CGM - Department Dynamics & Stability of Genomes

Chromosome Dynamics

Group leader: Olivier ESPÉLI

  Last update: 24-Avril-2012

• Our team
• Our address
• Research theme 1
• Research theme 2
• Selected publications

 

Our team

Our address

First research theme : Control of the sister chromatid cohesion step in bacteria

Following their replication sister chromatids remain colocalized for 20 minutes before their segregation to each daugther cells, this step is called sister chromatid cohesion. In bacteria, little is known about sister chromosome cohesion and its possible functional role. The main goal of  our project is to reveal the structuring mechanisms involved in sister-chromatid cohesion in bacteria. Recently two major determinants of the extent of the co-localization period have been identified. We have demonstrated that macrodomain structuring of the chromosome participates in the establishment of the co-localization between sister chromatids (Espeli et al., 2008).In the absence of MatP the co-localization/cohesion period was dramatically reduced. On the other hand, the work performed in the group of Dr. David Sherratt established that Topoisomerase IV alteration also modulated the extent of the co-localization/cohesion period. Putative connections between MatP and Topoisomerase IV remain to be characterized.

Indirect evidences suggest that topological links (precatenanes) between newly replicated chromatids could promote cohesion of the sister chromatids in bacteria and for some regions of the eukaryotic chromosomes. It is of a particular interest to establish directly if precatenane links are formed during the replication of the E. coli chromosome, if they are maintained for a sufficient long time to allow cohesion and what are the elements involved in the regulation of their removal. We have developed a recombination test to measure precatenation of the chromatids in vivo.

To address the question of the spatial organization of the sister chromatids, we are combining  a recombination assay and Chromosome Conformation Capture (Hi-C) techniques that allow its characterization at the whole genome wide scale. The availability of high throughput “Illumina” sequencing facility on the Gif-sur-Yvette campus (IMAGIF) gives us the opportunity to survey molecular cohesion on the entire chromosome.

To study sister chromatid dynamics at the single cell level we are using new tools for cellular biology analysis of chromosome. With these tools, we should be able to transiently differentiate the two sisters chromatids, to analyse precisely their connections with high resolution using FRET assay and super-resolution microscopy.

Downloading of a 16 s movie that shows the growth of the bacteria E. coli observed during 2 hours by fluorescence microscopy (.avi file, 3 Mo ; movie by O. Espéli).

Second research theme : Chromosome dynamics in yeast Schizosaccharomyces pombe

Molecular mechanism for sister chromatid cohesion between sister chromatids have been investigated for a longer time in eukaryotic cells than in bacteria. It is well established that the loading of a specific subclass of SMC proteins (cohesins) concomitantly with replication is the main event promoting cohesion of the sister chromatids. Cohesin are loaded to specific regions corresponding to centromeres, silent chromatin and converging genes. From these points cohesins controls the cohesion of the entire sister chromatids.  

Taking into consideration that a correct chromatid alignment is crucial for bipolar attachment of sister kinetochores, for DNA repair, for chromosome morphogenesis and finally for transcription control of some genes, it is of a particular interest to better understand chromosome architecture inside a sister chromatid fibre. Recently several casesof mutations in genes involved in the cohesin complex have been identified in patient presenting cancers or genetic diseases.

The experiments proposed in this project are aimed to increase the resolution with which we can describe the structuring of sister chromatids during the S phase to anaphase transition. Yeast Schizosaccharomyces pombe has been chosen as model organism for this study because of the availability of a large number of genetic tools required for the development of the genetic, genomic and cell biology experiments envisaged. Moreover,  The cell cycle of S. pombe present a very long G2 phase (up to 80% of the cell cycle) during which sister chromatids remain cohesive, it is therefore an ideal model for our project.

 

Web sites of our collaborators and friends

 IMAGIF

The Boccard’s group

Ivan Junier’s group

Marc Boudvillain's group

Selected publications