Ontogeny of Mammalian Hematopoiesis
The first blood cells in the mammalian embryo emerge within yolk sac blood islands from hemangioblast precursors (Huber, et al. Nature, 2004). Also in collaboration with the laboratory of Gordon Keller, we identified two waves of hematopoietic progenitors emerging from the yolk sac prior to colonization of the liver (Palis, et al. Development, 1999). The first “primitive” wave is at least bilineage in nature, since it contains both primitive erythroid and megakaryocyte progenitors (Tober, et al. Blood, 2007). The second “definitive” wave contains definitive erythroid, megakaryocyte, and multiple myeloid lineages (Palis, et al. Proc Natl Acad Science, 2001). The lineage composition and relationships of these primitive and definitive progenitor waves and their contribution to hematopoiesis in the fetal liver are under active investigation. Taken together, our studies indicate that the onset of hematopoiesis within the yolk sac of mammals is much more complex than previously thought.
Immunohistochemical staining with anti-bH1-globin (blue) and anti-GP1bb (red) antibodies identifies a colony derived from a bipotential megakaryocyte/primitive erythroid progenitor derived from the murine yolk sac.
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