Ontogenèse de la mégacaryopoïèse humaine – Megon

This proposal has for goal to understand the ontogenic changes, which occur during human megakaryopoiesis. The background of this project is related to the fact that some oncogenic events leading to megakaryoblastic leukemia only occur on f'tal progenitors and that the thrombocytopenia of the TAR syndrome partially resumes after the first year after birth suggesting that profound changes in the regulation of megakaryocytic lineage occurs during ontogeny. A part of this project is also focused on primitive hematopoiesis where the megakaryocytic component is poorly known especially in human. Overall the project has also three major interests: 1) a better understanding of the ontogeny of the hematopoietic system which is a model system, 2) understanding if hematopoietic differentiation of ES cells reflects normal ontogeny and can be used as a cellular model in the future and 3) to characterize the role of the Notch pathway on the megakaryocytic ontogeny and fate from a bipotent erythro/megakaryocytic progenitor (MEP). The first aim of this project is to characterize the megakaryocyte phenotype changes occurring from primitive to adult hematopoiesis. To have access to the early stages of ontogeny we will use the model of human ES cell derived hematopoietic differentiation and will compare it to yolk sac and foetal liver hematopoiesis. From these different megakaryocytes we will perform gene profiling with the goal to characterize ontogenic stage specific transcription factors. If it is the case we will investigate their precise function. The second aim of the project will consist in the investigation of the emergence of the megakaryocytic lineage by characterization of the progenitor hierarchy all along ontogenesis. We will focus on the phenotypic and molecular topography of the MEP with a specific interest on primitive hematopoiesis. We will investigate the role of several candidate transcription factors such as FLI-1, AML-1, EKLF and MYB in the emergence of the MEP and on the megakaryocytic fate during ontogeny. We expect to characterize new mechanisms of the erythroid/megakaryocytic potential divergence from the MEP by means of gene and miRNA profiling during ontogeny. The third aim will consist in the investigation of the Notch pathway on megakaryocyte differentiation with three main questions: (i)- Do the different Notch ligands act similarly on megakarocyte differentiation during ontogeny '; (ii) Does the Notch pathway induce megakaryocytic fate from the MEP and (iii) what are the links between the Notch pathway and the above mentioned transcription factors ' We expect that this proposal will provide valuable tools for understanding the mechanisms of some human hemopathies.