MicroRNAs (miRNAs) are pivotal for regulation of hematopoiesis but their critical targets remain largely unknown. Here, we show that ectopic expression of miR-17, -20,-93 and -106, all AAAGUGC seedcontaining miRNAs, increases proliferation, colony outgrowth and replating capacity of myeloid progenitors and results in enhanced P-ERK levels. We found that these miRNAs are endogenously and abundantly expressed in myeloid progenitors and down-regulated in mature neutrophils. Quantitative proteomics identified sequestosome 1 (SQSTM1), an ubiquitinbinding protein and regulator of autophagy-mediated protein degradation, as a major target for these miRNAs in myeloid progenitors. In addition, we found increased expression of IntroductionMiRNAs are transcribed as long primary transcripts that are processed by RNaseIII endonucleases DROSHA and DICER into single-stranded RNAs of ϳ 22nt. 1 The nucleotides 2-7 at the 5Ј-end of miRNAs, referred to as the miRNA seed region, are important for miRNA target recognition. 2 MiRNAs regulate gene expression by pairing with the seed complementary sequences in the 3Ј untranslated region (UTR) of mRNAs. Most mammalian miRNAs both repress translation and enhance decay of their target transcript. 3,4 MiRNAs containing homologous seeds such as, for example, the Let-7 family of miRNAs, are believed to regulate the same targets. 2 Involvement of miRNAs in hematopoiesis is strongly suggested by the position of miRNA genes near translocation breakpoints and by their presence in loci targeted for deletion in human leukemias. 5 Furthermore, expression profiling data suggest a major role for miRNAs in regulation of hematopoietic cell commitment, proliferation, apoptosis, survival, and differentiation. [6][7][8][9] The importance of miRNAs during hematopoiesis has been shown by disruption of miRNA biogenesis in mice. For instance, Dicer-deleted hematopoietic stem cells are unable to reconstitute the hematopoietic system. 10 Further, conditional deletion of Dicer in T and B cells results in strong reduction of lymphocytes and diminished cell survival and functions. [11][12][13] Argonaute-2 knock-out in hematopoiesis results in impaired differentiation of B-lymphocytes and erythroid cells. 14,15 MiRNAs can be expressed in a cell type or tissue specific manner. For instance, miR-223 and miR-142 are almost exclusively expressed in hematopoietic cells. 16 MiR-223 is transcriptionally controlled by CCAAT/enhancer-binding protein ␣ (CEBPA) and suppresses the myeloid transcription factor MEF2C, a major regulator of progenitor cell proliferation and granulocyte specific functions. 17,18 In addition, specific miRNAs control cellular processes important for proliferation, survival, cytokine production and cell lineage decisions of developing T and B cells. 8,12 In hematopoietic stem cells, sustained expression of miR-155 causes a myeloproliferative disorder in mice. 19 Furthermore, forced miR-29a in hematopoietic precursors induces aberrant self-renewal and acute myeloid leukemia by still unidentified mechan...

Key Points The CEBPA locus harbors 14 enhancers of which distinct combinations are active in different CEBPA-expressing tissues. A +42-kb enhancer is required for myeloid-lineage priming to drive adequate CEBPA expression levels necessary for neutrophilic maturation.

MicroRNAs (miRNA) play a crucial role in the regulation of diverse biological processes by post-transcriptional modulation of gene expression. Genetic polymorphisms in miRNA-related genes can potentially contribute to a wide range of phenotypes. The effect of such variants on cardiometabolic diseases has not yet been defined. We systematically investigated the association of genetic variants in the seed region of miRNAs with cardiometabolic phenotypes, using the thus far largest genome-wide association studies on 17 cardiometabolic traits/diseases. We found that rs2168518:G>A, a seed region variant of miR-4513, associates with fasting glucose, low-density lipoprotein-cholesterol, total cholesterol, systolic and diastolic blood pressure, and risk of coronary artery disease. We experimentally showed that miR-4513 expression is significantly reduced in the presence of the rs2168518 mutant allele. We sought to identify miR-4513 target genes that may mediate these associations and revealed five genes (PCSK1, BNC2, MTMR3, ANK3, and GOSR2) through which these effects might be taking place. Using luciferase reporter assays, we validated GOSR2 as a target of miR-4513 and further demonstrated that the miRNA-mediated regulation of this gene is changed by rs2168518. Our findings indicate a pleiotropic effect of miR-4513 on cardiometabolic phenotypes and may improve our understanding of the pathophysiology of cardiometabolic diseases.

The differentiation of hematopoietic stem cells (HSCs) is tightly controlled to ensure a proper balance between myeloid and lymphoid cell output. GATA2 is a pivotal hematopoietic transcription factor required for generation and maintenance of HSCs. GATA2 is expressed throughout development, but because of early embryonic lethality in mice, its role during adult hematopoiesis is incompletely understood. Zebrafish contains 2 orthologs of GATA2: Gata2a and Gata2b, which are expressed in different cell types. We show that the mammalian functions of GATA2 are split between these orthologs. Gata2b-deficient zebrafish have a reduction in embryonic definitive hematopoietic stem and progenitor cell (HSPC) numbers, but are viable. This allows us to uniquely study the role of GATA2 in adult hematopoiesis. gata2b mutants have impaired myeloid lineage differentiation. Interestingly, this defect arises not in granulocyte-monocyte progenitors, but in HSPCs. Gata2b-deficient HSPCs showed impaired progression of the myeloid transcriptional program, concomitant with increased coexpression of lymphoid genes. This resulted in a decrease in myeloid-programmed progenitors and a relative increase in lymphoid-programmed progenitors. This shift in the lineage output could function as an escape mechanism to avoid a block in lineage differentiation. Our study helps to deconstruct the functions of GATA2 during hematopoiesis and shows that lineage differentiation flows toward a lymphoid lineage in the absence of Gata2b.