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Summary: Isolation of long-term hematopoietic stem cell (HSC) is possible by utilizing flow cytometry with multiple cell surface markers. However, those cell surface phenotypes do not represent functional HSCs after in vitro culture. Here we show that cultured HSCs express mast cell-related genes including Cd244. After in vitro culture, phenotypic HSCs were divided into CD244- and CD244+ subpopulations, and only CD244- cells that have low mast cell gene expression and maintain HSC-related genes sustain reconstitution potential. The result was same when HSCs were cultured in an efficient expansion medium containing polyvinyl alcohol. Chemically induced endoplasmic reticulum (ER) stress signal increased the CD244+ subpopulation, whereas ER stress suppression using a molecular chaperone, TUDCA, decreased CD244+ population, which was correlated to improved reconstitution output. These data suggest CD244 is a potent marker to exclude non-functional HSCs after in vitro culture thereby useful to elucidate mechanism of functional decline of HSCs during ex vivo treatment.

Adult progeria Werner syndrome (WS), a rare autosomal recessive disorder, is characterized by accelerated aging symptoms after puberty. The causative gene, WRN, is a member of the RecQ DNA helicase family and is predominantly involved in DNA replication, repair, and telomere maintenance. Here, we report the generation of iPS cells from a patient with WS and correction of the WRN gene by the CRISPR/Cas9-mediated method. These iPSC lines would be a valuable resource for deciphering the pathogenesis of WS.

Abstract: KDM2B together with RING1B, PCGF1, and BCOR or BCORL1 comprise polycomb repressive complex 1.1 (PRC1.1), a noncanonical PRC1 that catalyzes H2AK119ub1. It binds to nonmethylated CpG islands through its zinc finger-CxxC DNA binding domain and recruits the complex to target gene loci. Recent studies identified the loss of function mutations in the PRC1.1 gene, BCOR and BCORL1 in human T-cell acute lymphoblastic leukemia (T-ALL). We previously reported that Bcor insufficiency induces T-ALL in mice, supporting a tumor suppressor role for BCOR. However, the function of BCOR responsible for tumor suppression, either its corepressor function for BCL6 or that as a component of PRC1.1, remains unclear. We herein examined mice specifically lacking the zinc finger-CxxC domain of KDM2B in hematopoietic cells. Similar to Bcor-deficient mice, Kdm2b-deficient mice developed lethal T-ALL mostly in a NOTCH1-dependent manner. A chromatin immunoprecipitation sequence analysis of thymocytes revealed the binding of KDM2B at promoter regions, at which BCOR and EZH2 colocalized. KDM2B target genes markedly overlapped with those of NOTCH1 in human T-ALL cells, suggesting that noncanonical PRC1.1 antagonizes NOTCH1-mediated gene activation. KDM2B target genes were expressed at higher levels than the others and were marked with high levels of H2AK119ub1 and H3K4me3, but low levels of H3K27me3, suggesting that KDM2B target genes are transcriptionally active or primed for activation. These results indicate that PRC1.1 plays a key role in restricting excessive transcriptional activation by active NOTCH1, thereby acting as a tumor suppressor in the initiation of T-cell leukemogenesis.

Summary: Polycomb repressive complex (PRC) 2 represses transcription through histone H3K27 trimethylation (H3K27me3). We previously reported that the hematopoietic-cell-specific deletion of Ezh2, encoding a PRC2 enzyme, induced myelodysplastic syndrome (MDS) in mice, whereas the concurrent Ezh1 deletion depleted hematopoietic stem and progenitor cells (HSPCs). We herein demonstrated that mice with only one Ezh1 allele (Ezh1+/-Ezh2Δ/Δ) maintained HSPCs. A chromatin immunopreciptation sequence analysis revealed that residual PRC2 preferentially targeted genes with high levels of H3K27me3 and H2AK119 monoubiquitination (H2AK119ub1) in HSPCs (designated as Ezh1 core target genes), which were mostly developmental regulators, and maintained H3K27me3 levels in Ezh1+/-Ezh2Δ/Δ HSPCs. Even upon the complete depletion of Ezh1 and Ezh2, H2AK119ub1 levels were largely retained, and only a minimal number of Ezh1 core targets were de-repressed. These results indicate that genes marked with high levels of H3K27me3 and H2AK119ub1 are the core targets of polycomb complexes in HSPCs as well as MDS stem cells. : Biological Sciences; Genetics; Molecular Biology; Immunology; Cell Biology; Developmental Biology Subject Areas: Biological Sciences, Genetics, Molecular Biology, Immunology, Cell Biology, Developmental Biology

Abstract: High-mobility group AT-hook 2 (HMGA2) is crucial for the self-renewal of fetal hematopoietic stem cells (HSCs) but is downregulated in adult HSCs via repression by MIRlet-7 and the polycomb-recessive complex 2 (PRC2) including EZH2. The HMGA2 messenger RNA (mRNA) level is often elevated in patients with myelofibrosis that exhibits an advanced myeloproliferative neoplasm (MPN) subtype, and deletion of Ezh2 promotes the progression of severe myelofibrosis in JAK2V617F mice with upregulation of several oncogenes such as Hmga2. However, the direct role of HMGA2 in the pathogenesis of MPNs remains unknown. To clarify the impact of HMGA2 on MPNs carrying the driver mutation, we generated ΔHmga2/JAK2V617F mice overexpressing Hmga2 due to deletion of the 3′ untranslated region. Compared with JAK2V617F mice, ΔHmga2/JAK2V617F mice exhibited more severe leukocytosis, anemia and splenomegaly, and shortened survival, whereas severity of myelofibrosis was comparable. ΔHmga2/JAK2V617F cells showed a greater repopulating ability that reproduced the severe MPN compared with JAK2V617F cells in serial bone marrow transplants, indicating that Hmga2 promotes MPN progression at the HSC level. Hmga2 also enhanced apoptosis of JAK2V617F erythroblasts that may worsen anemia. Relative to JAK2V617F hematopoietic stem and progenitor cells (HSPCs), over 30% of genes upregulated in ΔHmga2/JAK2V617F HSPCs overlapped with those derepressed by Ezh2 loss in JAK2V617F/Ezh2Δ/Δ HSPCs, suggesting that Hmga2 may facilitate upregulation of Ezh2 targets. Correspondingly, deletion of Hmga2 ameliorated anemia and splenomegaly in JAK2V617F/Ezh2Δ/wild-type mice, and MIRlet-7 suppression and PRC2 mutations correlated with the elevated HMGA2 mRNA levels in patients with MPNs, especially myelofibrosis. These findings suggest the crucial role of HMGA2 in MPN progression.

Myeloproliferative neoplasms (MPNs) are clinically characterized by the chronic overproduction of differentiated peripheral blood cells and the gradual expansion of malignant intramedullary/extramedullary hematopoiesis. In MPNs mutations in JAK2 MPL or CALR are detected mutually exclusive in more than 90% of cases [1,2]. Mutations in them lead to the abnormal activation of JAK/STAT signaling and the autonomous growth of differentiated cells therefore they are considered as “driver” gene mutations. In addition to the above driver gene mutations mutations in epigenetic regulators such as TET2 DNMT3A ASXL1 EZH2 or IDH1/2 are detected in about 5%–30% of cases respectively [3]. Mutations in TET2 DNMT3A EZH2 or IDH1/2 commonly confer the increased self-renewal capacity on normal hematopoietic stem cells (HSCs) but they do not lead to the autonomous growth of differentiated cells and only exhibit subtle clinical phenotypes [4,6–8,5]. It was unclear how mutations in such epigenetic regulators influenced abnormal HSCs with driver gene mutations how they influenced the disease phenotype or whether a single driver gene mutation was sufficient for the initiation of human MPNs. Therefore we focused on JAK2V617F and loss of TET2—the former as a representative of driver gene mutations and the latter as a representative of mutations in epigenetic regulators—and examined the influence of single or double mutations on HSCs (Lineage−Sca-1+c-Kit+ cells (LSKs)) by functional analyses and microarray whole-genome expression analyses [9]. Gene expression profiling showed that the HSC fingerprint genes [10] was statistically equally enriched in TET2-knockdown-LSKs but negatively enriched in JAK2V617F–LSKs compared to that in wild-type-LSKs. Double-mutant-LSKs showed the same tendency as JAK2V617F–LSKs in terms of their HSC fingerprint genes but the expression of individual genes differed between the two groups. Among 245 HSC fingerprint genes 100 were more highly expressed in double-mutant-LSKs than in JAK2V617F–LSKs. These altered gene expressions might partly explain the mechanisms of initiation and progression of MPNs which was observed in the functional analyses [9]. Here we describe gene expression profiles deposited at the Gene Expression Omnibus (GEO) under the accession number GSE62302 including experimental methods and quality control analyses.

TIF1β is a transcriptional corepressor that recruits repressive chromatin modifiers to target genes. Its biological function and physiological targets in somatic stem cells remain largely unknown. Here, we show that TIF1β is essential for the maintenance of hematopoietic stem cells (HSCs). Deletion of Tif1b in mice induced active cycling and apoptosis of HSCs and promoted egression of HSCs from the bone marrow, leading to rapid depletion of HSCs. Strikingly, Tif1b-deficient HSCs showed a strong trend of ectopic expression of nonhematopoietic genes. Levels of heterochromatin protein 1 (HP1α, β and γ) proteins, which form a complex with TIF1β, were significantly reduced in the absence of TIF1β and depletion of HP1 recapitulated a part of the phenotypes of Tif1b-deficient HSCs. These results demonstrate that the TIF1β-HP1 system functions as a critical repressive machinery that targets genes not normally activated in the hematopoietic compartment, thereby maintaining the transcriptional signature specific to HSCs.