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1.
J Cell Sci ; 128(20): 3720-30, 2015 Oct 15.
Article in English | MEDLINE | ID: mdl-26359299

ABSTRACT

In higher eukaryotes, efficient chromosome congression relies, among other players, on the activity of chromokinesins. Here, we provide a quantitative analysis of kinetochore oscillations and positioning in Schizosaccharomyces pombe, a model organism lacking chromokinesins. In wild-type cells, chromosomes align during prophase and, while oscillating, maintain this alignment throughout metaphase. Chromosome oscillations are dispensable both for kinetochore congression and stable kinetochore alignment during metaphase. In higher eukaryotes, kinesin-8 family members control chromosome congression by regulating their oscillations. By contrast, here, we demonstrate that fission yeast kinesin-8 controls chromosome congression by an alternative mechanism. We propose that kinesin-8 aligns chromosomes by controlling pulling forces in a length-dependent manner. A coarse-grained model of chromosome segregation implemented with a length-dependent process that controls the force at kinetochores is necessary and sufficient to mimic kinetochore alignment, and prevents the appearance of lagging chromosomes. Taken together, these data illustrate how the local action of a motor protein at kinetochores provides spatial cues within the spindle to align chromosomes and to prevent aneuploidy.


Subject(s)
Biological Clocks/physiology , Chromosome Segregation/physiology , Chromosomes, Fungal/metabolism , Kinesins/metabolism , Models, Biological , Schizosaccharomyces/metabolism , Chromosomes, Fungal/genetics , Kinesins/genetics , Schizosaccharomyces/genetics
2.
Exp Gerontol ; 69: 202-10, 2015 Sep.
Article in English | MEDLINE | ID: mdl-26163343

ABSTRACT

Many experiments have shown that dietary restriction, for instance by removing live yeast or modifying the protein/carbohydrate ratio, can modulate lifespan, fecundity, resistance to severe stresses and behaviour in Drosophila melanogaster flies. The present study tested whether feeding flies with frozen yeast rather than with fresh yeast could have some effect on these traits, the other components of the food being similar in the two groups. Freezing altered live yeast quality and flies feeding on frozen yeast lived slightly less (males), were less fecund at older ages, and poorly resisted to some severe stresses (cold and starvation), no negative effect being observed on resistance to heat. It seems that, like in humans, feeding on a low quality food can negatively impact healthspan and that an appropriate food is not only a food with optimal number of calories and appropriate ratios of proteins, carbohydrates, and fat.


Subject(s)
Fertility/physiology , Frozen Foods , Longevity/physiology , Saccharomyces cerevisiae/physiology , Yeast, Dried/analysis , Adaptation, Physiological/physiology , Animals , Drosophila melanogaster , Food Quality
3.
EMBO J ; 34(14): 1942-58, 2015 Jul 14.
Article in English | MEDLINE | ID: mdl-26041456

ABSTRACT

Replication protein A (RPA) is a highly conserved heterotrimeric single-stranded DNA-binding protein involved in DNA replication, recombination, and repair. In fission yeast, the Rpa1-D223Y mutation provokes telomere shortening. Here, we show that this mutation impairs lagging-strand telomere replication and leads to the accumulation of secondary structures and recruitment of the homologous recombination factor Rad52. The presence of these secondary DNA structures correlates with reduced association of shelterin subunits Pot1 and Ccq1 at telomeres. Strikingly, heterologous expression of the budding yeast Pif1 known to efficiently unwind G-quadruplex rescues all the telomeric defects of the D223Y cells. Furthermore, in vitro data show that the identical D to Y mutation in human RPA specifically affects its ability to bind G-quadruplex. We propose that RPA prevents the formation of G-quadruplex structures at lagging-strand telomeres to promote shelterin association and facilitate telomerase action at telomeres.


Subject(s)
Chromosomes, Fungal/metabolism , Replication Protein A/metabolism , Schizosaccharomyces pombe Proteins/metabolism , Schizosaccharomyces/genetics , Telomere/metabolism , DNA Helicases/genetics , DNA Helicases/metabolism , DNA Polymerase I/metabolism , DNA Polymerase II/metabolism , DNA Replication , DNA, Single-Stranded , DNA-Binding Proteins/genetics , DNA-Binding Proteins/metabolism , G-Quadruplexes , Mutation , Replication Protein A/genetics , Schizosaccharomyces pombe Proteins/genetics , Shelterin Complex , Telomere/chemistry , Telomere Shortening , Telomere-Binding Proteins/metabolism
4.
J Cell Biol ; 208(6): 713-27, 2015 Mar 16.
Article in English | MEDLINE | ID: mdl-25778919

ABSTRACT

The segregation of centromeres and telomeres at mitosis is coordinated at multiple levels to prevent the formation of aneuploid cells, a phenotype frequently observed in cancer. Mitotic instability arises from chromosome segregation defects, giving rise to chromatin bridges at anaphase. Most of these defects are corrected before anaphase onset by a mechanism involving Aurora B kinase, a key regulator of mitosis in a wide range of organisms. Here, we describe a new role for Aurora B in telomere dispersion and disjunction during fission yeast mitosis. Telomere dispersion initiates in metaphase, whereas disjunction takes place in anaphase. Dispersion is promoted by the dissociation of Swi6/HP1 and cohesin Rad21 from telomeres, whereas disjunction occurs at anaphase after the phosphorylation of condensin subunit Cnd2. Strikingly, we demonstrate that deletion of Ccq1, a telomeric shelterin component, rescued cell death after Aurora inhibition by promoting the loading of condensin on chromosome arms. Our findings reveal an essential role for telomeres in chromosome arm segregation.


Subject(s)
Aurora Kinases/physiology , Chromosomes, Fungal/physiology , Schizosaccharomyces pombe Proteins/physiology , Schizosaccharomyces/enzymology , Telomere/metabolism , Adenosine Triphosphatases/metabolism , Cell Cycle Proteins/metabolism , Chromatin/metabolism , Chromosomal Proteins, Non-Histone/metabolism , DNA-Binding Proteins/metabolism , Mitosis , Multiprotein Complexes/metabolism , Nondisjunction, Genetic , Nuclear Proteins/metabolism , Phosphoproteins/metabolism , Phosphorylation , Protein Processing, Post-Translational , Schizosaccharomyces/cytology , Schizosaccharomyces/genetics , Schizosaccharomyces pombe Proteins/metabolism , Shelterin Complex , Spindle Apparatus/metabolism , Telomere-Binding Proteins/metabolism
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