Showing papers by "Walter and Eliza Hall Institute of Medical Research published in 1988"
TL;DR: Plasmid expression vectors have been constructed that direct the synthesis of foreign polypeptides in Escherichia coli as fusions with the C terminus of Sj26, a 26-kDa glutathione S-transferase (GST; EC 2.5.1.18) encoded by the parasitic helminth Schistosoma japonicum.
6,003 citations
TL;DR: Results argue that bcl-2 provided a distinct survival signal to the cell and may contribute to neoplasia by allowing a clone to persist until other oncogenes, such as c-myc, become activated.
Abstract: A common feature of follicular lymphoma, the most prevalent haematological malignancy in humans, is a chromosome translocation (t(14;18] that has coupled the immunoglobulin heavy chain locus to a chromosome 18 gene denoted bcl-2. By analogy with the translocated c-myc oncogene in other B-lymphoid tumours bcl-2 is a candidate oncogene, but no biological effects of bcl-2 have yet been reported. To test whether bcl-2 influences the growth of haematopoietic cells, either alone or together with a deregulated c-myc gene, we have introduced a human bcl-2 complementary DNA using a retroviral vector into bone marrow cells from either normal or E mu-myc transgenic mice, in which B-lineage cells constitutively express the c-myc gene. Bcl-2 cooperated with c-myc to promote proliferation of B-cell precursors, some of which became tumorigenic. To determine how bcl-2 expression impinges on growth factor requirements, the gene was introduced into a lymphoid and a myeloid cell line that require interleukin 3 (IL-3). In the absence of IL-3, bcl-2 promoted the survival of the infected cells but they persisted in a G0 state, rather than proliferating. These results argue that bcl-2 provided a distinct survival signal to the cell and may contribute to neoplasia by allowing a clone to persist until other oncogenes, such as c-myc, become activated.
3,238 citations
TL;DR: In this paper, a recombinant myeloid leukaemia inhibitory factor (LIF) was used to replace DIA in the maintenance of totipotent ES cell lines that retain the potential to form chimaeric mice.
Abstract: Embryonic stem (ES) cells, the totipotent outgrowths of blastocysts, can be cultured and manipulated in vitro and then returned to the embryonic environment where they develop normally and can contribute to all cell lineages. Maintenance of the stem-cell phenotype in vitro requires the presence of a feeder layer of fibroblasts or of a soluble factor, differentiation inhibitory activity (DIA) produced by a number of sources; in the absence of DIA the ES cells differentiate into a wide variety of cell types. We recently noted several similarities between partially purified DIA and a haemopoietic regulator, myeloid leukaemia inhibitory factor (LIF), a molecule which induces differentiation in M1 myeloid leukaemic cells and which we have recently purified, cloned and characterized. We demonstrate here that purified, recombinant LIF can substitute for DIA in the maintenance of totipotent ES cell lines that retain the potential to form chimaeric mice.
2,140 citations
887 citations
TL;DR: G-CSF administration followingmelphalan reduced the period of neutropenia caused by melphalan and reductions in the number of days of neutrophils following cytotoxic chemotherapy may reduce the morbidity and mortality of chemotherapy.
708 citations
TL;DR: The absolute number of circulating progenitor cells of granulocyte-macrophage, erythroid, and megakaryocyte lineages showed a dose-related increase up to 100-fold after four days of treatment with rG-CSF and often remained elevated two days after the cessation of therapy and in most patients was slightly decreased.
595 citations
TL;DR: The isolation and the sequence of the gene for the bifunctional enzyme dihydrofolate reductase-thymidylate synthase (DHFR-TS) from two pyrimethamine-resistant clones of Plasmodium falciparum, HB3 and 7G8 is described and it is highly likely that this difference is involved in the mechanism of drug resistance in HB3.
Abstract: We describe the isolation and the sequence of the gene for the bifunctional enzyme dihydrofolate reductase-thymidylate synthase (DHFR-TS; EC 1.5.1.3 and EC 2.1.1.45, respectively) from two pyrimethamine-resistant clones of Plasmodium falciparum, HB3 and 7G8. We have also derived the sequence of the DHFR portion of the gene, by amplification using polymerase chain reaction, for the pyrimethamine-sensitive clone 3D7 and the pyrimethamine-resistant strains V-1, K-1, Csl-2, and Palo-alto. The deduced protein sequence of the resistant DHFR portion of the enzyme from HB3 contained a single amino acid difference from the pyrimethamine-sensitive clone 3D7. It is highly likely that this difference is involved in the mechanism of drug resistance in HB3. The sequence of the DHFR gene from other pyrimethamine-resistant strains contains the same amino acid difference from the sensitive clone 3D7. However, they all differ at one other site that may influence pyrimethamine resistance. The DHFR-TS gene is present as a single copy on chromosome 4 in all pyrimethamine-sensitive and pyrimethamine-resistant isolates tested. Therefore, the molecular basis of pyrimethamine resistance in the parasites tested is not amplification of the DHFR-TS gene.
499 citations
TL;DR: Mice transgenic for a c-myc gene driven by the IgH enhancer were shown to almost invariably develop lymphomas, 90% succumbing in the first 5 mo of life, and appeared to arise at random from a population of pre-B cells expanded by constitutive expression of the myc transgene.
Abstract: Mice transgenic for a c-myc gene driven by the IgH enhancer (E mu-myc) were shown to almost invariably develop lymphomas, 90% succumbing in the first 5 mo of life. The tumors typically presented as rapidly progressive lymphadenopathy with thymic involvement and were highly malignant by transplantation assay. Morphologically, they were lymphoblastic lymphomas, usually accompanied by lymphoid leukemia and granulocytosis, and were distinct from the tumors that arose much later in 37% of nontransgenic mice of the same (C57BL/6 x SJL)F2 genetic background. Cell-surface markers on 31 E mu-myc tumors identified 52% as pre-B lymphomas, 29% as mixed pre-B and B lymphomas, and 19% as B lymphomas. The tumors appeared to arise at random from a population of pre-B cells expanded by constitutive expression of the myc transgene. A majority of the animals initiated malignancy at the rate of 17% per week. The rate at which the cycling, benign pre-B cells spontaneously convert to malignancy was estimated to about 10(-10) per cell per generation. A transient leukocytosis identified in young E mu-myc mice was developed into a rapid assay for inheritance of the transgene.
418 citations
TL;DR: An extremely simple procedure for preparing cytoplasmic RNA from small numbers of cells is described and RNA is ready for Northern gel analysis in less than 30 min.
413 citations
TL;DR: The findings show that the ICAM-1 molecule is a central component of the mechanism of lymphocyte-endothelial cell adhesion, and a pivotal role for this molecule in both the T-cell/T-cell and T- cell/B-cell interactions, which underpin the regulation of the immune response, and in the mechanisms of cell-mediated cytotoxicity.
Abstract: The role of intercellular adhesion molecule 1 (ICAM-1) in immune function was probed by using the Wehi-CAM-1 (W-CAM-1) monoclonal antibody. This antibody blocks aggregation of cell lines mediated by the ICAM-1 molecule and is here shown to block homotypic binding of purified populations of activated T and B lymphocytes (blasts) and also aggregation of mixed T- and B-cell blasts. We also demonstrate that W-CAM-1 inhibited T-cell adhesion to normal human endothelial cells, the first step in lymphocyte egress into the tissues. In tests of immune function, W-CAM-1 had a modest inhibitory effect on T- and B-cell activation by potent mitogens and no effect on the response of activated lymphocytes to lymphokines. By contrast, activation induced by cell-cell contact (mixed lymphocyte reaction, T-cell-mediated B-cell activation) was significantly inhibited. Moreover, the antibody was shown to block elements of both effector arms of the immune system (cytotoxic cell function and immunoglobulin production). These findings show that the ICAM-1 molecule is a central component of the mechanism of lymphocyte-endothelial cell adhesion. The studies of lymphoid function demonstrate a pivotal role for this molecule in both the T-cell/T-cell and T-cell/B-cell interactions, which underpin the regulation of the immune response, and in the mechanism of cell-mediated cytotoxicity.
311 citations
TL;DR: Considering the functional homology that was previously established between these two proteins, HP1 should be renamed murine interleukin 6, and a cDNA sequence isolated from a library prepared using mRNA of a murine helper T cell clone activated with a clonotypic antibody is described.
Abstract: Interleukin-HP1 (HP1) is a murine T cell-derived lymphokine, originally described as a growth factor for B cell hybridomas and plasmacytomas, that was recently shown to stimulate growth and differentiation of normal B and T lymphocytes Here, we describe a cDNA for HP1 that was isolated from a library prepared using mRNA of a murine helper T cell clone activated with a clonotypic antibody The cDNA, which hybridizes with a mRNA of approximately 1300 bp, encodes a polypeptide consisting of 211 amino acids with a typical signal sequence of 24 residues followed by 187 amino acids, which form the mature protein (Mr = 21,710) No N-glycosylation site but several potential O-glycosylation sites were identified in the predicted sequence Comparison of the cDNA sequence of HP1 with that of human interleukin 6 disclosed a homology of 65% at the DNA level and of 42% at the protein level with a maximum of 57% for the segment spanning residues 42-102 of mature HP1 Considering the functional homology that was previously established between these two proteins, we therefore propose that HP1 be renamed murine interleukin 6
TL;DR: A class I histocompatibility gene, H-2Kb, linked to the rat insulin promoter, is overexpressed in the pancreatic β cells of transgenic mice, suggesting a direct, non-immune role for the transgenic class I molecules in the disease process.
Abstract: A class I histocompatibility gene, H-2Kb, linked to the rat insulin promoter, is overexpressed in the pancreatic beta cells of transgenic mice. The mice, whether syngeneic or allogeneic to the transgene, develop insulin dependent diabetes without detectable T cell infiltration, suggesting a direct, non-immune role for the transgenic class I molecules in the disease process.
TL;DR: Similarities in the C-terminal sequences of the Mr 45,000 merozoite surface antigen and the Trypanosoma brucei variant surface glycoproteins provides further evidence that this antigen has a glycosylphosphatidylinositol anchor.
Abstract: We describe the isolation and cloning of two integral membrane protein antigens of Plasmodium falciparum. The antigens were isolated by Triton X-114 temperature-dependent phase separation, electrophoretically transferred to nitrocellulose, and used to affinity-purify monospecific human antibodies. These antibodies were used to isolate the corresponding cDNA clones from a phage lambda gt11-Amp3 cDNA expression library. Clone Ag512 corresponds to a Mr 55,000 merozoite rhoptry antigen, and clone Ag513 corresponds to a Mr 45,000 merozoite surface antigen. Both proteins can be biosynthetically labeled with [3H]glucosamine and [3H]myristic acid, suggesting that they may be anchored in membranes via a glycosylphosphatidylinositol moiety. Similarities in the C-terminal sequences of the Mr 45,000 merozoite surface antigen and the Trypanosoma brucei variant surface glycoproteins provides further evidence that this antigen has a glycosylphosphatidylinositol anchor.
TL;DR: A human cDNA clone encoding the complete amino acid sequence of this autoantigen is identified and the predicted structure has significant similarity with the dihydrolipoamide acetyltransferase of the Escherichia coli pyruvate dehydrogenase multienzyme complex.
Abstract: Primary biliary cirrhosis is a chronic, destructive autoimmune liver disease of humans. Patient sera are characterized by a high frequency (greater than 95%) of autoantibodies to a Mr 70,000 mitochondrial antigen, a component of the M2 antigen complex. We have identified a human cDNA clone encoding the complete amino acid sequence of this autoantigen. The predicted structure has significant similarity with the dihydrolipoamide acetyltransferase (EC 2.3.1.12) of the Escherichia coli pyruvate dehydrogenase multienzyme complex. The human sequence preserves the Glu-Thr-Asp-Lys-Ala motif of the lipoyl-binding site and has two potential binding sites. Expressed fragments of the cDNA react strongly with sera from patients with primary biliary cirrhosis but not with sera from patients with autoimmune chronic active hepatitis or sera from healthy subjects.
Journal Article•
TL;DR: The synergistic functional and cytotoxic effects of IFN-gamma and TNF-alpha are consistent with a direct role for these cytokines in the destruction of beta-cells in insulin-dependent diabetes.
Abstract: We have previously reported that the cytokines IFN-gamma and TNF-alpha each upregulate the expression of class I MHC proteins and, in combination, induce the expression of class II MHC proteins on pancreatic islet cells. IFN-gamma and TNF-alpha are therefore implicated in the immunologic destruction of beta-cells in insulin-dependent diabetes mellitus. The objective of the present study was to define the effects of IFN-gamma and TNF-alpha on the function and viability of murine pancreatic islet beta-cells in vitro. Exposure of islets for 3 days to 200 U/ml of either IFN-gamma or TNF-alpha did not affect glucose-stimulated insulin release, but at higher concentrations (2000 U/ml) of either cytokine there was significant inhibition of glucose-stimulated insulin release. In combination, IFN-gamma and TNF-alpha each at 200 U/ml caused significant inhibition of glucose-stimulated insulin release; at 2000 U/ml glucose-stimulated insulin release was abolished. In time-course experiments, glucose-stimulated insulin release from islets exposed to IFN-gamma and TNF-alpha each at 1000 U/ml was significantly increased at 4-h (twofold increase compared with control islets), decreased back to control levels at 18 h, significantly inhibited by 24 h (threefold decrease compared with control islets), and completely abolished by 48 h. The progressive impairment of beta-cell function mediated by IFN-gamma plus TNF-alpha was associated with morphologic derangement of the islets that were almost totally disintegrated by day 6 of exposure to the cytokines. At day 6, insulin content of the islets was significantly reduced by exposure to TNF-alpha but not IFN-gamma. The combination of IFN-gamma and TNF-alpha resulted in a further dose-dependent depletion in insulin content compared with TNF-alpha alone. The synergistic functional and cytotoxic effects of IFN-gamma and TNF-alpha are consistent with a direct role for these cytokines in the destruction of beta-cells in insulin-dependent diabetes.
TL;DR: The chromosome length polymorphisms can therefore be largely explained by recombination within blocks of repeats, a mechanism that is also important in the generation of diversity in genes for repetitive antigens of P. falciparum.
TL;DR: A human homologue of the recently cloned murine leukemia-inhibitory factor (LIF) gene was isolated from a genomic library by using the murine cDNA as a hybridization probe and could be induced with galactose to produce high levels of a factor that induced the differentiation of murine M1 leukemic cells in a manner analogous to murine LIF.
Abstract: A human homologue of the recently cloned murine leukemia-inhibitory factor (LIF) gene was isolated from a genomic library by using the murine cDNA as a hybridization probe. The nucleotide sequence of the human gene indicated that human LIF has 78% amino acid sequence identity with murine LIF, with no insertions or deletions, and that the region of the human gene encoding the mature protein has one intervening sequence. After oligonucleotide-mediated mutagenesis, the mature protein-coding region of the LIF gene was introduced into the yeast expression vector YEpsec1. Yeast cells transformed with the resulting recombinant could be induced with galactose to produce high levels of a factor that induced the differentiation of murine M1 leukemic cells in a manner analogous to murine LIF. This factor competed with 125I-labeled native murine LIF for binding to specific cellular receptors on murine cells, compatible with a high degree of structural similarity between the murine and human factors.
TL;DR: It is tentatively concluded that none of the TcR+ CD4- CD8- cells are precursors of the major thymocyte subsets or of typical peripheral T cells, and no evidence so far of separate precursor for the different mature subsets of thymocytes or peripheral T Cells is found.
Abstract: In this chapter we have summarized our view of the subsets of murine CD4- CD8- thymocytes which can be identified with a range of monoclonal antibodies. We have shown the division rate and turnover time of the main subsets and have listed what we know of the TcR gene rearrangement, and expression at the RNA and protein levels. We have been unable to completely segregate gamma delta-TcR-expressing cells from alpha beta-TcR-expressing cells by any of the markers we have used, although the proportions of the two receptor forms vary widely in the different subsets. Experiments involving intrathymic transfer of the CD4- CD8- subsets are described, which indicate that all the TcR- subsets of the CD4- CD8- thymocytes display some precursor activity and which suggest a progression of at least five stages through the TcR- subpopulations of CD4- CD8- cells. The earliest precursor is a Thy 1 low, HSA low, Pgp-1 high cell which has unrearranged C beta and is non-dividing and which closely resembles the bone marrow prothymocyte. The later precursors are Thy 1 high, HSA high, Pgp-1 low, have rearranged C beta and are rapidly dividing. We tentatively conclude that none of the TcR+ CD4- CD8- cells are precursors of the major thymocyte subsets or of typical peripheral T cells, and we have found no evidence so far of separate precursors for the different mature subsets of thymocytes or peripheral T cells.
TL;DR: It is suggested that constitutive myc plus raf expression can provoke genetic reprogramming in lymphocytes and be breached by concomitant expression of the c-myc and v-raf oncogenes.
Journal Article•
TL;DR: Both bcr-abl and v-abl efficiently rendered the myeloid cells factor independent and tumorigenic and may feature in CML development and Abelson virus transformation.
Abstract: In chronic myeloid leukemia (CML), a chromosome translocation has fused the bcr gene to the c-abl oncogene, such that a chimeric bcr-abl polypeptide can be made. To explore the biological properties of bcr-abl and compare them with those of the Abelson virus (AMuLV) transforming gene (gag-v-abl), we have used either a synthetic bcr-v-abl gene that mimics the translocation product or, in some experiments, a bcr-c-abl cDNA. A new retroviral vector was used to introduce the genes into the factor-dependent myeloid line FDC-P1. Both bcr-abl and v-abl efficiently rendered the myeloid cells factor independent and tumorigenic. Their fully autonomous growth may be due to the myeloid growth factor interleukin-3 (IL-3) made in small amounts by the infected cells. Hence autocrine factor production may feature in CML development and Abelson virus transformation.
TL;DR: It is proposed that macrophages present β-cell antigen to L3T4+ cells, which induce cytotoxic Lyt2+ cells to specifically destroy β-cells in NOD mice.
Abstract: The cellular pathway of beta-cell destruction in type I (insulin-dependent) diabetes is still undefined. L3T4+ T-lymphocytes have a role in both the initiation of insulitis and in recurrent disease in transplanted allogeneic islets in nonobese diabetic (NOD) mice. The roles of macrophages and Lyt2+ T-lymphocytes in beta-cell destruction were studied in cyclophosphamide-induced diabetic NOD mice with silica particles and a rat anti-Lyt2 monoclonal antibody. After administration of cyclophosphamide, 10 of 26 untreated mice and 1 of 21 anti-Lyt2-treated mice became diabetic. Insulitis was significantly reduced in anti-Lyt2-treated mice, and immunocytochemical staining showed a lack of Lyt2+ cells. Only 1 of 19 silica-treated mice became diabetic, compared to 8 of 19 control mice. This study demonstrates that both Lyt2+ T-lymphocytes and macrophages are necessary, but not sufficient, for beta-cell destruction in NOD mice. Therefore, we propose that macrophages present beta-cell antigen to L3T4+ cells, which induce cytotoxic Lyt2+ cells to specifically destroy beta-cells.
TL;DR: It has been shown that the cloned cell line 2.3D can differentiate into astrocytes, containing glial fibrillary acidic protein, and neurons, expressing the A2B5 marker and neurofilaments, which indicates that some cells in the neuroepithelium at embryonic day 10 are multipotent and are not restricted to either the glial or neuronal cell lineage.
Abstract: Immortalized cell lines have been generated from embryonic mouse neuroepithelium by infection with a retrovirus containing the c-myc oncogene The morphology and the antigenic phenotype of the cloned cell lines are characteristic of normal neuroepithelium Although the cell lines are stable and do not spontaneously differentiate, morphological changes can be induced with both acidic and basic fibroblast growth factor Fibroblast growth factor at 5 ng/ml stimulates differentiation of the neuroepithelial cells, and it has been shown that the cloned cell line 23D can differentiate into astrocytes, containing glial fibrillary acidic protein, and neurons, expressing the A2B5 marker and neurofilaments This indicates that some cells in the neuroepithelium at embryonic day 10 are multipotent and are not restricted to either the glial or neuronal cell lineage The cell lines also can be induced with interferon gamma to express class I and class II histocompatibility antigens The response of the c-myc-immortalized cell lines to these two factors is similar to that observed with freshly isolated neuroepithelium and suggests that such immortalized precursor populations are representative of the cells found in the developing neuroepithelium
TL;DR: Several mouse and human genes encoding the DNA‐binding homeobox domain are implicated here in haematopoiesis, a differentiation process maintained throughout life that may influence developmental decisions within the haemopoietic system.
Abstract: Several mouse and human genes encoding the DNA-binding homeobox domain are implicated here in haematopoiesis, a differentiation process maintained throughout life. Four homeobox cDNA clones were isolated from bone marrow and spleen of adult mice and two from the human leukaemia cell line K562. They derive from the Hox 1.1, Hox 2.3, Hox 6.1 genes and two previously undescribed genes, one of a type (paired) not found before in vertebrates. A survey of 36 cell lines of the lymphoid, myeloid and erythroid lineages revealed that certain homeobox transcripts were almost ubiquitous, while others were restricted to certain lineages or even particular cell lines. The expression pattern altered in a myeloid and an erythroid line induced to terminal differentiation, and in novel lines that had switched from a lymphoid to a myeloid phenotype. Altogether, the haemopoietic compartment may contain up to 20 homeobox transcripts. In one myeloid leukaemia, DNA rearrangement has perturbed expression. These findings suggest that homeobox genes may influence developmental decisions within the haemopoietic system.
TL;DR: A factor capable of inducing terminal differentiation in the murine myeloid leukemia cell line M1 has been purified to apparent homogeneity from the medium conditioned by Krebs II ascites tumor cells to allow structural and functional analysis of the molecule and comparison with other know differentiation inducers.
TL;DR: Autoradiography revealed macrophages, monocytes, and their precursors to be the major cell types responsible for 125I-labeled LIF binding within these tissues including the bone marrow, the spleen, and the peritoneal cavity.
Abstract: Leukemia inhibitory factor (LIF), a glycoprotein capable of suppressing the clonogenicity and inducing the differentiation of the murine myeloid leukemia cell line M1, was radioiodinated to a high specific radioactivity with retention of full biological activity. Binding of 125I-labeled LIF to M1 cells reached a steady state at 37 degrees C after approximately equal to 40 min and was in competition with unlabeled LIF but not granulocyte colony-stimulating factor or a range of other cytokines or differentiation-inducing agents. Specific binding was demonstrable to cells from a range of murine hemopoietic tissues including the bone marrow, the spleen, and the peritoneal cavity. Autoradiography revealed macrophages, monocytes, and their precursors to be the major cell types responsible for 125I-labeled LIF binding within these tissues. Receptors on M1 cells were of high affinity (apparent Kd, 100-200 pM) and few in number (300-500 per cell).
TL;DR: Biochemically fractionated medium conditioned by Krebs II ascites cells and assayed fractions for their bone marrow colony-stimulating activity as well as their differentiation-inducing activity for WEHI-3B D+ and M1 cells resulted in the resolution of four distinct molecular species with differentiation- inducing activity.
TL;DR: How transgenic animals are produced, how the rules for oncogene cooperativity can be evaluated within diverse cell types, and the current state of transgenic oncogenes is considered.
Abstract: The creation of transgenic mice carrying specific cancer-promoting genes has opened an exciting new era in oncology. The biological effects of an individual oncogene on diverse cell types can now be assessed directly within the living animal. While transgenic animals bear the introduced oncogene in every tissue, expression of that gene may either be widespread or directed to a particular cell lineage, depending upon the regulatory sequences chosen. The transgene should behave identically in every animal of an established lineage and, indeed, perhaps in every cell of a given type. Thus, a well-characterized transgenic line becomes a permanent resource. Perhaps the most significant opportunity provided by these transgenic animals is the possibility of exploring the pre-neoplastic state. One can attempt to assess whether an oncogene has perturbed differentiation within particular lineages. The perturbations may help to delineate early matu ration stages and to clarify how differentiation is controlled. Thus, new insights may emerge regarding the normal biological functions of proto oncogenes. The rules for oncogene cooperativity can also be evaluated within diverse cell types. For example, one can isolate the relevant cells from a pre-neoplastic animal bearing an oncogene and attempt to trans form them fully in vitro with retroviruses carrying other oncogenes. Alter natively, the second oncogene could be introduced simply by breeding mice of two independent transgenic lines. While the study of transgenic oncogenes is still in its infancy, major new insights have already been gained. This chapter briefly summarizes how transgenic animals are produced, and then considers our current state of
TL;DR: Comparing viral RNA levels in cells infected with several different recombinant viruses and constructing a vector that employs an internal beta-actin promoter suggest approaches to the design of improved vectors for effective expression of genes in hemopoietic cells.
Abstract: In order to identify factors that influence expression by retroviral vectors in hemopoietic cells, we have compared viral RNA levels in cells infected with several different recombinant viruses. All of the vectors tested carry the neomycin resistance gene and provide for the insertion of a second gene which, in these studies, comprised sequences from the myc or myb oncogenes or the gene encoding granulocyte-macrophage colony-stimulating factor. The vectors utilize two different strategies for the coexpression of the two genes: alternate splicing and the use of a separate internal promoter. We found that expression in hemopoietic cells could be increased by substituting sequences from the myeloproliferative sarcoma virus long terminal repeat for those of the Moloney murine leukemia virus long terminal repeat. However, none of the vectors examined was able to express a second gene at levels equivalent to those achieved by the parental vectors carrying only the neomycin resistance gene. The reasons for this varied with the different vectors and included inefficient splicing and/or a reduction in the level of unspliced transcripts upon insertion of a second gene. Although the basis of the latter phenomenon is not clear, it is probably related to the position--near the 5' long terminal repeat--at which the second gene was inserted, since insertion of the same genes near the 3' end of another vector had no effect on viral RNA levels. In an attempt to circumvent some of these problems, we constructed a vector that employs an internal beta-actin promoter. Although this vector could express granulocyte-macrophage colony-stimulating factor sequences in a responsive hemopoietic cell line, the level of granulocyte-macrophage colony-stimulating factor produced was disappointingly low. The results from these studies suggest approaches to the design of improved vectors for effective expression of genes in hemopoietic cells.
TL;DR: Examination of lymphokine gene expression in a panel of 116 short-term murine T-lymphocyte clones derived by single-cell micromanipulation from allogeneic mixed leukocyte cultures found all were found to correspond to the values predicted for random assortment of the individual frequencies.
Abstract: Lymphokine gene expression was examined in a panel of 116 short-term murine T-lymphocyte clones derived by single-cell micromanipulation from allogeneic mixed leukocyte cultures. About 30% of clonable T cells, including both CD4+ CD8- and CD4- CD8+ cells, could be expanded for assay at an average of 22 days after cloning. By RNA blot-hybridization analysis, most clones (85-96%) expressed detectable granulocyte-macrophage colony-stimulating factor, interleukin 3, and gamma interferon mRNAs, and 11% expressed interleukin 4 mRNA. Although no differences were noted between CD4+ and CD8+ clones in the combinations of lymphokines produced, CD4+ clones on average transcribed and secreted higher levels. When the frequencies of coexpression of any pair of lymphokine mRNAs were determined, all were found to correspond to the values predicted for random assortment of the individual frequencies. For example, among 13 interleukin 4-positive clones, 11 also transcribed gamma interferon, giving the frequency of double-positive clones expected for random association (9.6% versus 10.8%). Therefore, expression of the four lymphokine genes segregated independently among the clones and did not allow the division of T cells into subsets with distinct patterns of lymphokine synthesis.
TL;DR: All factor-independent mutants were tumorigenic, consistent with the hypothesis that growth-factor independence initiated by aberrant growth factor gene activation is an important and early step in tumorigenesis.