Sister Chromatid Cohesion and Aneuploidy

International audiencen.a

MAU2 and NIPBL variants impair the heterodimerization of the cohesin loader subunits and cause Cornelia de Lange syndrome

The NIPBL/MAU2 heterodimer loads cohesin onto chromatin. Mutations inNIPBLaccount for most cases ofthe rare developmental disorder Cornelia de Lange syndrome (CdLS). Here we report aMAU2 variant causing CdLS, a deletion of seven amino acids that impairs the interaction between MAU2 and the NIPBL N terminus.Investigating this interaction, we discovered that MAU2 and the NIPBL N terminus are largely dispensable fornormal cohesin and NIPBL function in cells with a NIPBL early truncating mutation. Despite a predicted fataloutcome of an out-of-frame single nucleotide duplication inNIPBL, engineered in two different cell lines,alternative translation initiation yields a form of NIPBL missing N-terminal residues. This form cannot interactwith MAU2, but binds DNA and mediates cohesin loading. Altogether, our work reveals that cohesin loading can occur independently of functional NIPBL/MAU2 complexes and highlights a novel mechanism protectiveagainst out-of-frame mutations that is potentially relevant for other genetic conditions

Contribution of hCAP-D2, a Non-SMC Subunit of Condensin I, to Chromosome and Chromosomal Protein Dynamics during Mitosis

Condensins are heteropentameric complexes that were first identified as structural components of mitotic chromosomes. They are composed of two SMC (structural maintenance of chromosomes) and three non-SMC subunits. Condensins play a role in the resolution and segregation of sister chromatids during mitosis, as well as in some aspects of mitotic chromosome assembly. Two distinct condensin complexes, condensin I and condensin II, which differ only in their non-SMC subunits, exist. Here, we used an RNA interference approach to deplete hCAP-D2, a non-SMC subunit of condensin I, in HeLa cells. We found that the association of hCAP-H, another non-SMC subunit of condensin I, with mitotic chromosomes depends on the presence of hCAP-D2. Moreover, chromatid axes, as defined by topoisomerase II and hCAP-E localization, are disorganized in the absence of hCAP-D2, and the resolution and segregation of sister chromatids are impaired. In addition, hCAP-D2 depletion affects chromosome alignment in metaphase and delays entry into anaphase. This suggests that condensin I is involved in the correct attachment between chromosome kinetochores and microtubules of the mitotic spindle. These results are discussed relative to the effects of depleting both condensin complexes

Introduction to chromosome dynamics in mitosis.

International audienceTo ensure that the genetic information, replicated in the S-phase of the cell cycle, is correctly distributed between daughter cells at mitosis, chromatin duplication and chromosome segregation are highly regulated events. Since the early 1980's, our knowledge of the mechanisms governing these two events has greatly increased due to the use of genetic and biochemical approaches. We present here, first, an overview of the replication process, highlighting molecular aspects involved in coupling replication with chromatin dynamics in mitosis. The second part will present the current understanding of chromosome condensation and segregation during mitosis in higher eukaryotes. Finally, we will underline the links that exist between replication and mitosis

Etude fonctionnelle de pEg7/CAP-D2, une protéine impliquée dans la formation des chromosomes en mitose

Pendant la mitose, la chromatine interphasique est convertie en chromosomes condensés, ce qui permet la ségrégation des chromatides sœurs. J'ai étudié la sous-unité CAP-D2 du complexe condensine, impliqué dans la formation des chromosomes mitotiques. J'ai montré que l'inactivation de l'expression de CAP-D2 au cours de la maturation ovocytaire entraîne des défauts de structure et de résolution des chromatides sœurs dans un ovocyte mature de xénope. J'ai inactivé l'expression de CAP-D2 dans des cellules en culture par interférence à l'ARN. J'ai montré que CAP-D2 est nécessaire à l'adressage de CAP-H, une autre sous-unité, sur les chromosomes. Dans les cellules appauvries en CAP-D2, la résolution des chromatides sœurs est affectée, ce qui se traduit par des défauts de séparation des chromosomes en anaphase. Des observations préliminaires suggèrent également que la répression de CAP-D2 perturbe la localisation chromosomique de la topoisomérase II en mitose.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Sororin pre-mRNA splicing is required for proper sister chromatid cohesion in human cells.

International audienceSister chromatid cohesion, which depends on cohesin, is essential for the faithful segregation of replicated chromosomes. Here, we report that splicing complex Prp19 is essential for cohesion in both G2 and mitosis, and consequently for the proper progression of the cell through mitosis. Inactivation of splicing factors SF3a120 and U2AF65 induces similar cohesion defects to Prp19 complex inactivation. Our data indicate that these splicing factors are all required for the accumulation of cohesion factor Sororin, by facilitating the proper splicing of its pre-mRNA. Finally, we show that ectopic expression of Sororin corrects defective cohesion caused by Prp19 complex inactivation. We propose that the Prp19 complex and the splicing machinery contribute to the establishment of cohesion by promoting Sororin accumulation during S phase, and are, therefore, essential to the maintenance of genome stability

Multiple roles of Condensins: a complex story.

International audienceCondensins are pentameric complexes that were initially described as being involved in the dynamics of chromosomes during mitosis. It has been recently established that two related complexes (Condensin I and Condensin II) contribute to this process. An increasing sum of studies, using different approaches in various organisms, leads to the paradigm that Condensins are required for the correct segregation of replicated chromosomes by cooperating somehow with Topoisomerase II in sister chromatid resolution. Depending on species and/or experimental studies, these complexes also contribute to some aspects of the assembly and compaction of mitotic chromosomes. Recent studies provided evidences that Condensins and related complexes also function in non-mitotic processes such as replication and transcription. Biochemical studies have highlighted mechanistic aspects of Condensin function and initiated a fine functional dissection of core and regulatory subunits. However, the exact contribution of each subunit remains largely elusive as well as the functional interplay between Condensin I and Condensin II