Expanded polyglutamine proteins are known to be the causative agents of a number of human neurodegenerative diseases but the molecular basis of their cytoxicity is still poorly understood. Polyglutamine tracts may impede the activity of the proteasome, and evidence from single cell imaging suggests that the sequestration of polyglutamine proteins into inclusion bodies can reduce the proteasomal burden and promote cell survival, at least in the short term. The presence of misfolded protein also leads to activation of stress kinases such as p38MAPK, which can be cytotoxic. The relationships of these systems are not well understood. We have used fluorescent reporter systems imaged in living cells, and stochastic computer modeling to explore the relationships of expanded polyglutamine proteins, p38MAPK activation, generation of reactive oxygen species (ROS), proteasome inhibition, and inclusion body formation. In cells expressing a polyglutamine protein, inclusion body formation was preceded by proteasome inhibition but cytotoxicity was greatly reduced by administration of a p38MAPK inhibitor. Computer simulations suggested that without the generation of ROS, the proteasome inhibition and activation of p38MAPK would have significantly reduced toxicity. Our data suggest a vicious cycle of stress kinase activation and proteasome inhibition that is ultimately lethal to cells. There was close agreement between experimental data and the predictions of a stochastic computer model, supporting a central role for proteasome inhibition and p38MAPK activation in inclusion body formation and ROS-mediated cell death.

Expanded polyglutamine proteins are known to be the causative agents of a number of human neurodegenerative diseases but the molecular basis of their cytoxicity is still poorly understood. Polyglutamine tracts may impede the activity of the proteasome, and evidence from single cell imaging suggests that the sequestration of polyglutamine proteins into inclusion bodies can reduce the proteasomal burden and promote cell survival, at least in the short term. The presence of misfolded protein also leads to activation of stress kinases such as p38MAPK, which can be cytotoxic. The relationships of these systems are not well understood. We have used fluorescent reporter systems imaged in living cells, and stochastic computer modeling to explore the relationships of expanded polyglutamine proteins, p38MAPK activation, generation of reactive oxygen species (ROS), proteasome inhibition, and inclusion body formation. In cells expressing a polyglutamine protein, inclusion body formation was preceded by proteasome inhibition but cytotoxicity was greatly reduced by administration of a p38MAPK inhibitor. Computer simulations suggested that without the generation of ROS, the proteasome inhibition and activation of p38MAPK would have significantly reduced toxicity. Our data suggest a vicious cycle of stress kinase activation and proteasome inhibition that is ultimately lethal to cells. There was close agreement between experimental data and the predictions of a stochastic computer model, supporting a central role for proteasome inhibition and p38MAPK activation in inclusion body formation and ROS-mediated cell death.

The objective of this work is to investigate the elastic modulus of gastrula-stage avian embryos and the effect of substrate stiffness on presumptive precardiac cell fate. Our overall hypothesis is that the mechanical microenvironment, specifically, tissue modulus and substrate stiffness, influences gastrulation and cardiac induction. Large-scale morphogenetic movements during early embryo development are driven by complex changes in biochemical and biophysical factors. Current models for amniote primitive streak morphogenesis and gastrulation take into account numerous genetic pathways but largely ignore the role of mechanical forces. Here, we used atomic force microscopy (AFM) to obtain for the first time precise biomechanical properties of the early avian embryo. Our data reveal that the primitive streak is significantly stiffer than neighboring regions of the epiblast, and that it is stiffer than the pre-primitive streak epiblast. To test our hypothesis that these changes in mechanical properties are due to a localized increase of actomyosin contractility, we inhibited actomyosin contractility via the Rho kinase (ROCK) pathway using the small-molecule inhibitor Y-27632. Our results using several different assays show the following: 1) primitive streak formation was blocked; 2) the time-dependent increase in primitive streak stiffness was abolished; and 3) convergence of epiblast cells to the midline was inhibited. Taken together, our data suggest that actomyosin contractility is necessary for primitive streak morphogenesis, and specifically, ROCK plays a critical role. To better understand the underlying mechanisms of this fundamental process, future models should account for the findings presented in this study. As presumptive cardiac cells traverse the course of differentiation into cardiac myocytes during cardiogenesis, the sequence, magnitude, and spatiotemporal map of biomechanical and biochemical signals has not been fully explored. There have been many studies detailing the induction of cardiogenesis on a variety of substrates and extracellular matrix (ECM) proteins, but none have completed a rigorous study of the effects of substrate stiffness on the induction of precardiac cells prior to the onset of cardiac gene expression (smooth muscle alpha actin [SMAA] at stage 5.) We investigate the effects of the mechanical environment on precardiac cell behaviors in an in vitro setting to elucidate the effect of substrate stiffness and inducing factors on precardiac tissue and the potential connection between them. The cells in the anterior portion of the primitive streak are fated to form the heart, and we show differing levels of SMAA expression on substrates of differing moduli, which suggests that substrate stiffness may play a role in cardiac differentiation. We cannot determine the physical mechanisms during morphogenesis without understanding the response of precardiac cells to changes in their mechanical environment.

Expanded polyglutamine proteins are known to be the causative agents of a number of human neurodegenerative diseases but the molecular basis of their cytoxicity is still poorly understood. Polyglutamine tracts may impede the activity of the proteasome, and evidence from single cell imaging suggests that the sequestration of polyglutamine proteins into inclusion bodies can reduce the proteasomal burden and promote cell survival, at least in the short term. The presence of misfolded protein also leads to activation of stress kinases such as p38MAPK, which can be cytotoxic. The relationships of these systems are not well understood. We have used fluorescent reporter systems imaged in living cells, and stochastic computer modeling to explore the relationships of expanded polyglutamine proteins, p38MAPK activation, generation of reactive oxygen species (ROS), proteasome inhibition, and inclusion body formation. In cells expressing a polyglutamine protein, inclusion body formation was preceded by proteasome inhibition but cytotoxicity was greatly reduced by administration of a p38MAPK inhibitor. Computer simulations suggested that without the generation of ROS, the proteasome inhibition and activation of p38MAPK would have significantly reduced toxicity. Our data suggest a vicious cycle of stress kinase activation and proteasome inhibition that is ultimately lethal to cells. There was close agreement between experimental data and the predictions of a stochastic computer model, supporting a central role for proteasome inhibition and p38MAPK activation in inclusion body formation and ROS-mediated cell death.

Expanded polyglutamine proteins are known to be the causative agents of a number of human neurodegenerative diseases but the molecular basis of their cytoxicity is still poorly understood. Polyglutamine tracts may impede the activity of the proteasome, and evidence from single cell imaging suggests that the sequestration of polyglutamine proteins into inclusion bodies can reduce the proteasomal burden and promote cell survival, at least in the short term. The presence of misfolded protein also leads to activation of stress kinases such as p38MAPK, which can be cytotoxic. The relationships of these systems are not well understood. We have used fluorescent reporter systems imaged in living cells, and stochastic computer modeling to explore the relationships of expanded polyglutamine proteins, p38MAPK activation, generation of reactive oxygen species (ROS), proteasome inhibition, and inclusion body formation. In cells expressing a polyglutamine protein, inclusion body formation was preceded by proteasome inhibition but cytotoxicity was greatly reduced by administration of a p38MAPK inhibitor. Computer simulations suggested that without the generation of ROS, the proteasome inhibition and activation of p38MAPK would have significantly reduced toxicity. Our data suggest a vicious cycle of stress kinase activation and proteasome inhibition that is ultimately lethal to cells. There was close agreement between experimental data and the predictions of a stochastic computer model, supporting a central role for proteasome inhibition and p38MAPK activation in inclusion body formation and ROS-mediated cell death.

Optical recording of various brain signals is becoming an indispensable technique for biological studies, accelerated by the development of new or improved biosensors and microscopy technology. A major challenge in leveraging the technique is to identify and quantify the rich patterns embedded in the data. However, existing methods often struggle, either due to their limited signal analysis capabilities or poor performance. Here we present Activity Quantification and Analysis (AQuA2), an innovative analysis platform built upon machine learning theory. AQuA2 features a novel event detection pipeline for precise quantification of intricate brain signals and incorporates a Consensus Functional Unit (CFU) module to explore interactions among potential functional units driving repetitive signals. To enhance efficiency, we developed BIdirectional pushing with Linear Component Operations (BILCO) algorithm to handle propagation analysis, a time-consuming step using traditional algorithms. Furthermore, considering user-friendliness, AQuA2 is implemented as both a MATLAB package and a Fiji plugin, complete with a graphical interface for enhanced usability. AQuA2's validation through both simulation and real-world applications demonstrates its superior performance compared to its peers. Applied across various sensors (Calcium, NE, and ATP), cell types (astrocytes, oligodendrocytes, and neurons), animal models (zebrafish and mouse), and imaging modalities (two-photon, light sheet, and confocal), AQuA2 consistently delivers promising results and novel insights, showcasing its versatility in fluorescent imaging data analysis. / Doctor of Philosophy / Understanding and effectively treating brain diseases requires a deep insight into how the brain operates. A crucial aspect of this exploration involves directly visualizing different signals within the brain, allowing researchers to delve into the functions of brain cells and their interactions. However, as data collection expands rapidly, analyzing this wealth of information presents a significant challenge. Existing methods often fall short due to their limited capacity to analyze signals or their subpar performance, failing to keep pace with current demands. In this work, we introduce Activity Quantification and Analysis (AQuA2), an innovative platform rooted in machine learning principles. AQuA2 features a novel event detection pipeline for accurately quantifying intricate brain signals. Additionally, it incorporates a Consensus Functional Unit (CFU) module, which facilitates the exploration of interactions among potential functional units associated with repetitive signals. To enhance efficiency and usability, we have developed acceleration algorithms and released AQuA2 in two versions: a MATLAB package and a Fiji plugin, each designed to address unique user requirements. AQuA2 has demonstrated its efficacy through real-world applications, effectively quantifying and analyzing signals across various platforms such as biosensors, cell types, animal models, and imaging modalities, with promising outcomes. Furthermore, the utilization of AQuA2 has facilitated the discovery of new insights, thereby augmenting its value. These findings emphasize its versatility as software for comprehensive analysis of diverse fluorescent imaging data, enabling a wide range of scientific inquiries.

La formation d'un organe repose sur la coordination spatio-temporelle du positionnement et de la différenciation de progéniteurs. La finalité de ces évènements permet la constitution structurelle de l'organe et la production de la diversité cellulaire nécessaire pour assurer ses fonctions. L'épithélium olfactif de l'embryon de poisson-zèbre est issu de la migration de progéniteurs qui vont générer entre autres les neurones olfactifs. Au cours de ma thèse je me suis intéressé aux bases génétiques et moléculaires de la coordination de la morphogenèse et de la neurogenèse de cet épithélium tout en étudiant l'origine de la diversité des types cellulaires olfactifs. L'imagerie en temps réel m'a permis de caractériser la migration de ces progéniteurs en générant une carte morphométrique de leur déplacement. Mon travail de thèse révèle que le proneural Neurog1 régule directement l'expression de cxcr4b, un récepteur au chimiokine, dans les progéniteurs olfactifs assurant leur positionnement. Ainsi, Neurog1 coordonnerait la position et l'identité des progéniteurs olfactifs via ses cibles transcriptionnelles. Au sein de l'épithélium olfactif dans l'embryon, deux populations cellulaires (neurones à GnRH et neurones à microvillosités) ont été décrites comme provenant des crêtes neurales céphaliques (CNC). J'ai pu montrer que l'expression de marqueurs spécifiques de ces populations n'est pas affectée dans un contexte d'absence de différenciation des CNCs (sox10-/-) suggérant que ces types cellulaires ne dérivent pas de ce territoire. Afin d'identifier leur territoire d'origine, j'ai développé une méthode d'imagerie en temps réel, le backtracking, qui m'a permis de déterminer que la région de la placode olfactive, et non les crêtes neurales, génère ces deux types cellulaires. Ainsi j'ai pu définir la source de ces deux populations neuronales tout en minimisant la contribution des crêtes neurales. En conclusion mes résultats suggèrent que la diversité des neurones olfactifs serait produite localement et ceci conjointement à la morphogenèse de l'épithélium. / The correct development of sensory organs relies on the coordination between changes in progenitor positioning over time and the differentiation/specification of different neural subtypes. The outcome of this coordination is proper organ shape and cell diversity, which are required for functionality. The zebrafish embryonic olfactory epithelium arises from progenitor migration and differentiation. During my PhD, I studied the genetic and molecular basis of morphogenesis in this tissue, and how this is coordinated with neurogenesis, as well as revisiting the origin of olfactory cell type diversity.First, I generated a morphometric map of olfactory progenitors through the characterization of their migration in live embryos. Next, I showed that the proneural transcription factor Neurog1 directly regulates cxcr4b expression, a chemokine receptor that has already been shown to govern olfactory progenitor positioning. Thus, Neurog1 orchestrates olfactory progenitor position and the generation of olfactory neurons via distinct transcriptional targets. Secondly, I addressed the origin of olfactory neuron diversity. Within the embryonic olfactory epithelium, two cell populations (GnRH neurons and microvillous neurons) have been described as cephalic neural crest (CNC) derivatives. I found, however, that the expression of specific markers of both populations is unaffected in a genetic context blocking CNC differentiation. To revisit the lineage assignment of these cell types, I developed a backtracking approach through time-lapse live imaging. I found that both populations are derived from classical olfactory placode progenitor and not the CNC. In conclusion, my results indicate that heterogeneity of olfactory cell-types is locally generated, and concomitant with morphogenesis of the placode.

Abstract Kidney diseases affect an increasing number of people worldwide, and there is a growing demand to develop new treatments and increase the number of transplantable organs. New treatments can be designed when new knowledge is gained by studying the details of kidney development. The ex vivo culture techniques have been used for over a century to study the development of kidneys, but they are not optimal for long-term imaging and following the nephrogenesis process over time. Kidney organoids, which are cellular aggregates resembling the in vivo kidney, together with intact embryonic kidneys, present a platform for these studies. However, there are limitations when working with primary embryonic kidney cells. Primary embryonic metanephric mesenchymal cells are usually low in number and lose the ability to undergo nephrogenesis rapidly. New ways to culture, biobank, and transfect cells can offer ways for functional testing of the effects of different genes on the nephrogenesis. This study presents new tools for studying nephrogenesis. Time-lapse imaging of organ development may be enhanced by using a Fixed Z-direction (FiZD) culture system where the kidney explant is grown in a restricted 70μm space. The technique enables the segmentation of the individual cells in a two-dimensional image and a dynamic analysis of the time-lapse data. This study also presents a technique of dissociation and reaggregation of the uninduced kidney metanephric mesenchyme (MM). With this novel method of culturing the dissociated MM cells in a growth factor medium for 24 hours, the cells can keep their competence for nephrogenesis. This technique allows the genetic manipulation of the MM cells before the induction to form nephrons, allowing functional testing of genes in the metanephric mesenchyme. This study further presents different techniques for gene editing of MM cells and introduces biobanking of primary kidney cells. It is shown here that the MM and ureteric bud (UB) cells have the capability to remember their fates and build nephron-like structures or continue branching after the cryopreservation in the liquid nitrogen. The methods introduced here provide new ways to create kidney organoids, manipulate their genome, and biobank the primary embryonic kidney cells. The developed FiZD culture system enhances the imaging of kidney development compared to the previously used culture methods. Using this method, the morphogenesis of the developing kidney can be followed more precisely, even in a single cell level. This culture method may also be used to culturing other organs, such as ovary, and may help provide insights into the development of other tissues as well. / Tiivistelmä Munuaissairauksiin sairastuvien määrä on lisääntynyt maailmanlaajuisesti, ja se on aikaansaanut tarpeen uusien hoitokeinojen sekä siirtoelimien kehitykseen. Näiden kehittämiseksi tarvitsemme uutta tietoa munuaisen kehityksestä ja toiminnasta. Munuaisen kehitystä on tutkittu ex vivo -viljelyn avulla jo yli vuosisadan ajan, mutta nykyiset elinviljelytekniikat eivät ole kuitenkaan optimaalisia pitkäkestoiseen time-lapse-kuvaukseen. Tässä työssä käytetään munuaisen kehityksen tutkimiseen hiiren alkion munuaisia sekä munuaisorganoideja, jotka ovat munuaissoluista koostuvia ja aitoa munuaista mallintavia soluaggregaatteja. Primaaristen munuaissolujen käyttöön sisältyy rajoitteita, ja tämä luo tarpeen uusien organoiditekniikoiden kehitykseen ja optimointiin. Primaarisia munuaissoluja on yleensä käytettävissä pieniä määriä, ja ne eivät myöskään sovellu pitkäkestoiseen kasvatukseen, koska ne menettävät nopeasti kykynsä muodostaa nefroneita. Uusien tekniikoiden avulla voidaan parantaa näiden solujen kasvatusta, säilytystä ja transfektointia ja edistää eri geenien vaikutuksia tutkivat funktionaaliset testaukset. Tässä tutkimuksessa esitetään uusia työkaluja nefrogeneesin tutkimiseen. Elinten kehitystä seuraavan time-lapse-kuvauksen laatua voidaan parantaa käyttämällä tässä työssä esitettyä FiZD-kasvatusmenetelmää, jossa munuaiseksplantti kasvaa rajoitetussa 70μm:n tilassa. Kuvat ovat korkealaatuisia, ja se mahdollistaa 2D-kuvan yksittäisten solujen segmentoinnin ja solujen liikkeiden dynaamisen analyysin. Lisäksi tässä tutkimuksessa esitetään ei-indusoidun munuaismesenkyymin käsittelyyn kehitetty dissosiaatio- ja reaggregaatiomenetelmä. Munuaisen kehityksen alkuvaiheessa on mahdollistaerottaa nefroneja muodostava metanefrinen mesenkyymi (MM) sekä munuaisen kokoajaputkiston muodostava ureterin silmu. Metanefrinen mesenkyymi voidaan hajottaa yksisolususpensioksi, säilyttää 24 tuntia kasvutekijämediumissa ja tämän jälkeen reaggregoida ja indusoida muodostamaan nefroneita. Tämä tekniikka mahdollistaa MM-solujen geneettisen muokkauksen, ennen kuin munuaisen kehitys alkaa. Tämä tekniikka mahdollistaa myös dissosioitujen MM solujen geneettiset muokkaukset. Geenien yliekspression tai hiljentämisen avulla voidaan tehdä funktionaalisia kokeita näiden muutosten vaikutuksesta nefrogeneesiin. Lisäksi tässä työssä esitetään munuaisprogenitorisolujen säilömistä syväjäädytyksellä. Munuaisprogenitorisolut voidaan säilöä nestetyppeen, minkä jälkeen ne ovat edelleen kykeneviä muodostamaan nefronirakenteita tai haarautumaan. Tässä väitöskirjatyössä esitettyjen menetelmien avulla on tulevaisuudessa mahdollista saada lisätietoa munuaisten kehitysprosessista. Kehitetty FiZD-kasvatusmenetelmä parantaa munuaisen kehityksen kuvantamista ja mahdollistaa yksittäisten solujen seuraamisen. Tämä kasvatusmenetelmä sopii myös muiden elinten, kuten munarauhasten, ja kudosten kasvatukseen, ja sen avulla voidaan saada tietoa myös niiden kehityksestä.

Les microfaisceaux d’ions ont, au cours de ces dernières décennies, montré leur efficacité dansl’étude des effets des rayonnements ionisants sur le vivant notamment concernant les effets des faiblesdoses ou l’étude de l’effet de proximité. Le CENBG dispose depuis 2003 d’un dispositif permettant la micro-irradiation ciblée d’échantillons biologiques vivants. Les applications des microfaisceaux dans ce domainese sont récemment diversifiées et des études plus fines sur les mécanismes de réparation desdommages ADN radio-induits aux échelles cellulaire et multicellulaire sont devenues possibles via lesévolutions en imagerie par fluorescence et en biologie cellulaire. Ces approches ont nécessité une évolutionimportante de l'instrumentation de la ligne de micro-irradiation du CENBG qui a été entièrementredessinée et reconstruite dans un souci d’optimisation d’apport de nouvelles fonctionnalités. Les objectifsde mes travaux ont été i) la mise en service du dispositif, ii) la caractérisation des performances dusystème, iii) la mise en place de protocoles pour l’irradiation ciblée à dose contrôlée aux échelles cellulaireet multicellulaire, in vitro et in vivo, et le suivi en ligne des conséquences précoces de cette irradiation,iv) la modélisation des irradiations afin d’interpréter les observables biologiques au regard des donnéesphysiques calculées.Ces travaux ont permis i) de caractériser les performances du dispositif : une taille de faisceau d’environ2 μm sur cible et une précision de tir de ± 2 μm, de développer des systèmes de détection d’ions pour uncontrôle absolu de la dose délivrée, ii) d’induire des dommages ADN fortement localisés in vitro, et devisualiser en ligne le recrutement de protéines impliquées dans la réparation de ces dommages,iii) d’appliquer ces protocoles pour générer des dommages ADN in vivo au sein d’un organisme multicellulaireau stade embryonnaire, Caenorhabditis elegans.Ces résultats ouvrent la voie vers des expériences plus fines sur la ligne de micro-irradiation ciblée duCENBG pour étudier les effets de l’interaction des rayonnements ionisants avec le vivant, aux échellescellulaire et multicellulaire, in vitro et in vivo. / The main goal of radiobiology is to understand the effects of ionizing radiations on the living.These past decades, ion microbeams have shown to be important tools to study for example the effects oflow dose exposure, or the bystander effect. Since 2003, the CENBG has been equipped with a system toperform targeted micro-irradiation of living samples. Recently, microbeams applications on this subjecthave diversified and the study of DNA repair mechanisms at the cellular and multicellular scales, in vitroand in vivo, has become possible thanks to important evolutions of fluorescence imaging techniques andcellular biology. To take into account these new approaches, the CENBG micro-irradiation beamline hasbeen entirely redesigned and rebuilt to implement new features and to improve the existing ones. My PhDobjectives were i) commissioning the facility, ii) characterizing the system on track etch detectors, and onliving samples, iii) implementing protocols to perform targeted irradiations of living samples with a controlleddelivered dose, at the cellular and multicellular scales, and to visualize the early consequencesonline, iv) modelling these irradiations to explain the biological results using the calculated physical data.The work of these past years has allowed us i) to measure the performances of our system: a beam spotsize of about 2 μm and a targeting accuracy of ± 2 μm, and to develop ion detection systems for an absolutedelivered dose control, ii) to create highly localized radiation-induced DNA damages and to see onlinethe recruitment of DNA repair proteins, iii) to apply these protocols to generate radiation-induced DNAdamages in vivo inside a multicellular organism at the embryonic stage: Caenorhabditis elegans.These results have opened up many perspectives on the study of the interaction between ionizing radiationsand the living, at the cellular and multicellular scales, in vitro and in vivo.

Le suivi temporel est un processus d’acquisition et d’analyse d’acquisitions multiples répétées au même endroit sur la même cible à différentes périodes de temps. Cela s’applique bien à l’exploration sismique quand les propriétés de la cible varient au cours du temps comme pour les réservoirs pétroliers. Cette technique de sismique, dite 4D en raison de l’intégration du temps dans la construction des images, permet une détection et une estimation des variations du sous-sol survenues lors de l’évolution en temps du milieu. En particulier, dans l’industrie, le suivi et la surveillance peuvent améliorer notre compréhension d’un réservoir de pétrole/gaz ou d’un site de stockage de CO2. Analyser la sismique 4D peut aider à mieux gérer les programmes de production des réservoirs. Ainsi, des acquisitions répétées permettent de suivre l’évolutiondes fronts de fluide injectés: on peut optimiser les programmes d’injection de fluides pour une récupération améliorée des hydrocarbures (enhanced oil recovery). Plusieurs méthodes ont été développées pour l’imagerie variable dans le temps en utilisant les informations des ondes sismiques. Dans ma thèse, je montre que l’inversion de forme d’onde complété (FWI) peut être utilisée pour cette imagerie. Cette m´méthode offre des images sismiques quantitatives haute résolution. Elle est une technique prometteuse pour reconstruire les petites variations de propriétés physiques macro-échelle du sous-sol. Sur une cible identifiée pour ces imageries 4D, plusieurs informations a priori sont souvent disponibles et peuvent être utilisées pour augmenter la résolution de l’image. J’ai introduit ces informations grâce à la définition d’un modèle a priori dans une approche classique FWI en l’accompagnant de la construction d’un modèle d’incertitudes a priori. On peut réaliser deux reconstructions indépendantes et faire la différence les reconstruits: on parle de différence parallèle. On peut aussi effectuer une différence séquentielle o`u l’inversion de l’ensemble de données de la second acquisition, dite moniteur, se fait `a partir du modèle de base et non plus à partir du modèle utilisé initialement. Enfin, l’approche double-différence conduit à l’inversion des différences entre les deux jeux de données que l’on rajoute aux données synthétiques du modèle de base reconstruit. J’étudie quelle stratégie est à adopter pour obtenir des changements vitesse plus précis et plus robustes. En plus, je propose une imagerie 4D ciblée en construisant un modèle d’incertitude a priori grâce `a une information (si elle existe) sur la localisation potentielle des variations attendues. Il est démontré que l’inversion 4D ciblée empêche l’apparition d’artéfacts en dehors des zones cibles: on évite la contamination des zones extérieures qui pourrait compromettre la reconstruction des changements 4D réels. Une étude de sensibilité, concernant l’échantillonnage en fréquence pour cette imagerie 4D, montre qu’il est nécessaire de faire agir simultanément un grand nombre de fréquences au cours d’un cycle d’inversion. Ce faisant, l’inversion fournit un modèle de base plus précis que l’approche temporelle, ainsi qu’un modèle des variations 4D plus robuste avec moins d’artéfacts. Toutefois, la FWI effectuée dans le domaine temporel semble être une approche plus intéressante pour l’imagerie 4D. Enfin, l’approche d’inversion 4D régularisée avec un modèle a priori est appliquée sur des ensembles de données réelles d’acquisitions sismiques répétées fournis par TOTAL. Cette reconstruction des variations locales s’inscrit dans un projet d’injection de vapeur pour améliorer la récupération des hydro-carbures: Il est possible de reconstituer des variations de vitesse fines causées par la vapeur injectée. / Time-lapse monitoring is the process of acquiring and analysing multiple seismic surveys, repeatedat the same place at different time periods. This seismic technique, called 4D becauseof the integration time in the construction of images, allows detection and estimation of thesubsurface parameter variations occured through a time evolution. Particularly, in industries,the monitoring can improve our understanding of a producing oil/gas reservoir and CO2 storagesite. Analyzing the time-lapse seismics can help to better manage production programsof reservoirs. In addition, repeated surveys can monitor the evolution of injected fluid frontsand can permit to optimize injection programs which are considered for enhanced oil recovery(EOR) techniques.Several methods have been developed for time-lapse imaging using seismic wave information.In my thesis, I show that full waveform inversion (FWI) can be used for time-lapseimaging, since this method delivers high-resolution quantitative seismic images. It is a promisingtechnique to recover small variations of macro-scale physical properties of the subsurface.In time-lapse applications, several sources of prior information are often available and shouldbe used to increase the image reliability and its resolution. I have introduced this informationthrough a definition of a prior model in a classical FWI approach by also considering a prioruncertainty model. In addition, I have suggested a dynamic weighting to reduce the importanceof these prior models in the final convergence. In realistic synthetic cases, I have shownhow the prior model can reduce the sensitivity of FWI to a less accurate initial model. It istherefore possible to obtain a highly accurate baseline model for 4D imaging.Once the baseline reconstruction is achieved, several strategies can be used to assess thephysical parameter changes. We can make two independent reconstructions of baseline andmonitor models and make subtraction of the two reconstructed models. This strategy is calledparallel difference. The sequential difference strategy inverts the monitor dataset starting fromthe recovered baseline model, and not from the model used initially. Finally, the doubledifferencestrategy inverts the difference data between two datasets which are added to thecalculated baseline data computed in the recovered baseline model. I investigate which strategyshould be adopted to get more robust and more accurate time-lapse velocity changes. Inaddition, I propose a target-oriented time-lapse imaging using regularized FWI including priormodel and model weighting, if the prior information exists on the location of expected variations.It is shown that the target-oriented inversion prevents the occurrence of artifacts outsidethe target areas, which could contaminate and compromise the reconstruction of the effectivetime-lapse changes.A sensitivity study, concerning several frequency decimations for time-lapse imaging, showsthat the frequency-domain FWI requires a large number of frequencies inverting simultaneously.By doing so, the inversion provides a more precise baseline model and more robust time-lapsevariation model with less artifacts. However, the FWI performed in the time domain appearsto be a more interesting approach for time-lapse imaging considering all frequency content.Finally, the regularized time-lapse FWI with prior model is applied to the real field timelapsedatasets provided by TOTAL. The reconstruction of local variations is part of a steaminjection project to improve the recovery of hydrocarbons: it is possible to reconstruct thevelocity variations caused by the injected steam.