M/F-PhD Deciphering the cellular and molecular mechanisms of the Cnidarian-Dinoflagellate symbiosis...

IRCAN (Institut de Recherche sur le Cancer et le vieillissement de Nice) is a thematic laboratory aiming to understand the links between ageing and cancer by developing a continuum of research, ranging from fundamental to applied approaches. The IRCAN was created on 1 January 2012, it is located at the Faculty of Medicine of the Université Côte d'Azur and is associated with the Institut National de la Santé et de la Recherche Médicale (Inserm), and the Centre National de la Recherche Scientifique (CNRS).
The projects carried out at the IRCAN involve many disciplines, including biochemistry, molecular and cellular biology, fundamental and medical genetics, epigenetics, genomics, immunology, metabolism, pharmacology and neurology, geriatrics and oncology, and benefit from the use of a variety of classical and emerging biomedical research models (cell cultures, reconstituted tissue/organoids, yeast, corals and sea anemones, fish, rodents) as well as clinical studies.
Our Stress-response, Regeneration & Longevity research team uses Cnidarians as a model for studying marine organisms. Indeed, Cnidarians (sea anemones, corals and jellyfish) present interesting and intriguing biological characteristics: extreme regeneration capacity, ability to resist extreme conditions (considered in humans as pro-ageing) such as exposure to free radicals. Moreover, this extreme regeneration potential, this impressive resistance to ROS and their phenotypic plasticity allowing them to adapt to drastic environmental variations are accompanied by a prolonged lifespan/immortality in many of these marine animals.
One of our main themes is therefore to understand the cellular, molecular and genetic bases of adaptation to life in symbiosis and of the response to stress in a symbiotic Cnidaria thanks to an innovative cell culture model developed by our team. More specifically, based on our in vitro model, we wish to develop an in vitro symbiosis system.

Context and Objectives: Interactions between different organisms can range from symbiosis to parasitism to predation. Symbiosis between two organisms can be seen as a key factor in evolution to acquire new properties (symbiogenesis) or to colonise new habitats that would not be viable or accessible for one of these organisms alone. One of the best examples is the coral reef ecosystem, which contains 1/3 of marine biodiversity on less than 0.2% of the ocean substrate. The rich biodiversity of species present in this ecosystem is partly due to the symbiotic association of Cnidarians (corals, sea anemones, gorgonians) with microalgae, photosynthetic Dinoflagellates of the Symbiodiniaceae family. This symbiosis is an intracellular endosymbiosis: the symbionts residing within the cells of the gastrodermal tissue of the animal host. This intimate relationship therefore requires a constant molecular dialogue between the animal host and its symbiont from the recognition stage to the maintenance stage and up to the breakdown of the symbiosis induced by environmental disturbances (a phenomenon called bleaching).
Recognition between the host and the symbiont is a key step in the symbiosis. However, the mechanisms and recognition molecules involved in this symbiont selection system remain to be defined. Even if certain studies tend to show the importance of the presence of antigenic determinants on the surface of symbionts, nothing is known to date about the attractiveness of the two partners in this symbiosis.
The thesis project is part of an ANR project (CES20-COUP de FOUDRE), which brings together 4 teams with complementary expertise ranging from sequencing to chemistry and host-symbiont interactions. The objective is to decipher the molecular and cellular mechanisms involved in the attractiveness and recognition of Cnidaria/Dinoflagellates by means of an innovative and original approach in these organisms: cell culture. The thesis project will focus on: i) determining the respective roles of the symbiotic partners in the attraction stage using chemoattraction tests and exometabolome analysis; ii) characterising the molecules and signalling pathways involved in partner recognition using genetic engineering; iii) studying the impact of environmental disturbances (linked to global change) on the establishment of symbiosis, and the resulting cellular and molecular alterations. This project is part of the stress response axis of Dr Eric Röttinger's "Stress Response, Regeneration and Longevity" team at IRCAN.
Methodology: The experiments will be carried out using primo-cultures from a symbiotic Cnidaria, the sea anemone Anemonia viridis, as well as cultures of the symbiotic Dinoflagellate isolated from this sea anemone.
Chemoattraction experiments will be carried out by setting up co-cultures of the partners of the Cnidaria-Dinoflagellate symbiosis. The characterisation of the molecules involved in the attraction and recognition processes, and of the exometabolome, will be carried out in collaboration with the other project partners.
The characterisation of the molecules involved in the recognition of symbiosis partners is based on the modification of the expression (i.e. overexpression or inactivation) of candidate genes in a stable or transient manner using two strategies: transfection (lipofection, magnetofection) or genome editing (TALEN, Crispr/Cas9).
The evaluation of the impact of global change on the establishment of the symbiosis is based on the measurement of the behaviour (i.e. growth, attraction, etc.) and cellular and molecular analyses of the cultures and co-cultures of the symbiosis partners, subjected to different stresses such as increased temperature or increased UV radiation.
Expected results: The results obtained in the framework of this thesis project should enable us to characterise the molecules and signalling pathways required for the establishment of the Cnidaria-Dinoflagellate symbiosis and to define their modifications and the consequences induced in the presence of environmental perturbations.
Candidate profile: We are looking for a motivated, curious person who enjoys teamwork and the exchange of ideas. This person should have a good knowledge of marine biology as well as skills in cell biology (cell culture) and molecular biology (cloning, transfections). Knowledge of the marine environment and symbiotic interactions will also be highly valued. This project will also require the PhD student to develop and optimise methodologies (transfection, genome editing).