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

1993 ◽  
Vol 121 (6) ◽  
pp. 1343-1355 ◽  
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.

scholarly journals Arp2/3 mediates early endosome dynamics necessary for the maintenance of PAR asymmetry in Caenorhabditis elegans

2012 ◽  
Vol 23 (10) ◽  
pp. 1917-1927 ◽  
Author(s):  
Jessica M. Shivas ◽  
Ahna R. Skop
Keyword(s):  
Caenorhabditis Elegans ◽  
Maintenance Phase ◽  
Early Endosome ◽  
Actin Dynamics ◽  
Cellular Polarity ◽  
Cortical Actin ◽  
Endocytic Recycling ◽  
C Elegans ◽  
Early Endosomes ◽  
Stable Maintenance

The widely conserved Arp2/3 complex regulates branched actin dynamics that are necessary for a variety of cellular processes. In Caenorhabditis elegans, the actin cytoskeleton has been extensively characterized in its role in establishing PAR asymmetry; however, the contributions of actin to the maintenance of polarity before the onset of mitosis are less clear. Endocytic recycling has emerged as a key mechanism in the dynamic stabilization of cellular polarity, and the large GTPase dynamin participates in the stabilization of cortical polarity during maintenance phase via endocytosis in C. elegans. Here we show that disruption of Arp2/3 function affects the formation and localization of short cortical actin filaments and foci, endocytic regulators, and polarity proteins during maintenance phase. We detect actin associated with events similar to early endosomal fission, movement of endosomes into the cytoplasm, and endosomal movement from the cytoplasm to the plasma membrane, suggesting the involvement of actin in regulating processes at the early endosome. We also observe aberrant accumulations of PAR-6 cytoplasmic puncta near the centrosome along with early endosomes. We propose a model in which Arp2/3 affects the efficiency of rapid endocytic recycling of polarity cues that ultimately contributes to their stable maintenance.

scholarly journals MEI-1/MEI-2 katanin-like microtubule severing activity is required for Caenorhabditis elegans meiosis

2000 ◽  
Vol 14 (9) ◽  
pp. 1072-1084
Author(s):  
Martin Srayko ◽  
Dan W. Buster ◽  
Omar A. Bazirgan ◽  
Francis J. McNally ◽  
Paul E. Mains
Keyword(s):  
Caenorhabditis Elegans ◽  
Hela Cells ◽  
Mitotic Spindle ◽  
Subcellular Location ◽  
Meiotic Spindle ◽  
Aaa Atpase ◽  
C Elegans ◽  
Microtubule Severing ◽  
Acid Protein ◽  
Spindle Function

The Caenorhabditis elegans meiotic spindle is morphologically distinct from the first mitotic spindle, yet both structures form in the same cytoplasm ∼20 minutes apart. Themei-1 and mei-2 genes of C. elegans are required for the establishment of the oocyte meiotic spindle but are not required for mitotic spindle function. mei-1 encodes an AAA ATPase family member with similarity to the p60 catalytic subunit of the heterodimeric sea urchin microtubule-severing protein, katanin. We report that mei-2 encodes a 280-amino acid protein containing a region similar to the p80-targeting subunit of katanin. MEI-1 and MEI-2 antibodies decorate the polar ends of meiotic spindle microtubules and meiotic chromatin. We find that the subcellular location of MEI-2 depends on wild-type mei-1 activity and vice versa. These experiments, combined with MEI-1 and MEI-2's similarity to p60 and p80 katanin, suggest that the C. elegans proteins function as a complex. In support of this idea, MEI-1 and MEI-2 physically associate in HeLa cells. Furthermore, co-expression of MEI-1 and MEI-2 in HeLa cells results in the disassembly of microtubules. These data lead us to conclude that MEI-1/MEI-2 microtubule-severing activity is required for meiotic spindle organization in C. elegans.

scholarly journals How cortical waves drive fission of motile cells

2020 ◽  
Vol 117 (12) ◽  
pp. 6330-6338 ◽  
Author(s):  
Sven Flemming ◽  
Francesc Font ◽  
Sergio Alonso ◽  
Carsten Beta
Keyword(s):  
Reaction Diffusion ◽  
Cortical Actin ◽  
Animal Cells ◽  
Contractile Ring ◽  
Daughter Cells ◽  
Reaction Diffusion Model ◽  
Motile Cells ◽  
A Cell ◽  
Actin Waves ◽  
Cell Growth And Proliferation

Cytokinesis—the division of a cell into two daughter cells—is a key step in cell growth and proliferation. It typically occurs in synchrony with the cell cycle to ensure that a complete copy of the genetic information is passed on to the next generation of daughter cells. In animal cells, cytokinesis commonly relies on an actomyosin contractile ring that drives equatorial furrowing and separation into the two daughter cells. However, also contractile ring-independent forms of cell division are known that depend on substrate-mediated traction forces. Here, we report evidence of an as yet unknown type of contractile ring-independent cytokinesis that we termed wave-mediated cytofission. It is driven by self-organized cortical actin waves that travel across the ventral membrane of oversized, multinucleatedDictyostelium discoideumcells. Upon collision with the cell border, waves may initiate the formation of protrusions that elongate and eventually pinch off to form separate daughter cells. They are composed of a stable elongated wave segment that is enclosed by a cell membrane and moves in a highly persistent fashion. We rationalize our observations based on a noisy excitable reaction–diffusion model in combination with a dynamic phase field to account for the cell shape and demonstrate that daughter cells emerging from wave-mediated cytofission exhibit a well-controlled size.

scholarly journals A lineage-resolved molecular atlas of C. elegans embryogenesis at single-cell resolution

Science ◽  
2019 ◽  
Vol 365 (6459) ◽  
pp. eaax1971 ◽  
Author(s):  
Jonathan S. Packer ◽  
Qin Zhu ◽  
Chau Huynh ◽  
Priya Sivaramakrishnan ◽  
Elicia Preston ◽  
...  
Keyword(s):  
Nervous System ◽  
Caenorhabditis Elegans ◽  
Single Cell ◽  
Molecular Basis ◽  
Cell Types ◽  
Embryonic Cells ◽  
Cell Type ◽  
C Elegans ◽  
Exact Position ◽  
Sister Cells

Caenorhabditis elegans is an animal with few cells but a wide diversity of cell types. In this study, we characterize the molecular basis for their specification by profiling the transcriptomes of 86,024 single embryonic cells. We identify 502 terminal and preterminal cell types, mapping most single-cell transcriptomes to their exact position in C. elegans’ invariant lineage. Using these annotations, we find that (i) the correlation between a cell’s lineage and its transcriptome increases from middle to late gastrulation, then falls substantially as cells in the nervous system and pharynx adopt their terminal fates; (ii) multilineage priming contributes to the differentiation of sister cells at dozens of lineage branches; and (iii) most distinct lineages that produce the same anatomical cell type converge to a homogenous transcriptomic state.

scholarly journals Characterization and dynamics of cytoplasmic F-actin in higher plant endosperm cells during interphase, mitosis, and cytokinesis.

1987 ◽  
Vol 105 (5) ◽  
pp. 2157-2166 ◽  
Author(s):  
A C Schmit ◽  
A M Lambert
Keyword(s):  
Mitotic Spindle ◽  
Fluorescent Labeling ◽  
Cell Cortex ◽  
Cortical Actin ◽  
Higher Plant ◽  
Mitotic Apparatus ◽  
Rhodamine Phalloidin ◽  
Cytoplasmic Actin ◽  
Cytoskeletal Network ◽  
Cross Links

We have identified an F-actin cytoskeletal network that remains throughout interphase, mitosis, and cytokinesis of higher plant endosperm cells. Fluorescent labeling was obtained using actin monoclonal antibodies and/or rhodamine-phalloidin. Video-enhanced microscopy and ultrastructural observations of immunogold-labeled preparations illustrated microfilament-microtubule co-distribution and interactions. Actin was also identified in cell crude extract with Western blotting. During interphase, microfilament and microtubule arrays formed two distinct networks that intermingled. At the onset of mitosis, when microtubules rearranged into the mitotic spindle, microfilaments were redistributed to the cell cortex, while few microfilaments remained in the spindle. During mitosis, the cortical actin network remained as an elastic cage around the mitotic apparatus and was stretched parallel to the spindle axis during poleward movement of chromosomes. This suggested the presence of dynamic cross-links that rearrange when they are submitted to slow and regular mitotic forces. At the poles, the regular network is maintained. After midanaphase, new, short microfilaments invaded the equator when interzonal vesicles were transported along the phragmoplast microtubules. Colchicine did not affect actin distribution, and cytochalasin B or D did not inhibit chromosome transport. Our data on endosperm cells suggested that plant cytoplasmic actin has an important role in the cell cortex integrity and in the structural dynamics of the poorly understood cytoplasm-mitotic spindle interface. F-actin may contribute to the regulatory mechanisms of microtubule-dependent or guided transport of vesicles during mitosis and cytokinesis in higher plant cells.

scholarly journals ZYG-9, A Caenorhabditis elegans Protein Required for Microtubule Organization and Function, Is a Component of Meiotic and Mitotic Spindle Poles

1998 ◽  
Vol 141 (5) ◽  
pp. 1159-1168 ◽  
Author(s):  
Lisa R. Matthews ◽  
Philip Carter ◽  
Danielle Thierry-Mieg ◽  
Ken Kemphues
Keyword(s):  
Caenorhabditis Elegans ◽  
Mitotic Spindle ◽  
Meiotic Spindle ◽  
Microtubule Organization ◽  
Mitotic Apparatus ◽  
Meiotic Chromosomes ◽  
Spindle Poles ◽  
Common Activity ◽  
Early Anaphase ◽  
And Function

We describe the molecular characterization of zyg-9, a maternally acting gene essential for microtubule organization and function in early Caenorhabditis elegans embryos. Defects in zyg-9 mutants suggest that the zyg-9 product functions in the organization of the meiotic spindle and the formation of long microtubules. One-cell zyg-9 embryos exhibit both meiotic and mitotic spindle defects. Meiotic spindles are disorganized, pronuclear migration fails, and the mitotic apparatus forms at the posterior, orients incorrectly, and contains unusually short microtubules. We find that zyg-9 encodes a component of the meiotic and mitotic spindle poles. In addition to the strong staining of spindle poles, we consistently detect staining in the region of the kinetochore microtubules at metaphase and early anaphase in mitotic spindles. The ZYG-9 signal at the mitotic centrosomes is not reduced by nocodazole treatment, indicating that ZYG-9 localization to the mitotic centrosomes is not dependent upon long astral microtubules. Interestingly, in embryos lacking an organized meiotic spindle, produced either by nocodazole treatment or mutations in the mei-1 gene, ZYG-9 forms a halo around the meiotic chromosomes. The protein sequence shows partial similarity to a small set of proteins that also localize to spindle poles, suggesting a common activity of the proteins.

scholarly journals Conditional Dominant Mutations in the Caenorhabditis elegans Gene act-2 Identify Cytoplasmic and Muscle Roles for a Redundant Actin Isoform

2006 ◽  
Vol 17 (3) ◽  
pp. 1051-1064 ◽  
Author(s):  
John H. Willis ◽  
Edwin Munro ◽  
Rebecca Lyczak ◽  
Bruce Bowerman
Keyword(s):  
Caenorhabditis Elegans ◽  
Muscle Cells ◽  
Binding Pocket ◽  
Embryonic Cell ◽  
Temperature Sensitive ◽  
Restrictive Temperature ◽  
Embryonic Cells ◽  
Actin Isoforms ◽  
C Elegans ◽  
Actin Isoform

Animal genomes each encode multiple highly conserved actin isoforms that polymerize to form the microfilament cytoskeleton. Previous studies of vertebrates and invertebrates have shown that many actin isoforms are restricted to either nonmuscle (cytoplasmic) functions, or to myofibril force generation in muscle cells. We have identified two temperature-sensitive and semidominant embryonic-lethal Caenorhabditis elegans mutants, each with a single mis-sense mutation in act-2, one of five C. elegans genes that encode actin isoforms. These mutations alter conserved and adjacent amino acids predicted to form part of the ATP binding pocket of actin. At the restrictive temperature, both mutations resulted in aberrant distributions of cortical microfilaments associated with abnormal and striking membrane ingressions and protrusions. In contrast to the defects caused by these dominant mis-sense mutations, an act-2 deletion did not result in early embryonic cell division defects, suggesting that additional and redundant actin isoforms are involved. Accordingly, we found that two additional actin isoforms, act-1 and act-3, were required redundantly with act-2 for cytoplasmic function in early embryonic cells. The act-1 and -3 genes also have been implicated previously in muscle function. We found that an ACT-2::GFP reporter was expressed cytoplasmically in embryonic cells and also was incorporated into contractile filaments in adult muscle cells. Furthermore, one of the dominant act-2 mutations resulted in uncoordinated adult movement. We conclude that redundant C. elegans actin isoforms function in both muscle and nonmuscle contractile processes.

scholarly journals Localized accumulation of tubulin during semi-open mitosis in the Caenorhabditis elegans embryo

2012 ◽  
Vol 23 (9) ◽  
pp. 1688-1699 ◽  
Author(s):  
Hanako Hayashi ◽  
Kenji Kimura ◽  
Akatsuki Kimura
Keyword(s):  
Caenorhabditis Elegans ◽  
Nuclear Envelope ◽  
Mitotic Spindle ◽  
Fluorescence Recovery After Photobleaching ◽  
Spindle Assembly ◽  
Small Gtpase ◽  
Microtubule Assembly ◽  
C Elegans ◽  
Nuclear Envelope Breakdown ◽  
Mitotic Spindle Assembly

The assembly of microtubules inside the cell is controlled both spatially and temporally. During mitosis, microtubule assembly must be activated locally at the nascent spindle region for mitotic spindle assembly to occur efficiently. In this paper, we report that mitotic spindle components, such as free tubulin subunits, accumulated in the nascent spindle region, independent of spindle formation in the Caenorhabditis elegans embryo. This accumulation coincided with nuclear envelope permeabilization, suggesting that permeabilization might trigger the accumulation. When permeabilization was induced earlier by knockdown of lamin, tubulin also accumulated earlier. The boundaries of the region of accumulation coincided with the remnant nuclear envelope, which remains after nuclear envelope breakdown in cells that undergo semi-open mitosis, such as those of C. elegans. Ran, a small GTPase protein, was required for tubulin accumulation. Fluorescence recovery after photobleaching analysis revealed that the accumulation was accompanied by an increase in the immobile fraction of free tubulin inside the remnant nuclear envelope. We propose that this newly identified mechanism of accumulation of free tubulin—and probably of other molecules—at the nascent spindle region contributes to efficient assembly of the mitotic spindle in the C. elegans embryo.

scholarly journals Flow-independent accumulation of motor-competent non-muscle myosin II in the contractile ring is essential for cytokinesis

2018 ◽  
Author(s):  
DS Osorio ◽  
FY Chan ◽  
J Saramago ◽  
J Leite ◽  
AM Silva ◽  
...  
Keyword(s):  
Motor Activity ◽  
Myosin Ii ◽  
Minor Role ◽  
Cortical Actin ◽  
Animal Cells ◽  
Contractile Ring ◽  
Myosin Motor ◽  
C Elegans ◽  
Ring Assembly ◽  
Muscle Myosin

AbstractCytokinesis in animal cells requires the assembly of a contractile actomyosin ring, whose subsequent constriction physically separates the two daughter cells. Non-muscle myosin II (myosin) is essential for cytokinesis, but the role of its motor activity remains poorly defined. Here, we examine cytokinesis in C. elegans one-cell embryos expressing myosin motor mutants generated by genome editing. Motor-dead myosin, which is capable of binding F-actin, does not support cytokinesis, and embryos co-expressing motor-dead and wild-type myosin are delayed in cytokinesis. Partially motor-impaired myosin also delays cytokinesis and renders contractile rings more sensitive to reduced myosin levels. Thus, myosin motor activity, rather than its ability to cross-link actin filaments, drives contractile ring assembly and constriction. We further demonstrate that myosin motor activity is required for long-range cortical actin flows, but that flows per se play a minor role in contractile ring assembly. Our results suggest that flow-independent recruitment of motor-competent myosin to the cell equator is both essential and rate-limiting for cytokinesis.

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