Analyse cellulaire des gènes impliqués dans la reprogrammation épithélio-neuronale chez C. Elegans

Cellular analysis of genes involved in an epithelial-neuronal reprogramming in C. Elegans

• Auteur / Autrice : Jai Prakash Richard
• Direction : Sophie Jarriault
• Type : Thèse de doctorat
• Discipline(s) : Biologie du développement
• Date : Soutenance en 2009
• Etablissement(s) : Strasbourg

Mots clés

Mots clés contrôlés

Caenorhabditis elegans

Thérapeutique cellulaire

Cellules épithéliales

Détermination cellulaire

Résumé

La reprogrammation cellulaire se définit comme la conversion d’une cellule différenciée en un autre type de cellule différenciée, en altérant le profil d’expression des gènes d’une cellule (1,2,3,4). Ce processus de reprogrammation peut résulter en la conversion d’une cellule différenciée vers un état pluripotent ou progéniteur (ou dédifférenciation). Un autre type de reprogrammation consiste en la conversion d’une cellule différenciée en un autre type de cellule différenciée, un processus appelé transdifférenciation. Bien que des exemples de reprogrammation cellulaire soient connus, les mécanismes exacts par lesquels une cellule d’un type particulier peut changer d’identité sont toujours peu compris. De plus, l’analyse d’un tel phénomène chez les organismes multicellulaires est compliquée par l’impossibilité d’identifier et de suivre in vivo la reprogrammation d’une cellule donnée, ainsi que d’implémenter des approches systématiques et non biaisées.

Cellular reprogramming is defined as the ability of a cell to change its identity. Various examples of cellular reprogramming like reprogramming of a nucleus (dedifferentiation), reprogramming of a committed cell (transdetermination) or that of a differentiated cell (trans‐differentiation) have been described. Even though extensive work has been performed for the past two decades the exact mechanism by which a cell changes its identity is not clearly understood. Understanding the molecular and cellular mechanisms involved in reprogramming cells will not only provide a comprehensive knowledge about normal development but also about pathological processes like cancer. It will also help to generate cell‐based therapies for debilitating diseases like diabetes, Parkinson’s disease etc in regenerative medicine and to develop diagnostic tools for the early detection of cancer. This research project uses the powerful genetics of C. Elegans to dissect the process and identify molecular players at a single cell level. In C. Elegans, during the 2nd larval developmental stage, one cell named ‘Y’, a differentiated epithelial cell of the rectum, migrates anteriorly and becomes a motor neuron ‘PDA’ which has a characteristic axon emanating from the cell body. Simultaneously, another neighbouring cell named ‘P12. Pa’ takes the position of Y in the rectum. This process happens in the absence of cell division. To identify players involved in the process a forward genetic screen by EMS mutagenesis was performed to isolate mutants that are affected at various steps of trans‐differentiation. One of the mutants, “fp8”, obtained is found to be a new allele of unc3, the sole COE (Collier‐Olfactory‐Early B cell factor) transcription factor in C. Elegans that is widely conserved among species. An elaborate analysis of unc3( 0) mutant shows that the “Y” cell that fails to trans‐differentiate into “PDA” is exhibiting neither epithelial nor neuronal characteristics and is blocked in an intermediate state suggesting that the transition of epithelial‐to‐neuronal identity proceeds through intermediary cellular steps and not by concomitant expression of epithelial and neuronal characteristics. This study will shed light on the factors that are used in a physiological process to reprogram a cell and will likely contribute to better understanding of developmental process and improve reprogramming strategies in regenerative medicine.