ERC FUNDED PROJECTS

The cell cortex is a highly dynamic layer of crosslinked actin filaments and myosin molecular motors beneath the cell membrane. It plays a central role in large scale rearrangements that occur inside cells. Many molecular mechanisms contribute to cortex structure and dynamics. However, cell scale physical properties of the cortex are difficult to grasp. This is problematic because for large scale rearrangements inside a cell, such as coherent flow of the cell cortex, it is the cell scale emergent properties that are important for the realization of such events. I will investigate how the actomyosin cytoskeleton behaves at a coarse grained and cellular scale, and will study how this emergent active behaviour is influenced by molecular mechanisms. We will study the cell cortex in the one cell stage C. elegans embryo, which undergoes large scale cortical flow during polarization and cytokinesis. We will combine theory and experiment. We will characterize cortex structure and dynamics with biophysical techniques such as cortical laser ablation and quantitative photobleaching experiments. We will develop and employ novel theoretical approaches to describe the cell scale mechanical behaviour in terms of an active complex fluid. We will utilize genetic approaches to understand how these emergent mechanical properties are influenced by molecular activities. A central goal is to arrive at a coarse grained description of the cortex that can predict future dynamic behaviour from the past structure, which is conceptually similar to how weather forecasting is accomplished. To date, systematic approaches to link molecular scale physical mechanisms to those on cellular scales are missing. This work will open new opportunities for cell biological and cell biophysical research, by providing a methodological approach for bridging scales, for studying emergent and large-scale active mechanical behaviours and linking them to molecular mechanisms.

1 500 000 €

Start date: 2011-12-01, End date: 2017-08-31

Integrins are transmembrane cell adhesion receptors controlling cell proliferation and migration. Our objective is to gain fundamentally novel mechanistic insight into the emerging new roles of integrins in cancer and to generate a road map of integrin dependent pathways critical in mammary gland development and integrin signalling thus opening new targets for therapeutic interventions. We will combine an in vivo based translational approach with cell and molecular biological studies aiming to identify entirely novel concepts in integrin function using cutting edge techniques and synthetic-biology tools. The specific objectives are: 1) Integrin inactivation in branching morphogenesis and cancer invasion. Integrins regulate mammary gland development and cancer invasion but the role of integrin inactivating proteins in these processes is currently completely unknown. We will investigate this using genetically modified mice, ex-vivo organoid models and human tissues with the aim to identify beneficial combinational treatments against cancer invasion. 2) Endosomal adhesomes – cross-talk between integrin activity and integrin “inside-in signaling”. We hypothesize that endocytosed active integrins engage in specialized endosomal signaling that governs cell survival especially in cancer. RNAi cell arrays, super-resolution STED imaging and endosomal proteomics will be used to investigate integrin signaling in endosomes. 3) Spatio-temporal co-ordination of adhesion and endocytosis. Several cytosolic proteins compete for integrin binding to regulate activation, endocytosis and recycling. Photoactivatable protein-traps and predefined matrix micropatterns will be employed to mechanistically dissect the spatio-temporal dynamics and hierarchy of their recruitment. We will employ innovative and unconventional techniques to address three major unanswered questions in the field and significantly advance our understanding of integrin function in development and cancer.

1 887 910 €

Start date: 2014-05-01, End date: 2019-04-30

The skeleton and the sinusoidal vasculature form a functional unit with great relevance in health, regeneration, and disease. Currently, fundamental aspects of sinusoidal vessel growth, specialization, arteriovenous organization and the consequences for tissue perfusion, or the changes occurring during ageing remain unknown. Our preliminary data indicate that key principles of bone vascularization and the role of molecular regulators are highly distinct from other organs. I therefore propose to use powerful combination of mouse genetics, fate mapping, transcriptional profiling, computational biology, confocal and two-photon microscopy, micro-CT and PET imaging, biochemistry and cell biology to characterize the growth, differentiation, dynamics, and ageing of the bone vasculature. In addition to established angiogenic pathways, the role of highly promising novel candidate regulators will be investigated in endothelial cells and perivascular osteoprogenitors with sophisticated inducible and cell type-specific genetic methods in the mouse. Complementing these powerful in vivo approaches, 3D co-cultures generated by cell printing technologies will provide insight into the communication between different cell types. The dynamics of sinusoidal vessel growth and regeneration will be monitored by two-photon imaging in the skull. Finally, I will explore the architectural, cellular and molecular changes and the role of capillary endothelial subpopulations in the sinusoidal vasculature of ageing and osteoporotic mice. Technological advancements, such as new transgenic strains, mutant models or cell printing approaches, are important aspects of this proposal. AngioBone will provide a first conceptual framework for normal and deregulated function of the bone sinusoidal vasculature. It will also break new ground by analyzing the role of blood vessels in ageing and identifying novel strategies for tissue engineering and, potentially, the prevention/treatment of osteoporosis.

2 478 750 €

Start date: 2014-02-01, End date: 2019-01-31

Apoptotic cell death is essential for development, immune function or tissue homeostasis, and it is often deregulated in disease. Mitochondrial outer membrane permeabilization (MOMP) is central for apoptosis execution and plays a key role in its inflammatory outcome. Knowing the architecture of the macromolecular machineries mediating MOMP is crucial for understanding their function and for the clinical use of apoptosis. Our recent work reveals that Bax and Bak dimers form distinct line, arc and ring assemblies at specific apoptotic foci to mediate MOMP. However, the molecular structure and mechanisms controlling the spatiotemporal formation and range of action of the apoptotic foci are missing. To address this fundamental gap in our knowledge, we aim to unravel the composition, dynamics and structure of apoptotic foci and to understand how they are integrated to orchestrate function. We will reach this goal by building on our expertise in cell death and cutting-edge imaging and by developing a new analytical pipeline to: 1) Identify the composition of apoptotic foci using in situ proximity-dependent labeling and extraction of near-native Bax/Bak membrane complexes coupled to mass spectrometry. 2) Define their contribution to apoptosis and its immunogenicity and establish their assembly dynamics to correlate it with apoptosis progression by live cell imaging. 3) Determine the stoichiometry and structural organization of the apoptotic foci by combining single molecule fluorescence and advanced electron microscopies. This multidisciplinary approach offers high chances to solve the long-standing question of how Bax and Bak mediate MOMP. APOSITE will provide textbook knowledge of the mitochondrial contribution to cell death and inflammation. The implementation of this new analytical framework will open novel research avenues in membrane and organelle biology. Ultimately, understanding of Bax and Bak structure/function will help develop apoptosis modulators for medicine.

2 000 000 €

Start date: 2019-04-01, End date: 2024-03-31

Cellular organelles are continuously remodelled by numerous cytosolic proteins that associate transiently with their lipid membrane. Some distort the bilayer, others change its composition, extract lipids or bridge membranes at distance. Previous works from my laboratory have underlined the importance of membrane sensors, i.e. elements within proteins that help to organize membrane-remodelling events by sensing the physical and chemical state of the underlying membrane. A membrane sensor is not necessarily of well-folded domain that interacts with a specific lipid polar head: some intrinsically unfolded motifs harboring deceptively simple sequences can display remarkable membrane adhesive properties. Among these are some amphipathic helices: the ALPS motif with a polar face made mostly by small uncharged polar residues, the Spo20 helix with several histidines in its polar face and, like a mirror image of the ALPS motif, the alpha-synuclein helix with very small hydrophobic residues. Using biochemistry and molecular dynamics, we will compare the membrane binding properties of these sequences (effect of curvature, charge, lipid unsaturation); using bioinformatics we will look for new motifs, using cell biology we will assess the adaptation of these motifs to the physical and chemical features of organelle membranes. Concurrently, we will use reconstitution approaches on artificial membranes to dissect how membrane sensors contribute to the organization of vesicle tethering by golgins and sterol transport by ORP proteins. We surmise that the combination of a molecular ¿switch¿, a small G protein of the Arf family, and of membrane sensors permit to organize these complex reactions in time and in space.

1 997 321 €

Start date: 2011-05-01, End date: 2015-04-30

It is a basic textbook notion that the plasma membranes of virtually all organisms display an asymmetric lipid distribution between inner and outer leaflets far removed from thermodynamic equilibrium. As a fundamental biological principle, lipid asymmetry has been linked to numerous cellular processes. However, a clear mechanistic justification for the continued existence of lipid asymmetry throughout evolution has yet to be established. We propose here that lipid asymmetry serves as a store of potential energy that is used to fuel energy-intense membrane remodelling and signalling events for instance during membrane fusion and fission. This implies that rapid, local changes of trans-membrane lipid distribution rather than a continuously maintained out-of-equilibrium situation are crucial for cellular function. Consequently, new methods for quantifying the kinetics of lipid trans-bilayer movement are required, as traditional approaches are mostly suited for analysing quasi-steady-state conditions. Addressing this need, we will develop and employ novel photochemical lipid probes and lipid biosensors to quantify localized trans-bilayer lipid movement. We will use these tools for identifying yet unknown protein components of the lipid asymmetry regulating machinery and analyse their function with regard to membrane dynamics and signalling in cell motility. Focussing on cell motility enables targeted chemical and genetic perturbations while monitoring lipid dynamics on timescales and in membrane structures that are well suited for light microscopy. Ultimately, we aim to reconstitute lipid asymmetry as a driving force for membrane remodelling in vitro. We expect that our work will break new ground in explaining one of the least understood features of the plasma membrane and pave the way for a new, dynamic membrane model. Since the plasma membrane serves as the major signalling hub, this will have impact in almost every area of the life sciences.

1 500 000 €

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

The phytohormone auxin has profound importance for plant development. The extracellular AUXIN BINDING PROTEIN1 (ABP1) and the nuclear AUXIN F-BOX PROTEINs (TIR1/AFBs) auxin receptors perceive fast, non-genomic and slow, genomic auxin responses, respectively. Despite the fact that ABP1 mainly localizes to the endoplasmic reticulum (ER), until now it has been proposed to be active only in the extracellular matrix (reviewed in Sauer and Kleine-Vehn, 2011). Just recently, ABP1 function was also linked to genomic responses, modulating TIR1/AFB-dependent processes (Tromas et al., 2013). Intriguingly, the genomic effect of ABP1 appears to be at least partially independent of the endogenous auxin indole 3-acetic acid (IAA) (Paque et al., 2014). In this proposal my main research objective is to unravel the importance of the ER for genomic auxin responses. The PIN-LIKES (PILS) putative carriers for auxinic compounds also localize to the ER and determine the cellular sensitivity to auxin. PILS5 gain-of-function reduces canonical auxin signaling (Barbez et al., 2012) and phenocopies abp1 knock down lines (Barbez et al., 2012, Paque et al., 2014). Accordingly, a PILS-dependent substrate could be a negative regulator of ABP1 function in the ER. Based on our unpublished data, an IAA metabolite could play a role in ABP1-dependent processes in the ER, possibly providing feedback on the canonical nuclear IAA-signaling. I hypothesize that the genomic auxin response may be an integration of auxin- and auxin-metabolite-dependent nuclear and ER localized signaling, respectively. This proposed project aims to characterize a novel auxin-signaling paradigm in plants. We will employ state of the art interdisciplinary (biochemical, biophysical, computational modeling, molecular, and genetic) methods to assess the projected research. The identification of the proposed auxin conjugate-dependent signal could have far reaching plant developmental and biotechnological importance.

1 441 125 €

Start date: 2015-06-01, End date: 2020-05-31

When triggered by nutrient limitation, the Gram-positive bacterium Bacillus subtilis and its relatives enter a pathway of cellular differentiation culminating in the formation of a dormant cell type called a spore, the most resilient cell type known. Bacterial spores can survive for long periods of time and are able to endure extremes of heat, radiation and chemical assault. Remarkably, dormant spores can rapidly convert back to actively growing cells by a process called germination. Consequently, spore forming bacteria, including dangerous pathogens, (such as C. botulinum and B. anthracis) are highly resistant to antibacterial treatments and difficult to eradicate. Despite significant advances in our understanding of the process of spore formation, little is known about the nature of the mature spore. It is unrevealed how dormancy is maintained within the spore and how it is ceased, as the organization and the dynamics of the spore macromolecules remain obscure. The unusual biochemical and biophysical characteristics of the dormant spore make it a challenging biological system to investigate using conventional methods, and thus set the need to develop innovative approaches to study spore biology. We propose to explore the nature of spores by using B. subtilis as a primary experimental system. We intend to: (1) define the architecture of the spore chromosome, (2) track the complexity and fate of mRNA and protein molecules during sporulation, dormancy and germination, (3) revisit the basic notion of the spore dormancy (is it metabolically inert?), (4) compare the characteristics of bacilli spores from diverse ecophysiological groups, (5) investigate the features of spores belonging to distant bacterial genera, (6) generate an integrative database that categorizes the molecular features of spores. Our study will provide original insights and introduce novel concepts to the field of spore biology and may help devise innovative ways to combat spore forming pathogens.

1 630 000 €

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

Asymmetric cell division is a key mechanism for the generation of cell diversity in eukaryotes. During this process, a polarized mother cell divides into non-equivalent daughters. These may differentially inherit fate determinants, irreparable damages or age determinants. Our aim is to decipher the mechanisms governing the individualization of daughters from each other. In the past ten years, our studies identified several lateral diffusion barriers located in the plasma membrane and the endoplasmic reticulum of budding yeast. These barriers all restrict molecular exchanges between the mother cell and its bud, and thereby compartmentalize the cell already long before its division. They play key roles in the asymmetric segregation of various factors. On one side, they help maintain polarized factors into the bud. Thereby, they reinforce cell polarity and sequester daughter-specific fate determinants into the bud. On the other side they prevent aging factors of the mother from entering the bud. Hence, they play key roles in the rejuvenation of the bud, in the aging of the mother, and in the differentiation of mother and daughter from each other. Recently, we accumulated evidence that some of these barriers are subject to regulation, such as to help modulate the longevity of the mother cell in response to environmental signals. Our data also suggest that barriers help the mother cell keep traces of its life history, thereby contributing to its individuation and adaption to the environment. In this project, we will address the following questions: 1 How are these barriers assembled, functioning, and regulated? 2 What type of differentiation processes are they involved in? 3 Are they conserved in other eukaryotes, and what are their functions outside of budding yeast? These studies will shed light into the principles underlying and linking aging, rejuvenation and differentiation.

2 200 000 €

Start date: 2010-05-01, End date: 2015-04-30