title: Lack of Phenotypical and Morphological Evidences of Endothelial to Hematopoietic Transition in the Murine Embryonic Head during Hematopoietic Stem Cell Emergence.
abstract: During mouse ontogeny, hematopoietic cells arise from specialized endothelial cells, i.e., the hemogenic endothelium, and form clusters in the lumen of arterial vessels. Hemogenic endothelial cells have been observed in several embryonic tissues, such as the dorsal aorta, the placenta and the yolk sac. Recent work suggests that the mouse embryonic head also produces hematopoietic stem cells (HSCs)/progenitors. However, a histological basis for HSC generation in the head has not yet been determined because the hematopoietic clusters and hemogenic endothelium in the head region have not been well characterized. In this study, we used whole-mount immunostaining and 3D confocal reconstruction techniques to analyze both c-Kit+ hematopoietic clusters and Runx1+ hemogenic endothelium in the whole-head vasculature. The number of c-Kit+ hematopoietic cells was 20-fold less in the head arteries than in the dorsal aorta. In addition, apparent nascent hematopoietic cells, which are characterized by a "budding" structure and a Runx1+ hemogenic endothelium, were not observed in the head. These results suggest that head HSCs may not be or are rarely generated from the endothelium in the same manner as aortic HSCs.
authors.affiliation: Department of Hematology, Juntendo University School of Medicine, Tokyo, Japan.
authors.forename: Kazuhide
authors.initials: K
authors.lastname: Iizuka
authors.affiliation: Department of Hematology, Juntendo University School of Medicine, Tokyo, Japan.|International Research Center for Medical Sciences, Kumamoto University, Kumamoto, Japan.
authors.forename: Tomomasa
authors.initials: T
authors.lastname: Yokomizo
authors.affiliation: Department of Hematology, Juntendo University School of Medicine, Tokyo, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Watanabe
authors.affiliation: Laboratory of Stem Cell Biology, Center for Developmental Biology, RIKEN Kobe, Kobe, Japan.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Tanaka
authors.affiliation: International Research Center for Medical Sciences, Kumamoto University, Kumamoto, Japan.|Cancer Science Institute of Singapore, National University of Singapore, Singapore, Singapore.|Department of Paediatrics, National University of Singapore, Singapore, Singapore.
authors.forename: Motomi
authors.initials: M
authors.lastname: Osato
authors.affiliation: Department of Hematology, Juntendo University School of Medicine, Tokyo, Japan.
authors.forename: Tomoiku
authors.initials: T
authors.lastname: Takaku
authors.affiliation: Department of Hematology, Juntendo University School of Medicine, Tokyo, Japan.
authors.forename: Norio
authors.initials: N
authors.lastname: Komatsu
mesh_terms: D000818:Animals; D004622:Embryo, Mammalian / Q000166:cytology / Q000196:embryology; D042783:Endothelial Cells / Q000166:cytology / Q000378:metabolism; D004730:Endothelium, Vascular / Q000166:cytology / Q000196:embryology; D006257:Head / Q000196:embryology*; D006410:Hematopoiesis / Q000502:physiology*; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic