scholarly journals The Interplay of the N- and C-Terminal Domains of MCAK Control Microtubule Depolymerization Activity and Spindle Assembly

2007 ◽  
Vol 18 (1) ◽  
pp. 282-294 ◽  
Author(s):  
Stephanie C. Ems-McClung ◽  
Kathleen M. Hertzer ◽  
Xin Zhang ◽  
Mill W. Miller ◽  
Claire E. Walczak
Keyword(s):  
High Activity ◽  
Chromosome Segregation ◽  
Spindle Assembly ◽  
Microtubule Dynamics ◽  
Microtubule Depolymerization ◽  
Terminal Domain ◽  
Egg Extracts ◽  
Assembly Activity ◽  
Terminal Domains

Spindle assembly and accurate chromosome segregation require the proper regulation of microtubule dynamics. MCAK, a Kinesin-13, catalytically depolymerizes microtubules, regulates physiological microtubule dynamics, and is the major catastrophe factor in egg extracts. Purified GFP-tagged MCAK domain mutants were assayed to address how the different MCAK domains contribute to in vitro microtubule depolymerization activity and physiological spindle assembly activity in egg extracts. Our biochemical results demonstrate that both the neck and the C-terminal domain are necessary for robust in vitro microtubule depolymerization activity. In particular, the neck is essential for microtubule end binding, and the C-terminal domain is essential for tight microtubule binding in the presence of excess tubulin heterodimer. Our physiological results illustrate that the N-terminal domain is essential for regulating microtubule dynamics, stimulating spindle bipolarity, and kinetochore targeting; whereas the C-terminal domain is necessary for robust microtubule depolymerization activity, limiting spindle bipolarity, and enhancing kinetochore targeting. Unexpectedly, robust MCAK microtubule (MT) depolymerization activity is not needed for sperm-induced spindle assembly. However, high activity is necessary for proper physiological MT dynamics as assayed by Ran-induced aster assembly. We propose that MCAK activity is spatially controlled by an interplay between the N- and C-terminal domains during spindle assembly.

scholarly journals ISWI is a RanGTP-dependent MAP required for chromosome segregation

2009 ◽  
Vol 187 (6) ◽  
pp. 813-829 ◽  
Author(s):  
Hideki Yokoyama ◽  
Sofia Rybina ◽  
Rachel Santarella-Mellwig ◽  
Iain W. Mattaj ◽  
Eric Karsenti
Keyword(s):  
Chromatin Remodeling ◽  
Chromosome Segregation ◽  
Spindle Assembly ◽  
S2 Cells ◽  
Culture Cells ◽  
Egg Extract ◽  
Drosophila S2 Cells ◽  
Egg Extracts ◽  
Localization Signal

Production of RanGTP around chromosomes induces spindle assembly by activating nuclear localization signal (NLS)–containing factors. Here, we show that the NLS protein ISWI, a known chromatin-remodeling ATPase, is a RanGTP-dependent microtubule (MT)-associated protein. Recombinant ISWI induces MT nucleation, stabilization, and bundling in vitro. In Xenopus culture cells and egg extract, ISWI localizes within the nucleus in interphase and on spindles during mitosis. Depletion of ISWI in egg extracts does not affect spindle assembly, but in anaphase spindle MTs disappear and chromosomes do not segregate. We show directly that ISWI is required for the RanGTP-dependent stabilization of MTs during anaphase independently of its effect on chromosomes. ISWI depletion in Drosophila S2 cells induces defects in spindle MTs and chromosome segregation in anaphase, and the cells eventually stop growing. Our results demonstrate that distinctly from its role in spindle assembly, RanGTP maintains spindle MTs in anaphase through the local activation of ISWI and that this is essential for proper chromosome segregation.

scholarly journals Differentiation of Cytoplasmic and Meiotic Spindle Assembly MCAK Functions by Aurora B-dependent Phosphorylation

2004 ◽  
Vol 15 (6) ◽  
pp. 2895-2906 ◽  
Author(s):  
Ryoma Ohi ◽  
Tanuj Sapra ◽  
Jonathan Howard ◽  
Timothy J. Mitchison
Keyword(s):  
Chromosome Segregation ◽  
Spindle Assembly ◽  
Microtubule Dynamics ◽  
Meiotic Spindle ◽  
Aurora B ◽  
Dependent Manner ◽  
Dynamic Nature ◽  
Spindle Microtubule ◽  
Bipolar Spindles

The KinI kinesin MCAK is a microtubule depolymerase important for governing spindle microtubule dynamics during chromosome segregation. The dynamic nature of spindle assembly and chromosome-microtubule interactions suggest that mechanisms must exist that modulate the activity of MCAK, both spatially and temporally. In Xenopus extracts, MCAK associates with and is stimulated by the inner centromere protein ICIS. The inner centromere kinase Aurora B also interacts with ICIS and MCAK raising the possibility that Aurora B may regulate MCAK activity as well. Herein, we demonstrate that recombinant Aurora B-INCENP inhibits Xenopus MCAK activity in vitro in a phosphorylation-dependent manner. Substituting endogenous MCAK in Xenopus extracts with the alanine mutant XMCAK-4A, which is resistant to inhibition by Aurora B-INCENP, led to assembly of mono-astral and monopolar structures instead of bipolar spindles. The size of these structures and extent of tubulin polymerization in XMCAK-4A extracts indicate that XM-CAK-4A is not defective for microtubule dynamics regulation throughout the cytoplasm. We further demonstrate that the ability of XMCAK-4A to localize to inner centromeres is abolished. Our results show that MCAK regulation of cytoplasmic and spindle-associated microtubules can be differentiated by Aurora B-dependent phosphorylation, and they further demonstrate that this regulation is required for bipolar meiotic spindle assembly.

scholarly journals Nup98 regulates bipolar spindle assembly through association with microtubules and opposition of MCAK

2011 ◽  
Vol 22 (5) ◽  
pp. 661-672 ◽  
Author(s):  
Marie K. Cross ◽  
Maureen A. Powers
Keyword(s):  
Nuclear Pore Complex ◽  
Mitotic Spindle ◽  
Spindle Assembly ◽  
Microtubule Dynamics ◽  
Nuclear Pore ◽  
Bipolar Spindle ◽  
Terminal Domain ◽  
C Terminus ◽  
Mitotic Spindle Assembly

During mitosis, the nuclear pore complex is disassembled and, increasingly, nucleoporins are proving to have mitotic functions when released from the pore. We find a contribution of the nucleoporin Nup98 to mitotic spindle assembly through regulation of microtubule dynamics. When added to Xenopus extract spindle assembly assays, the C-terminal domain of Nup98 stimulates uncontrolled growth of microtubules. Conversely, inhibition or depletion of Nup98 leads to formation of stable monopolar spindles. Spindle bipolarity is restored by addition of purified, recombinant Nup98 C-terminus. The minimal required region of Nup98 corresponds to a portion of the C-terminal domain lacking a previously characterized function. We show association between this region of the C-terminus of Nup98 and both Taxol-stabilized microtubules and the microtubule-depolymerizing mitotic centromere–associated kinesin (MCAK). Importantly, we demonstrate that this domain of Nup98 inhibits MCAK depolymerization activity in vitro. These data support a model in which Nup98 interacts with microtubules and antagonizes MCAK activity, thus promoting bipolar spindle assembly.

scholarly journals Characterization of the TPX2 Domains Involved in Microtubule Nucleation and Spindle Assembly in Xenopus Egg Extracts

2004 ◽  
Vol 15 (12) ◽  
pp. 5318-5328 ◽  
Author(s):  
Stéphane Brunet ◽  
Teresa Sardon ◽  
Timo Zimmerman ◽  
Torsten Wittmann ◽  
Rainer Pepperkok ◽  
...  
Keyword(s):  
Spindle Assembly ◽  
Aurora A Kinase ◽  
Aurora A ◽  
Microtubule Nucleation ◽  
Terminal Domain ◽  
Large N ◽  
Egg Extracts ◽  
Xenopus Egg ◽  
Domain Functional ◽  
Xenopus Egg Extracts

TPX2 has multiple functions during mitosis, including microtubule nucleation around the chromosomes and the targeting of Xklp2 and Aurora A to the spindle. We have performed a detailed domain functional analysis of TPX2 and found that a large N-terminal domain containing the Aurora A binding peptide interacts directly with and nucleates microtubules in pure tubulin solutions. However, it cannot substitute the endogenous TPX2 to support microtubule nucleation in response to Ran guanosine triphosphate (GTP) and spindle assembly in egg extracts. By contrast, a large C-terminal domain of TPX2 that does not bind directly to pure microtubules and does not bind Aurora A kinase rescues microtubule nucleation in response to RanGTP and spindle assembly in TPX2-depleted extract. These and previous results suggest that under physiological conditions, TPX2 is essential for microtubule nucleation around chromatin and functions in a network of other molecules, some of which also are regulated by RanGTP.

scholarly journals PP2A-B56 opposes Mps1 phosphorylation of Knl1 and thereby promotes spindle assembly checkpoint silencing

2014 ◽  
Vol 206 (7) ◽  
pp. 833-842 ◽  
Author(s):  
Antonio Espert ◽  
Pelin Uluocak ◽  
Ricardo Nunes Bastos ◽  
Davinderpreet Mangat ◽  
Philipp Graab ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Mammalian Cells ◽  
Feedback Loop ◽  
Spindle Assembly Checkpoint ◽  
Spindle Assembly ◽  
Eukaryotic Cells ◽  
Aurora B ◽  
Safeguard Mechanism

The spindle assembly checkpoint (SAC) monitors correct attachment of chromosomes to microtubules, an important safeguard mechanism ensuring faithful chromosome segregation in eukaryotic cells. How the SAC signal is turned off once all the chromosomes have successfully attached to the spindle remains an unresolved question. Mps1 phosphorylation of Knl1 results in recruitment of the SAC proteins Bub1, Bub3, and BubR1 to the kinetochore and production of the wait-anaphase signal. SAC silencing is therefore expected to involve a phosphatase opposing Mps1. Here we demonstrate in vivo and in vitro that BubR1-associated PP2A-B56 is a key phosphatase for the removal of the Mps1-mediated Knl1 phosphorylations necessary for Bub1/BubR1 recruitment in mammalian cells. SAC silencing is thus promoted by a negative feedback loop involving the Mps1-dependent recruitment of a phosphatase opposing Mps1. Our findings extend the previously reported role for BubR1-associated PP2A-B56 in opposing Aurora B and suggest that BubR1-bound PP2A-B56 integrates kinetochore surveillance and silencing of the SAC.

scholarly journals Stepwise Reconstitution of Interphase Microtubule Dynamics in Permeabilized Cells and Comparison to Dynamic Mechanisms in Intact Cells

1998 ◽  
Vol 142 (6) ◽  
pp. 1519-1532 ◽  
Author(s):  
Yasmina Saoudi ◽  
Rati Fotedar ◽  
Ariane Abrieu ◽  
Marcel Dorée ◽  
Jürgen Wehland ◽  
...  
Keyword(s):  
Model System ◽  
Microtubule Dynamics ◽  
In Vitro Assays ◽  
Microtubule Depolymerization ◽  
Dynamic Activity ◽  
Intact Cells ◽  
Permeabilized Cells ◽  
Cell Extracts

Microtubules in permeabilized cells are devoid of dynamic activity and are insensitive to depolymerizing drugs such as nocodazole. Using this model system we have established conditions for stepwise reconstitution of microtubule dynamics in permeabilized interphase cells when supplemented with various cell extracts. When permeabilized cells are supplemented with mammalian cell extracts in the presence of protein phosphatase inhibitors, microtubules become sensitive to nocodazole. Depolymerization induced by nocodazole proceeds from microtubule plus ends, whereas microtubule minus ends remain inactive. Such nocodazole-sensitive microtubules do not exhibit subunit turnover. By contrast, when permeabilized cells are supplemented with Xenopus egg extracts, microtubules actively turn over. This involves continuous creation of free microtubule minus ends through microtubule fragmentation. Newly created minus ends apparently serve as sites of microtubule depolymerization, while net microtubule polymerization occurs at microtubule plus ends. We provide evidence that similar microtubule fragmentation and minus end–directed disassembly occur at the whole-cell level in intact cells. These data suggest that microtubule dynamics resembling dynamics observed in vivo can be reconstituted in permeabilized cells. This model system should provide means for in vitro assays to identify molecules important in regulating microtubule dynamics. Furthermore, our data support recent work suggesting that microtubule treadmilling is an important mechanism of microtubule turnover.

scholarly journals Spastin Interacts with CRMP5 to Promote  Spindle Organization of Mouse Oocytes by  Severing Microtubules.

2020 ◽  
Author(s):  
Hua-Feng Shou ◽  
Lei-lei Gao ◽  
Zhen Jin ◽  
Jin-Wei Liu ◽  
Shan-Shan Jiang ◽  
...  
Keyword(s):  
Developmental Disorders ◽  
Spindle Assembly ◽  
Microtubule Dynamics ◽  
Spindle Microtubule ◽  
Microtubule Severing ◽  
Abnormal Phenotype ◽  
Mammalian Oocyte ◽  
Spindle Microtubules ◽  
Normal Meiosis

Abstract Background ： Microtubule-severing protein (MTSP) is highly critical for the survival of both mitotic and post-mitotic cells.However, the study of MTSP in the meiosis of mammalian oocyte has not been reported. Results ：We found that spastin, a member of the MTSP family, was highly expressed in oocyte and aggregated in spindle microtubules. After knocking down spastin by specific siRNA, the spindle microtubule density of meiotic oocyte decreased significantly. When the oocyte was cultured in vitro, the oocyte lacking spastin showed obvious maturation obstacles. Combining with the microtubule severing activity of spastin, we speculate that spastin on spindle may increase the microtubule broken ends by severing microtubules, thus playing a nucleating role, promoting spindle assembly and ensuring normal meiosis. In addition, we found that there was co-localization and interaction between CRMP5 and spastin in oocyte. The knockdown of CRMP5 may also lead to spindle abnormalities and developmental disorders in oocyte. Overexpression of spastin may save the abnormal phenotype caused by deletion of CRMP5. Conclusions ：To sum up, our data support a model in which the interaction between spastin and CRMP5 promotes the assembly of spindle microtubules in oocyte by controlling microtubule dynamics, thus ensuring normal meiosis.

Topoisomerase II forms multimers in vitro: effects of metals, beta-glycerophosphate, and phosphorylation of its C-terminal domain

1994 ◽  
Vol 14 (10) ◽  
pp. 6962-6974
Author(s):  
Y S Vassetzky ◽  
Q Dang ◽  
P Benedetti ◽  
S M Gasser
Keyword(s):  
Chromosome Segregation ◽  
Protein Interactions ◽  
Topoisomerase Ii ◽  
Dna Topoisomerase Ii ◽  
Protein Protein Interactions ◽  
Dna Topoisomerase ◽  
Terminal Domain ◽  
Terminal Amino ◽  
In Vitro Effects

We present a novel assay for the study of protein-protein interactions involving DNA topoisomerase II. Under various conditions of incubation we observe that topoisomerase II forms complexes at least tetrameric in size, which can be sedimented by centrifugation through glycerol. The multimers are enzymatically active and can be visualized by electron microscopy. Dephosphorylation of topoisomerase II inhibits its multimerization, which can be restored at least partially by rephosphorylation of multiple sites within its 200 C-terminal amino acids by casein kinase II. Truncation of topoisomerase II just upstream of the major phosphoacceptor sites reduces its aggregation, rendering the truncated enzyme insensitive to either kinase treatments or phosphatase treatments. This is consistent with a model in which interactions involving the phosphorylated C-terminal domain of topoisomerase II aid either in chromosome segregation or in chromosome condensation.

scholarly journals MukB ATPases are regulated independently by the N- and C-terminal domains of MukF kleisin

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Katarzyna Zawadzka ◽  
Pawel Zawadzki ◽  
Rachel Baker ◽  
Karthik V Rajasekar ◽  
Florence Wagner ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Chromosome Segregation ◽  
Atp Hydrolysis ◽  
Helix Bundle ◽  
Terminal Domain ◽  
Terminal Domains

The Escherichia coli SMC complex, MukBEF, acts in chromosome segregation. MukBEF shares the distinctive architecture of other SMC complexes, with one prominent difference; unlike other kleisins, MukF forms dimers through its N-terminal domain. We show that a 4-helix bundle adjacent to the MukF dimerisation domain interacts functionally with the MukB coiled-coiled ‘neck’ adjacent to the ATPase head. We propose that this interaction leads to an asymmetric tripartite complex, as in other SMC complexes. Since MukF dimerisation is preserved during this interaction, MukF directs the formation of dimer of dimer MukBEF complexes, observed previously in vivo. The MukF N- and C-terminal domains stimulate MukB ATPase independently and additively. We demonstrate that impairment of the MukF interaction with MukB in vivo leads to ATP hydrolysis-dependent release of MukBEF complexes from chromosomes.

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