4 research outputs found
Mécanismes Moléculaires de la Condensation Mitotique des Chromosomes chez la levure Schizosaccharomyces pombe
From yeasts to human, Condensin is essential for mitotic chromosome condensation. However, how Condensin binds to chromatin and, in this context, shapes mitotic chromosome remain poorly understood. Mappings performed from yeasts to mouse have revealed that condensin is enriched near highly expressed genes along chromosome arms, suggesting that as yet identified features associated with transcription take part in condensin binding to chromatin. To identify factors that collaborate with Condensin we performed a synthetically lethal genetic screen in fission yeast. We searched for mutants that are alive when Condensin is fully functional but dead when Condensin is partly defective. We identified 7 proteins never known for their roles in the mitotic condensation, such as some chromatin remodelling and some transcription factors. All these results were consistent with a link between condensation and transcription. Among theses 7 proteins, we found Gcn5, which encodes a conserved HAT, well known for the role it plays as a transcriptional co-activator. Gcn5 binds to gene promoters where it acetylates mainly H3K9, K14 and K18, and its occupancy correlates with transcription rates. Remarkably, although the bulk of chromatin is de-acetylated and Gcn5 reduced from chromatin upon mitosis entry, traces of Gcn5 dependant H3K9 acetylated persist at condensin binding sites. Here, we provide evidence that Gcn5-mediated histone H3 K9 acetylation could assist the binding of Condensin to chromatinLa condensation mitotique des chromosomes est l'un des mĂ©canismes assurant la transmission fidĂšle de l'information gĂ©nĂ©tique. Les complexes condensines et leur association Ă la chromatine sont nĂ©cessaires Ă cette condensation. Cependant, les mĂ©canismes par lesquels ces complexes s'associent aux chromosomes et contribuent Ă leur condensation sont mal compris. L'objectif de ma thĂšse Ă©tait d'identifier et de caractĂ©riser des facteurs de condensation encore inconnus collaborant avec le complexe condensine prĂ©sent chez S. pombe. Par un crible gĂ©nĂ©tique, nous avons recherchĂ© des mutants viables lorsque le complexe condensine est complĂštement fonctionnel mais morts lorsque ce complexe est partiellement dĂ©fectif. Nous avons ainsi identifiĂ© 7 protĂ©ines jusqu'alors jamais impliquĂ©es dans la condensation mitotique. Parmi ces derniĂšres, nous avons identifiĂ© des protĂ©ines impliquĂ©es dans le remodelage de la chromatine et des facteurs de transcription comme Gcn5, une HAT trĂšs conservĂ©e, connue pour son rĂŽle de coactivateur de la transcription ; suggĂ©rant un lien entre la condensation et la machinerie transcriptionnelle. Gcn5 s'associe Ă la chromatine au niveau des promoteurs des gĂšnes oĂč elle acĂ©tyle principalement H3K9, H3K14 et H3K18. Sa prĂ©sence au niveau des promoteurs est directement corrĂ©lĂ©e avec le niveau de transcription des gĂšnes correspondants. Bien que la majoritĂ© de la chromatine soit dĂ©-acĂ©tylĂ©e et que la prĂ©sence de Gcn5 soit rĂ©duite au niveau des chromosomes en mitose, des traces de H3K9 acĂ©tylĂ©e persistent au niveau de certains promoteurs. Nos rĂ©sultats suggĂšrent que cette acĂ©tylation persistante pourrait ĂȘtre liĂ©e au recrutement du complexe condensine Ă la chromatin
Molecular mechanism of mitotic chromosome in the fission yeast Schizosaccharamyces pombe
La condensation mitotique des chromosomes est l'un des mĂ©canismes assurant la transmission fidĂšle de l'information gĂ©nĂ©tique. Les complexes condensines et leur association Ă la chromatine sont nĂ©cessaires Ă cette condensation. Cependant, les mĂ©canismes par lesquels ces complexes s'associent aux chromosomes et contribuent Ă leur condensation sont mal compris. L'objectif de ma thĂšse Ă©tait d'identifier et de caractĂ©riser des facteurs de condensation encore inconnus collaborant avec le complexe condensine prĂ©sent chez S. pombe. Par un crible gĂ©nĂ©tique, nous avons recherchĂ© des mutants viables lorsque le complexe condensine est complĂštement fonctionnel mais morts lorsque ce complexe est partiellement dĂ©fectif. Nous avons ainsi identifiĂ© 7 protĂ©ines jusqu'alors jamais impliquĂ©es dans la condensation mitotique. Parmi ces derniĂšres, nous avons identifiĂ© des protĂ©ines impliquĂ©es dans le remodelage de la chromatine et des facteurs de transcription comme Gcn5, une HAT trĂšs conservĂ©e, connue pour son rĂŽle de coactivateur de la transcription ; suggĂ©rant un lien entre la condensation et la machinerie transcriptionnelle. Gcn5 s'associe Ă la chromatine au niveau des promoteurs des gĂšnes oĂč elle acĂ©tyle principalement H3K9, H3K14 et H3K18. Sa prĂ©sence au niveau des promoteurs est directement corrĂ©lĂ©e avec le niveau de transcription des gĂšnes correspondants. Bien que la majoritĂ© de la chromatine soit dĂ©-acĂ©tylĂ©e et que la prĂ©sence de Gcn5 soit rĂ©duite au niveau des chromosomes en mitose, des traces de H3K9 acĂ©tylĂ©e persistent au niveau de certains promoteurs. Nos rĂ©sultats suggĂšrent que cette acĂ©tylation persistante pourrait ĂȘtre liĂ©e au recrutement du complexe condensine Ă la chromatineFrom yeasts to human, Condensin is essential for mitotic chromosome condensation. However, how Condensin binds to chromatin and, in this context, shapes mitotic chromosome remain poorly understood. Mappings performed from yeasts to mouse have revealed that condensin is enriched near highly expressed genes along chromosome arms, suggesting that as yet identified features associated with transcription take part in condensin binding to chromatin. To identify factors that collaborate with Condensin we performed a synthetically lethal genetic screen in fission yeast. We searched for mutants that are alive when Condensin is fully functional but dead when Condensin is partly defective. We identified 7 proteins never known for their roles in the mitotic condensation, such as some chromatin remodelling and some transcription factors. All these results were consistent with a link between condensation and transcription. Among theses 7 proteins, we found Gcn5, which encodes a conserved HAT, well known for the role it plays as a transcriptional co-activator. Gcn5 binds to gene promoters where it acetylates mainly H3K9, K14 and K18, and its occupancy correlates with transcription rates. Remarkably, although the bulk of chromatin is de-acetylated and Gcn5 reduced from chromatin upon mitosis entry, traces of Gcn5 dependant H3K9 acetylated persist at condensin binding sites. Here, we provide evidence that Gcn5-mediated histone H3 K9 acetylation could assist the binding of Condensin to chromati
A genetic screen for functional partners of condensin in fission yeast
Mitotic chromosome condensation is a prerequisite for the accurate segregation of chromosomes during cell division, and the conserved condensin complex a central player of this process. However, how condensin binds chromatin and shapes mitotic chromosomes remain poorly understood. Recent genome-wide binding studies showing that in most species condensin is enriched near highly expressed genes suggest a conserved link between condensin occupancy and high transcription rates. To gain insight into the mechanisms of condensin binding and mitotic chromosome condensation, we searched for factors that collaborate with condensin through a synthetic lethal genetic screen in the fission yeast Schizosaccharomyces pombe. We isolated novel mutations affecting condensin, as well as mutations in four genes not previously implicated in mitotic chromosome condensation in fission yeast. These mutations cause chromosome segregation defects similar to those provoked by defects in condensation. We also identified a suppressor of the cut3-477 condensin mutation, which largely rescued chromosome segregation during anaphase. Remarkably, of the five genes identified in this study, four encode transcription co-factors. Our results therefore provide strong additional evidence for a functional connection between chromosome condensation and transcription