Résultats de recherche

Deux chercheurs du Département de physique de l’UNamur, le professeur Michaël Lobet et son doctorant Adrien Debacq, s’intéressent de près à un sujet qui fascine la communauté scientifique : celui de la superradiance dans les milieux à indice de réfraction proche de zéro. Dans un article publié cet été dans la prestigieuse revue Light : science & applications du groupe Nature, en collaboration avec l’Université de Harvard (USA), la Michigan Technological University (MTU) et Sparrow Quantum, ils contribuent ainsi aux développements de l’informatique quantique.

Abstract The distribution of malaria in Sub-Saharan Africa is becoming increasingly heterogeneous, with emerging hotspots and a growing urban burden rather than following traditional vector suitability gradients. This pattern has been observed in Senegal, where malaria transmission ranges from very low to high. In this context, disease risk maps can help to identify hotspots and improve the targeting of interventions. However, previous studies have often relied on freely available, low-resolution remote sensing data and focused primarily on environmental factors related to vector presence—the hazard—while overlooking population vulnerability (e.g. influenced by access to healthcare). This thesis presents an open-source malaria risk mapping framework incorporating high-resolution, open-access data on both hazard and vulnerability, and identifies the key factors sustaining transmission in Senegal.Interpolated surfaces of vulnerability indicators were integrated with Sentinel-based hazard variables to model survey-based malaria prevalence, used as an indicator of risk. The framework was then extended to model malaria incidence from routine health facility data, using dasymetric disaggregation to create fine-scale incidence maps. The findings reveal that vulnerability is a key determinant of malaria and that both hazard and vulnerability risk factors vary with urbanisation level, transmission intensity, seasonality and spatial scale. Discrepancies emerged between malaria prevalence and incidence, such as low incidence but high prevalence in remote areas, suggesting potential underdiagnosis. This thesis also offers a comparative overview of various modelling approaches, ranging from machine learning to Bayesian geostatistics, with implementation code and guidance for future malaria research. Anticipated improvements in malaria epidemiological data will further enable elimination strategies to leverage the full potential of geospatial methods for fine-scale risk mapping. Composition du Jury Prof. Sabine HENRY (UNamur), PrésidenteProf. Catherine LINARD (UNamur), SecrétaireDr Ibrahima DIA (Institut Pasteur de Dakar)Dr Annelise TRAN (CIRAD, Montpellier)Prof. Christel FAES (Université de Hasselt)

Des bottes en caoutchouc, des bleus de travail, le bêlement des brebis, l’odeur de la paille… Le décor est planté. À la ferme du Centre de Recherche Ovine, située dans la campagne namuroise, les étudiants en médecine vétérinaire vivent, l’espace de quelques jours, au rythme des naissances des agneaux. Une expérience intense et formatrice, remplie de gestes techniques et d’émotions, encadrée par une équipe composée d'une vétérinaire, d'un professeur et de trois techniciens de l'Université de Namur.

Abstract Primarily described as an alarmone, secondary messenger (p)ppGpp, when accumulated, binds to many targets involved in DNA replication, translation, and transcription. In the asymmetrically-dividing a-proteobacterium Caulobacter crescentus, (p)ppGpp has been shown to strongly impact cell cycle progression and differentiation, promoting the non-replicating G1/swarmer phase. Mutations in the major subunits of transcriptional complex, b or b’ subunits, were able to display the (p)ppGpp-related phenotypes even in the absence of the alarmone. We identified that the transcriptional holo-enzyme, RNA polymerase (RNAP) is a primary target of (p)ppGpp in C. crescentus. Furthermore, mutations that inactivate (p)ppGpp binding to RNAP annihilated the (p)ppGpp-related phenotypes and phenocopied a (p)ppGpp0 strain. Our RNAseq analysis further elucidated the changes in the transcriptional landscape of C. crescentus cells displaying different (p)ppGpp levels and expressing RNAP mutants. Since the DNA replication initiation protein DnaA is required to exit the G1 phase, we observed that it was significantly less abundant in cells accumulating (p)ppGpp. We further explored its proteolysis under the influence of (p)ppGpp. Our work suggests that (p)ppGpp regulates cell cycle and differentiation in C. crescentus by reprogramming transcription and triggering proteolytic degradation of key cell cycle regulators by yet unknown mechanisms. In Part II, we identified two σ factors belonging to the ECF family that might be involved in this (p)ppGpp-accompanied phenotypes. In Part III, we propose an overlapping role of the ω subunit, RpoZ, and the heat shock subunit, RpoH, in carbon metabolism.JuryProf. Gipsi LIMA MENDEZ (UNamur), PresidentProf Régis HALLEZ (UNamur), SecretaryDr Emanuele BIONDI (CNRS-Université Paris-Saclay)Prof. Justine COLLIER (University of Lausanne)Dr Marie DELABY (Université de Montréal)

Abstract Estrogens originating from human and animal excretion, as well as from anthropogenic sources such as cosmetics, plastics, pesticides, detergents, and pharmaceuticals, are among the most concerning endocrine-disrupting compounds in aquatic environments due to their potent estrogenic activity. While their effects on fish reproduction are well documented, their impact on development, particularly metamorphosis, remains poorly studied. This hormonal transition, mainly controlled by the thyroid axis, is essential for the shift from the larval to the juvenile stage in teleosts.The effects of two contraceptive estrogens on zebrafish (Danio rerio) metamorphosis were evaluated: 17α-ethinylestradiol (EE2), a synthetic reference estrogen, and estetrol (E4), a natural estrogen recently introduced in a new combined oral contraceptive formulation. Continuous exposure from fertilization to the end of metamorphosis allowed the assessment of morphological changes, disruptions of the thyroid axis, and modifications of additional molecular pathways potentially involved in metamorphic regulation.EE2 induced significant delays and disturbances in metamorphosis, affecting both internal and external morphological traits, confirming its role as an endocrine disruptor of concern. In contrast, E4 did not cause any detectable morphological alterations even at concentrations far exceeding those expected in the environment, indicating a limited ecotoxicological risk. Molecular analyses showed that EE2 strongly affected thyroid signaling and energy metabolism during metamorphosis, whereas E4 induced only minor transcriptional and proteomic changes.This study provides the first evidence that EE2 can disrupt zebrafish metamorphosis and highlights the importance of including this developmental stage in ecotoxicological assessments. The results also suggest a larger environmental safety margin for E4, although further research is needed to clarify the mechanisms linking estrogen exposure to metamorphic regulation.JuryProf. Frederik DE LAENDER (UNamur), PrésidentProf. Patrick KESTEMONT (UNamur), SecrétaireDr Sébastien BAEKELANDT (UNamur)Dr Valérie CORNET (UNamur)Prof. Jean-Baptiste FINI (Muséum National d’Histoire Naturelle de Paris)Dr Marc MULLER (ULiège)Prof. Veerle DARRAS (KULeuven) 

AbstractThe Simbu serogroup, part of the Peribunyaviridae family, includes arboviruses associated with febrile disease and fetal congenital malformations due to viral neurotropism. These viruses possess a tripartite, negative-sense RNA genome that lacks the poly(A) tail. Notably, the 3' non-translated region of the small (S) genomic segment contains conserved RNA elements, including a stem loop (SL) structure and a sequence-based motif (GC signal) flanking the termination site for messenger RNA (mRNA) synthesis. Although their functions remain unclear, their conservation and specific positions suggest a potential role in mRNA transcription termination and translation initiation. A reverse genetics system for Schmallenberg virus (SBV), a ruminant pathogen, was used to generate a viral recombinant library bearing deliberate mutations. The replication kinetics, S segment transcription termination profile, and nucleoprotein (N) abundance were evaluated in mammalian and insect cell lines. At the same time, the virulence was assessed in an immunocompetent mouse model. Characterization of the mutant viruses indicated that the SL structure is essential for viral production, with the stem length being a key feature; at least five complementary base pairs are necessary between the stem arms. A shorter stem length impaired replicative fitness, N protein abundance, and altered the mRNA to complementary RNA ratio. Point mutations in the GC signal disrupted proper mRNA termination, thereby limiting viral N protein synthesis and, thus, virion assembly. In vivo, attenuated viruses resulted in lower viral loads, reduced neuroinvasion, and improved survival rates compared to the wild type SBV. The GC signal mutants exhibited strong attenuation while still maintaining active transcription. Overall, these findings indicate that the SL and GC signal serve as cis-regulatory elements and are indirect determinants of SBV virulence, regulating viral replication and neuropathogenesis.JuryProf. Patsy RENARD (UNamur), PrésidenteDr Damien COUPEAU (UNamur) SecrétaireProf. Damien VITOUR (Ecole Vétérinaire de Maisons-Alfort)Prof. Ludovic MARTINELLE (ULiège)Prof. Lionel TAFFOREAU (UMons)Prof. Charles NICAISE (UNamur)Prof. Benoît MUYLKENS (UNamur)