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.

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 Evidence for a Role of CLIP-170 in the Establishment of Metaphase Chromosome Alignment

1998 ◽  
Vol 141 (4) ◽  
pp. 849-862 ◽  
Author(s):  
Denis Dujardin ◽  
U. Irene Wacker ◽  
Anne Moreau ◽  
Trina A. Schroer ◽  
Janet E. Rickard ◽  
...  
Keyword(s):  
Metaphase Plate ◽  
Polar Regions ◽  
Static Interaction ◽  
Transport Vesicles ◽  
Vitro Binding ◽  
Chromosome Alignment ◽  
Dynactin Complex

CLIPs (cytoplasmic linker proteins) are a class of proteins believed to mediate the initial, static interaction of organelles with microtubules. CLIP-170, the CLIP best characterized to date, is required for in vitro binding of endocytic transport vesicles to microtubules. We report here that CLIP-170 transiently associates with prometaphase chromosome kinetochores and codistributes with dynein and dynactin at kinetochores, but not polar regions, during mitosis. Like dynein and dynactin, a fraction of the total CLIP-170 pool can be detected on kinetochores of unattached chromosomes but not on those that have become aligned at the metaphase plate. The COOH-terminal domain of CLIP-170, when transiently overexpressed, localizes to kinetochores and causes endogenous full-length CLIP-170 to be lost from the kinetochores, resulting in a delay in prometaphase. Overexpression of the dynactin subunit, dynamitin, strongly reduces the amount of CLIP-170 at kinetochores suggesting that CLIP-170 targeting may involve the dynein/dynactin complex. Thus, CLIP-170 may be a linker for cargo in mitosis as well as interphase. However, dynein and dynactin staining at kinetochores are unaffected by this treatment and further overexpression studies indicate that neither CLIP-170 nor dynein and dynactin are required for the formation of kinetochore fibers. Nevertheless, these results strongly suggest that CLIP-170 contributes in some way to kinetochore function in vivo.

Meiotic CENP-C is a shepherd: bridging the space between the centromere and the kinetochore in time and space

2020 ◽  
Vol 64 (2) ◽  
pp. 251-261
Author(s):  
Jessica E. Fellmeth ◽  
Kim S. McKim
Keyword(s):  
Chromosome Segregation ◽  
New Technologies ◽  
Early Prophase ◽  
Unique Role ◽  
Kinetochore Assembly ◽  
M Phase ◽  
In Vivo Analysis ◽  
Meiosis I

Abstract While many of the proteins involved in the mitotic centromere and kinetochore are conserved in meiosis, they often gain a novel function due to the unique needs of homolog segregation during meiosis I (MI). CENP-C is a critical component of the centromere for kinetochore assembly in mitosis. Recent work, however, has highlighted the unique features of meiotic CENP-C. Centromere establishment and stability require CENP-C loading at the centromere for CENP-A function. Pre-meiotic loading of proteins necessary for homolog recombination as well as cohesion also rely on CENP-C, as do the main scaffolding components of the kinetochore. Much of this work relies on new technologies that enable in vivo analysis of meiosis like never before. Here, we strive to highlight the unique role of this highly conserved centromere protein that loads on to centromeres prior to M-phase onset, but continues to perform critical functions through chromosome segregation. CENP-C is not merely a structural link between the centromere and the kinetochore, but also a functional one joining the processes of early prophase homolog synapsis to late metaphase kinetochore assembly and signaling.

scholarly journals The equatorial position of the metaphase plate ensures symmetric cell divisions

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Chia Huei Tan ◽  
Ivana Gasic ◽  
Sabina P Huber-Reggi ◽  
Damian Dudka ◽  
Marin Barisic ◽  
...  
Keyword(s):  
Spindle Assembly Checkpoint ◽  
Metaphase Plate ◽  
Spindle Assembly ◽  
Equatorial Position ◽  
Asymmetric Cell Divisions ◽  
Daughter Cells ◽  
Cell Divisions ◽  
Microtubule Stability ◽  
Chromosome Alignment ◽  
Metazoan Cell

Chromosome alignment in the middle of the bipolar spindle is a hallmark of metazoan cell divisions. When we offset the metaphase plate position by creating an asymmetric centriole distribution on each pole, we find that metaphase plates relocate to the middle of the spindle before anaphase. The spindle assembly checkpoint enables this centering mechanism by providing cells enough time to correct metaphase plate position. The checkpoint responds to unstable kinetochore–microtubule attachments resulting from an imbalance in microtubule stability between the two half-spindles in cells with an asymmetric centriole distribution. Inactivation of the checkpoint prior to metaphase plate centering leads to asymmetric cell divisions and daughter cells of unequal size; in contrast, if the checkpoint is inactivated after the metaphase plate has centered its position, symmetric cell divisions ensue. This indicates that the equatorial position of the metaphase plate is essential for symmetric cell divisions.

scholarly journals Early Spindle Assembly in Drosophila Embryos: Role of a Force Balance Involving Cytoskeletal Dynamics and Nuclear Mechanics

2005 ◽  
Vol 16 (10) ◽  
pp. 4967-4981 ◽  
Author(s):  
E. N. Cytrynbaum ◽  
P. Sommi ◽  
I. Brust-Mascher ◽  
J. M. Scholey ◽  
A. Mogilner
Keyword(s):  
Spindle Assembly ◽  
Spindle Pole ◽  
Cortical Reorganization ◽  
Force Balance ◽  
Cell Cortex ◽  
Nuclear Dynamics ◽  
Nuclear Mechanics ◽  
Cytoskeletal Dynamics ◽  
Drosophila Embryos

Mitotic spindle morphogenesis depends upon the action of microtubules (MTs), motors and the cell cortex. Previously, we proposed that cortical- and MT-based motors acting alone can coordinate early spindle assembly in Drosophila embryos. Here, we tested this model using microscopy of living embryos to analyze spindle pole separation, cortical reorganization, and nuclear dynamics in interphase-prophase of cycles 11-13. We observe that actin caps remain flat as they expand and that furrows do not ingress. As centrosomes separate, they follow a linear trajectory, maintaining a constant pole-to-furrow distance while the nucleus progressively deforms along the elongating pole-pole axis. These observations are incorporated into a model in which outward forces generated by zones of active cortical dynein are balanced by inward forces produced by nuclear elasticity and during cycle 13, by Ncd, which localizes to interpolar MTs. Thus, the force-balance driving early spindle morphogenesis depends upon MT-based motors acting in concert with the cortex and nucleus.

scholarly journals The essential role of LIS1, NDEL1 and Aurora-A in polarity formation and microtubule organization during neurogensis

2010 ◽  
Vol 4 (2) ◽  
pp. 180-184 ◽  
Author(s):  
Masami Yamada ◽  
Shinji Hirotsune ◽  
Anthony Wynshaw-Boris
Keyword(s):  
Essential Role ◽  
Aurora A ◽  
Microtubule Organization

scholarly journals Interaction of Aurora-A and centrosomin at the microtubule-nucleating site in Drosophila and mammalian cells

2003 ◽  
Vol 162 (5) ◽  
pp. 757-764 ◽  
Author(s):  
Yasuhiko Terada ◽  
Yumi Uetake ◽  
Ryoko Kuriyama
Keyword(s):  
Mammalian Cells ◽  
Aurora A Kinase ◽  
Aurora A ◽  
Mitotic Spindles ◽  
Microtubule Nucleation ◽  
Microtubule Organization ◽  
Centrosomal Protein ◽  
Spindle Poles

A mitosis-specific Aurora-A kinase has been implicated in microtubule organization and spindle assembly in diverse organisms. However, exactly how Aurora-A controls the microtubule nucleation onto centrosomes is unknown. Here, we show that Aurora-A specifically binds to the COOH-terminal domain of a Drosophila centrosomal protein, centrosomin (CNN), which has been shown to be important for assembly of mitotic spindles and spindle poles. Aurora-A and CNN are mutually dependent for localization at spindle poles, which is required for proper targeting of γ-tubulin and other centrosomal components to the centrosome. The NH2-terminal half of CNN interacts with γ-tubulin, and induces cytoplasmic foci that can initiate microtubule nucleation in vivo and in vitro in both Drosophila and mammalian cells. These results suggest that Aurora-A regulates centrosome assembly by controlling the CNN's ability to targeting and/or anchoring γ-tubulin to the centrosome and organizing microtubule-nucleating sites via its interaction with the COOH-terminal sequence of CNN.

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 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 Cdk1 and Plk1 mediate a CLASP2 phospho-switch that stabilizes kinetochore–microtubule attachments

2012 ◽  
Vol 199 (2) ◽  
pp. 285-301 ◽  
Author(s):  
Ana R.R. Maia ◽  
Zaira Garcia ◽  
Lilian Kabeche ◽  
Marin Barisic ◽  
Stefano Maffini ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Spindle Assembly Checkpoint ◽  
Regulatory Mechanism ◽  
Stable Condition ◽  
Spindle Assembly ◽  
Chromosome Alignment ◽  
Chromosome Movements

Accurate chromosome segregation during mitosis relies on a dynamic kinetochore (KT)–microtubule (MT) interface that switches from a labile to a stable condition in response to correct MT attachments. This transition is essential to satisfy the spindle-assembly checkpoint (SAC) and couple MT-generated force with chromosome movements, but the underlying regulatory mechanism remains unclear. In this study, we show that during mitosis the MT- and KT-associated protein CLASP2 is progressively and distinctively phosphorylated by Cdk1 and Plk1 kinases, concomitant with the establishment of KT–MT attachments. CLASP2 S1234 was phosphorylated by Cdk1, which primed CLASP2 for association with Plk1. Plk1 recruitment to KTs was enhanced by CLASP2 phosphorylation on S1234. This was specifically required to stabilize KT–MT attachments important for chromosome alignment and to coordinate KT and non-KT MT dynamics necessary to maintain spindle bipolarity. CLASP2 C-terminal phosphorylation by Plk1 was also required for chromosome alignment and timely satisfaction of the SAC. We propose that Cdk1 and Plk1 mediate a fine CLASP2 “phospho-switch” that temporally regulates KT–MT attachment stability.

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