title: Primitive erythropoiesis and megakaryopoiesis in the yolk sac are independent of c-myb.
abstract: Hematopoiesis initiates within the yolk sac of mammalian embryos in overlapping primitive and definitive waves, each containing erythroid and megakaryocyte progenitors. c-myb-null mouse fetuses lack definitive erythrocytes but contain primitive erythroblasts and hepatic megakaryocytes. However, it is unclear if c-myb-null embryos harbor definitive erythroid or any megakaryocyte progenitors. We determined that c-myb was not expressed in primitive erythroid precursors and that c-myb-null embryos had normal primitive erythroid and megakaryocyte progenitor numbers and kinetics between embryonic day (E) 7.0 and E9.0. While primitive hematopoiesis is c-myb-independent, no definitive erythroid potential was detected in c-myb-null embryos, confirming that definitive erythropoiesis, beginning at E8.25 in the yolk sac, is completely c-myb-dependent. In contrast, reduced numbers of megakaryocyte progenitors with restricted proliferative capacity persist in E10.5 yolk sac and E11.5 liver. Despite this impaired megakaryocyte potential, c-myb-null fetuses had normal platelet numbers at E12.5 but became thrombocytopenic by E15.5, suggesting that c-myb is required for sustained thrombopoiesis.
authors.affiliation: Center for Pediatric Biomedical Research, Department of Pediatrics, University of Rochester Medical Center, Rochester, NY 14642, USA.
authors.forename: Joanna
authors.initials: J
authors.lastname: Tober
authors.forename: Kathleen E
authors.initials: KE
authors.lastname: McGrath
authors.forename: James
authors.initials: J
authors.lastname: Palis
mesh_terms: D000818:Animals; D002452:Cell Count; D019070:Cell Lineage; D004622:Embryo, Mammalian / Q000166:cytology; D041905:Erythroid Cells / Q000166:cytology; D004920:Erythropoiesis; D006579:Heterozygote; D008533:Megakaryocytes / Q000166:cytology*; D051379:Mice; D020598:Proto-Oncogene Proteins c-myb / Q000172:deficiency / Q000378:metabolism; D034061:Thrombopoiesis; D015017:Yolk Sac / Q000166:cytology*
chemical_list: D020598:Proto-Oncogene Proteins c-myb