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Flt3 ligand (Flt3L) is a nonredundant cytokine in type I interferon-producing cell (IPC) and dendritic cell (DC) development,and IPC and DC differentiation potential is confined to Flt3+ hematopoietic progenitor cells. Here,we show that overexpression of human Flt3 in Flt3- (Flt3(-)Lin(-)IL-7Ralpha(-)Thy1.1(-)c-Kit+) and Flt3+ (Flt3(+)Lin(-)IL-7Ralpha(-)Thy1.1(-)c-Kit+) hematopoietic progenitors rescues and enhances their IPC and DC differentiation potential,respectively. In defined hematopoietic cell populations,such as Flt3- megakaryocyte/erythrocyte-restricted progenitors (MEPs),enforced Flt3 signaling induces transcription of IPC,DC,and granulocyte/macrophage (GM) development-affiliated genes,including STAT3,PU.1,and G-/M-/GM-CSFR,and activates differentiation capacities to these lineages. Moreover,ectopic expression of Flt3 downstream transcription factors STAT3 or PU.1 in Flt3- MEPs evokes Flt3 receptor expression and instructs differentiation into IPCs,DCs,and myelomonocytic cells,whereas GATA-1 expression and consecutive megakaryocyte/erythrocyte development is suppressed. Based on these data,we propose a demand-regulated,cytokine-driven DC and IPC regeneration model,in which high Flt3L levels initiate a self-sustaining,Flt3-STAT3- and Flt3-PU.1-mediated IPC and DC differentiation program in Flt3+ hematopoietic progenitor cells. View Publication

Menin is the product of the tumor suppressor gene Men1 that is mutated in the inherited tumor syndrome multiple endocrine neoplasia type 1 (MEN1). Menin has been shown to interact with SET-1 domain-containing histone 3 lysine 4 (H3K4) methyltransferases including mixed lineage leukemia proteins to regulate homeobox (Hox) gene expression in vitro. Using conditional Men1 knockout mice,we have investigated the requirement for menin in hematopoiesis and myeloid transformation. Men1 excision causes reduction of Hoxa9 expression,colony formation by hematopoietic progenitors,and the peripheral white blood cell count. Menin directly activates Hoxa9 expression,at least in part,by binding to the Hoxa9 locus,facilitating methylation of H3K4,and recruiting the methylated H3K4 binding protein chd1 to the locus. Consistent with signaling downstream of menin,ectopic expression of both Hoxa9 and Meis1 rescues colony formation defects in Men1-excised bone marrow. Moreover,Men1 excision also suppresses proliferation of leukemogenic mixed lineage leukemia-AF9 fusion-protein-transformed myeloid cells and Hoxa9 expression. These studies uncover an important role for menin in both normal hematopoiesis and myeloid transformation and provide a mechanistic understanding of menin's function in these processes that may be used for therapy. View Publication

It has been shown that Notch signaling mediated by ligands of both Jagged and Delta families expands the hematopoietic stem cell compartment while blocking or delaying terminal myeloid differentiation. Here we show that Delta1- and Jagged1-expressing stromal cells have distinct effects on the clonogenic and differentiation capacities of human CD34(+) CD38(+) cells. Jagged1 increases the number of bipotent colony-forming unit-granulocyte macrophage (CFU-GM) and unipotent progenitors (CFU-granulocytes and CFU-macrophages),without quantitatively affecting terminal cell differentiation,whereas Delta1 reduces the number of CFU-GM and differentiated monocytic cells. Expression analysis of genes coding for Notch receptors,Notch targets,and Notch signaling modulators in supernatant CD34(+) cells arising upon contact with Jagged1 and Delta1 shows dynamic and differential gene expression profiles over time. At early time points,modest upregulation of Notch1,Notch3,and Hes1 was observed in Jagged1-CD34(+) cells,whereas those in contact with Delta1 strikingly upregulated Notch3 and Hes1. Later,myeloid progenitors with strong clonogenic potential emerging upon contact with Jagged1 upregulated Notch1 and Deltex and downregulated Notch signaling modulators,whereas T/NK progenitors originated by Delta1 strikingly upregulated Notch3 and Deltex and,to a lesser extent,Hes1,Lunatic Fringe,and Numb. Together,the data unravel previously unrecognized expression patterns of Notch signaling-related genes in CD34(+) CD38(+) cells as they develop in Jagged1- or Delta1-stromal cell environments,which appear to reflect sequential maturational stages of CD34(+) cells into distinct cell lineages. View Publication

The existence of mammary stem cells (MaSCs) has been postulated from evidence that the mammary gland can be regenerated by transplantation of epithelial fragments in mice. Interest in MaSCs has been further stimulated by their potential role in breast tumorigenesis. However,the identity and purification of MaSCs has proved elusive owing to the lack of defined markers. We isolated discrete populations of mouse mammary cells on the basis of cell-surface markers and identified a subpopulation (Lin-CD29hiCD24+) that is highly enriched for MaSCs by transplantation. Here we show that a single cell,marked with a LacZ transgene,can reconstitute a complete mammary gland in vivo. The transplanted cell contributed to both the luminal and myoepithelial lineages and generated functional lobuloalveolar units during pregnancy. The self-renewing capacity of these cells was demonstrated by serial transplantation of clonal outgrowths. In support of a potential role for MaSCs in breast cancer,the stem-cell-enriched subpopulation was expanded in premalignant mammary tissue from MMTV-wnt-1 mice and contained a higher number of MaSCs. Our data establish that single cells within the Lin-CD29hiCD24+ population are multipotent and self-renewing,properties that define them as MaSCs. View Publication

We assessed viable Pax7(-/-) mice in 129Sv/J background and observed reduced growth and marked muscle wasting together with a complete absence of functional satellite cells. Acute injury resulted in an extreme deficit in muscle regeneration. However,a small number of regenerated myofibers were detected,suggesting the presence of residual myogenic cells in Pax7-deficient muscle. Rare Pax3(+)/MyoD+ myoblasts were recovered from Pax7(-/-) muscle homogenates and cultures of myofiber bundles but not from single myofibers free of interstitial tissues. Finally,we identified Pax3+ cells in the muscle interstitial environment and demonstrated that they coexpressed MyoD during regeneration. Sublaminar satellite cells in hind limb muscle did not express detectable levels of Pax3 protein or messenger RNA. Therefore,we conclude that interstitial Pax3+ cells represent a novel myogenic population that is distinct from the sublaminar satellite cell lineage and that Pax7 is essential for the formation of functional myogenic progenitors from sublaminar satellite cells. View Publication

We have previously reported that high concentrations of basic fibroblast growth factor (bFGF) support feeder-independent growth of human embryonic stem (ES) cells,but those conditions included poorly defined serum and matrix components. Here we report feeder-independent human ES cell culture that includes protein components solely derived from recombinant sources or purified from human material. We describe the derivation of two new human ES cell lines in these defined culture conditions. View Publication

Stem cells are highly conserved biological units of development and regeneration. Here we formally demonstrate that stem cell lineages are also legitimate units of natural selection. In a colonial ascidian,Botryllus schlosseri,vascular fusion between genetically distinct individuals results in cellular parasitism of somatic tissues,gametes,or both. We show that genetic hierarchies of somatic and gametic parasitism following fusion can be replicated by transplanting cells between colonies. We prospectively isolate a population of multipotent,self-renewing stem cells that retain their competitive phenotype upon transplantation. Their single-cell contribution to either somatic or germline fates,but not to both,is consistent with separate lineages of somatic and germline stem cells or pluripotent stem cells that differentiate according to the niche in which they land. Since fusion is restricted to individuals that share a fusion/histocompatibility allele,these data suggest that histocompatibility genes in Botryllus evolved to protect the body from parasitic stem cells usurping asexual or sexual inheritance. View Publication

Interleukin-6 (IL-6) and its soluble receptor (sIL-6R) are major factors for maintenance and expansion of hematopoietic stem cells (HSCs). Sensitivity of HSCs to IL-6 has been previously studied,in part by measuring the expression of IL-6R on the membrane (mIL-6R). Several studies have described the regulation of cell surface expression of IL-6R by several cytokines,but the role of glycoprotein 130 activation has not yet been investigated. In this study,CD133(+) cells were purified from adult peripheral blood and were precultured in the absence or presence of 5-fluorouracil (5-FU) for selection of quiescent HSCs. Cells were cultured with continuous or pulsed stimulations of an IL-6-sIL-6R fusion protein (hyperinterleukin-6 [HIL-6]) to 1) detect mIL-6R by flow cytometry,2) assess mIL-6R and sIL-6R RNAs by reverse transcription-polymerase chain reaction,3) measure sIL-6R in supernatants by enzyme-linked immunosorbent assay,4) analyze cell-cycle status,and 5) perform long-term culture-initiating cell assays. The level of mIL-6R(-) cells was preserved by 5-FU incubation. HIL-6 increased steady-state mIL-6R RNA and expression rate on HSCs,independently of treatment with 5-FU. Enhanced production of sIL-6R was observed with short pulses of HIL-6 on CD133(+) 5-FU-pretreated cells. This overproduction of sIL-6R was abrogated by tumor necrosis factor-alpha protease inhibitor-1,an inhibitor of a disintegrin and metalloprotease proteases,suggesting the shedding of mIL-6R. This phenomenon was mediated through the phosphatidylinositol-3'-kinase pathway and was involved in the maintenance of primitive HSCs. In conclusion,expression and production of IL-6R are tightly regulated and stage specific. We assume that sIL-6R produced by shedding should be involved in autocrine and paracrine loops in the HSC microenvironment. View Publication

Spinal muscular atrophy with respiratory distress type 1 (SMARD1) is an infantile autosomal-recessive motor neuron disease caused by mutations in the immunoglobulin micro-binding protein 2. We investigated the potential of a spinal cord neural stem cell population isolated on the basis of aldehyde dehydrogenase (ALDH) activity to modify disease progression of nmd mice,an animal model of SMARD1. ALDH(hi)SSC(lo) stem cells are self-renewing and multipotent and when intrathecally transplanted in nmd mice generate motor neurons properly localized in the spinal cord ventral horns. Transplanted nmd animals presented delayed disease progression,sparing of motor neurons and ventral root axons and increased lifespan. To further investigate the molecular events responsible for these differences,microarray and real-time reverse transcription-polymerase chain reaction analyses of wild-type,mutated and transplanted nmd spinal cord were undertaken. We demonstrated a down-regulation of genes involved in excitatory amino acid toxicity and oxidative stress handling,as well as an up-regulation of genes related to the chromatin organization in nmd compared with wild-type mice,suggesting that they may play a role in SMARD1 pathogenesis. Spinal cord of nmd-transplanted mice expressed high transcript levels for genes related to neurogenesis such as doublecortin (DCX),LIS1 and drebrin. The presence of DCX-expressing cells in adult nmd spinal cord suggests that both exogenous and endogenous neurogeneses may contribute to the observed nmd phenotype amelioration. View Publication

BACKGROUND: The dose-limiting toxicity of doxorubicin on hematopoietic stem cells reduces the maximum benefit from this powerful drug. Melatonin may play a role in reducing this toxicity. MATERIALS AND METHODS: Melatonin at 10 microM was used while challenging human peripheral blood stem cells (PBSC) with doxorubicin (0.6 microM and 1 microM),and colony formation was used to evaluate the protective effect of melatonin. RESULTS: Melatonin was protective for the myeloid and erythroid series when given during or 1 hour after,but not before,doxorubicin,as measured by colony assay. This protection was independent from its antioxidant function as measured by 2',7'-dichlodihydro-fluorescein diacetate and was selective for PBSC when compared to the MCF-7 cancer cell line. CONCLUSION: The results suggest the importance of the time sequence for melatonin administration to exert its protective effect in relation to doxorubicin treatment,as well as its protective effect on both erythroid and myeloid elements independent from its antioxidant function. View Publication

Resident host microflora condition and prime the immune system. However,systemic and mucosal immune responses to bacteria may be divergent. Our aim was to compare,in vitro,cytokine production by human mononuclear and dendritic cells (DCs) from mesenteric lymph nodes (MLNs) and peripheral blood mononuclear cells (PBMCs) to defined microbial stimuli. Mononuclear cells and DCs isolated from the MLN (n = 10) and peripheral blood (n = 12) of patients with active colitis were incubated in vitro with the probiotic bacteria Lactobacillus salivarius UCC118 or Bifidobacterium infantis 35624 or the pathogenic organism Salmonella typhimurium UK1. Interleukin (IL)-12,tumor necrosis factor (TNF)-alpha,transforming growth factor (TGF)-beta,and IL-10 cytokine levels were quantified by ELISA. PBMCs and PBMC-derived DCs secreted TNF-alpha in response to the Lactobacillus,Bifidobacteria,and Salmonella strains,whereas MLN cells and MLN-derived DCs secreted TNF-alpha only in response to Salmonella challenge. Cells from the systemic compartment secreted IL-12 after coincubation with Salmonella or Lactobacilli,whereas MLN-derived cells produced IL-12 only in response to Salmonella. PBMCs secreted IL-10 in response to the Bifidobacterium strain but not in response to the Lactobacillus or Salmonella strain. However,MLN cells secreted IL-10 in response to Bifidobacteria and Lactobacilli but not in response to Salmonella. In conclusion,commensal bacteria induced regulatory cytokine production by MLN cells,whereas pathogenic bacteria induce T cell helper 1-polarizing cytokines. Commensal-pathogen divergence in cytokine responses is more marked in cells isolated from the mucosal immune system compared with PBMCs. View Publication

The molecular mechanism responsible for a decline of stem cell functioning after replicative stress remains unknown. We used mouse embryonic fibroblasts (MEFs) and hematopoietic stem cells (HSCs) to identify genes involved in the process of cellular aging. In proliferating and senescent MEFs one of the most differentially expressed transcripts was Enhancer of zeste homolog 2 (Ezh2),a Polycomb group protein (PcG) involved in histone methylation and deacetylation. Retroviral overexpression of Ezh2 in MEFs resulted in bypassing of the senescence program. More importantly,whereas normal HSCs were rapidly exhausted after serial transplantations,overexpression of Ezh2 completely conserved long-term repopulating potential. Animals that were reconstituted with 3 times serially transplanted control bone marrow cells all died due to hematopoietic failure. In contrast,similarly transplanted Ezh2-overexpressing stem cells restored stem cell quality to normal levels. In a genetic genomics" screen� View Publication