Whole-transcriptome analysis of endothelial-to-hematopoietic stem cell transition. Mus musculus

Hematopoietic stem cells (HSCs) are generated via a natural transdifferentiation process known as endothelial-to-hematopoietic cell transition (EHT). Due to small numbers of embryonal arterial cells undergoing EHT and the paucity of markers to enrich for hemogenic endothelial cells, the genetic program driving HSC emergence is largely unknown. Here, we use a highly sensitive RNAseq method to examine the whole transcriptome of small numbers of enriched aortic HSCs, hemogenic endothelial cells and endothelial cells. Gpr56, a G-coupled protein receptor, is one of the most highly upregulated of the 530 differentially expressed genes. Also, highly upregulated are hematopoietic transcription factors, including the ‘heptad’ complex of factors. We show that Gpr56 (mouse and human) is a target of the heptad complex and is required for hematopoietic cluster formation during EHT. Our results identify the processes and regulators involved in EHT and reveal the surprising requirement for Gpr56 in generating the first HSCs.