1: Cancer Res. 2005 Sep 1;65(17):7596-602. The proto-oncogene ERG in megakaryoblastic leukemias. Rainis L, Toki T, Pimanda JE, Rosenthal E, Machol K, Strehl S, Gottgens B, Ito E, Izraeli S. Department of Pediatric Hematology-Oncology, Safra Children's Hospital and Hematology Institute, Sheba Cancer Research Center, Sheba Medical Center, Tel-Hashomer, Israel. Aneuploidy is one of the hallmarks of cancer. Acquired additions of chromosome 21 are a common finding in leukemias, suggesting a contributory role to leukemogenesis. About 10% of patients with a germ line trisomy 21 (Down syndrome) are born with transient megakaryoblastic leukemia. We and others have shown acquired mutations in the X chromosome gene GATA1 in all these cases. The gene or genes on chromosome 21 whose overexpression promote the megakaryoblastic phenotype are presently unknown. We propose that ERG, an Ets transcription factor situated on chromosome 21, is one such candidate. We show that ERG is expressed in hematopoietic stem cells, megakaryoblastic cell lines, and in primary leukemic cells from Down syndrome patients. ERG expression is induced upon megakaryocytic differentiation of the erythroleukemia cell lines K562 and UT-7, and forced expression of ERG in K562 cells induces erythroid to megakaryoblastic phenotypic switch. We also show that ERG activates the gpIb megakaryocytic promoter and binds the gpIIb promoter in vivo. Furthermore, both ERG and ETS2 bind in vivo the hematopoietic enhancer of SCL/TAL1, a key regulator of hematopoietic stem cell and megakaryocytic development. We propose that trisomy 21 facilitates the occurrence of megakaryoblastic leukemias through a shift toward the megakaryoblastic lineage caused by the excess expression of ERG, and possibly by other chromosome 21 genes, such as RUNX1 and ETS2, in hematopoietic progenitor cells, coupled with a differentiation arrest caused by the acquisition of mutations in GATA1. PMID: 16140924 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 2: Cell Biol Int. 2005 Aug;29(8):654-61. In vitro hematopoietic differentiation of human embryonic stem cells induced by co-culture with human bone marrow stromal cells and low dose cytokines. Wang J, Zhao HP, Lin G, Xie CQ, Nie DS, Wang QR, Lu GX. National Stem Cell Engineering Centre, Institute of Human Reproductive and Stem Cell Engineering, Central South University, Changsha, China. Human embryonic stem (hES) cells randomly differentiate into multiple cell types during embryoid body (EB) development and limited studies have focused on directed hematopoietic differentiation. Here, we report that the treatment of hES cells during EBs development with a combination of low dose hematopoietic cytokines, including stem cell factor (SCF), Flt-3 ligand, vascular endothelial growth factor (VEGF) and human bone marrow stromal cells (hBMSCs), generated cell clusters that contained 8.81% KDR-positive hemangioblasts, 9.94% CD34-positive hematopoietic stem cells and 25.7% CD45-positive mature hematopoietic cells, and expressed hematopoietic genes such as KDR, stem cell leukemia (scl) and runt-related transcription factor 1 (Runx1). We provide the first evidence for the role of the cytokine-hBMSCs combination in promoting hematopoietic differentiation of hES cells, and thus provide the potential for generation of hematopoietic cells, as well as for understanding early developmental events that govern the initiation of hematopoiesis in humans. PMID: 15950498 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 3: Development. 2005 Mar;132(5):1117-26. Epub 2005 Feb 2. RBPjkappa-dependent Notch function regulates Gata2 and is essential for the formation of intra-embryonic hematopoietic cells. Robert-Moreno A, Espinosa L, de la Pompa JL, Bigas A. Centre Oncologia Molecular, IDIBELL-Institut de Recerca Oncologica, Hospitalet, Barcelona 08907, Spain. Definitive hematopoiesis in the mouse embryo originates from the aortic floor in the P-Sp/AGM region in close association with endothelial cells. An important role for Notch1 in the control of hematopoietic ontogeny has been recently established, although its mechanism of action is poorly understood. Here, we show detailed analysis of Notch family gene expression in the aorta endothelium between embryonic day (E) 9.5 and E10.5. Since Notch requires binding to RBPjkappa transcription factor to activate transcription, we analyzed the aorta of the para-aortic splanchnopleura/AGM in RBPjkappa mutant embryos. We found specific patterns of expression of Notch receptors, ligands and Hes genes that were lost in RBPjkappa mutants. Analysis of these mutants revealed the absence of hematopoietic progenitors, accompanied by the lack of expression of the hematopoietic transcription factors Aml1/Runx1, Gata2 and Scl/Tal1. We show that in wild-type embryos, a few cells lining the aorta endothelium at E9.5 simultaneously expressed Notch1 and Gata2, and demonstrate by chromatin immunoprecipitation that Notch1 specifically associated with the Gata2 promoter in E9.5 wild-type embryos and 32D myeloid cells, an interaction lost in RBPjkappamutants. Consistent with a role for Notch1 in regulating Gata2, we observe increased expression of this gene in 32D cells expressing activated Notch1. Taken together, these data strongly suggest that activation of Gata2 expression by Notch1/RBPjkappa is a crucial event for the onset of definitive hematopoiesis in the embryo. PMID: 15689374 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 4: Development. 2003 Nov;130(22):5437-44. Epub 2003 Sep 24. Mouse placenta is a major hematopoietic organ. Alvarez-Silva M, Belo-Diabangouaya P, Salaun J, Dieterlen-Lievre F. Laboratoire d'Embryologie cellulaire et moleculaire du CNRS et du College de France, 49 bis, avenue de la Belle Gabrielle, 94736 Nogent s/Marne cedex, France. Placenta and yolk sac from 8- to 17-day-old (E8-E17) mouse embryos/fetuses were investigated for the presence of in vitro clonogenic progenitors. At E8-E9, the embryonic body from the umbilicus caudalwards was also analysed. Fetal liver was analysed beginning on E10. At E8, between five and nine somite pairs (sp), placenta, yolk sac and embryonic body yielded no progenitors. The first progenitors appeared at E8.5 at the stage of 15 sp in the yolk sac, 18 sp in the embryonic body, 20 sp in the placenta and only at E12 in the fetal liver (absent at E10, at E11 not determined). Progenitors with a high proliferation potential that could be replated for two months, as well as the whole range of myeloid progenitors, were found at all stages in all organs. However, the earliest of these progenitors (these yielding large, multilineage colonies) were 2-4 times more frequent in the placenta than in the yolk sac or fetal liver. In the fetal liver, late progenitors were more frequent and the cellularity increased steeply with developmental age. Thus, the fetal liver, which is a recognized site for amplification and commitment, has a very different hematopoietic developmental profile from placenta or yolk sac. Placentas were obtained from GFP transgenic embryos in which only the embryonic contribution expressed the transgene. 80% of the colonies derived from these placental cells were GFP+, and so originated from the fetal component of the placenta. These data point to the placenta as a major hematopoietic organ that is active during most of pregnancy. PMID: 14507780 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 5: Trends Cardiovasc Med. 2003 Aug;13(6):254-9. Cell fate decisions in early blood vessel formation. Ema M, Rossant J. Samuel Lunenfeld Research Institute and the Department of Molecular and Medical Genetics, University of Toronto, Mount Sinai Hospital, 600 University Avenue, Toronto, Ontario, Canada M5G 1X5. The close spatial relationship between endothelial and hematopoietic cells at different stages of development has led to the concept of a common progenitor, the hemangioblast. The vascular endothelial growth factor receptor, Flk1 or KDR, is a common marker of all cells--whether embryonic or adult--that have putative hemangioblast properties. In this article, a model is proposed in which Flk1 marks a common mesodermal precursor that segregates successive subsets of Flk1-expressing or Flk1-nonexpressing cells whose fate is determined by coexpression of lineage-specific transcription factors. Cells that retain Flk1 activity have endothelial potential, cells that also activate downstream transcription factors such as Tal1 and Runx1 gain primitive or definitive hematopoietic activity, and cells that lose Flk1 expression but gain expression of other transcription factors become smooth muscle or other cell types. Publication Types: Review Review, Tutorial PMID: 12922023 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 6: Blood. 2003 Jan 15;101(2):508-16. Epub 2002 Sep 19. Expression of CD41 marks the initiation of definitive hematopoiesis in the mouse embryo. Mikkola HK, Fujiwara Y, Schlaeger TM, Traver D, Orkin SH. Department of Hematology/Oncology, Children's Hospital, Boston, MA, USA. Murine hematopoietic stem cells (HSCs) originate from mesoderm in a process that requires the transcription factor SCL/Tal1. To define steps in the commitment to blood cell fate, we compared wild-type and SCL(-/-) embryonic stem cell differentiation in vitro and identified CD41 (GpIIb) as the earliest surface marker missing from SCL(-/-) embryoid bodies (EBs). Culture of fluorescence-activated cell sorter (FACS) purified cells from EBs showed that definitive hematopoietic progenitors were highly enriched in the CD41(+) fraction, whereas endothelial cells developed from CD41(-) cells. In the mouse embryo, expression of CD41 was detected in yolk sac blood islands and in fetal liver. In yolk sac and EBs, the panhematopoietic marker CD45 appeared in a subpopulation of CD41(+) cells. However, multilineage hematopoietic colonies developed not only from CD45(+)CD41(+) cells but also from CD45(-)CD41(+) cells, suggesting that CD41 rather than CD45 marks the definitive culture colony-forming unit (CFU-C) at the embryonic stage. In contrast, fetal liver CFU-C was CD45(+), and only a subfraction expressed CD41, demonstrating down-regulation of CD41 by the fetal liver stage. In yolk sac and EBs, CD41 was coexpressed with embryonic HSC markers c-kit and CD34. Sorting for CD41 and c-kit expression resulted in enrichment of definitive hematopoietic progenitors. Furthermore, the CD41(+) c-kit(+) population was missing from runx1/AML1(-/-) EBs that lack definitive hematopoiesis. These results suggest that the expression of CD41, a candidate target gene of SCL/Tal1, and c-kit define the divergence of definitive hematopoiesis from endothelial cells during development. Although CD41 is commonly referred to as megakaryocyte-platelet integrin in adult hematopoiesis, these results implicate a wider role for CD41 during murine ontogeny. PMID: 12393529 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 7: Curr Opin Cell Biol. 2001 Dec;13(6):673-8. A complex linkage in the developmental pathway of endothelial and hematopoietic cells. Nishikawa SI. Department of Molecular Genetics, Graduate School of Medicine, Kyoto University and Riken Center for Developmental Biology, Shogoin-Kawaharacho 53, Sakyo-ku, Kyoto, 606-8507, Japan. snishika@virus.Kyoto-u.ac.jp During normal vertebrate development, hematopoietic and endothelial cells form closely situated and interacting populations. Although the close proximity of cells to each other does not necessarily mean that they are relatives, accumulating evidence indicates that hematopoietic and endothelial cells are indeed close kin; they share common progenitors and each is able to become the other under certain circumstances. This article summarizes recent advances in the developmental relationship between hematopoietic and endothelial cells. Publication Types: Review Review, Tutorial PMID: 11698182 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 8: Ann N Y Acad Sci. 2001 Jun;938:96-107; discussion 108. Regulation of hemangioblast development. Lacaud G, Robertson S, Palis J, Kennedy M, Keller G. Institute for Gene Therapy and Molecular Medicine, Mount Sinai School of Medicine, Box 1496, 1425 Madison Avenue, New York, New York 10029-6514, USA. The in vitro differentiation of embryonic stem (ES) cells provides a powerful approach for studying the earliest events involved in the commitment of the hematopoietic and endothelial lineages. Using this model system, we have identified a precursor with the potential to generate both primitive and definitive hematopoietic cells as well as cells with endothelial characteristics. The developmental potential of this precursor suggests that it represents the in vitro equivalent of the hemangioblast, a common stem cell for both lineages. ES cells deficient for the transcription factor scl/tal-1 are unable to generate hemangioblasts, while those deficient for Runx1 generate reduced numbers of these precursors. These findings indicate that both genes play pivotal roles at the earliest stages of hematopoietic and endothelial development. In addition, they highlight the strength of this model system in studying the function of genes in embryonic development. Publication Types: Review Review, Tutorial PMID: 11458531 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 9: Br J Haematol. 2001 Apr;113(1):52-7. Decreased expression of transcription factor GATA-2 in haematopoietic stem cells in patients with aplastic anaemia. Fujimaki S, Harigae H, Sugawara T, Takasawa N, Sasaki T, Kaku M. Department of Molecular Diagnostics, Tohoku University School of Medicine, Sendai, Japan. Aplastic anaemia is characterized by reduced haematopoiesis resulting in pancytopenia. It has been speculated that there is an injury in haematopoietic stem cells in the bone marrow; however, the precise nature of the injury has not been elucidated. In this study, the levels of expression of mRNAs for three transcription factors, GATA-2, SCL and AML1, which function in the early stages of haematopoiesis, were examined by quantitative polymerase chain reaction in patients with aplastic anaemia, idiopathic thrombocytopenic purpura (ITP) and normal subjects. Among these factors, expression of GATA-2 mRNA in purified CD34-positive cells was markedly decreased in aplastic anaemia compared with that in ITP and in normal subjects. The expression levels of SCL and AML1 mRNA in CD34-positive cells in aplastic anaemia were not different from those in normal subjects. When the expression of GATA-2 protein in CD34-positive cells was examined by immunocytochemical analysis, the percentage of GATA-2-positive cells in aplastic anaemia was lower than that in normal subjects. These findings strongly suggest that there is an aberrant expression of transcription factors in stem cells in aplastic anaemia, which may be responsible for the development of the disease. PMID: 11328281 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 10: Tanpakushitsu Kakusan Koso. 2000 Jun;45(9 Suppl):1565-72. [Regulation of hematopoiesis by transcription factors] [Article in Japanese] Kurokawa M, Hirai H. Department of Hematology & Oncology, Graduate School of Medicine, University of Tokyo, Japan. kurokawa-tky@umin.ac.jp Publication Types: Review Review, Tutorial PMID: 10879135 [PubMed - indexed for MEDLINE] ---------------------------------------------------------------