Fate Tracing Reveals the Endothelial Origin of Hematopoietic Stem Cells

Department of Molecular, Cell, and Developmental Biology, University of California, Los Angeles, CA 90095, USA.
Cell stem cell (Impact Factor: 22.27). 01/2009; 3(6):625-36. DOI: 10.1016/j.stem.2008.09.018
Source: PubMed


Hematopoietic stem cells (HSCs) originate within the aortic-gonado-mesonephros (AGM) region of the midgestation embryo, but the cell type responsible for their emergence is unknown since critical hematopoietic factors are expressed in both the AGM endothelium and its underlying mesenchyme. Here we employ a temporally restricted genetic tracing strategy to selectively label the endothelium, and separately its underlying mesenchyme, during AGM development. Lineage tracing endothelium, via an inducible VE-cadherin Cre line, reveals that the endothelium is capable of HSC emergence. The endothelial progeny migrate to the fetal liver, and later to the bone marrow, and are capable of expansion, self-renewal, and multilineage hematopoietic differentiation. HSC capacity is exclusively endothelial, as ex vivo analyses demonstrate lack of VE-cadherin Cre induction in circulating and fetal liver hematopoietic populations. Moreover, AGM mesenchyme, as selectively traced via a myocardin Cre line, is incapable of hematopoiesis. Our genetic tracing strategy therefore reveals an endothelial origin of HSCs.

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    • "Endothelial to hematopoietic transition (EHT) during embryogenesis provides the first long term hematopoietic stem and progenitor cells (HSPC) for the organism. Fate tracing (Zovein et al., 2008), live imaging (Bertrand et al., 2010; Boisset et al., 2010; Eilken et al., 2009), and loss of function studies (Chen et al., 2009) have demonstrated that a subset of endothelial cells, termed hemogenic endothelium, is capable of generating HSPCs, which first appear as cell clusters of rounded cells attached to the endothelium (North et al., 1999). The most well studied site for HSPC emergence is the developing aorta located in the embryonic aorta-gonad-mesonephros (AGM) region (de Bruijn et al., 2000; North et al., 1999). "
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    ABSTRACT: Endothelial-to-hematopoietic transition (EHT) occurs within a population of hemogenic endothelial cells during embryogenesis, and leads to the formation of the adult hematopoietic system. Currently, the prospective identification of specific endothelial cells that will undergo EHT, and the cellular events enabling this transition, are not known. We set out to define precisely the morphological events of EHT, and to correlate cellular morphology with the expression of the transcription factors RUNX1 and SOX17. A novel strategy was developed to allow for correlation of immunofluorescence data with the ultrastructural resolution of scanning electron microscopy. The approach can identify single endothelial cells undergoing EHT, as identified by the ratio of RUNX1 to SOX17 immunofluorescence levels, and the morphological changes associated with the transition. Furthermore, this work details a new technical resource that is widely applicable for correlative analyses of single cells in their native tissue environments. © 2015. Published by The Company of Biologists Ltd.
    Full-text · Article · Aug 2015 · Development
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    • "These early waves of hematopoiesis successively give rise to primitive erythroid, myeloid, definitive erythroid, and lymphoid progenitors (Costa et al., 2012; Lin et al., 2014). Several studies, including lineage tracing (Zovein et al., 2008) and in vivo imaging (Boisset et al., 2010) studies, have revealed the endothelial origin of HSCs emerging from a hemogenic endothelium (HE) population within the AGM region. Similarly, earlier waves of hematopoietic progenitors were also shown to derive from the HE (Ema et al., 2006; Lancrin et al., 2010; Nishikawa et al., 1998). "
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    ABSTRACT: The generation of in vivo repopulating hematopoietic cells from in vitro differentiating embryonic stem cells has remained a long-standing challenge. To date, hematopoietic engraftment has mostly been achieved through the enforced expression of ectopic transcription factors. Here, we describe serum-free culture conditions that allow the generation of in vivo repopulating hematopoietic cells in the absence of ectopically expressed factors. We show that repopulating activity arises immediately upon the commitment of mesodermal precursors to the blood program, within the first wave of hematopoietic specification. We establish that the formation of these progenitors is extremely transient and exquisitely sensitive to the cytokine milieu. Our findings define the precise differentiating stage at which hematopoietic repopulating activity first appears in vitro, and suggest that during embryonic stem cell differentiation, all hematopoietic programs are unraveled simultaneously from the mesoderm in the absence of cues that restrict the coordinated emergence of each lineage as is normally observed during embryogenesis.
    Full-text · Article · Feb 2015 · Stem Cell Reports
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    • "The detection of primitive erythrocytes expressing the embryonic bH1-hemoglobin also suggests that these TFs are inducing early developmental steps. Moreover, the presence of a transient hemogenic endothelium population resembles the endothelial-to-hematopoietic transition that takes place during blood development in the yolk sac or dorsal aorta (Boisset et al., 2010; Jaffredo et al., 1998; Lancrin et al., 2009; Zovein et al., 2008). "
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    ABSTRACT: Recent reports have shown that somatic cells, under appropriate culture conditions, could be directly reprogrammed to cardiac, hepatic, or neuronal phenotype by lineage-specific transcription factors. In this study, we demonstrate that both embryonic and adult somatic fibroblasts can be efficiently reprogrammed to clonal multilineage hematopoietic progenitors by the ectopic expression of the transcription factors ERG, GATA2, LMO2, RUNX1c, and SCL. These reprogrammed cells were stably expanded on stromal cells and possessed short-term reconstitution ability in vivo. Loss of p53 function facilitated reprogramming to blood, and p53(-/-) reprogrammed cells efficiently generated erythroid, megakaryocytic, myeloid, and lymphoid lineages. Genome-wide analyses revealed that generation of hematopoietic progenitors was preceded by the appearance of hemogenic endothelial cells expressing endothelial and hematopoietic genes. Altogether, our findings suggest that direct reprogramming could represent a valid alternative approach to the differentiation of embryonic stem cells (ESCs) or induced pluripotent stem cells (iPSCs) for disease modeling and autologous blood cell therapies. Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.
    Full-text · Article · Nov 2014 · Cell Reports
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