Résumé
The translation apparatus has long been viewed as a mere factory until recent findings this last decade have unraveled its unexpected role in orchestrating real time gene regulation. Far from being a molecular monolith, the ribosome displays a remarkable heterogeneity along with a striking ability to orchestrate real-time control of gene expression. In the meantime, several reports connect alteration of the translation machinery with elevated cancer risk as well as in tumor initiation and progression. We aim to decipher the variety of translation mechanisms by modeling dedicated Ribo-sequencing experiments. We have designed a new set of Ribo-seq experiments with purified polysomes in order to understand the role of the ribosome density onto translation and to characterized biophysical parameters of translations (hopping rates of ribosomes, initiation rate, termination rate). Preliminary data will be modeled as a proof of concept to pave the way to a genome wide analysis with morefinely regulated genes in charge, e.g., for cell phenotype. After a presentation of the physical perspective of translation, I will discuss the usefulness of biophysical modeling approaches to estimate the codon-dependent hopping, initiation and termination rates of ribosomes from Ribo-seq data. I will discuss designed Ribo-seq experiments (purified polysomes) obtained at IGF suggesting that the ribosome dynamics depends on various conditions: modified dynamics of the first ribosome entering the newly transcripted mRNA, different paradigms for translation (cytoplasmic versus membrane translation), effect of inhomogeneous hopping rates on ribosome traffic etc. Finally, I will consider how these findings will help to understand the epithelial-mesenchymal transition: we have performed designed Ribo-seq experiments inducing a change of the ribosomes concentration level in vivo in tumor human cells and observed induced change of phenotype to mezenchymal cells.