The aim of the GASPER project is to develop and fully characterize a new concept of gas diffusion photoelectrodes with backside illumination for CO2 conversion under solar light. To this end, we will take advantage of a very recent discovery by one of our partners that has made backside illumination of a CIGS solar cell possible (patent pending). We will then implement this device by adding a porous layer to the front of the photoelectrode into which we will insert a molecular catalyst. Several investigation tools will be employed, including fast time-resolved spectroscopy, to understand the elementary phenomena at play in the photoelectrode. At the same time, the data collected will be used to feed a multi-physics model simulating the transfer and transport steps and the associated kinetics, in order to optimize the photoelectrode structure by inverse design. Finally, the catalytic properties of the photoelectrode thus developed will be studied in detail for CO2 conversion.

Duplication of the genome prior to cell division occurs in a spatially and temporally organized manner. The temporal order of replication (replication timing) reflects the higher order organization of the genome. During the first half of the S-phase, euchromatic regions are replicated followed by facultative heterochromatin during mid S-phase and finally constitutive heterochromatin regions in the second half of the S-phase. In the nucleus, euchromatin is localized in the interior while constitutive heterochromatin is rather located at the periphery. The spatio-temporal program of genome replication changes throughout development and cellular differentiation and has been correlated with changes in chromatin dynamics, histone marks, and nuclear architecture indicating that genome reorganization is associated with epigenetic and gene expression changes. Abnormal replication timing has also been reported in many diseases, including cancer. A growing body of evidence indicates that the replication-timing program strongly influences the spatial distribution of mutagenic events such that certain regions of the genome that are replicated in late S-phase present increased spontaneous mutagenesis compared to surrounding regions replicated in early S-phase. This has been observed during the evolution of species as well as during the evolution of cancer. In addition, a recent report showed that the dominant determinant of regional mutation rate variation is chromatin organization, with mutation rates elevated in more heterochromatin-like domains and repressed in more open chromatin. Although different hypotheses have been advanced, the cause of this increasing gradient of point mutation rates with later replication timing and the underlying mechanisms remain elusive. Although no mutagenic profile has been reported so far from pluripotent cells undergoing differentiation, one can expect that genome reorganization influences the mutagenic landscape. Obvious and important questions emerge from these observations: how and why elevated mutation rates are associated with heterochromatin-like domains which are replicated in late S-phase? What can be the “cost” for the cell when global genome reorganization takes place after differentiation/dedifferentiation (e.g. pre-cancerous cells) or reprogramming (e.g. iPS cells) if late-replicating regions containing point mutations become early and are actively transcribed? Point mutations arising in the genome are mainly caused by a special class of DNA polymerases (TLS polymerases) that support replication directly past template lesions (or unusual DNA secondary structures) that cannot be negotiated by the replicative high-fidelity polymerases. However, these specialized polymerases can be highly error-prone on undamaged DNA. An emerging concept proposes that these enzymes may also function during the unchallenged S-phase. On the basis of solid preliminary results, we assume that the essential error-prone DNA polymerase zeta (Pol zeta) is required to replicate through condensed chromatin regions and could be involved in the gradient of spontaneous mutagenesis. Therefore, this ambitious SPUR project aims to decipher the involvement of Pol zeta??and its catalytic subunit Rev3) in the regulation of the spatio-temporal program of DNA replication during embryonic stem cell differentiation and comprehensively evaluate the role of this error-prone polymerase in the point mutation frequencies which increase in late-replicating regions.

Bacteria can sense and respond to myriad chemical and physical signals to survive and reproduce. Signal transduction in prokaryotes is dominated by one-component systems, in which the sensing domain is directly fused to the DNA binding domain, a simple yet efficient solution to transduce incoming signals into a transcriptional output. Most one-component systems are cytoplasmic, and thus only responsive to chemical cues entering the cell. Transmembrane systems, in contrast, provide versatile and efficient bridges between the extra and intracellular environments. Although controlling key signaling pathways, such as virulence activation in pathogenic bacteria, these only represent 3% of the known one-component systems and are harder to study. Despite their abundance and pivotal role in bacterial signaling and pathogenicity, the regulatory mechanisms, structure, and dynamics of membrane-bound one-component systems remain largely unexplored. The goal of this project is to decipher the mechanisms controlling signal transmission heterogeneity in membrane-bound one-component systems. We will then apply this knowledge to improve the engineering of modular receptors with wide applications in biosensing. We will combine our expertise in synthetic biology, structural biology, and biophysics to systematically rebuild non-native signaling pathways in a surrogate host, the non-pathogenic and genetically tractable bacterium Escherichia coli, and alter them to decipher their structure-function relationships. As a model system, we will use a synthetic receptor platform derived from the CadC one-component system recently engineered by our group to trigger gene expression in response to caffeine. This work will advance our general understanding of one-component systems and provide design principles for the engineering of versatile programmable bacterial receptors crucially needed for many applications (e.g. diagnosis, bioproduction, and bacterial-based therapeutics).

mtDNA depletion syndrome (MDS) is a group of mitochondrial disorders characterized by a reduced mtDNA copy number which occurr in early childhood and for which no curative therapy is yet available. Depletion of mtDNA result from mutations in nuclear genes especially involved in the regulation of mitochondrial deoxyribonucleotides (dNTP) pool. In this context, the discovery of new drugs allowing efficient and targeted delivery of nucleotides to mitochondria is of great interest in the focus of a new treatment strategies in MDS. Our project proposes the development of an original approach combining prodrug and mitochondria-targeted nucleotides strategies. A first screening of model compounds was performed in induced pluripotent stem cell (iPSC)-based cultures modelling MDS disease. Thus, promising compounds able to restore ATP production in mitochondria have been identified. In addition, mitochondria-targeted prodrugs of nucleoside and nucleotide derivatives have been synthesized and studied by fluorescence microscopy experiments. Among them, two compounds were indeed able to localized in mitochondria. Our main objective is now to combine these two structural moieties (targeting vector and pronucleotide) in a single compound and to study their in vitro and in vivo potential in order to validate our proof of concept. In addition, stability in various media, toxicity and their impact on the main mitochondrial functions will be determined for the best compounds.

The neocortex underlies higher cognitive functions in mammals and humans. Its computational abilities are essential for categorizing external objects into supramodal percepts. This natural categorization depends on multisensory integration, to become largely independent of the sensory modality channels through which relevant input is acquired. In contrast, this remarkable emergence of percept invariance is poorly emulated by artificial systems. The anatomical cortical architecture shows extensive connectivity across its different sensory areas, departing from the classically assumed hierarchical processing scheme. Recent studies demonstrated that primary sensory cortical areas coding for distinct modalities are already interconnected, but the computational role of these heteromodal connections is unknown. The goal is to test whether heteromodal interactions in primary sensory cortical areas transmit inferences about the identity of behaviorally relevant objects perceived across multiple sensory channels. The working hypothesis is that these interactions modify the primary representation of unimodal sensory stimuli, resulting in supramodal perceptual invariance, even in ambiguous unimodal contexts. This study will be carried out in awake behaving mice trained to discriminate between two multimodal objects, which require the two sensory modalities to be fully distinguished. State-of-the art techniques (two-photon calcium imaging and multisite electrode arrays) to record from large scale neural assemblies will be combined with modern analysis of neural population dynamics and network simulations. Underlying mechanisms will be explored by optogenetic targeting of specific neuronal populations, to quantitatively challenge mechanistic hypotheses proposed in simulated models. The long-term aim is to quantitatively explain encoding and classification of multisensory cues across primary sensory cortical areas, with the aim of deriving novel generic computational principles by which brain circuits build invariant representations of the environment from ever-changing multisensory input streams.