Development 126, 793-803 (1999) 793 Printed in Great Britain © The Company of Biologists Limited 1999 DEV2372 Emergence of intraembryonic hematopoietic precursors in the pre-liver human embryo Manuela Tavian*, Marie-France Hallais and Bruno Péault Institut d’Embryologie Cellulaire et Moléculaire du CNRS, UPR 9064, 49bis avenue de la Belle Gabrielle, 94736 Nogent-sur-Marne Cedex, France *Author for correspondence (e-mail:
[email protected]) Accepted 3 December 1998; published on WWW 20 January 1999 SUMMARY Hepatic hematopoiesis in the mouse embryo is preceded by arteries and embryonic liver from 21 to 58 days of two hematopoietic waves, one in the yolk sac, and the other development. The chronology of blood precursor cell in the paraaortic splanchnopleura, the presumptive aorta- emergence in these distinct tissues suggests a pivotal role in gonad-mesonephros region that gives rise to prenatal and the settlement of liver hematopoiesis of endothelium- postnatal blood stem cells. An homologous intraembryonic associated stem cell clusters, which emerge not only in the site of stem cell emergence was previously identified at 5 dorsal aorta but also in the vitelline artery. Anatomic weeks of human gestation, when hundreds of CD34++ Lin− features and in vitro functionality indicate that stem cells high-proliferative potential hematopoietic cells border the develop intrinsically to embryonic artery walls from a aortic endothelium in the preumbilical region. In the presumptive territory whose blood-forming potential exists present study, we have combined immunohistochemistry, from at least 24 days of gestation. semithin section histology, fluorescence-activated cell sorting and blood cell culture in an integrated study of Key words: Hematopoietic stem cell, Hematopoiesis, Human, Yolk incipient hematopoiesis in the human yolk sac, truncal sac, Liver INTRODUCTION ventral mesoderm, a YS equivalent, is transitory and does not supply the adult with full hematopoietic potential.