PLK1 plays dual roles in centralspindlin regulation during cytokinesis

AbstractCytokinesis starts in anaphase with the formation of an actomyosin-based contractile ring at the equatorial cortex, which is governed by the local activation of the small GTPase RhoA. Here we delineated the contributions of PLK1 and Aurora B to RhoA activation and cytokinesis initiation in human cells. Knock-down of PRC1, which disrupts the spindle midzone, revealed the existence of two pathways that can initiate cleavage furrow ingression. One pathway depends on a well-organized spindle midzone and PLK1, while the other depends on Aurora B activity and centralspindlin oligomerization at the equatorial cortex and can operate independently of PLK1. We further show that PLK1 inhibition sequesters centralspindlin onto the spindle midzone making it unavailable for Aurora B-dependent oligomerization at the equatorial cortex. We propose that PLK1 activity promotes the release of centralspindlin from the spindle midzone through inhibition of PRC1, allowing centralspindlin to function as a regulator of spindle midzone formation and as an activator of RhoA at the equatorial cortex.

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PLK1 plays dual roles in centralspindlin regulation during cytokinesis

The Journal of Cell Biology ◽

10.1083/jcb.201805036 ◽

2019 ◽

Vol 218 (4) ◽

pp. 1250-1264 ◽

Cited By ~ 10

Author(s):

Ingrid E. Adriaans ◽

Angika Basant ◽

Bas Ponsioen ◽

Michael Glotzer ◽

Susanne M.A. Lens

Keyword(s):

Small Gtpase ◽

The Other ◽

Aurora B ◽

Cleavage Furrow ◽

Contractile Ring ◽

Dual Roles ◽

Early Step ◽

Rhoa Activation ◽

Anaphase Onset ◽

Spindle Midzone

Cytokinesis begins upon anaphase onset. An early step involves local activation of the small GTPase RhoA, which triggers assembly of an actomyosin-based contractile ring at the equatorial cortex. Here, we delineated the contributions of PLK1 and Aurora B to RhoA activation and cytokinesis initiation in human cells. Knock-down of PRC1, which disrupts the spindle midzone, revealed the existence of two pathways that can initiate cleavage furrow ingression. One pathway depends on a well-organized spindle midzone and PLK1, while the other depends on Aurora B activity and centralspindlin at the equatorial cortex and can operate independently of PLK1. We further show that PLK1 inhibition sequesters centralspindlin onto the spindle midzone, making it unavailable for Aurora B at the equatorial cortex. We propose that PLK1 activity promotes the release of centralspindlin from the spindle midzone through inhibition of PRC1, allowing centralspindlin to function as a regulator of spindle midzone formation and as an activator of RhoA at the equatorial cortex.

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Microtubule plus-tips act as signaling hubs for positioning the cleavage furrow during cytokinesis

10.1101/339119 ◽

2018 ◽

Author(s):

Vikash Verma ◽

Thomas J. Maresca

Keyword(s):

Drosophila Melanogaster ◽

Cell Division ◽

Aurora B ◽

Cleavage Furrow ◽

Myosin Regulatory Light Chain ◽

Animal Cells ◽

Contractile Ring ◽

Rhoa Activation ◽

Polo Kinase ◽

Molecular Nature

ABSTRACTCell division in animal cells culminates with the formation of a contractile ring that divides the cytosol through formation of a cleavage furrow. Microtubules (MTs) are essential for furrow positioning, but the molecular nature of MT-derived spatial signals is unresolved. In this study essential cytokinesis regulators (the centralspindlin complex, aurora B kinase (ABK), and polo kinase) were visualized in Drosophila melanogaster (Dm) cells and found localize to and track MT plus-ends during cytokinesis. The RhoA GEF Pebble (Dm ECT2) did not robustly tip-track but became enriched at MT plus-tips rapidly following cortical contact resulting in RhoA activation and enrichment of myosin-regulatory light chain. Abrogation of cytokinesis regulator tip-tracking by EB1 depletion or deletion of a novel EB1-interaction motif (hxxPTxh) in the centralspindlin component RacGAP50C resulted in higher incidences of cytokinesis failure. We propose that EB1-dependent, MT plus-tip-based signaling hubs recruit cortical Dm ECT2 upon contact to locally activate RhoA.

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Contractile Ring-independent Localization of DdINCENP, a Protein Important for Spindle Stability and Cytokinesis

Molecular Biology of the Cell ◽

10.1091/mbc.e05-08-0704 ◽

2006 ◽

Vol 17 (2) ◽

pp. 779-788 ◽

Cited By ~ 11

Author(s):

Qian Chen ◽

Hui Li ◽

Arturo De Lozanne

Keyword(s):

Myosin Ii ◽

Cleavage Furrow ◽

Contractile Ring ◽

Subsequent Formation ◽

Daughter Cells ◽

Chromosomal Passenger ◽

Spindle Midzone ◽

Spindle Stability ◽

Passenger Protein

Dictyostelium DdINCENP is a chromosomal passenger protein associated with centromeres, the spindle midzone, and poles during mitosis and the cleavage furrow during cytokinesis. Disruption of the single DdINCENP gene revealed important roles for this protein in mitosis and cytokinesis. DdINCENP null cells lack a robust spindle midzone and are hypersensitive to microtubule-depolymerizing drugs, suggesting that their spindles may not be stable. Furthermore DdCP224, a protein homologous to the microtubule-stabilizing protein TOGp/XMAP215, was absent from the spindle midzone of DdINCENP null cells. Overexpression of DdCP224 rescued the weak spindle midzone defect of DdINCENP null cells. Although not required for the localization of the myosin II contractile ring and subsequent formation of a cleavage furrow, DdINCENP is important for the abscission of daughter cells at the end of cytokinesis. Finally, we show that the localization of DdINCENP at the cleavage furrow is modulated by myosin II but it occurs by a mechanism different from that controlling the formation of the contractile ring.

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A GAP that Divides

F1000Research ◽

10.12688/f1000research.12064.1 ◽

2017 ◽

Vol 6 ◽

pp. 1788 ◽

Cited By ~ 6

Author(s):

Angika Basant ◽

Michael Glotzer

Keyword(s):

Small Gtpase ◽

Nucleotide Exchange ◽

Contractile Ring ◽

C Elegans ◽

Rhoa Activation ◽

Guanine Nucleotide Exchange ◽

Nucleotide Exchange Factor ◽

Parallel Pathway ◽

Mutant Phenotypes

Cytokinesis in metazoan cells is mediated by an actomyosin-based contractile ring that assembles in response to activation of the small GTPase RhoA. The guanine nucleotide exchange factor that activates RhoA during cytokinesis, ECT-2, is highly regulated. In most metazoan cells, with the notable exception of the early Caenorhabditis elegans embryo, RhoA activation and furrow ingression require the centralspindlin complex. This exception is due to the existence of a parallel pathway for RhoA activation in C. elegans. Centralspindlin contains CYK-4 which contains a predicted Rho family GTPase-activating protein (GAP) domain. The function of this domain has been the subject of considerable debate. Some publications suggest that the GAP domain promotes RhoA activation (for example, Zhang and Glotzer, 2015; Loria, Longhini and Glotzer, 2012), whereas others suggest that it functions to inactivate the GTPase Rac1 (for example, Zhuravlev et al., 2017). Here, we review the mechanisms underlying RhoA activation during cytokinesis, primarily focusing on data in C. elegans. We highlight the importance of considering the parallel pathway for RhoA activation and detailed analyses of cyk-4 mutant phenotypes when evaluating the role of the GAP domain of CYK-4.

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A Role for Dictyostelium RacE in Cortical Tension and Cleavage Furrow Progression

The Journal of Cell Biology ◽

10.1083/jcb.141.2.483 ◽

1998 ◽

Vol 141 (2) ◽

pp. 483-492 ◽

Cited By ~ 67

Author(s):

Noel Gerald ◽

Jianwu Dai ◽

H. Ping Ting-Beall ◽

Arturo De Lozanne

Keyword(s):

Signaling Pathways ◽

Small Gtpase ◽

Cleavage Furrow ◽

Wild Type ◽

Contractile Ring ◽

Cortical Tension ◽

Low Level ◽

Cortical Cytoskeleton

The small GTPase racE is essential for cytokinesis in Dictyostelium. We found that this requirement is restricted to cells grown in suspension. When attached to a substrate, racE null cells form an actomyosin contractile ring and complete cytokinesis normally. Nonetheless, racE null cells fail completely in cytokinesis when in suspension. To understand this conditional requirement for racE, we developed a method to observe cytokinesis in suspension. Using this approach, we found that racE null cells attempt cytokinesis in suspension by forming a contractile ring and cleavage furrow. However, the cells form multiple blebs and fail in cytokinesis by regression of the cleavage furrow. We believe this phenotype is caused by the extremely low level of cortical tension found in racE null cells compared to wild-type cells. The reduced cortical tension of racE null cells is not caused by a decrease in their content of F-actin. Instead, mitotic racE null cells contain abnormal F-actin aggregates. These results suggest that racE is essential for the organization of the cortical cytoskeleton to maintain proper cortical integrity. This function of racE is independent of attachment to a substrate, but can be bypassed by other signaling pathways induced by adhesion to a substrate.

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Identification of secreted and cytosolic gelsolin in Drosophila.

The Journal of Cell Biology ◽

10.1083/jcb.125.3.607 ◽

1994 ◽

Vol 125 (3) ◽

pp. 607-616 ◽

Cited By ~ 20

Author(s):

M C Stella ◽

H Schauerte ◽

K L Straub ◽

M Leptin

Keyword(s):

Fat Body ◽

Extracellular Fluid ◽

Early Embryo ◽

The Other ◽

Cleavage Furrow ◽

Secreted Protein ◽

Differential Splicing ◽

Contractile Ring ◽

Dividing Cells

We have cloned the gene for Drosophila gelsolin. Two mRNAs are produced from this gene by differential splicing. The protein encoded by the longer mRNA has a signal peptide and its electrophoretic mobility when translated in vitro in the presence of microsomes is higher than when it is translated without microsomes. The protein translated from the shorter mRNA does not show this difference. This indicates that Drosophila like vertebrates has two forms of gelsolin, one secreted, the other cytoplasmic. The mRNA for both is present ubiquitously in the early embryo. Later, the cytoplasmic form is expressed in parts of the gut. The RNA for the secreted form is expressed in the fat body, and the secreted protein is abundant in extracellular fluid (hemolymph). The cytoplasmic form of gelsolin co-localizes with F-actin in the cortex of the cells in the embryo and in larval epithelia. However, during cellularization of the blastoderm it is reduced at the base of the cleavage furrow, a structure similar to the contractile ring in dividing cells.

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Aurora-B Kinase Translocates to the Midzone in Endomitotic Megakaryocytes.

Blood ◽

10.1182/blood.v104.11.1263.1263 ◽

2004 ◽

Vol 104 (11) ◽

pp. 1263-1263

Author(s):

Amy E. Geddis ◽

Kenneth Kaushansky

Keyword(s):

Actin Dynamics ◽

Aurora B ◽

Cleavage Furrow ◽

Aurora B Kinase ◽

Metaphase Chromosomes ◽

Late Anaphase ◽

Chromosomal Passenger ◽

Chromosomal Passenger Proteins ◽

Spindle Midzone ◽

Passenger Proteins

Abstract Megakaryocyte (MK) differentiation is marked by the development of progressive polyploidy, facilitating platelet production by the creation of a large cytoplasmic volume. MKs become polyploid through repeated cycles of endomitosis (EnM), in which mitosis is initiated but subsequently aborted in late anaphase with failure to complete karyokinesis and cytokinesis. However, the mechanisms underlying EnM remain poorly understood. Recent hypotheses explored in the literature have focused on the possible absence or mislocalization of the chromosomal passenger protein Aurora-B kinase, as it has a pivotal role in many aspects of cytokinesis. Along with the other passenger proteins, Aurora-B kinase transits from the centromeres of metaphase chromosomes to the bundled microtubules of the spindle midzone and overlying cortex between separating chromosomes in anaphase. The midzone and its associated proteins, are thought to be critical for determining the position of the cleavage furrow. One of these proteins, the kinesin MKLP-2, is required for the translocation of Aurora-B kinase to the midzone, where it co-localizes with the GTPase MgcRacGAP and stimulates its activity towards RhoA, potentially regulating actin dynamics at the cleavage furrow. We have previously demonstrated that several chromosomal passenger proteins including Aurora-B kinase are normally expressed and localized to centromeres in EnM MKs. In this work, we use deconvolution microscopy in primary murine and human MKs to extend those findings and demonstrate that EnM MKs form midzone structures that are characteristic of late anaphase; in addition, Aurora-B kinase is clearly present on the spindle midzone, as are MKLP-2 and MgcRacGAP. Although we found images suggestive of initial cleavage furrow formation with cortical localization of Aurora-B kinase in late phase cells, we were unable to demonstrate enhanced localization of actin or anillin to the furrow in EnM cells, despite their normal localization in diploid control cells. Therefore, many of the components of the central spindle are intact during MK EnM, but the formation of the cleavage furrow appears to be incomplete. These data add to our understanding of the possible mechanisms underlying EnM and offer an alternative hypothesis to that of failed expression or localization of the chromosomal passenger proteins. Ongoing studies will focus on the assembly and function of the cleavage furrow in this enigmatic process.

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Cdc14-regulated midzone assembly controls anaphase B

The Journal of Cell Biology ◽

10.1083/jcb.200702145 ◽

2007 ◽

Vol 177 (6) ◽

pp. 981-993 ◽

Cited By ~ 101

Author(s):

Anton Khmelinskii ◽

Clare Lawrence ◽

Johanna Roostalu ◽

Elmar Schiebel

Keyword(s):

Cell Cycle ◽

Protein Phosphatase ◽

Cross Linking ◽

Aurora B ◽

Aurora B Kinase ◽

Spindle Midzone ◽

A Cell ◽

Spindle Elongation ◽

And Function ◽

Anaphase B

Spindle elongation in anaphase of mitosis is a cell cycle–regulated process that requires coordination between polymerization, cross-linking, and sliding of microtubules (MTs). Proteins that assemble at the spindle midzone may be important for this process. In this study, we show that Ase1 and the separase–Slk19 complex drive midzone assembly in yeast. Whereas the conserved MT-bundling protein Ase1 establishes a midzone, separase–Slk19 is required to focus and center midzone components. An important step leading to spindle midzone assembly is the dephosphorylation of Ase1 by the protein phosphatase Cdc14 at the beginning of anaphase. Failure to dephosphorylate Ase1 delocalizes midzone proteins and delays the second, slower phase of anaphase B. In contrast, in cells expressing nonphosphorylated Ase1, anaphase spindle extension is faster, and spindles frequently break. Cdc14 also controls the separase–Slk19 complex indirectly via the Aurora B kinase. Thus, Cdc14 regulates spindle midzone assembly and function directly through Ase1 and indirectly via the separase–Slk19 complex.

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Guardianship and Parental Connections: Connections and Departures in Jeremy Bentham’s Account

Journal of Bentham Studies ◽

10.14324/111.2045-757x.045 ◽

2011 ◽

Author(s):

Brian E Cox

Keyword(s):

Present Article ◽

Legal Status ◽

The Other ◽

Previous Article ◽

Dual Roles ◽

Other Hand ◽

Special Relations ◽

Similarities And Differences ◽

Personal Perspectives ◽

The One

This article follows an earlier assessment of Bentham’s views on guardianship 1 that touched on but did not explore connections or departures between guardian-ward and parent-offspring relations, about which Bentham was not as precise as he might have been. Further, he added complexity to the issue by describing parents as occupying dual roles: guardians and ‘masters’ (employers) of their own offspring. These relations are now considered, on the one hand, in the wider context of ‘special relations’ and ‘duties’ and, on the other hand, alongside some appreciation of Bentham’s personal perspectives. However, the main object of the present article is to assess similarities and differences between parents and guardians in legal, status and functional terms. It uses the profile of guardian-ward relations provided by the previous article 2 as a benchmark. The article concludes by affirming that ‘being a parent’ and ‘being a guardian’ have quite different meanings.

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