Long-lived lung megakaryocytes contribute to platelet recovery in thrombocytopenia models.

Lung megakaryocytes (Mks) are largely extravascular with an immune phenotype (1). Because bone marrow (BM) Mks are short lived, it has been assumed that extravascular lung Mks are constantly "seeded" from the BM. To investigate lung Mk origins and how origin affects their functions, we developed methods to specifically label lung Mks using CFSE dye and biotin delivered via the oropharyngeal route.

BMI1 regulates human erythroid self-renewal through both gene repression and gene activation.

The limited proliferative capacity of erythroid precursors is a major obstacle to generate sufficient numbers of in vitro-derived red blood cells (RBC) for clinical purposes. We and others have determined that BMI1, a member of the polycomb repressive complex 1 (PRC1), is both necessary and sufficient to drive extensive proliferation of self-renewing erythroblasts (SREs). However, the mechanisms of BMI1 action remain poorly understood.

regulates age-dependent differences in murine platelet function.

Platelets are essential for hemostasis; however, several studies have identified age-dependent differences in platelet function. To better understand the origins of fetal platelet function, we have evaluated the contribution of the fetal-specific RNA binding protein in the megakaryocyte/platelet lineage. Because activated fetal platelets have very low levels of P-selectin, we hypothesized that the expression of platelet P-selectin is part of a fetal-specific hematopoietic program conferred by Lin28b.

Functional Analysis of Erythroid Progenitors by Colony-Forming Assays.

The capacity of erythroid-lineage progenitors to form colonies of maturing red blood cells in semisolid media has provided a functional assay for these progenitors and has greatly contributed to our understanding of erythropoiesis. Studies since the 1970s have led to the development of a model of the erythron, whereby the earliest erythroid-committed progenitor, the immature burst-forming unit erythroid (BFU-E), gives rise sequentially to late-stage BFU-E and to colony-forming units erythroid (CFU-E). CFU-E give rise, in turn, to maturing erythroblast precursors that hemoglobinize.

Distinct Sources of Hematopoietic Progenitors Emerge before HSCs and Provide Functional Blood Cells in the Mammalian Embryo.

Hematopoietic potential arises in mammalian embryos before adult-repopulating hematopoietic stem cells (HSCs). At embryonic day 9.5 (E9.

Regulation of primitive hematopoiesis by class I histone deacetylases.

Background: Histone deacetylases (HDACs) regulate multiple developmental processes and cellular functions. However, their roles in blood development have not been determined, and in Xenopus laevis a specific function for HDACs has yet to be identified. Here, we employed the class I selective HDAC inhibitor, valproic acid (VPA), to show that HDAC activity is required for primitive hematopoiesis.

EPO-mediated expansion of late-stage erythroid progenitors in the bone marrow initiates recovery from sublethal radiation stress.

Erythropoiesis is a robust process of cellular expansion and maturation occurring in murine bone marrow and spleen. We previously determined that sublethal irradiation, unlike bleeding or hemolysis, depletes almost all marrow and splenic erythroblasts but leaves peripheral erythrocytes intact. To better understand the erythroid stress response, we analyzed progenitor, precursor, and peripheral blood compartments of mice post-4 Gy total body irradiation.

A transient definitive erythroid lineage with unique regulation of the β-globin locus in the mammalian embryo.

A transient erythromyeloid wave of definitive hematopoietic progenitors (erythroid/myeloid progenitors [EMPs]) emerges in the yolk sac beginning at embryonic day 8.25 (E8.25) and colonizes the liver by E10.

Sublethal radiation injury uncovers a functional transition during erythroid maturation.

Objective: Clastogenic injury of the erythroid lineage results in anemia, reticulocytopenia, and transient appearance of micronucleated reticulocytes. However, the micronucleated reticulocyte dose-response in murine models is only linear to 2 Gy total body irradiation and paradoxically decreases at higher exposures, suggesting complex radiation effects on erythroid intermediates. To better understand this phenomenon, we investigated the kinetics and apoptotic response of the erythron to sublethal radiation injury.

Foxp3 regulates megakaryopoiesis and platelet function.

Objective: Platelets are crucial for hemostasis and are vital regulators of inflammation. Foxp3 is a key transcription factor for T regulatory cell development. Humans with IPEX (immune dysregulation, polyendocrinopathy, enteropathy, x-linked) and the scurfy (Foxp3(sf)) mouse have mutations in the Foxp3 gene that lead to a host of pathologies including autoimmunity and skin diseases.

Enucleation of primitive erythroid cells generates a transient population of "pyrenocytes" in the mammalian fetus.

Enucleation is the hallmark of erythropoiesis in mammals. Previously, we determined that yolk sac-derived primitive erythroblasts mature in the bloodstream and enucleate between embryonic day (E)14.5 and E16.

The megakaryocyte lineage originates from hemangioblast precursors and is an integral component both of primitive and of definitive hematopoiesis.

In the adult, platelets are derived from unipotential megakaryocyte colony-forming cells (Meg-CFCs) that arise from bipotential megakaryocyte/erythroid progenitors (MEPs). To better define the developmental origin of the megakaryocyte lineage, several aspects of megakaryopoiesis, including progenitors, maturing megakaryocytes, and circulating platelets, were examined in the murine embryo. We found that a majority of hemangioblast precursors during early gastrulation contains megakaryocyte potential.

Analysis of hematopoietic progenitors in the mouse embryo.

All mature blood cells are derived from hematopoietic progenitors that have been defined by their ability to generate colonies of cells in semisolid media. Investigation of the cellular components of these colonies has confirmed the existence of unilineage, bilineage, and multilineage progenitors. Furthermore, it has led to a better understanding of the relationships that exist among the erythroid, myeloid, and megakaryocyte lineages that compose much of the hematopoietic hierarchy in the adult.

Circulation is established in a stepwise pattern in the mammalian embryo.

To better understand the relationship between the embryonic hematopoietic and vascular systems, we investigated the establishment of circulation in mouse embryos by examining the redistribution of yolk sac-derived primitive erythroblasts and definitive hematopoietic progenitors. Our studies revealed that small numbers of erythroblasts first enter the embryo proper at 4 to 8 somite pairs (sp) (embryonic day 8.25 [E8.