scholarly journals Quantitative analysis of an anaphase B switch: predicted role for a microtubule catastrophe gradient

2007 ◽  
Vol 177 (6) ◽  
pp. 995-1004 ◽  
Author(s):  
Dhanya K. Cheerambathur ◽  
Gul Civelekoglu-Scholey ◽  
Ingrid Brust-Mascher ◽  
Patrizia Sommi ◽  
Alex Mogilner ◽  
...  
Keyword(s):  
Fluorescence Recovery After Photobleaching ◽  
Complete Recovery ◽  
Cyclin B ◽  
Spatial Gradient ◽  
Spindle Poles ◽  
Spindle Elongation ◽  
Anaphase B ◽  
Mechanical Switch ◽  
Lower Recovery ◽  
Drosophila Embryos

Anaphase B in Drosophila embryos is initiated by the inhibition of microtubule (MT) depolymerization at spindle poles, which allows outwardly sliding interpolar (ip) MTs to drive pole–pole separation. Using fluorescence recovery after photobleaching, we observed that MTs throughout the preanaphase B spindle are very dynamic and display complete recovery of fluorescence, but during anaphase B, MTs proximal to the poles stabilize and therefore display lower recovery than those elsewhere. Fluorescence microscopy of the MT tip tracker EB1 revealed that growing MT plus ends localize throughout the preanaphase B spindle but concentrate in the overlap region of interpolar MTs (ipMTs) at anaphase B onset. None of these changes occurred in the presence of nondegradable cyclin B. Modeling suggests that they depend on the establishment of a spatial gradient of MT plus-end catastrophe frequencies, decreasing toward the equator. The resulting redistribution of ipMT plus ends to the overlap zone, together with the suppression of minus-end depolymerization at the poles, could constitute a mechanical switch that initiates spindle elongation.

Mitotic motors and chromosome segregation: the mechanism of anaphase B

2011 ◽  
Vol 39 (5) ◽  
pp. 1149-1153 ◽  
Author(s):  
Ingrid Brust-Mascher ◽  
Jonathan M. Scholey
Keyword(s):  
Chromosome Segregation ◽  
Cyclin B ◽  
Spindle Poles ◽  
Mitotic Motors ◽  
Balance Of Forces ◽  
Spindle Elongation ◽  
Anaphase B ◽  
Relationship Of ◽  
The Relationship ◽  
Acting In Concert

Anaphase B spindle elongation plays an important role in chromosome segregation. In the present paper, we discuss our model for anaphase B in Drosophila syncytial embryos, in which spindle elongation depends on an ip (interpolar) MT (microtubule) sliding filament mechanism generated by homotetrameric kinesin-5 motors acting in concert with poleward ipMT flux, which acts as an ‘on/off’ switch. Specifically, the pre-anaphase B spindle is maintained at a steady-state length by the balance between ipMT sliding and ipMT depolymerization at spindle poles, producing poleward flux. Cyclin B degradation at anaphase B onset triggers: (i) an MT catastrophe gradient causing ipMT plus ends to invade the overlap zone where ipMT sliding forces are generated; and (ii) the inhibition of ipMT minus-end depolymerization so flux is turned ‘off’, tipping the balance of forces to allow outward ipMT sliding to push apart the spindle poles. We briefly comment on the relationship of this model to anaphase B in other systems.

scholarly journals The microtubule cross-linker Feo controls the midzone stability, motor composition, and elongation of the anaphase B spindle in Drosophila embryos

2015 ◽  
Vol 26 (8) ◽  
pp. 1452-1462 ◽  
Author(s):  
Haifeng Wang ◽  
Ingrid Brust-Mascher ◽  
Jonathan M. Scholey
Keyword(s):  
Chromosome Segregation ◽  
Cross Linking ◽  
Cross Link ◽  
Spindle Poles ◽  
Cross Linker ◽  
Spindle Elongation ◽  
Anaphase B ◽  
Drosophila Embryos ◽  
Poleward Flux

Chromosome segregation during anaphase depends on chromosome-to-pole motility and pole-to-pole separation. We propose that in Drosophila embryos, the latter process (anaphase B) depends on a persistent kinesin-5–generated interpolar (ip) microtubule (MT) sliding filament mechanism that “engages” to push apart the spindle poles when poleward flux is turned off. Here we investigated the contribution of the midzonal, antiparallel MT-cross-linking nonmotor MAP, Feo, to this “slide-and-flux-or-elongate” mechanism. Whereas Feo homologues in other systems enhance the midzone localization of the MT-MT cross-linking motors kinesin-4, -5 and -6, the midzone localization of these motors is respectively enhanced, reduced, and unaffected by Feo. Strikingly, kinesin-5 localizes all along ipMTs of the anaphase B spindle in the presence of Feo, including at the midzone, but the antibody-induced dissociation of Feo increases kinesin-5 association with the midzone, which becomes abnormally narrow, leading to impaired anaphase B and incomplete chromosome segregation. Thus, although Feo and kinesin-5 both preferentially cross-link MTs into antiparallel polarity patterns, kinesin-5 cannot substitute for loss of Feo function. We propose that Feo controls the organization, stability, and motor composition of antiparallel ipMTs at the midzone, thereby facilitating the kinesin-5–driven sliding filament mechanism underlying proper anaphase B spindle elongation and chromosome segregation.

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.

Structure-function analysis of anaphase spindle elongation using isolated diatom spindles

1991 ◽  
Vol 49 ◽  
pp. 206-207
Author(s):  
W. Z. Cande ◽  
C.J. Hogan ◽  
M. Lee
Keyword(s):  
Morphological Changes ◽  
Function Analysis ◽  
Light And Electron Microscopy ◽  
Near Neighbor ◽  
Model Systems ◽  
Central Spindle ◽  
Spindle Poles ◽  
Spindle Elongation ◽  
Anaphase B

Diatom spindles are important model systems for describing the morphological changes associated with anaphase chromosome movement because the fibrous systems responsible for anaphase A (chromosome-to-pole movement) and anaphase B (spindle elongation) are spatially separate and the central spindle is a paracrystalline array of microtubules. The diatom central spindle, which is responsible for anaphase B, is constructed of two sets of interdigiting microtubules that originate from plate-like spindle poles and display specific near-neighbor interactions in the zone of microtubule overlap. The microtubules of each half-spindle are of relatively unifrom length such that the plus ends are clustered together in narrow zones at each edge of the zone of microtubule overlap. This has allowed us to monitor changes in extent of microtubule overlap in the light microscope with polarization optics. We have isolated spindles from synchronized populations of several species of dividing diatom cells to study the mechanochemistry of anaphase spindle elongation in vitro and to analyze the rearrangement of spindle components by light and electron microscopy during reactivation.

scholarly journals Drosophila EB1 is important for proper assembly, dynamics, and positioning of the mitotic spindle

2002 ◽  
Vol 158 (5) ◽  
pp. 873-884 ◽  
Author(s):  
Stephen L. Rogers ◽  
Gregory C. Rogers ◽  
David J. Sharp ◽  
Ronald D. Vale
Keyword(s):  
Cell Attachment ◽  
Cell Cortex ◽  
Mitotic Spindles ◽  
Microtubule Organization ◽  
Chromosomal Segregation ◽  
Spindle Poles ◽  
Evolutionarily Conserved ◽  
Interphase Cells ◽  
Spindle Elongation ◽  
Drosophila Embryos

EB1 is an evolutionarily conserved protein that localizes to the plus ends of growing microtubules. In yeast, the EB1 homologue (BIM1) has been shown to modulate microtubule dynamics and link microtubules to the cortex, but the functions of metazoan EB1 proteins remain unknown. Using a novel preparation of the Drosophila S2 cell line that promotes cell attachment and spreading, we visualized dynamics of single microtubules in real time and found that depletion of EB1 by RNA-mediated inhibition (RNAi) in interphase cells causes a dramatic increase in nondynamic microtubules (neither growing nor shrinking), but does not alter overall microtubule organization. In contrast, several defects in microtubule organization are observed in RNAi-treated mitotic cells, including a drastic reduction in astral microtubules, malformed mitotic spindles, defocused spindle poles, and mispositioning of spindles away from the cell center. Similar phenotypes were observed in mitotic spindles of Drosophila embryos that were microinjected with anti-EB1 antibodies. In addition, live cell imaging of mitosis in Drosophila embryos reveals defective spindle elongation and chromosomal segregation during anaphase after antibody injection. Our results reveal crucial roles for EB1 in mitosis, which we postulate involves its ability to promote the growth and interactions of microtubules within the central spindle and at the cell cortex.

scholarly journals Evidence for anaphase pulling forces during C. elegans meiosis

2020 ◽  
Vol 219 (12) ◽  
Author(s):  
Brennan M. Danlasky ◽  
Michelle T. Panzica ◽  
Karen P. McNally ◽  
Elizabeth Vargas ◽  
Cynthia Bailey ◽  
...  
Keyword(s):  
Spindle Pole ◽  
Outer Face ◽  
Chromosome Movement ◽  
Female Meiosis ◽  
Homologous Chromosomes ◽  
C Elegans ◽  
Spindle Poles ◽  
Pulling Forces ◽  
Spindle Elongation ◽  
Anaphase B

Anaphase chromosome movement is thought to be mediated by pulling forces generated by end-on attachment of microtubules to the outer face of kinetochores. However, it has been suggested that during C. elegans female meiosis, anaphase is mediated by a kinetochore-independent pushing mechanism with microtubules only attached to the inner face of segregating chromosomes. We found that the kinetochore proteins KNL-1 and KNL-3 are required for preanaphase chromosome stretching, suggesting a role in pulling forces. In the absence of KNL-1,3, pairs of homologous chromosomes did not separate and did not move toward a spindle pole. Instead, each homolog pair moved together with the same spindle pole during anaphase B spindle elongation. Two masses of chromatin thus ended up at opposite spindle poles, giving the appearance of successful anaphase.

scholarly journals Functional Coordination of Three Mitotic Motors inDrosophila Embryos

2000 ◽  
Vol 11 (1) ◽  
pp. 241-253 ◽  
Author(s):  
David J. Sharp ◽  
Heather M. Brown ◽  
Mijung Kwon ◽  
Gregory C. Rogers ◽  
Gina Holland ◽  
...  
Keyword(s):  
Nuclear Envelope ◽  
Cytoplasmic Dynein ◽  
Spindle Pole ◽  
Nuclear Envelope Breakdown ◽  
Mitotic Motors ◽  
Balance Of Forces ◽  
Spindle Elongation ◽  
And Function ◽  
Anaphase B ◽  
Drosophila Embryos

It is well established that multiple microtubule-based motors contribute to the formation and function of the mitotic spindle, but how the activities of these motors interrelate remains unclear. Here we visualize spindle formation in living Drosophila embryos to show that spindle pole movements are directed by a temporally coordinated balance of forces generated by three mitotic motors, cytoplasmic dynein, KLP61F, and Ncd. Specifically, our findings suggest that dynein acts to move the poles apart throughout mitosis and that this activity is augmented by KLP61F after the fenestration of the nuclear envelope, a process analogous to nuclear envelope breakdown, which occurs at the onset of prometaphase. Conversely, we find that Ncd generates forces that pull the poles together between interphase and metaphase, antagonizing the activity of both dynein and KLP61F and serving as a brake for spindle assembly. During anaphase, however, Ncd appears to have no effect on spindle pole movements, suggesting that its activity is down-regulated at this time, allowing dynein and KLP61F to drive spindle elongation during anaphase B.

Sharpening the anaphase switch

2015 ◽  
Vol 43 (1) ◽  
pp. 19-22 ◽  
Author(s):  
John C. Meadows ◽  
Jonathan B.A. Millar
Keyword(s):  
Cyclin B ◽  
Anaphase Promoting Complex ◽  
Mitotic Chromosomes ◽  
Anaphase Onset ◽  
Sister Chromatids ◽  
Chromatid Cohesion ◽  
Substantial Progress ◽  
A Cell ◽  
Spindle Elongation ◽  
Anaphase B

The segregation of sister chromatids during mitosis is one of the most easily visualized, yet most remarkable, events during the life cycle of a cell. The accuracy of this process is essential to maintain ploidy during cell duplication. Over the past 20 years, substantial progress has been made in identifying components of both the kinetochore and the mitotic spindle that generate the force to move mitotic chromosomes. Additionally, we now have a reasonable, albeit incomplete, understanding of the molecular and biochemical events that are involved in establishing and dissolving sister-chromatid cohesion. However, it is less well-understood how this dissolution of cohesion occurs synchronously on all chromosomes at the onset of anaphase. At the centre of the action is the anaphase-promoting complex/cyclosome (APC/C), an E3 ubiquitin ligase that, in association with its activator cell-division cycle protein 20 homologue (Cdc20), is responsible for the destruction of securin. This leads to the activation of separase, a specialized protease that cleaves the kleisin-subunit of the cohesin complex, to relieve cohesion between sister chromatids. APC/C–Cdc20 is also responsible for the destruction of cyclin B and therefore inactivation of the cyclin B–cyclin-dependent kinase 1 (Cdk1). This latter event induces a change in the microtubule dynamics that results in the movement of sister chromatids to spindle poles (anaphase A), spindle elongation (anaphase B) and the onset of cytokinesis. In the present paper, we review the emerging evidence that multiple, spatially and temporally regulated feedback loops ensure anaphase onset is rapid, co-ordinated and irreversible.

scholarly journals Patronin mediates a switch from kinesin-13–dependent poleward flux to anaphase B spindle elongation

2013 ◽  
Vol 203 (1) ◽  
pp. 35-46 ◽  
Author(s):  
Haifeng Wang ◽  
Ingrid Brust-Mascher ◽  
Gul Civelekoglu-Scholey ◽  
Jonathan M. Scholey
Keyword(s):  
Drosophila Melanogaster ◽  
Chromosome Segregation ◽  
Present Evidence ◽  
Spindle Poles ◽  
Spindle Elongation ◽  
Anaphase B ◽  
Poleward Flux

Anaphase B spindle elongation contributes to chromosome segregation during Drosophila melanogaster embryo mitosis. We propose that this process is driven by a kinesin-5–generated interpolar microtubule (MT; ipMT) sliding filament mechanism that engages when poleward flux is turned off. In this paper, we present evidence that anaphase B is induced by the minus end–stabilizing protein Patronin, which antagonizes the kinesin-13 depolymerase KLP10A at spindle poles, thereby switching off the depolymerization of the minus ends of outwardly sliding ipMTs to suppress flux. Although intact cortices, kinetochore MTs, and midzone augmentation are dispensable, this Patronin-based change in ipMT minus-end dynamics is sufficient to induce the elongation of spindles capable of separating chromosomes.

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