ERC FUNDED PROJECTS

This project investigates the two-way relationship between spatio-temporal genome organization and coordinated gene regulation, through an approach at the interface between physics, computer science and biology. In the nucleus, preferred positions are observed from chromosomes to single genes, in relation to normal and pathological cellular states. Evidence indicates a complex spatio-temporal coupling between co-regulated genes: e.g. certain genes cluster spatially when responding to similar factors and transcriptional noise patterns suggest domain-wide mechanisms. Yet, no individual experiment allows probing transcriptional coordination in 4 dimensions (FISH, live locus tracking, Hi-C...). Interpreting such data also critically requires theory (stochastic processes, statistical physics…). A lack of appropriate experimental/analytical approaches is impairing our understanding of the 4D genome. Our proposal combines cutting-edge single-molecule imaging, signal-theory data analysis and physical modeling to study how genes coordinate in space and time in a single nucleus. Our objectives are to understand (a) competition/recycling of shared resources between genes within subnuclear compartments, (b) how enhancers communicate with genes domain-wide, and (c) the role of local conformational dynamics and supercoiling in gene co-regulation. Our organizing hypothesis is that, by acting on their microenvironment, genes shape their co-expression with other genes. Building upon my expertise, we will use dual-color MS2/PP7 RNA labeling to visualize for the first time transcription and motion of pairs of hormone-responsive genes in real time. With our innovative signal analysis tools, we will extract spatio-temporal signatures of underlying processes, which we will investigate with stochastic modeling and validate through experimental perturbations. We expect to uncover how the functional organization of the linear genome relates to its physical properties and dynamics in 4D.

1 499 750 €

Start date: 2018-04-01, End date: 2023-03-31

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

Faithful chromosome segregation in all eukaryotes relies on centromeres, the chromosomal sites that recruit kinetochore proteins and mediate spindle attachment during cell division. Fundamental to centromere function is a histone H3 variant, CenH3, that initiates kinetochore assembly on centromeric DNA. CenH3 is conserved throughout most eukaryotes; its deletion is lethal in all organisms tested. These findings established the paradigm that CenH3 is an absolute requirement for centromere function. My recent findings undermined this paradigm of CenH3 essentiality. I showed that CenH3 was lost independently in four lineages of insects. These losses are concomitant with dramatic changes in their centromeric architecture, in which each lineage independently transitioned from monocentromeres (where microtubules attach to a single chromosomal region) to holocentromeres (where microtubules attach along the entire length of the chromosome). Here, I aim to characterize this unique CenH3-deficient chromosome segregation pathway. Using proteomic and genomic approaches in lepidopteran cell lines, I will determine the mechanism of CenH3-independent kinetochore assembly that led to the establishment of their holocentric architecture. Using comparative genomic approaches, I will determine whether this kinetochore assembly pathway has recurrently evolved over the course of 400 million years of evolution and its impact on the chromosome segregation machinery. My discovery of CenH3 loss in holocentric insects establishes a new class of centromeres. My research will reveal how CenH3 that is essential in most other eukaryotes, could have become dispensable in holocentric insects. Since the evolution of this CenH3-independent chromosome segregation pathway is associated with the independent rises of holocentric architectures, my research will also provide the first insights into the transition from a monocentromere to a holocentromere.

1 497 500 €

Start date: 2018-04-01, End date: 2023-03-31

The three-dimensional organization of the genome, which strikingly correlates with gene activity, is critical for many cellular processes. The evolution of molecular techniques has allowed us to unveil chromatin structure at an unprecedented resolution. The most intriguing chromatin structures observed in animals are TADs (Topologically Associating Domains), which represent the functional and structural chromatin domains demarcating the genome. Structural proteins such as insulators proteins, on the other hand, have been shown to play crucial roles in mediating the formation of TADs. However, major structural factors relevant to chromatin structure are still waiting to be discovered in land plants. My preliminary work shows that TADs are widely distributed across the rice genome, and motif sequence analysis suggests the enrichment of plant-specific transcription factors at TAD boundaries, which jointly give rise to an exciting hypothesis that these proteins might be the long-sought-after insulators in land plants. By using various state-of-the-art molecular and computational tools, this timely project aims to fill a huge gap in plant functional genomics and substantially advance our understanding of three-dimensional chromatin structure. This project consists four major aims, which collectively will uncover the identities of plant insulator proteins and generate insights into the dynamics of structural chromatin domains during stress adaptation. Aim 1 will identify and characterize the stability and plasticity of functional chromatin domains in the rice genome during temperature stress adaptation. Aim 2 will identify insulator elements and other structural features of chromatin packing in the Marchantia polymorpha genome from a structural genomics approach. Aim 3 will establish the role of candidate proteins as plant insulators. Lastly, Aim 4 will generate functional insights into the molecular mechanism by which plant insulators shape the three-dimensional genome.

1 498 216 €

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