Comparative vertebrate neural crest contribution to the hematopoietic stem cell specification niche

About This Grant

Project Summary Hematopoietic stem cells (HSCs) sustain blood production throughout an organism’s lifetime. They are clinically significant as the key therapeutic component of bone marrow transplants for treating a multitude of hematological and non-hematological disorders. However, HSC transplantation is limited by scarcity of compatible donors. Despite significant efforts, generating large numbers of bona fide HSCs in vitro from induced pluripotent stem cells (iPSCs) remains a major challenge. This inability likely stems from an incomplete understanding of the developmental cues necessary for HSC specification. In vertebrate embryos, HSCs are specified from hemogenic endothelium lining the ventral wall of the dorsal aorta (DA) and require signals from the surrounding microenvironment. Previous work in our laboratory demonstrated that neural crest cells (NCC) migrate to the DA and direct HSCs specification in zebrafish via locally secreted or displayed signals. NCCs of the trunk differentiate into sympathetic neurons, which secrete catecholamines. In mice, catecholamines are required for HSC maturation. However, inhibition of catecholamine production in zebrafish did not affect HSC specification, pointing to the idea that an earlier phase of HSC specification directed by NCCs is independent of catecholamines. Although HSC programming is highly conserved across vertebrates, the requirement for NCCs in specifying HSCs has not yet been examined in mouse, and the cues provided by NCCs for HSC specification remain elusive. My preliminary data in mouse reveal that NCCs migrate into proximity of the DA during the HSC specification window and are found closely associated with nascent HSCs locating them at the right time and place to provide inductive signals for HSC specification. Interestingly, preliminary data in mouse and zebrafish show that NCCs do not contact the DA directly, except via filopodial extensions. To determine whether NCCs mediate HSC specification in mouse, I will map the association of migrating NCCs to the DA and emerging NCCs by lineage tracing and specifically ablate NCCs before they reach the DA with an inducible diphtheria toxin receptor mouse model. Finally, I will determine if NCCs mediate HSC specification through filopodial communication with the DA by generating a novel optogenetic zebrafish line permitting tissue specific knock out of Myosin X, required for filopodia formation and maintenance, in living animals and visualize any loss of HSCs using advanced live imaging technology.