Mitotic spindle morphogenesis: Ran on the microtubule cytoskeleton and beyond

2006 ◽  
Vol 34 (5) ◽  
pp. 716-721 ◽  
Author(s):  
B. Goodman ◽  
Y. Zheng
Keyword(s):  
Cell Division ◽  
Chromosome Segregation ◽  
Mitotic Spindle ◽  
Spindle Assembly ◽  
Microtubule Assembly ◽  
Microtubule Organization ◽  
Spindle Matrix ◽  
Small G Protein ◽  
Important Regulator

Assembly and disassembly of the mitotic spindle are essential for both chromosome segregation and cell division. The small G-protein Ran has emerged as an important regulator of spindle assembly. In this review, we look at the role of Ran in different aspects of spindle assembly, including its effects on microtubule assembly dynamics and microtubule organization. In addition, we examine the possibility of a spindle matrix and the role Ran might play in such a structure.

scholarly journals The Drosophila Kinesin-like Protein KLP67A Is Essential for Mitotic and Male Meiotic Spindle Assembly

2004 ◽  
Vol 15 (1) ◽  
pp. 121-131 ◽  
Author(s):  
Rita Gandhi ◽  
Silvia Bonaccorsi ◽  
Diana Wentworth ◽  
Stephen Doxsey ◽  
Maurizio Gatti ◽  
...  
Keyword(s):  
Cell Division ◽  
Chromosome Segregation ◽  
Mutational Analysis ◽  
Spindle Assembly ◽  
Male Meiosis ◽  
Meiotic Spindle ◽  
Drosophila Cell ◽  
Centrosome Separation ◽  
Mutant Cells

We have performed a mutational analysis together with RNA interference to determine the role of the kinesin-like protein KLP67A in Drosophila cell division. During both mitosis and male meiosis, Klp67A mutations cause an increase in MT length and disrupt discrete aspects of spindle assembly, as well as cytokinesis. Mutant cells exhibit greatly enlarged metaphase spindle as a result of excessive MT polymerization. The analysis of both living and fixed cells also shows perturbations in centrosome separation, chromosome segregation, and central spindle assembly. These data demonstrate that the MT plus end-directed motor KLP67A is essential for spindle assembly during mitosis and male meiosis and suggest that the regulation of MT plus-end polymerization is a key determinant of spindle architecture throughout cell division.

scholarly journals Moesin and its activating kinase Slik are required for cortical stability and microtubule organization in mitotic cells

2008 ◽  
Vol 180 (4) ◽  
pp. 739-746 ◽  
Author(s):  
Sébastien Carreno ◽  
Ilektra Kouranti ◽  
Edith Szafer Glusman ◽  
Margaret T. Fuller ◽  
Arnaud Echard ◽  
...  
Keyword(s):  
Cell Division ◽  
Chromosome Segregation ◽  
Mitotic Spindle ◽  
Cortical Actin ◽  
Microtubule Organization ◽  
Abnormal Distribution ◽  
Multistep Process ◽  
Cortical Contractility ◽  
Spatiotemporal Control ◽  
Shape Changes

Cell division requires cell shape changes involving the localized reorganization of cortical actin, which must be tightly linked with chromosome segregation operated by the mitotic spindle. How this multistep process is coordinated remains poorly understood. In this study, we show that the actin/membrane linker moesin, the single ERM (ezrin, radixin, and moesin) protein in Drosophila melanogaster, is required to maintain cortical stability during mitosis. Mitosis onset is characterized by a burst of moesin activation mediated by a Slik kinase–dependent phosphorylation. Activated moesin homogenously localizes at the cortex in prometaphase and is progressively restricted at the equator in later stages. Lack of moesin or inhibition of its activation destabilized the cortex throughout mitosis, resulting in severe cortical deformations and abnormal distribution of actomyosin regulators. Inhibiting moesin activation also impaired microtubule organization and precluded stable positioning of the mitotic spindle. We propose that the spatiotemporal control of moesin activation at the mitotic cortex provides localized cues to coordinate cortical contractility and microtubule interactions during cell division.

scholarly journals Ran Is Required before Metaphase for Spindle Assembly and Chromosome Alignment and after Metaphase for Chromosome Segregation and Spindle Midbody Organization

2006 ◽  
Vol 17 (4) ◽  
pp. 2069-2080 ◽  
Author(s):  
Rosalind V. Silverman-Gavrila ◽  
Andrew Wilde
Keyword(s):  
Chromosome Segregation ◽  
Metaphase Plate ◽  
Spindle Assembly ◽  
Aurora A ◽  
Microtubule Organization ◽  
Chromosome Alignment ◽  
Production Organization ◽  
Drosophila Embryos

The Ran pathway has been shown to have a role in spindle assembly. However, the extent of the role of the Ran pathway in mitosis in vivo is unclear. We report that perturbation of the Ran pathway disrupted multiple steps of mitosis in syncytial Drosophila embryos and uncovered new mitotic processes that are regulated by Ran. During the onset of mitosis, the Ran pathway is required for the production, organization, and targeting of centrosomally nucleated microtubules to chromosomes. However, the role of Ran is not restricted to microtubule organization, because Ran is also required for the alignment of chromosomes at the metaphase plate. In addition, the Ran pathway is required for postmetaphase events, including chromosome segregation and the assembly of the microtubule midbody. The Ran pathway mediates these mitotic events, in part, by facilitating the correct targeting of the kinase Aurora A and the kinesins KLP61F and KLP3A to spindles.

scholarly journals The nonmotor adaptor HMMR dampens Eg5-mediated forces to preserve the kinetics and integrity of chromosome segregation

2018 ◽  
Vol 29 (7) ◽  
pp. 786-796 ◽  
Author(s):  
Helen Chen ◽  
Marisa Connell ◽  
Lin Mei ◽  
Gregor S. D. Reid ◽  
Christopher A. Maxwell
Keyword(s):  
Chromosome Segregation ◽  
Mitotic Spindle ◽  
Spindle Assembly ◽  
Adaptor Proteins ◽  
Microtubule Organization ◽  
Assembly Factor ◽  
Mitotic Spindle Assembly ◽  
Chemical Inhibition ◽  
Kinesin Eg5 ◽  
Interfering Rna

Mitotic spindle assembly and organization require forces generated by motor proteins. The activity of these motors is regulated by nonmotor adaptor proteins. However, there are limited studies reporting the functional importance of adaptors on the balance of motor forces and the promotion of faithful and timely cell division. Here we show that genomic deletion or small interfering RNA silencing of the nonmotor adaptor Hmmr/HMMR disturbs spindle microtubule organization and bipolar chromosome–kinetochore attachments with a consequent elevated occurrence of aneuploidy. Rescue experiments show a conserved motif in HMMR is required to generate interkinetochore tension and promote anaphase entry. This motif bears high homology with the kinesin Kif15 and is known to interact with TPX2, a spindle assembly factor. We find that HMMR is required to dampen kinesin Eg5-mediated forces through localizing TPX2 and promoting the formation of inhibitory TPX2-Eg5 complexes. In HMMR-silenced cells, K-fiber stability is reduced while the frequency of unattached chromosomes and the time needed for chromosome segregation are both increased. These defects can be alleviated in HMMR-silenced cells with chemical inhibition of Eg5 but not through the silencing of Kif15. Together, our findings indicate that HMMR balances Eg5-­mediated forces to preserve the kinetics and integrity of chromosome segregation.

FANCA Controls Mitotic Phosphosignaling Networks To Ensure Genome Stability During Cell Division

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 801-801
Author(s):  
Rikki Enzor ◽  
Zahi Abdul Sater ◽  
Donna Cerabona ◽  
Zejin Sun ◽  
Su-jung Park ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Division ◽  
Chromosome Segregation ◽  
Fanconi Anemia ◽  
Spindle Assembly Checkpoint ◽  
Spindle Assembly ◽  
Signaling Network ◽  
Mitotic Apparatus ◽  
Risk Of Cancer

Abstract Fanconi anemia (FA) is a heterogenous genome instability syndrome with a high risk of cancer. The FA proteins are essential for interphase DNA damage repair. However, it is incompletely understood why FA-deficient cells also develop gross aneuploidy and multinucleation, which are symptoms of error-prone chromosome segregation. Emerging evidence indicates that the FA signaling network functions as a guardian of the genome throughout the cell cycle, including chromosome segregation during mitosis. However, the mechanistic aspects of the critical role of the FA signaling in mitosis remain poorly understood. We have recently shown that the FA signaling network localizes to the mitotic apparatus to control the spindle assembly checkpoint and centrosome maintenance (J Clin Invest 2013, in press). The spindle assembly checkpoint (SAC) is a complex tumor suppressor signaling network that prevents premature separation of sister chromatids by delaying the metaphase-to-anaphase transition until all the kinetochores are properly attached to the mitotic spindle. Since weakened SAC promotes stochastic chromosome segregation, mutagenesis and cancer, these findings shed new light on the role of FA signaling in maintenance of genomic stability. We found the subcellular localization of FA proteins to the mitotic apparatus is spatiotemporally regulated as cells divide. Our new data revealed the pathways connecting the FANCA protein with canonical mitotic phosphosignaling networks. We have employed unbiased kinome-wide phospho-mass spectrometry to compare the landscape of abnormalities of mitotic signaling pathways in primary FANCA-/- patient cells and gene-corrected isogenic cells. These experiments led us to identify and quantify a wide range of phosphorylation abnormalities of multiple FANCA-dependent centrosome-, kinetochore- and chromosome-associated regulators of mitosis. Our data illuminated the role for FA signaling in three critical stages of cell division: (1) the spindle assembly checkpoint, (2) anaphase and (3) cytokinesis. Thus, we employed live phase-contrast imaging of primary FANCA-/- patient cells in comparison to gene-corrected cells to separately quantify aberrations in (1) chromosome congression and metaphase-anaphase transition (SAC malfunction), (2) execution of anaphase and (3) completion of cytokinesis. Our findings further our understanding of human cell cycle control and provide new insights into the origins of genomic instability in Fanconi anemia by establishing mechanistic connection between the FANCA protein and key mitotic signaling networks. The identification of cell division pathways regulated by FANCA has implications for future targeted drug development in Fanconi anemia and FA-deficient malignancies in the general population. Disclosures: No relevant conflicts of interest to declare.

fumble Encodes a Pantothenate Kinase Homolog Required for Proper Mitosis and Meiosis in Drosophila melanogaster

Genetics ◽  
2001 ◽  
Vol 157 (3) ◽  
pp. 1267-1276
Author(s):  
Katayoun Afshar ◽  
Pierre Gönczy ◽  
Stephen DiNardo ◽  
Steven A Wasserman
Keyword(s):  
Cell Division ◽  
Chromosome Segregation ◽  
Cell Division Cycle ◽  
Protein Isoforms ◽  
Pantothenate Kinase ◽  
Male Germline ◽  
Dividing Cells ◽  
Mutant Cells ◽  
Mitosis And Meiosis

Abstract A number of fundamental processes comprise the cell division cycle, including spindle formation, chromosome segregation, and cytokinesis. Our current understanding of these processes has benefited from the isolation and analysis of mutants, with the meiotic divisions in the male germline of Drosophila being particularly well suited to the identification of the required genes. We show here that the fumble (fbl) gene is required for cell division in Drosophila. We find that dividing cells in fbl-deficient testes exhibit abnormalities in bipolar spindle organization, chromosome segregation, and contractile ring formation. Cytological analysis of larval neuroblasts from null mutants reveals a reduced mitotic index and the presence of polyploid cells. Molecular analysis demonstrates that fbl encodes three protein isoforms, all of which contain a domain with high similarity to the pantothenate kinases of A. nidulans and mouse. The largest Fumble isoform is dispersed in the cytoplasm during interphase, concentrates around the spindle at metaphase, and localizes to the spindle midbody at telophase. During early embryonic development, the protein localizes to areas of membrane deposition and/or rearrangement, such as the metaphase and cellularization furrows. Given the role of pantothenate kinase in production of Coenzyme A and in phospholipid biosynthesis, this pattern of localization is suggestive of a role for fbl in membrane synthesis. We propose that abnormalities in synthesis and redistribution of membranous structures during the cell division cycle underlie the cell division defects in fbl mutant cells.

The role of gamma-tubulin in mitotic spindle formation and cell cycle progression in Aspergillus nidulans

1997 ◽  
Vol 110 (5) ◽  
pp. 623-633 ◽  
Author(s):  
M.A. Martin ◽  
S.A. Osmani ◽  
B.R. Oakley
Keyword(s):  
Cell Cycle ◽  
Mitotic Spindle ◽  
Cell Cycle Progression ◽  
Spindle Pole ◽  
Microtubule Assembly ◽  
Cytoplasmic Microtubule ◽  
Cycle Progression ◽  
Spindle Microtubules ◽  
Gamma Tubulin

gamma-Tubulin has been hypothesized to be essential for the nucleation of the assembly of mitotic spindle microtubules, but some recent results suggest that this may not be the case. To clarify the role of gamma-tubulin in microtubule assembly and cell-cycle progression, we have developed a novel variation of the gene disruption/heterokaryon rescue technique of Aspergillus nidulans. We have used temperature-sensitive cell-cycle mutations to synchronize germlings carrying a gamma-tubulin disruption and observe the phenotypes caused by the disruption in the first cell cycle after germination. Our results indicate that gamma-tubulin is absolutely required for the assembly of mitotic spindle microtubules, a finding that supports the hypothesis that gamma-tubulin is involved in spindle microtubule nucleation. In the absence of functional gamma-tubulin, nuclei are blocked with condensed chromosomes for about the length of one cell cycle before chromatin decondenses without nuclear division. Our results indicate that gamma-tubulin is not essential for progression from G1 to G2, for entry into mitosis nor for spindle pole body replication. It is also not required for reactivity of spindle pole bodies with the MPM-2 antibody which recognizes a phosphoepitope important to mitotic spindle formation. Finally, it does not appear to be absolutely required for cytoplasmic microtubule assembly but may play a role in the formation of normal cytoplasmic microtubule arrays.

Regulation of Microtubule Assembly: The View From The End

2000 ◽  
Vol 6 (S2) ◽  
pp. 80-81
Author(s):  
L. Cassimeris ◽  
C. Spittle ◽  
M. Kratzer
Keyword(s):  
Chromosome Segregation ◽  
Mitotic Spindle ◽  
Dynamic Instability ◽  
Intrinsic Property ◽  
Microtubule Dynamics ◽  
Microtubule Assembly ◽  
Chromosome Movement ◽  
Spindle Formation ◽  
Associated Proteins

The mitotic spindle is responsible for chromosome movement during mitosis. It is composed of a dynamic array of microtubules and associated proteins whose assembly and constant turnover are required for both spindle formation and chromosome movement. Because microtubule assembly and turnover are necessary for chromosome segregation, we are studying how cells regulate microtubule dynamics. Microtubules are polarized polymers composed of tubulin subunits; they assemble by a process of dynamic instability where individual microtubules exist in persistent phases of elongation or rapid shortening with abrupt transitions between these two states. The switch from elongation to shortening is termed catastrophe, and the switch from shortening to elongation, rescue. Although dynamic instability is an intrinsic property of the tubulin subunits, cells use associated proteins to both speed elongation (∼ 10 fold) and regulate transitions.The only protein isolated to date capable of promoting fast polymerization consistent with rates in vivo is XMAP215, a 215 kD protein from Xenopus eggs.

scholarly journals Synergistic role of fission yeast Alp16GCP6 and Mzt1MOZART1 in γ-tubulin complex recruitment to mitotic spindle pole bodies and spindle assembly

2016 ◽  
Vol 27 (11) ◽  
pp. 1753-1763 ◽  
Author(s):  
Hirohisa Masuda ◽  
Takashi Toda
Keyword(s):  
Fission Yeast ◽  
Mitotic Spindle ◽  
Spindle Assembly Checkpoint ◽  
Synthetic Lethality ◽  
Spindle Assembly ◽  
Spindle Pole ◽  
Microtubule Assembly ◽  
Spindle Microtubule ◽  
Spindle Pole Bodies ◽  
Mitotic Spindle Pole

In fission yeast, γ-tubulin ring complex (γTuRC)–specific components Gfh1GCP4, Mod21GCP5, and Alp16GCP6 are nonessential for cell growth. Of these deletion mutants, only alp16Δ shows synthetic lethality with temperature-sensitive mutants of Mzt1MOZART1, a component of the γTuRC required for recruitment of the complex to microtubule-organizing centers. γ-Tubulin small complex levels at mitotic spindle pole bodies (SPBs, the centrosome equivalent in fungi) and microtubule levels for preanaphase spindles are significantly reduced in alp16Δ cells but not in gfh1Δ or mod21Δ cells. Furthermore, alp16Δ cells often form monopolar spindles and frequently lose a minichromosome when the spindle assembly checkpoint is inactivated. Alp16GCP6 promotes Mzt1-dependent γTuRC recruitment to mitotic SPBs and enhances spindle microtubule assembly in a manner dependent on its expression levels. Gfh1GCP4 and Mod21GCP5 are not required for Alp16GCP6-dependent γTuRC recruitment. Mzt1 has an additional role in the activation of the γTuRC for spindle microtubule assembly. The ratio of Mzt1 to γTuRC levels for preanaphase spindles is higher than at other stages of the cell cycle. Mzt1 overproduction enhances spindle microtubule assembly without affecting γTuRC levels at mitotic SPBs. We propose that Alp16GCP6 and Mzt1 act synergistically for efficient bipolar spindle assembly to ensure faithful chromosome segregation.

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