ED Sciences Physiques et de l'Ingénieur
Mechanics and morphodynamics of three-dimensional epithelial assemblies of human induced pluripotent stem cells
by Anirban JANA (Laboratoire Photonique, Numérique & Nanosciences)
The defense will take place at 10h00 - Amphithéâtre Institut D'optique d'Aquitaine (IOA), 1 rue François Mitterrand, 33400 Talence
in front of the jury composed of
- Pierre NASSOY - Directeur de recherche - Université de Bordeaux - Directeur de these
- Timo BETZ - Professeur - Georg August University Göttingen - Rapporteur
- Matthieu PIEL - Directeur de recherche - Institut Curie - Rapporteur
- Jose Luis GARCIA CORDERO - Professeur - Roche Institute of Human Biology - Examinateur
- Sham TLILI - Chargée de recherche - Institut de Biologie du Développement de Marseille (IBDM) - Examinateur
- Jacques LENG - Directeur de recherche - Solvay Laboratoire du Futur - Examinateur
In vitro cell culture systems recapitulating a physio-mimetic environment has been of increasing interest in stem cell research and in unlocking the potential of human induced pluripotent stem cells (hiPSCs)-based applications. hiPSCs when embedded in a reconstituted basement membrane, self-organize into a fluid-filled, polarized epithelial shell, also defined as cysts. This lumen-containing structure has been shown to model morphologically and phenotypically the epiblast, which is one key stage in embryo development. In this work, I have developed a customised bright field microscope inside an incubator with pseudo-three dimensional imaging, coined as the zincubascope. Extensive live imaging with this setup over days, co-supported by optical coherence microscopy and standard confocal imaging reveals unique morphodynamics of these hIPSCs assemblies. The hiPSC cysts exhibit epithelial thickening with an increase in the lumen radius, in contrast to lumenized assemblies of most other epithelial cell types (MDCK, Caco2, and MCF10A). Unlike these mature, lineage committed epithelial cell types, the iPSC epiblast undergoes significant mechanical changes, deforming from a sphere to a disc during growth in-vivo. This morphogenesis has been shown to be orchestrated by bio-chemical signalling, but how the physical state and mechanics of of the epiblast may contribute to such deformations has never been investigated. In this work, we report direct measurements of the mechanical properties of hiPSCs cysts. Using inflation–deflation assays and high-resolution imaging, we find that these fluid-filled shells are weakly-pressurized and achieve extreme deformability through reversible soft modes of deformation accommodated by the cytoskeleton. We have developed a “nano-inflation apparatus” to probe the luminal pressure and also pressurize the lumen to observe the response of the epithelium to this mechanical perturbation. A glass micro-capillary is inserted into the cyst and fluid is injected inside using a pressure-driven pump. Combined with live imaging, we observe that, the monolayer of cells does not collapse when it is poked with a micropipette, suggesting that the cyst is weakly pressurized, also implying a lack of tension in the cell layer; upon inflation, the lumen volume increases from 0.5 nl to 4 nl, corresponding to an area-strain of 300 %, and on releasing the external pressure, the initial state of the assembly is completely recovered. Repeated inflation-deflation upto twice the initial radius results a complete reversal with no mechanical hysterisis. Using a linear elastic model of a thick shell in the low deformation regime, a Young's modulus of 4.6±1.4 kPa is obtained. Previous in-vitro mechanical studies of 2D-epithelial monolayers report a stiffness of 10-30 kPa, highlighting the softness of this epiblast-like epithelium. Luminal pressure-strain plots over higher elastic deformations indicate a softening trait, reminiscent of non-linear elastic materials. To decipher the mechanism of softening at the cellular scale, we performed live fluorescent imaging of the assemblies during inflation. We observe extensive bending/buckling and shearing of the cells edges in the monolayer and an elastic recovery of the structure of the cellular constituents upon depressurization. We propose a simple simulation model that captures and quantifies the underlying mechanism, showing that during rapid inflation, lateral-edge soft modes buffer the mechanics by decoupling radial thinning from the pressure-strain response.
ED Sociétés, Politique, Santé Publique
Greater Bordeaux Area Waters: a public entreprise in the making. Sociohistory of an urban network service's reconfigurations
by Colin BROWN (Environnement, Territoires en Transition, Infrastructures, Sociétés)
The defense will take place at 14h00 - Salle du conseil Université de Bordeaux, Campus Victoire, 3ter Place de la Victoire, 33000 Bordeaux
in front of the jury composed of
- Kévin CAILLAUD - Chargé de recherche - INRAE - UBdx - Directeur de these
- Rémi BARBIER - Professeur des universités - L'École nationale du génie de l'eau et de l'environnement de Strasbourg (ENGEES) UMR SAGE (Sociétés, Acteurs, Gouvernement en Europe) - Rapporteur
- Marie-Hélène ZéRAH - Directrice de recherche - L'Institut de recherche pour le développement (IRD), CESSMA (Centre d'études en sciences sociales sur les mondes africains, américains et asiatiques) - Rapporteur
- Anne-Cécile DOUILLET - Professeure des universités - Université de Lille, UMR CERAPS (Centre d'études et de recherches administratives, politiques et sociales) - Examinateur
- Olivier COUTARD - Directeur de recherche - ENPC, CNRS, UMR LATTS (Laboratoire Techniques Territoires Sociétés) - Examinateur
In 2020, the Greater Bordeaux Area council decided to join the ranks of other French metropolitan areas and large urban cities, that are increasingly abandoning more or less long-standing public-private partnerships (PPP) to manage their drinking water and sanitation services, opting instead for a fully public model. Thus, the Greater Bordeaux Area water company had to be created in the form of a ringfenced corporate utility and made operations-ready for January 1st, 2023. This thesis offers a sociohistorical analysis of this process, focusing on its political, technical, and organizational dimensions, to shed light on the dynamics of restructuring the local public water service and its governance framework. Specifically, four sequences or segments of its history are analyzed: (i) the reappraisal of the public-private partnership model from the 1990s to 2020; (ii) creating the public water company and operationalizing it ; (iii) redefining a governance model between the Greater Bordeaux Area and its new public company ; (iv) and establishing a new professional and organizational doctrine at the service level. This thesis is conducted within the framework of an Industrial Convention for Training through Research (Cifre), meaning it was co-financed by the water company and carried out with the collaboration of a public research institute (INRAE). This context being particularly amenable to immersion in the field, socio-ethnographic methods were adopted allowing for close observation of action as it happens – here, the transition to public management. This thesis emphasizes that the implementation of this public policy has the traits of innovation processes. That is, the establishment of the novelty that the policy proponents aim to introduce is conditioned by the enrollment of coalitions who, through diverse forms of appropriation, continuously readjust and hybridize these aims. The capacity of this transition to public management to represent a paradigm shift is notably challenged by coexisting paradigms at the political-administrative level (New Public Management, for example), the professional level (managerial ideals, notably), and the organizational level (local orders). These manifest themselves both through the cognitive traits of the political and administrative stakeholders involved in implementation, and through the instruments of government designed to structure the public company's daily operations and decision-making processes. It follows that competing paradigms impose other meanings of "public" on the policy than that originally envisioned by its protagonists, which focuses on the ethical and symbolic dimensions of water conceived as a common good. Ultimately, the espousal of the modern rational meaning of "public" contributes to containing water within a predominantly managerial prism.