Differential gene expression profiling of adult murine hematopoietic stem cells

TET2 deficiency increases the competitive advantage of hematopoietic stem and progenitor cells through upregulation of thrombopoietin receptor signaling

Ten-Eleven Translocation-2 (TET2) mutations drive the expansion of mutant hematopoietic stem cells (HSCs) in clonal hematopoiesis (CH). However, the precise mechanisms by which TET2 mutations confer a competitive advantage to HSCs remain unclear. Here, through an epigenetic drug screen, we discover that inhibition of disruptor of telomeric silencing 1-like (DOT1L), a H3K79 methyltransferase, selectively reduces the fitness of Tet2 knockout (Tet2KO) hematopoietic stem and progenitor cells (HSPCs). Mechanistically, we find that TET2 deficiency increases H3K79 dimethylation and expression of Mpl, which encodes the thrombopoietin receptor (TPO-R). Correspondingly, TET2 deficiency is associated with a higher proportion of primitive Mpl-expressing (Mpl+) cells in the HSC compartment. Importantly, inhibition of Mpl expression or the signaling downstream of TPO-R is sufficient to reduce the competitive advantage of murine and human TET2-deficient HSPCs. Our findings demonstrate a critical role for aberrant TPO-R signaling in TET2 mutation-driven CH and uncover potential therapeutic strategies against this condition.

Ing4-deficiency promotes a quiescent yet transcriptionally poised state in hematopoietic stem cells

Defining the mechanisms that regulate stem cell maintenance, proliferation, and differentiation is critical for identifying therapies for improving stem cell function under stress. Here, we have identified the tumor suppressor, inhibitor of growth 4 (Ing4), as a critical regulator of hematopoietic stem cell (HSC) homeostasis. Cancer cell line models with Ing4 deficiency have shown that Ing4 functions as a tumor suppressor, in part, due to Ing4-mediated regulation of several major signaling pathways, including c-Myc. In HSCs, we show Ing4 deficiency promotes gene expression signatures associated with activation, yet HSCs are arrested in G0, expressing several markers of quiescence. Functionally, Ing4-deficient HSCs demonstrate robust regenerative capacity following transplantation. Our findings suggest Ing4 deficiency promotes a poised state in HSCs, where they appear transcriptionally primed for activation but remain in a resting state. Our model provides key tools for further identification and characterization of pathways that control quiescence and self-renewal in HSCs.

Cyclin-dependent kinase inhibitors in malignant hematopoiesis

The cell-cycle is a tightly orchestrated process where sequential steps guarantee cellular growth linked to a correct DNA replication. The entire cell division is controlled by cyclin-dependent kinases (CDKs). CDK activation is balanced by the activating cyclins and CDK inhibitors whose correct expression, accumulation and degradation schedule the time-flow through the cell cycle phases. Dysregulation of the cell cycle regulatory proteins causes the loss of a controlled cell division and is inevitably linked to neoplastic transformation. Due to their function as cell-cycle brakes, CDK inhibitors are considered as tumor suppressors. The CDK inhibitors p16^INK4a and p15^INK4b are among the most frequently altered genes in cancer, including hematopoietic malignancies. Aberrant cell cycle regulation in hematopoietic stem cells (HSCs) bears severe consequences on hematopoiesis and provokes hematological disorders with a broad array of symptoms. In this review, we focus on the importance and prevalence of deregulated CDK inhibitors in hematological malignancies.

Expanded circulating hematopoietic stem/progenitor cells as novel cell source for the treatment of TCIRG1 osteopetrosis

Allogeneic hematopoietic stem cell transplantation is the treatment of choice for autosomal recessive osteopetrosis caused by defects in the TCIRG1 gene. Despite recent progress in conditioning, a relevant number of patients are not eligible for allogeneic stem cell transplantation because of the severity of the disease and significant transplant-related morbidity. We exploited peripheral CD34+ cells, known to circulate at high frequency in the peripheral blood of TCIRG1-deficient patients, as a novel cell source for autologous transplantation of gene corrected cells. Detailed phenotypical analysis showed that circulating CD34+ cells have a cellular composition that resembles bone marrow, supporting their use in gene therapy protocols. Transcriptomic profile revealed enrichment in genes expressed by hematopoietic stem and progenitor cells (HSPCs). To overcome the limit of bone marrow harvest/ HSPC mobilization and serial blood drawings in TCIRG1 patients, we applied UM171-based ex-vivo expansion of HSPCs coupled with lentiviral gene transfer. Circulating CD34+ cells from TCIRG1-defective patients were transduced with a clinically-optimized lentiviral vector (LV) expressing TCIRG1 under the control of phosphoglycerate promoter and expanded ex vivo. Expanded cells maintained long-term engraftment capacity and multi-lineage repopulating potential when transplanted in vivo both in primary and secondary NSG recipients. Moreover, when CD34+ cells were differentiated in vitro, genetically corrected osteoclasts resorbed the bone efficiently. Overall, we provide evidence that expansion of circulating HSPCs coupled to gene therapy can overcome the limit of stem cell harvest in osteopetrotic patients, thus opening the way to future gene-based treatment of skeletal diseases caused by bone marrow fibrosis.

Constitutive Activation of NF-κB Pathway in Hematopoietic Stem Cells Causes Loss of Quiescence and Deregulated Transcription Factor Networks

Identifying physiological roles of specific signaling pathways that regulate hematopoietic stem cell (HSC) functions may lead to new treatment strategies and therapeutic interventions for hematologic disorders. Here, we provide genetic evidence that constitutive activation of NF-κB in HSCs results in reduced pool size, repopulation capacities, and quiescence of HSCs. Global transcriptional profiling and bioinformatics studies identified loss of ‘stemness’ and ‘quiescence’ signatures in HSCs with deregulated NF-κB activation. In particular, gene set enrichment analysis identified upregulation of cyclin dependent kinase- Ccnd1 and down regulation of cyclin dependent kinase inhibitor p57^kip2. Interestingly, constitutive activation of NF-κB is sufficient to alter the regulatory circuits of transcription factors (TFs) that are critical to HSC self-renewal and functions. Molecular studies identified Junb, as one of the direct targets of NF-κB in hematopoietic cells. In essence, these studies demonstrate that aberrant activation of NF-κB signals impairs HSC quiescence and functions and alters the ‘TF networks’ in HSCs.

Effector CD4 T cells with progenitor potential mediate chronic intestinal inflammation

Effector CD4 T cells with progenitor properties are present during chronic intestinal inflammation, and these cells support the maintenance of disease. The expression of the glycosyltransferase ST6Gal-I by these cells promotes cell survival and TCF1 levels.

Dysregulated CD4 T cell responses are causally linked to autoimmune and chronic inflammatory disorders, yet the cellular attributes responsible for maintaining the disease remain poorly understood. Herein, we identify a discrete population of effector CD4 T cells that is able to both sustain and confer intestinal inflammation. This subset of pathogenic CD4 T cells possesses a unique gene signature consistent with self-renewing T cells and hematopoietic progenitor cells, exhibits enhanced survival, and continually seeds the terminally differentiated IFNγ-producing cells in the inflamed intestine. Mechanistically, this population selectively expresses the glycosyltransferase ST6Gal-I, which is required for optimal expression of the stemness-associated molecule TCF1 by effector CD4 T cells. Our findings indicate that the chronicity of T cell–mediated inflammation is perpetuated by specific effector CD4 T cells with stem-like properties.

Depletion of Mageb16 induces differentiation of pluripotent stem cells predominantly into mesodermal derivatives

The Melanoma-associated Antigen gene family (MAGE) generally encodes for tumour antigens. We had identified that one of the MAGE gene members, Mageb16 was highly expressed in undifferentiated murine embryonic stem cells (ESCs). While the role of Mageb16 in stemness and differentiation of pluripotent stem cells is completely unknown, here, in our current study, we have demonstrated that Mageb16 (41 kDa) is distributed in cytosol and/or in surface membrane in undifferentiated ESCs. A transcriptome study performed at  differentiated short hairpin RNA (shRNA)-mediated Mageb16 knockdown (KD) ESCs and scrambled control (SCR) ESCs until a period of 22 days, revealed that Mageb16 KD ESCs mainly differentiated towards cells expressing mesodermal and cardiovascular lineage - gene markers. Gene markers of other mesoderm-oriented biological processes such as adipogenesis, osteogenesis, limb morphogenesis and spermatogenesis were also significantly enriched in the differentiated Mageb16 KD ESCs. The expression levels of contractile genes were higher in differentiated Mageb16 KD ESCs when compared to differentiated SCR and wild ESCs, suggesting a higher cardiomyogenic potential of Mageb16 depleted ESCs. Further analysis indicates  that regulative epigenetic networks and nucleocytoplasmic modifications induced by the depletion of Mageb16, may play a probable role in differentiation.

Single cell transcriptomics reveals unanticipated features of early hematopoietic precursors

Molecular changes underlying stem cell differentiation are of fundamental interest. scRNA-seq on murine hematopoietic stem cells (HSC) and their progeny MPP1 separated the cells into 3 main clusters with distinct features: active, quiescent, and an un-characterized cluster. Induction of anemia resulted in mobilization of the quiescent to the active cluster and of the early to later stage of cell cycle, with marked increase in expression of certain transcription factors (TFs) while maintaining expression of interferon response genes. Cells with surface markers of long term HSC increased the expression of a group of TFs expressed highly in normal cycling MPP1 cells. However, at least Id1 and Hes1 were significantly activated in both HSC and MPP1 cells in anemic mice. Lineage-specific genes were differently expressed between cells, and correlated with the cell cycle stages with a specific augmentation of erythroid related genes in the G2/M phase. Most lineage specific TFs were stochastically expressed in the early precursor cells, but a few, such as Klf1, were detected only at very low levels in few precursor cells. The activation of these factors may correlate with stages of differentiation. This study reveals effects of cell cycle progression on the expression of lineage specific genes in precursor cells, and suggests that hematopoietic stress changes the balance of renewal and differentiation in these homeostatic cells.

KATapulting toward Pluripotency and Cancer

Development is generally regarded as a unidirectional process that results in the acquisition of specialized cell fates. During this process, cellular identity is precisely defined by signaling cues that tailor the chromatin landscape for cell-specific gene expression programs. Once established, these pathways and cell states are typically resistant to disruption. However, loss of cell identity occurs during tumor initiation and upon injury response. Moreover, terminally differentiated cells can be experimentally provoked to become pluripotent. Chromatin reorganization is key to the establishment of new gene expression signatures and thus new cell identity. Here, we explore an emerging concept that lysine acetyltransferase (KAT) enzymes drive cellular plasticity in the context of somatic cell reprogramming and tumorigenesis.

Acetylation of C/EBPα inhibits its granulopoietic function

CCAAT/enhancer-binding protein alpha (C/EBPα) is an essential transcription factor for myeloid lineage commitment. Here we demonstrate that acetylation of C/EBPα at lysine residues K298 and K302, mediated at least in part by general control non-derepressible 5 (GCN5), impairs C/EBPα DNA-binding ability and modulates C/EBPα transcriptional activity. Acetylated C/EBPα is enriched in human myeloid leukaemia cell lines and acute myeloid leukaemia (AML) samples, and downregulated upon granulocyte-colony stimulating factor (G-CSF)- mediated granulocytic differentiation of 32Dcl3 cells. C/EBPα mutants that mimic acetylation failed to induce granulocytic differentiation in C/EBPα-dependent assays, in both cell lines and in primary hematopoietic cells. Our data uncover GCN5 as a negative regulator of C/EBPα and demonstrate the importance of C/EBPα acetylation in myeloid differentiation.

C/EBPα is an essential transcription factor for myeloid lineage commitment. Here, the authors show that acetylation of C/EBPα at K298 and K302, mediated at least in part by GCN5, impairs C/EBPα DNA binding ability and modulates C/EBPα transcriptional activity.

Molecular mechanism of extrinsic factors affecting anti-aging of stem cells

Scientific evidence suggests that stem cells possess the anti-aging ability to self-renew and maintain differentiation potentials, and quiescent state. The objective of this review is to discuss the micro-environment where stem cells reside in vivo, the secreted factors to which stem cells are exposed, the hypoxic environment, and intracellular factors including genome stability, mitochondria integrity, epigenetic regulators, calorie restrictions, nutrients, and vitamin D. Secreted tumor growth factor-β and fibroblast growth factor-2 are reported to play a role in stem cell quiescence. Extracellular matrices may interact with caveolin-1, the lipid raft on cell membrane to regulate quiescence. N-cadherin, the adhesive protein on niche cells provides support for stem cells. The hypoxic micro-environment turns on hypoxia-inducible factor-1 to prevent mesenchymal stem cells aging through p16 and p21 down-regulation. Mitochondria express glucosephosphate isomerase to undergo glycolysis and prevent cellular aging. Epigenetic regulators such as p300, protein inhibitors of activated Stats and H19 help maintain stem cell quiescence. In addition, calorie restriction may lead to secretion of paracrines cyclic ADP-ribose by intestinal niche cells, which help maintain intestinal stem cells. In conclusion, it is crucial to understand the anti-aging phenomena of stem cells at the molecular level so that the key to solving the aging mystery may be unlocked.

Fam40b is required for lineage commitment of murine embryonic stem cells

FAM40B (STRIP2) is a member of the striatin-interacting phosphatase and kinase (STRIPAK) complex that is involved in the regulation of various processes such as cell proliferation and differentiation. Its role for differentiation processes in embryonic stem cells (ESCs) is till now completely unknown. Short hairpin RNA (shRNA)-mediated silencing of Fam40b expression in ESCs and differentiating embryoid bodies (EBs) led to perturbed differentiation to embryonic germ layers and their derivatives including a complete abrogation of cardiomyogenesis. Pluripotency factors such as Nanog, Oct4 and Sox2 as well as epigenetic factors such as histone acetyltransferase type B (HAT1) and DNA (cytosine-5)-methyltransferase 3-β (Dnmt3b) were highly upregulated in Fam40b knockdown EBs as compared with control and scrambled EBs. To examine the relevance of Fam40b for development in vivo, Fam40b was knocked down in developing zebrafish. Morpholino-mediated knockdown of Fam40b led to severe abnormalities of the cardiovascular system, including an impaired expression of ventricular myosin heavy chain (vmhc) and of cardiac myosin light chain 2 (cmlc2) in the heart. We identified the gene product of Fam40b in ESCs as a perinuclear and nucleolar protein with a molecular weight of 96 kDa. We conclude that the expression of Fam40b is essential for the lineage commitment of murine embryonic stem cells (mESCs) into differentiated somatic cells via mechanisms involving pluripotency and epigenetic networks.

Fgd5 identifies hematopoietic stem cells in the murine bone marrow

Fdg5 identifies bone marrow cells with potent hematopoietic stem cell activity.

Hematopoietic stem cells (HSCs) are the best-characterized tissue-specific stem cells, yet experimental study of HSCs remains challenging, as they are exceedingly rare and methods to purify them are cumbersome. Moreover, genetic tools for specifically investigating HSC biology are lacking. To address this we sought to identify genes uniquely expressed in HSCs within the hematopoietic system and to develop a reporter strain that specifically labels them. Using microarray profiling we identified several genes with HSC-restricted expression. Generation of mice with targeted reporter knock-in/knock-out alleles of one such gene, Fgd5, revealed that though Fgd5 was required for embryonic development, it was not required for definitive hematopoiesis or HSC function. Fgd5 reporter expression near exclusively labeled cells that expressed markers consistent with HSCs. Bone marrow cells isolated based solely on Fgd5 reporter signal showed potent HSC activity that was comparable to stringently purified HSCs. The labeled fraction of the Fgd5 reporter mice contained all HSC activity, and HSC-specific labeling was retained after transplantation. Derivation of next generation mice bearing an Fgd5-CreERT2 allele allowed tamoxifen-inducible deletion of a conditional allele specifically in HSCs. In summary, reporter expression from the Fgd5 locus permits identification and purification of HSCs based on single-color fluorescence.

Dynamic equilibrium of heterogeneous and interconvertible multipotent hematopoietic cell subsets

Populations of hematopoietic stem cells and progenitors are quite heterogeneous and consist of multiple cell subsets with distinct phenotypic and functional characteristics. Some of these subsets also appear to be interconvertible and oscillate between functionally distinct states. The multipotent hematopoietic cell line EML has emerged as a unique model to study the heterogeneity and interconvertibility of multipotent hematopoietic cells. Here we describe extensive phenotypic and functional heterogeneity of EML cells which stems from the coexistence of multiple cell subsets. Each of these subsets is phenotypically and functionally heterogeneous, and displays distinct multilineage differentiation potential, cell cycle profile, proliferation kinetics, and expression pattern of HSC markers and some of the key lineage-associated transcription factors. Analysis of their maintenance revealed that on a population level all EML cell subsets exhibit cell-autonomous interconvertible properties, with the capacity to generate all other subsets and re-establish complete parental EML cell population. Moreover, all EML cell subsets generated during multiple cell generations maintain their distinct phenotypic and functional signatures and interconvertible properties. The model of EML cell line suggests that interconvertible multipotent hematopoietic cell subsets coexist in a homeostatically maintained dynamic equilibrium which is regulated by currently unknown cell-intrinsic mechanisms.

Aldehyde dehydrogenases in acute myeloid leukemia

Acute myeloid leukemia (AML) affects approximately 15,000 persons per year in the United States and is the sixth leading cause of cancer-related deaths. The treatment of AML has advanced little in the past thirty years, in part because of the biologic heterogeneity of the disease and the difficulty in targeting AML cells while sparing normal hematopoietic cells. Advances in preventing and treating AML are likely to occur once the cellular and molecular differences between leukemia and normal hematopoietic cells are better understood. Aldehyde dehydrogenase (ALDH) activity is highly expressed in hematopoietic stem cells (HSCs), while, in contrast, a subset of AMLs are lacking this activity. This difference may be relevant to the development of AML and may also provide a better avenue for treating this disease. In this review, we summarize what is known about the ALDHs in normal HSCs and AML and propose strategies for capitalizing on these differences in the treatment of acute leukemia, and possibly other cancers as well.

Spatiotemporal pattern of RNA-binding motif protein 3 expression after spinal cord injury in rats

RNA-binding motif protein 3 (RBM3) belongs to a very small group of cold inducible proteins with anti-apoptotic and proliferative functions. To elucidate the expression and possible function of RBM3 in central nervous system (CNS) lesion and repair, we performed a spinal cord injury (SCI) model in adult rats. Western blot analysis revealed that RBM3 level significantly increased at 1 day after damage, and then declined during the following days. Immunohistochemistry further confirmed that RBM3 immunoactivity was expressed at low levels in gray and white matters in normal condition and increased at 1 day after SCI. Besides, double immunofluorescence staining showed RBM3 was primarily expressed in the neurons and a few of astrocytes in the normal group. While after injury, the expression of RBM3 increased both in neurons and astrocytes at 1 day. We also examined the expression profiles of proliferating cell nuclear antigen (PCNA) and active caspase-3 in injured spinal cords by western blot. Importantly, double immunofluorescence staining revealed that cell proliferation evaluated by PCNA appeared in many RBM3-expressing cells and rare caspase-3 was observed in RBM3-expressing cells at 1 day after injury. Our data suggested that RBM3 might play important roles in CNS pathophysiology after SCI.

Deletion of Mecom in mouse results in early-onset spinal deformity and osteopenia

Recent studies have indicated a role for a MECOM allele in susceptibility to osteoporotic fractures in humans. We have generated a mutation in Mecom in mouse (termed ME(m1)) via lacZ knock-in into the upstream transcription start site for the gene, resulting in disruption of Mds1 and Mds1-Evi1 transcripts, but not of Evi1 transcripts. We demonstrate that ME(m1/m1) mice have severe kyphoscoliosis that is reminiscent of human congenital or primary kyphoscoliosis. ME(m1/m1) mice appear normal at birth, but by 2weeks, they exhibit a slight lumbar lordosis and narrowed intervertebral space. This progresses to severe lordosis with disc collapse and synostosis, together with kyphoscoliosis. Bone formation and strength testing show that ME(m1/m1) mice have normal bone formation and composition but are osteopenic. While endochondral bone development is normal, it is markedly dysplastic in its organization. Electron micrographs of the 1week postnatal intervertebral discs reveals marked disarray of collagen fibers, consistent with an inherent weakness in the non-osseous connective tissue associated with the spine. These findings indicate that lack of ME leads to a complex defect in both osseous and non-osseous musculoskeletal tissues, including a marked vertebral osteopenia, degeneration of the IVD, and disarray of connective tissues, which is likely due to an inherent inability to establish and/or maintain components of these tissues.

Calcineurin regulates coordinated outgrowth of zebrafish regenerating fins

Vertebrates develop organs and appendages in a proportionally coordinated manner, and animals that regenerate them do so to the same dimensions as the original structures. Coordinated proportional growth involves controlled regulation between allometric and isometric growth programs, but it is unclear what executes this control. We show that calcineurin inhibition results in continued allometric outgrowth of regenerating fins beyond their original dimensions. Calcineurin inhibition also maintains allometric growth of juvenile fins and induces it in adult fins. Furthermore, calcineurin activity is low when the regeneration rate is highest, and its activity increases as the rate decreases. Growth measurements and morphometric analysis of proximodistal asymmetry indicate that calcineurin inhibition shifts fin regeneration from a distal growth program to a proximal program. This shift is associated with the promotion of retinoic acid signaling. Thus, we identified a calcineurin-mediated mechanism that operates as a molecular switch between position-associated isometric and allometric growth programs.

Gene expression profile and functionality of ESC-derived Lin-ckit+Sca-1+ cells are distinct from Lin-ckit+Sca-1+ cells isolated from fetal liver or bone marrow

In vitro bioreactor-based cultures are being extensively investigated for large-scale production of differentiated cells from embryonic stem cells (ESCs). However, it is unclear whether in vitro ESC-derived progenitors have similar gene expression profiles and functionalities as their in vivo counterparts. This is crucial in establishing the validity of ESC-derived cells as replacements for adult-isolated cells for clinical therapies. In this study, we compared the gene expression profiles of Lin-ckit+Sca-1+ (LKS) cells generated in vitro from mouse ESCs using either static or bioreactor-based cultures, with that of native LKS cells isolated from mouse fetal liver (FL) or bone marrow (BM). We found that in vitro-generated LKS cells were more similar to FL- than to BM LKS cells in gene expression. Further, when compared to cells derived from bioreactor cultures, static culture-derived LKS cells showed fewer differentially expressed genes relative to both in vivo LKS populations. Overall, the expression of hematopoietic genes was lower in ESC-derived LKS cells compared to cells from BM and FL, while the levels of non-hematopoietic genes were up-regulated. In order to determine if these molecular profiles correlated with functionality, we evaluated ESC-derived LKS cells for in vitro hematopoietic-differentiation and colony formation (CFU assay). Although static culture-generated cells failed to form any colonies, they did differentiate into CD11c+ and B220+ cells indicating some hematopoietic potential. In contrast, bioreactor-derived LKS cells, when differentiated under the same conditions failed to produce any B220+ or CD11c+ cells and did not form colonies, indicating that these cells are not hematopoietic progenitors. We conclude that in vitro culture conditions significantly affect the transcriptome and functionality of ESC-derived LKS cells and although in vitro differentiated LKS cells were lineage negative and expressed both ckit and Sca-1, these cells, especially those obtained from dynamic cultures, are significantly different from native cells of the same phenotype.

Gene Expression Commons: an open platform for absolute gene expression profiling

Gene expression profiling using microarrays has been limited to comparisons of gene expression between small numbers of samples within individual experiments. However, the unknown and variable sensitivities of each probeset have rendered the absolute expression of any given gene nearly impossible to estimate. We have overcome this limitation by using a very large number (>10,000) of varied microarray data as a common reference, so that statistical attributes of each probeset, such as the dynamic range and threshold between low and high expression, can be reliably discovered through meta-analysis. This strategy is implemented in a web-based platform named "Gene Expression Commons" (https://gexc.stanford.edu/) which contains data of 39 distinct highly purified mouse hematopoietic stem/progenitor/differentiated cell populations covering almost the entire hematopoietic system. Since the Gene Expression Commons is designed as an open platform, investigators can explore the expression level of any gene, search by expression patterns of interest, submit their own microarray data, and design their own working models representing biological relationship among samples.

Possible therapeutic use of spermatogonial stem cells in the treatment of male infertility: a brief overview

Development of germ cells is a process starting in fetus and completed only in puberty. Spermatogonial stem cells maintain spermatogenesis throughout the reproductive life of mammals. They are undifferentiated cells defined by their ability to both self-renew and differentiate into mature spermatozoa. This self-renewal and differentiation in turn is tightly regulated by a combination of intrinsic gene expression as well as the extrinsic gene signals from the local tissue microenvironment. The human testis is prone to damage, either for therapeutic reasons or because of toxic agents from the environment. For preservation of fertility, patients who will undergo radiotherapy and/or chemotherapy have an attractive possibility to keep in store and afterwards make a transfer of spermatogonial stem cells. Germ cell transplantation is not yet ready for the human fertility clinic, but it may be reasonable for young cancer patients, with no other options to preserve their fertility. Whereas this technique has become an important research tool in rodents, a clinical application must still be regarded as experimental, and many aspects of the procedure need to be optimized prior to a clinical application in men. In future, a range of options for the preservation of male fertility will get a new significance.

Angiopoietin1 contributes to the maintenance of cell quiescence in EVI1(high) leukemia cells

Ecotropic viral integration site-1 (EVI1) is an oncogenic transcription factor in human acute myeloid leukemia (AML) associated with poor prognosis. Because the drug-resistance of leukemia cells is partly dependent on cell quiescence in the bone marrow niche, EVI1 may be involved in cell cycle regulation in leukemia cells. As a candidate regulator of the cell cycle in leukemia cells with high EVI1 expression (EVI1(high)), we analyzed angiopoietin1 (Ang1), which is a down-regulated gene in EVI1-deficient mice and is involved in the quiescence of hematopoietic stem cells. The results of real-time PCR analyses showed that Ang1 is highly expressed in leukemia cell lines and primary AML cells with EVI1(high) expression. Introduction of shRNA against EVI1 into EVI1(high) leukemia cells down-regulated Ang1 expression. Moreover, knockdown of Ang1 in EVI1(high) leukemia cells promoted cell cycle progression and down-regulated the CDK inhibitor p18 (INK4c). Treatment with a decoy Tie2/Fc protein also down-regulated the expression of p18. These results suggest that Ang1/Tie2 signaling may suppress cell cycle progression via maintenance of G0/G1 phase through up-regulation of p18 expression. This mechanism may help to maintain EVI1(high) leukemia cells in the bone marrow niche and promote resistance to anti-cancer drugs.

Efficient hematopoietic redifferentiation of induced pluripotent stem cells derived from primitive murine bone marrow cells

Heterogeneity among induced pluripotent stem cell (iPSC) lines with regard to their gene expression profile and differentiation potential has been described and at least partly linked to the tissue of origin. Here, we generated iPSCs from primitive [lineage negative (Lin(neg))] and nonadherent differentiated [lineage positive (Lin(pos))] bone marrow cells (BM-iPSC), and compared their differentiation potential to that of fibroblast-derived iPSCs (Fib-iPSC) and embryonic stem cells (ESC). In the undifferentiated state, individual iPSC clones but also ESCs proved remarkably similar when analyzed for alkaline phosphatase and SSEA-1 staining, endogenous expression of the pluripotency genes Nanog, Oct4, and Sox2, or global gene expression profiles. However, substantial differences between iPSC clones were observed after induction of differentiation, which became most obvious upon cytokine-mediated instruction toward the hematopoietic lineage. All 3 BM-iPSC lines derived from undifferentiated Lin(neg) cells yielded high proportions of cells expressing the hematopoietic differentiation marker CD41 and in 2 of these lines high proportions of CD41+/ CD45+ cells were detected. In contrast, little hematopoiesis-specific surface marker expression was detected in 4 Lin(pos) BM-iPSC and 3 Fib-iPSC lines. These results were corroborated by functional studies demonstrating robust colony outgrowth from hematopoietic progenitors in 2 of the Lin(neg) BM-iPSCs only. Thus, in conclusion, our data demonstrate efficient generation of iPSCs from primitive hematopoietic tissue as well as efficient hematopoietic redifferentiation for Lin(neg) BM-iPSC lines, thereby supporting the notion of an epigenetic memory in iPSCs.

PR-domain-containing Mds1-Evi1 is critical for long-term hematopoietic stem cell function

The Mds1 and Evi1 complex locus (Mecom) gives rise to several alternative transcripts implicated in leukemogenesis. However, the contribution that Mecom-derived gene products make to normal hematopoiesis remains largely unexplored. To investigate the role of the upstream transcription start site of Mecom in adult hematopoiesis, we created a mouse model with a lacZ knock-in at this site, termed ME(m1), which eliminates Mds1-Evi1 (ME), the longer, PR-domain-containing isoform produced by the gene (also known as PRDM3). β-galactosidase-marking studies revealed that, within hematopoietic cells, ME is exclusively expressed in the stem cell compartment. ME deficiency leads to a reduction in the number of HSCs and a complete loss of long-term repopulation capacity, whereas the stem cell compartment is shifted from quiescence to active cycling. Genetic exploration of the relative roles of endogenous ME and EVI1 isoforms revealed that ME preferentially rescues long-term HSC defects. RNA-seq analysis in Lin(-)Sca-1(+)c-Kit(+) cells (LSKs) of ME(m1) documents near complete silencing of Cdkn1c, encoding negative cell-cycle regulator p57-Kip2. Reintroduction of ME into ME(m1) LSKs leads to normalization of both p57-Kip2 expression and growth control. Our results clearly demonstrate a critical role of PR-domain-containing ME in linking p57-kip2 regulation to long-term HSC function.

Hematopoietic stem cell: self-renewal versus differentiation

The mammalian blood system, containing more than 10 distinct mature cell types, stands on one specific cell type, hematopoietic stem cell (HSC). Within the system, only HSCs possess the ability of both multipotency and self-renewal. Multipotency is the ability to differentiate into all functional blood cells. Self-renewal is the ability to give rise to HSC itself without differentiation. Since mature blood cells (MBCs) are predominantly short-lived, HSCs continuously provide more differentiated progenitors while properly maintaining the HSC pool size throughout life by precisely balancing self-renewal and differentiation. Thus, understanding the mechanisms of self-renewal and differentiation of HSC has been a central issue. In this review, we focus on the hierarchical structure of the hematopoietic system, the current understanding of microenvironment and molecular cues regulating self-renewal and differentiation of adult HSCs, and the currently emerging systems approaches to understand HSC biology.

The gene encoding the hematopoietic stem cell regulator CCN3/NOV is under direct cytokine control through the transcription factors STAT5A/B

Cytokines control the biology of hematopoietic stem cells (HSCs) and progenitor cells in part through the transcription factors STAT5A/B. To investigate the target genes of STAT5A/B activated by cytokines in HSCs and progenitors, we performed microarray analyses using Lineage(-) Sca-1(+) c-Kit(+) (KSL) cells in the presence and absence of STAT5A/B. Stimulation with a mixture containing IL-3, IL-6, stem cell factor, thrombopoietin, and Flt3 ligand induced Ccn3/Nov mRNA over 100-fold in WT (control) but not Stat5a/b-null KSL cells. CCN3/NOV is a positive regulator of human HSC self-renewal and development of committed blood cells. Without stimulation, the Ccn3/Nov signal level was low in control KSL cells similar to Stat5a/b-null KSL cells. To determine which cytokine activates the Ccn3/Nov gene, we analyzed Lineage(-) c-Kit(+) (KL) and 32D cells using quantitative PCR and ChIP assays. Although stimulation with a mixture lacking IL-3 prevented the induction of Ccn3/Nov in control KL cells, IL-3 alone could induce Ccn3/Nov mRNA in control KL and 32D cells. ChIP assays using 32D cells revealed IL-3-induced binding of STAT5A/B to a γ-interferon-activated sequences site in the Ccn3/Nov gene promoter. This is the first report that Ccn3/Nov is directly induced by cytokines through STAT5A/B.

Therapeutic implications of the cancer stem cell hypothesis

A growing body of evidence indicates that subpopulations of cancer stem cells (CSCs) drive and maintain many types of human malignancies. These findings have important implications for the development and evaluation of oncologic therapies and present opportunities for potential gains in patient outcome. The existence of CSCs mandates careful analysis and comparison of normal tissue stem cells and CSCs to identify differences between the two cell types. The development of CSC-targeted treatments will face a number of potential hurdles, including normal stem cell toxicity and the acquisition of treatment resistance, which must be considered in order to maximize the chance that such therapies will be successful.

Detection of low-abundant novel transcripts in mouse hematopoietic stem cells

Gene expression profiles of hematopoietic stem cells (HSCs) provide clues for understanding molecular mechanisms of HSC behavior, including self-renewal and differentiation. We took advantage of serial analysis of gene expression (SAGE) to identify medium- and low-abundant transcripts expressed in HSCs/hematopoietic progenitor cells (HPCs). Among a total of 31,380 unique transcripts, 17,326 (55%) correspond to known genes and, 14,054 (45%) are low-copy transcripts that have no matches to currently known genes. Among the former class, 3,899 (23%) were alternatively spliced transcripts and 3,754 (22%) represent anti-sense transcripts from known genes. Mapping of the SAGE tags to the mouse genome showed that differences in gene expression exist among chromosomes. In addition, comparison of the HSCs/HPCs SAGE data to that of myeloid progenitor cells revealed that massive genetic reprogramming occurs in hematopoietic cell differentiation. Our results demonstrate a previously unrecognized complexity of gene expression in HSCs/HPCs, and indicate the need for further efforts to fully identify and characterize the transcripts expressed in this cell type.

T-cell differentiation of multipotent hematopoietic cell line EML in the OP9-DL1 coculture system

OBJECTIVE

Multipotent hematopoietic cell line EML can differentiate into myeloid, erythroid, megakaryocytic, and B-lymphoid lineages, but it remained unknown whether EML cells have T-cell developmental potential as well. The goal of this study was to determine whether the coculture with OP9 stromal cells expressing Notch ligand Delta-like 1 (OP9-DL1) could induce differentiation of EML cells into T-cell lineage.

MATERIALS AND METHODS

EML cells were cocultured with control OP9 or OP9-DL1 stromal cells in the presence of cytokines (stem cell factor, interleukin-7, and Fms-like tyrosine kinase 3 ligand). Their T-cell lineage differentiation was assessed through flow cytometry and reverse transcription polymerase chain reaction expression analysis of cell surface markers and genes characterizing and associated with specific stages of T-cell development.

RESULTS

The phenotypic, molecular, and functional analysis has revealed that in EML/OP9-DL1 cocultures with cytokines, but not in control EML/OP9 cocultures, EML cell line undergoes T-cell lineage commitment and differentiation. In OP9-DL1 cocultures, EML cell line has differentiated into cells that 1) resembled double-negative, double-positive, and single-positive stages of T-cell development; 2) initiated expression of GATA-3, Pre-Talpha, RAG-1, and T-cell receptor-Vbeta genes; and 3) produced interferon-gamma in response to T-cell receptor stimulation.

CONCLUSIONS

These results support the notion that EML cell line has the capacity for T-cell differentiation. Remarkably, induction of T-lineage gene expression and differentiation of EML cells into distinct stages of T-cell development were very similar to previously described T-cell differentiation of adult hematopoietic stem cells and progenitors in OP9-DL1 cocultures. Thus, EML/OP9-DL1 coculture could be a useful experimental system to study the role of particular genes in T-cell lineage specification, commitment, and differentiation.

Genetic network analysis of human CD34+ hematopoietic stem/precursor cells

OBJECTIVE

Somatic CD34+ hematopoietic stem/precursor cells (HSPCs) give rise to hematopoietic cells and endothelial cells and have been used in clinical applications. Understanding the genes responsible for stemness and how they interact with each other will help us to manipulate these cells more efficiently in the future.

MATERIALS AND METHODS

We performed microarray analysis on human CD34+ HSPCs and on two different progeny cell types, i.e. microvascular endothelial cells and peripheral blood mononuclear cells. Systems biology and advanced bioinformatics tools were used to help clarify the genetic networks associated with these stem cell genes.

RESULTS

We identified CD34+ HSPC genes and found that they were involved in critical biologic processes such as cell cycle regulation, chromosome organization, and DNA repair. We also identified a novel precursor gene cluster on chromosome 19p13.3. Analysis of HSPC-enriched genes using systems biology tools revealed a complex genetic network functioning in CD34+ cells, in which several genes acted as hubs to maintain the stability (such as GATA1) or connectivity (such as hepatic growth factor) of the whole network.

CONCLUSION

This study provides the foundation for a more detailed understanding of CD34+ HSPCs.

Dysregulated gene expression networks in human acute myelogenous leukemia stem cells

We performed the first genome-wide expression analysis directly comparing the expression profile of highly enriched normal human hematopoietic stem cells (HSC) and leukemic stem cells (LSC) from patients with acute myeloid leukemia (AML). Comparing the expression signature of normal HSC to that of LSC, we identified 3,005 differentially expressed genes. Using 2 independent analyses, we identified multiple pathways that are aberrantly regulated in leukemic stem cells compared with normal HSC. Several pathways, including Wnt signaling, MAP Kinase signaling, and Adherens Junction, are well known for their role in cancer development and stem cell biology. Other pathways have not been previously implicated in the regulation of cancer stem cell functions, including Ribosome and T Cell Receptor Signaling pathway. This study demonstrates that combining global gene expression analysis with detailed annotated pathway resources applied to highly enriched normal and malignant stem cell populations, can yield an understanding of the critical pathways regulating cancer stem cells.

Change in gene expression of mouse embryonic stem cells derived from parthenogenetic activation

BACKGROUND

We previously established parthenogenetic mouse embryonic stem cells (ESCs) and this study was subsequently conducted for elucidating the influence of oocyte parthenogenesis on gene expression profile of ESCs.

METHODS

Gene expression of parthenogenetic ESC (pESC)-1 or pESC-2 was separately compared with that of two normally fertilized ESC (nfESC) lines (B6D2F1 and R1 strains), and quantification of mRNA expression was conducted for validating microarray data.

RESULTS

In two sets of comparison, reaction of 11 347 and 15 454 gene probes were altered by parthenogenesis, while strain difference changed the expression of 15 750 and 14 944 probes. Level of correlation coefficient was higher in the comparisons between normal fertilization and parthenogenesis (0.974-0.985) than in the comparisons between strains of nfESCs (0.97-0.971). Overall, the expression of 3276-3329 genes was changed after parthenogenesis, and 88% (96/109) of major functional genes differentially (P < 0.01) expressed in one comparison set showed the same change in the other. When we monitored imprinted genes, expression of nine paternal and eight maternal genes were altered after parthenogenesis and 88% (14/16) of these was confirmed by mRNA quantification.

CONCLUSIONS

The change in gene expression after parthenogenesis was similar to, or less than, the change induced by a strain difference under a certain genetic background. These results may suggest the clinical feasibility of parthenogenesis-derived, pluripotent cells.

Transcriptional profiling of hematopoietic stem cells by high-throughput sequencing

Microarray analysis has made it feasible to carry out extensive gene expression profiling in a single assay. Various hematopoietic stem cell (HSC) populations have been subjected to microarray analyses and their profiles of gene expression have been reported. However, this approach is not suitable to identify novel transcripts or for profiling of genes with low expression levels. To obtain a detailed gene expression profile of CD34(-)c-Kit(+)Sca-1(+)lineage marker-negative (Lin(-)) (CD34(-)KSL) HSCs, we constructed a CD34(-)KSL cDNA library, performed high-throughput sequencing, and compared the generated profile with that of another HSC fraction, side population (SP) Lin(-) (SP Lin(-)) cells. Sequencing of the 5'-termini of about 9,500 cDNAs from each HSC library identified 1,424 and 2,078 different genes from the CD34(-)KSL and SP Lin(-) libraries, respectively. To exclude ubiquitously expressed genes including housekeeping genes, digital subtraction was successfully performed against EST databases of other organs, leaving 25 HSC-specific genes including five novel genes. Among 4,450 transcripts from the CD34(-)KSL cDNA library that showed no homology to the presumable protein-coding genes, 29 were identified as strong candidates for mRNA-like non-coding RNAs by in silico analyses. Our cyclopedic approaches may contribute to understanding of novel molecular aspects of HSC function.

Murine hematopoietic stem cells and multipotent progenitors express truncated intracellular form of c-kit receptor

The c-kit receptor plays a vital role in self-renewal and differentiation of hematopoietic stem cells (HSCs) and multipotent progenitors (MPPs). We have discovered that besides c-kit, the murine multipotent HSC/MPP-like cell line EML expresses the transcript and protein for a truncated intracellular form of c-kit receptor, called tr-kit. Notably, the tr-kit transcript and protein levels were down-regulated during cytokine-induced differentiation of the HSC/MPP-like cell line EML into myeloerythroid lineages. These findings prompted us to analyze tr-kit expression in purified murine fetal liver and bone marrow cell populations containing long-term repopulating (LTR) HSCs, short-term repopulating (STR) HSCs, MPPs, lineage-committed progenitors, and immature blood cells. Remarkably, these studies have revealed that in contrast to more widespread expression of c-kit, tr-kit is transcribed solely in cell populations enriched for LTR-HSCs, STR-HSCs, and MPPs. On the other hand, cell populations in which HSCs and MPPs are either present at a much lower frequency or are absent altogether, cells representing more advanced stages of differentiation into lymphoid and myeloid lineages do not express tr-kit. The observation that tr-kit is co-expressed with c-kit only in more primitive HSC- and MPP-enriched cell populations raises an exciting possibility that tr-kit functions either as a new component of the stem cell factor (SCF)/c-kit pathway or is involved in a novel signaling pathway, present exclusively in HSC and MPPs. Taken together, these findings necessitate functional characterization of tr-kit and analysis of its potential role in the self-renewal, proliferation, and/or differentiation of HSC and multipotent progenitors.

Long-term propagation of distinct hematopoietic differentiation programs in vivo

Heterogeneity in the differentiation behavior of hematopoietic stem cells is well documented but poorly understood. To investigate this question at a clonal level, we isolated a subpopulation of adult mouse bone marrow that is highly enriched for multilineage in vivo repopulating cells and transplanted these as single cells, or their short-term clonal progeny generated in vitro, into 352 recipients. Of the mice, 93 showed a donor-derived contribution to the circulating white blood cells for at least 4 months in one of four distinct patterns. Serial transplantation experiments indicated that two of the patterns were associated with extensive self-renewal of the original cell transplanted. However, within 4 days in vitro, the repopulation patterns subsequently obtained in vivo shifted in a clone-specific fashion to those with less myeloid contribution. Thus, primitive hematopoietic cells can maintain distinct repopulation properties upon serial transplantation in vivo, although these properties can also alter rapidly in vitro.

Gene expression profiling related to the enhanced erythropoiesis in mouse bone marrow cells

Peroxiredoxin II knockout (Prdx II(-/-)) mice had a spontaneous phenotype of hemolytic anemia. In this study, we found that Ter-119(+)CD71(+) cells increased in Prdx II(-/-) mice bone marrow (BM) at 8 weeks of age. We examined the differential expression profiles to bone marrow cells (BMCs) between Prdx II(+/+) and Prdx II(-/-) mice using a cDNA microarray. We identified the 136 candidates were differentially expressed a greater twofold increase or decrease than EPO receptor. In this study, we focused on the up-regulated NBPs during erythropoietic differentiation. According to cDNA microarray results, six NBPs except zfp-127 were up-regulated during erythropoiesis in Prdx II(-/-) mice. Among the six candidates, eIF3-p44, hnRNPH1, G3bp, and Zfpm-1 were dramatically increased at day 7 of the in vitro erythropoietic differentiation of human CD34(+) cells. However, DJ-1 and Rbm3 were slightly increased only at day 12. Our results suggest that up-regulated NBPs might be involved during erythropoietic differentiation.

MLLT3 regulates early human erythroid and megakaryocytic cell fate

Regulatory mechanisms of human hematopoiesis remain largely uncharacterized. Through expression profiling of prospectively isolated stem and primitive progenitor cells as well as committed progenitors from cord blood (CB), we identified MLLT3 as a candidate regulator of erythroid/megakaryocytic (E/Meg) lineage decisions. Through the analysis of the hematopoietic potential of primitive cord blood cells in which MLLT3 expression has been knocked down, we identify a requirement for MLLT3 in the elaboration of the erythroid and megakaryocytic lineages. Conversely, forced expression of MLLT3 promotes the output of erythroid and megakaryocytic progenitors, and analysis of MLLT3 mutants suggests that this capacity of MLLT3 depends on its transcriptional regulatory activity. Gene expression and cis-regulatory element analyses reveal crossregulatory interactions between MLLT3 and E/Meg-affiliated transcription factor GATA-1. Taken together, the data identify MLLT3 as a regulator of early erythroid and megakaryocytic cell fate in the human system.

Renal repair: role of bone marrow stem cells

Acute kidney injury carries severe consequences and has limited treatment options. Bone marrow stem cells may offer the potential for treatment of acute kidney injury. The purpose of this review is twofold. The first purpose is to provide a concise overview of the biology of bone marrow stem cells, including hematopoietic stem cells and mesenchymal stem cells, for clinical nephrologists and renal researchers. The second purpose is to summarize published data regarding the role of bone marrow stem cells in renal repair after acute kidney injury. Currently, much of our knowledge of renal protective effect of bone marrow stem cells is obtained through animal research. Our goal is to understand the mechanism of renal protection by bone marrow stem cells and to develop strategies utilizing these stem cells for the eventual treatment of humans with kidney disease.

The MDS1-EVI1 gene complex as a retrovirus integration site: impact on behavior of hematopoietic cells and implications for gene therapy

Gene therapy trials have been performed with virus-based vectors that have the ability to integrate permanently into genomic DNA and thus allow prolonged expression of corrective genes after transduction of hematopoietic stem and progenitor cells. Adverse events observed during the X-linked severe combined immunodeficiency gene therapy trial revealed a significant risk of genotoxicity related to retrovirus vector integration and activation of adjacent proto-oncogenes, with several cases of T-cell leukemia linked to vector activation of the LMO2 gene. In patients with chronic granulomatous disease (CGD), rhesus macaques, and mice receiving hematopoietic stem and progenitor cells transduced with retrovirus vectors, a highly non-random pattern of vector integration has been reported. The most striking finding has been overrepresentation of integrations in one specific genomic locus, a complex containing the MDS1 and the EVI1 genes. Most evidence suggests that this overrepresentation is primarily due to a modification of primitive myeloid cell behavior by overexpression of EVI1 or MDS1-EVI1, as opposed to a specific predilection for integration at this site. Three different proteins can be produced from this complex locus: MDS1, MDS1-EVI1, and EVI1. This review will summarize current knowledge regarding this locus and its gene products, with specific focus on issues with relevance to gene therapy, leukemogenesis, and hematopoiesis. Insights into the mechanisms that result in altered hematopoiesis and leukemogenesis when this locus is dysregulated could improve the safety of gene therapy in the future.

The biology of cancer stem cells

Cancers originally develop from normal cells that gain the ability to proliferate aberrantly and eventually turn malignant. These cancerous cells then grow clonally into tumors and eventually have the potential to metastasize. A central question in cancer biology is, which cells can be transformed to form tumors? Recent studies elucidated the presence of cancer stem cells that have the exclusive ability to regenerate tumors. These cancer stem cells share many characteristics with normal stem cells, including self-renewal and differentiation. With the growing evidence that cancer stem cells exist in a wide array of tumors, it is becoming increasingly important to understand the molecular mechanisms that regulate self-renewal and differentiation because corruption of genes involved in these pathways likely participates in tumor growth. This new paradigm of oncogenesis has been validated in a growing list of tumors. Studies of normal and cancer stem cells from the same tissue have shed light on the ontogeny of tumors. That signaling pathways such as Bmi1 and Wnt have similar effects in normal and cancer stem cell self-renewal suggests that common molecular pathways regulate both populations. Understanding the biology of cancer stem cells will contribute to the identification of molecular targets important for future therapies.

Differential contributions of haematopoietic stem cells to foetal and adult haematopoiesis: insights from functional analysis of transcriptional regulators

An increasing number of molecules have been identified as candidate regulators of stem cell fates through their involvement in leukaemia or via post-genomic gene discovery approaches. A full understanding of the function of these molecules requires (1) detailed knowledge of the gene networks in which they participate and (2) an appreciation of how these networks vary as cells progress through the haematopoietic cell hierarchy. An additional layer of complexity is added by the occurrence of different haematopoietic cell hierarchies at different stages of ontogeny. Beyond these issues of cell context dependence, it is important from a mechanistic point of view to define the particular cell fate pathway impacted by any given regulator. Herein, we advance the notion that haematopoietic stem cells (HSC), which sustain haematopoiesis throughout adult life and are specified in foetal life, have a minimal or late contribution to foetal haematopoiesis but instead largely proliferate during the foetal period. In light of this notion, we revisit published data on mouse knockouts of haematopoietically-affiliated transcription factors highlighting novel insights that may be gained from taking such a view.

Adult mouse hematopoietic stem cells: purification and single-cell assays

Mouse hematopoietic stem cells (HSCs) are the best-studied stem cells because functional assays for mouse HSCs were established earliest and purification techniques for mouse HSCs have progressed furthest. Here we describe our current protocols for the purification of CD34-/lowc-Kit+Sca-1+lineage marker- (CD34-KSL) cells, the HSC population making up approximately 0.005% of bone marrow cells in adult C557BL/6 mice. Purified HSCs have been characterized at cellular and molecular levels. Since clonal analysis is essential for the study of self-renewal and lineage commitment in HSCs, here we present our single-cell colony assay and single-cell transplantation procedures. We also introduce our immunostaining procedures for small numbers of HSCs, which are useful for signal transduction analysis. The purification of CD34-KSL cells requires approximately 6 h. Initialization of single-cell culture requires approximately 1 h. Single-cell transplantation requires approximately 6 h. Single-cell immunostaining requires approximately 2 d.

Hat1: the emerging cellular roles of a type B histone acetyltransferase

Hat1 is the sole known example of a type B histone acetyltransferase. While it has long been presumed that type B histone acetyltransferases participate in the acetylation of newly synthesized histones during the process of chromatin assembly, definitive evidence linking these enzymes to this process has been scarce. This review will discuss recent results that have begun to shed light on the roles of Hat1 and also address several outstanding questions relating to the cellular function of this enzyme.

Reduced expression of INK4a/ARF genes in stem-like sphere cells from rat sarcomas

The presence of cancer stem cells, in both hematopoietic and solid malignancies, has been recently linked to their pathogenesis. We aimed to identify the characteristics and stem-like properties of sphere-colony forming cells in rat osteosarcoma and malignant fibrous histiocytoma cell lines. The results showed that both cell lines possessed an ability to form spherical, clonally expanding colonies in anchorage-independent, serum-starved conditions in N2/1% methylcellulose medium. The sphere cells showed stem-like properties with the ability to self-renew, and expressed the stem cell-related STAT3 and Bmi1 genes. Interestingly, spheres from both sarcomas remarkably decreased the expression of INK4a/ARF locus genes, p16(INK4a) and p19(ARF), which could be related to the resistance against cell senescence and apoptosis. Spheres showed strong tumorigenicity with metastatic potential in vivo via the inoculation into syngeneic rats, suggesting the presence of these populations might contribute to the tumor development such as metastasis via the resistance to apoptotic stimuli.

Leukemogenesis of the EVI1/MEL1 gene family

Leukemia is a group of monoclonal diseases that arise from hematopoietic stem and progenitor cells in the bone marrow or other hematopoietic organs. Retroviral infections are one of the major events leading to leukemogenesis in mice, because retroviruses can induce hematopoietic disease via the insertional mutagenesis of oncogenes; therefore, the cloning of viral-integration sites in murine leukemia has provided valuable molecular tags for oncogene discovery. Transcription of the murine gene ecotropic viral-integration site 1 (Evi1) is activated by nearby viral integration. In humans, the Evi1 homologue EVI1 is activated by chromosomal translocations. This review discusses the roles of the overexpression of EVI1/MEL1 gene family members in leukemogenesis, the relationships of various translocations in EVI1 overexpression, and the importance of PR domains in tumor suppression and oncogenesis. The functions of EVI1/MEL1 members as transcription factors and the concept of EVI1-positive leukemia as a stem cell disease are also reviewed.

Genome-wide differential gene expression profiling of human bone marrow stromal cells

Bone marrow stromal cells (BMSCs) reside in bone marrow and provide a lifelong source of new cells for various connective tissues. Although human BMSCs are regarded as highly suitable for the development of cell therapeutics and regenerative medicine, the molecular factors and the networks of signaling pathways responsible for their biological properties are as yet unclear. To gain a comprehensive understanding of human BMSCs at the transcriptional level, we have performed DNA microarray-based, genome-wide differential gene expression analysis with the use of peripheral blood-derived mononuclear cells (MNCs) as a baseline. The resulting molecular profile of BMSCs was revealed to share no meaningful overlap with those of other human stem cell types, suggesting that the cells might express a unique set of genes for their stemness. By contrast, the distinct molecular signature, consisting of 92 different genes whose expression strengths are at least 50-fold higher in BMSCs compared with MNCs, was shown to encompass largely a gene subset of umbilical cord blood-derived adherent cells, suggesting that adherent cells derived from bone marrow and umbilical cord blood may be defined by a common set of genes, regardless of their origin. Intriguingly, a large number of these genes, particularly ones for extracellular matrix products, coincide with normal or tumor endothelium-specific markers. Taken together, our results here provide a BMSC-specific genetic catalog that may facilitate future studies on molecular mechanisms governing core properties of these cells.

Trithorax-group protein ASH1 methylates histone H3 lysine 36

Drosophila discs absent, small, or homeotic-1 (ASH1) is a member of trithorax-group proteins that play essential roles in epigenetic regulation of Hox genes. Drosophila ASH1 genetically interacts with trithorax and has been reported to methylate histone H3 lysine 4 (K4) as well as H3 K9 and H4 K20. The function of mammalian ASH1, by contrast, has remained largely unknown. Here we report a histone lysine scanning mutation assay using recombinant core histones and in vitro reconstituted nucleosomes to identify targets of mammalian methyltransferases by fluorographic, Western blot, and mass spectrometric analyses. The assay reproduced specificities of previously known histone methyltransferases and further revealed unexpectedly that mammalian ASH1 mono- or di-methylates histone H3 K36 but not any other lysine residues of recombinant unmodified mammalian histones. Under the same experimental condition, lysine to arginine substitution of histone H3 at position 36 abolished the methyltransferase activity of Drosophila ASH1, suggesting that K36 is their specific target. We also demonstrate that native ASH1 proteins, consisting of the carboxy-terminal domains including the catalytic site, retain the specificity for K36. Taken together, our data suggest that ASH1 subfamily of SET domain proteins have K36-specific methyltransferase activities evolutionarily conserved from flies to mammals.

Stem cells for regeneration of urological structures

OBJECTIVES

This review focuses on advances in regenerative therapies using stem cells in urology.

METHODS

A detailed literature search was performed using the PubMed database of the National Center of Biotechnology Information. Publications of experimental investigations and clinical trials using stem cells in reconstructive urology have been summarized and critically reviewed.

RESULTS

Tissue engineering and autologous cell therapy techniques have been developed to generate prostheses for different urological tissues and organ systems. During the last decade, increasing numbers of studies have described stem cells in the context of therapeutic tools. The ability of adult and embryonic stem cells as well as progenitors to improve bladder wall architecture, improve renal tubule formation, or promote restoration of spermatogenesis or recovery of continence has been investigated in several animal models. Although results have been encouraging, only a myoblast-based therapy of incontinence has reached clinical trials.

CONCLUSIONS

Several populations of adult stem cells and progenitor cells have been studied as useful cellular sources in the treatment and reconstruction of urological organs. However, considerable basic research still needs to be performed to ensure the controlled differentiation and long-term fate of stem cells following transplantation.

Targeted degradation of the AML1/MDS1/EVI1 oncoprotein by arsenic trioxide

Arsenic trioxide (ATO) has been found to be an effective treatment for acute promyelocytic leukemia patients and is being tested for treating other hematologic malignancies. We have previously shown that AML1/MDS1/EVI1 (AME), a fusion gene generated by a t(3;21)(q26;q22) translocation found in patients with chronic myelogenous leukemia during blast phase, myelodysplastic syndrome, or acute myelogenous leukemia (AML), impairs hematopoiesis and eventually induces an AML in mice. Both fusion partners of AME, AML1 and MDS1/EVI1, encode transcription factors and are also targets of a variety of genetic abnormalities in human hematologic malignancies. In addition, aberrant expression of ectopic viral integration site 1 (EVI1) has also been found in solid tumors, such as ovarian and colon cancers. In this study, we examined whether ATO could target AME and related oncoproteins. We found that ATO used at therapeutic levels degrades AME. The ATO treatment induces differentiation and apoptosis in AME leukemic cells in vitro as well as reduces tumor load and increases the survival of mice transplanted with these cells. We further found that ATO targets AME via both myelodysplastic syndrome 1 (MDS1) and EVI1 moieties and degrades EVI1 via the ubiquitin-proteasome pathway and MDS1 in a proteasome-independent manner. Our results suggest that ATO could be used as a part of targeted therapy for AME-, AML1/MDS1-, MDS1/EVI1-, and EVI1-positive human cancers.