ED Sciences de la Vie et de la Santé
Regulation of cohesin by the TORC1 complex in the yeast Schizosaccharomyces pombe
by Dorian BESSON (Institut de Biochimie et Génétique Cellulaires)
The defense will take place at 14h30 - Salle de conférence I.B.G.C. - UMR 5095 1 rue Camille Saint Saens, 33077, Bordeaux Cedex
in front of the jury composed of
- Valérie BORDE - Directrice de recherche - Institut Curie - Rapporteur
- Frédéric BECKOUET - Chargé de recherche - C.B.I. (Centre de Biologie Intégrative) - Rapporteur
- Pascal BERNARD - Directeur de recherche - L.B.M.C. (Laboratoire de Biologie et Modélisation de la Cellule) - Examinateur
- Sophie JAVERZAT - Professeure - Université de Bordeaux - M.R.G.M. (Rare diseases : Genetics and Metabolism) - Examinateur
Cohesin is a protein complex capable of capturing DNA molecules. Cohesin ensures the cohesion of sister chromatids, which is essential for chromosome segregation during nuclear divisions. It is also involved in interphase via the formation of intra-chromosomal DNA loops that shape the functional architecture of the genome. Gene expression is thus regulated by the spatial organisation of chromosomes, particularly during development and differentiation. The many functions of cohesin suggest fine regulation in time and space. The laboratory is addressing this question using a genetic approach in the model organism Schizosaccharomyces pombe. DNA capture by cohesin requires the intervention of a loading complex, Mis4/Ssl3 (hNIPBL/MAU2). The mis4-G1487D mutant is thermosensitive to growth at 36°C, has a defect in cohesin loading on chromosomes and a high frequency of chromosome segregation defects during mitosis. A genetic screen identified extragenic mutations capable of restoring the growth of mis4-G1487D at 36°C. Five of these mutations affect the mip1 gene and one the tor2 gene. Mip1 and Tor2 are components of the TORC1 complex, the equivalent of mTOR (Mammalian Target Of Rapamycin), which is a major regulatory kinase for cell metabolism and growth. Its activity is stimulated by signals such as the availability of nutrients, energy levels, hormones and growth factors. In S. pombe, Tor2 is the catalytic subunit and Mip1 (hRaptor) is involved in substrate selection. The tor2 and mip1 genes are essential for cell viability, indicating that the alleles produced by the screen are hypomorphic. We focused our work on mip1-R401G, which causes virtually no growth defects while being an excellent suppressor. Remarkably, mip1-R401G restored cohesin association with chromosomes and reduced the frequency of abnormal chromosome segregation in the mis4-G1487D mutant at 36°C. In the mis4+ background, mip1-R401G increased the amount of cohesin associated with chromosomes. Similar results were obtained by treating the cells with Rapamycin, a TORC1 inhibitor. These data suggest that TORC1 activity negatively regulates the cohesin loading complex in S. pombe. All subunits of the TORC1 complex co-purify with cohesin and Mis4. The Psm1 subunit of cohesin and Mis4 are hypophosphorylated in the mip1-R401G background. The combination of mutations mimicking the non-phosphorylated state reduces the frequency of mis4-G1487D segregation defects. Conversely, segregation defects are exacerbated by mutations mimicking the phosphorylated state. These data indicate that TORC1 controls the phosphorylation state of Psm1 and Mis4. Given that TORC1's known function is to adapt the cell to environmental changes, we carried out a transcriptome analysis in various experimental situations (culture medium composition, temperature, cell cycle phase). Taking all experiments together, 337 genes were differentially expressed in the mis4-G1487D background compared with the wild-type control. Remarkably, the genes affected differed widely from one condition to another, suggesting that mis4-G1487D cells have a defective adaptive response. Almost all the genes deregulated by mis4-G1487D were also deregulated by mip1-R401G. These genes are preferentially located at the ends of chromosomes and are involved in the stress response and sexual differentiation. Taken together, the data suggest that cohesin is an effector of the TORC1 pathway for adapting the cell to environmental changes. Mechanistically, this might involve a change in gene expression induced by a modification in the spatial organization of the genome.
ED Sciences Physiques et de l'Ingénieur
Constraining the origin of Earth's volatiles with dynamical simulations and isotopic measurements of noble gases in meteorites
by Sarah JOIRET (Laboratoire d'Astrophysique de Bordeaux)
The defense will take place at 14h00 - Salle Univers, Laboratoire d'Astrophysique de Bordeaux, All. Geoffroy Saint-Hilaire, 33600 Pessac
in front of the jury composed of
- Sean RAYMOND - Directeur de recherche - CNRS - Laboratoire d'Astrophysique de Bordeaux - Directeur de these
- Sébastien CHARNOZ - Professeur des universités - Université Paris Cité - Institut de Physique du Globe - Rapporteur
- Rita PARAI - Assistant professor - Washington University in St. Louis - Rapporteur
- Aurélie GUILBERT LEPOUTRE - Directrice de recherche - Laboratoire de Géologie de Lyon : Terre, Planète, Environnement - Examinateur
- Alessandro MORBIDELLI - Directeur de recherche - Université de Côte d'Azur - Examinateur
The origin of volatiles, such as water or noble gases, on the terrestrial planets is closely related to the early dynamical evolution of the solar system. In particular, it is believed that a dynamical instability among the giant planets triggered a bombardment of comets and asteroids in the inner solar system. The timing of this instability is constrained to the first 100 million years after gas disk dispersal, possibly before the last giant impact on Earth. Such a timing, however, appears in conflict with the disparate signatures of xenon isotopes in Earth's mantle compared to its atmosphere. In this thesis, I assess the dynamical effects of an Early Instability on the delivery of carbonaceous asteroids and comets to the terrestrial planets, in particular Earth, and address the implications for their volatile budget. I approach this issue with N-body simulations of the solar system's early evolution, calculations of collision probability, impact simulations and isotopic measurements of noble gases. In Joiret et al. (2023), the stochasticity of the cometary bombardment is emphasized, as very large comets should have been numerous in the primordial outer disk of cometesimals. Building from these results, Joiret et al. (2024) demonstrate that an increase in cometary flux relative to carbonaceous asteroids at late times is possible, and may notably offer an explanation for the xenon signature dichotomy between the Earth's mantle and atmosphere. Hydrocode simulations show that comets implanted in the inner solar system as a result of the instability could have been highly efficient at delivering volatiles to Earth. Finally, our mass spectrometry measurements indicate that HED meteorites, thought to originate from Vesta's crust, do not contain any cometary signature. Using numerical simulations, I show that it is likely related to Vesta's weak gravitational attraction resulting in a low accretion efficiency of cometary impactors having realistic velocities.
Compaction of biopharmaceutics: control of formulation and process parameters to obtain biological activity and stability
by Charbel MADI (I2M - Institut de Mécanique et d'Ingénierie de Bordeaux)
The defense will take place at 14h00 - Module 2.1 146 rue Léo Saignat, 33076, Bordeaux
in front of the jury composed of
- Virginie BUSIGNIES - Professeure des universités - Université de Bordeaux - Directeur de these
- Christine CHARRUEAU - Professeure des universités - Université Paris cité - Rapporteur
- Pierre TCHORELOFF - Professeur des universités - Université de Bordeaux - CoDirecteur de these
- Tahmer SHARKAWI - Maître de conférences - Université de Montpellier - Rapporteur
- Sophie CAZALBOU - Maîtresse de conférences - Université Paul Sabatier - Toulouse III - Examinateur
- Mehdi CHERIF - Professeur des universités - Art et Métier ParisTech, ENSAM - Examinateur
Currently, the market for biopharmaceutics could reach 390 billion dollars by 2024 with the emergence of new therapeutic approaches using, for example, monoclonal antibodies, recombinant proteins, gene material such as small interfering RNAs or mRNAs. The possibility of formulating these biomolecules as tablets can only be achieved with the knowledge of formulation effects and process parameters. The compression process must necessarily be preceded by freeze-drying to obtain biomolecules in a granular solid. First, we need to propose freeze-drying conditions to maintain the activity of the biomolecules. The second objective is to evaluate the influence of the lyophilized solid on its behavior in compaction. The study of pharmaceutical processes will be coupled with an evaluation of the biological activity of model biomolecules and the stability of tablets. All the obtained results obtained should make it possible to propose elements for defining the critical parameters integrated in process design spaces in order to consider the large-scale development of biopharmaceutic tablets.