"Matière et Systèmes Complexes"
27 avril 2009 à 11h30
Bâtiment Condorcet, 4ème
étage, salle 454 A.
Imaging & Modeling Group, Institut Pasteur, Paris)
Mapping nuclear organization in living cells by computational imaging
spatial position of chromosomes and genes inside eukaryotic cell nuclei
is not random and plays a role in fundamental biological processes,
including gene expression, DNA repair and replication. However, despite
its functional importance, the spatial organization of the genome in
living cells is still largely uncharted. This is due to several
technical limitations, including the diffraction limited resolution of
optical microscopy and a lack of analysis tools. To better describe and
understand nuclear organization, we have developed an imaging and
analysis approach that allows to create high-resolution probability
maps of chromosomal loci within the living yeast nucleus.
This is achieved by automated processing of microscopy images
containing thousands of cells, combined with fluorescent tagging of two
nuclear landmarks. In contrast to the images themselves, the resolution
of these probability maps is not limited by diffraction. The technique
thereby allowed us to visualize a strong spatial organization, with
several genes confined to probabilistic territories significantly
smaller than the nucleus. We could observe remodeling of galactose gene
territories during transcriptional activation, but also spatial
segregation of coregulated genes.
Our data on various loci including many telomeres quantitatively
describe the Rabl-configuration of yeast chromosomes. Loci positions
strongly correlate with genomic location, suggesting that the spatial
organization of the yeast genome may be predictable by relatively
simple physical models.