ED Sciences de la Vie et de la Santé
Role of the polar cortex on the mechanics of cytokinesis in diverse cell types and consequences of its disruption on cell fate and tissue organization
by Irène DEDUYER (Institut de Biochimie et Génétique Cellulaires)
The defense will take place at 14h00 - Salle de conférence IBGC RDC 1 rue Camille Saint Saëns, 33077 Bordeaux IBGC UMR 5095 Salle de conférence RDC
in front of the jury composed of
- Anne ROYOU - Directrice de recherche - Université de Bordeaux - Directeur de these
- Mélanie BONHIVERS - Directrice de recherche - Université de Bordeaux - Examinateur
- Arnaud ECHARD - Directeur de recherche - Sorbonne Université - Examinateur
- Roland LE BORGNE - Directeur de recherche - Université de Rennes - Rapporteur
- Yohanns BELLAICHE - Directeur de recherche - Sorbonne Université - Rapporteur
Cytokinesis is the final step of cell division, ensuring faithful partitioning of cellular material between daughter cells. In metazoans, it relies on the assembly and constriction of an actomyosin contractile ring (CR) that drives plasma membrane ingression between segregating chromatids. Activation of the small GTPase Rho1 by its conserved RhoGEF, Pbl-A, is essential for CR assembly and constriction. The pathway specifying the equatorial zone of Rho1 activity is well established: Pbl-A accumulates at the cell equator through its interaction with the centralspindlin complex. While equatorial contractility has long been recognized as the main driver of furrow ingression, less is known about the contribution of the polar cortex contractility for robust cytokinesis. Using Drosophila neuroblasts as a model, I and other team members uncovered the role of a novel Pbl isoform, Pbl-B, during cytokinesis in parallel to the canonical Pbl-A. While Pbl-A was enriched at the equator, Pbl-B was localized at the plasma membrane and relocated prematurely in the nucleus at the end of cytokinesis. Alternative expression of Pbl-A and B revealed that Pbl-A functioned to focus Rho1 activity at the ring to sustain efficient constriction, while Pbl-B increased contractility at the poles, which was critical to adjust furrow position, thereby preserving correct daughter cell size asymmetry. Our work highlighted how the use of isoforms with distinct localisation makes an essential process more robust. These findings provided the groundwork for my first main thesis project, which focused on understanding how cytokinesis adapts to diverse cell types with specific intrinsic and extrinsic constraints. We reasoned that the two Pbl isoforms with different spatio-temporal patterns of Rho1 activity may provide flexibility to a process that is challenged by diverse tissue features. To address this question, we used the alternative expression of Pbl-A and -B isoforms to manipulate Rho1 activity at the equator and poles in two different cell types: the large, and non-adherent spermatocytes undergoing incomplete cytokinesis, and the adherent and polarized epithelial cells of the notum. Quantitative live imaging revealed that the loss of either isoforms produces similar changes in myosin dynamics in both cell types but with different outcome. In spermatocytes, Pbl-B but not –A was essential for spermatocyte cytokinesis by promoting timely myosin recruitment and efficient CR assembly. Conversely, Pbl-A but no –B was required for robust epithelial cell cytokinesis, by providing the necessary equatorial contractile force to disengage adherens junctions from neighbor cells, a critical step in epithelial cell division. Our comparative study illustrates how cytokinesis adapts to tissue specificity via the modulation of polar and equatorial contractility through the use of Pbl isoforms with distinct spatial activities. The high rate of cytokinesis failure in ∆pbl-A epithelia generated multinucleated cells, providing a unique opportunity to explore the impact of polyploidy on tissue organization. Detailed examination of ∆pbl-A notum architecture identified large multinucleated cells as well as a population of small cells en route to delamination. Long-term imaging showed that many daughter cells delaminated, despite initially completing cytokinesis. Delamination was neither due to spindle orientation defects, nor apoptosis signaling, the two known triggers of epithelial cell extrusion. Instead, it was correlated with an increase in polar cortex contractility associated with blebbing during the preceding cytokinesis. Importantly, delaminated cells were not eliminated and persisted within the basal layer of the tissue, posing the threat that they complete their mesenchymal transition by acquiring oncogenic mutations. Our work identifies a novel mechanism of epithelial-to-mesenchymal transition stemming from mild changes in myosin dynamics during the preceding cytokinesis.
ED Sciences Physiques et de l'Ingénieur
Study and development of an innovative broadband transmission architecture for 5G applications
by Rémi QUEHEILLE (Laboratoire de l'Intégration du Matériau au Système)
The defense will take place at 13h30 - Amphi Jean-Paul DOM 351 Cours de la Libération, Bâtiment A31, Laboratoire IMS 33405 Talence Cedex, France
in front of the jury composed of
- Nathalie DELTIMPLE - Professeure des universités - Bordeaux INP - Directeur de these
- François RIVET - Maître de conférences - Bordeaux INP - CoDirecteur de these
- Audrey MARTIN - Maîtresse de conférences - Université de Limoges - Rapporteur
- Sylvain BOURDEL - Professeur des universités - Grenoble INP - Rapporteur
- Philippe CATHELIN - Ingénieur - STMicroelectronics - Examinateur
- Cédric DEHOS - Ingénieur - CEA-Leti - Examinateur
- Yann DEVAL - Professeur des universités - Bordeaux INP - Examinateur
- Eric KERHERVE - Professeur des universités - Bordeaux INP - Examinateur
The 5th Generation (5G) of communications offers very high data rates by using multiple carrier frequencies simultaneously in the 617 MHz to 5 GHz band. The main challenge is to achieve intelligent carrier aggregation without increasing power consumption, while considering the constraints of multi-standard operation, resolution, speed, and integration. This work presents research results related to the design of wideband power amplifiers in 28 nm FD-SOI CMOS technology for 5G FR1 bands. Harmonic control methods are investigated to optimize the efficiency of the amplifiers over a wide bandwidth. The design approaches leading to these architectures, the implemented circuits, and the obtained measurement results are presented and discussed.
ED Sociétés, Politique, Santé Publique
The Haitian diaspora in France. The great forgotten people of French colonial history.
by Joseph CARMIL (Passages)
The defense will take place at 14h00 - Salle du Conseil Faculté d'Anthropologie Sociale et d'Ethnologie – Université de Bordeaux 3ter, Place de la Victoire, 33000 Bordeaux
in front of the jury composed of
- Capucine BOIDIN-CARAVIAS - Professeure - Université Sorbonne Nouvelle PARIS 3 - Examinateur
- Cédric AUDEBERT - Directeur de recherche - CNRS - Examinateur
- Abdoulaye GUEYE - Professeur - Université d'Ottawa - School of Sociological and Anthropological Studies - Examinateur
- Michèle BAUSSANT - Directrice de recherche - CNRS - Rapporteur
- Chantal CREEN - Professeure des universités - Université Paul Valéry-Montpellier 3 - Rapporteur
- Christine CHIVALLON - Directrice de recherche - Université de Martinique - Directeur de these
- Isabelle GOBATTO - Professeure des universités - Universié de Bordeaux - CoDirecteur de these
This research offers an analysis of the relationship between the Haitian diaspora living in France and the memory of the founding act of the creation of the State of Haiti, the Saint-Domingue Revolution, carried out against the French colonial empire in the early 19th century. This proposal is based on the fact that France has long been amnesiac about its colonial slave-owning past, and more particularly about its defeat by the insurgents of Saint-Domingue, who were once enslaved in the service of its empire. Haitian immigrants and their descendants who form a diaspora in contemporary France come from most of the popular categories of Haiti forced into mass emigration to the Caribbean, North America and to a lesser extent Europe since the 1960s and 1970s, due to the dictatorship and the disastrous socio-economic conditions in Haiti.In France, while this population has gradually acquired French nationality as prospects for returning to their country of origin have dwindled, the political, economic, and social improvements hoped for in Haiti following the end of the dictatorship in 1986 have not materialized, leaving this population to face racism and discrimination. Thus, like postcolonial minorities perceived as “non-white,” Haitian immigrants and their descendants, perceived as “black,” are constantly reminded of their origins. This work shows how this exclusion from the “imagined national community” attracts the descendants of Haitian immigrants to the Saint-Domingue revolution led by their ancestors. It posits that this founding event is becoming increasingly meaningful for generations of Haitian immigrant children born in France, especially as they face a racialized existence and aspire to greater equality in contemporary French society, with memories of past events always linked to the present. He also shows that the diaspora is adopting a conciliatory stance in order to preserve the memory of the Haitian Revolution in the French context. This research is divided into three parts. The first part deals with the conditions of Haitian immigration to France, placing it within the context of the global emigration of the Haitian population to other countries, which has intensified since the second half of the 20th century, with a view to improving their living conditions. The second part presents the confrontation of Haitians and their descendants with a racialized historical condition in contemporary France. Finally, the work analyzes the Haitian diaspora's memory of the Haitian Revolution as a founding event and the appropriation of this event by the descendants of Haitian migrants in France, a country whose relationship with its colonial slave-owning past remains ambiguous, as evidenced by the preeminence of the republican abolitionist regime on the one hand, and on the other hand, the evacuation of the national memory of Saint-Domingue, the richest of the French colonies in the 18th century, separated from France by a revolution led by enslaved people demanding the opening and application of the ideal of liberty, equality, and fraternity to the colonized, particularly Africans, who were treated as inferior beings, considered to be below the threshold of humanity in the colonies.