Early dynamic fate changes in haemogenic endothelium characterized at the single-cell level.
Swiers G., Baumann C., O'Rourke J., Giannoulatou E., Taylor S., Joshi A., Moignard V., Pina C., Bee T., Kokkaliaris KD., Yoshimoto M., Yoder MC., Frampton J., Schroeder T., Enver T., Göttgens B., de Bruijn MFTR.
Haematopoietic stem cells (HSCs) are the founding cells of the adult haematopoietic system, born during ontogeny from a specialized subset of endothelium, the haemogenic endothelium (HE) via an endothelial-to-haematopoietic transition (EHT). Although recently imaged in real time, the underlying mechanism of EHT is still poorly understood. We have generated a Runx1 +23 enhancer-reporter transgenic mouse (23GFP) for the prospective isolation of HE throughout embryonic development. Here we perform functional analysis of over 1,800 and transcriptional analysis of 268 single 23GFP(+) HE cells to explore the onset of EHT at the single-cell level. We show that initiation of the haematopoietic programme occurs in cells still embedded in the endothelial layer, and is accompanied by a previously unrecognized early loss of endothelial potential before HSCs emerge. Our data therefore provide important insights on the timeline of early haematopoietic commitment.