Inducible Fli-1 gene deletion in adult mice modifies several myeloid lineage commitment decisions and accelerates proliferation arrest and terminal erythrocytic differentiation

Abstract

This study investigated the role of the ETS transcription factor Fli-1 in adult myelopoiesis using new transgenic mice allowing inducible Fli-1 gene deletion. Fli-1 deletion in adult induced mild thrombocytopenia associated with a drastic decrease in large mature megakaryocytes number. Bone marrow bipotent megakaryocyticerythrocytic progenitors (MEPs) increased by 50% without increase in erythrocytic and megakaryocytic common myeloid progenitor progeny, suggesting increased production from upstream stem cells. These MEPs were almost unable to generate pure colonies containing large mature megakaryocytes, but generated the same total number of colonies mainly identifiable as erythroid colonies containing a reduced number of more differentiated cells. Cytological and fluorescenceactivated cell sorting analyses of MEP progeny in semisolid and liquid cultures confirmed the drastic decrease in large mature megakaryocytes but revealed a surprisingly modest (50%) reduction of CD41-positive cells indicating the persistence of a megakaryocytic commitment potential. Symmetrical increase and decrease of monocytic and granulocytic progenitors were also observed in the progeny of purified granulocytic-monocytic progenitors and common myeloid progenitors. In summary, this study indicates that Fli-1 controls several lineages commitment decisions at the stem cell, MEP, and granulocytic-monocytic progenitor levels, stimulates the proliferation of committed erythrocytic progenitors at the expense of their differentiation, and is a major regulator of late stages of megakaryocytic differentiation. (Blood. 2010;116(23):4795-4805) IntroductionMature blood cells in adults are permanently regenerated from a limited pool of pluripotent hematopoietic stem cells (HSCs) localized in the bone marrow. This process occurs through the hierarchical generation of intermediate progenitors with more and more restricted differentiation and proliferation potential that can be prospectively purified. According to current models, myeloid lineages are derived from a common myeloid progenitor (CMP) generating 2 distinct bipotent progenitors, the megakaryocyticerythrocytic progenitors (MEPs) and the granulocytic-monocytic progenitors (GMP). 1 MEPs generate in turn erythrocytic and megakaryocytic monopotent progenitors, whereas GMP generate granulocytic and monocytic monopotent progenitors. Increasing data also indicate an alternative pathway generating MEPs directly from HSCs. [2][3][4] All this process is controlled by permanent crosstalk between extracellular signals and intracellular regulatory networks of transcription factors. Although having no instructive role, erythropoietin (EPO) is the major cytokine controlling erythropoiesis through the stimulation of proliferation and survival of committed erythrocytic progenitors expressing the specific receptor EPOR. 5 Thrombopoietin (TPO) is the major cytokine controlling megakaryopoiesis through the stimulation of proliferation and differentiation of committed megakaryocytic progenitors expressing the sp...

Transcriptional Regulation of Platelet Formation: Harnessing the Complexity for Efficient Platelet Production In Vitro

“…2.4.2) where it acts in synergy with GATA1 and FOG1 [113]. Inducible deletion of FLI1 in the haematopoietic compartment showed a marked increase in bipotent MEPs, which, in colony assays, were biased towards the erythroid compartment [114]. This observation is consistent with the concept that FLI1 and EKLF act as a toggle switch in MEPs each favouring differentiation towards the MK or erythroid lineage, respectively [115].…”

Erg is required for self-renewal of hematopoietic stem cells during stress hematopoiesis in mice

“…This suggests that Erg may regulate the balance of erythroidmegakaryocyte lineage specification from bipotential megakaryocyte-erythroid progenitors, as has recently been suggested for Fli-1. 49 Although reconstitution of B-cells was sensitive to haploinsufficiency of functional Erg, T-cell reconstitution from Erg ϩ/Mld2 bone marrow paralleled wild-type reconstitution. Importantly, as early lymphoid progenitors must first seed the thymus before donor-derived mature T cells can emerge, 30 this observation may be biased by the lag of mature T-cell reconstitution behind other lineages.…”

Ubiquitin-mediated interaction of p210 BCR/ABL with β-catenin supports disease progression in a murine model for chronic myelogenous leukemia

“…For reporter assays in the progenitors, common myeloid progenitors (CMPs) and megakaryocyte-erythrocyte progenitors (MEPs) were sorted by flow cytometry and cultured as previously described. 15,16 The progenitors were then co-transduced with lentiviral particles containing a TCF/LEF reporter and a Renilla control to normalize transfection efficiency (Qiagen, Valencia, CA). Firefly and Renilla luciferase activities were measured with a Dual-Luciferase Reporter Assay system following the manufacturer's instructions (Promega, Madison, WI).…”