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Project acronym BIOMOTIV
Project Why do we do what we do? Biological, psychological and computational bases of motivation
Researcher (PI) Mathias Pessiglione
Summary We are largely unaware of our own motives. Understanding our motives can be reduced to knowing how we form goals and these goals translate into behavior. Goals can be defined as pleasurable situations that we particularly value and that we intend to reach. Recent investigation in the emerging field of neuro-economics has put forward a neuronal network constituting a brain valuation system (BVS). We wish to build a more comprehensive account of motivational processes, investigating not only valuation and choice but also effort (how much energy we would spend to attain a goal). More specifically, our aims are to better describe 1) how the brain assigns values to various objects and actions, 2) how values depend on parameters such as reward magnitude, probability, delay and cost, 3) how values are affected by social contexts, 4) how values are modified through learning and 5) how values influence the brain systems (perceptual, cognitive and motor) that underpin behavioral performance. To these aims, we would combine three approaches: 1) human cognitive neuroscience, which is central as we ultimately wish to understand ourselves, as well as human pathological conditions where motivation is either deficient (apathy) or out of control (compulsion), 2) primate neurophysiology, which is essential to describe information processing at the single-unit level and to derive causality by observing behavioral consequences of brain manipulations, 3) computational modeling, which is mandatory to link quantitatively the different descriptions levels (single-unit recordings, local field potentials, regional BOLD signal, vegetative manifestations and motor outputs). A bayesian framework will be developed to infer from experimental measures the subjects prior beliefs and value functions. We believe that our team, bringing together three complementary perspectives on motivation within a clinical environment, would represent a unique education and research center in Europe.
We are largely unaware of our own motives. Understanding our motives can be reduced to knowing how we form goals and these goals translate into behavior. Goals can be defined as pleasurable situations that we particularly value and that we intend to reach. Recent investigation in the emerging field of neuro-economics has put forward a neuronal network constituting a brain valuation system (BVS). We wish to build a more comprehensive account of motivational processes, investigating not only valuation and choice but also effort (how much energy we would spend to attain a goal). More specifically, our aims are to better describe 1) how the brain assigns values to various objects and actions, 2) how values depend on parameters such as reward magnitude, probability, delay and cost, 3) how values are affected by social contexts, 4) how values are modified through learning and 5) how values influence the brain systems (perceptual, cognitive and motor) that underpin behavioral performance. To these aims, we would combine three approaches: 1) human cognitive neuroscience, which is central as we ultimately wish to understand ourselves, as well as human pathological conditions where motivation is either deficient (apathy) or out of control (compulsion), 2) primate neurophysiology, which is essential to describe information processing at the single-unit level and to derive causality by observing behavioral consequences of brain manipulations, 3) computational modeling, which is mandatory to link quantitatively the different descriptions levels (single-unit recordings, local field potentials, regional BOLD signal, vegetative manifestations and motor outputs). A bayesian framework will be developed to infer from experimental measures the subjects prior beliefs and value functions. We believe that our team, bringing together three complementary perspectives on motivation within a clinical environment, would represent a unique education and research center in Europe.
Project acronym CDNF
Project Compartmentalization and dynamics of Nuclear functions
Researcher (PI) Angela Taddei
Host Institution (HI) INSTITUT CURIE
Summary The eukaryotic genome is packaged into large-scale chromatin structures that occupy distinct domains in the nucleus and this organization is now seen as a key contributor to genome functions. Two key functions of the genome can take advantage of nuclear organization: regulated gene expression and the propagation of a stable genome. To understand these fundamental processes, we have chosen to use yeast as a model system that allows genetics, molecular biology and advanced live microscopy approaches to be combined. Budding yeast have been very powerful to demonstrate that gene position can play an active role in regulating gene expression. Distinct subcompartments dedicated to either gene silencing or activation of specific genes are positioned at the nuclear periphery. To gain insight into the mechanisms underlying this sub-compartmentalization, we will address three complementary issues: - What are the mechanisms involved in the establishment and maintenance of silent nuclear compartments? - How and why are some activated genes recruited to the nuclear periphery? - What are the relationships between repressive and activating nuclear compartments? Concerning the maintenance of genome integrity, recent advances in yeast highlight the importance of nuclear architecture. However, how nuclear organization influences the formation and processing of DNA lesions remain poorly understood. We will focus on two main questions: - How and where in the nucleus are double strand breaks recognized, processed, and repaired? - Where do breaks or gaps resulting from replicative stress at 'fragile sites' arise in the nucleus and how does nuclear organization influence their stability? We hope to gain a better understanding of the mechanisms presiding nuclear organization and its importance for genome functions. These mechanisms are likely to be conserved and will be subsequently tested in higher eukaryotic cells.
The eukaryotic genome is packaged into large-scale chromatin structures that occupy distinct domains in the nucleus and this organization is now seen as a key contributor to genome functions. Two key functions of the genome can take advantage of nuclear organization: regulated gene expression and the propagation of a stable genome. To understand these fundamental processes, we have chosen to use yeast as a model system that allows genetics, molecular biology and advanced live microscopy approaches to be combined. Budding yeast have been very powerful to demonstrate that gene position can play an active role in regulating gene expression. Distinct subcompartments dedicated to either gene silencing or activation of specific genes are positioned at the nuclear periphery. To gain insight into the mechanisms underlying this sub-compartmentalization, we will address three complementary issues: - What are the mechanisms involved in the establishment and maintenance of silent nuclear compartments? - How and why are some activated genes recruited to the nuclear periphery? - What are the relationships between repressive and activating nuclear compartments? Concerning the maintenance of genome integrity, recent advances in yeast highlight the importance of nuclear architecture. However, how nuclear organization influences the formation and processing of DNA lesions remain poorly understood. We will focus on two main questions: - How and where in the nucleus are double strand breaks recognized, processed, and repaired? - Where do breaks or gaps resulting from replicative stress at 'fragile sites' arise in the nucleus and how does nuclear organization influence their stability? We hope to gain a better understanding of the mechanisms presiding nuclear organization and its importance for genome functions. These mechanisms are likely to be conserved and will be subsequently tested in higher eukaryotic cells.
Project acronym CEPODRO
Project Cell polarization in Drosophila
Researcher (PI) Yohanns Bellaiche
Summary Cell polarity is fundamental to many aspects of cell and developmental biology and it is implicated in differentiation, proliferation and morphogenesis in both unicellular and multi-cellular organisms. We study the mechanisms that regulate cell polarity during both asymmetric cell division and epithelial cell polarization in Drosophila. To understand these fundamental processes, we are currently using two complementary approaches. Firstly, we are coupling genetic tools to state of the art time-lapse microscopy to genetically dissect the mechanisms of cortical cell polarization and mitotic spindle orientation. Secondly, we are introducing two innovative inter-disciplinary methodologies into the fields of cell and developmental biology: 1) single molecule imaging during asymmetric cell division, to unravel the mechanism of polarized protein distribution within the cell; 2) multi-scale tensor analysis of epithelial tissues to describe and understand how epithelial tissues grow, acquire and maintain their shape and organization during development. Using both conventional and innovative methodologies, our goals over the next four years are to better understand how molecules and protein complexes move and are activated at different locations within the cell and how cell polarization impacts on cell identities and on epithelial tissue growth and morphogenesis. Since the mechanisms underlying cell polarization are conserved throughout evolution, the proposed experiments will improve our understanding of these processes not only in Drosophila, but in all animals.
Cell polarity is fundamental to many aspects of cell and developmental biology and it is implicated in differentiation, proliferation and morphogenesis in both unicellular and multi-cellular organisms. We study the mechanisms that regulate cell polarity during both asymmetric cell division and epithelial cell polarization in Drosophila. To understand these fundamental processes, we are currently using two complementary approaches. Firstly, we are coupling genetic tools to state of the art time-lapse microscopy to genetically dissect the mechanisms of cortical cell polarization and mitotic spindle orientation. Secondly, we are introducing two innovative inter-disciplinary methodologies into the fields of cell and developmental biology: 1) single molecule imaging during asymmetric cell division, to unravel the mechanism of polarized protein distribution within the cell; 2) multi-scale tensor analysis of epithelial tissues to describe and understand how epithelial tissues grow, acquire and maintain their shape and organization during development. Using both conventional and innovative methodologies, our goals over the next four years are to better understand how molecules and protein complexes move and are activated at different locations within the cell and how cell polarization impacts on cell identities and on epithelial tissue growth and morphogenesis. Since the mechanisms underlying cell polarization are conserved throughout evolution, the proposed experiments will improve our understanding of these processes not only in Drosophila, but in all animals.
Project acronym CORTEXSELFCONTROL
Project Self-Modulating Neurons in the Cerebral Cortex: From Molecular Mechanisms to Cortical Network Activities
Researcher (PI) Alberto Bacci
Host Institution (HI) INSTITUT DU CERVEAU ET DE LA MOELLE EPINIERE
Summary In the mammalian brain, the neocortex is the site where sensory information is integrated into complex cognitive functions. This is accomplished by the activity of both principal glutamatergic neurons and locally-projecting inhibitory GABAergic interneurons, interconnected in complex networks. Inhibitory neurons play several key roles in neocortical function. For example, they shape sensory receptive fields and drive several high frequency network oscillations. On the other hand, defects in their function can lead to devastating diseases, such as epilepsy and schizophrenia. Cortical interneurons represent a highly heterogeneous cell population. Understanding the specific role of each interneuron subtype within cortical microcircuits is still a crucial open question. We have examined properties of two major functional interneuron subclasses in neocortical layer V: fast-spiking (FS) and low-threshold spiking (LTS) cells. Our previous data indicate that each group expresses a novel form of self inhibition, namely autaptic inhibitory transmission in FS cells and an endocannabinoid-mediated slow self inhibition in LTS interneurons. In this proposal we will address three major questions relevant to self-inhibition of neocortical interneurons: 1) What is the role of FS cell autapses in coordinating fast network synchrony? 2) What are the molecular mechanisms underlying autaptic asynchronous release, prolonging FS cell self-inhibition by several seconds, and what is its relevance during physiological and pathological network activities? 3) What are the induction mechanisms, the molecular players involved and the functional roles within cortical microcircuits of the endocannabinoid-mediated long-lasting self-inhibition in LTS interneurons? Results of these experiments will lead to a better understanding of GABAergic interneuron regulation of neocortical excitability, relevant to both normal and pathological cortical function.
In the mammalian brain, the neocortex is the site where sensory information is integrated into complex cognitive functions. This is accomplished by the activity of both principal glutamatergic neurons and locally-projecting inhibitory GABAergic interneurons, interconnected in complex networks. Inhibitory neurons play several key roles in neocortical function. For example, they shape sensory receptive fields and drive several high frequency network oscillations. On the other hand, defects in their function can lead to devastating diseases, such as epilepsy and schizophrenia. Cortical interneurons represent a highly heterogeneous cell population. Understanding the specific role of each interneuron subtype within cortical microcircuits is still a crucial open question. We have examined properties of two major functional interneuron subclasses in neocortical layer V: fast-spiking (FS) and low-threshold spiking (LTS) cells. Our previous data indicate that each group expresses a novel form of self inhibition, namely autaptic inhibitory transmission in FS cells and an endocannabinoid-mediated slow self inhibition in LTS interneurons. In this proposal we will address three major questions relevant to self-inhibition of neocortical interneurons: 1) What is the role of FS cell autapses in coordinating fast network synchrony? 2) What are the molecular mechanisms underlying autaptic asynchronous release, prolonging FS cell self-inhibition by several seconds, and what is its relevance during physiological and pathological network activities? 3) What are the induction mechanisms, the molecular players involved and the functional roles within cortical microcircuits of the endocannabinoid-mediated long-lasting self-inhibition in LTS interneurons? Results of these experiments will lead to a better understanding of GABAergic interneuron regulation of neocortical excitability, relevant to both normal and pathological cortical function.
Project acronym COSIRIS
Project Investigating the terrestrial carbon and water cycles with a multi-tracer approach
Researcher (PI) Ulrike Seibt
Host Institution (HI) UNIVERSITE PIERRE ET MARIE CURIE - PARIS 6
Summary The aim of COSIRIS is to isolate the simultaneous fluxes of photosynthesis and respiration of the terrestrial biosphere. With explicit knowledge of the component fluxes, we will: 1) test process based models of photosynthesis and respiration, 2) determine the sensitivity of each flux to environmental conditions, and 3) derive predictions of their responses to climate change. Specifically, COSIRIS aims to build a research facility to integrate a new tracer, carbonyl sulfide (COS) with CO2, water and their stable isotopes in a multi-tracer framework as a tool to separately investigate photosynthesis and respiration. In terrestrial ecosystems, CO2 is often taken up and released at the same time. Similar to CO2, COS is taken up during photosynthesis, but unlike CO2, concurrent COS emissions are small. Parallel COS and CO2 measurements thus promise to provide estimates of gross photosynthetic fluxes – impossible to measure directly at scales larger than a few leaves. The use of COS to derive CO2 fluxes has not been verified yet, but enough is known about their parallel pathways to suggest that COS, CO2 and its isotopes can be combined to yield powerful and unique constraints on gross carbon fluxes. COSIRIS will develop the expertise necessary to achieve this goal by providing: 1. an in-depth analysis of processes involved in COS uptake by vegetation, and of potentially interfering influences such as uptake by soil, 2. a novel process-based multi-tracer modelling framework of COS, CO2, water and their isotopes at the ecosystem scale, 3. extensive datasets on concurrent fluctuations of COS, CO2, water and their isotopes in ecosystems. This innovative approach promises advances in understanding and determining gross carbon fluxes at ecosystem to continental scales, particularly their variations in response to climate anomalies.
The aim of COSIRIS is to isolate the simultaneous fluxes of photosynthesis and respiration of the terrestrial biosphere. With explicit knowledge of the component fluxes, we will: 1) test process based models of photosynthesis and respiration, 2) determine the sensitivity of each flux to environmental conditions, and 3) derive predictions of their responses to climate change. Specifically, COSIRIS aims to build a research facility to integrate a new tracer, carbonyl sulfide (COS) with CO2, water and their stable isotopes in a multi-tracer framework as a tool to separately investigate photosynthesis and respiration. In terrestrial ecosystems, CO2 is often taken up and released at the same time. Similar to CO2, COS is taken up during photosynthesis, but unlike CO2, concurrent COS emissions are small. Parallel COS and CO2 measurements thus promise to provide estimates of gross photosynthetic fluxes – impossible to measure directly at scales larger than a few leaves. The use of COS to derive CO2 fluxes has not been verified yet, but enough is known about their parallel pathways to suggest that COS, CO2 and its isotopes can be combined to yield powerful and unique constraints on gross carbon fluxes. COSIRIS will develop the expertise necessary to achieve this goal by providing: 1. an in-depth analysis of processes involved in COS uptake by vegetation, and of potentially interfering influences such as uptake by soil, 2. a novel process-based multi-tracer modelling framework of COS, CO2, water and their isotopes at the ecosystem scale, 3. extensive datasets on concurrent fluctuations of COS, CO2, water and their isotopes in ecosystems. This innovative approach promises advances in understanding and determining gross carbon fluxes at ecosystem to continental scales, particularly their variations in response to climate anomalies.
Project acronym D-END
Project Telomeres: from the DNA end replication problem to the control of cell proliferation
Researcher (PI) Maria Teresa Teixeira Fernandes Bernardo
Summary Linear chromosomes of eukaryotes end with telomeres that ensure their stability. Because of the inability of semi-conservative DNA replication machinery to fully replicate DNA ends, telomeres require dedicated mechanisms to be duplicated and their length is eroded at each cell division. For this reason, telomeres constitute molecular clocks that determine cell proliferation potential in eukaryotes. Strikingly, we have shown recently that it is the shortest telomere in the cell that determines the onset of replicative senescence. This project aims a complete and detailed dissection of the in vivo DNA-end replication problem and the deep understanding of its impact for cell division capability. Specifically my goals are (1) the determination of the exact structures that result from the replication of DNA extremities, (2) the examination of the activities operating at the shortest telomere that triggers replicative senescence and (3) the investigation of the correspondence between telomere molecular structure and cell proliferation state at individual cell scale. To achieve this, I will undertake in Saccharomyces cerevisiae original and innovative single-molecule and single-cell approaches, that, in combination with genome-wide screens and sophisticated cellular settings, will allow to track and challenge a specified telomere of defined length. I anticipate that this work will lead to an in-depth understanding of how telomeres are replicated and how they enable the control of cell proliferation in eukaryotic cells, a matter at the intersection of the fundamentals of molecular genetics, cell biology of aging and oncology.
Linear chromosomes of eukaryotes end with telomeres that ensure their stability. Because of the inability of semi-conservative DNA replication machinery to fully replicate DNA ends, telomeres require dedicated mechanisms to be duplicated and their length is eroded at each cell division. For this reason, telomeres constitute molecular clocks that determine cell proliferation potential in eukaryotes. Strikingly, we have shown recently that it is the shortest telomere in the cell that determines the onset of replicative senescence. This project aims a complete and detailed dissection of the in vivo DNA-end replication problem and the deep understanding of its impact for cell division capability. Specifically my goals are (1) the determination of the exact structures that result from the replication of DNA extremities, (2) the examination of the activities operating at the shortest telomere that triggers replicative senescence and (3) the investigation of the correspondence between telomere molecular structure and cell proliferation state at individual cell scale. To achieve this, I will undertake in Saccharomyces cerevisiae original and innovative single-molecule and single-cell approaches, that, in combination with genome-wide screens and sophisticated cellular settings, will allow to track and challenge a specified telomere of defined length. I anticipate that this work will lead to an in-depth understanding of how telomeres are replicated and how they enable the control of cell proliferation in eukaryotic cells, a matter at the intersection of the fundamentals of molecular genetics, cell biology of aging and oncology.
Project acronym DECORE
Project Deep Earth Chemistry of the Core
Researcher (PI) James Badro
Host Institution (HI) INSTITUT DE PHYSIQUE DU GLOBE DE PARIS
Summary Core formation represents the major chemical differentiation event on the terrestrial planets, involving the separation of a metallic liquid from the silicate matrix that subsequently evolves into the current silicate crust and mantle. The generation of the Earth's magnetic field is ultimately tied to the segregation and crystallization of the core, and is an important factor in establishing planetary habitability. The processes that control core segregation and the depths and temperatures at which this process took place are poorly understood, however. We propose to study those processes. Specifically, the density of the core is lower than would be expected for pure iron, indicating that a light component (O, Si, S, C, H) must be present. Similarly, the Earth's mantle is richer in iron-loving ("siderophile") elements, e.g, V, W, Mo, Ru, Pd, etc., than would be expected based upon low pressure metal-silicate partitioning data. Solutions to these problems are hampered by the pressure range of existing experimental data, < 25 GPa, equivalent to ~700 km in the Earth. We propose to extend the accessible range of pressures and temperatures by developing protocols that link the laser-heated diamond anvil cell with analytical techniques such as (i) the NanoSIMS, (ii) the focused ion beam device (FIB), (iii) and transmission and secondary electron microscopy, allowing us to obtain quantitative data on element partitioning and chemical composition at extreme conditions relevant to the Earth's lower mantle. The technical motivation follows from the fact that the real limitation on trace element partitioning studies at ultra high-pressure has been the grain size of the phases produced at high P-T, relative to the spatial resolution of the analytical methods available to probe the experiments; we can bridge the gap by combining state-of-the-art laser heating experiments with new nano-scale analytical techniques.
Core formation represents the major chemical differentiation event on the terrestrial planets, involving the separation of a metallic liquid from the silicate matrix that subsequently evolves into the current silicate crust and mantle. The generation of the Earth's magnetic field is ultimately tied to the segregation and crystallization of the core, and is an important factor in establishing planetary habitability. The processes that control core segregation and the depths and temperatures at which this process took place are poorly understood, however. We propose to study those processes. Specifically, the density of the core is lower than would be expected for pure iron, indicating that a light component (O, Si, S, C, H) must be present. Similarly, the Earth's mantle is richer in iron-loving ("siderophile") elements, e.g, V, W, Mo, Ru, Pd, etc., than would be expected based upon low pressure metal-silicate partitioning data. Solutions to these problems are hampered by the pressure range of existing experimental data, < 25 GPa, equivalent to ~700 km in the Earth. We propose to extend the accessible range of pressures and temperatures by developing protocols that link the laser-heated diamond anvil cell with analytical techniques such as (i) the NanoSIMS, (ii) the focused ion beam device (FIB), (iii) and transmission and secondary electron microscopy, allowing us to obtain quantitative data on element partitioning and chemical composition at extreme conditions relevant to the Earth's lower mantle. The technical motivation follows from the fact that the real limitation on trace element partitioning studies at ultra high-pressure has been the grain size of the phases produced at high P-T, relative to the spatial resolution of the analytical methods available to probe the experiments; we can bridge the gap by combining state-of-the-art laser heating experiments with new nano-scale analytical techniques.
Project acronym DEMONS
Project Deciphering Eruptions by Modeling Outputs of Natural Systems
Researcher (PI) Alain Burgisser
Summary Active volcanoes emit high temperature gases that modify the chemical composition of the Earth's atmosphere. It is crucial to be able to quantify the contribution of volcanogenic gases to the atmosphere so that the global atmospheric effects of a major eruption can be predicted and so that volcanogenic effects can be discriminated from anthropogenic emissions. At the scale of one volcano, monitoring of gas plumes is a major tool in volcanic risk management. Volcanologists have long measured gas composition and fluxes between and during eruptions and often noted a decoupling between degassing flux and magmatic flux. In parallel, experimental petrologists are now able to calculate the gas composition that is in equilibrium with the magma at depth. However, when the calculated gas composition is compared to that measured at the surface, a general disagreement arises. As a result, it is currently impossible to determine whether a plume is generated in response to passive degassing or to magma ascent. This is a serious drawback as these processes have opposite implications for volcanic activity. Such difficulties are mainly due to the fact that the interplay between degassing mechanisms and gas chemistry has not been addressed. To improve the application of volcanic gas analyses to understanding global geochemical budgets and for the mitigation of volcanic risk, we propose to link deep magmatic processes and surface emissions. Our objective is to model the quantity and composition of volcanic gases as a function of the petrology of the magma at depth and the eruptive regime, and compare those calculations with new measures of plumes at active volcanoes. We will achieve this by modeling the chemical kinetics of degassing in volcanic conduits by using a combination of experimental, field, and numerical approaches. We anticipate building a tool linking flux and composition of gases to eruptive regime, thus opening the door to inverse modeling of volcanic gas observations.
Active volcanoes emit high temperature gases that modify the chemical composition of the Earth's atmosphere. It is crucial to be able to quantify the contribution of volcanogenic gases to the atmosphere so that the global atmospheric effects of a major eruption can be predicted and so that volcanogenic effects can be discriminated from anthropogenic emissions. At the scale of one volcano, monitoring of gas plumes is a major tool in volcanic risk management. Volcanologists have long measured gas composition and fluxes between and during eruptions and often noted a decoupling between degassing flux and magmatic flux. In parallel, experimental petrologists are now able to calculate the gas composition that is in equilibrium with the magma at depth. However, when the calculated gas composition is compared to that measured at the surface, a general disagreement arises. As a result, it is currently impossible to determine whether a plume is generated in response to passive degassing or to magma ascent. This is a serious drawback as these processes have opposite implications for volcanic activity. Such difficulties are mainly due to the fact that the interplay between degassing mechanisms and gas chemistry has not been addressed. To improve the application of volcanic gas analyses to understanding global geochemical budgets and for the mitigation of volcanic risk, we propose to link deep magmatic processes and surface emissions. Our objective is to model the quantity and composition of volcanic gases as a function of the petrology of the magma at depth and the eruptive regime, and compare those calculations with new measures of plumes at active volcanoes. We will achieve this by modeling the chemical kinetics of degassing in volcanic conduits by using a combination of experimental, field, and numerical approaches. We anticipate building a tool linking flux and composition of gases to eruptive regime, thus opening the door to inverse modeling of volcanic gas observations.
Project acronym DICIG
Project Dynamic Interplay between Eukaryotic Chromosomes: Impact on Genome Stability
Researcher (PI) Romain Nicolas André Koszul
Host Institution (HI) INSTITUT PASTEUR
Summary The structure and role of the DNA molecule raise fascinating questions regarding its dynamics, i.e. not only the tri-dimensional reorganisation associated with functional events at short time-scale, but also the structural changes, i.e. rearrangements, that occur in the chromosome over generations. It is increasingly obvious that the physical properties of both the chromosomes and their environment the nucleoplasm, the nuclear periphery, cytoskeleton, etc. are playing important roles in the dynamic changes observed. For instance, we recently showed that chromosome movements during mid-prophase of meiosis in budding yeast result from a trans-acting force generated at the level of the global cytoskeleton network, suggesting that extranuclear mechanical trans-acting signals could also regulate chromosomal metabolism in other ways. Our objectives are to make important contributions to the understanding of the mechanical and functional interplay between the cytoskeleton, the nuclear periphery, and chromosomes through in vitro and in vivo interdisciplinary approaches. We will investigate three questions of fundamental importance: i) the potential transmission and function of mechanical forces from the cytoskeleton to chromatin during interphase, ii) the physical principles that govern chromosome reorganization under mechanical force in vitro, and iii) the global chromatin dynamics during the fundamental S phase and its impact on genome stability. We will use a combination of high-resolution imaging, micromanipulation, and high-throughput molecular techniques (chromosome conformation capture and ChIP-Seq) to reach our goals. Most of these studies will be performed in budding yeast, but will have repercussions in our understanding of higher eukaryotes metabolism.
The structure and role of the DNA molecule raise fascinating questions regarding its dynamics, i.e. not only the tri-dimensional reorganisation associated with functional events at short time-scale, but also the structural changes, i.e. rearrangements, that occur in the chromosome over generations. It is increasingly obvious that the physical properties of both the chromosomes and their environment the nucleoplasm, the nuclear periphery, cytoskeleton, etc. are playing important roles in the dynamic changes observed. For instance, we recently showed that chromosome movements during mid-prophase of meiosis in budding yeast result from a trans-acting force generated at the level of the global cytoskeleton network, suggesting that extranuclear mechanical trans-acting signals could also regulate chromosomal metabolism in other ways. Our objectives are to make important contributions to the understanding of the mechanical and functional interplay between the cytoskeleton, the nuclear periphery, and chromosomes through in vitro and in vivo interdisciplinary approaches. We will investigate three questions of fundamental importance: i) the potential transmission and function of mechanical forces from the cytoskeleton to chromatin during interphase, ii) the physical principles that govern chromosome reorganization under mechanical force in vitro, and iii) the global chromatin dynamics during the fundamental S phase and its impact on genome stability. We will use a combination of high-resolution imaging, micromanipulation, and high-throughput molecular techniques (chromosome conformation capture and ChIP-Seq) to reach our goals. Most of these studies will be performed in budding yeast, but will have repercussions in our understanding of higher eukaryotes metabolism.
Project acronym DOME
Project Dissecting a Novel Mechanism of Cell Motility
Researcher (PI) Tâm Mignot
Summary Cell motility is essential for many biological processes, including development and pathogenesis. Thus, the molecular mechanisms underlying this process have been intensively studied in many cell systems, for example, leukocytes, amoeba and even bacteria. Intriguingly, bacteria are also able to move across solid surfaces (gliding motility) like eukaryotic cells by a process that has remained largely mysterious. The emergence of bacterial cell biology: the discovery that the bacterial cell also has a dynamic cytoskeleton and specialized subcellular regions now provides new research angles to study the motility mechanism. Using cell biology approaches, we previously suggested that the mechanism may be akin to acto-myosin-based motility in eukaryotic cells and proposed that bacterial focal adhesion complexes also power locomotion. In this project, we propose two complementary research axes to define both the mechanism and its spatial regulation in the cell at molecular resolution. Using the model motility bacterium Myxococcus xanthus, we first propose to develop a "toolbox" of biophysical and cell biology assays to analyze the motility process. Specifically, we will construct a Traction Force Microscopy assay designed to image the motility forces directly by live moving cells and use microfluidics to quantitate the secretion of a mucus that may participate directly in the motility process. These assays, combined with a newly developed laser trap system to visualize dynamic focal adhesions in the cell envelope, will be instrumental not only to define new features of the motility process, but also to study the function of novel motility genes which may encode the components of the elusive motility engine. This way, we hope to establish the mechanism and structure function relationships within an entirely novel motility machinery. In a second part, we propose to investigate the mechanism that controls a polarity switch, allowing M. xanthus cells to change their direction of movement. We have previously shown that dynamic motility protein pole-to-pole oscillations convert the initial leading cell pole into the lagging pole. Here, we propose that like in a eukaryotic cells, a bacterial counterpart of small GTPases of the Ras superfamily, MglA controls the polarity cycle. To test this hypothesis, we will study both the MglA upstream regulation and the MglA downstream effectors. We thus hope to establish a model of dynamic polarity control in a bacterial
Cell motility is essential for many biological processes, including development and pathogenesis. Thus, the molecular mechanisms underlying this process have been intensively studied in many cell systems, for example, leukocytes, amoeba and even bacteria. Intriguingly, bacteria are also able to move across solid surfaces (gliding motility) like eukaryotic cells by a process that has remained largely mysterious. The emergence of bacterial cell biology: the discovery that the bacterial cell also has a dynamic cytoskeleton and specialized subcellular regions now provides new research angles to study the motility mechanism. Using cell biology approaches, we previously suggested that the mechanism may be akin to acto-myosin-based motility in eukaryotic cells and proposed that bacterial focal adhesion complexes also power locomotion. In this project, we propose two complementary research axes to define both the mechanism and its spatial regulation in the cell at molecular resolution. Using the model motility bacterium Myxococcus xanthus, we first propose to develop a "toolbox" of biophysical and cell biology assays to analyze the motility process. Specifically, we will construct a Traction Force Microscopy assay designed to image the motility forces directly by live moving cells and use microfluidics to quantitate the secretion of a mucus that may participate directly in the motility process. These assays, combined with a newly developed laser trap system to visualize dynamic focal adhesions in the cell envelope, will be instrumental not only to define new features of the motility process, but also to study the function of novel motility genes which may encode the components of the elusive motility engine. This way, we hope to establish the mechanism and structure function relationships within an entirely novel motility machinery. In a second part, we propose to investigate the mechanism that controls a polarity switch, allowing M. xanthus cells to change their direction of movement. We have previously shown that dynamic motility protein pole-to-pole oscillations convert the initial leading cell pole into the lagging pole. Here, we propose that like in a eukaryotic cells, a bacterial counterpart of small GTPases of the Ras superfamily, MglA controls the polarity cycle. To test this hypothesis, we will study both the MglA upstream regulation and the MglA downstream effectors. We thus hope to establish a model of dynamic polarity control in a bacterial