Using the Four-Cell C. elegans Embryo to Study Contractile Ring Dynamics During Cytokinesis

AbstractCytokinesis in animal cells requires the constriction of an actomyosin contractile ring, whose architecture and mechanism remain poorly understood. We use laser microsurgery to explore the biophysical properties of constricting contractile rings in C. elegans embryos. Laser cutting causes rings to snap open, which is a sign of tension release. However, instead of disintegrating, ring topology recovers and constriction proceeds. In response to severing, a finite gap forms that is proportional to ring perimeters before cutting, demonstrating that tension along the ring decreases throughout constriction. Severed rings repair their gaps by recruiting new material and subsequently increase constriction rate and complete cytokinesis with the same timing as uncut rings. Rings repair successive cuts and exhibit substantial constriction when gap repair is prevented. Our analysis suggests that cytokinesis is accomplished by contractile modules that assemble and contract autonomously, enabling local repair of the actomyosin network throughout constriction. Consequently, cytokinesis is a highly robust process impervious to discontinuities in contractile ring structure.

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Polar relaxation by dynein-mediated removal of cortical myosin II

The Journal of Cell Biology ◽

10.1083/jcb.201903080 ◽

2020 ◽

Vol 219 (8) ◽

Cited By ~ 4

Author(s):

Bernardo Chapa-y-Lazo ◽

Motonari Hamanaka ◽

Alexander Wray ◽

Mohan K. Balasubramanian ◽

Masanori Mishima

Keyword(s):

Recent Work ◽

Molecular Mechanism ◽

Molecular Mechanisms ◽

Myosin Ii ◽

Cell Cortex ◽

Cleavage Furrow ◽

Contractile Ring ◽

C Elegans ◽

Polar Cell

Nearly six decades ago, Lewis Wolpert proposed the relaxation of the polar cell cortex by the radial arrays of astral microtubules as a mechanism for cleavage furrow induction. While this mechanism has remained controversial, recent work has provided evidence for polar relaxation by astral microtubules, although its molecular mechanisms remain elusive. Here, using C. elegans embryos, we show that polar relaxation is achieved through dynein-mediated removal of myosin II from the polar cortexes. Mutants that position centrosomes closer to the polar cortex accelerated furrow induction, whereas suppression of dynein activity delayed furrowing. We show that dynein-mediated removal of myosin II from the polar cortexes triggers a bidirectional cortical flow toward the cell equator, which induces the assembly of the actomyosin contractile ring. These results provide a molecular mechanism for the aster-dependent polar relaxation, which works in parallel with equatorial stimulation to promote robust cytokinesis.

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Mitochondrial morphology and activity regulate furrow ingression and contractile ring dynamics in Drosophila cellularization

Molecular Biology of the Cell ◽

10.1091/mbc.e20-03-0177 ◽

2020 ◽

Vol 31 (21) ◽

pp. 2331-2347

Author(s):

Sayali Chowdhary ◽

Somya Madan ◽

Darshika Tomer ◽

Manos Mavrakis ◽

Richa Rikhy

Keyword(s):

Mitochondrial Fission ◽

Cell Formation ◽

Mitochondrial Morphology ◽

Contractile Ring ◽

Drosophila Embryogenesis ◽

Ring Dynamics ◽

Mitochondrial Distribution ◽

Ring Constriction

Drp1-regulated mitochondrial fission is essential for mitochondrial distribution across the cell in cellularization during Drosophila embryogenesis. Loss of mitochondrial fission in Drp1 mutant embryos leads to defects in morphogenetic events of cell formation and contractile ring constriction in cellularization.

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Sticky/Citron kinase maintains proper RhoA localization at the cleavage site during cytokinesis

The Journal of Cell Biology ◽

10.1083/jcb.201105136 ◽

2011 ◽

Vol 195 (4) ◽

pp. 595-603 ◽

Cited By ~ 40

Author(s):

Zuni I. Bassi ◽

Koen J. Verbrugghe ◽

Luisa Capalbo ◽

Stephen Gregory ◽

Emilie Montembault ◽

...

Keyword(s):

Cleavage Site ◽

Kinase Activity ◽

Rho Kinase ◽

Compact Ring ◽

Contractile Ring ◽

Rhoa Activity ◽

Ring Dynamics ◽

Citron Kinase ◽

Guanosine Triphosphatase

In many organisms, the small guanosine triphosphatase RhoA controls assembly and contraction of the actomyosin ring during cytokinesis by activating different effectors. Although the role of some RhoA effectors like formins and Rho kinase is reasonably understood, the functions of another putative effector, Citron kinase (CIT-K), are still debated. In this paper, we show that, contrary to previous models, the Drosophila melanogaster CIT-K orthologue Sticky (Sti) does not require interaction with RhoA to localize to the cleavage site. Instead, RhoA fails to form a compact ring in late cytokinesis after Sti depletion, and this function requires Sti kinase activity. Moreover, we found that the Sti Citron-Nik1 homology domain interacts with RhoA regardless of its status, indicating that Sti is not a canonical RhoA effector. Finally, Sti depletion caused an increase of phosphorylated myosin regulatory light chain at the cleavage site in late cytokinesis. We propose that Sti/CIT-K maintains correct RhoA localization at the cleavage site, which is necessary for proper RhoA activity and contractile ring dynamics.

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A positive feedback-based mechanism for constriction rate acceleration during cytokinesis in C. elegans

10.1101/161133 ◽

2017 ◽

Cited By ~ 1

Author(s):

Renat N. Khaliullin ◽

Rebecca A. Green ◽

Linda Z. Shi ◽

J. Sebastian Gomez-Cavazos ◽

Michael W. Berns ◽

...

Keyword(s):

Positive Feedback ◽

Cell Biology ◽

Unit Length ◽

Mathematical Formulation ◽

Ring Closure ◽

Cortical Surface ◽

Contractile Ring ◽

Closure Rate ◽

C Elegans ◽

Rate Acceleration

ABSTRACTDuring cytokinesis, an equatorial actomyosin contractile ring constricts at a relatively constant overall rate despite its progressively decreasing size. Thus, the per-unit-length rate of ring closure increases as ring perimeter decreases. To understand this acceleration, we monitored cortical surface and ring component dynamics during the first division of the C. elegans embryo. We show that the polar cortex expands during ring constriction to provide the cortical surface area required for division. Polar expansion also allows ring myosin to compress cortical surface along the pole-to-pole axis, leading to a continuous flow of cortical surface into the ring. We propose that feedback between ring myosin and compression-driven cortical flow drives an exponential increase in the amount of ring myosin that maintains the high overall closure rate as ring perimeter decreases. We further show that an analytical mathematical formulation of the proposed feedback, called the Compression Feedback model, recapitulates the experimental observations.IMPACT STATEMENTDuring cytokinesis, positive feedback between myosin motors in the contractile ring and compression-driven cortical flow along the axis perpendicular to the ring drives constriction rate acceleration to ensure timely cell separation.MAJOR SUBJECT AREASCell biology, Computational and Systems Biology

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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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Effect of ring topology in a stochastic model for Z-ring dynamics in bacteria

10.1101/452441 ◽

2018 ◽

Author(s):

A. Swain Sumedha ◽

A. V. A Kumar

Keyword(s):

Cell Division ◽

Stochastic Model ◽

Contractile Ring ◽

Additional Mechanism ◽

Ring Topology ◽

Ring Dynamics ◽

Mechanism Of Hydrolysis ◽

Long Time ◽

Z Ring

AbstractUnderstanding the mechanisms responsible for dynamics of theZ-ring is important for our understanding of cell division in prokaryotic cells. In this work, we present a minimal stochastic model that qualititatively reproduces observations of polymerization, of formation of dynamic contractile ring that is stable for a long time and of depolymerization shown by FtsZ polymer. We explore different mechanisms for ring breaking and hydrolysis. Hydrolysis is known to regulate the dynamics of other tubulin polymers like microtubules. We find that the presence of the ring allows for an additional mechanism for regulating the dynamics of FtsZ polymers. Ring breaking dynamics in the presence of hydrolysis naturally induce rescue and catastrophe events, irrespective of the mechanism of hydrolysis. Based on our model, we conclude that theZ-ring undergoes random breaking and closing during the process of cell division.

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Cortical and cytoplasmic flow polarity in early embryonic cells of Caenorhabditis elegans.

The Journal of Cell Biology ◽

10.1083/jcb.121.6.1343 ◽

1993 ◽

Vol 121 (6) ◽

pp. 1343-1355 ◽

Cited By ~ 183

Author(s):

S N Hird ◽

J G White

Keyword(s):

Caenorhabditis Elegans ◽

Mitotic Spindle ◽

Embryonic Cells ◽

Cortical Actin ◽

Contractile Ring ◽

Mitotic Apparatus ◽

C Elegans ◽

Microtubule Polymerization ◽

Polymerization Inhibitor ◽

Motile Cells

We have examined the cortex of Caenorhabditis elegans eggs during pseudocleavage (PC), a period of the first cell cycle which is important for the generation of asymmetry at first cleavage (Strome, S. 1989. Int. Rev. Cytol. 114: 81-123). We have found that directed, actin dependent, cytoplasmic, and cortical flow occurs during this period coincident with a rearrangement of the cortical actin cytoskeleton (Strome, S. 1986. J. Cell Biol. 103: 2241-2252). The flow velocity (4-7 microns/min) is similar to previously determined particle movements driven by cortical actin flows in motile cells. We show that directed flows occur in one of the daughters of the first division that itself divides asymmetrically, but not in its sister that divides symmetrically. The cortical and cytoplasmic events of PC can be mimicked in other cells during cytokinesis by displacing the mitotic apparatus with the microtubule polymerization inhibitor nocodazole. In all cases, the polarity of the resulting cortical and cytoplasmic flows correlates with the position of the attenuated mitotic spindle formed. These cortical flows are also accompanied by a change in the distribution of the cortical actin network. The polarity of this redistribution is similarly correlated with the location of the attenuated spindle. These observations suggest a mechanism for generating polarized flows of cytoplasmic and cortical material during embryonic cleavages. We present a model for the events of PC and suggest how the poles of the mitotic spindle mediate the formation of the contractile ring during cytokinesis in C. elegans.

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Mutations in sticky lead to defective organization of the contractile ring during cytokinesis and are enhanced by Rho and suppressed by Rac

The Journal of Cell Biology ◽

10.1083/jcb.200402157 ◽

2004 ◽

Vol 166 (1) ◽

pp. 61-71 ◽

Cited By ~ 88

Author(s):

Pier Paolo D'Avino ◽

Matthew S. Savoian ◽

David M. Glover

Keyword(s):

Rna Interference ◽

Cultured Cells ◽

Dynamic Structure ◽

Genetic Interactions ◽

Genetic Evidence ◽

Contractile Ring ◽

Central Spindle ◽

Drosophila Gene ◽

Unusual Distribution ◽

Ring Dynamics

The contractile ring is a highly dynamic structure, but how this dynamism is accomplished remains unclear. Here, we report the identification and analysis of a novel Drosophila gene, sticky (sti), essential for cytokinesis in all fly proliferating tissues. sti encodes the Drosophila orthologue of the mammalian Citron kinase. RNA interference–mediated silencing of sti in cultured cells causes them to become multinucleate. Components of the contractile ring and central spindle are recruited normally in such STICKY-depleted cells that nevertheless display asymmetric furrowing and aberrant blebbing. Together with an unusual distribution of F-actin and Anillin, these phenotypes are consistent with defective organization of the contractile ring. sti shows opposite genetic interactions with Rho and Rac genes suggesting that these GTPases antagonistically regulate STICKY functions. Similar genetic evidence indicates that RacGAP50C inhibits Rac during cytokinesis. We discuss that antagonism between Rho and Rac pathways may control contractile ring dynamics during cytokinesis.

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Cortical recruitment of centralspindlin and RhoA effectors during meiosis I of Caenorhabditiselegans primary spermatocytes

Journal of Cell Science ◽

10.1242/jcs.238543 ◽

2021 ◽

Vol 134 (3) ◽

pp. jcs238543 ◽

Cited By ~ 1

Author(s):

Xiangchuan Wang ◽

Dandan Zhang ◽

Cunni Zheng ◽

Shian Wu ◽

Michael Glotzer ◽

...

Keyword(s):

Cell Biology ◽

Time Lapse ◽

Contractile Ring ◽

Cellular Division ◽

C Elegans ◽

Ring Assembly ◽

Male Gametes ◽

Spatiotemporal Regulation ◽

Haploid Male ◽

Meiosis I

ABSTRACTHaploid male gametes are produced through meiosis during gametogenesis. Whereas the cell biology of mitosis and meiosis is well studied in the nematode Caenorhabditis elegans, comparatively little is known regarding the physical division of primary spermatocytes during meiosis I. Here, we investigated this process using high-resolution time-lapse confocal microscopy and examined the spatiotemporal regulation of contractile ring assembly in C. elegans primary spermatocytes. We found that centralspindlin and RhoA effectors were recruited to the equatorial cortex of dividing primary spermatocytes for contractile ring assembly before segregation of homologous chromosomes. We also observed that perturbations shown to promote centralspindlin oligomerization regulated the cortical recruitment of NMY-2 and impacted the order in which primary spermatocytes along the proximal–distal axis of the gonad enter meiosis I. These results expand our understanding of the cellular division of primary spermatocytes into secondary spermatocytes during meiosis I.This article has an associated First Person interview with the first author of the paper.

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