Hock, H. et al. Gfi-1 restricts proliferation and preserves functional integrity of haematopoietic stem cells. Nature 431, 1002-1007
Division of Hematology/Oncology, Children's Hospital, Boston, Massachusetts 02115, USA. Nature
(Impact Factor: 41.46).
11/2004; 431(7011):1002-7. DOI: 10.1038/nature02994
Haematopoietic stem cells (HSCs) sustain blood production throughout life. HSCs are capable of extensive proliferative expansion, as a single HSC may reconstitute lethally irradiated hosts. In steady-state, HSCs remain largely quiescent and self-renew at a constant low rate, forestalling their exhaustion during adult life. Whereas nuclear regulatory factors promoting proliferative programmes of HSCs in vivo and ex vivo have been identified, transcription factors restricting their cycling have remained elusive. Here we report that the zinc-finger repressor Gfi-1 (growth factor independent 1), a cooperating oncogene in lymphoid cells, unexpectedly restricts proliferation of HSCs. After loss of Gfi-1, HSCs display elevated proliferation rates as assessed by 5-bromodeoxyuridine incorporation and cell-cycle analysis. Gfi-1-/- HSCs are functionally compromised in competitive repopulation and serial transplantation assays, and are rapidly out-competed in the bone marrow of mouse chimaeras generated with Gfi-1-/- embryonic stem cells. Thus, Gfi-1 is essential to restrict HSC proliferation and to preserve HSC functional integrity.
Available from: Peter Zandstra
- "The in vitro data allowed us to uncover what signals each of the 12 cell types feeds back to HSC-e. For instance, the mature cells, particularly Mono and granulocytes (Neut, Baso, and Eos), were found to express mainly inhibitory signals for HSC-e proliferation and inducing signals for HSC-e differentiation , which in combination can exhaust the HSC population because of the extensive cell cycling and division involved in the proliferation and differentiation processes (Hock et al, 2004;Zhang et al, 2006). However, under a normal in vivo condition, monocytes and granulocytes mainly circulate in the peripheral tissues; their secreted ligands have limited access to HSC in the bone marrow compartment because of the blood–bone marrow barrier. "
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ABSTRACT: The hematopoietic system is a distributed tissue that consists of functionally distinct cell types continuously produced through hematopoietic stem cell (HSC) differentiation. Combining genomic and phenotypic data with high-content experiments, we have built a directional cell–cell communication network between 12 cell types isolated from human umbilical cord blood. Network structure analysis revealed that ligand production is cell type dependent, whereas ligand binding is promiscuous. Consequently, additional control strategies such as cell frequency modulation and compartmentalization were needed to achieve specificity in HSC fate regulation. Incorporating the in vitro effects (quiescence, self-renewal, proliferation, or differentiation) of 27 HSC binding ligands into the topology of the cell–cell communication network allowed coding of cell type-dependent feedback regulation of HSC fate. Pathway enrichment analysis identified intracellular regulatory motifs enriched in these cell type- and ligand-coupled responses. This study uncovers cellular mechanisms of hematopoietic cell feedback in HSC fate regulation, provides insight into the design principles of the human hematopoietic system, and serves as a foundation for the analysis of intercellular regulation in multicellular systems.
Available from: PubMed Central
- "HSC quiescence is controlled by both HSC-intrinsic mechanisms and extrinsic factors from the BM microenvironment . Several transcription factors have been implicated in the regulation of HSC quiescence, including Gfi-1, Pbx1 and MEF/ELF4 –. With regard to HSC-extrinsic niche-derived factors, it has been reported that angiopoietin-1 and thrombopoietin regulate the quiescence of HSCs in the BM through receptors expressed on HSCs –. "
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ABSTRACT: Hematopoietic stem cells in the bone marrow have the capacity to both self-renew and to generate all cells of the hematopoietic system. The balance of these two activities is controlled by hematopoietic stem cell-intrinsic regulatory mechanisms as well as extrinsic signals from the microenvironment. Here we demonstrate that Meis1, a TALE family homeodomain transcription factor involved in numerous embryonic developmental processes, is selectively expressed in hematopoietic stem/progenitor cells. Conditional Meis1 knockout in adult hematopoietic cells resulted in a significant reduction in the hematopoietic stem/progenitor cells. Suppression of hematopoiesis by Meis1 deletion appears to be caused by impaired self-renewal activity and reduced cellular quiescence of hematopoietic stem/progenitor cells in a cell autonomous manner, resulting in stem cell exhaustion and defective long-term hematopoiesis. Meis1 deficiency down-regulated a subset of Pbx1-dependent hematopoietic stem cell signature genes, suggesting a functional link between them in the maintenance of hematopoietic stem/progenitor cells. These results show the importance of Meis1 in adult hematopoiesis.
Available from: Timothy Sendall
- "The transcription factor Gfi1 is expressed in multiple tissues, including haematopoietic progenitors and stem cells, lymphoid and myeloid cells (Karsunky et al., 2002; Hock et al., 2004; Yücel et al., 2004; Rosenbauer and Tenen, 2007; Wilson et al., 2010a; Lancrin et al., 2012). We have previously identified an enhancer that is located around 35 kb upstream of Gfi1 (referred to as the Gfi1-35 enhancer) within an intron of the neighbouring gene Evi5 (Wilson et al., 2010a). "
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ABSTRACT: Comprehensive analysis of cis-regulatory elements is key to understanding the dynamic gene regulatory networks that control embryonic development. While transgenic animals represent the gold standard assay, their generation is costly, entails significant animal usage, and in utero development complicates time-course studies. As an alternative, embryonic stem (ES) cells can readily be differentiated in a process that correlates well with developing embryos. Here, we describe a highly effective platform for enhancer assays using an Hsp68/Venus reporter cassette that targets to the Hprt locus in mouse ES cells. This platform combines the flexibility of Gateway® cloning, live cell trackability of a fluorescent reporter, low background and the advantages of single copy insertion into a defined genomic locus. We demonstrate the successful recapitulation of tissue-specific enhancer activity for two cardiac and two haematopoietic enhancers. In addition, we used this assay to dissect the functionality of the highly conserved Ets/Ets/Gata motif in the Scl+19 enhancer, which revealed that the Gata motif is not required for initiation of enhancer activity. We further confirmed that Gata2 is not required for endothelial activity of the Scl+19 enhancer using Gata2(-/-) Scl+19 transgenic embryos. We have therefore established a valuable toolbox to study gene regulatory networks with broad applicability.
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