Abstract
PU.1 (SPI1) is pivotal in hematopoiesis, yet its role in human endothelial-to-hematopoietic transition (EHT) remains unclear. Comparing human in vivo and in vitro EHT transcriptomes revealed SPI1's regulatory role. Knocking down SPI1 during in vitro EHT led to a decrease in the generation of hematopoietic progenitor cells (HPCs) and their differentiation potential. Through multi-omic analysis, we identified KLF1 and LYL1 - transcription factors specific to erythroid/myeloid and lymphoid cells, respectively - as downstream targets of SPI1. Overexpressing KLF1 or LYL1 partially rescues the SPI1 knockdown-induced reduction in HPC formation. Specifically, KLF1 overexpression restores myeloid lineage potential, while LYL1 overexpression re-establishes lymphoid lineage potential. We also observed a SPI1-LYL1 axis in the regulatory network in in vivo EHT. Taken together, our findings shed new light on the role of SPI1 in regulating lineage commitment during EHT, potentially contributing to the heterogeneity of hematopoietic stem cells (HSCs).