Characterization of Early Hematopoietic Stem and Progenitor Cell Formation, Maturation, and Function

Hemogenic endothelial (HE) cells are a unique subset of vascular endothelial cells endowed with the capacity to generate hematopoietic stem and progenitor cells (HSPCs) through a process called endothelial-to-hematopoietic transition (EHT). This process results in the formation of sizeable HSPC clusters attached to the endothelial wall. While the existence of HE cells is well known, the multi-step process of HSPC cluster formation and maturation following EHT have not been characterized. The dorsal aorta is a well-established hemogenic vascular bed that harbors HSPCs termed intra-aortic hematopoietic clusters (IAHCs). In order to characterize HSPC cluster formation and maturation, I sought to visualize the formation of IAHCs in the dorsal aorta through live-imaging, and to evaluate their cell cycle and proliferation, and their molecular signatures from their initial appearance (E10.5) to the point when cluster cells are capable of adult engraftment (E11.5). I uncovered the dynamic behavior of IAHCs and the appearance of transient filopodial structures, their polyclonal origin of formation, and their distinct temporal molecular signature with differing cell cycle, migration, and cell signaling attributes. In addition, I found that genes of the complement cascade are highly enriched in later IAHCs (E11.5), possibly delineating a new role for this pathway in their maturation and function