Thrombopoietin Does Not Induce Lineage-Restricted Commitment of Mpl-R Expressing Pluripotent Progenitors But Permits Their Complete Erythroid and Megakaryocytic Differentiation

In this study, we examined the in vitro and in vivo effects of forced expression of Mpl-R (the thrombopoietin receptor) on the progeny of murine hematopoietic stem cells. Bone marrow cells from 5-FU–treated mice were transduced with retroviral vectors containing the human Mpl-R cDNA, or the neomycine gene as a control. After 7 days cocultivation on virus-producer cells, GpE86-Mpl-R or Gp86-Neo, the types of hematopoietic progenitor cells responding to thrombopoietin (TPO) were studied by clonogenic assays. Mpl-R–infected cells gave rise to CFU-GEMM, BFU-E, CFU-MK, but not CFU-GM while Neo-infected cells produced only megakaryocytic colonies. In addition, when nonadherent cells from GpE86-Mpl-R cocultures were grown with TPO as the only stimulus for 7 days, a marked expansion of CFU-GEMM, BFU-E, and CFU-MK was observed, while no change in CFU-GM number was seen. Erythroid and megakaryocytic maturation occurred in the presence of TPO while a block in granulocytic differentiation was observed at the myeloblast stage. The direct effects of TPO on Mpl-R–transduced progenitor cells were demonstrated by single cell cloning experiments. To analyze the effects of the constitutive expression of Mpl-R on the determination of multipotent progenitors (CFU-S) and long-term repopulating stem cells, Mpl-R– or Neo-infected cells were injected into lethally irradiated recipient mice. No difference was seen in (1) the number of committed progenitor cells contained in individual CFU-S12 whether colonies arose from noninfected or Mpl-R–infected CFU-S; (2) the mean numbers of progenitor cells per leg or spleen of mice reconstituted with Mpl-R– or Neo-infected cells, 1 or 7 months after the graft; and (3) the blood parameters of the two groups of animals, with the exception of a 50% reduction in circulating platelet counts after 7 months in mice repopulated with Mpl-R–infected bone marrow cells. These results indicate that retrovirus-mediated expression of Mpl-R in murine stem cells does not modify their ability to reconstitute all myeloid lineages of differentiation and does not result in a preferential commitment toward the megakaryocytic lineage.

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Thrombopoietin Does Not Induce Lineage-Restricted Commitment of Mpl-R Expressing Pluripotent Progenitors But Permits Their Complete Erythroid and Megakaryocytic Differentiation

Blood ◽

10.1182/blood.v89.10.3544 ◽

1997 ◽

Vol 89 (10) ◽

pp. 3544-3553 ◽

Cited By ~ 37

Author(s):

Frédérique Goncalves ◽

Catherine Lacout ◽

Jean-Luc Villeval ◽

Françoise Wendling ◽

William Vainchenker ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Progenitor Cells ◽

Bone Marrow Cells ◽

Constitutive Expression ◽

Retroviral Vectors ◽

Granulocytic Differentiation ◽

Hematopoietic Stem ◽

Infected Cells ◽

Marrow Cells

Abstract In this study, we examined the in vitro and in vivo effects of forced expression of Mpl-R (the thrombopoietin receptor) on the progeny of murine hematopoietic stem cells. Bone marrow cells from 5-FU–treated mice were transduced with retroviral vectors containing the human Mpl-R cDNA, or the neomycine gene as a control. After 7 days cocultivation on virus-producer cells, GpE86-Mpl-R or Gp86-Neo, the types of hematopoietic progenitor cells responding to thrombopoietin (TPO) were studied by clonogenic assays. Mpl-R–infected cells gave rise to CFU-GEMM, BFU-E, CFU-MK, but not CFU-GM while Neo-infected cells produced only megakaryocytic colonies. In addition, when nonadherent cells from GpE86-Mpl-R cocultures were grown with TPO as the only stimulus for 7 days, a marked expansion of CFU-GEMM, BFU-E, and CFU-MK was observed, while no change in CFU-GM number was seen. Erythroid and megakaryocytic maturation occurred in the presence of TPO while a block in granulocytic differentiation was observed at the myeloblast stage. The direct effects of TPO on Mpl-R–transduced progenitor cells were demonstrated by single cell cloning experiments. To analyze the effects of the constitutive expression of Mpl-R on the determination of multipotent progenitors (CFU-S) and long-term repopulating stem cells, Mpl-R– or Neo-infected cells were injected into lethally irradiated recipient mice. No difference was seen in (1) the number of committed progenitor cells contained in individual CFU-S12 whether colonies arose from noninfected or Mpl-R–infected CFU-S; (2) the mean numbers of progenitor cells per leg or spleen of mice reconstituted with Mpl-R– or Neo-infected cells, 1 or 7 months after the graft; and (3) the blood parameters of the two groups of animals, with the exception of a 50% reduction in circulating platelet counts after 7 months in mice repopulated with Mpl-R–infected bone marrow cells. These results indicate that retrovirus-mediated expression of Mpl-R in murine stem cells does not modify their ability to reconstitute all myeloid lineages of differentiation and does not result in a preferential commitment toward the megakaryocytic lineage.

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Serial transplantation of methotrexate-resistant bone marrow: protection of murine recipients from drug toxicity by progeny of transduced stem cells

Blood ◽

10.1182/blood.v75.2.337.bloodjournal752337 ◽

1990 ◽

Vol 75 (2) ◽

pp. 337-343 ◽

Cited By ~ 2

Author(s):

CA Corey ◽

AD DeSilva ◽

CA Holland ◽

DA Williams

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Gene Transfer ◽

Hematopoietic Stem Cells ◽

Bone Marrow Cells ◽

Retroviral Vectors ◽

Hematopoietic Stem ◽

Genetic Sequences ◽

Marrow Cells

Recombinant retroviral vectors have been used to transfer a variety of genetic sequences into hematopoietic stem cells. Although transfer and expression of foreign genetic sequences into reconstituting stem cells is one approach to somatic gene therapy, few studies have shown long lasting phenotypic changes in recipient mice in vivo. In this study, we show successful transfer of a methotrexate-resistant cDNA (DHFRr) into reconstituting hematopoietic stem cells using a retroviral vector, FrDHFRr, in which the DHFR cDNA is expressed off a hybrid Friend/Moloney long term repeat. Both primary and secondary recipients transplanted with bone marrow cells infected with this recombinant retrovirus show improved survival and protection from methotrexate- induced marrow toxicity when compared with control animals. These data suggest that retroviral-mediated gene transfer of DHFRr cDNA leads to a stable change in the phenotype of hematopoietic stem cells and progeny derived from those cells in vivo after bone marrow transplantation. Gene transfer using recombinant retroviral vectors seems to be one rational approach to establishing chemotherapy-resistant bone marrow cells.

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Serial transplantation of methotrexate-resistant bone marrow: protection of murine recipients from drug toxicity by progeny of transduced stem cells

Blood ◽

10.1182/blood.v75.2.337.337 ◽

1990 ◽

Vol 75 (2) ◽

pp. 337-343 ◽

Cited By ~ 99

Author(s):

CA Corey ◽

AD DeSilva ◽

CA Holland ◽

DA Williams

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Gene Transfer ◽

Hematopoietic Stem Cells ◽

Bone Marrow Cells ◽

Retroviral Vectors ◽

Hematopoietic Stem ◽

Genetic Sequences ◽

Marrow Cells

Abstract Recombinant retroviral vectors have been used to transfer a variety of genetic sequences into hematopoietic stem cells. Although transfer and expression of foreign genetic sequences into reconstituting stem cells is one approach to somatic gene therapy, few studies have shown long lasting phenotypic changes in recipient mice in vivo. In this study, we show successful transfer of a methotrexate-resistant cDNA (DHFRr) into reconstituting hematopoietic stem cells using a retroviral vector, FrDHFRr, in which the DHFR cDNA is expressed off a hybrid Friend/Moloney long term repeat. Both primary and secondary recipients transplanted with bone marrow cells infected with this recombinant retrovirus show improved survival and protection from methotrexate- induced marrow toxicity when compared with control animals. These data suggest that retroviral-mediated gene transfer of DHFRr cDNA leads to a stable change in the phenotype of hematopoietic stem cells and progeny derived from those cells in vivo after bone marrow transplantation. Gene transfer using recombinant retroviral vectors seems to be one rational approach to establishing chemotherapy-resistant bone marrow cells.

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Phenotypic correction of Fanconi anemia group C knockout mice

Blood ◽

10.1182/blood.v95.2.700 ◽

2000 ◽

Vol 95 (2) ◽

pp. 700-704 ◽

Cited By ~ 40

Author(s):

Kimberly A. Gush ◽

Kai-Ling Fu ◽

Markus Grompe ◽

Christopher E. Walsh

Keyword(s):

Bone Marrow ◽

Progenitor Cells ◽

Mitomycin C ◽

Fanconi Anemia ◽

Bone Marrow Cells ◽

Bone Marrow Failure ◽

Genetic Disorder ◽

Hematopoietic Stem ◽

Marrow Cells

Fanconi anemia (FA) is a genetic disorder characterized by bone marrow failure, congenital anomalies, and a predisposition to malignancy. FA cells demonstrate hypersensitivity to DNA cross-linking agents, such as mitomycin C (MMC). Mice with a targeted disruption of the FANCC gene (fancc −/− nullizygous mice) exhibit many of the characteristic features of FA and provide a valuable tool for testing novel therapeutic strategies. We have exploited the inherent hypersensitivity offancc −/− hematopoietic cells to assay for phenotypic correction following transfer of the FANCC complementary DNA (cDNA) into bone marrow cells. Murine fancc −/− bone marrow cells were transduced with the use of retrovirus carrying the humanfancc cDNA and injected into lethally irradiated recipients. Mitomycin C (MMC) dosing, known to induce pancytopenia, was used to challenge the transplanted animals. Phenotypic correction was determined by assessment of peripheral blood counts. Mice that received cells transduced with virus carrying the wild-type gene maintained normal blood counts following MMC administration. All nullizygous control animals receiving MMC exhibited pancytopenia shortly before death. Clonogenic assay and polymerase chain reaction analysis confirmed gene transfer of progenitor cells. These results indicate that selective pressure promotes in vivo enrichment offancc-transduced hematopoietic stem/progenitor cells. In addition, MMC resistance coupled with detection of the transgene in secondary recipients suggests transduction and phenotypic correction of long-term repopulating stem cells.

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Long-term monoclonal reconstitution of erythropoiesis in genetically anemic W/Wv mice by injection of 5-fluorouracil-treated bone marrow cells of Pgk-1b/Pgk-1a mice

Blood ◽

10.1182/blood.v70.6.1758.1758 ◽

1987 ◽

Vol 70 (6) ◽

pp. 1758-1763 ◽

Cited By ~ 12

Author(s):

T Nakano ◽

N Waki ◽

H Asai ◽

Y Kitamura

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Stem Cell ◽

Bone Marrow Cells ◽

Electrophoretic Pattern ◽

Phosphoglycerate Kinase ◽

X Chromosomes ◽

Hematopoietic Stem ◽

Colony Forming Units ◽

Marrow Cells

Abstract The spleen colony-forming assay does not represent the number of hematopoietic stem cells with extensive self-maintaining capacity because five to 50 spleen colony-forming units (CFU-S) are necessary to rescue a genetically anemic (WB X C57BL/6)F1-W/Wv(WBB6F1-W/Wv) mouse. We investigated which is more important for the reconstitution of erythropoiesis, the transplantation of multiple CFU-S or that of a single stem cell with extensive self-maintaining potential. The electrophoretic pattern of hemoglobin was used as a marker of reconstitution and that of phosphoglycerate kinase (PGK), an X chromosome-linked enzyme, as a tool for estimating the number of stem cells. For this purpose, we developed the C57BL/6 congeneic strain with the Pgk-1a gene. Bone marrow cells were harvested after injection of 5- fluorouracil from C57BL/6-Pgk-1b/Pgk-1a female mice in which each stem cell had either A-type PGK or B-type PGK due to the random inactivation of one or two X chromosomes. When a relatively small number of bone marrow cells (ie, 10(3) or 3 X 10(3] were injected into 200-rad- irradiated WBB6F1-W/Wv mice, the hemoglobin pattern changed from the recipient type (Hbbd/Hbbs) to the donor type (Hbbs/Hbbs) in seven of 150 mice for at least 8 weeks. Erythrocytes of all these WBB6F1-W/Wv mice showed either A-type PGK alone or B-type PGK alone during the time of reconstitution, which suggests that a single stem cell with extensive self-maintaining potential may sustain the whole erythropoiesis of a mouse for at least 8 weeks.

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Hemangiogenic Role of ELF4 in Bone Marrow Post Myeloablation.

Blood ◽

10.1182/blood.v108.11.1783.1783 ◽

2006 ◽

Vol 108 (11) ◽

pp. 1783-1783

Author(s):

Mariela Sivina ◽

Takeshi Yamada ◽

Natalie Dang ◽

H. Daniel Lacorazza

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Endothelial Cells ◽

Hematopoietic Stem Cells ◽

Blood Vessels ◽

Progenitor Cells ◽

Endothelial Progenitor Cells ◽

Bone Marrow Cells ◽

Hematopoietic Stem ◽

Huvec Cells

Abstract Bone marrow suppression is an important cause of death in patients exposed to radiation or in cancer patients treated with conventional chemotherapeutic agents. Myeloablative treatments (i.e. 5-fluorouracil administration) lead to apoptosis of blood forming cells and to regression of blood vessels in bone marrow. It is well known that hematological recovery post-bone marrow insult depends on the capacity of hematopoietic stem cells to regenerate the entire hematopoietic system, however, the transcriptional machinery involved in the regeneration of sinusoidal blood vessels in bone marrow from endothelial progenitor cells is largely unknown. Endothelial cells express the Tie2 receptor tyrosine kinase (a.k.a. Tek), which is involved in the angiogenic remodeling and vessel stabilization. Gene targeting of Tie2 showed that it is not required for differentiation and proliferation of definitive hematopoietic lineages in the embryo although Tie2 is needed during postnatal bone marrow hematopoiesis. ELF is a subgroup of the ETS family of transcription factors composed by ELF1, ELF2 (a.k.a. NERF), ELF3, ELF4 (a.k.a. MEF) and ELF5. ELF1 and ELF2 have been shown to regulate Tie2 expression in vitro. Recently we showed that ELF4 modulates the exit of hematopoietic stem cells (HSC) from quiescence (Lacorazza et al., Cancer Cell2006, 9:175–187). Given the high homology between ELF1 and ELF4 and the same origin of HSC and endothelial progenitor cells, we hypothesize that ELF4 regulates proliferation and Tie2 expression of endothelial cells. We used a luciferase gene reporter system in COS-7 and HEK cells to examine the capacity of ELF proteins to activate Tie2. ELF4 is the strongest activator of Tie2 expression following the hierarchy ELF4>ELF1>ELF2 variant 1>ELF2 variant 2. Site directed mutagenesis of each of the five ETS-binding sites (EBS) present in the Tie2 promoter shows that ELF4 binds preferentially to EBS 1, 3 and 5. Binding of ELF4 to the Tie2 promoter was confirmed by chromatin immunoprecipitation and EMSA. Although Elf1 gene expression is essentially normal in Elf4−/− bone marrow cells collected after 5-FU treatment, we detected diminished Tie2 expression compared to Elf4+/+ bone marrow cells. The association of this effect to human endothelial cells derived from umbilical cord (HUVEC cells) was investigated. All-trans retinoic acid (ATRA) and vascular-endothelial growth factor (VEGF) induced ELF4 expression in HUVEC cells in a dose and time dependent manner which was followed by increased Tie2 expression, suggesting that expression of ELF4 is modulated by angiogenic signals. Moreover, endothelial cells treated with ATRA showed rapid wound colonization in a wound assay. Expression of the pan-endothelial marker MECA-32 was determined by immunohistochemistry to correlate Tie2 with the regeneration of blood vessels: myeloablated Elf4−/− femurs exhibited a reduction of MECA-32 positive arterioles. Finally, temporal and spatial expression of Tie2 during hematological recovery post ablation was measured in bone marrow using transgenic Tie2-LacZ mice crossed to Elf4−/− mice. Collectively, our data suggests that ELF4 regulates Tie2 expression in endothelial cells but most importantly their proliferative capacity in response to angiogenic signals.

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Requirement for p85α Regulatory Subunit of Class IA PI3Kinase and Rac2 GTPase in Myeloproliferative Disease Driven by Activation Loop Mutant of KIT.

Blood ◽

10.1182/blood.v110.11.89.89 ◽

2007 ◽

Vol 110 (11) ◽

pp. 89-89

Author(s):

Veerendra Munugalavadla ◽

Emily C. Sims ◽

Stephen D. Lenz ◽

Reuben Kapur

Keyword(s):

Bone Marrow ◽

Mast Cells ◽

Progenitor Cells ◽

Bone Marrow Cells ◽

Regulatory Subunit ◽

Activation Loop ◽

Myeloproliferative Disease ◽

Hematopoietic Stem ◽

Marrow Cells

Abstract Oncogenic activation-loop mutants of KIT, the receptor for stem cell factor (SCF), are commonly observed in acute myeloid leukemia (AML) and systemic mastocytosis (SM); however, unlike the KIT juxtamembrane mutants (found in patients with gastrointestinal stromal tumors [GISTs]), the activation-loop mutants are commonly insensitive to inhibition by tyrosine kinase inhibitors. Furthermore, little is known about the signaling pathways that contribute to oncogenic KIT-induced transformation in SM or AML. We demonstrate that expression of KITD814V (KIT activation-loop mutant) in primary hematopoietic stem and progenitor cells induces constitutive KIT autophosphorylation, promotes ligand-independent hyperproliferation, skews myeloid differentiation towards the granulocytic lineage, and promotes promiscuous cooperation with multiple cytokines, including G-CSF, M-CSF and IL-3. KITD814V expressing primary mast cells also demonstrated hyperproliferation in response to SCF, IL-3, IL-4 and IL-10. Biochemical analyses of KITD814V expressing cells revealed constitutively elevated levels of phosphatidylinositol-3-kinase (PI3K) and its downstream substrate, the Rho family GTPase Rac. Genetic disruption of p85a, the regulatory subunit of class IA PI-3Kinase, but not of p85β, or genetic disruption of the hematopoietic cell-specific Rho GTPase, Rac2, normalized KITD814V-induced ligand independent hyperproliferation in vitro. Additionally, deficiency of p85α or Rac2 corrected the promiscuous hyperproliferation observed in response to multiple cytokines in both KITD814V expressing stem/progenitor cells as well as mast cells in vitro. Although p85α is hyperphosphorylated and constitutively bound to KITD814V in bone marrow cells in vitro; its physiologic role in transformation in vivo is not known. To address this, we generated a new mouse model to study KITD814V induced transformation in myeloid cells as opposed to previously described models that primarily result in the generation of phenotypes resembling acute lymphocytic leukemia via this mutation. Our results show that transplantation of KITD814V expressing bone marrow cells from C57/BL6 strain of mice into syngeneic recipients results in a fatal myeloproliferative disease (MPD) characterized by leukocytosis, splenomegaly, disruption of the splenic architecture as well as myeloid cell infiltration in the lung and liver. Importantly, in this model, transplantation of KITD814V expressing p85α deficient bone marrow cells rescued the MPD phenotype, including splenomegaly, peripheral blood leukocytosis and the reduced life span associated with the transplantation of KITD814V expressing wildtype bone marrow cells. Treatment of KITD814V-expressing hematopoietic progenitors with either a Rac inhibitor (NC23766) or rapamycin showed a dose-dependent suppression in KITD814V induced growth. Taken together, our results describe the generation of a new murine transplant model to study KITD814V induced transformation and identify p85a and Rac2 as potential novel therapeutic target for the treatment of KITD814V-bearing diseases including SM and AML.

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Dnmt3a is Required For Aberrant Self-Renewal Driven by PML-RARA

Blood ◽

10.1182/blood.v122.21.477.477 ◽

2013 ◽

Vol 122 (21) ◽

pp. 477-477

Author(s):

Christopher B Cole ◽

Angela M. Verdoni ◽

David H Spencer ◽

Timothy J. Ley

Keyword(s):

Dna Methylation ◽

Bone Marrow ◽

Progenitor Cells ◽

Bone Marrow Cells ◽

Ex Vivo ◽

Myeloid Cells ◽

Cd11b Expression ◽

Self Renewal ◽

Hematopoietic Stem ◽

Marrow Cells

We previously identified recurrent mutations in the DNA methyltransferase DNMT3A in patients with acute myeloid leukemia (AML). DNMT3A and the highly homologous gene DNMT3B encode the two methyltransferases that are primarily responsible for mediating de novo methylation of specific CpG residues during differentiation. Loss of Dnmt3a in hematopoietic stem cells impairs their ability to differentiate into committed progenitors (Challen et al Nat Gen 44:23, 2011). Importantly, DNMT3A mutations are mutually exclusive of the favorable prognosis AML-initiating translocations, including the t(15;17) translocation (which creates the PML-RARA fusion gene), and translocations involving MLL. PML-RARA has been shown to interact with DNMT3A in vitro (Di Croce et al Science 295:1079,2002), and to require DNMT3A to induce methylation and transcriptional silencing of a subset of specific target genes. These findings, and the lack of DNMT3A mutations in APL patients, suggest that PML-RARA may require functional DNMT3A to initiate leukemia. To investigate this possibility, we utilized a well-characterized transgenic mouse model (in a pure B6 background) in which expression of PML-RARA is driven in hematopoietic stem/progenitor cells by the mouse Cathepsin G locus (Ctsg-PML-RARA+/- mice). These mice spontaneously develop acute promyelocytic leukemia (APL) with high penetrance and long latency, and also exhibit a preleukemic phenotype marked by the accumulation of myeloid cells in bone marrow and spleen. In addition, myeloid progenitor cells derived from these mice have the ability to serially replate in methylcellulose cultures, demonstrating aberrant self-renewal. We generated Ctsg-PML-RARA+/- mice lacking Dnmt3a (PML-RARA+/- x Dnmt3a-/-) as well as mice in which conditional ablation of Dnmt3b in hematopoietic cells is driven by Vav-Cre (PML-RARA+/- x Dnmt3b fl/fl x Vav-Cre+). Loss of Dnmt3a completely abrogated the ex vivo replating ability of PML-RARA bone marrow (Figure 1). Although colonies from both PML-RARA+/- and PML-RARA+/- x Dnmt3a-/- mice appeared similar in morphology and number on the first plating, PML-RARA+/- x Dnmt3a-/- marrow ceased to form colonies with subsequent replating (see Figure), and cultured cells lost the expression of the myeloid marker CD11b. The same phenotype was also observed using bone marrow from both genotypes that was secondarily transplanted into wild type recipients, indicating that it is intrinsic to transplantable hematopoietic progenitors. Reintroduction of DNMT3A into bone marrow cells derived from PML-RARA+/- x Dnmt3a-/- mice with retroviral transduction restored replating ability and CD11b expression. Competitive repopulation experiments with PML-RARA+/- x Dnmt3a-/- marrow revealed a decreased contribution to peripheral lymphoid and myeloid cells at 4 weeks, relative to PML-RARA+/- or WT control animals. Finally, 12 weeks after transplantation, recipients of PML-RARA+/- x Dnmt3a-/- bone marrow did not display an accumulation of myeloid cells in the bone marrow and spleen. Importantly, bone marrow from PML-RARA+/- x Dnmt3b fl/fl x Vav-Cre+/- mice displayed no replating deficit or loss of CD11b expression ex vivo, indicating different functions for Dnmt3a versus Dnmt3b in this model. Finally, we interrogated the effect of Dnmt3a loss on bone marrow DNA methylation patterns using a liquid phase DNA capture technique that sampled ∼1.9 million mouse CpGs at >10x coverage. Loss of Dnmt3a caused a widespread loss of DNA methylation in whole bone marrow cells, with 36,000 CpGs that were highly methylated (methylation value >0.7) in the PML-RARA+/- and WT mice, but hypomethylated (methylation value <0.4) in Dnmt3a-/- and PML-RARA+/- x Dnmt3a-/- mice. Characterization of the effect of Dnmt3a loss on leukemia latency, penetrance, and phenotype in PML-RARA+/- mice is currently being defined in a tumor watch. In summary, we have demonstrated that PML-RARA requires functional Dnmt3a (but not Dnmt3b) to drive aberrant self-renewal of myeloid progenitors ex vivo, and that loss of Dnmt3a leads to widespread DNA hypomethylation in bone marrow cells, and abrogates preleukemic changes in mice expressing PML-RARA. This data may explain why DNMT3A mutations are not found in patients with APL initiated by PML-RARA. Disclosures: No relevant conflicts of interest to declare.

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Role Of Sf3b1 On Hematopoiesis

Blood ◽

10.1182/blood.v122.21.600.600 ◽

2013 ◽

Vol 122 (21) ◽

pp. 600-600

Author(s):

Manabu Matsunawa ◽

Ryo Yamamoto ◽

Masashi Sanada ◽

Aiko Sato ◽

Yusuke Shiozawa ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Bone Marrow Transplantation ◽

Hematopoietic Stem Cells ◽

Marrow Transplantation ◽

Bone Marrow Cells ◽

Hematopoietic Stem ◽

Ring Sideroblasts ◽

Marrow Cells

Abstract Frequent pathway mutation involving multiple components of the RNA splicing machinery is a cardinal feature of myeloid neoplasms showing myeloid dysplasia, in which the major mutational targets include U2AF35, ZRSR2, SRSF2 and SF3B1. Among these, SF3B1 mutations were strongly associated with MDS subtypes characterized by increased ring sideroblasts, such as refractory anemia and refractory cytopenia with multiple lineage dysplasia with ring sideroblasts, suggesting the critical role of SF3B1 mutations in these MDS subtypes. However, currently, the molecular mechanism of SF3B1mutation leading to the ring sideroblasts formation and MDS remains unknown. The SF3B1 is a core component of the U2-small nuclear ribonucleoprotein (U2 snRNP), which recognizes the 3′ splice site at intron–exon junctions. It was demonstrated that Sf3b1 null mice were shown to be embryonic lethal, while Sf3b1 +/- mice exhibited various skeletal alterations that could be attributed to deregulation of Hox gene expression due to haploinsufficiency of Sf3b1. However, no detailed analysis of the functional role of Sf3b1 in hematopoietic system in these mice has been performed. So, to clarify the role of SF3B1 in hematopoiesis, we investigated the hematological phenotype of Sf3b1 +/- mice. There was no significant difference in peripheral blood counts, peripheral blood lineage distribution, bone marrow total cellularity or bone marrow lineage composition between Sf3b1 +/+ and Sf3b1 +/- mice. Morphologic abnormalities of bone marrow and increased ring sideroblasts were not observed. However, quantitative analysis of bone marrow cells from Sf3b1 +/- mice revealed a reduction of the number of hematopoietic stem cells (CD34 neg/low, cKit positive, Sca-1 positive, lineage-marker negative: CD34-KSL cells) measured by flow cytometry analysis, compared to Sf3b1 +/+ mice. Whereas examination of hematopoietic progenitor cells revealed a small decrease in KSL cell populations and megakaryocyte - erythroid progenitors (MEP) in Sf3b1 +/- mice, and common myeloid progenitors (CMP), granulocyte - monocyte progenitors (GMP) and common lymphoid progenitors (CLP) remained unchanged between Sf3b1 +/+ and Sf3b1 +/- mice. In accordance with the reduced number of hematopoietic stem cells in Sf3b1 +/- mice, the total number of colony-forming unit generated from equal number of whole bone marrow cells showed lower colony number in Sf3b1 +/- mice in vitro. Competitive whole bone marrow transplantation assay, which irradiated recipient mice were transplanted with donor whole bone marrow cells from Sf3b1 +/+ or Sf3b1 +/- mice with an equal number of competitor bone marrow cells, revealed impaired competitive whole bone marrow reconstitution capacity of Sf3b1 +/- mice in vivo. These data demonstrated Sf3b1 was required for hematopoietic stem cells maintenance. To further examine the function of hematopoietic stem cells in Sf3b1 +/- mice, we performed competitive transplantation of purified hematopoietic stem cells from Sf3b1 +/+ or Sf3b1 +/- mice into lethally irradiated mice together with competitor bone marrow cells. Sf3b1 +/- progenitors showed reduced hematopoietic stem cells reconstitution capacity compared to those from Sf3b1 +/+ mice. In serial transplantation experiments, progenitors from Sf3b1 +/- mice showed reduced repopulation ability in the primary bone marrow transplantation, which was even more pronounced after the second bone marrow transplantation. Taken together, these data demonstrate that Sf3b1 plays an important role in normal hematopoiesis by maintaining hematopoietic stem cell pool size and regulating hematopoietic stem cell function. To determine the molecular mechanism underlying the observed defect in hematopoietic stem cells of Sf3b1 +/- mice, we performed RNA-seq analysis. We will present the results of our biological assay and discuss the relation of Sf3b1 and hematopoiesis. Disclosures: No relevant conflicts of interest to declare.

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Identification of a novel bone marrow-derived B-cell progenitor population that coexpresses B220 and Thy-1 and is highly enriched for Abelson leukemia virus targets.

Molecular and Cellular Biology ◽

10.1128/mcb.9.6.2665 ◽

1989 ◽

Vol 9 (6) ◽

pp. 2665-2671 ◽

Cited By ~ 26

Author(s):

G F Tidmarsh ◽

S Heimfeld ◽

C A Whitlock ◽

I L Weissman ◽

C E Müller-Sieburg

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Bone Marrow Cells ◽

Leukemia Virus ◽

Cell Activity ◽

Mouse Bone Marrow ◽

Hematopoietic Stem ◽

Low Levels ◽

B Lineage ◽

Marrow Cells

A novel stage in early B-lymphocyte differentiation has been identified in normal mouse bone marrow cells. Earlier work had demonstrated that bone marrow cells characterized by low levels of Thy-1 and lack of a panel of lineage markers (Thy-1lo Lin- cells) were highly enriched for pluripotent hematopoietic stem cells. In this paper, we present evidence that another bone marrow population, which expressed low levels of Thy-1 and coexpressed B220, a B-lineage-specific form of the leukocyte common antigen, contained early and potent precursors for B lymphocytes upon in vivo transfer to irradiated hosts. These Thy-1lo B220+ cells, comprising 1 to 2% of bone marrow cells, were enriched for large cells in the mitotic cycle; the population lacked significant pluripotent hematopoietic stem cell activity and myeloid-erythroid progenitors. Most strikingly, Thy-1lo B220+ cells represented a highly enriched population of bone marrow cells that could be targets of Abelson murine leukemia virus transformation. We propose that Thy-1lo B220+ bone marrow cells represent the earliest stage of committed lymphocyte progenitors, intermediate in differentiation between Thy-1lo Lin- pluripotent stem cells and, in the B lineage, Thy-1- B220+ pre-B cells.

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