Suckling defect in mice lacking the soluble haemopoietin receptor NR6

Cytokines control a variety of cellular responses including proliferation, differentiation, survival and functional activation, via binding to specific receptors expressed on the surface of target cells [1]. The cytokine receptors of the haemopoietin family are defined by the presence of a conserved 200 amino acid extracellular domain known as the haemopoietin domain [2]. We report here the isolation of NR6, a haemopoietin receptor that, like the p40 subunit of interleukin-12 (IL-12) [3] and the EBI3 gene induced by Epstein-Barr virus infection in lymphocytes [4], contains a typical haemopoietin domain but lacks transmembrane and cytoplasmic domains. Although in situ hybridisation revealed NR6 expression at multiple sites in the developing embryo, mice lacking NR6 did not display obvious abnormalities and were born in the expected numbers. Neonatal NR6(-/-) mice failed to suckle, however, and died within 24 hours of birth, suggesting that NR6 is necessary for the recognition or processing of pheromonal signals or for the mechanics of suckling itself. In addition, NR6(-/-) mice had reduced numbers of haemopoietic progenitor cells, suggesting a potential role in the regulation of primitive haemopoiesis.

Functional analysis of mature hematopoietic cells from mice lacking the betac chain of the granulocyte-macrophage colony-stimulating factor receptor

Mice with a null mutation of the betac chain of the granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), and IL-5 receptors (betac-null mice) develop an alveolar proteinosis-like lung disease. The pathogenesis of this disease is uncertain and, although a defect in alveolar macrophage function has been postulated, no previous analysis of mature hematopoietic cells in mice with alveolar proteinosis has been reported. Therefore, we undertook a functional analysis of the mature hematopoietic cell compartment in betac-null mice. In addition, we reexamined the roles of the GM-CSF receptor chain and the betac chain in signaling by GM-CSF. Neutrophils and macrophages from betac-null mice were capable of normal survival and phagocytosis in the absence of stimulus and of similar levels of nitric oxide production in response to interferon-gamma and lipopolysaccharide. GM-CSF-mediated augmentation of survival, phagocytosis, and hydrogen-ion production were absent in neutrophils from betac-null mice. Interestingly, we were unable to show any ability of the GM-CSF receptor -chain alone to mediate glucose transport in these cells. In keeping with the betac-null mice lung pathology, examination of lavage fluid from the lungs of betac-null mice showed increased cellularity. This was caused by an increase in the number of lymphocytes, neutrophils, and macrophages. Large foamy cells in the lavage fluid from betac-null mice were identified as macrophages using immunohistochemistry. Functional analysis showed that these betac-null alveolar macrophages were capable of phagocytosis but uptake of colloidal carbon and cellular adhesion were reduced. In summary, mature hematopoietic cells with a null mutation of the betac receptor were unable to perform GM-CSF-mediated hematopoietic cell functions including glucose transport, but responded normally to a range of other ligands.

Characterization of hematopoietic progenitor cells that express the transcription factor SCL, using a lacZ "knock-in" strategy

Gene targeting experiments have demonstrated that the transcription factor SCL is essential for primitive and definitive hematopoiesis in the mouse. To study the functional properties of hematopoietic cells expressing SCL, we have generated mutant mice (SCLlacZ/w) in which the Escherichia coli lacZ reporter gene has been "knocked in" to the SCL locus, thereby linking beta-galactosidase expression to transcription from the SCL promoter. Bone marrow cells from heterozygous SCLlacZ/w mice were sorted into fractions expressing high, intermediate and low levels of beta-galactosidase (designated lacZhigh, lacZint, and lacZneg). Cells that were lacZhigh or lacZint were enriched for day 12 spleen colony-forming units and myeloid and erythroid colony-forming cells (CFCs). These fractions included >99% of the erythroid and >90% of the myeloid CFCs. Culture of sorted bone marrow populations on stromal cells secreting interleukin-7 or in fetal thymic organ cultures showed that B and T lymphoid progenitors were also present in the lacZhigh and lacZint fractions. These data provide a functional correlation between SCL expression and colony-forming ability in immature hematopoietic cells. Our data also suggested that expression of SCL was transient and confined to hematopoietic stem and/or progenitor cells, because the differentiated progeny of most lineages (except the erythroid) were beta-galactosidase-negative.

epicardin: A novel basic helix-loop-helix transcription factor gene expressed in epicardium, branchial arch myoblasts, and mesenchyme of developing lung, gut, kidney, and gonads

We report the cloning, chromosomal localization, and analysis of the expression pattern of epicardin, a member of the basic helix-loop-helix (bHLH) family of transcription factors. Within its bHLH domain, the human and murine epicardin genes were most similar to paraxis, a bHLH gene important for segmentation of embryonic paraxial mesoderm. In situ hybridization studies revealed strong epicardin expression in murine embryos at 9.5 days postcoitum (dpc) in a region of the septum transversum at the base of the heart known as the proepicardial organ. This mesenchymal structure extends villous projections from which epicardial precursor cells emerge and migrate out over the surface of the myocardium. Strong expression was seen in individual migratory cells and clusters at 9.5 dpc and in a continuous epicardial cell layer in more mature hearts. Also from 9.5 dpc, epicardin transcripts were seen in endocardial cushions of the atrioventricular canal and outflow tract, in skeletal myoblasts within branchial arches and in condensing mesenchyme of gut, kidney, urinary tract, gonads, spleen, and lung. Northern analysis showed that expression persisted in mature visceral organs and heart, but was transient in skeletal muscle. The central role played by bHLH factors in pathways for tissue determination in the embryo suggests a function for epicardin in specification of select mesodermal cell populations associated with heart, cranial skeletal muscle, gut, and urogenital system.

The hemangioblast--an elusive cell captured in culture

The close temporal and spatial association between blood and endothelial cell development during embryogenesis was first documented almost 100 years ago. In recent years, gene expression studies have further strengthened this link. Now, using cultures of mouse embryonic stem cells, a common progenitor cell that gives rise to both blood cells and vascular endothelial cells, has been identified. The existence of the hemangioblast has been proved and experiments addressing its unique properties can begin.

musculin: a murine basic helix-loop-helix transcription factor gene expressed in embryonic skeletal muscle

We describe the embryonic expression of musculin, a new murine member of the bHLH family of transcription factors. Musculin protein is closely related to human ABF-1, which is expressed in activated B cells, and to epicardin/capsulin/Pod-1, which is expressed in branchial myoblasts, visceral and urogenital mesoderm and epicardium. In situ hybridisation revealed musculin expression in embryos was largely restricted to the embryonic skeletal muscle lineage. While all skeletal muscles expressed the gene, only a subset of myocytes within each muscle were positive, indicating molecular heterogeneity within fetal muscle.

Cytokine production and function in c-mpl-deficient mice: no physiologic role for interleukin-3 in residual megakaryocyte and platelet production

Mice lacking thrombopoietin (TPO), or its receptor c-Mpl, display defective megakaryocyte and platelet development and deficiencies in progenitor cells of multiple hematopoietic lineages. The contribution of alternative cytokines to thrombopoiesis in the absence of TPO signalling was examined in mpl-/- mice. Analysis of serum and organ-conditioned media showed no evidence of a compensatory overproduction of megakaryocytopoietic cytokines. However, consistent with a potential role in vivo, when injected into mpl-/- mice, interleukin-6 (IL-6) and leukemia inhibitory factor (LIF) retained the capacity to elevate megakaryocytes and their progenitors in hematopoietic tissues and increase circulating platelet numbers. However, double mutant mice bred to carry genetic defects both in c-Mpl and IL-3 or the alpha chain of the IL-3 receptor, displayed no greater deficiencies in megakaryocytes or platelets than mpl-deficient animals, suggesting absence of a physiologic role for IL-3 in the residual megakaryocytopoiesis and platelet production in these mice.

Infertility in female mice lacking the receptor for interleukin 11 is due to a defective uterine response to implantation

During early pregnancy, in response to the implanting embryo, the surrounding uterine stroma undergoes a dramatic transformation into a specialized tissue known as the decidua. The decidua encapsulates the developing embryo, facilitating nutrient transfer and limiting trophoblast invasion. Here we show that female mice with a null mutation of the interleukin-11 receptor alpha chain are infertile because of defective decidualization. A temporal analysis revealed IL-11 expression is maximal in the normal pregnant uterus at the time of decidualization, and in situ hybridization studies showed expression of the IL-11 and the IL-11 receptor alpha chain in the developing decidual cells. These observations reveal a previously unrecognized critical role for IL-11 signaling in female reproduction.

The biological consequences of excess GM-CSF levels in transgenic mice also lacking high-affinity receptors for GM-CSF

GM-CSF transgenic mice were crossed with mice with homozygous inactivation of the gene encoding the common beta chain (beta c) of the GM-CSF receptor to produce mice with constitutively elevated GM-CSF levels but no high-affinity GM-CSF receptors. GM-CSF transgenic beta c -/- mice had exceptionally elevated serum GM-CSF levels but failed to develop the abnormal peritoneal cell population, eye destruction or tissue lesions characteristic of GM-CSF transgenic beta c +/+ mice. The alveolar proteinosis of beta c -/- mice was not altered in GM-CSF transgenic beta c -/- mice. Levels of GM-CSF mRNA in transgenic GM-CSF beta c -/- were elevated but lower than in transgenic beta +/+ mice and the higher serum GM-CSF levels were traced in part to the longer serum half-life of GM-CSF in beta c -/- than in beta c +/+ mice although urinary loss of GM-CSF was higher in beta c -/- than in +/+ mice. The data indicate that the transgenic phenotype was due to stimulation by GM-CSF and not an insertional effect, that low-affinity receptors are not capable of initiating tissue pathology even in the presence of excess GM-CSF levels and that autocrine production of GM-CSF by GM-CSF-responsive cells also fails to induce changes in these cells. The results support current dogma that the action of polypeptide regulators is mediated exclusively by activation of high-affinity membrane receptors.

The CD2-scl transgene alters the phenotype and frequency of T-lymphomas in N-ras transgenic or p53 deficient mice

Abnormal expression of SCL (TAL-1/TCL5) occurs in the majority of paediatric cases of acute T-cell lymphoblastic leukemia (T-ALL). Unexpectedly however, transgenic mice carrying scl coupled to the human T-cell specific CD2 enhancer (CD2-scl) did not spontaneously develop T-cell lymphomas despite high levels of scl expression in their thymocytes. Analogous to other transgenic models of lymphomagenesis, it is likely that additional genetic abnormalities are required to cooperate with scl to trigger lymphomagenesis. Two possible candidates are the p53 and N-ras genes which are mutated in some cases of T-ALL, particularly in relapsed disease. Therefore, we examined lymphomagenesis in the progeny of CD2-scl mice crossed with N-ras transgenic mice or p53 deficient. Surprisingly, the frequency of lymphomas in the p53 nullizygous or N-ras transgenic mice was not enhanced by expression of the scl transgene. In fact, expression of scl in both genetic backgrounds paradoxically reduced the frequency of thymic lymphomas and, at least in the p53 nullizygous mice, shifted the pattern of organ involvement to the peripheral lymphoid organs. In contrast, CD2-scl transgene expression accelerated lymphomagenesis in p53 heterozygous mice. These data suggest that the collaborative effects of scl with N-ras or p53 vary according to the developmental stage of the T-cell.

Differentiation commitment in normal hemopoiesis and leukemic transformation

Differentiation commitment events are essential for the initiation of hemopoiesis and, in one form or another, occur continuously during adult hemopoiesis. The most studied type of differentiation commitment decision a hemopoietic cell can make involves the alternative choice of self-renewal versus the formation of progeny destined for maturation. Aberration in this commitment choice is a key abnormality necessary for the formation of a leukemic population.

Adult mice with targeted mutation of the interleukin-11 receptor (IL11Ra) display normal hematopoiesis

Interleukin-11 (IL-11) is a pleiotropic growth factor with a prominent effect on megakaryopoiesis and thrombopoiesis. The receptor for IL-11 is a heterodimer of the signal transduction unit gp130 and a specific receptor component, the alpha-chain (IL-11R alpha). Two genes potentially encode the IL-11R alpha: the IL11Ra and IL11Ra2 genes. The IL11Ra gene is widely expressed in hematopoietic and other organs, whereas the IL11Ra2 gene is restricted to only some strains of mice and its expression is confined to testis, lymph node, and thymus. To investigate the essential actions mediated by the IL-11R alpha, we have generated mice with a null mutation of IL11Ra (IL11Ra-/-) by gene targeting. Analysis of IL11Ra expression by Northern blot and reverse transcriptase-polymerase chain reaction, as well as the absence of response of IL11Ra-/- bone marrow cells to IL-11 in hematopoietic assays, further confirmed the null mutation. Compensatory expression of the IL11Ra2 in bone marrow cells was not detected. IL11Ra-/- mice were healthy with normal numbers of peripheral blood white blood cells, hematocrit, and platelets. Bone marrow and spleen contained normal numbers of cells of all hematopoietic lineages, including megakaryocytes. Clonal cultures did not identify any perturbation of granulocyte-macrophage (GM), erythroid, or megakaryocyte progenitors. The number of day-12 colony-forming unit-spleen progenitors were similar in wild-type and IL11Ra-/- mice. The kinetics of recovery of peripheral blood white blood cells, platelets, and bone marrow GM progenitors after treatment with 5-flurouracil were the same in IL11Ra-/- and wild-type mice. Acute hemolytic stress was induced by phenylhydrazine and resulted in a 50% decrease in hematocrit. The recovery of hematocrit was comparable in IL11Ra-/ - and wild-type mice. These observations indicate that IL-11 receptor signalling is dispensable for adult hematopoiesis.

Factors involved in leukaemogenesis and haemopoiesis

This review describes the chromosomal abnormalities in T-cell acute lymphoblastic leukaemia (ALL) which result in the over-expression of the gene SCL, which encodes a helix-loop-helix transcription factor. Also described are how gene targeting studies have revealed a key role for SCL in normal haemopoiesis. Next, the BCR-ABL fusion protein, seen in chronic myeloid leukaemia (CML) and in some patients with ALL, is discussed. Finally, the involvement of members of the core-binding factor (CBF) gene family in leukaemogenesis are described. Members of this gene family are involved in the generation of fusion proteins as a result of t(8;21) and inv(16), the most common translocations associated with acute myeloid leukaemia (AML). They provide a useful model of the way in which aberrant transcriptional function, brought about through genetic alterations, can modify haemopoietic development.

Hematopoietic-specific genes are not induced during in vitro differentiation of scl-null embryonic stem cells

The helix-loop-helix transcription factor, scl, plays an essential role in hematopoietic development. Embryos in which the gene has been disrupted fail to develop yolk sac erythropoiesis, and scl-null embryonic stem cells do not contribute to hematopoiesis in chimeric mice. To analyze the molecular consequences of scl deficiency, we compared the gene expression profiles of control (wild-type and scl-heterozygous) and scl-null embryonic stem cells differentiated in vitro for up to 12 days. In control and scl-null embryoid bodies the temporal expression pattern of genes associated with the formation of ventral mesoderm, such as Brachyury, bone morphogenetic protein-4, and flk-1, was identical. Similarly, GATA-2, CD34, and c-kit, which are coexpressed in endothelial and hematopoietic lineages, were expressed normally in scl-null embryonic stem cell lines. However, hematopoietic-restricted genes, including the transcription factors GATA-1, EKLF, and PU.1 as well as globin genes and myeloperoxidase, were only expressed in wild-type and scl-heterozygous embryonic stem cells. Indirect immunofluorescence was used to confirm the observations that GATA-1 and globins were only present in control embryoid bodies but that CD34 was found on both control and scl-null embryoid bodies. These data extend the previous gene ablation studies and support a model whereby scl is absolutely required for commitment of a putative hemangioblast to the hematopoietic lineage but that it is dispensable for endothelial differentiation.

A C2055T transition in exon 8 of the ATP7A gene is associated with exon skipping in an occipital horn syndrome family

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The SCL/TAL1 gene: roles in normal and malignant haematopoiesis

SCL (TAL1/TCL5) is a member of the helix-loop-helix family of transcription factors. Originally identified because of its involvement in a tumour-specific chromosomal translocation, overexpression of the SCL gene is the most common molecular abnormality found in human T cell leukaemia. Transgenic models have now formally demonstrated that overexpression of SCL within the T cell lineage is capable of causing malignant transformation. Gene targeting experiments have revealed that the SCL gene is crucial for the development of primitive haematopoiesis in the mouse and is also required for the generation of all adult haematopoietic lineages. Biochemical studies have indicated some of the proteins which interact with SCL and this has refined the hypotheses concerning the mechanisms by which SCL plays a role in leukaemogenesis and haematopoietic development.

The gene for the human interleukin-11 receptor alpha chain locus is highly homologous to the murine gene and contains alternatively spliced first exons

The gene for the murine interleukin-11 receptor alpha chain (mIL-11R alpha) contains two loci (1 and 2), of which locus 2 is restricted to only some mouse strains. Two alternatively spliced exons (1a and 1b) encode the 5' untranslated region (5'UTR) of the murine locus 1. We have characterized the gene for the human interleukin-11 receptor alpha chain locus (hIL-11R alpha), examined its expression by Northern analysis and determined its chromosomal location by fluorescence in situ hybridization. The presence of exon(s) encoding the 5'UTR and mapping of transcription initiation sites was determined by reverse-transcriptase polymerase chain reaction and 5' rapid amplification of cDNA ends (5'RACE) techniques. The human locus spanned 10 kilobasepairs (kb) and consisted of 14 exons. Two alternatively spliced first exons (1a and 1b) encoding the 5'UTR were identified and shared 76 and 73% nucleotide identity with murine exons 1a and 1b. Multiple transcription start sites were demonstrated for human exon 1a. The promoter regions of both human exons 1a and 1b did not display a canonical TATA box. A predominant 1.8 kb transcript for the hIL-11R alpha was present in heart, brain, skeletal muscle, lymph nodes, thymus, appendix, pancreas and foetal liver. The hIL-11R alpha gene was localized to chromosome 9p13. In summary, the hIL-11R alpha gene was highly related to locus 1 of the murine gene and there was no evidence of a second hIL-11R alpha locus.

Genetic influences determining progenitor cell mobilization and leukocytosis induced by granulocyte colony-stimulating factor

The mechanisms involved in the mobilization of progenitor cells into the blood by granulocyte colony-stimulating factor (G-CSF) and other cytokines are poorly understood. To identify important influences on this complex process, in vivo murine models were used. Granulocyte-macrophage colony-stimulating factor (GM-CSF) transgenic, Max41 transgenic, W/Wv, Mpl-null, GM-CSF receptor (beta chain)-null mice, wild-type littermate controls, and six inbred strains of mice were injected with 200 microg/kg/d G-CSF for 5 days. Three parameters of response were monitored: white blood cell count (WCC), peripheral blood progenitor cell (PBPC) numbers, and spleen weight. In all genotypes studied, G-CSF induced increases in these three parameters. However, PBPC mobilization in W/Wv and Mpl-null mice was only 30% and 9%, respectively, of that observed in wild-type mice. In contrast, perturbations of GM-CSF signalling had no demonstrable effect on in vivo responses to G-CSF. Broad variability was evident between inbred strains for each parameter of the response to G-CSF. A 10-fold range in response was observed for circulating progenitor cell numbers, similar to that observed for normal human subjects receiving G-CSF. The interstrain differences were in the distribution of mature and progenitor cells between peripheral blood, bone marrow, and spleen rather than in the total numbers of these cells in the body. Results of an F2 intercross of low-responding C57BL/6 and intermediate-responding SJL mice indicated that regulation of progenitor cell mobilization is a complex genetic trait, that there is a correlation between this trait and WCC response (r2 = .5), and that this approach may serve as a useful model for the identification of genes involved in the mobilization process.

Identification of a second murine interleukin-11 receptor alpha-chain gene (IL11Ra2) with a restricted pattern of expression

The interleukin-11 receptor alpha-chain, a member of the hematopoietin receptor superfamily, forms, together with gp130, a functional high-affinity receptor complex for interleukin 11. We, and others, reported the cloning of the murine interleukin 11 receptor alpha-chain cDNA (IL11Ra) and recently described the structure of the IL11Ra locus. We also described the presence of a second IL11Ra-like locus in some mouse strains. In this study we report that the second locus, designated IL11Ra2, encodes an mRNA species. The transcript was 99% identical to the IL11Ra transcript in the coding and 3'-untranslated region, but had a different 5'-untranslated region. The complete genomic organization of the IL11Ra2 locus is presented, and the two loci are shown to be located on a 200-kb NaeI genomic fragment. Comparison of the expression pattern of the IL11Ra and IL11Ra2 genes using an RT-PCR restriction fragment length polymorphism strategy revealed that while the expression of IL11Ra was widespread, expression of IL11Ra2 was restricted to testis, lymph node, and thymus.

Nance-Horan syndrome: linkage analysis in 4 families refines localization in Xp22.31-p22.13 region

Nance-Horan syndrome (NHS) is an X-linked disease characterized by severe congenital cataract with microcornea, distinctive dental findings, evocative facial features and mental impairment in some cases. Previous linkage studies have placed the NHS gene in a large region from DXS143 (Xp22.31) to DXS451 (Xp22.13). To refine this localization further, we have performed linkage analysis in four families. As the maximum expected Lod score is reached in each family for several markers in the Xp22.31-p22.13 region and linkage to the rest of the X chromosome can be excluded, our study shows that NHS is a genetically homogeneous condition. An overall maximum two-point Lod score of 9.36 (theta = 0.00) is obtained with two closely linked markers taken together. DXS207 and DXS1053 in Xp22.2. Recombinant haplotypes indicate that the NHS gene lies between DXS85 and DXS1226. Multipoint analysis yield a maximum Lod score of 9.45 with the support interval spanning a 15-cM region that includes DXS16 and DXS1229/365. The deletion map of the Xp22.3-Xp21.3 region suggests that the phenotypic variability of NHS is not related to gross rearrangement of sequences of varying size but rather to allelic mutations in a single gene, presumably located proximal to DXS16 and distal to DXS1226. Comparison with the map position of the mouse Xcat mutation supports the location of the NHS gene between the GRPR and PDHA1 genes in Xp22.2.

Hematopoiesis: origin pinned down at last?

The sequence of events leading to definitive adult hematopoiesis in the mouse has long been debated. The traditional notion that yolk-sac-derived stem cells seed the adult compartment has now been challenged by evidence that intra-embryonic stem cells play a crucial role.

The influence of granulocyte/macrophage colony-stimulating factor on dendritic cell levels in mouse lymphoid organs

To ascertain whether the development of dendritic cells (DC) in mouse lymphoid organs is dependent on granulocyte/macrophage colony-stimulating factor (GM-CSF), we determined the number of DC in the thymus, spleen and lymph nodes of normal mice, of mice with the genes coding for GM-CSF or its receptor inactivated, and of transgenic mice with excessive levels of GM-CSE DC were extracted from the tissues and enriched prior to flow cytometric analysis. The total DC level and the incidence of DC expressing lymphoid-related markers (CD8(hi) CD11b(lo)) and myeloid-related markers (CD8(lo) CD11b(hi)) were monitored. Both in GM-CSF null mice, and GM-CSF receptor null mice, DC of all surface phenotypes were present in all lymphoid organs; only small decreases in DC levels were recorded, except for the lymph nodes of GM-CSF receptor null mice which showed a more pronounced (threefold) decrease in DC numbers. Since the GM-CSF receptor null mice lacked the beta chain common to the GM-CSF, interleukin (IL)-3 and IL-5 receptors, the development of DC in the absence of GM-CSF was not due to common beta chain mediated developmental signals elicited by IL-3 or IL-5. In GM-CSF transgenic mice, there was only a 50 % increase in DC numbers in thymus and spleen, paralleling an increase in overall cellularity, but a more pronounced (threefold) increase in DC numbers in lymph nodes. There was no evidence that GM-CSF had a selective effect on any particular DC subpopulation defined by CD8 or CD11b expression. We conclude that the development of most lymphoid tissue DC can proceed in the absence of GM-CSF, although this cytokine can produce some elevation of DC levels. It is not clear whether the enhancing effect of GM-CSF is direct or an indirect effect mediated by other cytokines.

The structural basis of the biological actions of the GM-CSF receptor

The receptor for granulocyte/macrophage colony-stimulating factor (GM-CSF) consists of a ligand-specific low-affinity binding chain (GM-CSFR alpha) and a second chain that is required for high-affinity binding and signal transduction. This second chain is shared by the ligand-specific alpha-chains for the interleukin 3 (IL-3) and IL-5 receptors and is therefore called beta common (beta c). In mice but not humans the IL-3 receptor can also use a closely related but IL-3-specific beta-chain (beta IL-3). In order to define the contributions of each chain to receptor signalling we generated mice in which either beta c or beta IL-3 expression was deleted. beta IL-3 null mice were phenotypically normal but displayed a decreased responsiveness to IL-3 in vitro. beta c null mice, on the other hand, were unresponsive to GM-CSF or IL-5 but still responded to IL-3. These data demonstrated that GM-CSF and IL-5 receptors can use only one beta-chain for signalling (beta c) while IL-3 can effectively use either beta-chain. The hierarchical basis of receptor transmodulation was shown to result from this differential usage of beta-chains. To define the regions required for different types of cell signalling, we constructed human beta c mutants with successive cytoplasmic truncation. By the use of appropriate biological read-out systems we found that the cytoplasmic region of the receptor has a modular design with distinct domains required for cell proliferation, cell survival, differentiation and growth suppression. Appropriate targeting of these domains and the signalling pathways they initiate may provide highly specific cell therapies in the future.

Role of granulocyte-macrophage colony-stimulating factor and granulocyte colony-stimulating factor in the development of an acute neutrophil inflammatory response in mice

The intraperitoneal injection into mice of casein preparations containing bacteria induced a rapid accumulation of neutrophils within 3 hours due to selective release of mature cells from the bone marrow. Significant increases in the concentrations of granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF) occurred in the peritoneal cavity during the process, but the intraperitoneal injection of neither CSF induced a significant accumulation of neutrophils and the coinjection of G-CSF and casein failed to enhance the neutrophil response. The lack of involvement of either CSF in the neutrophil migration was confirmed by the development of typical neutrophil exudates when casein was injected into mice with inactivation of the genes encoding GM-CSF, G-CSF, or the beta-common chain of the GM-CSF receptor. However, preinjection of G-CSF increased the number of marrow neutrophils available for migration and did result in increased numbers of neutrophils in the peritoneal cavity after casein injection. Typical eosinophil inflammatory responses to the injection of casein or thioglycollate occurred in GM-CSF -/ -mice but not in beta c -/- mice, suggesting that interleukin-5 was necessary for this response.

The scl gene product is required for the generation of all hematopoietic lineages in the adult mouse

Homozygosity for a null mutation in the scl gene causes mid-gestational embryonic lethality in the mouse due to failure of development of primitive hematopoiesis. Whilst this observation established the role of the scl gene product in primitive hematopoiesis, the death of the scl null embryos precluded analysis of the role of scl in later hematopoietic development. To address this question, we created embryonic stem cell lines with a homozygous null mutation of the scl gene (scl-/-) and used these lines to derive chimeric mice. Analysis of the chimeric mice demonstrates that the scl-/- embryonic stem cells make a substantial contribution to all non-hematopoietic tissues but do not contribute to any hematopoietic lineage. These observations reveal a crucial role for the scl gene product in definitive hematopoiesis. In addition, in vitro differentiation assays with scl-/- embryonic stem cells showed that the scl gene product was also required for formation of hematopoietic cells in this system.

Structural analysis of the gene encoding the murine interleukin-11 receptor alpha-chain and a related locus

In this study the gene for the murine interleukin-11 receptor alpha chain (IL-11Ralpha) has been characterized. The gene spans 9 kilobase pairs of DNA, and the organization of its 14 exons conforms to the pattern observed for other members of the hematopoietin receptor family. Analysis of the 5' end of the cDNA using 5' RACE showed that the first two exons, designated exons 1a and 1b, are spliced to form alternate transcripts. Transcripts initiating from exon 1b were not found in adult tissues but were present in embryonic stem cells. S1 nuclease and 5' rapid amplification of cDNA ends assays demonstrated multiple major and minor sites of transcription initiation for each exon. The putative promoter regions of both exons lacked TATA boxes, although potential recognition sites for several transcription factors including Sp1, AP1, and AP2 were present. A comparison of the murine and human IL-11Ralpha revealed that the 5' sequence upstream of the major site of transcription initiation site for exon 1b is highly conserved. Northern analysis showed that IL-11Ralpha is expressed in many adult murine tissues. A second IL-11Ralpha-like locus containing a sequence homologous to exons 2-13 was also identified.

The helix-loop-helix gene SCL: implicated in T-cell acute lymphoblastic leukaemia and in normal haematopoietic development

The SCL gene encodes a member of the helix-loop-helix family of transcription factors and was first identified through its involvement in a chromosomal translocation in a human leukaemic cell line. SCL is now recognized to be aberrantly expressed in most human T-cell leukaemias. In around 25% of cases SCL overexpression is associated with identifiable chromosomal abnormalities but in other cases the mechanism of ectopic expression has not yet been identified. SCL is normally expressed in haematopoietic progenitor cells, erythroid cells, mast cells and megakaryocytes. Gene delivery experiments using haematopoietic cell lines and the recent creation of mice with a null mutation of the SCL gene have demonstrated that SCL plays a crucial role in haematopoietic commitment and differentiation.

Functional inactivation in mice of the gene for the interleukin-3 (IL-3)-specific receptor beta-chain: implications for IL-3 function and the mechanism of receptor transmodulation in hematopoietic cells

The receptors for granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-3 and -5 (IL-3, IL-5) share a common signaling subunit (beta c). However, in the mouse, IL-3 can also use an alternative IL-3-specific receptor beta-chain (beta IL-3). To assess the relative contributions of beta c and beta IL-3 to IL-3 receptor formation and function, mice were generated in which the beta IL-3 gene was functionally inactivated by replacement of exons 9-13 with a neomycin resistance cassette. Bone marrow cells from these mice displayed a lower affinity IL-3 receptor than normal and were hyporesponsive to IL-3, but the mice displayed no obvious hematopoietic abnormalities. The data suggested that beta c and beta IL-3 are normally coexpressed on IL-3-responsive cells and have identical qualitative signaling capacities. Receptor transmodulation studies on bone marrow cells from wild-type, beta c -/-, and beta IL-3 -/- mice showed that the previously described hierarchical pattern of transmodulation was dependent on the relative numbers of both beta IL-3 and beta c receptor chains and also provided evidence for an unexpected interaction between beta c chains and G-CSF and M-CSF receptors.

Hematopoietic and lung abnormalities in mice with a null mutation of the common beta subunit of the receptors for granulocyte-macrophage colony-stimulating factor and interleukins 3 and 5

Gene targeting was used to create mice with a null mutation of the gene encoding the common beta subunit (beta C) of the granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin 3 (IL-3; multi-CSF), and interleukin 5 (IL-5) receptor complexes (beta C-/- mice). High-affinity binding of GM-CSF was abolished in beta C-/- bone marrow cells, while cells from heterozygous animals (beta C+/- mice) showed an intermediate number of high-affinity receptors. Binding of IL-3 was unaffected, confirming that the IL-3-specific beta chain remained intact. Eosinophil numbers in peripheral blood and bone marrow of beta C-/- animals were reduced, while other hematological parameters were normal. In clonal cultures of beta C-/- bone marrow cells, even high concentrations of GM-CSF and IL-5 failed to stimulate colony formation, but the cells exhibited normal quantitative responsiveness to stimulation by IL-3 and other growth factors. beta C-/- mice exhibited normal development and survived to young adult life, although they developed pulmonary peribronchovascular lymphoid infiltrates and areas resembling alveolar proteinosis. There was no detectable difference in the systemic clearance and distribution of GM-CSF between beta C-/- and wild-type littermates. The data establish that beta C is normally limiting for high-affinity binding of GM-CSF and demonstrate that systemic clearance of GM-CSF is not mediated via such high-affinity receptor complexes.

Lineage-restricted regulation of the murine SCL/TAL-1 promoter

The SCL/TAL-1 gene encodes a basic helix-loop-helix transcription factor that is expressed in multipotent hematopoietic progenitors before lineage commitment. Its expression is maintained during differentiation along erythroid, mast, and megakaryocytic lineages, but is repressed after commitment to nonexpressing lineages. To begin to address the molecular mechanisms underlying this complex pattern of expression, we have studied the regulation of the murine SCL promoter in erythroid and T-cell lines. Analysis of the methylation and chromatin structure of the SCL promoter region showed that SCL mRNA expression correlated with DNase hypersensitive sites and methylation status of the promoter. Transient reporter assays showed that promoter 1a was active in erythroid cells but not in T cells. Sequences between -187 and +26 were sufficient for lineage-restricted activity of promoter 1a. A joint promoter construct containing both promoter 1a and promoter 1b also exhibited lineage-restricted activity. Conserved GATA (-37), MAZ (+242), and ETS (+264) motifs were all shown to contribute to SCL promoter activity in erythroid cells, but several other motifs were not required for full promoter activity. The pattern of complexes binding to the +242 MAZ and +264 ETS sites were the same in erythroid and T cells. However, GATA-1 bound the -37 GATA site in erythroid cells, whereas in T cells GATA-3 was only able to bind weakly, if at all. Moreover, GATA-1 but not GATA-2 or GATA-3 was able to transactivate SCL promoter 1a in a T-cell environment. These results suggest that inactivity of SCL promoter 1a in T cells reflected the absence of GATA-1 rather than the presence of trans-dominant negative regulators.

Absence of yolk sac hematopoiesis from mice with a targeted disruption of the scl gene

The scl gene encodes a basic-helix-loop-helix transcription factor which was identified through its involvement in chromosomal translocations in T-cell leukemia. To elucidate its physiological role, scl was targeted in embryonic stem cells. Mice heterozygous for the scl null mutation were intercrossed and their offspring were genotyped. Homozygous mutant (scl-/-) pups were not detected in newborn litters, and analysis at earlier time points demonstrated that scl-/- embryos were dying around embryonic day 9.5. The scl-/- embryos were pale, edematous, and markedly growth retarded after embryonic day 8.75. Histological studies showed complete absence of recognizable hematopoiesis in the yolk sac of these embryos. Early organogenesis appeared to be otherwise normal. Culture of yolk sac cells of wild-type, heterozygous, and homozygous littermates confirmed the absence of hematopoietic cells in scl-/- yolk sacs. Reverse transcription PCR was used to examine the transcripts of several genes implicated in early hematopoiesis. Transcripts of GATA-1 and PU.1 transcription factors were absent from RNA from scl-/- yolk sacs and embryos. These results implicate scl as a crucial regulator of early hematopoiesis.

L206W mutation of the cystic fibrosis gene, relatively frequent in French Canadians, is associated with atypical presentations of cystic fibrosis

Cystic fibrosis is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Over 400 mutations have been reported at this locus. Although severe forms of cystic fibrosis are usually associated with pancreatic insufficiency, pulmonary dysfunction, and elevated sweat chloride, there is a wide range of phenotypes, including congenital absence of the vas deferens, observed with some of the milder mutations. The L206W mutation, which was first identified in patients from South France, is relatively frequent in French Canadians from Quebec. In this report, we document the atypical form of cystic fibrosis associated with this mutation, in a cohort of 7 French Canadian probands.

Myogenic and morphogenetic defects in the heart tubes of murine embryos lacking the homeo box gene Nkx2-5

The murine homeo box gene Nkx2-5 is expressed in precardiac mesoderm and in the myocardium of embryonic and fetal hearts. Targeted interruption of Nkx2-5 resulted in abnormal heart morphogenesis, growth retardation and embryonic lethality at approximately 9-10 days postcoitum (p.c.). Heart tube formation occurred normally in mutant embryos, but looping morphogenesis, a critical determinant of heart form, was not initiated at the linear heart tube stage (8.25-8.5 days p.c.). Commitment to the cardiac muscle lineage, expression of most myofilament genes and myofibrillogenesis were not compromised. However, the myosin light-chain 2V gene (MLC2V) was not expressed in mutant hearts nor in mutant ES cell-derived cardiocytes. MLC2V expression normally occurs only in ventricular cells and is the earliest known molecular marker of ventricular differentiation. The regional expression in mutant hearts of two other ventricular markers, myosin heavy-chain beta and cyclin D2, indicated that not all ventricle-specific gene expression is dependent on Nkx2-5. The data demonstrate that Nkx2-5 is essential for normal heart morphogenesis, myogenesis, and function. Furthermore, this gene is a component of a genetic pathway required for myogenic specialization of the ventricles.

scl, a gene frequently activated in human T cell leukaemia, does not induce lymphomas in transgenic mice

The scl gene is implicated in human T cell acute lymphoblastic leukaemia (T-ALL) through its involvement in the t(1;14)(p32;q11) chromosomal translocation and, more frequently, as a result of a tumour-specific interstitial deletion on chromosome 1. The consequence of both these chromosomal alterations is overexpression of scl in the leukaemic cells. Despite the strong inference of a role in human T-ALL, scl has not yet been demonstrated to be causally involved in neoplastic transformation. We attempted to do this by generating transgenic mice in which scl expression was directed to the T cell lineage using the CD2 enhancer and the strong SR alpha viral promoter (CD2-scl mice). Three transgenic lines, all of which expressed the scl transgene at a high level, were bred and analysed. No alterations in T cell development were seen in the mice. Unexpectedly CD2-scl mice did not develop tumours, nor did the transgene enhance tumourigenesis by Moloney murine leukaemia virus. These findings throw into question the mechanism by which aberrant scl expression contributes to T cell leukaemogenesis.

Constitutive expression of the putative transcription factor SCL associated with proviral insertion in the myeloid leukemic cell line WEHI-3BD-

The murine myeloid leukemia WEHI-3B contains an intracisternal A-particle insertion in a growth factor gene (IL-3) and a homeobox gene (Hox 2.4). Southern blot analysis of the differentiation unresponsive subline WEHI-3BD- demonstrated a rearrangement of the SCL gene, a gene that encodes a protein of the helix-loop-helix class of transcription factors. Northern blot analysis demonstrated an abnormal SCL transcript in the WEHI-3BD- cells, although SCL expression was not detected in the parental cells. The rearrangement was cloned and confirmed as an insertion of an intracisternal A-particle in the 3' untranslated region of the SCL gene. Although SCL is implicated in up to 25% of human T-cell acute lymphoblastic leukemia, this is the first example of SCL involvement in a myeloid leukemia.

Structure of the gene encoding the murine SCL protein

We have determined the molecular structure of the gene encoding the murine SCL protein (helix-loop-helix transcription factor). The gene consists of seven exons spanning approx. 20 kb. The intron/exon structure, coding region sequences and sequences present at the splice junctions were highly conserved between mouse and human. The 5' flanking sequence contains CCAAT and TATA consensus motifs with several putative binding sites for SP-1, AP-1 and GATA-1. Multiple mRNA transcripts were generated by alternate exon usage. The transcripts differed primarily in the 5' untranslated region (UTR), but potentially also encode a smaller SCL protein. Despite the high degree of conservation between species, the heptamer/nonamer signal sequences in the 5' region of the human SCL gene (the frequent site of SCL disruption in human leukemia) were poorly represented in the murine sequence. In keeping with this, structural abnormalities of murine SCL were uncommon in murine leukemias that express the SCL transcript.

Acrania: a manifestation of the Adams-Oliver syndrome

A 10-year-old male with acrania, distal limb anomalies, and abnormal arterial and venous cranial blood vessels is reported. Parental films and examination are normal. This case supports the hypothesis that acrania is a severe form of aplasia cutis congenita and is within the spectrum of Adams-Oliver syndrome. It is proposed that the diagnosis of acrania requires assessment of both parents and proband to assess other manifestations of vascular disruption in order to provide accurate genetic counselling.

Brain stem encephalitis due to herpes simplex virus

A 6 year old child is described with infection due to herpes simplex virus type 1 causing brain stem encephalitis. The diagnosis was established by enzyme immunosorbent assays of the cerebrospinal fluid and serum which demonstrated antibody responses to herpes simplex virus. Recovery occurred and the importance of early use of acyclovir in achieving a good outcome is emphasized.

Extraction of human organ-specific cancer neoantigens from cancer cells and plasma membranes with 1-butanol

Immunoprotective tumor antigens of experimental tumors are selectively extracted by 1-butanol. Human organ-specific cancer neoantigens (OSNs) are tumor substances in cancer extracts to which patients with cancer of the same organ respond in the in vitro assay of leukocyte adherence inhibition. Here we determined whether OSNs as measured by leukocyte adherence inhibition assay are also selectively solubilized by 2.5% (v/v) 1-butanol. Butanol extracts of live tissue-cultured human cancer cells as well as extracts of primary breast cancer contained OSNs as determined by leukocyte reactivity in leukocyte adherence inhibition. With two-phase butanol, OSN activity was recovered in the aqueous and not in the organic phase, indicating that OSN is not a lipoprotein. The butanol-soluble OSN, whether allogeneic or autologous, was recognized by the T4 subset of T-cells in association with Class II major histocompatibility complex antigens of monocytes. Autologous OSN was extracted from membrane preparations of autologous primary cancer. Butanol extracts contained the previously identified Mr 40,000 protein OSN. Butanol removed about 50% of the Mr 40,000 protein OSN from live cancer cell membranes. Probably because of residual OSN in the membrane fragments and the ability of OSN to reassociate with the membrane, the T8 subset of pure T-cells responded positively to autologous cancer extracts. Passage of the autologous extract through an anti-Class I major histocompatibility complex antigen affinity column but not through a control affinity column negated the activity of the extract with pure autologous T-cells. The results indicate that human OSNs share with immunoprotective tumor antigens of experimental tumors the unique physicochemical property of being selectively extracted by 2.5% butanol.

Effects of low ambient pH on perivitelline fluid of Ambystoma maculatum (Shaw) eggs

Egg clumps of Ambystoma maculatum were collected from a pond on the south side of the Gaspereau Valley, Kings County, Nova Scotia, to determine the effects of low ambient pH levels on the perivitelline fluid pH. Egg masses were placed in aquaria filled with pond water adjusted to pH 4.0, 5.0, 6.0 and 7.0. Perivitelline fluid was withdrawn from the eggs at 1, 3, 5, 7, 24, 48, 96 and 120 h after initial immersion, and its pH measured. Initial perivitelline fluid values decreased significantly 7 to 96 h after initial immersion in treatments altered to pH 4.0 and 5.0. Rate of H(+) influx into the perivitelline fluid is much greater in eggs immersed in water at pH 4 than in water at pH 5 or 6. Median Tolerance Limit tests indicated a critical pH value between 3.5 and 4.0 for newly hatched larvae.

Blood transfusion and tumour growth: an experimental study

An animal model using RIII mice, which have a high incidence of spontaneously occurring mammary tumours, was used to study the effects of blood transfusion on tumour growth. Virgin female mice were transfused with various dilutions of blood from C57b1 mice either before or both before and after inoculation of tumour cells from a tumour line. Allogeneic transfusion prior to inoculation did not affect survival compared with syngeneic transfusion. Both allogeneic and syngeneic blood given before and after tumour inoculation led to a prolonged survival compared with saline infusion. Survival was longest following syngeneic blood. The effect was attributed to the general beneficial effects of blood transfusion and not the result of immunological changes.

Haemoglobin LeporeBaltimore in a Spanish family

Description of the clinical, haematological and biochemical aspects of a new family with heterozygous haemoglobin LeporeBaltimore. Of the 6 members affected. 4 were totally asymptomatic. All of them showed morphologic features of heterozygous beta-thalassaemia. The levels of haemoglobin Lepore ranged from 12.2 to 15% (mean value: 13.7 +/- 1.1%). The analysis of the primary structure of the haemoglobin shows that crossing over takes place between amino acid 50 of the delta-chain and amino acid 86 of the beta-chain. This is the third family, to our knowledge, with haemoglobin LeporeBaltimore so far described.