Origins of the Vertebrate Erythro/Megakaryocytic System

Figure 2

Models of mammalian adult hematopoiesis with respect to the megakaryocytic-erythroid compartment (grey box). Hierarchical [20, 21] (black arrows) and myeloid bypass [25] (red arrowheads) models of hematopoiesis are shown. According to the conventional hierarchical model of hematopoiesis, the bipotent megakaryocyte-erythroid progenitors (MEPs) are able to give rise to megakaryocytes and erythrocytes. The alternative myeloid bypass model predicts the existence of various myeloid repopulating progenitors (MyRPs) as a subset of long-term hematopoietic stem cells (LT-HSCs), such as common myeloid repopulating progenitors (CMRPs), megakaryocyte repopulating progenitors (MkRPs), and megakaryocyte-erythroid repopulating progenitors (MERPs). These progenitors are capable of long-term repopulation and differentiation into the particular cell lineages. ST-HSC: short-term HSC; MPP: multipotent progenitor cell; CLP: common lymphoid progenitor; GMP: granulocyte/monocyte progenitor; CFU-Mk: colony-forming unit-megakaryocyte; BFU-E: burst-forming units-erythroid; CFU-E: colony-forming units-erythroid.