scholarly journals Dynamics of Centromeres during Metaphase–Anaphase Transition in Fission Yeast: Dis1 Is Implicated in Force Balance in Metaphase Bipolar Spindle

1998 ◽  
Vol 9 (11) ◽  
pp. 3211-3225 ◽  
Author(s):  
Kentaro Nabeshima ◽  
Takashi Nakagawa ◽  
Aaron F. Straight ◽  
Andrew Murray ◽  
Yuji Chikashige ◽  
...  
Keyword(s):  
Fission Yeast ◽  
Topoisomerase Ii ◽  
Fluorescent Protein ◽  
Phase 1 ◽  
Force Balance ◽  
Yeast Cells ◽  
Phase 2 ◽  
Metaphase Chromosomes ◽  
Spindle Elongation ◽  
Green Fluorescent

In higher eukaryotic cells, the spindle forms along with chromosome condensation in mitotic prophase. In metaphase, chromosomes are aligned on the spindle with sister kinetochores facing toward the opposite poles. In anaphase A, sister chromatids separate from each other without spindle extension, whereas spindle elongation takes place during anaphase B. We have critically examined whether such mitotic stages also occur in a lower eukaryote, Schizosaccharomyces pombe. Using the green fluorescent protein tagging technique, early mitotic to late anaphase events were observed in living fission yeast cells. S. pombe has three phases in spindle dynamics, spindle formation (phase 1), constant spindle length (phase 2), and spindle extension (phase 3). Sister centromere separation (anaphase A) rapidly occurred at the end of phase 2. The centromere showed dynamic movements throughout phase 2 as it moved back and forth and was transiently split in two before its separation, suggesting that the centromere was positioned in a bioriented manner toward the poles at metaphase. Microtubule-associating Dis1 was required for the occurrence of constant spindle length and centromere movement in phase 2. Normal transition from phase 2 to 3 needed DNA topoisomerase II and Cut1 but not Cut14. The duration of each phase was highly dependent on temperature.

scholarly journals Cpc2, a Fission Yeast Homologue of Mammalian RACK1 Protein, Interacts with Ran1 (Pat1) Kinase To Regulate Cell Cycle Progression and Meiotic Development

2000 ◽  
Vol 20 (11) ◽  
pp. 4016-4027 ◽  
Author(s):  
Maureen McLeod ◽  
Boris Shor ◽  
Anthony Caporaso ◽  
Wei Wang ◽  
Hua Chen ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Fission Yeast ◽  
Mammalian Cells ◽  
Cell Cycle Progression ◽  
Fluorescent Protein ◽  
Yeast Cells ◽  
Anchoring Protein ◽  
Signal Transduction Proteins ◽  
Green Fluorescent

ABSTRACT The Schizosaccharomyces pombe ran1/pat1 gene regulates the transition between mitosis and meiosis. Inactivation of Ran1 (Pat1) kinase is necessary and sufficient for cells to exit the cell cycle and undergo meiosis. The yeast two-hybrid interaction trap was used to identify protein partners for Ran1/Pat1. Here we report the identification of one of these, Cpc2. Cpc2 encodes a homologue of RACK1, a WD protein with homology to the β subunit of heterotrimeric G proteins. RACK1 is a highly conserved protein, although its function remains undefined. In mammalian cells, RACK1 physically associates with some signal transduction proteins, including Src and protein kinase C. Fission yeast cells containing a cpc2 null allele are viable but cell cycle delayed. cpc2Δ cells fail to accumulate in G1 when starved of nitrogen. This leads to defects in conjugation and meiosis. Copurification studies show that although Cpc2 and Ran1 (Pat1) physically associate, Cpc2 does not alter Ran1 (Pat1) kinase activity in vitro. Using a Ran1 (Pat1) fusion to green fluorescent protein, we show that localization of the kinase is impaired in cpc2Δ cells. Thus, in parallel with the proposed role of RACK1 in mammalian cells, fission yeast cpc2 may function as an anchoring protein for Ran1 (Pat1) kinase. All defects associated with loss of cpc2 are reversed in cells expressing mammalian RACK1, demonstrating that the fission yeast and mammalian gene products are indeed functional homologues.

scholarly journals The Sorting of Mitochondrial DNA and Mitochondrial Proteins in Zygotes: Preferential Transmission of Mitochondrial DNA to the Medial Bud

1998 ◽  
Vol 142 (3) ◽  
pp. 613-623 ◽  
Author(s):  
Koji Okamoto ◽  
Philip S. Perlman ◽  
Ronald A. Butow
Keyword(s):  
Mitochondrial Dna ◽  
Fluorescent Protein ◽  
Yeast Cells ◽  
Mitochondrial Matrix ◽  
Outer Membranes ◽  
Marker Proteins ◽  
The Matrix ◽  
Green Fluorescent ◽  
Mitochondrial Reticulum

Green fluorescent protein (GFP) was used to tag proteins of the mitochondrial matrix, inner, and outer membranes to examine their sorting patterns relative to mtDNA in zygotes of synchronously mated yeast cells in ρ+ × ρ0 crosses. When transiently expressed in one of the haploid parents, each of the marker proteins distributes throughout the fused mitochondrial reticulum of the zygote before equilibration of mtDNA, although the membrane markers equilibrate slower than the matrix marker. A GFP-tagged form of Abf2p, a mtDNA binding protein required for faithful transmission of ρ+ mtDNA in vegetatively growing cells, colocalizes with mtDNA in situ. In zygotes of a ρ+ × ρ+ cross, in which there is little mixing of parental mtDNAs, Abf2p–GFP prelabeled in one parent rapidly equilibrates to most or all of the mtDNA, showing that the mtDNA compartment is accessible to exchange of proteins. In ρ+ × ρ0 crosses, mtDNA is preferentially transmitted to the medial diploid bud, whereas mitochondrial GFP marker proteins distribute throughout the zygote and the bud. In zygotes lacking Abf2p, mtDNA sorting is delayed and preferential sorting is reduced. These findings argue for the existence of a segregation apparatus that directs mtDNA to the emerging bud.

scholarly journals The Positioning and Dynamics of Origins of Replication in the Budding Yeast Nucleus

2001 ◽  
Vol 152 (2) ◽  
pp. 385-400 ◽  
Author(s):  
Patrick Heun ◽  
Thierry Laroche ◽  
M.K. Raghuraman ◽  
Susan M. Gasser
Keyword(s):  
Nuclear Envelope ◽  
Chromatin Structure ◽  
Fluorescent Protein ◽  
Time Lapse ◽  
Yeast Cells ◽  
G1 Phase ◽  
Nuclear Pore ◽  
Origin Firing ◽  
Green Fluorescent

We have analyzed the subnuclear position of early- and late-firing origins of DNA replication in intact yeast cells using fluorescence in situ hybridization and green fluorescent protein (GFP)–tagged chromosomal domains. In both cases, origin position was determined with respect to the nuclear envelope, as identified by nuclear pore staining or a NUP49-GFP fusion protein. We find that in G1 phase nontelomeric late-firing origins are enriched in a zone immediately adjacent to the nuclear envelope, although this localization does not necessarily persist in S phase. In contrast, early firing origins are randomly localized within the nucleus throughout the cell cycle. If a late-firing telomere-proximal origin is excised from its chromosomal context in G1 phase, it remains late-firing but moves rapidly away from the telomere with which it was associated, suggesting that the positioning of yeast chromosomal domains is highly dynamic. This is confirmed by time-lapse microscopy of GFP-tagged origins in vivo. We propose that sequences flanking late-firing origins help target them to the periphery of the G1-phase nucleus, where a modified chromatin structure can be established. The modified chromatin structure, which would in turn retard origin firing, is both autonomous and mobile within the nucleus.

scholarly journals Ase1/Prc1-dependent spindle elongation corrects merotely during anaphase in fission yeast

2009 ◽  
Vol 187 (3) ◽  
pp. 399-412 ◽  
Author(s):  
Thibault Courtheoux ◽  
Guillaume Gay ◽  
Yannick Gachet ◽  
Sylvie Tournier
Keyword(s):  
Fission Yeast ◽  
Mechanical Model ◽  
Elongation Rate ◽  
Force Balance ◽  
Balance Model ◽  
Spindle Poles ◽  
Sister Chromatids ◽  
Spindle Elongation ◽  
Dependent Mechanism

Faithful segregation of sister chromatids requires the attachment of each kinetochore (Kt) to microtubules (MTs) that extend from opposite spindle poles. Merotelic Kt orientation is a Kt–MT misattachment in which a single Kt binds MTs from both spindle poles rather than just one. Genetic induction of merotelic Kt attachment during anaphase in fission yeast resulted in intra-Kt stretching followed by either correction or Kt disruption. Laser ablation of spindle MTs revealed that intra-Kt stretching and merotelic correction were dependent on MT forces. The presence of multiple merotelic chromosomes linearly antagonized the spindle elongation rate, and this phenomenon could be solved numerically using a simple force balance model. Based on the predictions of our mechanical model, we provide in vivo evidence that correction of merotelic attachment in anaphase is tension dependent and requires an Ase1/Prc1-dependent mechanism that prevents spindle collapse and thus asymmetric division and/or the appearance of the cut phenotype.

scholarly journals Hsp104 Overexpression Cures Saccharomyces cerevisiae [ PSI + ] by Causing Dissolution of the Prion Seeds

2014 ◽  
Vol 13 (5) ◽  
pp. 635-647 ◽  
Author(s):  
Yang-Nim Park ◽  
Xiaohong Zhao ◽  
Yang-In Yim ◽  
Horia Todor ◽  
Robyn Ellerbrock ◽  
...  
Keyword(s):  
Molecular Chaperone ◽  
Fluorescent Protein ◽  
Yeast Cells ◽  
Yeast Prion ◽  
Yeast Prions ◽  
Daughter Cells ◽  
Amyloid Aggregates ◽  
Mother And Daughter ◽  
Green Fluorescent ◽  
Kinetics Of

ABSTRACT The [ PSI + ] yeast prion is formed when Sup35 misfolds into amyloid aggregates. [ PSI + ], like other yeast prions, is dependent on the molecular chaperone Hsp104, which severs the prion seeds so that they pass on as the yeast cells divide. Surprisingly, however, overexpression of Hsp104 also cures [ PSI + ]. Several models have been proposed to explain this effect: inhibition of severing, asymmetric segregation of the seeds between mother and daughter cells, and dissolution of the prion seeds. First, we found that neither the kinetics of curing nor the heterogeneity in the distribution of the green fluorescent protein (GFP)-labeled Sup35 foci in partially cured yeast cells is compatible with Hsp104 overexpression curing [ PSI + ] by inhibiting severing. Second, we ruled out the asymmetric segregation model by showing that the extent of curing was essentially the same in mother and daughter cells and that the fluorescent foci did not distribute asymmetrically, but rather, there was marked loss of foci in both mother and daughter cells. These results suggest that Hsp104 overexpression cures [ PSI + ] by dissolution of the prion seeds in a two-step process. First, trimming of the prion seeds by Hsp104 reduces their size, and second, their amyloid core is eliminated, most likely by proteolysis.

scholarly journals Development and Application of a Green Fluorescent Protein Sentinel System for Identification of RNA Interference in Blastomyces dermatitidis Illuminates the Role of Septin in Morphogenesis and Sporulation

2007 ◽  
Vol 6 (8) ◽  
pp. 1299-1309 ◽  
Author(s):  
T. Krajaejun ◽  
G. M. Gauthier ◽  
C. A. Rappleye ◽  
T. D. Sullivan ◽  
B. S. Klein
Keyword(s):  
Green Fluorescent Protein ◽  
Rna Interference ◽  
Gene Silencing ◽  
Rapid Detection ◽  
Target Gene ◽  
Fluorescent Protein ◽  
Yeast Cells ◽  
Blastomyces Dermatitidis ◽  
Dimorphic Fungus ◽  
Green Fluorescent

ABSTRACT A high-throughput strategy for testing gene function would accelerate progress in our understanding of disease pathogenesis for the dimorphic fungus Blastomyces dermatitidis, whose genome is being completed. We developed a green fluorescent protein (GFP) sentinel system of gene silencing to rapidly study genes of unknown function. Using Gateway technology to efficiently generate RNA interference plasmids, we cloned a target gene, “X,” next to GFP to create one hairpin to knock down the expression of both genes so that diminished GFP reports target gene expression. To test this approach in B. dermatitidis, we first used LACZ and the virulence gene BAD1 as targets. The level of GFP reliably reported interference of their expression, leading to rapid detection of gene-silenced transformants. We next investigated a previously unstudied gene encoding septin and explored its possible role in morphogenesis and sporulation. A CDC11 septin homolog in B. dermatitidis localized to the neck of budding yeast cells. CDC11-silenced transformants identified with the sentinel system grew slowly as flat or rough colonies on agar. Microscopically, they formed ballooned, distorted yeast cells that failed to bud, and they sporulated poorly as mold. Hence, this GFP sentinel system enables rapid detection of gene silencing and has revealed a pronounced role for septin in morphogenesis, budding, and sporulation of B. dermatitidis.

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