scholarly journals Long astral microtubules uncouple mitotic spindles from the cytokinetic furrow

2010 ◽  
Vol 190 (1) ◽  
pp. 35-43 ◽  
Author(s):  
Kathleen E. Rankin ◽  
Linda Wordeman
Keyword(s):  
Mitotic Spindle ◽  
Contractile Activity ◽  
Mitotic Spindles ◽  
Cortical Actin ◽  
Spindle Positioning ◽  
Actin Cortex ◽  
Nonmuscle Myosin Ii ◽  
Early Anaphase ◽  
Cortical Contractility ◽  
Spindle Position

Astral microtubules (MTs) are known to be important for cleavage furrow induction and spindle positioning, and loss of astral MTs has been reported to increase cortical contractility. To investigate the effect of excess astral MT activity, we depleted the MT depolymerizer mitotic centromere-associated kinesin (MCAK) from HeLa cells to produce ultra-long, astral MTs during mitosis. MCAK depletion promoted dramatic spindle rocking in early anaphase, wherein the entire mitotic spindle oscillated along the spindle axis from one proto-daughter cell to the other, driven by oscillations of cortical nonmuscle myosin II. The effect was phenocopied by taxol treatment. Live imaging revealed that cortical actin partially vacates the polar cortex in favor of the equatorial cortex during anaphase. We propose that this renders the polar actin cortex vulnerable to rupture during normal contractile activity and that long astral MTs enlarge the blebs. Excessively large blebs displace mitotic spindle position by cytoplasmic flow, triggering the oscillations as the blebs resolve.

scholarly journals Cell shape impacts on the positioning of the mitotic spindle with respect to the substratum

2015 ◽  
Vol 26 (7) ◽  
pp. 1286-1295 ◽  
Author(s):  
Francisco Lázaro-Diéguez ◽  
Iaroslav Ispolatov ◽  
Anne Müsch
Keyword(s):  
Mitotic Spindle ◽  
Cell Shape ◽  
Spindle Assembly Checkpoint ◽  
Mdck Cells ◽  
Spindle Pole ◽  
Spindle Orientation ◽  
Cell Cortex ◽  
Spindle Positioning ◽  
Spindle Poles ◽  
Spindle Position

All known mechanisms of mitotic spindle orientation rely on astral microtubules. We report that even in the absence of astral microtubules, metaphase spindles in MDCK and HeLa cells are not randomly positioned along their x-z dimension, but preferentially adopt shallow β angles between spindle pole axis and substratum. The nonrandom spindle positioning is due to constraints imposed by the cell cortex in flat cells that drive spindles that are longer and/or wider than the cell's height into a tilted, quasidiagonal x-z position. In rounder cells, which are taller, fewer cortical constraints make the x-z spindle position more random. Reestablishment of astral microtubule–mediated forces align the spindle poles with cortical cues parallel to the substratum in all cells. However, in flat cells, they frequently cause spindle deformations. Similar deformations are apparent when confined spindles rotate from tilted to parallel positions while MDCK cells progress from prometaphase to metaphase. The spindle disruptions cause the engagement of the spindle assembly checkpoint. We propose that cell rounding serves to maintain spindle integrity during its positioning.

scholarly journals Control of Mitotic Spindle Position by the Saccharomyces cerevisiae Formin Bni1p

1999 ◽  
Vol 144 (5) ◽  
pp. 947-961 ◽  
Author(s):  
Laifong Lee ◽  
Saskia K. Klee ◽  
Marie Evangelista ◽  
Charles Boone ◽  
David Pellman
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Mitotic Spindle ◽  
Cortical Microtubule ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Spindle Orientation ◽  
Cell Cortex ◽  
Cortical Actin ◽  
Bud Site ◽  
Spindle Position

Alignment of the mitotic spindle with the axis of cell division is an essential process in Saccharomyces cerevisiae that is mediated by interactions between cytoplasmic microtubules and the cell cortex. We found that a cortical protein, the yeast formin Bni1p, was required for spindle orientation. Two striking abnormalities were observed in bni1Δ cells. First, the initial movement of the spindle pole body (SPB) toward the emerging bud was defective. This phenotype is similar to that previously observed in cells lacking the kinesin Kip3p and, in fact, BNI1 and KIP3 were found to be in the same genetic pathway. Second, abnormal pulling interactions between microtubules and the cortex appeared to cause preanaphase spindles in bni1Δ cells to transit back and forth between the mother and the bud. We therefore propose that Bni1p may localize or alter the function of cortical microtubule-binding sites in the bud. Additionally, we present evidence that other bipolar bud site determinants together with cortical actin are also required for spindle orientation.

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 Control of nuclear centration in the C. elegans zygote by receptor-independent Gα signaling and myosin II

2007 ◽  
Vol 178 (7) ◽  
pp. 1177-1191 ◽  
Author(s):  
Morgan B. Goulding ◽  
Julie C. Canman ◽  
Eric N. Senning ◽  
Andrew H. Marcus ◽  
Bruce Bowerman
Keyword(s):  
Mitotic Spindle ◽  
Myosin Ii ◽  
Nonmuscle Myosin ◽  
Wild Type ◽  
Spindle Positioning ◽  
C Elegans ◽  
Nonmuscle Myosin Ii ◽  
Pulling Forces ◽  
Actomyosin Contraction

Mitotic spindle positioning in the Caenorhabditis elegans zygote involves microtubule-dependent pulling forces applied to centrosomes. In this study, we investigate the role of actomyosin in centration, the movement of the nucleus–centrosome complex (NCC) to the cell center. We find that the rate of wild-type centration depends equally on the nonmuscle myosin II NMY-2 and the Gα proteins GOA-1/GPA-16. In centration- defective let-99(−) mutant zygotes, GOA-1/GPA-16 and NMY-2 act abnormally to oppose centration. This suggests that LET-99 determines the direction of a force on the NCC that is promoted by Gα signaling and actomyosin. During wild-type centration, NMY-2–GFP aggregates anterior to the NCC tend to move further anterior, suggesting that actomyosin contraction could pull the NCC. In GOA-1/GPA-16–depleted zygotes, NMY-2 aggregate displacement is reduced and largely randomized, whereas in a let-99(−) mutant, NMY-2 aggregates tend to make large posterior displacements. These results suggest that Gα signaling and LET-99 control centration by regulating polarized actomyosin contraction.

scholarly journals Dynein-dependent Movements of the Mitotic Spindle inSaccharomyces cerevisiae Do Not Require Filamentous Actin

2000 ◽  
Vol 11 (3) ◽  
pp. 863-872 ◽  
Author(s):  
Richard A. Heil-Chapdelaine ◽  
Nguyen K. Tran ◽  
John A. Cooper
Keyword(s):  
Mitotic Spindle ◽  
Living Cell ◽  
Living Cells ◽  
Cell Populations ◽  
Cell Analysis ◽  
Mitotic Spindles ◽  
Filamentous Actin ◽  
Spindle Positioning ◽  
Latrunculin A ◽  
Two Phases

In budding yeast, the mitotic spindle is positioned in the neck between the mother and the bud so that both cells inherit one nucleus. The movement of the mitotic spindle into the neck can be divided into two phases: (1) Kip3p-dependent movement of the nucleus to the neck and alignment of the short spindle, followed by (2) dynein-dependent movement of the spindle into the neck and oscillation of the elongating spindle within the neck. Actin has been hypothesized to be involved in all these movements. To test this hypothesis, we disrupted the actin cytoskeleton with the use of mutations and latrunculin A (latrunculin). We assayed nuclear segregation in synchronized cell populations and observed spindle movements in individual living cells. In synchronized cell populations, no actin cytoskeletal mutant segregated nuclei as poorly as cells lacking dynein function. Furthermore, nuclei segregated efficiently in latrunculin-treated cells. Individual living cell analysis revealed that the preanaphase spindle was mispositioned and misaligned in latrunculin-treated cells and that astral microtubules were misoriented, confirming a role for filamentous actin in the early, Kip3p-dependent phase of spindle positioning. Surprisingly, mispositioned and misaligned mitotic spindles moved into the neck in the absence of filamentous actin, albeit less efficiently. Finally, dynein-dependent sliding of astral microtubules along the cortex and oscillation of the elongating mitotic spindle in the neck occurred in the absence of filamentous actin.

scholarly journals Automated mitotic spindle tracking suggests a link between spindle dynamics, spindle orientation, and anaphase onset in epithelial cells

2017 ◽  
Vol 28 (6) ◽  
pp. 746-759 ◽  
Author(s):  
Matthew E. Larson ◽  
William M. Bement
Keyword(s):  
Mitotic Spindle ◽  
Spindle Positioning ◽  
Tissue Organization ◽  
Anaphase Onset ◽  
Spindle Dynamics ◽  
And Function ◽  
Spindle Position ◽  
The Relationship ◽  
Rotational Oscillations ◽  
Final Orientation

Proper spindle positioning at anaphase onset is essential for normal tissue organization and function. Here we develop automated spindle-tracking software and apply it to characterize mitotic spindle dynamics in the Xenopus laevis embryonic epithelium. We find that metaphase spindles first undergo a sustained rotation that brings them on-axis with their final orientation. This sustained rotation is followed by a set of striking stereotyped rotational oscillations that bring the spindle into near contact with the cortex and then move it rapidly away from the cortex. These oscillations begin to subside soon before anaphase onset. Metrics extracted from the automatically tracked spindles indicate that final spindle position is determined largely by cell morphology and that spindles consistently center themselves in the XY-plane before anaphase onset. Finally, analysis of the relationship between spindle oscillations and spindle position relative to the cortex reveals an association between cortical contact and anaphase onset. We conclude that metaphase spindles in epithelia engage in a stereotyped “dance,” that this dance culminates in proper spindle positioning and orientation, and that completion of the dance is linked to anaphase onset.

scholarly journals The Kip3-Like Kinesin KipB Moves along Microtubules and Determines Spindle Position during Synchronized Mitoses in Aspergillus nidulans Hyphae

2004 ◽  
Vol 3 (3) ◽  
pp. 632-645 ◽  
Author(s):  
Patricia E. Rischitor ◽  
Sven Konzack ◽  
Reinhard Fischer
Keyword(s):  
Aspergillus Nidulans ◽  
Fluorescent Protein ◽  
Temperature Sensitive ◽  
Mitotic Spindles ◽  
Spindle Positioning ◽  
High Concentrations ◽  
Synthetically Lethal ◽  
Green Fluorescent ◽  
Spindle Position

ABSTRACT Kinesins are motor proteins which are classified into 11 different families. We identified 11 kinesin-like proteins in the genome of the filamentous fungus Aspergillus nidulans. Relatedness analyses based on the motor domains grouped them into nine families. In this paper, we characterize KipB as a member of the Kip3 family of microtubule depolymerases. The closest homologues of KipB are Saccharomyces cerevisiae Kip3 and Schizosaccharomyces pombe Klp5 and Klp6, but sequence similarities outside the motor domain are very low. A disruption of kipB demonstrated that it is not essential for vegetative growth. kipB mutant strains were resistant to high concentrations of the microtubule-destabilizing drug benomyl, suggesting that KipB destabilizes microtubules. kipB mutations caused a failure of spindle positioning in the cell, a delay in mitotic progression, an increased number of bent mitotic spindles, and a decrease in the depolymerization of cytoplasmic microtubules during interphase and mitosis. Meiosis and ascospore formation were not affected. Disruption of the kipB gene was synthetically lethal in combination with the temperature-sensitive mitotic kinesin motor mutation bimC4, suggesting an important but redundant role of KipB in mitosis. KipB localized to cytoplasmic, astral, and mitotic microtubules in a discontinuous pattern, and spots of green fluorescent protein moved along microtubules toward the plus ends.

scholarly journals Akt regulates centrosome migration and spindle orientation in the early Drosophila melanogaster embryo

2008 ◽  
Vol 180 (3) ◽  
pp. 537-548 ◽  
Author(s):  
Graham J. Buttrick ◽  
Luke M.A. Beaumont ◽  
Jessica Leitch ◽  
Christopher Yau ◽  
Julian R. Hughes ◽  
...  
Keyword(s):  
Drosophila Melanogaster ◽  
Mitotic Spindle ◽  
Glycogen Synthase ◽  
Early Embryo ◽  
Spindle Orientation ◽  
Mitotic Spindles ◽  
Polyposis Coli ◽  
Cortical Actin ◽  
Centrosome Separation ◽  
Protein Kinase Akt

Correct positioning and morphology of the mitotic spindle is achieved through regulating the interaction between microtubules (MTs) and cortical actin. Here we find that, in the Drosophila melanogaster early embryo, reduced levels of the protein kinase Akt result in incomplete centrosome migration around cortical nuclei, bent mitotic spindles, and loss of nuclei into the interior of the embryo. We show that Akt is enriched at the embryonic cortex and is required for phosphorylation of the glycogen synthase kinase-3β homologue Zeste-white 3 kinase (Zw3) and for the cortical localizations of the adenomatosis polyposis coli (APC)–related protein APC2/E-APC and the MT + Tip protein EB1. We also show that reduced levels of Akt result in mislocalization of APC2 in postcellularized embryonic mitoses and misorientation of epithelial mitotic spindles. Together, our results suggest that Akt regulates a complex containing Zw3, Armadillo, APC2, and EB1 and that this complex has a role in stabilizing MT–cortex interactions, facilitating both centrosome separation and mitotic spindle orientation.

scholarly journals Spindle position dictates division site during asymmetric cell division in moss

2020 ◽  
Author(s):  
Elena Kozgunova ◽  
Mari W. Yoshida ◽  
Gohta Goshima
Keyword(s):  
Cell Division ◽  
Mitotic Spindle ◽  
Actin Filaments ◽  
Asymmetric Cell Division ◽  
Physcomitrella Patens ◽  
Plant Cells ◽  
Spindle Positioning ◽  
Division Site ◽  
Multicellular Organisms ◽  
Spindle Position

AbstractAsymmetric cell division (ACD) underlies the development of multicellular organisms. The division site in plant cells is predetermined prior to mitosis and the localization of the mitotic spindle is considered static, unlike in animal ACD, where the cell division site is defined by active spindle-positioning mechanisms. Here, we isolated a novel mutant of the microtubule-associated protein TPX2 in the moss Physcomitrella patens and observed abnormal spindle motility, which led to inverted asymmetric division during organ development. This phenotype was rescued by restoring endogenous TPX2 function and, unexpectedly, by depolymerizing actin filaments. Thus, we identify an active spindle-positioning mechanism involving microtubules and actin filaments that sets the division site in plants, which is reminiscent of the acentrosomal ACD in animals, and suggests the existence of a common ancestral mechanism.

scholarly journals Loss of spatial control of the mitotic spindle apparatus in a Chlamydomonas reinhardtii mutant strain lacking basal bodies.

Genetics ◽  
1995 ◽  
Vol 141 (3) ◽  
pp. 945-960 ◽  
Author(s):  
L L Ehler ◽  
J A Holmes ◽  
S K Dutcher
Keyword(s):  
Cell Division ◽  
Chlamydomonas Reinhardtii ◽  
Mitotic Spindle ◽  
Basal Bodies ◽  
Cleavage Furrow ◽  
Wild Type ◽  
Spindle Positioning ◽  
Spindle Apparatus ◽  
Variable Distribution ◽  
Spindle Position

Abstract The bld2-1 mutation in the green alga Chlamydomonas reinhardtii is the only known mutation that results in the loss of centrioles/basal bodies and the loss of coordination between spindle position and cleavage furrow position during cell division. Based on several different assays, bld2-1 cells lack basal bodies in > 99% of cells. The stereotypical cytoskeletal morphology and precise positioning of the cleavage furrow observed in wild-type cells is disrupted in bld2-1 cells. The positions of the mitotic spindle and of the cleavage furrow are not correlated with respect to each other or with a specific cellular landmark during cell division in bld2-1 cells. Actin has a variable distribution during mitosis in bld2-1 cells, but this aberrant distribution is not correlated with the spindle positioning defect. In both wild-type and bld2-1 cells, the position of the cleavage furrow is coincident with a specialized set of microtubules found in green algae known as the rootlet microtubules. We propose that the rootlet microtubules perform the functions of astral microtubules and that functional centrioles are necessary for the organization of the cytoskeletal superstructure critical for correct spindle and cleavage furrow placement in Chlamydomonas.

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