Role of the chromatin architecture in the regulation of gene transcription – ChromaTranscript

Inside the nucleus of eukaryotic cells, the genetic material displays a complex multi-scale architecture. While the smallest scales, that is the DNA double helix wrapped around the nucleosome, is now quite well described, we still miss a clear picture of the higher order structures. Another aspect which remains poorly characterized is the dynamics of this architecture. While at “steady state” the chromatin organization is thought to be relatively stable along the entire interphase, dramatic modifications of this architecture has been observed in response to external stimuli. In particular, the activation or repression of gene transcription is often associated with local changes in the level of chromatin compaction and with gene repositioning inside the nucleus. However, a precise understanding of the mechanism underlying this chromatin reorganization is impeded by the lack of a complete description of the dynamics of the restructuring process. In addition, we do not know if the observed nuclear reorganization is the cause or the consequence of the changes in transcriptional activity. With the current research project we propose to try to address these questions using an original approach at the interface between biology, physics and advanced microscopy.

This project will be coordinated by Sébastien Huet, a biophysicist specialized in the imaging of dynamic processes in living cells. Sébastien Huet recently created a team entitled “Dynamics of the chromatin architecture” at the Institut de Génétique et du Développement de Rennes. A research technician specialized in molecular biology will join the team in May 2011. This project also involves two other partners with a strong expertise in the analysis of the dynamics of the chromatin architecture: i) the group headed by Kerstin Bystricky in the Laboratoire de Biologie Moléculaire des Eucaryotes in Toulouse and ii) the group of Gilles Salbert in the Laboratoire des Interactions Cellulaires et Moléculaires in Rennes.

In this project, we propose to investigate the process of nuclear restructuring in association to transcriptional activation or repression using the estrogen-regulated genes as a “model” system. Estrogens control the expression of multiple genes involved in the growth and differentiation of both normal and malignant cells, in particular in the case of breast epithelial cells. Recent findings from the team headed by Kerstin Bystricky indicates that transcription up- or down-regulation induced by estrogens is associated to massive nuclear reorganizations both in terms of chromatin compaction level and concerning gene position inside the nucleus. We aim to gain insight into this reorganization process by trying to answer the three following questions

1) What is the dynamic of the nuclear reorganization process at the scale of a single chromosome ?

2) What are the changes in the fine chromatin structure underlying the micron-scale nuclear reorganizations studied in 1) ?

3) Is nuclear reorganization the cause or the consequence of the change in transcription activity ?

To address these three questions, we propose an innovative interdisciplinary approach combining tagging methods used to label in fluorescence single chromosome or specific gene loci in living cells and advanced light microscopy methods allowing to monitor at different scales in space and time the process of nuclear restructuring in association to transcription activation or repression.