title: Expression of CD41 marks the initiation of definitive hematopoiesis in the mouse embryo.
abstract: Murine hematopoietic stem cells (HSCs) originate from mesoderm in a process that requires the transcription factor SCL/Tal1. To define steps in the commitment to blood cell fate, we compared wild-type and SCL(-/-) embryonic stem cell differentiation in vitro and identified CD41 (GpIIb) as the earliest surface marker missing from SCL(-/-) embryoid bodies (EBs). Culture of fluorescence-activated cell sorter (FACS) purified cells from EBs showed that definitive hematopoietic progenitors were highly enriched in the CD41(+) fraction, whereas endothelial cells developed from CD41(-) cells. In the mouse embryo, expression of CD41 was detected in yolk sac blood islands and in fetal liver. In yolk sac and EBs, the panhematopoietic marker CD45 appeared in a subpopulation of CD41(+) cells. However, multilineage hematopoietic colonies developed not only from CD45(+)CD41(+) cells but also from CD45(-)CD41(+) cells, suggesting that CD41 rather than CD45 marks the definitive culture colony-forming unit (CFU-C) at the embryonic stage. In contrast, fetal liver CFU-C was CD45(+), and only a subfraction expressed CD41, demonstrating down-regulation of CD41 by the fetal liver stage. In yolk sac and EBs, CD41 was coexpressed with embryonic HSC markers c-kit and CD34. Sorting for CD41 and c-kit expression resulted in enrichment of definitive hematopoietic progenitors. Furthermore, the CD41(+) c-kit(+) population was missing from runx1/AML1(-/-) EBs that lack definitive hematopoiesis. These results suggest that the expression of CD41, a candidate target gene of SCL/Tal1, and c-kit define the divergence of definitive hematopoiesis from endothelial cells during development. Although CD41 is commonly referred to as megakaryocyte-platelet integrin in adult hematopoiesis, these results implicate a wider role for CD41 during murine ontogeny.
authors.affiliation: Department of Hematology/Oncology, Children's Hospital, Boston, MA, USA.
authors.forename: Hanna K A
authors.initials: HK
authors.lastname: Mikkola
authors.forename: Yuko
authors.initials: Y
authors.lastname: Fujiwara
authors.forename: Thorsten M
authors.initials: TM
authors.lastname: Schlaeger
authors.forename: David
authors.initials: D
authors.lastname: Traver
authors.forename: Stuart H
authors.initials: SH
authors.lastname: Orkin
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D018929:Cell Culture Techniques; D004268:DNA-Binding Proteins / Q000235:genetics; D004622:Embryo, Mammalian / Q000502:physiology*; D004727:Endothelium / Q000166:cytology / Q000196:embryology; D006410:Hematopoiesis; D006412:Hematopoietic Stem Cells / Q000166:cytology; D016130:Immunophenotyping; D017493:Leukocyte Common Antigens / Q000096:biosynthesis; D051379:Mice; D040201:Platelet Membrane Glycoprotein IIb / Q000096:biosynthesis*; D011518:Proto-Oncogene Proteins / Q000235:genetics; D013234:Stem Cells / Q000166:cytology; D000073942:T-Cell Acute Lymphocytic Leukemia Protein 1; D014157:Transcription Factors / Q000235:genetics; D015017:Yolk Sac / Q000166:cytology
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D017493:Leukocyte Common Antigens; D040201:Platelet Membrane Glycoprotein IIb; D011518:Proto-Oncogene Proteins; D000073942:T-Cell Acute Lymphocytic Leukemia Protein 1; D014157:Transcription Factors; C489366:Tal1 protein, mouse