scholarly journals An allometric relationship between mitotic spindle width, spindle length, and ploidy in Caenorhabditis elegans embryos

2013 ◽  
Vol 24 (9) ◽  
pp. 1411-1419 ◽  
Author(s):  
Yuki Hara ◽  
Akatsuki Kimura
Keyword(s):  
Caenorhabditis Elegans ◽  
Aspect Ratio ◽  
Mitotic Spindle ◽  
Metaphase Plate ◽  
Spindle Pole ◽  
Allometric Equation ◽  
Force Balance ◽  
Balance Model ◽  
Allometric Relationship ◽  
Cell Stage

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.

scholarly journals SPDL-1 functions as a kinetochore receptor for MDF-1 in Caenorhabditis elegans

2008 ◽  
Vol 183 (2) ◽  
pp. 187-194 ◽  
Author(s):  
Takaharu G. Yamamoto ◽  
Sonoko Watanabe ◽  
Anthony Essex ◽  
Risa Kitagawa
Keyword(s):  
Rna Interference ◽  
Caenorhabditis Elegans ◽  
Chromosome Segregation ◽  
Spindle Assembly Checkpoint ◽  
Spindle Pole ◽  
Cell Stage ◽  
Anaphase Onset ◽  
Mitotic Delay ◽  
Bipolar Spindles

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.

scholarly journals A Potential Role for Human Cohesin in Mitotic Spindle Aster Assembly

2001 ◽  
Vol 276 (50) ◽  
pp. 47575-47582 ◽  
Author(s):  
Heather C. Gregson ◽  
John A. Schmiesing ◽  
Jong-Soo Kim ◽  
Toshiki Kobayashi ◽  
Sharleen Zhou ◽  
...  
Keyword(s):  
Sister Chromatid ◽  
Mitotic Spindle ◽  
Potential Role ◽  
Metaphase Plate ◽  
Spindle Pole ◽  
Sister Chromatid Cohesion ◽  
Cycle Arrest ◽  
Spindle Poles ◽  
Chromatid Cohesion

The cohesin multiprotein complex containing SMC1, SMC3, Scc3 (SA), and Scc1 (Rad21) is required for sister chromatid cohesion in eukaryotes. Although metazoan cohesin associates with chromosomes and was shown to function in the establishment of sister chromatid cohesion during interphase, the majority of cohesin was found to be off chromosomes and reside in the cytoplasm in metaphase. Despite its dissociation from chromosomes, however, microinjection of an antibody against human SMC1 led to disorganization of the metaphase plate and cell cycle arrest, indicating that human cohesin still plays an important role in metaphase. To address the mitotic function of human cohesin, the subcellular localization of cohesin components was reexamined in human cells. Interestingly, we found that cohesin localizes to the spindle poles during mitosis and interacts with NuMA, a spindle pole-associated factor required for mitotic spindle organization. The interaction with NuMA persists during interphase. Similar to NuMA, a significant amount of cohesin was found to associate with the nuclear matrix. Furthermore, in the absence of cohesin, mitotic spindle asters failed to formin vitro. Our results raise the intriguing possibility that in addition to its well demonstrated function in sister chromatid cohesion, cohesin may be involved in spindle assembly during mitosis.

scholarly journals Directing multicellular organization by varying the aspect ratio of soft hydrogel microwells

2021 ◽  
Author(s):  
Gayatri Jayant Pahapale ◽  
Jiaxiang Tao ◽  
Milos Nikolic ◽  
Sammy Gao ◽  
Giuliano Scarcelli ◽  
...  
Keyword(s):  
Aspect Ratio ◽  
Three Dimensional ◽  
Force Balance ◽  
Substrate Stiffness ◽  
Self Organization ◽  
Balance Model ◽  
Physical Factors ◽  
Biological Processes ◽  
Chemical Patterning ◽  
Wide Range

Multicellular organization with precise spatial definition is an essential step in a wide range of biological processes, including morphogenesis, development, and healing. Gradients and patterns of chemoattractants are well-described guides of multicellular organization, but the influences of three-dimensional geometry of soft hydrogels on multicellular organization are less well defined. Here, we report the discovery of a new mode of self-organization of endothelial cells in ring-like patterns on the perimeters of hydrogel microwells that is independent of protein or chemical patterning and is driven only by geometry and substrate stiffness. We observe quantitatively striking influences of both the microwell aspect ratio (ε = perimeter/depth) and the hydrogel modulus. We systematically investigate the physical factors of cells and substrates that drive this multicellular behavior and present a mathematical model that explains the multicellular organization based upon balancing extracellular and cytoskeletal forces. These forces are determined in part by substrate stiffness, geometry, and cell density. The force balance model predicts the direction and distance of translational cell migration based on the dynamic interaction between tangential cytoskeletal tension and cell-cell and cell-substrate adhesion. We further show that the experimental observations can be leveraged to drive customized multicellular self-organization. Our observation of this multicellular behavior demonstrates the importance of the combinatorial effects of geometry and stiffness in complex biological processes. It also provides a new methodology for direction of cell organization that may facilitate the engineering of bionics and integrated model organoid systems.

scholarly journals Theory of cytoskeletal reorganization during crosslinker-mediated mitotic spindle assembly

2018 ◽  
Author(s):  
A. R. Lamson ◽  
C. J. Edelmaier ◽  
M. A. Glaser ◽  
M. D. Betterton
Keyword(s):  
Mitotic Spindle ◽  
Large Scale ◽  
Dynamic Instability ◽  
Kinetic Monte Carlo ◽  
Spindle Assembly ◽  
Spindle Pole ◽  
Balance Model ◽  
Cytoskeletal Reorganization ◽  
Bipolar Spindle ◽  
Mitotic Spindle Assembly

AbstractCells grow, move, and respond to outside stimuli by large-scale cytoskeletal reorganization. A prototypical example of cytoskeletal remodeling is mitotic spindle assembly, during which micro-tubules nucleate, undergo dynamic instability, bundle, and organize into a bipolar spindle. Key mechanisms of this process include regulated filament polymerization, crosslinking, and motor-protein activity. Remarkably, using passive crosslinkers, fission yeast can assemble a bipolar spindle in the absence of motor proteins. We develop a torque-balance model that describes this reorganization due to dynamic microtubule bundles, spindle-pole bodies, the nuclear envelope, and passive crosslinkers to predict spindle-assembly dynamics. We compare these results to those obtained with kinetic Monte Carlo-Brownian dynamics simulations, which include crosslinker-binding kinetics and other stochastic effects. Our results show that rapid crosslinker reorganization to microtubule overlaps facilitates crosslinker-driven spindle assembly, a testable prediction for future experiments. Combining these two modeling techniques, we illustrate a general method for studying cytoskeletal network reorganization.

scholarly journals A Force Balance Model of Early Spindle Pole Separation in Drosophila Embryos

2003 ◽  
Vol 84 (2) ◽  
pp. 757-769 ◽  
Author(s):  
E.N. Cytrynbaum ◽  
J.M. Scholey ◽  
A. Mogilner
Keyword(s):  
Spindle Pole ◽  
Force Balance ◽  
Balance Model ◽  
Drosophila Embryos

scholarly journals A comparison of the distribution of actin and tubulin in the mammalian mitotic spindle as seen by indirect immunofluorescence.

1977 ◽  
Vol 72 (3) ◽  
pp. 552-567 ◽  
Author(s):  
W Z Cande ◽  
E Lazarides ◽  
J R McIntosh
Keyword(s):  
Indirect Immunofluorescence ◽  
Mitotic Spindle ◽  
Metaphase Plate ◽  
Spindle Pole ◽  
Early Prophase ◽  
Chromosome Movement ◽  
Late Prophase ◽  
Small Ball ◽  
Nuclear Envelope Breakdown ◽  
Daughter Cells

Rabbit antibodies against actin and tubulin were used in an indirect immunofluorescence study of the structure of the mitotic spindle of PtK1 cells after lysis under conditions that preserve anaphase chromosome movement. During early prophase there is no antiactin staining associated with the mitotic centers, but by late prophase, as the spindle is beginning to form, a small ball of actin antigenicity is found beside the nucleus; After nuclear envelope breakdown, the actiactin stains the region around each mitotic center, and becomes organized into fibers that run between the chromosomes and the poles. Colchicine blocks this organization, but does not disrupt the staining at the poles. At metaphase the antiactin reveals a halo of ill-defined radius around each spindle pole and fibers that run from the poles to the metaphase plate. Antitubulin shows astral rays, fibers running from chromosomes to poles, and some fibers that run across the metaphase plate. At anaphase, there is a shortening of the antiactin-stained fibers, leaving a zone which is essentially free of actin-staining fluorescence between the separating chromosomes. Antitubulin stains the region between chromosomes and poles, but also reveals substantial fibers running through the zone between separating chromosomes. Cells fixed during cytokinesis show actin in the region of the cleavage furrow, while antitubulin reveals the fibrous spindle remnant that runs between daughter cells. These results suggest that actin is a component of the mammalian mitotic spindle, that the distribution of actin differs from that of tubulin and that the distributions of these two fibrous proteins change in different ways during anaphase.

scholarly journals GTSE1 regulates spindle microtubule dynamics to control Aurora B kinase and Kif4A chromokinesin on chromosome arms

2017 ◽  
Vol 216 (10) ◽  
pp. 3117-3132 ◽  
Author(s):  
Aaron R. Tipton ◽  
Jonathan D. Wren ◽  
John R. Daum ◽  
Joseph C. Siefert ◽  
Gary J. Gorbsky
Keyword(s):  
Mitotic Spindle ◽  
Meta Analysis ◽  
Metaphase Plate ◽  
Spindle Pole ◽  
Aurora B ◽  
Chromosome Movement ◽  
Aurora B Kinase ◽  
Nuclear Envelope Breakdown ◽  
M Phase ◽  
Spindle Microtubules

In mitosis, the dynamic assembly and disassembly of microtubules are critical for normal chromosome movement and segregation. Microtubule turnover varies among different mitotic spindle microtubules, dictated by their spatial distribution within the spindle. How turnover among the various classes of spindle microtubules is differentially regulated and the resulting significance of differential turnover for chromosome movement remains a mystery. As a new tactic, we used global microarray meta-analysis (GAMMA), a bioinformatic method, to identify novel regulators of mitosis, and in this study, we describe G2- and S phase–expressed protein 1 (GTSE1). GTSE1 is expressed exclusively in late G2 and M phase. From nuclear envelope breakdown until anaphase onset, GTSE1 binds preferentially to the most stable mitotic spindle microtubules and promotes their turnover. Cells depleted of GTSE1 show defects in chromosome alignment at the metaphase plate and in spindle pole integrity. These defects are coupled with an increase in the proportion of stable mitotic spindle microtubules. A consequence of this reduced microtubule turnover is diminished recruitment and activity of Aurora B kinase on chromosome arms. This decrease in Aurora B results in diminished binding of the chromokinesin Kif4A to chromosome arms.

scholarly journals The collapse of the spindle following ablation in S. pombe is mediated by microtubules and the motor protein dynein

2020 ◽  
Author(s):  
Parsa Zareiesfandabadi ◽  
Mary Williard Elting
Keyword(s):  
Laser Ablation ◽  
Molecular Motors ◽  
Mitotic Spindle ◽  
Motor Protein ◽  
Spindle Pole ◽  
Force Balance ◽  
Single Bundle ◽  
Spindle Pole Bodies ◽  
Basic Behavior ◽  
Supporting Force

AbstractA microtubule-based machine called the mitotic spindle segregates chromosomes when eukaryotic cells divide. In the fission yeast S. pombe, which undergoes closed mitosis, the spindle forms a single bundle of microtubules inside the nucleus. During elongation, the spindle extends via antiparallel microtubule sliding by molecular motors. These extensile forces from the spindle are thought to resist compressive forces from the nucleus. We probe the mechanism and maintenance of this force balance via laser ablation of spindles at various stages of mitosis. We find that spindle pole bodies collapse toward each other following ablation, but spindle geometry is often rescued, allowing spindles to resume elongation and segregate chromosomes. While this basic behavior has been previously observed, many questions remain about this phenomenon’s dynamics, mechanics, and molecular requirements. In this work, we find that previously hypothesized viscoelastic relaxation of the nucleus cannot fully explain spindle shortening in response to laser ablation. Instead, spindle collapse requires microtubule dynamics and is powered at least partly by the minus-end directed motor protein dynein. These results suggest a role for dynein in redundantly supporting force balance and bipolarity in the S. pombe spindle.

par-4, a gene required for cytoplasmic localization and determination of specific cell types in Caenorhabditis elegans embryogenesis.

Genetics ◽  
1992 ◽  
Vol 130 (4) ◽  
pp. 771-790 ◽  
Author(s):  
D G Morton ◽  
J M Roos ◽  
K J Kemphues
Keyword(s):  
Caenorhabditis Elegans ◽  
Cell Types ◽  
Intestinal Cells ◽  
Specific Cell ◽  
Cytoplasmic Localization ◽  
Loss Of Function ◽  
Embryo Viability ◽  
Cell Stage ◽  
Maternal Genome

Abstract Specification of some cell fates in the early Caenorhabditis elegans embryo is mediated by cytoplasmic localization under control of the maternal genome. Using nine newly isolated mutations, and two existing mutations, we have analyzed the role of the maternally expressed gene par-4 in cytoplasmic localization. We recovered seven new par-4 alleles in screens for maternal effect lethal mutations that result in failure to differentiate intestinal cells. Two additional par-4 mutations were identified in noncomplementation screens using strains with a high frequency of transposon mobility. All 11 mutations cause defects early in development of embryos produced by homozygous mutant mothers. Analysis with a deficiency in the region indicates that it33 is a strong loss-of-function mutation. par-4(it33) terminal stage embryos contain many cells, but show no morphogenesis, and are lacking intestinal cells. Temperature shifts with the it57ts allele suggest that the critical period for both intestinal differentiation and embryo viability begins during oogenesis, about 1.5 hr before fertilization, and ends before the four-cell stage. We propose that the primary function of the par-4 gene is to act as part of a maternally encoded system for cytoplasmic localization in the first cell cycle, with par-4 playing a particularly important role in the determination of intestine. Analysis of a par-4; par-2 double mutant suggests that par-4 and par-2 gene products interact in this system.

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