Spatial gradients controlling spindle assembly

2015 ◽  
Vol 43 (1) ◽  
pp. 7-12 ◽  
Author(s):  
Lesley N. Weaver ◽  
Claire E. Walczak
Keyword(s):  
Self Assembly ◽  
Mitotic Spindle ◽  
Spindle Assembly ◽  
Present Review ◽  
Aurora B ◽  
Spatial Gradients ◽  
Self Organized ◽  
Ran Gtp ◽  
And Function ◽  
In Cells

The mitotic spindle is the macromolecular machine utilized to accurately segregate chromosomes in cells. How this self-organized structure assembles is a key aspect of understanding spindle morphogenesis. In the present review, we focus on understanding mechanisms of spindle self-assembly and address how subcellular signalling gradients, such as Ran-GTP and Aurora B, contribute to spindle organization and function.

scholarly journals Ran GTP and importin β regulate meiosis I spindle assembly and function in mouse oocytes

2019 ◽  
Vol 39 (1) ◽  
Author(s):  
David Drutovic ◽  
Xing Duan ◽  
Rong Li ◽  
Petr Kalab ◽  
Petr Solc
Keyword(s):  
Spindle Assembly ◽  
Mouse Oocytes ◽  
Ran Gtp ◽  
And Function ◽  
Meiosis I

scholarly journals TPX2 regulates the localization and activity of Eg5 in the mammalian mitotic spindle

2011 ◽  
Vol 195 (1) ◽  
pp. 87-98 ◽  
Author(s):  
Nan Ma ◽  
Janel Titus ◽  
Alyssa Gable ◽  
Jennifer L. Ross ◽  
Patricia Wadsworth
Keyword(s):  
Mitotic Spindle ◽  
Mammalian Cells ◽  
Spindle Assembly ◽  
Artificial Chromosome ◽  
Fiber Formation ◽  
Interaction Domain ◽  
Spindle Poles ◽  
Spindle Elongation ◽  
Multiple Spindle ◽  
And Function

Mitotic spindle assembly requires the regulated activity of numerous spindle-associated proteins. In mammalian cells, the Kinesin-5 motor Eg5 interacts with the spindle assembly factor TPX2, but how this interaction contributes to spindle formation and function is not established. Using bacterial artificial chromosome technology, we generated cells expressing TPX2 lacking the Eg5 interaction domain. Spindles in these cells were highly disorganized with multiple spindle poles. The TPX2–Eg5 interaction was required for kinetochore fiber formation and contributed to Eg5 localization to spindle microtubules but not spindle poles. Microinjection of the Eg5-binding domain of TPX2 resulted in spindle elongation, indicating that the interaction of Eg5 with TPX2 reduces motor activity. Consistent with this possibility, we found that TPX2 reduced the velocity of Eg5-dependent microtubule gliding, inhibited microtubule sliding, and resulted in the accumulation of motor on microtubules. These results establish a novel function of TPX2 in regulating the location and activity of the mitotic motor Eg5.

Regulation of kinetochore–microtubule attachments by Aurora B kinase

2009 ◽  
Vol 37 (5) ◽  
pp. 976-980 ◽  
Author(s):  
Dan Liu ◽  
Michael A. Lampson
Keyword(s):  
Opposite Direction ◽  
Mitotic Spindle ◽  
Present Review ◽  
Aurora B ◽  
Aurora B Kinase ◽  
Spindle Microtubules ◽  
Segregation Of Chromosomes

Accurate segregation of chromosomes in mitosis requires that spindle microtubules attach sister kinetochores to opposite poles of the mitotic spindle (biorientation). To achieve biorientation of all chromosomes, incorrect attachments are selectively destabilized, providing a fresh opportunity to biorient, whereas correct attachments are stabilized. Tension across the centromere may be the signal that distinguishes different attachment states, as spindle microtubules pull bioriented sister kinetochores in the opposite direction. Destabilization of incorrect attachments requires the Ipl1/Aurora B kinase, which phosphorylates kinetochore substrates that directly interact with microtubules. The present review focuses on how Aurora B regulates attachments in response to centromere tension.

scholarly journals The Kinesin-Related Protein, Hset, Opposes the Activity of Eg5 and Cross-Links Microtubules in the Mammalian Mitotic Spindle

1999 ◽  
Vol 147 (2) ◽  
pp. 351-366 ◽  
Author(s):  
Vicki Mountain ◽  
Calvin Simerly ◽  
Louisa Howard ◽  
Asako Ando ◽  
Gerald Schatten ◽  
...  
Keyword(s):  
Mitotic Spindle ◽  
Cultured Cells ◽  
Spindle Assembly ◽  
Meiotic Spindle ◽  
Cross Linking ◽  
Simultaneous Inhibition ◽  
Balance Of Forces ◽  
And Function

We have prepared antibodies specific for HSET, the human homologue of the KAR3 family of minus end-directed motors. Immuno-EM with these antibodies indicates that HSET frequently localizes between microtubules within the mammalian metaphase spindle consistent with a microtubule cross-linking function. Microinjection experiments show that HSET activity is essential for meiotic spindle organization in murine oocytes and taxol-induced aster assembly in cultured cells. However, inhibition of HSET did not affect mitotic spindle architecture or function in cultured cells, indicating that centrosomes mask the role of HSET during mitosis. We also show that (acentrosomal) microtubule asters fail to assemble in vitro without HSET activity, but simultaneous inhibition of HSET and Eg5, a plus end-directed motor, redresses the balance of forces acting on microtubules and restores aster organization. In vivo, centrosomes fail to separate and monopolar spindles assemble without Eg5 activity. Simultaneous inhibition of HSET and Eg5 restores centrosome separation and, in some cases, bipolar spindle formation. Thus, through microtubule cross-linking and oppositely oriented motor activity, HSET and Eg5 participate in spindle assembly and promote spindle bipolarity, although the activity of HSET is not essential for spindle assembly and function in cultured cells because of centrosomes.

scholarly journals The BUBR1 pseudokinase domain promotes efficient kinetochore PP2A-B56 recruitment to regulate spindle checkpoint silencing and chromosome alignment

2019 ◽  
Author(s):  
Luciano Gama Braga ◽  
Angel F. Cisneros ◽  
Michelle Mathieu ◽  
Maxime Clerc ◽  
Pauline Garcia ◽  
...  
Keyword(s):  
Mitotic Spindle ◽  
Spindle Assembly Checkpoint ◽  
Spindle Assembly ◽  
Aurora B ◽  
Dependent Manner ◽  
Regulatory Domain ◽  
Checkpoint Protein ◽  
Major Player ◽  
Chromosome Alignment ◽  
Spindle Assembly Checkpoint Protein

ABSTRACTThe balance of phospho-signalling at outer-kinetochores during mitosis is critical for the accurate attachments between kinetochores and the mitotic spindle and timely exit from mitosis. In humans, a major player in determining this balance is the PP2A-B56 phosphatase which is recruited to the Kinase Attachment Regulatory Domain (KARD) of the Spindle Assembly Checkpoint protein Budding Uninhibited by Benzimidazole 1-related 1 (BUBR1) in a phospho-dependent manner. This event unleashes a rapid, switch-like phosphatase relay that reverses phosphorylation at the kinetochore, extinguishing the checkpoint and promoting anaphase entry. Here, we conclusively demonstrate that the pseudokinase domain of human BUBR1 lacks phosphotransfer activity and that it was maintained in vertebrates because it allosterically promotes KARD phosphorylation. Mutation or removal of this domain results in decreased PP2A-B56 recruitment to the outer kinetochore, attenuated checkpoint silencing and errors in chromosome alignment as a result of imbalance in Aurora B activity. We demonstrate that the functions of the BUBR1 pseudokinase and the BUB1 kinase domains are intertwined, providing an explanation for retention of the pseudokinase domain in certain eukaryotes.

scholarly journals NuMA regulates mitotic spindle assembly, structural dynamics and function via phase separation

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Mengjie Sun ◽  
Mingkang Jia ◽  
He Ren ◽  
Biying Yang ◽  
Wangfei Chi ◽  
...  
Keyword(s):  
Phase Separation ◽  
Liquid Phase ◽  
Structural Dynamics ◽  
Mitotic Spindle ◽  
Spindle Assembly ◽  
Spindle Poles ◽  
Mitotic Spindle Assembly ◽  
Dynamics And Function ◽  
And Function ◽  
Liquid Liquid Phase Separation

AbstractA functional mitotic spindle is essential for accurate chromosome congression and segregation during cell proliferation; however, the underlying mechanisms of its assembly remain unclear. Here we show that NuMA regulates this assembly process via phase separation regulated by Aurora A. NuMA undergoes liquid-liquid phase separation during mitotic entry and KifC1 facilitates NuMA condensates concentrating on spindle poles. Phase separation of NuMA is mediated by its C-terminus, whereas its dynein-dynactin binding motif also facilitates this process. Phase-separated NuMA droplets concentrate tubulins, bind microtubules, and enrich crucial regulators, including Kif2A, at the spindle poles, which then depolymerizes spindle microtubules and promotes poleward spindle microtubule flux for spindle assembly and structural dynamics. In this work, we show that NuMA orchestrates mitotic spindle assembly, structural dynamics and function via liquid-liquid phase separation regulated by Aurora A phosphorylation.

Ran–GTP coordinates regulation of microtubule nucleation and dynamics during mitotic-spindle assembly

2001 ◽  
Vol 3 (3) ◽  
pp. 228-234 ◽  
Author(s):  
Rafael E. Carazo-Salas ◽  
Oliver J. Gruss ◽  
Iain W. Mattaj ◽  
Eric Karsenti
Keyword(s):  
Mitotic Spindle ◽  
Spindle Assembly ◽  
Microtubule Nucleation ◽  
Mitotic Spindle Assembly ◽  
Ran Gtp

scholarly journals An organelle-exclusion envelope assists mitosis and underlies distinct molecular crowding in the spindle region

2015 ◽  
Vol 210 (5) ◽  
pp. 695-704 ◽  
Author(s):  
Nina Schweizer ◽  
Nisha Pawar ◽  
Matthias Weiss ◽  
Helder Maiato
Keyword(s):  
Chromosome Segregation ◽  
Mitotic Spindle ◽  
Spindle Assembly ◽  
Membrane System ◽  
Correlation Spectroscopy ◽  
Molecular Crowding ◽  
Exclusion Zone ◽  
Drosophila Melanogaster S2 Cells ◽  
Spatio Temporal ◽  
And Function

The mitotic spindle is a microtubular assembly required for chromosome segregation during mitosis. Additionally, a spindle matrix has long been proposed to assist this process, but its nature has remained elusive. By combining live-cell imaging with laser microsurgery, fluorescence recovery after photobleaching, and fluorescence correlation spectroscopy in Drosophila melanogaster S2 cells, we uncovered a microtubule-independent mechanism that underlies the accumulation of molecules in the spindle region. This mechanism relies on a membranous system surrounding the mitotic spindle that defines an organelle-exclusion zone that is conserved in human cells. Supported by mathematical modeling, we demonstrate that organelle exclusion by a membrane system causes spatio-temporal differences in molecular crowding states that are sufficient to drive accumulation of mitotic regulators, such as Mad2 and Megator/Tpr, as well as soluble tubulin, in the spindle region. This membranous “spindle envelope” confined spindle assembly, and its mechanical disruption compromised faithful chromosome segregation. Thus, cytoplasmic compartmentalization persists during early mitosis to promote spindle assembly and function.

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