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PDF, English - main document Download (5MB) | Lizenz: An Investigation of the role of the microenvironment in haematopoiesis and T cell development by Jolly, Adrien underlies the terms of Creative Commons Attribution 4.0

Abstract

The microenvironment is essential to the development of blood cells. Hematopoietic progenitors receive stimuli from neighbouring cells in the form of secreted cytokines or direct contacts via adhesion molecules. These signals regulate the proliferation and differentiation of the developing cells. In this work, we study interactions between haematopoetic progenitors and their microenvironment from different angles and in different biological systems. We first develop a method to identify candidate ligands-receptors interactions based on transcriptomic data, and using this method, we recover known interactions and predict new candidate interactions between hematopoietic stem and progenitor cells and their niche in the bone marrow. Our analysis notably emphasizes the unique role of mesenchymal stem cells and endothelial cells and further reveals that a niche cell population expressing a certain ligand often expresses its antagonist. This finding suggests a dynamic regulation of HSPCs by the niche. We then undertake to characterize quantitatively cell proliferation, a feature which can be regulated by the microenvironment in vivo. We develop a method to determine the length of each cell cycle phase as well as the relative size of the quiescent fraction. We show that our method, which combines a short pulse-chase experiment with EdU, a thymidin analogue, and mathematical modeling, can accurately determine the cell cycle length of a cancer cell line (Tet21N). We apply our method to double positive thymocytes and establish that most cells from this population are quiescent but that a small fraction of these cells is highly proliferative with a mean cell cycle length of 9h, half the time of the Tet21N. In a final part, we study T cell development in the thymus. We study how the murine thymus, an organ which normally depends on influx from bone marrow progenitor can become self sufficient when transplanted in a mouse which does not produce competent bone marrow progenitors. We show that in this context where resident thymocytes do not have to compete for Il-7with incoming 3 progenitors, a specific population, the double negative 3 (DN3), can self-renew despite receiving the preTCR signal which normally drives their differentiation. We further show that the longer dwelling time of these DN3 progenitors permits their differentiation into γ δ T cells which is normally precluded by the preTCR signal. We show how the limited resources available in the thymus and the flow of incoming progenitor shape the cellular response to the preTCR signal and thereby directly influence the fate of the DN3.