ED Sciences de la Vie et de la Santé
Axonal guidance signaling in glioblastoma and stromal dynamics : Role of Robo/Slit and PlexinA/Nrp1/Sema3a
by Teo LEBOUCQ (BoRdeaux Institute of onCology)
The defense will take place at 10h00 - Amphitheatre RDC 146 Rue Leo Saignat, Batiment BBS, 33000, Bordeaux
in front of the jury composed of
- Giorgio SEANO - Directeur de recherche - INSERM / Institut Curie - Chimie - Biologie des Cancers - UMR1339/UMR3666 - Rapporteur
- Samuel VALABLE - Directeur de recherche - CNRS / Imagerie et Stratégies Thérapeutiques pour les Cancers et Tissus Cérébraux - UMR6030 - Rapporteur
- Florian ALONZO - Chargé de recherche - INSERM / Biotis – UMR 1026 - Examinateur
- Oceane MARTIN - Maîtresse de conférences - Université de Bordeaux / Institut de Biochimie et Génétique cellulaire - UMR5095 - Examinateur
- Julie GAVARD - Directrice de recherche - CNRS / Centre de Recherche en Cancérologie et Immunologie Intégrée de Nantes - UMR - Examinateur
- Thomas MATHIVET - Chargé de recherche - INSERM U1312 - BRIC / Université de Bordeaux - Directeur de these
Glioblastoma (GB) is the most aggressive primary brain tumor, characterized by marked heterogeneity, extensive parenchymal infiltration and treatment resistance, with outcomes improving only marginally since the Stupp protocol. Two major barriers limit therapeutic progress: the diffuse invasion of tumor cells, which precludes complete surgical resection, and a profoundly immunosuppressive tumor microenvironment (TME) dominated by tumor-associated macrophages (TAMs) that restrict T-cell infiltration and blunt immunotherapy. We investigated two axon guidance systems, SLIT2/ROBO and SEMA3A/NRP1/PLXNA1, whose tumoral expression correlates with poor patient survival, as convergent drivers of these two processes. In the tumor invasion context, we evidenced that GB cells themselves express ROBO receptors at the invading tumor front, at both transcriptomic and protein levels in patient samples. In vitro, SLIT2 promoted oriented migration and spheroid invasion of patient-derived GB cells. RNA-sequencing of ROBO1/2 knocked-down cells from three patients revealed differential gene expression and pathway enrichment associated with extracellular matrix (ECM) production and cell adhesion. In vivo, ROBO1/2 knockdown in patient-derived xenografts caused a marked growth delay, altered tumor stiffness and matrix over-production, and prolonged survival. In fact, SLIT/ROBO signaling depletion unleashes TGFbeta pathway signaling and subsequent fibrotic-like response limiting mechanotransduction-dependent invasion. In the stromal dynamics context, shRNA-mediated SEMA3A knockdown in murine glioma cells reduced tumor progression and prolonged survival in an immunocompetent model. SEMA3A depletion decreased TAM accumulation in vivo and limits the TAM immunosuppressive phenotypical switch, potentiating adaptative immunity (T-cell) recruitment in tumor microenvironment. Mechanistically, recombinant SEMA3A was sufficient to trigger chemotaxis of THP-1 monocytes and bone-marrow-derived macrophages, an effect abrogated by NRP1 or PLXNA1 silencing, confirming a receptor-dependent chemoattractant activity. SEMA3A also upregulated M2-like markers in THP-1 cells without inducing a broad pro-inflammatory or checkpoint-associated program. Combining SEMA3A knockdown with triple immune checkpoint blockade (anti-PD-1/CTLA-4/LAG-3) showed a trend toward additional survival benefit, a preliminary observation requiring validation in larger cohorts. Together, these data establish axon guidance signaling as a dual vulnerability in GB: SLIT2/ROBO sustains cell-autonomous invasion and ECM remodeling, while tumor-derived SEMA3A non-cell-autonomously recruits and polarizes immunosuppressive TAMs. Co-targeting these axes represents an innovative strategy to simultaneously limit GB infiltration and enhance immunotherapy responsiveness.
Deciphering the cellular and molecular responses of tomato meristems to the heat stress.
by Eline CLERCKX (BFP - Biologie du Fruit et Pathologie)
The defense will take place at 16h00 - Bâtiment amphithéatre C & J Bové INRAE Bordeaux-Aquitaine Bât. IBVM, 71 av. Edouard Bourlaux - CS 20032 - 33882 Villenave d'Ornon Cedex - France
in front of the jury composed of
- Norbert BOLLIER - Maître de conférences - Université de Bordeaux - Directeur de these
- CLAIRE PERILLEUX - Professeure des universités - Université de Liège - Rapporteur
- Björn USADEL - Professeur des universités - Heinrich Heine University Düsseldorf - Rapporteur
- Matthias BENOIT - Chargé de recherche - INRAE - Examinateur
- Valérie SCHURDI-LEVRAUD - Professeure des universités - Université de Bordeaux - Examinateur
Demographic growth and global warming represent major challenges for future food production. Rising temperatures and increasingly frequent heat waves negatively affect plant growth, development and yield. Tomato is one of the most widely produced fruit crops worldwide, yet many cultivars are highly sensitive to heat stress (HS). The shoot apical meristem (SAM), from which the aerial parts of the plant originate, must maintain its function throughout development and undergoes the transition from vegetative to reproductive growth required for flower and fruit production. Despite its developmental importance, the molecular response of the SAM to HS remains poorly understood, partly because of its small size and limited accessibility. This thesis therefore aimed to characterise the molecular response of the tomato SAM to acute HS. Transcriptomic analysis of vegetative SAMs from four genetically distinct tomato genotypes exposed to HS (45°C) revealed extensive conserved and genotype dependent transcriptional responses. HS rapidly activated HSFs, HSPs and other proteostasis components while simultaneously modifying developmental, hormonal and proliferative programmes. Changes in CLV/BAM signalling, auxin- and cytokinin-associated pathways and cell cycle related genes highlighted coordination between cellular protection and meristem development. Extensive genotype × HS interactions further demonstrated that genetic background strongly influences the SAM response. RT-qPCR revealed genotype dependent differences in the dynamics of HSF and HSP expression during HS and recovery, while in situ hybridisation demonstrated localised induction of SlHSP17-6a within the meristematic dome and developing vascular tissues and supported reduced proliferative activity during HS. Co-expression analysis further identified an HSF-HSP-BAG proteostasis network and connections between stress and developmental regulation. To resolve the cellular context underlying these bulk responses, the RNA-seq data were deconvoluted using a reconstructed tomato SAM single-nucleus atlas. BayesPrism showed the best performance among three tested approaches. Integrated deconvolution and DEG mapping indicated reduced meristematic and protodermal/epidermal transcriptomic contributions under HS and identified an early phloem/sieve element associated response, suggesting that HS effects are structured according to developmental population identity. Three HS-responsive BAG genes were subsequently characterised in greater detail. Phylogenetic analysis placed them within the IQ-domain BAG clade, while coding sequence and promoter comparisons revealed genotype-specific sequence and cis-regulatory variation. Their expression showed distinct temporal and genotype dependent responses to HS and recovery. In situ hybridisation demonstrated that SlBAG9 was strongly concentrated within the meristematic dome, supporting a potential role in the SAM HS response, while its protein showed an unexpected association with nuclear actin structures.
ED Sciences Physiques et de l'Ingénieur
Development of methods for predicting the service life of assemblies of electronic components subjected to thermomechanical stresses
by Vincent SISOMSEUN (Laboratoire de l'Intégration du Matériau au Système)
The defense will take place at 9h30 - Amphithéâtre J.P DOM Bâtiment A31, 351 Cr de la Libération, 33400 Talence
in front of the jury composed of
- Hélène FREMONT - Professeur - Université de Bordeaux - Directeur de these
- Sébastien MERCIER - Professeur - Université de Lorraine - Rapporteur
- Rafael ESTEVEZ - Professeur - Université de Grenoble - Rapporteur
- Alexandrine GUEDON-GRACIA - Maître de conférences - Université de Bordeaux - CoDirecteur de these
- Lahouari BENABOU - Professeur - Université de Versailles Saint-Quentin en Yvelines - Examinateur
- Rachid JAOUI - Ingénieur - Agence de l'Innivation Défense - Examinateur
The reliability of solder joints is assessed either through experimental testing, which is costly and time-consuming, or through modelling approaches, which are faster and less expensive. The models are not able to accurately predict the lifetime of assemblies involving complex electronic packages such as Quad Flat No-lead (QFN) components. The objective of this thesis is therefore to develop a methodology capable of overcoming these limitations and improving lifetime predictions for such assemblies. To achieve this objective, the study relies on failure data obtained from accelerated thermal cycling tests together with thermomechanical characterizations performed at both the constituent material scale and the assembly scale. These data are used to calibrate finite element models as well as the semi-empirical lifetime prediction model. Two investigation approaches were explored. The first, referred to as the "classical" approach, represents the thermomechanical behaviour of the assembly through thermal expansion characterized by an effective coefficient of thermal expansion (CTE). Accelerated thermal cycling tests revealed complex phenomena, such as the influence of the opposing component, which cannot be explained solely by the thermal expansion of the assembly. This approach proved to be insufficient and required a reassessment of the underlying modelling assumptions. This led to the development of a new "extended" approach, in which the warpage phenomenon is explicitly considered and further investigated. This approach demonstrated that warpage is the dominant deformation mode and accounts for most of the observations made during both thermomechanical characterizations and accelerated testing. The study conducted using this extended approach enabled the definition of a new metric to describe the assembly behaviour and exploited its specific features to redefine a key parameter that could potentially be incorporated into future lifetime prediction models.
development of very high repetition rate laser sources in the multi-kW power range
by Duncan SARTON (Centre Lasers Intenses et Applications)
The defense will take place at 9h30 - amphithéâtre C 351 Cr de la Libération, 33400 Talence, bâtiment A29
in front of the jury composed of
- Philippe BALCOU - Directeur de recherche - Université de Bordeaux - Directeur de these
- Vincent COUDERC - Directeur de recherche - Université de Limoges, XLIM - Rapporteur
- Sébastien MONTANT - Directeur de recherche - CEA CESTA - Rapporteur
- Sophie KAZAMIAS - Professeure des universités - Université Paris-Saclay, IJCLab - Examinateur
- Adrien AUBOURG - Docteur - Synthwave lasers - Examinateur
- Inka MANEK-HöNNINGER - Professeur des universités - Université de Bordeaux, CELIA - Examinateur
- François COURVOISIER - Directeur de recherche - FEMTO-ST - Examinateur
The increase of the average power delivered by ultrafast lasers represents one of the major challenges in modern laser physics. An intense international effort is currently underway to reach, and ultimately surpass, the kilowatt average power threshold for chirped pulse amplification (CPA) systems, a technology recognized by the 2018 Nobel Prize in Physics. At such power levels, thermal effects within the gain medium, active-ion spectroscopy, population dynamics, radiative transfer, thermally induced mechanical stresses, and their impact on beam propagation all become strongly coupled, making the design and optimization of these laser systems particularly challenging. This PhD work contributes to the development of a new generation of high-average-power laser amplifiers intended to overcome the limitations of current state-of-the-art technologies, particularly thin-disk amplifiers. The proposed architecture is based on multiple rotating gain disks fully immersed in a coolant, providing highly efficient heat extraction. The work includes the optical alignment of an off-axis vacuum multipass amplifier, numerical modeling of laser beam propagation and nonlinear effects (B-integral) using Python, and thermal and hydrodynamic simulations of the cooling system using COMSOL Multiphysics. The objective is to achieve stable operation in the kilowatt average power regime at kilohertz repetition rates. In parallel, an innovative electro-optic pulse source operating in the multi-GHz regime has been developed. Unlike conventional pulsed laser architectures based on mode-locking or Q-switching, this source generates ultrashort pulses through the electro-optic modulation of a continuous-wave laser. Radio-frequency signals with precisely controlled amplitude, frequency, and phase drive electro-optic modulators to first broaden the optical spectrum through phase modulation and then generate a spectral phase suitable for pulse formation and compression close to the Fourier transform limit. This approach provides unprecedented flexibility, allowing electronic tuning of the repetition rate over the multi-GHz range while maintaining sub-picosecond pulse durations and precise control over the temporal pulse shape. Additional stages for spectral shaping, amplification, pulse compression, and automated system control have been developed to produce a robust and user-friendly laser source suitable for a wide range of applications. The ultimate goal of this thesis is to combine this electro-optic multi-GHz source with the high-average-power amplifier to demonstrate a laser system simultaneously operating in the GHz repetition-rate and kilowatt average-power regimes, a performance combination that remains largely unexplored. Such a laser source would enable new opportunities in laser material processing, including micromachining, surface structuring, polishing, and hardening, as well as high-flux laser-driven X-ray generation for radiography, pumping of high-energy optical parametric amplifiers, and other applications requiring ultrafast lasers with unprecedented average power and repetition rates.