Key Points• Differential gene and miRNA expression analysis in PMF granulocytes identifies new biomarkers and putative therapeutic targets.• Activation of the miR-155/ JARID2 axis in PMF CD341 cells results in overproduction of MK precursors.Primary myelofibrosis (PMF) is a myeloproliferative neoplasm characterized by megakaryocyte (MK) hyperplasia, bone marrow fibrosis, and abnormal stem cell trafficking. PMF may be associated with somatic mutations in JAK2, MPL, or CALR. Previous studies have shown that abnormal MKs play a central role in the pathophysiology of PMF. In this work, we studied both gene and microRNA (miRNA) expression profiles in CD34 1 cells from PMF patients. We identified several biomarkers and putative molecular targets such as FGR, LCN2, and OLFM4. By means of miRNA-gene expression integrative analysis, we found different regulatory networks involved in the dysregulation of transcriptional control and chromatin remodeling. In particular, we identified a network gathering several miRNAs with oncogenic potential (eg, miR-155-5p) and targeted genes whose abnormal function has been previously associated with myeloid neoplasms, including JARID2, NR4A3, CDC42, and HMGB3. Because the validation of miRNA-target interactions unveiled JARID2/miR-155-5p as the strongest relationship in the network, we studied the function of this axis in normal and PMF CD34 1 cells. We showed that JARID2 downregulation mediated by miR-155-5p overexpression leads to increased in vitro formation of CD41 1 MK precursors. These findings suggest that overexpression of miR-155-5p and the resulting downregulation of JARID2 may contribute to MK hyperplasia in PMF. (Blood. 2014;124(13):e21-e32)

This study was aimed at the characterization of a gene expression signature of the pluripotent hematopoietic CD34؉ stem cell in idiopathic myelofibrosis (IM), which would eventually provide novel pathogenetic insights and/or diagnostic/prognostic information. Aberrantly regulated genes were revealed by transcriptome comparative microarray analysis of normal and IM CD34 ؉ cells; selected genes were also assayed in granulocytes. One-hundred seventy four differentially expressed genes were identified and in part validated by quantitative polymerase chain reaction. Altered gene expression was corroborated by the detection of abnormally high CD9 or CD164, and low CXCR4, membrane protein expression in IM CD34 ؉ cells. According to class prediction analysis, a set of eight genes (CD9, GAS2, DLK1, CDH1, WT1, NFE2, HMGA2, and CXCR4) properly recognized IM from normal CD34 ؉ cells. These genes were aberrantly regulated also in IM granulocytes that could be reliably differentiated from control polycythemia vera and essential thrombocythemia granulocytes in 100% and 81% of cases, respectively. Abnormal expression of HMGA2 and CXCR4 in IM granulocytes was dependent on the presence and the mutational status of JAK2 V617F mutation. The expression levels of both CD9 and DLK1 were associated with the platelet count, whereas higher WT1 expression levels identified IM patients with more active disease, as revealed by elevated CD34 ؉ cell count and higher severity score. In conclusion, molecular profiling of IM CD34؉ cells uncovered a limited number of genes with altered expression that, beyond their putative role in disease pathogenesis, are associated with patients' clinical characteristics and may have potential prognostic application. STEM CELLS 2007;25: 165-173

The c-myb transcription factor is highly expressed in immature hematopoietic cells and down-regulated during differentiation. To define its role during the hematopoietic lineage commitment, we silenced c-myb in human CD34 ؉ hematopoietic stem/ progenitor cells. Noteworthy, c-myb silencing increased the commitment capacity toward the macrophage and megakaryocyte lineages, whereas erythroid differentiation was impaired, as demonstrated by clonogenic assay, morphologic and immunophenotypic data. Gene expression profiling and computational analysis of

The initiation, execution, and completion of complex locomotor behaviors are depending on precisely integrated neural circuitries consisting of motor pathways that activate muscles in the extremities and sensory afferents that deliver feedback to motoneurons. These projections form in tight temporal and spatial vicinities during development, yet the molecular mechanisms and cues coordinating these processes are not well understood. Using cell-type specific ablation of the axon guidance receptor Neuropilin-1 (Npn-1) in spinal motoneurons or in sensory neurons in the dorsal root ganglia (DRG), we have explored the contribution of this signaling pathway to correct innervation of the limb. We show that Npn-1 controls the fasciculation of both projections and mediates inter-axonal communication. Removal of Npn-1 from sensory neurons results in defasciculation of sensory axons and, surprisingly, also of motor axons. In addition, the tight coupling between these two heterotypic axonal populations is lifted with sensory fibers now leading the spinal nerve projection. These findings are corroborated by partial genetic elimination of sensory neurons, which causes defasciculation of motor projections to the limb. Deletion of Npn-1 from motoneurons leads to severe defasciculation of motor axons in the distal limb and dorsal-ventral pathfinding errors, while outgrowth and fasciculation of sensory trajectories into the limb remain unaffected. Genetic elimination of motoneurons, however, revealed that sensory axons need only minimal scaffolding by motor axons to establish their projections in the distal limb. Thus, motor and sensory axons are mutually dependent on each other for the generation of their trajectories and interact in part through Npn-1-mediated fasciculation before and within the plexus region of the limbs.

Megakaryopoiesis is a complex, stepwise process that takes place largely in the bone marrow. At the apex of the hierarchy, hematopoietic stem cells undergo a number of lineage commitment decisions that ultimately lead to the production of polyploid megakaryocytes. On average, megakaryocytes release 1011 platelets per day into the blood that repair vascular injuries and prevent excessive bleeding. This differentiation process is tightly controlled by exogenous and endogenous factors, which have been the topics of intense research in the hematopoietic field. Indeed, a skewing of megakaryocyte commitment and differentiation may entail the onset of myeloproliferative neoplasms and other preleukemic disorders together with acute megakaryoblastic leukemia, whereas quantitative or qualitative defects in platelet production can lead to inherited platelet disorders. The recent advent of next-generation sequencing has prompted mapping of the genomic landscape of these conditions to provide an accurate view of the underlying lesions. The aims of this review are to introduce the physiological pathways of megakaryopoiesis and to present landmark studies on acquired and inherited disorders that target them. These studies have not only introduced a new era in the fields of molecular medicine and targeted therapies but may also provide us with a better understanding of the mechanisms underlying normal megakaryopoiesis and thrombopoiesis that can inform efforts to create alternative sources of megakaryocytes and platelets.

The transcription factor MYB has a key role in hematopoietic progenitor cells (HPCs) lineage choice, by enhancing erythropoiesis at the expense of megakaryopoiesis. We previously demonstrated that MYB controls erythroid versus megakaryocyte lineage decision by transactivating KLF1 and LMO2 expression. To further unravel the molecular mechanisms through which MYB affects lineage fate decision, we performed the integrative analysis of miRNA and mRNA changes in MYB-silenced human primary CD34+ HPCs. Among the miRNAs with the highest number of predicted targets, we focused our studies on hsa-miR-486-3p by demonstrating that MYB controls miR-486-3p expression through the transactivation of its host gene, ankyrin-1 (ANK1) and that miR-486-3p affects HPCs commitment. Indeed, overexpression and knockdown experiments demonstrated that miR-486-3p supports the erythropoiesis while restraining the megakaryopoiesis. Of note, miR-486-3p also favors granulocyte differentiation while repressing the macrophage differentiation. To shed some light on the molecular mechanisms through which miR-486-3p affects HPCs lineage commitment, we profiled the gene expression changes upon miR-486-3p overexpression in CD34+ cells. Among the genes downregulated in miR-486-3p-overexpressing HPCs and computationally predicted to be miR-486-3p targets, we identified MAF as a miR-486-3p target by 3′UTR luciferase reporter assay. Noteworthy, MAF overexpression was able to partially reverse the effects of miR-486-3p overexpression on erythroid versus megakaryocyte lineage choice. Moreover, the MYB/MAF co-silencing constrained the skewing of erythroid versus megakaryocyte lineage commitment in MYB-silenced CD34+ cells, by restraining the expansion of megakaryocyte lineage while partially rescuing the impairment of erythropoiesis. Therefore, our data collectively demonstrate that MYB favors erythropoiesis and restrains megakaryopoiesis through the transactivation of miR-486-3p expression and the subsequent downregulation of MAF. As a whole, our study uncovers the MYB/miR-486-3p/MAF axis as a new mechanism underlying the MYB-driven control of erythroid versus megakaryocyte lineage fate decision.

IntroductionSeveral studies have demonstrated that normal hematopoietic stem cells (HSCs) exist in 2 functional states that can be distinguished based on CD34 expression. 1 CD34 Ϫ cells represent a kinetically and functionally resting stem cell subset that needs to be activated to generate a CD34 ϩ cell population with high proliferative and engraftment potential. 2,3 Acquisition of CD34 expression on human HSCs is associated with in vitro hematopoietic activity and cell-cycle recruitment. 4 CD34 Ϫ /CD34 ϩ transition results in metabolic activation and down-regulation of growth-inhibitory pathways, and CD34 ϩ stem cells show a significant up-regulation of self-renewal-, commitment-, and engraftment-related genes. 5 No data are presently available on the existence of a stem cell population devoid of CD34 expression in leukemic hematopoiesis.Chronic myelogenous leukemia (CML) is a clonal myeloproliferative disorder of HSCs that have acquired a BCR-ABL fusion gene. The encoded 210-kDa protein has constitutively elevated tyrosine kinase activity that results in a large variety of biochemical changes in leukemic stem cells (LSCs) mainly inducing growth factor-independent proliferation, inhibition of apoptosis, and alteration of adhesive properties. 6 There is an increasing body of evidence indicating that, similar to normal hematopoiesis, a kinetically quiescent stem cell population can be isolated within the CD34 ϩ LSC compartment. 7 These G 0 CML cells are able to repopulate immunodeficient mice 8 and show a different transcriptional profile from dividing CD34 ϩ cells. 9 More importantly, the dissection of the stem cell pool in CML has allowed the characterization of subsets of CD34 ϩ LSCs resistant, in vitro and in vivo, to targeted therapies with BCR-ABL inhibitors. [10][11][12] Multiple mechanisms of drug resistance have been described, including kinetic quiescence per se, 10 increased expression level of BCR-ABL, and altered expression of ABCB1, ABCG2, and OCT1 cell membrane drug transporter genes in the most primitive CD34 ϩ /CD38 Ϫ LSCs. 13 Taken together, these findings stress the importance of gaining further understanding of the molecular and functional properties of the stem cell compartment in CML, in view of the development of more effective therapies.To this end, in the present study, we assessed the gene expression profile and the functional characteristics of a novel Lin Ϫ CD34 Ϫ stem cell population in CML patients at diagnosis. Our data demonstrate that approximately one-third of Lin Ϫ CD34 Ϫ cells are leukemic and capable of engraftment in immunodeficient mice. Overall, molecular analysis showed 1827 transcripts differentially expressed in CML HSC subpopulations compared with normal counterparts, genes affecting many cellular functions associated with the neoplastic phenotype. Microarray data also highlighted the highest transcriptome differences between CML Lin Ϫ CD34 Ϫ cells and their normal counterparts. Functional The online version of this article contains a data supplement.The publication co...

With the intent of dissecting the molecular complexity of Philadelphia-negative myeloproliferative neoplasms (MPN), we designed a target enrichment panel to explore, using next-generation sequencing (NGS), the mutational status of an extensive list of 2000 cancer-associated genes and microRNAs. The genomic DNA of granulocytes and in vitro-expanded CD3+T-lymphocytes, as a germline control, was target-enriched and sequenced in a learning cohort of 20 MPN patients using Roche 454 technology. We identified 141 genuine somatic mutations, most of which were not previously described. To test the frequency of the identified variants, a larger validation cohort of 189 MPN patients was additionally screened for these mutations using Ion Torrent AmpliSeq NGS. Excluding the genes already described in MPN, for 8 genes (SCRIB, MIR662, BARD1, TCF12, FAT4, DAP3, POLG and NRAS), we demonstrated a mutation frequency between 3 and 8%. We also found that mutations at codon 12 of NRAS (NRASG12V and NRASG12D) were significantly associated, for primary myelofibrosis (PMF), with highest dynamic international prognostic scoring system (DIPSS)-plus score categories. This association was then confirmed in 66 additional PMF patients composing a final dataset of 168 PMF showing a NRAS mutation frequency of 4.7%, which was associated with a worse outcome, as defined by the DIPSS plus score.