Biomedical subjects

D W Clapp

Publications and source records attributed to D W Clapp.

At least 19 recordsLinked to original sources

PubMed2005

Stimulus-evoked release of neuropeptides is enhanced in sensory neurons from mice with a heterozygous mutation of the Nf1 gene.

Neurofibromatosis type I is a common autosomal dominant disease characterized by formation of multiple benign and malignant tumors. People with this disorder also experience chronic pain, which can be disabling. Neurofibrinomin, the protein product of the NF1 gene (neurofibromin gene (human)), is a guanosine triphosphate activating protein for p21(ras). Loss of NF1 results in an increase in activity of the p21(ras) transduction cascade. Because of the growing evidence suggesting involvement of downstream components of the p21(ras) transduction cascade in the sensitization of nociceptive sensory neurons, we examined the stimulus-evoked release of the neuropeptides, substance P and calcitonin gene-related peptide, from primary sensory neurons of mice with a mutation of the Nf1 gene (neurofibromin gene (mouse)) (Nf1+/-). Measuring immunoreactive substance P and immunoreactive calcitonin gene-related peptide by radioimmunoassay, we demonstrated that capsaicin-stimulated release of neuropeptides is three to five-fold higher in spinal cord slices from Nf1+/- mice than from wildtype mouse tissue. In addition, the potassium and capsaicin-stimulated release of immunoreactive calcitonin gene-related peptide from cultures of sensory neurons isolated from Nf1+/- mice was more than double that from cultures of wildtype neurons. Treatment of wildtype sensory neurons with nerve growth factor for 5-7 days mimicked the enhanced stimulus-evoked release observed from the Nf1+/- neurons. When nerve growth factor was removed 48 h before conducting release experiments, nerve growth factor-induced augmentation of immunoreactive calcitonin gene-related peptide release from Nf1+/- neurons was more pronounced than in Nf1+/- sensory neurons that were treated with nerve growth factor continuously for 5-7 days. Thus, sensory neurons from mice with a heterozygous mutation of the Nf1 gene that is analogous to the human disease neurofibromatosis type I, exhibit increased sensitivity to chemical stimulation. This augmented responsiveness may explain the abnormal pain sensations experienced by people with neurofibromatosis type I and suggests an important role for guanosine triphosphate activating proteins, in the regulation of nociceptive sensory neuron sensitization.

Afferent Pathways↗

PubMed2004

Modern diagnostics in chronic myeloproliferative diseases (CMPDs).

According to the new WHO classification a group of chronic myeloproliferative diseases (CMPDs) were defined: chronic myeloid leukemia (CML), chronic neutrophilic leukemia (CNL), chronic eosinophilic leukemia and hypereosinophilic syndrome (CEL/HES), polycythemia vera (PV), chronic idiopathic myelofibrosis (with extramedullary hematopoiesis, CIMF), essential thrombocythemia (ET), and so called CMPD/unclassifiable. As clinical features and laboratory findings differ widely between these diseases several diagnostic approaches are mandatory at diagnosis for classification and are needed also for follow up studies, especially for the measurement of minimal residual disease (MRD). We here outline the laboratory set up at diagnosis and during follow up in CMPDs with specific focus on the respective therapeutical consequences. Only by using a comprehensive diagnostic panel including cytomorphology, cytogenetics, and molecular genetic methods establishing the correct diagnosis, optimizing treatment as well as evaluating treatment response is possible in CMPDs today.

Blood Cell Count↗

PubMed2001

Retargeting of viral vectors to the folate receptor endocytic pathway.

Viral vectors with high transfection efficiencies are not always those with optimal target cell binding specificities. As a consequence, virus pseudotyping has been developed to endow transfection competent viruses with improved cell binding specificities and affinities. We have hypothesized that chemical conjugation of a virus to a cell specific ligand might also alter its target cell specificity and produce a virus that would transfect only the desired cell type. To test this concept, an ecotropic replication-defective myeloproliferative sarcoma retrovirus and an amphotropic murine adenovirus containing the gene for beta-galactosidase were chemically derivatized with folic acid. As expected from its strong ecotropism, the unmodified retrovirus did not induce beta-galactosidase expression in nonhost KB cells, while the amphotropic adenovirus yielded high levels of gene expression in the same cell line. Surprisingly, although folate derivatization enabled avid binding of both viruses to folate receptor expressing KB cells, the folate conjugation did not promote retroviral gene expression and actually prevented the normal beta-galactosidase expression seen with the adenoviral vector. The fact that co-administration of excess free folic acid to block uptake by folate receptor-mediated endocytosis restored adenoviral gene expression to the level obtained with unmodified virus suggests that folate derivatization per se does not hamper viral activity. We, therefore, conclude that neither retroviral nor adenoviral delivery via the folate endocytosis pathway is compatible with viral gene expression in KB cells.

Adenoviridae↗

PubMed2001

Hyperactivation of p21(ras) and the hematopoietic-specific Rho GTPase, Rac2, cooperate to alter the proliferation of neurofibromin-deficient mast cells in vivo and in vitro.

Mutations in the NF1 tumor suppressor gene cause neurofibromatosis type I (NF1), a disease characterized by the formation of cutaneous neurofibromas infiltrated with a high density of degranulating mast cells. A hallmark of cell lines generated from NF1 patients or Nf1-deficient mice is their propensity to hyperproliferate. Neurofibromin, the protein encoded by NF1, negatively regulates p21(ras) activity by accelerating the conversion of Ras-GTP to Ras-GDP. However, identification of alterations in specific p21(ras) effector pathways that control proliferation in NF1-deficient cells is incomplete and critical for understanding disease pathogenesis. Recent studies have suggested that the proliferative effects of p21(ras) may depend on signaling outputs from the small Rho GTPases, Rac and Rho, but the physiologic importance of these interactions in an animal disease model has not been established. Using a genetic intercross between Nf1(+/)- and Rac2(-)(/)- mice, we now provide genetic evidence to support a biochemical model where hyperactivation of the extracellular signal-regulated kinase (ERK) via the hematopoietic-specific Rho GTPase, Rac2, directly contributes to the hyperproliferation of Nf1-deficient mast cells in vitro and in vivo. Further, we demonstrate that Rac2 functions as mediator of cross-talk between phosphoinositide 3-kinase (PI-3K) and the classical p21(ras)-Raf-Mek-ERK pathway to confer a distinct proliferative advantage to Nf1(+/)- mast cells. Thus, these studies identify Rac2 as a novel mediator of cross-talk between PI-3K and the p21(ras)-ERK pathway which functions to alter the cellular phenotype of a cell lineage involved in the pathologic complications of a common genetic disease.

Animals↗

PubMed2001

The Drosophila S3 multifunctional DNA repair/ribosomal protein protects Fanconi anemia cells against oxidative DNA damaging agents.

Cells harvested from Fanconi anemia (FA) patients show an increased hypersensitivity to the multifunctional DNA damaging agent mitomycin C (MMC), which causes cross-links in DNA as well as 7,8-dihydro-8-oxoguanine (8-oxoG) adducts indicative of escalated oxidative DNA damage. We show here that the Drosophila multifunctional S3 cDNA, which encodes an N-glycosylase/apurinic/apyrimidinic (AP) lyase activity was found to correct the FA Group A (FA(A)) and FA Group C (FA(C)) sensitivity to MMC and hydrogen peroxide (H2O2). Furthermore, the Drosophila S3 cDNA was shown to protect AP endonuclease deficient E. coli cells against H(2)O(2) and MMC, and also protect 8-oxoG repair deficient mutM E. coli strains against MMC and H2O2 cell toxicity. Conversely, the human S3 protein failed to complement the AP endonuclease deficient E. coli strain, most likely because it lacks N-glycosylase activity for the repair of oxidatively-damaged DNA bases. Although the human S3 gene is clearly not the genetic alteration in FA cells, our results suggest that oxidative DNA damage is intimately involved in the overall FA phenotype, and the cytotoxic effect of selective DNA damaging agents in FA cells can be overcome by trans-complementation with specific DNA repair cDNAs. Based on these findings, we would predict other oxidative repair proteins, or oxidative scavengers, could serve as protective agents against the oxidative DNA damage that occurs in FA.

Animals↗

PubMed2001

Quantitative effects of Nf1 inactivation on in vivo hematopoiesis.

The NF1 tumor-suppressor gene is frequently inactivated in juvenile myelomonocytic leukemia, and Nf1 mutant mice model this myeloproliferative disorder (MPD). Competitive repopulation assays were performed to quantify the proliferative advantage of Nf1(-/-) hematopoietic cells in vivo. Nf1 mutant stem cells demonstrated a growth advantage that was greatest in myeloid lineage cells and least pronounced in T lymphocytes. Surprisingly, although low numbers of Nf1-deficient cells consistently outcompeted wild-type cells, levels of chimerism were stable over months of observation, and MPD was not observed unless threshold numbers of mutant cells were injected. These data showing that normal competitor cells can strongly modulate the growth of mutant populations in vivo have general implications for modeling cancer in the mouse. In particular, strains in which cancer-associated mutations are expressed in fields of target cells may not accurately model early events in tumorigenesis because they eliminate the requirement for a mutant clone to outcompete resident normal cells.

Adoptive Transfer↗

PubMed2000

Neurofibromin GTPase-activating protein-related domains restore normal growth in Nf1-/- cells.

Members of the Ras superfamily of signaling proteins modulate fundamental cellular processes by cycling between an active GTP-bound conformation and an inactive GDP-bound form. Neurofibromin, the protein product of the NF1 tumor suppressor gene, and p120GAP are GTPase-activating proteins (GAPs) for p21(Ras) (Ras) and negatively regulate output by accelerating GTP hydrolysis on Ras. Neurofibromin and p120GAP differ markedly outside of their conserved GAP-related domains (GRDs), and it is therefore unknown if the respective GRDs contribute functional specificity. To address this question, we expressed the GRDs of neurofibromin and p120GAP in primary cells from Nf1 mutant mice in vitro and in vivo. Here we show that expression of neurofibromin GRD, but not the p120GAP GRD, restores normal growth and cytokine signaling in three lineages of primary Nf1-deficient cells that have been implicated in the pathogenesis of neurofibromatosis type 1 (NF1). Furthermore, utilizing a GAP-inactive mutant NF1 GRD identified in a family with NF1, we demonstrate that growth restoration is a function of NF1 GRD GAP activity on p21(Ras). Thus, the GRDs of neurofibromin and p120GAP specify nonoverlapping functions in multiple primary cell types.

Animals↗

PubMed2000

Genetic and biochemical evidence that haploinsufficiency of the Nf1 tumor suppressor gene modulates melanocyte and mast cell fates in vivo.

Neurofibromatosis type 1 (NF1) is a common autosomal-dominant disorder characterized by cutaneous neurofibromas infiltrated with large numbers of mast cells, melanocyte hyperplasia, and a predisposition to develop malignant neoplasms. NF1 encodes a GTPase activating protein (GAP) for Ras. Consistent with Knudson's "two hit" model of tumor suppressor genes, leukemias and malignant solid tumors in NF1 patients frequently demonstrate somatic loss of the normal NF1 allele. However, the phenotypic and biochemical consequences of heterozygous inactivation of Nf1 are largely unknown. Recently neurofibromin, the protein encoded by NF1, was shown to negatively regulate Ras activity in Nf1-/- murine myeloid hematopoietic cells in vitro through the c-kit receptor tyrosine kinase (dominant white spotting, W). Since the W and Nf1 locus appear to function along a common developmental pathway, we generated mice with mutations at both loci to examine potential interactions in vivo. Here, we show that haploinsufficiency at Nf1 perturbs cell fates in mast cells in vivo, and partially rescues coat color and mast cell defects in W(41) mice. Haploinsufficiency at Nf1 also increased mast cell proliferation, survival, and colony formation in response to Steel factor, the ligand for c-kit. Furthermore, haploinsufficiency was associated with enhanced Ras-mitogen-activated protein kinase activity, a major downstream effector of Ras, via wild-type and mutant (W(41)) c-kit receptors. These observations identify a novel interaction between c-kit and neurofibromin in vivo, and offer experimental evidence that haploinsufficiency of Nf1 alters both cellular and biochemical phenotypes in two cell lineages that are affected in individuals with NF1. Collectively, these data support the emerging concept that heterozygous inactivation of tumor suppressor genes may have profound biological effects in multiple cell types.

Animals↗

PubMed2000

Nf1 and Gmcsf interact in myeloid leukemogenesis.

The NF1 tumor suppressor gene encodes neurofibromin, a GTPase-activating protein (GAP) for p21ras (Ras). Children with NF1 are predisposed to juvenile myelomonocytic leukemia (JMML). Some heterozygous Nf1 mutant mice develop a similar myeloproliferative disorder (MPD), and adoptive transfer of Nf1-deficient fetal liver cells consistently induces this MPD. Human JMML and murine Nf1-deficient cells are hypersensitive to granulocyte-macrophage colony-stimulating factor (GM-CSF) in methylcellulose cultures. We generated hematopoietic cells deficient in both Nf1 and Gmcsf to test whether GM-CSF is required to drive excessive proliferation of Nf1-/- cells in vivo. Here we show that GM-CSF play a central role in establishing and maintaining the MPD and that recipients engrafted with Nf1-/- Gmcsf-/- hematopoietic cells are hypersensitive to exogenous GM-CSF.

Adoptive Transfer↗

PubMed1999

Loss of FancC function results in decreased hematopoietic stem cell repopulating ability.

Fanconi anemia (FA) is a complex genetic disorder characterized by progressive bone marrow (BM) aplasia, chromosomal instability, and acquisition of malignancies, particularly myeloid leukemia. We used a murine model containing a disruption of the murine homologue of FANCC (FancC) to evaluate short- and long-term multilineage repopulating ability of FancC -/- cells in vivo. Competitive repopulation assays were conducted where "test" FancC -/- or FancC +/+ BM cells (expressing CD45.2) were cotransplanted with congenic competitor cells (expressing CD45.1) into irradiated mice. In two independent experiments, we determined that FancC -/- BM cells have a profound decrease in short-term, as well as long-term, multilineage repopulating ability. To determine quantitatively the relative production of progeny cells by each test cell population, we calculated test cell contribution to chimerism as compared with 1 x 10(5) competitor cells. We determined that FancC -/- cells have a 7-fold to 12-fold decrease in repopulating ability compared with FancC +/+ cells. These data indicate that loss of FancC function results in reduced in vivo repopulating ability of pluripotential hematopoietic stem cells, which may play a role in the development of the BM failure in FA patients. This model system provides a powerful tool for evaluation of experimental therapeutics on hematopoietic stem cell function.

Animals↗

PubMed1999

Expression and functional characterization of the beta-isoform of the folate receptor on CD34(+) cells.

We have investigated the expression and functional competence of folate receptor (FR) isoforms on human hematopoietic cells. Using immunofluorescence and reverse transcriptase-polymerase chain reaction (RT-PCR) methodology, we find that a substantial fraction of low-density mononuclear and CD34(+) cells express both the beta and gamma isoforms of FR. The alpha isoform of FR (the form most commonly found on cancer cells) was surprisingly absent from all hematopoietic cells examined. Compared with KB cells (a human cell line known for its elevated expression of FR-alpha), the abundance of FR-beta on CD34(+) cell surfaces was relatively low (approximately 8% of KB cell levels). Because many antifolates and folic acid-linked chemotherapeutic agents enter malignant cells at least partially via FR endocytosis, it was important to evaluate the ability of FR on CD34(+) cells to bind folic acid (FA). Based on three FR binding assays, freshly isolated CD34(+) cells were found to display no affinity for FA. Thus, regardless of whether steps were taken to remove endogenous folates before receptor binding assays, FR on primitive hematopoietic cells failed to bind 3H-FA, fluorescein isothiocyanate (FITC)-linked FA, or FA-derivatized liposomes. In contrast, analogous studies on KB cells showed high levels of receptor binding for all three FR probes. These studies show that although multipotent hematopoietic progenitor cells express FR, the receptor does not transport significant amounts of FA. Consequently, antifolates and FA-linked chemotherapeutic agents that can be engineered to enter malignant cells exclusively through the FR should not harm progenitor/stem cell function.

Antigens, CD34↗

PubMed1998

Cell cycle-related changes in repopulating capacity of human mobilized peripheral blood CD34(+) cells in non-obese diabetic/severe combined immune-deficient mice.

Most primitive hematopoietic progenitor cells reside in vivo within the G0/G1 phase of the cell cycle. By simultaneous DNA/RNA staining it is possible to distinguish G0 and G1 states and to isolate cells in defined phases of the cell cycle. We report here the use of cell cycle fractionation to separate human mobilized peripheral blood (MPB) CD34(+) cells capable of repopulating the bone marrow (BM) of non-obese diabetic/severe combined immune-deficient (NOD/SCID) mice. In freshly isolated MPB, repopulating cells were predominant within the G0 phase, because transplantation of CD34(+) cells residing in G0 (G0CD34(+)) resulted on average in a 16.6- +/- 3.2-fold higher BM chimerism than infusion of equal numbers of CD34(+) cells isolated in G1. We then investigated the effect of ex vivo cell cycle progression, in the absence of cell division, on engraftment capacity. Freshly isolated G0CD34(+) cells were activated by interleukin-3 (IL-3), stem cell factor (SCF), and flt3-ligand (FL) for a 36-hour incubation period during which a fraction of cells progressed from G0 into G1 but did not complete a cell cycle. The repopulating capacity of stimulated cells was markedly diminished compared with that of unmanipulated G0CD34(+) cells. Cells that remained in G0 during the 36-hour incubation period and those that traversed into G1 were sorted and assayed separately in NOD/SCID recipients. The repopulating ability of cells remaining in G0 was insignificantly reduced compared with that of unstimulated G0CD34(+) cells. On the contrary, CD34(+) cells traversing from G0 into G1 were largely depleted of repopulating capacity. Similar results were obtained when G0CD34(+) cells were activated by the combination of thrombopoietin-SCF-FL. These studies provide direct evidence of the quiescent nature of cells capable of repopulating the BM of NOD/SCID mice. Furthermore, these data also demonstrate that G0-G1 progression in vitro is associated with a decrease in engraftment capacity.

Animals↗

PubMed1998

Nf1 regulates hematopoietic progenitor cell growth and ras signaling in response to multiple cytokines.

Neurofibromin, the protein encoded by the NF1 tumor-suppressor gene, negatively regulates the output of p21(ras) (Ras) proteins by accelerating the hydrolysis of active Ras-guanosine triphosphate to inactive Ras-guanosine diphosphate. Children with neurofibromatosis type 1 (NF1) are predisposed to juvenile chronic myelogenous leukemia (JCML) and other malignant myeloid disorders, and heterozygous Nf1 knockout mice spontaneously develop a myeloid disorder that resembles JCML. Both human and murine leukemias show loss of the normal allele. JCML cells and Nf1-/- hematopoietic cells isolated from fetal livers selectively form abnormally high numbers of colonies derived from granulocyte-macrophage progenitors in cultures supplemented with low concentrations of granulocyte-macrophage colony stimulating factor (GM-CSF). Taken together, these data suggest that neurofibromin is required to downregulate Ras activation in myeloid cells exposed to GM-CSF. We have investigated the growth and proliferation of purified populations of hematopoietic progenitor cells isolated from Nf1 knockout mice in response to the cytokines interleukin (IL)-3 and stem cell factor (SCF), as well as to GM-CSF. We found abnormal proliferation of both immature and lineage-restricted progenitor populations, and we observed increased synergy between SCF and either IL-3 or GM-CSF in Nf1-/- progenitors. Nf1-/- fetal livers also showed an absolute increase in the numbers of immature progenitors. We further demonstrate constitutive activation of the Ras-Raf-MAP (mitogen-activated protein) kinase signaling pathway in primary c-kit+ Nf1-/- progenitors and hyperactivation of MAP kinase after growth factor stimulation. The results of these experiments in primary hematopoietic cells implicate Nf1 as playing a central role in regulating the proliferation and survival of primitive and lineage-restricted myeloid progenitors in response to multiple cytokines by modulating Ras output.

Animals↗

PubMed1998

Multiple inhibitory cytokines induce deregulated progenitor growth and apoptosis in hematopoietic cells from Fac-/- mice.

We used a murine model containing a disruption of the murine homologue (Fac) of Fanconi Anemia group C (FAC) to evaluate the role of Fac in the pathogenesis of bone marrow (BM) failure. Methylcellulose cultures of BM cells from Fac-/- and Fac+/+ mice were established to examine the growth of multipotent and lineage-restricted progenitors containing inhibitory cytokines, including interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha), and macrophage inflammatory protein-1alpha (MIP-1alpha). Clonogenic growth of Fac-/- progenitors was reduced by 50% at 50- to 100-fold lower concentrations of all inhibitory cytokines evaluated. We hypothesized that the aberrant responsiveness to inhibitory cytokines in clonogenic cells may be a result of deregulated apoptosis. To test this hypothesis, we performed the TUNEL assay on purified populations of primary BM cells enriched for hematopoietic progenitors or differentiated myeloid cells. After stimulation with TNF-alpha, accentuated apoptosis was observed in both populations of Fac-/- cells. In addition, deregulated apoptosis was also noted in the most immature phenotypic population of hematopoietic cells after stimulation with MIP-1alpha. Together these data suggest a role of Fac in affecting the signaling of multiple cytokine pathways and support cytokine-mediated apoptosis as a major mechanism responsible for BM failure observed in FA patients.

Animals↗

PubMed1998

Osteoprogenitor cells as targets for ex vivo gene transfer.

We transduced osteoprogenitor cells with recombinant retrovirus and analyzed proviral integration patterns into chromosomal DNA to detect for the first time the clonal and cellular fate of osteoprogenitor-derived progeny cells. Metaphyseal bone cells and diaphyseal stromal cells were isolated from the distal femurs of young rats, transduced with the vM5neolacZ recombinant retrovirus, and selected in the neomycin analog, G418. Following surgical marrow ablation of a femur in one leg of mature rats, retroviral-transduced metaphyseal or diaphyseal cells were injected into the ablated site. These rats were killed 5-6 days later. Metaphyseal and diaphyseal cells were isolated from distal femurs, selected in G418, and stained for beta-galactosidase (beta-gal+). The number and clonal origin of transduced progenitor cells were determined. High numbers of beta-galactosidase colonies with an osteoblast phenotype were obtained following metaphyseal transplants and detected in 100% of metaphyseal and none of diaphyseal specimens. In contrast, beta-galactosidase colonies derived from diaphyseal transplants were detected in 50% of specimens in both the metaphysis and diaphysis, and the absolute number of progenitor cell colonies was 60-fold less than metaphyseal transplants. Provirus was only detected in the ablated bones and not in the contralateral bone or other tissues. Proviral integration fragment analysis showed a single integration site for recovered metaphyseal cell clones, consistent with their origination from a common single progenitor. This is one of the first demonstrations of successful transplantation of clonal osteoprogenitors to their site of origin in bone. It may be possible to use these cells to target genes to bone for therapeutic use in skeletal and hematopoietic diseases.

Animals↗

PubMed1997

LacZ and interleukin-3 expression in vivo after retroviral transduction of marrow-derived human osteogenic mesenchymal progenitors.

Human marrow-derived mesenchymal progenitor cells (hMPCs), which have the capacity for osteogenic and marrow stromal differentiation, were transduced with the myeloproliferative sarcoma virus (MPSV)-based retrovirus, vM5LacZ, that contains the LacZ and neo genes. Stable transduction and gene expression occurred in 18% of cells. After culture expansion and selection in G418, approximately 70% of neo(r) hMPCs co-expressed LacZ. G418-selected hMPC retain their osteogenic potential and form bone in vivo when seeded into porous calcium phosphate ceramic cubes implanted subcutaneously into SCID mice. LacZ expression was evident within osteoblasts and osteocytes in bone developing within the ceramics 6 and 9 weeks after implantation. Likewise, hMPCs transduced with human interleukin-3 (hIL-3) cDNA, adhered to ceramic cubes and implanted into SCID mice, formed bone and secreted detectable levels of hIL-3 into the systemic circulation for at least 12 weeks. These data indicate that genetically transduced, culture-expanded bone marrow-derived hMPCs retain a precursor phenotype and maintain similar levels of transgene expression during osteogenic lineage commitment and differentiation in vivo. Because MPCs have been shown to differentiate into bone, cartilage, and tendon, these cells may be a useful target for gene therapy.

Adult↗

PubMed1997

Variation in long-term engraftment of a large consecutive series of lambs transplanted in utero with human hematopoietic cells.

We investigated the survival and chimeric engraftment characteristics of a large consecutive series of lambs that were transplanted with human hematopoietic cells in utero. Approximately 50% of the fetal sheep survived. Neither the transplantation of human cells into fetal sheep, nor the parity of the ewe was associated with increased mortality, as compared with the risk of surgery alone. However, a breed-associated mortality was noted. Sixty percent of surviving recipient lambs contained donor, human hematopoietic cells in blood and bone marrow (BM) cells. Chimerism ranged from 0.0001-1%. Human hematopoietic progenitors were identified in the BM in 8 of 12 chimeric sheep examined. Some lambs engrafted with human cells maintained a human chimerism for up to at least 2 years. Our data demonstrate that a large proportion of fetal sheep are capable of engrafting human cells, albeit at widely variable levels of engraftment.

Abortion, Veterinary↗

PubMed1996

Loss of NF1 results in activation of the Ras signaling pathway and leads to aberrant growth in haematopoietic cells.

Individuals with neurofibromatosis type 1 (NF1) are predisposed to certain cancers including juvenile chronic myelogenous leukaemia (JCML). The NF1 tumour-suppressor gene encodes a protein (neurofibromin) that accelerates GTP hydrolysis on Ras proteins. Here we show that primary leukaemic cells from children with NF1 show a selective decrease in NF1-like GTPase activating protein (GAP) activity for Ras but retain normal cellular GAP activity. Leukaemic cells also show an elevated percentage of Ras in the GTP-bound conformation. JCML cells are hypersensitive to granulocyte-macrophage colony stimulating factor (GM-CSF), and we observed a similar pattern of aberrant growth in haematopoietic cells from Nf1-/- mouse embryos. These data define a specific role for neurofibromin in negatively regulating GM-CSF signaling through Ras in haematopoietic cells and they suggest that hypersensitivity to GM-CSF may be a primary event in the development of JCML.

Animals↗