title: Hematopoietic stem cell emergence in embryonic life: developmental hematology revisited.
abstract: In utero, hematopoiesis takes place initially in the extraembryonic yolk sac, then switches to the liver, thymus, and, finally, bone marrow. This chronologic sequence and the fact that all blood-forming tissues but the yolk sac sustain hematopoiesis after colonization by stem cells of external origin have led to the hypothesis that the whole prenatal and postnatal blood system is founded by yolk sac-derived stem cells. Experimental data recently obtained from bird and mouse embryo models strongly suggest, however, that definitive hematopoiesis is established from an intraembryonic source of stem cells arising in the vicinity of the developing aorta. In agreement, an abundant population of CD34+ primitive hematopoietic cells has been identified in the equivalent area of the human embryo. These novel findings will contribute to our understanding of blood cell homeostasis and may help to further develop therapeutic protocols making use of fetal hematopoietic cells transplanted in utero or in postnatal life.
authors.affiliation: Institut d'Embryologie Cellulaire et Moléculaire du CNRS et du Collège de France, Nogent-sur-Marne, France.
authors.forename: B
authors.initials: B
authors.lastname: Péault
mesh_terms: D000818:Animals; D018952:Antigens, CD34 / Q000032:analysis; D001001:Anura / Q000196:embryology; D001011:Aorta / Q000196:embryology; D001853:Bone Marrow / Q000196:embryology; D019070:Cell Lineage; D002465:Cell Movement; D002642:Chick Embryo; D002678:Chimera; D003370:Coturnix / Q000196:embryology; D005314:Embryonic and Fetal Development; D005312:Fetal Blood / Q000166:cytology; D016332:Fetal Tissue Transplantation; D005865:Gestational Age; D006410:Hematopoiesis; D018380:Hematopoietic Stem Cell Transplantation; D006412:Hematopoietic Stem Cells / Q000166:cytology; D006413:Hematopoietic System / Q000196:embryology*; D006801:Humans; D008099:Liver / Q000196:embryology; D051379:Mice; D016513:Mice, SCID; D013045:Species Specificity; D013950:Thymus Gland / Q000196:embryology; D014183:Transplantation, Heterologous; D014714:Vertebrates / Q000196:embryology; D015017:Yolk Sac / Q000166:cytology / Q000502:physiology
chemical_list: D018952:Antigens, CD34