Scw1p Antagonizes the Septation Initiation Network To Regulate Septum Formation and Cell Separation in the Fission Yeast Schizosaccharomyces pombe

ABSTRACT Cytokinesis in the fission yeast Schizosaccharomyces pombe is regulated by a signaling pathway termed the septation initiation network (SIN). The SIN is essential for initiation of actomyosin ring constriction and septum formation. In a screen to search for mutations that can rescue the sid2-250 SIN mutant, we obtained scw1-18. Both the scw1-18 mutant and the scw1 deletion mutant (scw1Δ mutant), have defects in cell separation. Both the scw1-18 and scw1Δ mutations rescue the growth defects of not just the sid2-250 mutant but also the other temperature-sensitive SIN mutants. Other cytokinesis mutants, such as those defective for actomyosin ring formation, are not rescued by scw1Δ. scw1Δ does not seem to rescue the SIN by restoring SIN signaling defects. However, scw1Δ may function downstream of the SIN to promote septum formation, since scw1Δ can rescue the septum formation defects of the cps1-191β-1,3-glucan synthase mutant, which is required for synthesis of the primary septum.

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Roles of Hof1p, Bni1p, Bnr1p, and Myo1p in Cytokinesis inSaccharomyces cerevisiae

Molecular Biology of the Cell ◽

10.1091/mbc.11.2.593 ◽

2000 ◽

Vol 11 (2) ◽

pp. 593-611 ◽

Cited By ~ 161

Author(s):

Elizabeth A. Vallen ◽

Juliane Caviston ◽

Erfei Bi

Keyword(s):

Cell Separation ◽

Synthetic Lethality ◽

Temperature Sensitive ◽

Concerted Action ◽

Septum Formation ◽

Primary Septum ◽

Bud Neck ◽

Single Ring ◽

Functional Pathway ◽

Actomyosin Contraction

Cytokinesis in Saccharomyces cerevisiae occurs by the concerted action of the actomyosin system and septum formation. Here we report on the roles of HOF1,BNI1, and BNR1 in cytokinesis, focusing on Hof1p. Deletion of HOF1 causes a temperature-sensitive defect in septum formation. A Hof1p ring forms on the mother side of the bud neck in G2/M, followed by the formation of a daughter-side ring. Around telophase, Hof1p is phosphorylated and the double rings merge into a single ring that contracts slightly and may colocalize with the actomyosin structure. Upon septum formation, Hof1p splits into two rings, disappearing upon cell separation. Hof1p localization is dependent on septins but not Myo1p. Synthetic lethality suggests that Bni1p and Myo1p belong to one functional pathway, whereas Hof1p and Bnr1p belong to another. These results suggest that Hof1p may function as an adapter linking the primary septum synthesis machinery to the actomyosin system. The formation of the actomyosin ring is not affected by bni1Δ, hof1Δ, orbnr1Δ. However, Myo1p contraction is affected bybni1Δ but not by hof1Δ orbnr1Δ. In bni1Δ cells that lack the actomyosin contraction, septum formation is often slow and asymmetric, suggesting that actomyosin contraction may provide directionality for efficient septum formation.

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An overview of the fission yeast septation initiation network (SIN)

Biochemical Society Transactions ◽

10.1042/bst0360411 ◽

2008 ◽

Vol 36 (3) ◽

pp. 411-415 ◽

Cited By ~ 84

Author(s):

Andrea Krapp ◽

Viesturs Simanis

Keyword(s):

Cell Cycle ◽

Signal Transduction ◽

Schizosaccharomyces Pombe ◽

Fission Yeast ◽

Protein Kinases ◽

Signal Transduction Network ◽

Septum Formation ◽

Ras Superfamily ◽

Septation Initiation Network

The fission yeast septation initiation network, or SIN, is a signal transduction network that is required for septum formation in Schizosaccharomyces pombe. Its activity is tightly regulated through the cell cycle, to ensure proper co-ordination of mitosis and cytokinesis. SIN signalling requires three protein kinases for its function and is mediated by a ras-superfamily GTPase. We discuss the elements of the SIN and how they are regulated.

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Cdc42 promotes Bgs1 recruitment for septum synthesis and glucanase localization for cell separation during cytokinesis in fission yeast

10.1101/754390 ◽

2019 ◽

Cited By ~ 1

Author(s):

Udo N. Onwubiko ◽

Julie Robinson ◽

Rose Albu Mustaf ◽

Maitreyi E. Das

Keyword(s):

Fission Yeast ◽

Membrane Trafficking ◽

Cell Separation ◽

Nucleotide Exchange ◽

Timely Initiation ◽

Division Site ◽

Guanine Nucleotide Exchange ◽

Nucleotide Exchange Factors ◽

Primary Septum ◽

Ring Constriction

AbstractCytokinesis in fission yeast involves actomyosin ring constriction concurrent to septum synthesis followed by septum digestion resulting in cell separation. A recent report indicates that endocytosis is required for septum synthesis and cell separation. The conserved GTPase Cdc42 is required for membrane trafficking and promotes endocytosis. Cdc42 is activated by Guanine nucleotide exchange factors (GEFs). Cdc42 GEFs have been shown to promote timely initiation of septum synthesis and proper septum morphology. Here we show that Cdc42 promotes the recruitment of the major primary septum synthesizing enzyme Bgs1 and consequent ring constriction. Cdc42 is also required for proper localization of the septum digesting glucanases at the division site. Thus, Cdc42 is required to promote multiple steps during cytokinesis.

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Profilin-mediated Competition between Capping Protein and Formin Cdc12p during Cytokinesis in Fission Yeast

Molecular Biology of the Cell ◽

10.1091/mbc.e04-09-0781 ◽

2005 ◽

Vol 16 (5) ◽

pp. 2313-2324 ◽

Cited By ~ 93

Author(s):

David R. Kovar ◽

Jian-Qiu Wu ◽

Thomas D. Pollard

Keyword(s):

Fission Yeast ◽

Actin Filament ◽

Actin Filaments ◽

Cell Separation ◽

The Other ◽

Temperature Sensitive ◽

Contractile Ring ◽

Capping Protein ◽

Division Site ◽

Ring Constriction

Fission yeast capping protein SpCP is a heterodimer of two subunits (Acp1p and Acp2p) that binds actin filament barbed ends. Neither acp1 nor acp2 is required for viability, but cells lacking either or both subunits have cytokinesis defects under stressful conditions, including elevated temperature, osmotic stress, or in combination with numerous mild mutations in genes important for cytokinesis. Defects arise as the contractile ring constricts and disassembles, resulting in delays in cell separation. Genetic and biochemical interactions show that the cytokinesis formin Cdc12p competes with capping protein for actin filament barbed ends in cells. Deletion of acp2 partly suppresses cytokinesis defects in temperature-sensitive cdc12-112 cells and mild overexpression of capping protein kills cdc12-112 cells. Biochemically, profilin has opposite effects on filaments capped with Cdc12p and capping protein. Profilin depolymerizes actin filaments capped by capping protein but allows filaments capped by Cdc12p to grow at their barbed ends. Once associated with a barbed end, either Cdc12p or capping protein prevents the other from influencing polymerization at that end. Given that capping protein arrives at the division site 20 min later than Cdc12p, capping protein may slowly replace Cdc12p on filament barbed ends in preparation for filament disassembly during ring constriction.

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Characterization of the roles of Blt1p in fission yeast cytokinesis

Molecular Biology of the Cell ◽

10.1091/mbc.e13-06-0300 ◽

2014 ◽

Vol 25 (13) ◽

pp. 1946-1957 ◽

Cited By ~ 17

Author(s):

John W. Goss ◽

Sunhee Kim ◽

Hannah Bledsoe ◽

Thomas D. Pollard

Keyword(s):

Cell Division ◽

Fission Yeast ◽

Cell Separation ◽

Analytical Ultracentrifugation ◽

Contractile Ring ◽

Glucan Synthase ◽

Temporal Regulation ◽

Septation Initiation Network ◽

Ring Constriction

Spatial and temporal regulation of cytokinesis is essential for cell division, yet the mechanisms that control the formation and constriction of the contractile ring are incompletely understood. In the fission yeast Schizosaccharomyces pombe proteins that contribute to the cytokinetic contractile ring accumulate during interphase in nodes—precursor structures around the equatorial cortex. During mitosis, additional proteins join these nodes, which condense to form the contractile ring. The cytokinesis protein Blt1p is unique in being present continuously in nodes from early interphase through to the contractile ring until cell separation. Blt1p was shown to stabilize interphase nodes, but its functions later in mitosis were unclear. We use analytical ultracentrifugation to show that purified Blt1p is a tetramer. We find that Blt1p interacts physically with Sid2p and Mob1p, a protein kinase complex of the septation initiation network, and confirm known interactions with F-BAR protein Cdc15p. Contractile rings assemble normally in blt1∆ cells, but the initiation of ring constriction and completion of cell division are delayed. We find three defects that likely contribute to this delay. Without Blt1p, contractile rings recruited and retained less Sid2p/Mob1p and Clp1p phosphatase, and β-glucan synthase Bgs1p accumulated slowly at the cleavage site.

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Rho3p Regulates Cell Separation by Modulating Exocyst Function in Schizosaccharomyces pombe

Genetics ◽

10.1093/genetics/164.4.1323 ◽

2003 ◽

Vol 164 (4) ◽

pp. 1323-1331

Author(s):

Hongyan Wang ◽

Xie Tang ◽

Mohan K Balasubramanian

Keyword(s):

Cell Division ◽

Schizosaccharomyces Pombe ◽

Cell Separation ◽

Model Organism ◽

Temperature Sensitive ◽

Complex Cells ◽

Exocyst Complex ◽

Primary Septum ◽

Rho Family ◽

Growth Phenotype

Abstract Cytokinesis is the final stage of the cell division cycle in which the mother cell is physically divided into two daughters. In recent years the fission yeast Schizosaccharomyces pombe has emerged as an attractive model organism for the study of cytokinesis, since it divides using an actomyosin ring whose constriction is coordinated with the centripetal deposition of new membranes and a division septum. The final step of cytokinesis in S. pombe requires the digestion of the primary septum to liberate two daughters. We have previously shown that the multiprotein exocyst complex is essential for this process. Here we report the isolation of rho3+, encoding a Rho family GTPase, as a high-copy suppressor of an exocyst mutant, sec8-1. Overproduction of Rho3p also suppressed the temperature-sensitive growth phenotype observed in cells lacking Exo70p, another conserved component of the S. pombe exocyst complex. Cells deleted for rho3 arrest at higher growth temperatures with two or more nuclei and uncleaved division septa between pairs of nuclei. rho3Δ cells accumulate ∼100-nm vesicle-like structures. These phenotypes are all similar to those observed in exocyst component mutants, consistent with a role for Rho3p in modulation of exocyst function. Taken together, our results suggest the possibility that S. pombe Rho3p regulates cell separation by modulation of exocyst function.

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The endo-beta-1,3-glucanase eng1p is required for dissolution of the primary septum during cell separation in Schizosaccharomyces pombe

Journal of Cell Science ◽

10.1242/jcs.00377 ◽

2003 ◽

Vol 116 (9) ◽

pp. 1689-1698 ◽

Cited By ~ 125

Author(s):

A. B. Martin-Cuadrado

Keyword(s):

Schizosaccharomyces Pombe ◽

Cell Separation ◽

Primary Septum

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Site-specific mutagenesis of cdc2+, a cell cycle control gene of the fission yeast Schizosaccharomyces pombe

Molecular and Cellular Biology ◽

10.1128/mcb.6.10.3523-3530.1986 ◽

1986 ◽

Vol 6 (10) ◽

pp. 3523-3530

Author(s):

R Booher ◽

D Beach

Keyword(s):

Schizosaccharomyces Pombe ◽

Fission Yeast ◽

Cell Cycle Control ◽

Temperature Sensitive ◽

Protein Kinase Activity ◽

Atp Binding Site ◽

Leu2 Gene ◽

Cdc2 Gene ◽

A Site

The cdc2+ gene of Schizosaccharomyces pombe is homologous to the CDC28 gene of Saccharomyces cerevisiae. Both genes share limited homology with vertebrate protein kinases and have protein kinase activity. cdc2+ has been subjected to mutagenesis in vitro. A null allele of the gene, constructed by insertion of the S. cerevisiae LEU2 gene into a site within the gene, has a phenotype similar to that of many temperature-sensitive alleles of cdc2. Mutations within the predicted ATP-binding site and in a region which may be a site of phosphorylation result in loss of cdc2+ activity. A single substitution of Gly-146 to Asp-146 has been identified in cdc2-1w, a dominant activated allele of the gene. The four introns within the cdc2+ gene have been deleted. The resulting gene not only functions in fission yeast but also rescues cdc28(Ts) strains of S. cerevisiae, a property which is not shared by the genomic cdc2+ gene.

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Phylogenetic and comparative functional analysis of the cell-separation α-glucanase Agn1p in Schizosaccharomyces

Microbiology ◽

10.1099/mic.0.077511-0 ◽

2014 ◽

Vol 160 (6) ◽

pp. 1063-1074 ◽

Cited By ~ 2

Author(s):

Matthias Sipiczki ◽

Anita Balazs ◽

Aniko Monus ◽

Laszlo Papp ◽

Anna Horvath ◽

...

Keyword(s):

Cell Wall ◽

Schizosaccharomyces Pombe ◽

Fission Yeast ◽

Mother Cell ◽

Cell Separation ◽

Yeast Cells ◽

Glycoside Hydrolase Family ◽

Binding Domains ◽

Yeast Phase ◽

Mother Cell Wall

The post-cytokinetic separation of cells in cell-walled organisms involves enzymic processes that degrade a specific layer of the division septum and the region of the mother cell wall that edges the septum. In the fission yeast Schizosaccharomyces pombe, the 1,3-α-glucanase Agn1p, originally identified as a mutanase-like glycoside hydrolase family 71 (GH71) enzyme, dissolves the mother cell wall around the septum edge. Our search in the genomes of completely sequenced fungi identified GH71 hydrolases in Basidiomycota, Taphrinomycotina and Pezizomycotina, but not in Saccharomycotina. The most likely Agn1p orthologues in Pezizomycotina species are not mutanases having mutanase-binding domains, but experimentally non-characterized hypothetical proteins that have no carbohydrate-binding domains. The analysis of the GH71 domains corroborated the phylogenetic relationships of the Schizosaccharomyces species determined by previous studies, but suggested a closer relationship to the Basidiomycota proteins than to the Ascomycota proteins. In the Schizosaccharomyces genus, the Agn1p proteins are structurally conserved: their GH71 domains are flanked by N-terminal secretion signals and C-terminal sequences containing the conserved block YNFNAY/HTG. The inactivation of the agn1Sj gene in Schizosaccharomyces japonicus, the only true dimorphic member of the genus, caused a severe cell-separation defect in its yeast phase, but had no effect on the hyphal growth and yeast-to-mycelium transition. It did not affect the mycelium-to-yeast transition either, only delaying the separation of the yeast cells arising from the fragmenting hyphae. The heterologous expression of agn1Sj partially rescued the separation defect of the agn1Δ cells of Schizosaccharomyces pombe. The results presented indicate that the fission yeast Agn1p 1,3-α-glucanases of Schizosaccharomyces japonicus and Schizosaccharomyces pombe share conserved functions in the yeast phase.

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