Gata2 in Hematopoietic Cell Generation

The mammalian hematopoietic system is maintained by hematopoietic stem cells (HSC). Whereas in the adult, they reside in the bone marrow, the first HSCs are generated in the main vasculature of the midgestation embryo as a result of tightly regulated extrinsic and intrinsic molecular signals. Transcriptional regulation is pivotal to the establishment of HSC fate during development and the Gata2 transcription factor is central to this process. Genetic deletion of Gata2 shows that it is essential for the embryonic generation of HSCs, hematopoietic progenitor cells (HPC), and also for the establishment of some mature blood lineages, such as mast cells. Although previous studies with HPC/HSC enriched populations indicate the importance of Gata2 in their generation, there has been no direct way for studying Gata2-expressing cells in normal embryonic development, and in in vitro hematopoietic differentiation assays. In this thesis research, I use a novel Gata2Venus reporter embryonic stem cell (ESC) system and mouse model to dissect the role of Gata2 in hematopoietic differentiation and development. I show that Venus expression discriminates progressive stages of hematopoietic cell generation in vitro that are highly analogous to the in vivo waves of hematopoietic cell generation. My results demonstrate the involvement of the Gata2 downstream target, Gpr56 (a putative HSC regulator), in the development of HPCs, and reveal the redundant expression and function of Gpr56 with another G-protein coupled receptor, Gpr97. This redundancy may explain the previous contradictory data in the field regarding the requirement for Gpr56 in HSCs, and opens the way for new strategies to delineate the role of Gpr56 in HSC emergence. In addition to HSCs and HPCs, the mast cell lineage is one of the few mature blood cell types that expresses Gata2. Taking advantage of the Gata2Venus ESC reporter line and human induced pluripotent stem cell (iPSC) lines, I found a novel and powerful approach to rapidly generate mast cells for inflammation and allergy research applications. This thesis research has furthered our understanding of the role of Gata2 in in vivo embryonic development, and in in vitro pluripotent stem cell hematopoietic differentiation approaches, providing the basis for the development of future therapeutic strategies in blood and inflammation research.