scholarly journals An astral simulacrum of the central spindle accounts for normal, spindle-less, and anucleate cytokinesis in echinoderm embryos

2014 ◽  
Vol 25 (25) ◽  
pp. 4049-4062 ◽  
Author(s):  
Kuan-Chung Su ◽  
William M. Bement ◽  
Mark Petronczki ◽  
George von Dassow
Keyword(s):  
Animal Cells ◽  
Spatial Cues ◽  
Multiple Signals ◽  
Central Spindle ◽  
Binding Partner ◽  
Spindle Midzone ◽  
And Function ◽  
Equatorial Band

Cytokinesis in animal cells depends on spindle-derived spatial cues that culminate in Rho activation, and thereby actomyosin assembly, in a narrow equatorial band. Although the nature, origin, and variety of such cues have long been obscure, one component is certainly the Rho activator Ect2. Here we describe the behavior and function of Ect2 in echinoderm embryos, showing that Ect2 migrates from spindle midzone to astral microtubules in anaphase and that Ect2 shapes the pattern of Rho activation in incipient furrows. Our key finding is that Ect2 and its binding partner Cyk4 accumulate not only at normal furrows, but also at furrows that form in the absence of associated spindle, midzone, or chromosomes. In all these cases, the cell assembles essentially the same cytokinetic signaling ensemble—opposed astral microtubules decorated with Ect2 and Cyk4. We conclude that if multiple signals contribute to furrow induction in echinoderm embryos, they likely converge on the same signaling ensemble on an analogous cytoskeletal scaffold.

scholarly journals The Mammalian Septin MSF Localizes with Microtubules and Is Required for Completion of Cytokinesis

2002 ◽  
Vol 13 (10) ◽  
pp. 3532-3545 ◽  
Author(s):  
Mark C. Surka ◽  
Christopher W. Tsang ◽  
William S. Trimble
Keyword(s):  
Cell Death ◽  
Cell Division ◽  
Nuclear Division ◽  
Cleavage Furrow ◽  
Small Interfering Rnas ◽  
Animal Cells ◽  
Central Spindle ◽  
Synchronized Cells ◽  
Binucleated Cells ◽  
And Function

Cytokinesis in animal cells involves the contraction of an actomyosin ring formed at the cleavage furrow. Nuclear division, or karyokinesis, must be precisely timed to occur before cytokinesis in order to prevent genetic anomalies that would result in either cell death or uncontrolled cell division. The septin family of GTPase proteins has been shown to be important for cytokinesis although little is known about their role during this process. Here we investigate the distribution and function of the mammalian septin MSF. We show that during interphase, MSF colocalizes with actin, microtubules, and another mammalian septin, Nedd5, and coprecipitates with six septin proteins. In addition, transfections of various MSF isoforms reveal that MSF-A specifically localizes with microtubules and that this localization is disrupted by nocodazole treatment. Furthermore, MSF isoforms localize primarily with tubulin at the central spindle during mitosis, whereas Nedd5 is mainly associated with actin. Microinjection of affinity-purified anti-MSF antibodies into synchronized cells, or depletion of MSF by small interfering RNAs, results in the accumulation of binucleated cells and in cells that have arrested during cytokinesis. These results reveal that MSF is required for the completion of cytokinesis and suggest a role that is distinct from that of Nedd5.

scholarly journals Essential roles of KIF4 and its binding partner PRC1 in organized central spindle midzone formation

2004 ◽  
Vol 23 (16) ◽  
pp. 3237-3248 ◽  
Author(s):  
Yasuhiro Kurasawa ◽  
William C Earnshaw ◽  
Yuko Mochizuki ◽  
Naoshi Dohmae ◽  
Kazuo Todokoro
Keyword(s):  
Central Spindle ◽  
Binding Partner ◽  
Spindle Midzone

scholarly journals Cdc14-regulated midzone assembly controls anaphase B

2007 ◽  
Vol 177 (6) ◽  
pp. 981-993 ◽  
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.

Meiosis in Coprinus Lagopus: A Comparative Study with Light and Electron Microscopy

1967 ◽  
Vol 2 (4) ◽  
pp. 529-536
Author(s):  
B. C. LU
Keyword(s):  
Nuclear Fusion ◽  
Light And Electron Microscopy ◽  
Central Component ◽  
Fruiting Bodies ◽  
Homologous Pairing ◽  
Animal Cells ◽  
Characteristic Structure ◽  
Homologous Chromosomes ◽  
Central Spindle ◽  
Spindle Microtubules

Meiosis within fruiting bodies of Coprinus lagopus Fr. is closely synchronized. This conveniently facilitates joint light- and electron-microscope observations. Before nuclear fusion the chromatin appears diffuse in the light microscope; after nuclear fusion individual chromosomes can be recognized. In the electron micrographs the chromatin of pre-fusion and early fusion nuclei cannot be recognized as defined structures with the fixation and staining procedures employed. At the time of synapsis the lateral components of the synaptinemal complexes can be seen in the micrographs. The pairing process of the two chromosomes of the homologous pairs is believed to involve two steps: (1) two homologous chromosomes become aligned in parallel, and (2) pairing occurs by formation of the synaptinemal complex including the central synaptic component. The term synaptic centre is coined for the central component, which is believed to be the zone where crossing-over occurs. The formation of this structure in relation to homologous pairing, and the structural organization of the synaptinemal complexes are discussed. At meiotic metaphase, the chromosomes congregate around the central spindle microtubules. They are contracted and contain densely packed chromatin fibrils. Two types of spindle microtubules are demonstrated: (1) the chromosomal microtubules directly connecting the chromosomes to the centrosomes, and (2) the central spindle microtubules connecting the two centrosomes. The centrosomes are round, fibril-containing bodies approximately 0.3 µ in diameter. They have been observed outside the nuclear envelope at pachytene, but do not show the characteristic structure normally found in animal cells.

scholarly journals Reconstitution of the Human tRNA Splicing Endonuclease Complex: insight into the regulation of pre-tRNA cleavage

2019 ◽  
Author(s):  
Cassandra K. Hayne ◽  
Casey A. Schmidt ◽  
A. Gregory Matera ◽  
Robin E. Stanley
Keyword(s):  
Animal Cells ◽  
Trna Splicing ◽  
Polynucleotide Kinase ◽  
Genes Encoding ◽  
Intron Removal ◽  
And Function ◽  
Insight Into ◽  
Negative Modulator

ABSTRACTThe splicing of tRNA introns is a critical step in pre-tRNA maturation. In archaea and eukaryotes, tRNA intron removal is catalyzed by the tRNA splicing endonuclease (TSEN) complex. Eukaryotic TSEN is comprised of four core subunits (TSEN54, TSEN2, TSEN34, and TSEN15). The human TSEN complex additionally co-purifies with the polynucleotide kinase CLP1; however, CLP1’s role in tRNA splicing remains unclear. Mutations in genes encoding all four TSEN subunits, as well as CLP1, are known to cause neurodegenerative disorders, yet the mechanisms underlying the pathogenesis of these disorders are unknown. Here, we developed a recombinant system that produces active TSEN complex. Co-expression of all four TSEN subunits is required for efficient formation and function of the complex. We show that human CLP1 associates with the active TSEN complex, but is not required for tRNA intron cleavage in vitro. Moreover, RNAi knockdown of the Drosophila CLP1 orthologue, cbc, promotes biogenesis of mature tRNAs and circularized tRNA introns (tricRNAs) in vivo. Collectively, these and other findings suggest that CLP1/cbc plays a regulatory role in tRNA splicing by serving as a negative modulator of the direct tRNA ligation pathway in animal cells.

scholarly journals The chromosomal passenger complex and centralspindlin independently contribute to contractile ring assembly

2011 ◽  
Vol 193 (1) ◽  
pp. 155-169 ◽  
Author(s):  
Lindsay Lewellyn ◽  
Ana Carvalho ◽  
Arshad Desai ◽  
Amy S. Maddox ◽  
Karen Oegema
Keyword(s):  
Contractile Ring ◽  
Chromosomal Passenger Complex ◽  
Ring Assembly ◽  
Assembly Pathway ◽  
Chromosomal Passenger ◽  
Spindle Midzone ◽  
Ring Constriction ◽  
Simultaneous Inhibition ◽  
Control Transformation ◽  
Equatorial Band

The chromosomal passenger complex (CPC) and centralspindlin are conserved cytokinesis regulators that localize to the spindle midzone, which forms between the separating chromosomes. Previous work placed the CPC and centralspindlin in a linear pathway that governs midzone formation. Using Caenorhabditis elegans embryos, we test whether there is a similar linear relationship between centralspindlin and the CPC in contractile ring constriction during cytokinesis. We show that simultaneous inhibition of the CPC kinase Aurora BAIR-2 and the centralspindlin component MKLP1ZEN-4 causes an additive constriction defect. Consistent with distinct roles for the proteins, inhibition of filamentous septin guanosine triphosphatases alleviates constriction defects in Aurora BAIR-2–inhibited embryos, whereas inhibition of Rac does so in MKLP1ZEN-4-inhibited embryos. Centralspindlin and the CPC are not required to enrich ring proteins at the cell equator but instead regulate formation of a compact mature ring. Therefore, in contrast to the linear midzone assembly pathway, centralspindlin and the CPC make independent contributions to control transformation of the sheet-like equatorial band into a ribbon-like contractile ring at the furrow tip.

scholarly journals Reconstitution of the human tRNA splicing endonuclease complex: insight into the regulation of pre-tRNA cleavage

2020 ◽  
Vol 48 (14) ◽  
pp. 7609-7622 ◽  
Author(s):  
Cassandra K Hayne ◽  
Casey A Schmidt ◽  
Maira I Haque ◽  
A Gregory Matera ◽  
Robin E Stanley
Keyword(s):  
Animal Cells ◽  
Trna Splicing ◽  
Polynucleotide Kinase ◽  
Genes Encoding ◽  
Intron Removal ◽  
And Function ◽  
Insight Into ◽  
Negative Modulator

Abstract The splicing of tRNA introns is a critical step in pre-tRNA maturation. In archaea and eukaryotes, tRNA intron removal is catalyzed by the tRNA splicing endonuclease (TSEN) complex. Eukaryotic TSEN is comprised of four core subunits (TSEN54, TSEN2, TSEN34 and TSEN15). The human TSEN complex additionally co-purifies with the polynucleotide kinase CLP1; however, CLP1’s role in tRNA splicing remains unclear. Mutations in genes encoding all four TSEN subunits, as well as CLP1, are known to cause neurodegenerative disorders, yet the mechanisms underlying the pathogenesis of these disorders are unknown. Here, we developed a recombinant system that produces active TSEN complex. Co-expression of all four TSEN subunits is required for efficient formation and function of the complex. We show that human CLP1 associates with the active TSEN complex, but is not required for tRNA intron cleavage in vitro. Moreover, RNAi knockdown of the Drosophila CLP1 orthologue, cbc, promotes biogenesis of mature tRNAs and circularized tRNA introns (tricRNAs) in vivo. Collectively, these and other findings suggest that CLP1/cbc plays a regulatory role in tRNA splicing by serving as a negative modulator of the direct tRNA ligation pathway in animal cells.

The GS-X Pump in Plant, Yeast, and Animal Cells: Structure, Function, and Gene Expression

1997 ◽  
Vol 17 (2) ◽  
pp. 189-207 ◽  
Author(s):  
Toshihisa Ishikawa ◽  
Ze-Sheng Li ◽  
Yu-Ping Lu ◽  
Philip A. Rea
Keyword(s):  
Cancer Drug ◽  
Animal Cells ◽  
New Class ◽  
Cancer Drug Resistance ◽  
Cellular Detoxification ◽  
Physiologic Function ◽  
Coordinated Expression ◽  
And Function ◽  
Rate Limiting ◽  
Molecular Structure And Function

This review addresses the recent molecular identification of several members of the glutathione S-conjugate (GS-X) pump family, a new class of ATP-binding cassette (ABC) transporters responsible for the elimination and/or sequestration of pharmacologically and agronomically important compounds in mammalian, yeast and plant cells. The molecular structure and function of GS-X pumps encoded by MRP, cMOAT, YCF1. and AtMRP genes, have been conserved throughout molecular evolution. The physiologic function of GS-X pumps is closely related with cellular detoxification, oxidative stress, inflammation, and cancer drug resistance. Coordinated expression of GS-X pump genes, e.g., MRP1 and YCF1, and γ-glutamylcystaine synthetase, a rate-limiting enzyme of cellular glutathione (GSH) biosynthesis, has been frequently observed.

Properties and metabolism of the aqueous cytoplasm and its boundaries

1984 ◽  
Vol 246 (2) ◽  
pp. R133-R151 ◽  
Author(s):  
J. S. Clegg
Keyword(s):  
Cell Biology ◽  
Cell Structure ◽  
Large Fraction ◽  
Pure Water ◽  
Cell Ultrastructure ◽  
Structure And Function ◽  
Cell Water ◽  
Animal Cells ◽  
Intact Cells ◽  
And Function

The nucleoplasm, the interiors of cytoplasmic membrane-bound organelles, and the aqueous cytoplasm make up the aqueous compartments of animal cells. The extent to which these compartments are concentrated solutions of macromolecules, metabolites, ions, and other solutes is a matter of some importance to current thinking about cell structure and function. This paper will focus on the aqueous cytoplasm. It will show that the composition and metabolic activities of the cytosol, obtained by methods of cell disruption and fractionation, bear almost no resemblance to those of the aqueous cytoplasm in intact cells. The consequences of this to contemporary views on cell structure and function are considered. A closely related topic concerns the physical properties of the dominant component of these compartments, water: Are these properties the same as those of water in aqueous solutions, or are they altered as a result of interaction with cell architecture? Available evidence strongly suggests that at least a large fraction of the total cell water exhibits properties that markedly differ from those of pure water. Selected examples of these studies will be reviewed, and the roles of cell water will be discussed, notably as they relate to metabolism and cell ultrastructure. Although dimly perceived at present, it appears that living cells exhibit an organization far greater than the current teachings of cell biology reveal.

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