ERC FUNDED PROJECTS

In mammals, transcriptional control of many genes relies on cis-regulatory elements such as enhancers, which are often located tens to hundreds of kilobases away from their cognate promoters. Functional interactions between distal regulatory elements and target promoters require mutual physical proximity, which is linked to the three-dimensional structure of the chromatin fiber. Chromosome conformation capture studies revealed that chromosomes are partitioned into Topologically Associating Domains (TADs), sub-megabase domains of preferential physical interactions of the chromatin fiber. Genetic evidence showed that TAD boundaries restrict the genomic range of enhancer-promoter communication, and that interactions between regulatory sequences within TADs are further fine-tuned by smaller-scale structures. However, the mechanistic details of how physical interactions translate into transcriptional outputs are totally unknown. Here we propose to explore the biophysical mechanisms that link chromosome conformation and long-range transcriptional regulation using molecular biology, genetic engineering, single-cell experiments and physical modeling. We will measure chromosomal interactions in single cells and in time using a novel method that relies on an enzymatic process in vivo. Genetic engineering will be used to establish a cell system that allows quantitative measurement of how enhancer-promoter interactions relate to transcription at the population and single-cell levels, and to test the effects of perturbations without confounding effects. Finally, we will develop physical models of promoter operation in the presence of distal enhancers, which will be used to interpret the experimental data and formulate new testable predictions. With this integrated approach we aim at providing an entirely new layer of description of the general principles underlying transcriptional control, which could establish new paradigms for research in epigenetics and gene regulation.

1 500 000 €

Start date: 2018-01-01, End date: 2022-12-31

The aim of this project is to understand the dynamics of protein-DNA interactomes underlying circadian oscillators in mammals, and how these shape circadian transcriptional output programs. Specifically our goal is to solve a fundamental issue in circadian biology: the phase specificity problem underlying circadian gene expression. We have taken a challenging and original multi-disciplinary approach in which molecular biology experiments will be tightly interlinked with computational analyses and biophysical modeling. The approach will generate time resolved protein-DNA interactomes in mouse liver for several key circadian repressors at unprecedented resolution. These experiments will be complemented with chromosome conformation capture (3C) experiments to monitor how looping interactions and 3D genome structure rearrange during the circadian cycle, which will inform on how circadian transcription networks use long-range gene regulatory mechanisms. Novel computational algorithms based on biophysical principles will be developed and implemented to optimally analyze interactome and 3C datasets. For the latter, statistical models from polymer physics will be used to reconstruct the chromatin networks and interaction maps from the 3C data. At the detailed level of individual cells, we will investigate transcription bursts, and how those are involved in the control of circadian gene expression. In particular we will exploit high temporal resolution bioluminescence reporters using a biophysical model of transcription coupled with a Hidden Markov Model (HMM). Through our innovative approach, we expect that the data generated and state-of-the-art analyses performed will lead novel insight into the role and mechanics of circadian transcription in controlling circadian outputs in mammals.

1 500 000 €

Start date: 2011-03-01, End date: 2016-02-29

Differentiation events in mammalian development involve stable resetting of transcriptional programs, which entails changes in the epigenetic state of target sequences defined by modifications of DNA and bound nucleosomes. These recently identified epigenetic layers modulate DNA accessibility in a positive and negative manner and thus could make genetic readouts context-dependent and dynamic. The proposed project aims to quantify the epigenetic contribution to cellular differentiation as a key event in development. By applying parallel genomic approaches we will comprehensively define the epigenome and its plasticity during cellular commitment of pluripotent murine stem cells into defined terminally differentiated cells. We will focus on DNA methylation and its interplay with several histone modifications as a way to achieve stable gene silencing. The resulting global profiles will gain insights into targeting principles and generate statistical, predictive models of regulation. From these mechanistic models will be derived and tested by genetically interfering with genetic and epigenetic regulatory pathways and by dissecting DNA sequence components involved in specifying targets. These experiments aim to unravel the crosstalk between epigenetic regulation and cell plasticity, the underlying molecular circuitry in pluripotent and unipotent cells and ultimately help to incorporate epigenetic regulation into current transcriptional regulatory models.

1 085 000 €

Start date: 2008-10-01, End date: 2013-09-30

In eukaryotes, silencing small (s)RNAs, including micro (mi)RNAs and small interfering (si)RNAs, regulate many aspects of biology, including cell differentiation, development, hormonal responses, or defense. In particular, many plant and metazoan miRNAs play crucial roles in embryonic/post-embryonic development; the precise timing and localization of their expression is thus crucial to their action. Hence, specific miRNA repertoires underlie specific cell identities, and deviations from such repertoires often have deleterious consequences such as cancer. Many miRNAs also help organisms to adapt to stress, thus, given their importance in virtually all aspects of biology, understanding how, when and where miRNAs exert their actions is of paramount importance. To date, however, the few approaches to miRNA-mediated silencing in whole organisms have not taken into account the exquisite definition, in space and time, of their biogenesis and action, leading to an inaccurate view of the biology of these molecules at the systems level. Using the root system of the model plant Arabidopsis thaliana, we propose to explore, at single-cell and subcellular resolution levels, the biology of the main miRNA effector protein, ARGONAUTE 1 (AGO1) in intact tissues. Using a combination of state-of the-art technologies for single-cell forward genetics, protein purification and RNA/polysome profiling, we will establish a functional spatiotemporal map of the root AGO1-sRNAome and identify cell-specific modifiers of sRNA biogenesis and action. As a complement to the above approaches, chemical genetics will isolate small molecules allowing direct and specific manipulation of AGO1-dependent sRNA pathways in planta. RNA silencing modifier compounds will also accelerate forward and reverse approaches of RNA silencing in plants with sensitized genetic backgrounds, and uncover novel connections between miRNA/siRNA and physiological or metabolic pathways.

2 251 600 €

Start date: 2013-07-01, End date: 2018-06-30