UC San Diego

Hematopoietic stem cells (HSCs) are a specialized cell population capable of self-renewal and differentiation into various lineages of the vertebrate blood system. In vertebrates, Notch signaling has been implicated to contribute to hematopoiesis through arterial specification and sclerotome formation. The involvement of several Notch ligands such as Delta-like ligand 4 (dll4), DeltaC (dlc), and Jagged 1a (jag1a) have been identified in regulating hematopoietic stem cell and progenitor cell (HSPC) development and differentiation. Using the zebrafish as a model, this study aimed to elucidate the roles of Notch ligands DeltaA (dla), DeltaB (dlb), and Jagged1b (jag1b) in the context of HSC development, which have not yet been studied extensively. To minimize the concern of transcriptional adaptation in indel mutants, we utilized a CRISPR/Cas9 system to successfully generate dla, dlb, and jag1b knockout mutants for loss-of-function (LOF) studies. Phenotypic analyses suggested that loss of dla alone does not significantly impair HSC development. Interestingly, jag1b mutants and dlb promoter-less mutants did not display a significant reduction of HSCs. In contrast, jag1b and dlb morphants exhibited a notable decrease in HSC numbers, necessitating the use of multiple LOF models to validate our findings. The results from this detailed approach will establish the foundation for further research to unravel the precise mechanisms governing hematopoiesis. This advancement will bring us one step closer to translating these in vivo findings to the engineering of HSCs in vitro, a currently unattainable feat.