Cristiana Barone, G Quattrini, Alessandro Muratore, Giorgio Anselmi, Yurim Park, Naeema T. Mehmood, Elena Morganti, Roberto Orsenigo, Filipa Timóteo-Ferreira, Anna Cazzola, Arianna Patelli, Thea Milanesi, Bianca Nesti, Francisca Soares‐da‐Silva, M. Gary Nicholls, Gloria Zambelli, Mario Mauri, Silvia Bombelli, Sofia De Marco, Deborah D’Aliberti, Silvia Spinelli, Veronica Bonalume, Alison Domingues, Mahdieh Naghavi Alhosseini, Gianluca Sala, A. Colonna, Elisabetta D’Errico, Cristina D’Orlando, Cristina Bianchi, R Perego, Raffaella Meneveri, Ana Cumano, Silvia Brunelli, Marella de Bruijn, Andrea Ditadi, Alessandro Fantin, Rocco Piazza, Emanuele Azzoni
Embryonic hematopoiesis involves successive waves of progenitors from distinct anatomical sites, but the origins and contributions of early hematopoietic stem and progenitor cells (HSPCs) remain incompletely defined. Here we use genetic fate mapping in mice to temporally label hemogenic endothelium (HE) subsets and track their progeny. We show that a wave of fetal-restricted HSPCs arises from HE in the vitelline and umbilical arteries between embryonic days 8.5 and 9.5, preceding the emergence of definitive hematopoietic stem cells. Lineage tracing, single-cell transcriptomic analyses and functional assays revealed that these progenitors are transient and distinct from erythro-myeloid progenitors, contribute extensively to fetal lympho-myelopoiesis but decline postnatally. Our findings reveal a previously unrecognized early HE wave as a key source of fetal-restricted HSPCs, refining the spatial-temporal understanding of layered hematopoiesis and informing developmental origins of blood cell diversity.