scholarly journals Ase1/Prc1-dependent spindle elongation corrects merotely during anaphase in fission yeast

2009 ◽  
Vol 187 (3) ◽  
pp. 399-412 ◽  
Author(s):  
Thibault Courtheoux ◽  
Guillaume Gay ◽  
Yannick Gachet ◽  
Sylvie Tournier
Keyword(s):  
Fission Yeast ◽  
Mechanical Model ◽  
Elongation Rate ◽  
Force Balance ◽  
Balance Model ◽  
Spindle Poles ◽  
Sister Chromatids ◽  
Spindle Elongation ◽  
Dependent Mechanism

Faithful segregation of sister chromatids requires the attachment of each kinetochore (Kt) to microtubules (MTs) that extend from opposite spindle poles. Merotelic Kt orientation is a Kt–MT misattachment in which a single Kt binds MTs from both spindle poles rather than just one. Genetic induction of merotelic Kt attachment during anaphase in fission yeast resulted in intra-Kt stretching followed by either correction or Kt disruption. Laser ablation of spindle MTs revealed that intra-Kt stretching and merotelic correction were dependent on MT forces. The presence of multiple merotelic chromosomes linearly antagonized the spindle elongation rate, and this phenomenon could be solved numerically using a simple force balance model. Based on the predictions of our mechanical model, we provide in vivo evidence that correction of merotelic attachment in anaphase is tension dependent and requires an Ase1/Prc1-dependent mechanism that prevents spindle collapse and thus asymmetric division and/or the appearance of the cut phenotype.

scholarly journals Prometaphase spindle maintenance by an antagonistic motor-dependent force balance made robust by a disassembling lamin-B envelope

2010 ◽  
Vol 188 (1) ◽  
pp. 49-68 ◽  
Author(s):  
Gul Civelekoglu-Scholey ◽  
Li Tao ◽  
Ingrid Brust-Mascher ◽  
Roy Wollman ◽  
Jonathan M. Scholey
Keyword(s):  
Narrow Range ◽  
Force Balance ◽  
Balance Model ◽  
Power Stroke ◽  
Mitotic Spindles ◽  
Stochastic Force ◽  
Lamin B ◽  
Spindle Poles

We tested the classical hypothesis that astral, prometaphase bipolar mitotic spindles are maintained by balanced outward and inward forces exerted on spindle poles by kinesin-5 and -14 using modeling of in vitro and in vivo data from Drosophila melanogaster embryos. Throughout prometaphase, puncta of both motors aligned on interpolar microtubules (MTs [ipMTs]), and motor perturbation changed spindle length, as predicted. Competitive motility of purified kinesin-5 and -14 was well described by a stochastic, opposing power stroke model incorporating motor kinetics and load-dependent detachment. Motor parameters from this model were applied to a new stochastic force-balance model for prometaphase spindles, providing a good fit to data from embryos. Maintenance of virtual spindles required dynamic ipMTs and a narrow range of kinesin-5 to kinesin-14 ratios matching that found in embryos. Functional perturbation and modeling suggest that this range can be extended significantly by a disassembling lamin-B envelope that surrounds the prometaphase spindle and augments the finely tuned, antagonistic kinesin force balance to maintain robust prometaphase spindles as MTs assemble and chromosomes are pushed to the equator.

scholarly journals Pericentric chromatin loops function as a nonlinear spring in mitotic force balance

2013 ◽  
Vol 200 (6) ◽  
pp. 757-772 ◽  
Author(s):  
Andrew D. Stephens ◽  
Rachel A. Haggerty ◽  
Paula A. Vasquez ◽  
Leandra Vicci ◽  
Chloe E. Snider ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Spindle Assembly Checkpoint ◽  
Force Balance ◽  
Nonlinear Spring ◽  
Sister Chromatids ◽  
Spindle Dynamics ◽  
Restoring Forces ◽  
Cross Links ◽  
Mean And Variance

The mechanisms by which sister chromatids maintain biorientation on the metaphase spindle are critical to the fidelity of chromosome segregation. Active force interplay exists between predominantly extensional microtubule-based spindle forces and restoring forces from chromatin. These forces regulate tension at the kinetochore that silences the spindle assembly checkpoint to ensure faithful chromosome segregation. Depletion of pericentric cohesin or condensin has been shown to increase the mean and variance of spindle length, which have been attributed to a softening of the linear chromatin spring. Models of the spindle apparatus with linear chromatin springs that match spindle dynamics fail to predict the behavior of pericentromeric chromatin in wild-type and mutant spindles. We demonstrate that a nonlinear spring with a threshold extension to switch between spring states predicts asymmetric chromatin stretching observed in vivo. The addition of cross-links between adjacent springs recapitulates coordination between pericentromeres of neighboring chromosomes.

scholarly journals Dynamics of Centromeres during Metaphase–Anaphase Transition in Fission Yeast: Dis1 Is Implicated in Force Balance in Metaphase Bipolar Spindle

1998 ◽  
Vol 9 (11) ◽  
pp. 3211-3225 ◽  
Author(s):  
Kentaro Nabeshima ◽  
Takashi Nakagawa ◽  
Aaron F. Straight ◽  
Andrew Murray ◽  
Yuji Chikashige ◽  
...  
Keyword(s):  
Fission Yeast ◽  
Topoisomerase Ii ◽  
Fluorescent Protein ◽  
Phase 1 ◽  
Force Balance ◽  
Yeast Cells ◽  
Phase 2 ◽  
Metaphase Chromosomes ◽  
Spindle Elongation ◽  
Green Fluorescent

In higher eukaryotic cells, the spindle forms along with chromosome condensation in mitotic prophase. In metaphase, chromosomes are aligned on the spindle with sister kinetochores facing toward the opposite poles. In anaphase A, sister chromatids separate from each other without spindle extension, whereas spindle elongation takes place during anaphase B. We have critically examined whether such mitotic stages also occur in a lower eukaryote, Schizosaccharomyces pombe. Using the green fluorescent protein tagging technique, early mitotic to late anaphase events were observed in living fission yeast cells. S. pombe has three phases in spindle dynamics, spindle formation (phase 1), constant spindle length (phase 2), and spindle extension (phase 3). Sister centromere separation (anaphase A) rapidly occurred at the end of phase 2. The centromere showed dynamic movements throughout phase 2 as it moved back and forth and was transiently split in two before its separation, suggesting that the centromere was positioned in a bioriented manner toward the poles at metaphase. Microtubule-associating Dis1 was required for the occurrence of constant spindle length and centromere movement in phase 2. Normal transition from phase 2 to 3 needed DNA topoisomerase II and Cut1 but not Cut14. The duration of each phase was highly dependent on temperature.

scholarly journals Anaphase A: Melting Microtubules Move Chromosomes toward Spindle Poles

2017 ◽  
Author(s):  
Charles L. Asbury
Keyword(s):  
Fluorescence Microscopy ◽  
Mechanistic Models ◽  
Chromosome Movement ◽  
Load Bearing ◽  
Spindle Poles ◽  
Sister Chromatids ◽  
Spindle Elongation ◽  
Anaphase B ◽  
Chromosome Movements ◽  
Cellular Movement

The separation of sister chromatids during anaphase is the culmination of mitosis and one of the most strikingly beautiful examples of cellular movement. It consists of two distinct processes: Anaphase A, the movement of chromosomes toward spindle poles via shortening of the connecting fibers, and anaphase B, separation of the two poles from one another via spindle elongation. I focus here on anaphase A chromosome-to-pole movement. The chapter begins by summarizing classical observations of chromosome movements, which support the current understanding of anaphase mechanisms. Live cell fluorescence microscopy studies showed that poleward chromosome movement is associated with disassembly, or ‘melting’ of the kinetochore-attached microtubule fibers that link chromosomes to poles. Microtubule-marking techniques established that kinetochore-fiber disassembly often occurs through a ‘pac-man’ mechanism, where tubulin subunits are lost from kinetochore-attached plus ends and the kinetochore appears to consume its microtubule track as it moves poleward. In addition, kinetochore-fiber disassembly in many cells occurs partly through ‘flux’, where the microtubules flow continuously toward the poles and tubulin subunits are lost from minus ends. Molecular mechanistic models for how load-bearing attachments are maintained to disassembling microtubule ends, and how the forces are generated to drive pac-man and flux-based movements, are discussed.

scholarly journals Alternative diastolic function models of ventricular longitudinal filling velocity are mathematically identical

2020 ◽  
Vol 318 (5) ◽  
pp. H1059-H1067 ◽  
Author(s):  
Druv Bhagavan ◽  
William M. Padovano ◽  
Sándor J. Kovács
Keyword(s):  
Diastolic Function ◽  
Longitudinal Velocity ◽  
Force Balance ◽  
Balance Model ◽  
Diastolic Filling ◽  
Restoring Force ◽  
Suction Pump ◽  
Restoring Forces ◽  
Pdf Model

The spatiotemporal features of normal in vivo cardiac motion are well established. Longitudinal velocity has become a focus of diastolic function (DF) characterization, particularly the tissue Doppler e′-wave, manifesting in early diastole when the left ventricle (LV) is a mechanical suction pump (dP/dV < 0). To characterize DF and elucidate mechanistic features, several models have been proposed and have been previously compared algebraically, numerically, and in their ability to fit physiological velocity data. We analyze two previously noncompared models of early rapid-filling lengthening velocity (Doppler e′-wave): parametrized diastolic filling (PDF) and force balance model (FBM). Our initial numerical experiments sampled FBM-generated e′( t) contours as input to determine PDF model predicted fit. The resulting exact numerical agreement [standard error of regression (SER) = 9.06 × 10−16] was not anticipated. Therefore, we analyzed all published FBM-generated e′( t) contours and observed identical agreement. We re-expressed FBM’s algebraic expressions for e′( t) and observed for the first time that model-based predictions for lengthening velocity by the FBM and the PDF model are mathematically identical: e′( t) = γe−α tsinh(β t), thereby providing exact algebraic relations between the three PDF parameters and the six FBM parameters. Previous pioneering experiments have independently established the unique determinants of e′( t) to be LV relaxation, restoring forces (stiffness), and load. In light of the exact intermodel agreement, we conclude that the three PDF parameters, relaxation, stiffness (restoring forces), and load, are unique determinants of DF and e′( t). Thus, we show that only the PDF formalism can compute the three unique, independent, physiological determinants of long-axis LV myocardial velocity from e′( t). NEW & NOTEWORTHY We show that two separate, independently derived physiological (kinematic) models predict mathematically identical expressions for LV-lengthening velocity (Doppler e′-wave), indicating that damped harmonic oscillatory motion is a physiologically accurate model of diastolic function. Although both models predict the same “overdamped” velocity contour, only one model solves the “inverse problem” and generates unique, lumped parameters of relaxation, stiffness (restoring force), and load from the e′-wave.

scholarly journals The inner centromere protein (INCENP) antigens: movement from inner centromere to midbody during mitosis.

1987 ◽  
Vol 105 (5) ◽  
pp. 2053-2067 ◽  
Author(s):  
C A Cooke ◽  
M M Heck ◽  
W C Earnshaw
Keyword(s):  
Metaphase Plate ◽  
Pericentromeric Region ◽  
Contractile Ring ◽  
Structural Localization ◽  
Spindle Poles ◽  
Sister Chromatids ◽  
Centromere Proteins ◽  
Coarse Fibers ◽  
Chromosome Scaffold

We describe a novel set of polypeptide antigens that shows a dramatic change in structural localization during mitosis. Through metaphase these antigens define a new chromosomal substructure that is located between the sister chromatids. Because the antigens are concentrated in the pericentromeric region, we have provisionally termed them the INCENPs (inner centromere proteins). The INCENPs (two polypeptides of 155 and 135 kD) were identified with a monoclonal antibody that was raised against the bulk proteins of the mitotic chromosome scaffold fraction. These two polypeptides are the most tightly bound chromosomal proteins known. When scaffolds are prepared, 100% of the detectable INCENPs remain scaffold associated. We were therefore unprepared for the fate of the INCENPs at anaphase. As the sister chromatids separate, the INCENPs dissociate fully from them, remaining behind at the metaphase plate as the chromatids migrate to the spindle poles. During anaphase the INCENPs are found on coarse fibers in the central spindle, and also in close apposition to the cell membrane in the region of the forming contractile ring. During telophase, the INCENPs gradually become focused onto the forming midbody, together with which they are ultimately discarded. Several possible in vivo roles for the INCENPs are suggested by these data: regulation of sister chromatid pairing, stabilization of the plane of cleavage, and separation of spindle poles at anaphase.

scholarly journals Fission yeast cells overproducing HSET/KIFC1 provides a useful tool for identification and evaluation of human kinesin-14 inhibitors

2018 ◽  
Author(s):  
Masashi Yukawa ◽  
Tomoaki Yamauchi ◽  
Ken-ichi Kimura ◽  
Takashi Toda
Keyword(s):  
Fission Yeast ◽  
Cancer Cells ◽  
Yeast Cells ◽  
Transformed Cells ◽  
Functional Assay ◽  
Spindle Poles ◽  
Multipolar Spindles ◽  
Protein Overproduction ◽  
Bipolar Spindles

ABSTRACTMany cancer cells contain more than two centrosomes, yet these cancer cells can form bipolar spindles and appear to proliferate normally, instead of committing lethal mitoses with multipolar spindles. It is shown that extra centrosomes are clustered into two pseudo-bipolar spindle poles, thereby escaping from multipolarity. Human kinesin-14 (HSET or KIFC1), a minus end-directed motor, plays a crucial role in centrosome clustering and as such, HSET is essential for cell viability only in cancer cells with supernumerary centrosomes, but not in non-transformed cells. Accordingly, HSET is deemed to be an efficient chemotherapeutic target to selectively kill cancer cells. Recently, three HSET inhibitors (AZ82, CW069 and SR31527) have been reported, but their specificity, efficacy and off-target cytotoxicity have not been evaluated rigorously. Here we show that these inhibitors on their own are cytotoxic to fission yeast, suggesting that they have other targets in vivo except for kinesin-14. Nonetheless, intriguingly, AZ82 can neutralize overproduced HSET and partially rescue its lethality. This methodology of protein overproduction in fission yeast provides a convenient, functional assay system by which to screen for not only selective human kinesin-14 inhibitors but also those against other molecules of interest.

scholarly journals Chromosome movement in lysed mitotic cells is inhibited by vanadate.

1978 ◽  
Vol 79 (2) ◽  
pp. 573-580 ◽  
Author(s):  
W Z Cande ◽  
S M Wolniak
Keyword(s):  
Atpase Activity ◽  
Metabolic Inhibitors ◽  
Chromosome Movement ◽  
Microtubule Polymerization ◽  
Spindle Poles ◽  
Brij 58 ◽  
Spindle Elongation ◽  
Chromosome Movements

Mitotic PtK1 cells, lysed at anaphase into a carbowax 20 M Brij 58 solution, continue to move chromosomes toward the spindle poles and to move the spindle poles apart at 50% in vivo rates for 10 min. Chromosome movements can be blocked by adding metabolic inhibitors to the lysis medium and inhibition of movement can be reversed by adding ATP to the medium. Vanadate at micromolar levels reversibly inhibits dynein ATPase activity and movement of demembranated flagella and cilia. It does not affect glycerinated myofibril contraction or myosin ATPase activty at less than millimolar concentrations. Vanadate at 10--100 micron reversibly inhibits anaphase movement of chromosomes and spindle elongation. After lysis in vanadate, spindles lose their fusiform appearance and become more barrel shaped. In vitro microtubule polymerization is insensitive to vanadate.

scholarly journals A force-balance model for centrosome positioning and spindle elongation during Interphase and Anaphase B

2021 ◽  
Author(s):  
Raja Paul ◽  
Apurba Sarkar ◽  
Arittri Mallick
Keyword(s):  
Computational Model ◽  
Underlying Mechanism ◽  
Force Balance ◽  
One Dimension ◽  
Balance Model ◽  
Cell Cortex ◽  
Bipolar Spindle ◽  
Spindle Elongation ◽  
Anaphase B

A computational model in one dimension is proposed to position a single centrosome using astral microtubules (MTs) interacting with the cell cortex. The mechanism exploits mutually antagonistic pulling and pushing forces arising from the astral MTs' binding to cortical dynein motors in the actin-rich cell cortex and their buckling while growing against the cell cortex, respectively. The underlying mechanism of astral MTs is also extended to account for the elongation and positioning of the bipolar spindle during mitotic anaphase B. The model for bipolar spindle involves both IPMTs and astral MTs, can predict its elongation and positioning under various circumstances. The model reveals that the bipolar spindle elongation, weakened by decreasing overlap between the antiparallel interpolar microtubules (IPMTs) in the spindle mid-zone, is recovered by the astral MTs.

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