Cohesion and Inversion in C. Flexa, The Closest

il y a 2 semaines

Paris Panthéon, Île-de-France CNRS Temps plein
Cette offre est disponible dans les langues suivantes:

- Français
- Anglais

Date Limite Candidature : mercredi 24 avril 2024

**Informations générales**:
**Intitulé de l'offre **:Cohésion et Inversion chez C. flexa, le plus proche cousin des animaux (H/F)**
Référence : UMR7190-JULPIE-001
Nombre de Postes : 1
Lieu de travail : PARIS 05
Date de publication : mercredi 3 avril 2024
Type de contrat : CDD Doctorant/Contrat doctoral
Durée du contrat : 36 mois
Date de début de la thèse : 1 octobre 2024
Quotité de travail : Temps complet
Rémunération : La rémunération est d'un minimum de 2135,00 € mensuel
Section(s) CN : Ingénierie des matériaux et des structures, mécanique des solides, biomécanique, acoustique

**Description du sujet de thèse**:

- 1) Contexte scientifique:

- La multicellularité est apparue plusieurs fois au cours de l'évolution dans les milieux marins. En particulier, les choanoflagellés sont des micro-organismes unicellulaires qui peuvent s'organiser en colonies. Ce sont aussi les plus proches cousins des animaux et leur étude apporte un éclairage sur l'évolution vers la multicellularité : l'humanité trouve le récit de ses origines chez les choanoflagellés.
- Choanoeca flexa est une espèce de choanoflagellés découverte en 2019 seulement, et sa caractérisation mécanique reste à faire. Comme toutes les choanoflagellés, les cellules de C. flexa présentent un flagelle qui crée des écoulements propulsifs, et une collerette qui filtre l'eau et capture des bactéries pour nourrir la cellule. Certaines espèces de choanoflagellés forment des colonies en rosette : les cellules sont attachées par une matrice extra-cellulaire, les flagelles pointant dans toutes les directions vers l'extérieur. C. flexa forme aussi des colonies, mais l'adhésion se fait au niveau des collerettes, sans matrice extra-cellulaire. Les cellules sont organisées en monocouche avec tous les flagelles du même côté. Cette couche de cellule a une courbure naturelle, imposée par l'angle d'ouverture des collerettes. En configuration 'relaxée', les flagelles sont à l'intérieur de la demi-sphère et génèrent un flux qui permet aux cellules de se nourrir, tandis qu'en configuration 'active', les flagelles sont à l'extérieur de la demi-sphère et la colonie nage. Les colonies de C. flexa ont la propriété absolument remarquable de s'inverser : la colonie entière s'ouvre et se ferme dans une sorte de gastrulation réversible.
- 2) Objectifs de la thèse : C. flexa a été découverte dans des flaques sur la côte de Curaçao : ces choanoflagellés évoluent dans un environnement transient, alimenté par les vagues et soumis à l'évaporation,où elles sont menacées par de nombreux prédateurs. La transition à la multicellularité a de multiples bénéfices, comme se nourrir plus efficacement, mieux se défendre, diminuer le coût énergétique d'un déplacement. Quels sont les avantages de la multicellularité chez C. flexa ?
- La thèse expérimentale s'organisera selon trois axes : tout d'abord, comment les colonies se forment-elles ? En particulier, nous modéliserons la force d'adhésion entre les cellules, qui ne secrètent pas de matrice extracellulaire pour maintenir la colonie. Ensuite, comment les colonies s'inversent-elles ? Nous étudierons la force fournie par une cellule lors de l'ouverture de sa collerette, et explorerons le rôle hydrodynamique des flagelles. Enfin, quelle est la dynamique d'inversion ? Nous quantifierons les facteurs environnementaux qui déclenchent l'inversion, et nous modéliserons la stabilité de la configuration 'active' avant qu'elle ne relaxe. Ces résultats démontreront l'avantage évolutif de former des colonies.
- 3) Compétence/connaissances:
- compétence solide en hydrodynamique
- compétence solide en bio-physique
- Avoir déjà manipuler des micro-organismes
- anglais courant

**Contexte de travail**:
L'Institut Jean Le Rond d'Alembert ( 'Alembert) est un laboratoire de recherche dont la vocation est d'étendre le champ des connaissances dans tous les domaines de la Mécanique, de l'Acoustique et de l'Energétique. 'Alembert est une Unité Mixte de Recherche de la Faculté des Sciences et d'Ingénierie de Sorbonne Université (ex UPMC- Université Pierre et Marie Curie) et du CNRS (UMR7190), également soutenue par le Ministère de la Culture. Rassemblant près de cent soixante dix personnes, dont environ quatre vingt permanents, environ soixante-dix doctorants et une vingtaine de personnels temporaires, ATER, post docs ou autres, il constitue le laboratoire de recherche le plus important d'Île-de-France par la taille dans son domaine d'activité.

**Contraintes et risques**:
Risques chimiques et biologiques inhérents au travail expérimental avec des organismes biologiques.

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