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The mechanisms that regulate hematopoietic stem cell (HSC) fate decisions between proliferation and multilineage differentiation are unclear. Members of the Wnt family of ligands that activate the canonical Wnt signaling pathway,which utilizes beta-catenin to relay the signal,have been demonstrated to regulate HSC function. In this study,we examined the role of noncanonical Wnt signaling in regulating HSC fate. We observed that noncanonical Wnt5a inhibited Wnt3a-mediated canonical Wnt signaling in HSCs and suppressed Wnt3a-mediated alterations in gene expression associated with HSC differentiation,such as increased expression of myc. Wnt5a increased short- and long-term HSC repopulation by maintaining HSCs in a quiescent G(0) state. From these data,we propose that Wnt5a regulates hematopoiesis by the antagonism of the canonical Wnt pathway,resulting in a pool of quiescent HSCs. View Publication

The mechanisms underlying deregulation of HOX gene expression in AML are poorly understood. The ParaHox gene CDX2 was shown to act as positive upstream regulator of several HOX genes. In this study,constitutive expression of Cdx2 caused perturbation of leukemogenic Hox genes such as Hoxa10 and Hoxb8 in murine hematopoietic progenitors. Deletion of the N-terminal domain of Cdx2 abrogated its ability to perturb Hox gene expression and to cause acute myeloid leukemia (AML) in mice. In contrast inactivation of the putative Pbx interacting site of Cdx2 did not change the leukemogenic potential of the gene. In an analysis of 115 patients with AML,expression levels of CDX2 were closely correlated with deregulated HOX gene expression. Patients with normal karyotype showed a 14-fold higher expression of CDX2 and deregulated HOX gene expression compared with patients with chromosomal translocations such as t(8:21) or t(15;17). All patients with AML with normal karyotype tested were negative for CDX1 and CDX4 expression. These data link the leukemogenic potential of Cdx2 to its ability to dysregulate Hox genes. They furthermore correlate the level of CDX2 expression with HOX gene expression in human AML and support a potential role of CDX2 in the development of human AML with aberrant Hox gene expression. View Publication

The histo-blood group i and I antigens have been characterized as straight and branched repeats of N-acetyllactosamine,respectively,and the conversion of the straight-chain i to the branched-chain I structure on red cells is regulated to occur after birth. It has been demonstrated that the human I locus expresses 3 IGnT transcripts,IGnTA,IGnTB,and IGnTC,and that the last of these is responsible for the I branching formation on red cells. In the present investigation,the K-562 cell line was used as a model to show that the i-to-I transition in erythroid differentiation is determined by the transcription factor CCAAT/enhancer binding protein alpha (C/EBPalpha),which enhances transcription of the IGnTC gene,consequently leading to formation of the I antigen. Further investigation suggested that C/EBPalpha IGnTC-activation activity is modulated at a posttranslational level,and that the phosphorylation status of C/EBPalpha may have a crucial effect. Results from studies using adult and cord erythropoietic cells agreed with those derived using the K-562 cell model,with lentiviral expression of C/EBPalpha in CD34(+) hemopoietic cells demonstrating the determining role of C/EBPalpha in the induction of the IGnTC gene as well as in I antigen expression. View Publication

OBJECTIVE: Studies in pulmonary arteries (PA) of patients with chronic obstructive pulmonary disease (COPD) suggest that bone marrow-derived endothelial progenitor cells (CD133(+)) may infiltrate the intima and differentiate into smooth muscle cells (SMC). This study aimed to evaluate the plasticity of CD133(+) cells to differentiate into SMC and endothelial cells (EC) in both cell culture and human isolated PA. METHODS: Plasticity of granulocyte-colony stimulator factor (G-CSF)-mobilized peripheral blood CD133(+) cells was assessed in co-cultures with primary lines of human PA endothelial cells (PAEC) or SMC (PASMC) and in isolated human PA. We also evaluated if the phenotype of differentiated progenitor cells was acquired by fusion or differentiation. RESULTS: The in vitro studies demonstrated CD133(+) cells may acquire the morphology and phenotype of the cells they were co-cultured with. CD133(+) cells co-incubated with human isolated PA were able to migrate into the intima and differentiate into SMC. Progenitor cell differentiation was produced without fusion with mature cells. CONCLUSIONS: We provide evidence of plasticity of CD133(+) cells to differentiate into both endothelial cells and SMC,reinforcing the idea of their potential role in the remodeling process of PA in COPD. This process was conducted by transdifferentiation and not by cell fusion. View Publication

Normal prion protein (PrP(c)),an essential substrate for development of prion disease,is widely distributed in hematopoietic cells. Recent evidence that variant Creutzfeldt-Jakob disease can be transmitted by transfusion of red cell preparations has highlighted the need for a greater understanding of the biology of PrP(c) in blood and blood-forming tissues. Here,we show that in contrast to another glycosylphosphoinositol-anchored protein CD59,PrP(c) at the cell surface of cultured human erythroblasts is rapidly internalized through the endosomal pathway,where it colocalizes with the tetraspanin CD63. In the plasma membrane,PrP(c) colocalizes with the tetraspanin CD81. Cross-linking with anti-PrP(c) or anti-CD81 causes clustering of PrP(c) and CD81,suggesting they can share the same microdomain. These data are consistent with a role for tetraspanin-enriched microdomains in trafficking of PrP(c). These results,when taken together with recent evidence that exosomes released from cells as a result of endosomal-mediated recycling to the plasma membrane contain prion infectivity,provide a pathway for the propagation of prion diseases. View Publication

The transcription factor Runx1/AML1 is an important regulator of hematopoiesis and is critically required for the generation of the first definitive hematopoietic stem cells (HSCs) in the major vasculature of the mouse embryo. As a pivotal factor in HSC ontogeny,its transcriptional regulation is of high interest but is largely undefined. In this study,we used a combination of comparative genomics and chromatin analysis to identify a highly conserved 531-bp enhancer located at position + 23.5 in the first intron of the 224-kb mouse Runx1 gene. We show that this enhancer contributes to the early hematopoietic expression of Runx1. Transcription factor binding in vivo and analysis of the mutated enhancer in transient transgenic mouse embryos implicate Gata2 and Ets proteins as critical factors for its function. We also show that the SCL/Lmo2/Ldb-1 complex is recruited to the enhancer in vivo. Importantly,transplantation experiments demonstrate that the intronic Runx1 enhancer targets all definitive HSCs in the mouse embryo,suggesting that it functions as a crucial cis-regulatory element that integrates the Gata,Ets,and SCL transcriptional networks to initiate HSC generation. View Publication

Specific mutations in the human gene encoding the Wiskott-Aldrich syndrome protein (WASp) that compromise normal auto-inhibition of WASp result in unregulated activation of the actin-related protein 2/3 complex and increased actin polymerizing activity. These activating mutations are associated with an X-linked form of neutropenia with an intrinsic failure of myelopoiesis and an increase in the incidence of cytogenetic abnormalities. To study the underlying mechanisms,active mutant WASp(I294T) was expressed by gene transfer. This caused enhanced and delocalized actin polymerization throughout the cell,decreased proliferation,and increased apoptosis. Cells became binucleated,suggesting a failure of cytokinesis,and micronuclei were formed,indicative of genomic instability. Live cell imaging demonstrated a delay in mitosis from prometaphase to anaphase and confirmed that multinucleation was a result of aborted cytokinesis. During mitosis,filamentous actin was abnormally localized around the spindle and chromosomes throughout their alignment and separation,and it accumulated within the cleavage furrow around the spindle midzone. These findings reveal a novel mechanism for inhibition of myelopoiesis through defective mitosis and cytokinesis due to hyperactivation and mislocalization of actin polymerization. View Publication

We show here that the process of megakaryocytic differentiation requires the presence of the recently discovered protein tescalcin. Tescalcin is dramatically upregulated during the differentiation and maturation of primary megakaryocytes or upon PMA-induced differentiation of K562 cells. This upregulation requires sustained signaling through the ERK pathway. Overexpression of tescalcin in K562 cells initiates events of spontaneous megakaryocytic differentiation,such as expression of specific cell surface antigens,inhibition of cell proliferation,and polyploidization. Conversely,knockdown of this protein in primary CD34+ hematopoietic progenitors and cell lines by RNA interference suppresses megakaryocytic differentiation. In cells lacking tescalcin,the expression of Fli-1,Ets-1,and Ets-2 transcription factors,but not GATA-1 or MafB,is blocked. Thus,tescalcin is essential for the coupling of ERK cascade activation with the expression of Ets family genes in megakaryocytic differentiation. View Publication

Human embryonic stem cells,because of their unique combination of long-term self-renewal properties and pluripotency,are providing new avenues of investigation of stem cell biology and human development and show promise in providing a new source of human cells for transplantation therapies and pharmaceutical testing. Current methods of propagating these cells using combinations of mouse fibroblast feeder cultures and bovine serum components are inexpensive and,in general,useful. However,the systematic investigation of the regulation of self-renewal and the production of safer sources of cells for transplantation depends on the elimination of animal products and the use of defined culture conditions. Both goals are served by the development of serum-free culture methods for human embryonic stem cells. View Publication

BACKGROUND AND OBJECTIVES: Primitive human hematopoietic cells contain higher levels of aldehyde dehydrogenase (ALDH) activity than their terminally differentiating progeny but the particular stages when ALDH levels change have not been well defined. The objective of this study was to compare ALDH levels among the earliest stages of hematopoietic cell differentiation and to determine whether these could be exploited to obtain improved purity of human cord blood cells with long-term lympho-myeloid repopulating activity in vivo. DESIGN AND METHODS: ALDEFLUOR-stained human cord blood cells displaying different levels of ALDH activity were first analyzed for co-expression of various surface markers. Subsets of these cells were then isolated by multi-parameter flow cytometry and assessed for short-and long-term repopulating activity in sublethally irradiated immunodeficient mice. RESULTS: Most short-term myeloid repopulating cells (STRC-M) and all long-term lympho-myeloid repopulating cells (LTRC-ML) stained selectively as ALDH+. Limiting dilution analysis of the frequencies of both STRC-M and LTRC-ML showed that they were similarly and most highly enriched in the 10% top ALDH+ cells. Removal of cells expressing CD2,CD3,CD7,CD14,CD16,CD24,CD36,CD38,CD56,CD66b,or glycophorin A from the ALDH+ low-density fraction of human cord blood cells with low light side-scattering properties yielded a population containing LTRC-ML at a frequency of 1/360. INTERPRETATION AND CONCLUSION: Elevated ALDH activity is a broadly inclusive property of primitive human cord blood cells that,in combination with other markers,allows easy isolation of the stem cell fraction at unprecedented purities. View Publication

OBJECTIVE: In murine hematopoietic tissue,direct repopulation experiments have demonstrated that the side population (SP) represents a remarkable enrichment of hematopoietic stem cells. Human SP has been phenotyped as negative for lineage antigens as well as CD34. However,in the 9 years since the original publication,no long-term hematopoietic reconstitution has been reported for the adult human SP/CD34(-) subset. Elevated levels of aldehyde dehydrogenase (ALDH) have been demonstrated in murine and human progenitor cells when compared to other hematopoietic cells. METHODS: Here,we report the phenotype of human cord blood SP cells. We established the technique of simultaneous phenotyping,Hoechst exclusion,and ALDH labeling on murine tissues. We then performed the simultaneous analysis of phenotype,SP,and ALDH activity on human cord blood and bone marrow cells. Finally,we analyzed the phenotype and functional potential of human cord blood ALDH(+) cells to determine whether Lin(-)/CD34(-) cells are identified via this technique. RESULTS: We demonstrate that human Lin(-)/CD34(-)/ALDH(+) cells are capable of long-term repopulation. Although the SP technique identifies cells that overlap with the ALDH(+) cell population,this is restricted to the CD34(+) cell subset. CONCLUSION: Hoechst exclusion ability does not seem to be the method of choice for the isolation of human hematopoietic stem cells. View Publication

Cited2 (cAMP-responsive elementbinding protein [CBP]/p300-interacting transactivators with glutamic acid [E] and aspartic acid [D]-rich tail 2) is a newly identified transcriptional modulator. Knockout of the Cited2 gene results in embryonic lethality with embryos manifesting heart and neural tube defects. Cited2-/- fetal liver displayed significant reduction in the numbers of Lin(-)c-Kit+Sca-1+ cells,Lin(-)c-Kit+ cells,and progenitor cells of different lineages. Fetal liver cells from Cited2-/- embryos gave rise to markedly reduced number of colonies in the colony-forming unit assay. Primary and secondary transplantation studies showed significantly compromised reconstitution of T-lymphoid,B-lymphoid,and myeloid lineages in mice that received a transplant of Cited2-/- fetal liver cells. Competitive reconstitution experiments further showed that fetal liver hematopoietic stem cell (HSC) function is severely impaired due to Cited2 deficiency. Microarray analysis showed decreased expression of Wnt5a and a panel of myeloid molecular markers such as PRTN3,MPO,Neutrophil elastase,Cathepsin G,and Eosinophil peroxidase in Cited2-/- fetal livers. Decreased expression of Bmi-1,Notch1,LEF-1,Mcl-1,and GATA2 was also observed in Cited2-/- Lin(-)c-Kit+ cells. The present study uncovers for the first time a novel role of Cited2 in the maintenance of hematopoietic homeostasis during embryogenesis and thus provides new insights into the molecular regulation of hematopoietic development. View Publication