinetochore-fibers in human mitotic spindles

2021 ◽  
Author(s):  
Robert Kiewisz ◽  
Gunar Fabig ◽  
William Conway ◽  
Daniel Needleman ◽  
Thomas Muller-Reichert
Keyword(s):  
Mammalian Cells ◽  
Large Scale ◽  
Electron Tomography ◽  
Three Dimensional ◽  
Spindle Pole ◽  
Dimensional Structure ◽  
Biophysical Modeling ◽  
Mitotic Spindles ◽  
Spindle Poles ◽  
Physical Linkage

During cell division, kinetochore microtubules (KMTs) provide a physical linkage between the spindle poles and the chromosomes. KMTs in mammalian cells are organized into bundles, so-called kinetochore-fibers (k-fibers), but the ultrastructure of these fibers is currently not well characterized. Here we show by large-scale electron tomography that each k-fiber in HeLa cells in metaphase is composed of approximately nine KMTs, only half of which reach the spindle pole. Our comprehensive reconstructions allowed us to analyze the three-dimensional (3D) morphology of k-fibers in detail, and we find that they exhibit remarkable variation. K-fibers display differences in circumference and KMT density along their length, with the pole-facing side showing a splayed-out appearance. We further observed that the association of KMTs with non-KMTs predominantly occurs in the spindle pole regions. Our 3D reconstructions have implications for models of KMT behavior and k-fiber self-organization as covered in a parallel publication applying complementary live-cell imaging in combination with biophysical modeling (Conway et al., 2021). The presented data will also serve as a resource for further studies on mitosis in human cells.

scholarly journals Bod1, a novel kinetochore protein required for chromosome biorientation

2007 ◽  
Vol 179 (2) ◽  
pp. 187-197 ◽  
Author(s):  
Iain M. Porter ◽  
Sarah E. McClelland ◽  
Guennadi A. Khoudoli ◽  
Christopher J. Hunter ◽  
Jens S. Andersen ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Hela Cells ◽  
Aurora B ◽  
Macromolecular Complex ◽  
Mitotic Spindles ◽  
Kinetochore Protein ◽  
Spindle Poles ◽  
Interfering Rna ◽  
Rna Depletion

We have combined the proteomic analysis of Xenopus laevis in vitro–assembled chromosomes with RNA interference and live cell imaging in HeLa cells to identify novel factors required for proper chromosome segregation. The first of these is Bod1, a protein conserved throughout metazoans that associates with a large macromolecular complex and localizes with kinetochores and spindle poles during mitosis. Small interfering RNA depletion of Bod1 in HeLa cells produces elongated mitotic spindles with severe biorientation defects. Bod1-depleted cells form syntelic attachments that can oscillate and generate enough force to separate sister kinetochores, suggesting that microtubule–kinetochore interactions were intact. Releasing Bod1-depleted cells from a monastrol block increases the frequency of syntelic attachments and the number of cells displaying biorientation defects. Bod1 depletion does not affect the activity or localization of Aurora B but does cause mislocalization of the microtubule depolymerase mitotic centromere- associated kinesin and prevents its efficient phosphorylation by Aurora B. Therefore, Bod1 is a novel kinetochore protein that is required for the detection or resolution of syntelic attachments in mitotic spindles.

scholarly journals Influence of Salt on the Self-Organization in Solutions of Star-Shaped Poly-2-alkyl-2-oxazoline and Poly-2-alkyl-2-oxazine on Heating

Polymers ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1152
Author(s):  
Tatyana Kirila ◽  
Anna Smirnova ◽  
Alla Razina ◽  
Andrey Tenkovtsev ◽  
Alexander Filippov
Keyword(s):  
Phase Separation ◽  
Salt Concentration ◽  
Monomer Unit ◽  
Salt Content ◽  
The Self ◽  
Self Organization ◽  
Phase Separation Temperature ◽  
The Core ◽  
Separation Temperature ◽  
Water Salt

The water–salt solutions of star-shaped six-arm poly-2-alkyl-2-oxazines and poly-2-alkyl-2-oxazolines were studied by light scattering and turbidimetry. The core was hexaaza[26]orthoparacyclophane and the arms were poly-2-ethyl-2-oxazine, poly-2-isopropyl-2-oxazine, poly-2-ethyl-2-oxazoline, and poly-2-isopropyl-2-oxazoline. NaCl and N-methylpyridinium p-toluenesulfonate were used as salts. Their concentration varied from 0–0.154 M. On heating, a phase transition was observed in all studied solutions. It was found that the effect of salt on the thermosensitivity of the investigated stars depends on the structure of the salt and polymer and on the salt content in the solution. The phase separation temperature decreased with an increase in the hydrophobicity of the polymers, which is caused by both a growth of the side radical size and an elongation of the monomer unit. For NaCl solutions, the phase separation temperature monotonically decreased with growth of salt concentration. In solutions with methylpyridinium p-toluenesulfonate, the dependence of the phase separation temperature on the salt concentration was non-monotonic with minimum at salt concentration corresponding to one salt molecule per one arm of a polymer star. Poly-2-alkyl-2-oxazine and poly-2-alkyl-2-oxazoline stars with a hexaaza[26]orthoparacyclophane core are more sensitive to the presence of salt in solution than the similar stars with a calix[n]arene branching center.

scholarly journals Modification of Mechanical Properties of High-Strength Titanium Alloys VT23 and VT23M Due to Impact-Oscillatory Loading

Metals ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 80 ◽  
Author(s):  
Mykola Chausov ◽  
Janette Brezinová ◽  
Andrii Pylypenko ◽  
Pavlo Maruschak ◽  
Liudmyla Titova ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Titanium Alloys ◽  
High Strength ◽  
The Self ◽  
Self Organization ◽  
Two Phase ◽  
Rolled Metal ◽  
Technological Method ◽  
Equilibrium Processes ◽  
Production Conditions

A simple technological method is proposed and tested experimentally, which allows for the improvement of mechanical properties in sheet two-phase high-strength titanium alloys VT23 and VT23M on the finished product (rolled metal), due to impact-oscillatory loading. Under impact-oscillatory loading and dynamic non-equilibrium processes (DNP) are realized in titanium alloys, leading to the self-organization of the structure. As a result, the mechanical properties of titanium alloys vary significantly with subsequent loading after the realization of DNP. In this study, the test modes are found, which can be used in the production conditions.

scholarly journals Compact Photonic Crystal Polarization Beam Splitter Based on the Self-Collimation Effect

Photonics ◽  
2021 ◽  
Vol 8 (6) ◽  
pp. 198
Author(s):  
Geyu Tang ◽  
Huamao Huang ◽  
Yuqi Liu ◽  
Hong Wang
Keyword(s):  
Optical Communications ◽  
Beam Splitter ◽  
Extinction Ratio ◽  
Polarized Light ◽  
The Self ◽  
Polarization Beam Splitter ◽  
Optical Interconnection ◽  
Beam Splitting ◽  
Beam Splitters ◽  
Polarization Extinction Ratio

We propose a new compact polarization beam splitter based on the self-collimation effect of two-dimensional photonic crystals and photonic bandgap characteristics. The device is composed of a rectangular air holes-based polarization beam splitting structure and circular air holes-based self-collimating structure. By inserting the polarization beam splitting structure into the self-collimating structure, the TE and TM polarized lights are orthogonally separated at their junction. When the number of rows in the hypotenuse of the inserted rectangular holes is 5, the transmittance of TE polarized light at 1550 nm is 95.4% and the corresponding polarization extinction ratio is 23 dB; on the other hand, the transmittance of TM polarized light is 88.5% and the corresponding polarization extinction ratio is 37 dB. For TE and TM polarized lights covering a 100 nm bandwidth, the TE and TM polarization extinction ratios are higher than 18 dB and 30 dB, respectively. Compared with the previous polarization beam splitters, our structure is simple, the size is small, and the extinction ratio is high, which meets the needs of modern optical communications, optical interconnection, and optical integrated systems.

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