"But not the music": psychopathic traits and difficulties recognising and resonating with the emotion in music

Recognising and responding appropriately to emotions is critical to adaptive psychological functioning. Psychopathic traits (e.g. callous, manipulative, impulsive, antisocial) are related to differences in recognition and response when emotion is conveyed through facial expressions and language. Use of emotional music stimuli represents a promising approach to improve our understanding of the specific emotion processing difficulties underlying psychopathic traits because it decouples recognition of emotion from cues directly conveyed by other people (e.g. facial signals). In Experiment 1, participants listened to clips of emotional music and identified the emotional content (Sample 1, N = 196) or reported on their feelings elicited by the music (Sample 2, N = 197). Participants accurately recognised (t(195) = 32.78, p < .001, d = 4.69) and reported feelings consistent with (t(196) = 7.84, p < .001, d = 1.12) the emotion conveyed in the music. However, psychopathic traits were associated with reduced emotion recognition accuracy (F(1, 191) = 19.39, p < .001) and reduced likelihood of feeling the emotion (F(1, 193) = 35.45, p < .001), particularly for fearful music. In Experiment 2, we replicated findings for broad difficulties with emotion recognition (Sample 3, N = 179) and emotional resonance (Sample 4, N = 199) associated with psychopathic traits. Results offer new insight into emotion recognition and response difficulties that are associated with psychopathic traits.

Epigenetic memory in induced pluripotent stem cells

Somatic cell nuclear transfer and transcription-factor-based reprogramming revert adult cells to an embryonic state, and yield pluripotent stem cells that can generate all tissues. Through different mechanisms and kinetics, these two reprogramming methods reset genomic methylation, an epigenetic modification of DNA that influences gene expression, leading us to hypothesize that the resulting pluripotent stem cells might have different properties. Here we observe that low-passage induced pluripotent stem cells (iPSCs) derived by factor-based reprogramming of adult murine tissues harbour residual DNA methylation signatures characteristic of their somatic tissue of origin, which favours their differentiation along lineages related to the donor cell, while restricting alternative cell fates. Such an 'epigenetic memory' of the donor tissue could be reset by differentiation and serial reprogramming, or by treatment of iPSCs with chromatin-modifying drugs. In contrast, the differentiation and methylation of nuclear-transfer-derived pluripotent stem cells were more similar to classical embryonic stem cells than were iPSCs. Our data indicate that nuclear transfer is more effective at establishing the ground state of pluripotency than factor-based reprogramming, which can leave an epigenetic memory of the tissue of origin that may influence efforts at directed differentiation for applications in disease modelling or treatment.

Common themes of dedifferentiation in somatic cell reprogramming and cancer

With its hallmarks of unregulated cell proliferation and compromised differentiation, cancer represents a derangement of normal tissue homeostasis. A common set of pathways are activated in the transformed state, through either mutation or altered epigenetic regulation, and both heritable effects sustain the tumor. Classical views of cancer have invoked tissue dedifferentiation in the oncogenic process, whereas modern views embodied in the cancer stem cell hypothesis hold that cancer emerges from primitive tissue stem cells or specific progenitor populations that through mutations assume the self-renewal properties of stem cells. Recently, somatic tissues have been reprogrammed to a pluripotent state resembling embryonic stem (ES) cells by ectopic expression of a cocktail of transcription factors. The factors that drive reprogramming are oncogenes or have been linked to cellular transformation, suggesting that tumorigenesis and somatic cell reprogramming might indeed share common mechanisms of dedifferentiation.

Quantitative monitoring by polymerase colony assay of known mutations resistant to ABL kinase inhibitors

Resistance to molecularly targeted chemotherapy, and the development of novel agents that are active against resistant forms of target proteins create the need for a sensitive and quantitative assay to monitor drug-resistant mutations in patients to guide treatment and assess response. Here, we describe an application of the polymerase colony (polony) method to identify and quantify known point mutations in the BCR-ABL oncogene in patients with chronic myelogenous leukemia who evolve resistance to ABL kinase inhibitors. The assay can detect mutations with a sensitivity of 10(-4), quantify the burden of drug-resistant cells, and simultaneously monitor the dynamics of several coexisting mutations. As a proof of concept, we analysed blood samples from three patients undergoing therapy with ABL kinase inhibitors and found that the patients' response to therapy correlated with our molecular monitoring. We were also able to detect mutations emerging in patients long before clinical relapse. Therefore, the polony assay could be applied to a larger patient sample to assess the utility of early mutation detection in patient-specific treatment decisions. Finally, this methodology could be a valuable research tool to shed light on the natural behavior of mutations pre-existing kinase inhibitors therapy and either disappearing over time or slowly taking over.

Progress and prospects: gene transfer into embryonic stem cells

With the isolation of human embryonic stem cells (hESCs) in 1998 came the realization of a long-sought aspiration for an unlimited source of human tissue. The difficulty of differentiating ESCs to pure, clinically exploitable cell populations to treat genetic and degenerative diseases is being solved in part with the help of genetically modified cell lines. With progress in genome editing and somatic cell nuclear transfer, it is theoretically possible to obtain genetically repaired isogenic cells. Moreover, the prospect of being able to select, isolate and expand a single cell to a vast population of cells could achieve a unique level of quality control, until now unattainable in the field of gene therapy. Most of the tools necessary to develop these strategies already exist in the mouse ESC system. We review here the advances accomplished in those fields and present some possible applications to hESC research.

231 HISTOCOMPATIBLE PARTHENOGENETIC EMBRYONIC STEM CELLS

Organ or tissue transplantation is the preferred treatment for numerous diseases but is hindered by immunologic barriers. Genetically matched pluripotent embryonic stem cells generated via nuclear transfer (ntES cells) or parthenogenesis (pES cells) are possible sources of histocompatible cells and tissues. We have developed two ways of isolating pES cells that carry the full complement of major histocompatibility complex (MHC) antigens of the oocyte donors. One method entails activation of oocytes after blockade of karyokinesis in meiosis II, followed by selection of predominantly homozygous pES cells that have undergone recombination in their MHC antigen region to restore the heterozygous maternal MHC genotype (parthenote recombinant, or prES cells). The second method involves activation of immature oocytes after blockade of karyokinesis of meiosis I, followed by selection of predominantly heterozygous pES lines that retain the MHC genotype of the oocyte donor (parthenote clone recombinant, or pcrES cells). The cells are pluripotent by several criteria: teratoma formation, in vitro differentiation into hematopoietic elements, and high-level skin chimerism in blastocyst chimeras. Breeding of 8 founder females and examination of over 700 progeny failed to demonstrate germ line transmission of the pES cells. Injection of over 50 tetraploid embryos with these lines and embryo transfer have failed to support full gestational development. However, differentiated tissues from these pluripotent ES cells engraft when transplanted into genetically matched immunocompetent recipients, demonstrating that selected pES cells can serve as a source of histocompatible tissues for transplantation.

Stem cells and their niche: a matter of fate

Embryonic stem cells provide an in vitro model for developmental biologists to study cell fate decisions during ontogenesis, while somatic stem cells allow physiologists to understand tissue homeostasis in the adult. The behavior of stem cells is dependent on an intimate relationship with a supportive niche. This brief review highlights some of the most important recent trends in stem cell biology, focusing in particular on the supportive microenvironments for both embryonic and adult stem cells. Known intrinsic and extrinsic molecular players from the best-characterized stem cell types are summarized, illuminating a number of shared environmental cues among tissues originating from all three embryonic germ layers.

Treatment by design in leukemia, a meeting report, Philadelphia, Pennsylvania, December 2002

Novel approaches have been designed to treat leukemia based on our understanding of the genetic and biochemical lesions present in different malignancies. This meeting report summarizes some of the recent advances in leukemia treatment. Based on the discoveries of cellular oncogenes, chromosomal translocations, monoclonal antibodies, multidrug resistance pumps, signal transduction pathways, genomics/proteonomic approaches to clinical diagnosis and mutations in biochemical pathways, clinicians and basic scientists have been able to identify the particular genetic mutations and signal transduction pathways involved as well as design more appropriate treatments for the leukemia patient. This meeting report discusses these exciting new therapies and the results obtained from ongoing clinical trials. Furthermore, rational approaches to treat complications of tumor lysis syndrome by administration of the recombinant urate oxidase protein, also known as rasburicase, which corrects the biochemical defect present in humans, were discussed. Clearly, over the past 25 years, molecular biology and biotechnology has provided the hematologist/oncologist novel bullets in their arsenal that will allow treatment by design in leukemia.

Single nucleotide polymorphisms in multiple novel thrombospondin genes may be associated with familial premature myocardial infarction

BACKGROUND

Recent advances in high-throughput genomics technology have expanded our ability to catalogue allelic variants in large sets of candidate genes related to premature coronary artery disease.

METHODS AND RESULTS

A total of 398 families were identified in 15 participating medical centers; they fulfilled the criteria of myocardial infarction, revascularization, or a significant coronary artery lesion diagnosed before 45 years in men or 50 years in women. A total of 62 vascular biology genes and 72 single-nucleotide polymorphisms were assessed. Previously undescribed variants in 3 related members of the thrombospondin protein family were prominent among a small set of single-nucleotide polymorphisms that showed a statistical association with premature coronary artery disease. A missense variant of thrombospondin 4 (A387P) showed the strongest association, with an adjusted odds ratio for myocardial infarction of 1.89 (P=0.002 adjusted for covariates) for individuals carrying the P allele. A variant in the 3' untranslated region of thrombospondin-2 (change of thymidine to guanine) seemed to have a protective effect against myocardial in individuals homozygous for the variant (adjusted odds ratio of 0.31; P=0.0018). A missense variant in thrombospondin-1 (N700S) was associated with an adjusted odds ratio for coronary artery disease of 11.90 (P=0.041) in homozygous individuals, who also had the lowest level of thrombospondin-1 by plasma assay (P=0.0019).

CONCLUSIONS

This large-scale genetic study has identified the potential of multiple novel variants in the thrombospondin gene family to be associated with familial premature myocardial infarction. Notwithstanding multiple caveats, thrombospondins specifically and high-throughput genomic technology in general deserve further study in familial ischemic heart disease.

Clonal analysis of differentiating embryonic stem cells reveals a hematopoietic progenitor with primitive erythroid and adult lymphoid-myeloid potential

Embryonic stem (ES) cells differentiate into multiple hematopoietic lineages during embryoid body formation in vitro, but to date, an ES-derived hematopoietic stem cell has not been identified and subjected to clonal analysis in a manner comparable with hematopoietic stem cells from adult bone marrow. As the chronic myeloid leukemia-associated BCR/ABL oncogene endows the adult hematopoietic stem cell with clonal dominance without inhibiting pluripotent lymphoid and myeloid differentiation, we have used BCR/ABL as a tool to enable engraftment and clonal analysis. We show that embryoid body-derived hematopoietic progenitors expressing BCR/ABL maintain a primitive hematopoietic blast stage of differentiation and generate only primitive erythroid cell types in vitro. These cells can be cloned, and when injected into irradiated adult mice, they differentiate into multiple myeloid cell types as well as T and B lymphocytes. While the injected cells express embryonic (β-H1) globin, donor-derived erythroid cells in the recipient express only adult (β-major) globin, suggesting that these cells undergo globin gene switching and developmental maturation in vivo. These data demonstrate that an embryonic hematopoietic stem cell arises in vitro during ES cell differentiation that constitutes a common progenitor for embryonic erythroid and definitive lymphoid-myeloid hematopoiesis.

Cooperative and redundant effects of STAT5 and Ras signaling in BCR/ABL transformed hematopoietic cells

The Akt, Ras and STAT5 signaling pathways have each been linked to transformation of hematopoietic cells by BCR/ABL. However the relative contributions of these signaling pathways to BCR/ABL mediated cytokine-independent survival, proliferation and resistance to DNA damage-induced apoptosis have not been systematically defined. Here we report that activation of either Akt, Ras or STAT5 confers cytokine-independent survival to IL-3 dependent BaF3 cells. Ras or STAT5, but not Akt, also drives cytokine-independent proliferation and imparts sustained resistance to DNA damage-induced apoptosis. We also show that dominant negative (DN) inhibition of STAT5, but not Ras or Akt, significantly reduces resistance to DNA damage-induced apoptosis in BCR/ABL transformed BaF3 cells. Whereas inhibition of STAT5 or Ras alone does not compromise cytokine-independent proliferation of BaF3-BCR/ABL cells, simultaneous blockade of both STAT5 and Ras reduces proliferation and maximally sensitizes BaF3-BCR/ABL cells to DNA damage induced by gamma-irradiation, suggesting a cooperative role for these two signaling pathways in BCR/ABL transformation. The anti-apoptotic properties of BCR/ABL can be partly explained by an increase in the expression of Pim-1 and Bcl-XL, as ectopic expression of these STAT5 target genes imparts both cytokine-independent survival and partial gamma-radiation resistance. These data illustrate both cooperative and redundant effects of STAT5 and Ras signaling in BCR/ABL transformed cells, with STAT5 playing a dominant role in resistance to DNA damage-induced apoptosis.

Expression of interferon consensus sequence binding protein induces potent immunity against BCR/ABL-induced leukemia

Mice deficient in the interferon consensus sequence binding protein (ICSBP) develop a disease resembling chronic myeloid leukemia (CML), which in humans is caused by the BCR/ABL oncoprotein. Interferon-α (IFN-α) induces ICSBP expression and is an effective therapy for CML. This study examined whether enforced expression of ICSBP might antagonize BCR/ABL-induced leukemia; results demonstrated that ICSBP-modified cells generated a protective CD8+ cytotoxic T-cell response against BCR/ABL-transformed BaF3 cells in a murine leukemia model. ICSBP expression represents a novel means of stimulating a host immune response to BCR/ABL+ leukemia cells and a potential strategy for immunotherapy of CML.

Autocrine and paracrine effects of an ES-cell derived, BCR/ABL-transformed hematopoietic cell line that induces leukemia in mice

During differentiation in vitro, Embryonic Stem (ES) cells generate both primitive erythroid and definitive myeloid lineages in a process that mimics hematopoiesis in the mammalian yolk sac. To investigate leukemic transformation of these embryonic hematopoietic progenitors, we infected differentiating cultures of ES cells with the Chronic Myeloid Leukemia-specific BCR/ABL oncoprotein. Following a period of liquid culture, we isolated two transformed subclones, EB57 and EB67, that retained characteristics of embryonic hematopoietic progenitors and induced a fatal leukemia in mice characterized by massive splenomegaly and granulocytosis. Histopathology of the spleen revealed an abundance of undifferentiated blast-like cells. Investigation of the clonal origins of the granulocytes in the peripheral blood demonstrated that the injected donor cells contributed modestly to the granulocyte population while the majority were host-derived. EB57 secretes IL-3 and unidentified cytokines that can stimulate autocrine and paracrine cell proliferation, presumably accounting for the reactive granulocytosis in diseased mice. These BCR/ABL transformed hematopoietic derivatives of ES cells recapitulate the relationship of BCR/ABL expression to IL-3 production that has been described for primitive hematopoietic progenitors from human CML patients, and illustrates the potential for autocrine and paracrine effects of BCR/ABL-infected cells in murine models.

Activity of the farnesyl protein transferase inhibitor SCH66336 against BCR/ABL-induced murine leukemia and primary cells from patients with chronic myeloid leukemia

BCR/ABL, the oncoprotein responsible for chronic myeloid leukemia (CML), transforms hematopoietic cells through both Ras-dependent and -independent mechanisms. Farnesyl protein transferase inhibitors (FTIs) were designed to block mutant Ras signaling, but they also inhibit the growth of transformed cells with wild-type Ras, implying that other farnesylated targets contribute to FTI action. In the current study, the clinical candidate FTI SCH66336 was characterized for its ability to inhibit BCR/ABL transformation. When tested against BCR/ABL-BaF3 cells, a murine cell line that is leukemogenic in mice, SCH66336 potently inhibited soft agar colony formation, slowed proliferation, and sensitized cells to apoptotic stimuli. Quantification of activated guanosine triphosphate (GTP)-bound Ras protein and electrophoretic mobility shift assays for AP-1 DNA binding showed that Ras effector pathways are inhibited by SCH66336. However, SCH66336 was more inhibitory than dominant-negative Ras in assays of soft agar colony formation and cell proliferation, suggesting activity against targets other than Ras. Cell cycle analysis of BCR/ABL-BaF3 cells treated with SCH66336 revealed G2/M blockade, consistent with recent reports that centromeric proteins that regulate the G2/M checkpoint are critical farnesylated targets of FTI action. Mice injected intravenously with BCR/ABL-BaF3 cells developed acute leukemia and died within 4 weeks with massive splenomegaly, elevated white blood cell counts, and anemia. In contrast, nearly all mice treated with SCH66336 survived and have remained disease-free for more than a year. Furthermore, SCH66336 selectively inhibited the hematopoietic colony formation of primary human CML cells. As an oral, nontoxic compound with a mechanism of action distinct from that of ABL tyrosine kinase inhibition, FTI SCH66336 shows promise for the treatment of BCR/ABL-induced leukemia.

Treatment of Bcr/Abl-positive acute lymphoblastic leukemia in P190 transgenic mice with the farnesyl transferase inhibitor SCH66336

The Philadelphia (Ph) chromosome is found in approximately 3% of pediatric patients with acute lymphoblastic leukemia (ALL) and the percentage markedly increases in adult patients. The prognosis for this class of patients is poor, and no standard chemotherapy combination so far has demonstrated long-term efficacy. The Ph-translocation joins the BCR and ABL genes and leads to expression of a chimeric Bcr/Abl protein with enhanced tyrosine kinase activity. This increase in activity leads to malignant transformation by interference with basic cellular functions such as the control of proliferation, adherence to stroma and extracellular matrix, and apoptosis. One important pathway activated by Bcr/Abl is the Ras pathway. Ras proteins have to undergo a series of posttranslational modifications to become biologically active. The first modification is the farnesylation of the C-terminus catalyzed by farnesyl transferase. We studied the effect of the farnesyl transferase inhibitor SCH66336 in an in vivo murine model of Bcr/Abl-positive acute lymphoblastic leukemia. In the early leukemic phase, mice were randomly assigned to a treatment, a vehicle, and a nontreatment group. The treatment was well tolerated without any detectable side effects. All animals of the control groups died of leukemia/lymphoma within 103 days (range, 18-103 days). In contrast, 80% of the drug-receiving group survived without any signs of leukemia or lymphoma until termination of treatment, after a median treatment period of 200 days (range, 179-232 days). We conclude that farnesyl transferase inhibitor SCH66336 is able to revert early signs of leukemia and significantly prolongs survival in a murine ALL model.

The heart SNPs a beat: polymorphisms in candidate genes for cardiovascular disease

Several environmental risk factors of cardiovascular disease are well established, but genetic risk alleles contributing to the disease in the general population are hotly debated. New strategies focusing on polymorphism discovery in candidate disease genes followed by tests of association to genes across the genome offer a pioneering approach to identifying risk alleles. Several hundred candidate genes for cardiovascular disease have been screened for common polymorphisms and these variants may provide susceptibility alleles which largely contribute to risk of cardiovascular disease in the general population. However, the impact of common susceptibility alleles for disease management will depend on many years of future investigation.

Senescence bypass screen identifies TBX2, which represses Cdkn2a (p19(ARF)) and is amplified in a subset of human breast cancers

To identify new immortalizing genes with potential roles in tumorigenesis, we performed a genetic screen aimed to bypass the rapid and tight senescence arrest of primary fibroblasts deficient for the oncogene Bmi1. We identified the T-box member TBX2 as a potent immortalizing gene that acts by downregulating Cdkn2a (p19(ARF)). TBX2 represses the Cdkn2a (p19(ARF)) promoter and attenuates E2F1, Myc or HRAS-mediated induction of Cdkn2a (p19(ARF)). We found TBX2 to be amplified in a subset of primary human breast cancers, indicating that it might contribute to breast cancer development.

Leukemia inhibitory factor (LIF) concentration modulates embryonic stem cell self-renewal and differentiation independently of proliferation

A major limitation of the widespread use of stem cells in a variety of biotechnological applications is the relatively low level of knowledge about how to maintain these cells in vitro without losing the long-term multilineage growth properties required for their clinical utility. An experimental and theoretical framework for predicting and controlling the outcome of stem cell stimulation by exogenous cytokines would thus be useful. An emerging theme from recent hematopoietic stem cell (HSC)-expansion studies is that a net gain in HSC numbers requires the maintenance of critical signaling ligand(s) above a threshold level. These ligand-receptor complex thresholds can be maintained, for example, by high concentrations of soluble cytokines or by cytokine presentation on cell surfaces. According to such a model, when the relevant ligand-receptor interaction falls below this threshold level, the probability of a differentiation response is increased; otherwise, self-renewal is favored. Taking advantage of the ability of the cytokine leukemia inhibitory factor (LIF) to maintain embryonic stem (ES) cell pluripotentiality at high concentrations, we are testing this model by investigating critical parameters in the control of ES cell responses. We have developed quantitative assays of ES cell differentiation by measuring cell-surface alkaline phosphatase activity, cell-surface stage specific embryonic antigen (SSEA)-1 expression, and the ability of ES cells to form embryoid bodies. Examination of ES cell responses over a range of LIF concentrations shows that LIF supplementation has little effect on ES cell-growth rate but significantly alters the probability of a cell undergoing a self-renewal vs. a differentiation division. In vitro culture parameters such as inoculum cell density, medium exchange, as well as cell-intrinsic processes such as autocrine secretion are shown to affect this decision. In addition to yielding new information on stem cell regulation by exogenous factors, these studies provide important clues about culture of these cells and should stimulate further investigations into the mechanistic basis of stem cell differentiation control.

Androgen metabolism and prostate cancer: establishing a model of genetic susceptibility

The prostate is an androgen-regulated organ, which has led to longstanding interest in the role of androgens in prostate carcinogenesis. Although evidence of a hormonal etiology for prostate cancer is strong, it is almost entirely circumstantial. Much of the problem in proving a causal relationship relates to the continued difficulties in reliably measuring human tissue-specific exposure to endogenous steroid hormones. The international and racial-ethnic variations in prostate cancer incidence, combined with the effects of migration on risk patterns, have suggested that genetic factors play a central role in determining prostate cancer risk. We are developing a polygenic model of prostate carcinogenesis, focused around a series of genes involved in androgen biosynthesis, transport and metabolism. We have begun to develop this model by utilizing sequence variants to study how polymorphic markers in two genes (SRD5A2 and AR) are related to prostate cancer risk within and between racial-ethnic groups. We are now collaborating with the Whitehead Institute/MIT, Center for Genome Research, to screen for single nucleotide polymorphisms in additional genes relevant to the androgen pathway and prostate cell growth. The model when fully developed can potentially provide a basis for targeting populations for screening interventions and for implementing primary preventive strategies.

A genetic screen to identify genes that rescue the slow growth phenotype of c-myc null fibroblasts

The c-myc gene is frequently over-expressed in human cancers and is involved in regulation of proliferation, differentiation and apoptosis. c-Myc is a transcription factor that acts primarily by regulating the expression of other genes. However, it has been very difficult to identify bona fide c-Myc target genes that explain its diverse biological activities. The recent generation of c-myc deficient Rat1A fibroblasts with a profound and stable growth defect provides a new system to search for genes that can substitute for c-myc in proliferation. In this study, we have attempted to identify genes that rescue the slow growth phenotype of c-myc null cells through introduction of a series of potent cell cycle regulatory genes and several retroviral cDNA expression libraries. None of the candidate genes tested, including SV40 T-antigen and adenovirus E1A, caused reversal of the c-myc null growth defect. Furthermore, extensive screens with high-complexity retroviral cDNA libraries from three different tissue sources revealed that only c-myc and N-myc rescued the c-myc null slow-growth phenotype. Our data support the notion that there are no functional equivalents of the myc family of proto-oncogenes and also suggest that there are no c-Myc-activated genes that alone can substitute for c-Myc in control of cell proliferation.

Mining for SNPs: putting the common variants--common disease hypothesis to the test

Classical molecular genetic strategies have succeeded in identifying mutations responsible for numerous rare diseases with Mendelian patterns of inheritance, but have been largely unsuccessful in unravelling the (genetic basis of complex medical conditions like cardiovascular disease' diabetes and mental illness. These common disorders are shaped by multiple genes that exert weak allelic effects in the setting of confounding environmental variables. Association study designs provide statistical povwer to reveal the modest contributions of weak alleles, and evidence is mounting that common genetic polymorphisms play a role in complex diseases. Cataloguing genetic variation in human populations is a prerequisite for further validation of the 'common variants-common disease' hypothesis, and polymorphism discovery has begun in earnest in the academic and private sector. We will review several strategies for high-throughput polymorphism discovery and discuss the implications of early results from polymorphism screens for future genetic studies.

The BCR/ABL oncogene alters the chemotactic response to stromal-derived factor-1alpha

The chemokine stromal-derived factor-1alpha (SDF-1alpha) is a chemoattractant for CD34(+) progenitor cells, in vitro and in vivo. The receptor for SDF-1alpha, CXCR-4, is a 7 transmembrane domain receptor, which is also a coreceptor for human immunodeficiency virus (HIV). Here we show that transformation of hematopoietic cell lines by BCR/ABL significantly impairs their response to SDF-1alpha. Three different hematopoietic cell lines, Ba/F3, 32Dcl3, and Mo7e, were found to express CXCR-4 and to respond to SDF-1alpha with increased migration in a transwell assay. In contrast, after transformation by the BCR/ABL oncogene, the chemotactic response to SDF-1alpha was reduced in all 3 lines. This effect was directly due to BCR/ABL, because Ba/F3 cells, in which the expression of BCR/ABL could be regulated by a tetracycline-inducible promoter, also had reduced chemotaxis to SDF-1alpha when BCR/ABL was induced. The reduced response to SDF-1alpha was not due to an inability of BCR/ABL-transformed cell lines to migrate in general, as spontaneous motility of BCR/ABL-transformed cells was increased. In mice, injection of SDF-1alpha into the spleen resulted in a transient accumulation of untransformed Ba/F3 cells, but not Ba/F3. p210(BCR/ABL) cells administered simultaneously. The mechanism may involve inhibition of CXCR-4 receptor function, because in BCR/ABL-transformed cells, CXCR-4 receptors were expressed on the cell surface, but SDF-1alpha calcium flux was inhibited. Because SDF-1alpha and CXCR-4 are felt to be involved in progenitor cell homing to marrow, the abnormality decribed here could contribute to the homing and retention defects typical of immature myeloid cells in chronic myelogenous leukemia.

BCR-ABL and v-SRC tyrosine kinase oncoproteins support normal erythroid development in erythropoietin receptor-deficient progenitor cells

Erythropoietin (Epo)-independent differentiation of erythroid progenitors is a major characteristic of myeloproliferative disorders, including chronic myeloid leukemia. Epo receptor (EpoR) signaling is crucial for normal erythroid development, as evidenced by the properties of Epo(-/-) and EpoR(-/-) mice, which contain a normal number of fetal liver erythroid progenitors but die in utero from a severe anemia attributable to the absence of red cell maturation. Here we show that two constitutively active cytoplasmic protein tyrosine kinases, P210(BCR-ABL) and v-SRC, can functionally replace the EpoR and support full proliferation, differentiation, and maturation of fetal liver erythroid progenitors from EpoR(-/-) mice. These protein tyrosine kinases can also partially complement the myeloid growth factors IL-3, IL-6, and Steel factor, which are normally required in addition to Epo for erythroid development. Additionally, BCR-ABL mutants that lack residues necessary for transformation of fibroblasts or bone marrow cells can fully support normal erythroid development. These results demonstrate that activated tyrosine kinase oncoproteins implicated in tumorigenesis and human leukemia can functionally complement for cytokine receptor signaling pathways to support normal erythropoiesis in EpoR-deficient cells. Moreover, terminal differentiation of erythroid cells requires generic signals provided by activated protein tyrosine kinases and does not require a specific signal unique to a cytokine receptor.

Growth factor independence and BCR/ABL transformation: promise and pitfalls of murine model systems and assays

The expression of the BCR-ABL fusion oncoprotein in primitive hematopoietic cells results in chronic myeloid leukemia. Over the past decade studies of several in vitro and in vivo cell systems revealed multiple signal transduction pathways activated by BCR-ABL. However, the precise function of BCR-ABL in the pathogenesis of CML is still unclear. The goal of this review is to synthesize data on intracellular signaling in the context of the diverse murine assay systems employed. We emphasize the importance of in vivo assays and assays using primary cells in understanding the biology of CML and the molecular mechanisms by which BCR-ABL exerts its effects.

Characterization of single-nucleotide polymorphisms in coding regions of human genes

A major goal in human genetics is to understand the role of common genetic variants in susceptibility to common diseases. This will require characterizing the nature of gene variation in human populations, assembling an extensive catalogue of single-nucleotide polymorphisms (SNPs) in candidate genes and performing association studies for particular diseases. At present, our knowledge of human gene variation remains rudimentary. Here we describe a systematic survey of SNPs in the coding regions of human genes. We identified SNPs in 106 genes relevant to cardiovascular disease, endocrinology and neuropsychiatry by screening an average of 114 independent alleles using 2 independent screening methods. To ensure high accuracy, all reported SNPs were confirmed by DNA sequencing. We identified 560 SNPs, including 392 coding-region SNPs (cSNPs) divided roughly equally between those causing synonymous and non-synonymous changes. We observed different rates of polymorphism among classes of sites within genes (non-coding, degenerate and non-degenerate) as well as between genes. The cSNPs most likely to influence disease, those that alter the amino acid sequence of the encoded protein, are found at a lower rate and with lower allele frequencies than silent substitutions. This likely reflects selection acting against deleterious alleles during human evolution. The lower allele frequency of missense cSNPs has implications for the compilation of a comprehensive catalogue, as well as for the subsequent application to disease association.

The P190, P210, and P230 forms of the BCR/ABL oncogene induce a similar chronic myeloid leukemia-like syndrome in mice but have different lymphoid leukemogenic activity

The product of the Philadelphia chromosome (Ph) translocation, the BCR/ABL oncogene, exists in three principal forms (P190, P210, and P230 BCR/ABL) that are found in distinct forms of Ph-positive leukemia, suggesting the three proteins have different leukemogenic activity. We have directly compared the tyrosine kinase activity, in vitro transformation properties, and in vivo leukemogenic activity of the P190, P210, and P230 forms of BCR/ABL. P230 exhibited lower intrinsic tyrosine kinase activity than P210 and P190. Although all three oncogenes transformed both myeloid (32D cl3) and lymphoid (Ba/F3) interleukin (IL)-3-dependent cell lines to become independent of IL-3 for survival and growth, their ability to stimulate proliferation of Ba/F3 lymphoid cells differed and correlated directly with tyrosine kinase activity. In a murine bone marrow transduction/transplantation model, the three forms of BCR/ABL were equally potent in the induction of a chronic myeloid leukemia (CML)-like myeloproliferative syndrome in recipient mice when 5-fluorouracil (5-FU)-treated donors were used. Analysis of proviral integration showed the CML-like disease to be polyclonal and to involve multiple myeloid and B lymphoid lineages, implicating a primitive multipotential target cell. Secondary transplantation revealed that only certain minor clones gave rise to day 12 spleen colonies and induced disease in secondary recipients, suggesting heterogeneity among the target cell population. In contrast, when marrow from non- 5-FU-treated donors was used, a mixture of CML-like disease, B lymphoid acute leukemia, and macrophage tumors was observed in recipients. P190 BCR/ABL induced lymphoid leukemia with shorter latency than P210 or P230. The lymphoid leukemias and macrophage tumors had provirus integration patterns that were oligo- or monoclonal and limited to the tumor cells, suggesting a lineage-restricted target cell with a requirement for additional events in addition to BCR/ABL transduction for full malignant transformation. These results do not support the hypothesis that P230 BCR/ABL induces a distinct and less aggressive form of CML in humans, and suggest that the rarity of P190 BCR/ABL in human CML may reflect infrequent BCR intron 1 breakpoints during the genesis of the Ph chromosome in stem cells, rather than intrinsic differences in myeloid leukemogenicity between P190 and P210.

Secondary mutation maintains the transformed state in BaF3 cells with inducible BCR/ABL expression

The BCR/ABL gene product of the Philadelphia (Ph) chromosome induces chronic myelogenous leukemia (CML). We generated a hematopoietic cell line, TonB210.1, with tetracycline-dependent BCR/ABL expression to investigate the pathways by which BCR/ABL transforms cells. TonB210.1 demonstrates conditional growth factor independence in tissue culture and rapidly forms tumors in mice fed the tetracycline analog doxycycline. The tumors regress completely upon doxycycline withdrawal, but ultimately reform in all animals. After a long latency, tumors also develop in animals never exposed to doxycycline. Subclones of TonB210.1 established from doxycycline-independent tumors demonstrate distinct mechanisms of transformation. Most subclones manifest increased basal levels of BCR/ABL expression; some have lost the capacity to augment expression upon induction, whereas others remain inducible. More interestingly, some subclones maintain tight conditional expression of BCR/ABL and are therefore transformed by secondary mechanisms that no longer require BCR/ABL expression. These subclones show constitutive phosphorylation of the STAT5 protein, suggesting that activating mutations have occurred upstream in the signaling pathway to STAT5. The tight conditional expression of BCR/ABL in the TonB210.1 cell line affords the opportunity to study several interesting aspects of the biology of BCR/ABL, including activation of critical signaling pathways and transcriptional programs, and its potential role in genomic instability.

Hematopoietic remodeling in interferon-gamma-deficient mice infected with mycobacteria

Control of intracellular bacterial infections requires interferon-gamma (IFN-gamma) both for establishing a Th1 T-cell response and for activating macrophages to kill the bacteria. Exposure of mice deficient in IFN-gamma to mycobacterial infection produces an immune response characterized by a Th2 T-cell phenotype, florid bacterial growth, and death. We report here that IFN-gamma-deficient mice infected with mycobacteria also undergo a dramatic remodeling of the hematopoietic system. Myeloid cell proliferation proceeds unchecked throughout the course of mycobacterial infection, resulting in a transition to extramedullary hematopoiesis. The splenic architecture of infected IFN-gamma-deficient mice is completely effaced by expansion of macrophages, granulocytes, and extramedullary hematopoietic tissue. These features coincide with splenomegaly, an increase in splenic myeloid colony-forming activity, and marked granulocytosis in the peripheral blood. Systemic levels of cytokines are elevated, particularly interleukin-6 (IL-6) and granulocyte colony-stimulating factor (G-CSF). These results suggest that in addition to its central role in cellular immunity, IFN-gamma may be a key cytokine in coordinate regulation of immune effector cells and myelopoiesis. This model should be valuable for deciphering the cross-talk between the immune response and hematopoiesis during bacterial infection and for improving our understanding of the mechanisms that control chronic infections.

A novel method to isolate cells with conditional gene expression using fluorescence activated cell sorting

An inducible expression system using control elements of the tetracycline resistance operon has recently shown promise for conditional gene expression of any gene of interest. However, intensive screening of multiple independent clones is often required to find cell lines with optimal induction characteristics. By coupling expression of the gene of interest with a fluorescent marker, we have developed a novel fluorescence activated cell sorting (FACS) based strategy to isolate cells with desirable expression characteristics, thus alleviating the laborious isolation and analysis of multiple independent clones.

Rationalizing autotransplant strategies for chronic myeloid leukemia

The molecular genetic basis of chronic myeloid leukemia (CML) is well-defined, but until recently therapeutic approaches have been largely empiric. Conventional chemotherapy and interferon offer palliation, but only bone marrow transplantation provides for cure. Because the majority of CML patients are not candidates for allogeneic transplantation, autologous strategies have emerged as an alternative. Data from murine models of CML provide insights into the mechanisms by which autotransplant might be effective in the treatment of CML. Further dissection of the molecular pathways by which the BCR/ABL protein can induce leukemia offers the promise of a more targeted, rationally-designed therapy. When used for remission maintenance therapy following autologous bone marrow transplantation, specific inhibitors of BCR/ABL should provide for long term disease-free survival.

Autologous transplant for CML revisited

A chronic myelogenous leukemia (CML)-like disease can be induced in mice by infecting hematopoietic stem cells with a BCR/ABL-containing retrovirus; serial transplantation produces either normal or leukemic animals. In many patients with CML, autografting produces transient Philadelphia chromosome (Ph)-negativity, but Ph-negative hematopoiesis is prolonged in some cases. These and other observations suggest that at diagnosis, CML patients may have substantial numbers of normal stem cells in their marrow, which may in certain circumstances regain a proliferative advantage if leukemic hematopoiesis can be suppressed by intensive chemotherapy. Thus autografting may have the capacity to restore normal hematopoiesis for long periods in patients not eligible for treatment by allogeneic bone marrow transplantation.

Animal models of BCR/ABL-induced leukemias

Chronic myelogenous leukemia (CML) serves as a valuable paradigm for understanding the molecular genetic origins of cancer. The cytogenetic standard of diagnosis, the Philadelphia chromosome, has been superseded by a molecular definition for the disease, that of BCR/ABL gene rearrangement. The use of BCR/ABL to recreate CML in mice fulfills Koch's postulates for molecular pathogenesis. The present murine systems facilitate research into the biology of BCR/ABL-induced leukemias, but fall short in their promise to provide models for testing new therapies for CML. A transgenic strain of mice with an inheritable predisposition to CML would be an invaluable tool.

Aging and reactivation of latent murine cytomegalovirus

BALB/c mice were experimentally infected with murine cytomegalovirus (MCMV) to discover whether latent MCMV persisted in aging mice and to examine the effect of aging on MCMV reactivation. Latently infected mice received saline, cyclophosphamide, or allogeneic blood at 6 and 18 months of age. MCMV DNA was detected by polymerase chain reaction in submaxillary salivary gland biopsy specimens from saline-treated young and old mice. Evidence of MCMV reactivation was sought by culture of biopsy specimens and by MCMV IgG ELISA of pre- and posttreatment sera from all animals. Very few cyclophosphamide- or saline-treated mice reactivated MCMV at either age, but young transfused mice reactivated MCMV significantly more often than did old transfused mice. These experiments indicate that MCMV DNA persists in the salivary gland of aging mice but that the likelihood of MCMV reactivation does not increase with age.

Nonmyristoylated Abl proteins transform a factor-dependent hematopoietic cell line

N-terminal myristoylation can promote the association of proteins with the plasma membrane, a property that is required for oncogenic variants of Src and Abl to transform fibroblastic cell types. The P210bcr/abl protein of chronic myelogenous leukemia cells is not myristoylated and does not stably transform NIH 3T3 fibroblasts; however, it will transform lymphoid and myeloid cell types in vitro and in vivo, suggesting that myristoylation is not required for Abl variants to transform hematopoietic cells. To test this hypothesis, we introduced point mutations that disrupt myristoylation into two activated Abl proteins, v-Abl and a deletion mutant of c-Abl (delta XB), and examined their ability to transform an interleukin-3-dependent lymphoblastoid cell line, Ba/F3. Neither of the nonmyristoylated Abl proteins transformed NIH 3T3 fibroblasts, but like P210bcr/abl, both were capable of transforming the Ba/F3 cells to factor independence and tumorigenicity. Nonmyristoylated Abl variants did not associate with the plasma membrane in the transformed Ba/F3 cells. These results demonstrate that Abl proteins can transform hematopoietic cells in the absence of membrane association and suggest that distinct functions of Abl are required for transformation of fibroblast and hematopoietic cell types.

Blast crisis in a murine model of chronic myelogenous leukemia

The P210bcr/abl protein is produced in cells from patients with Philadelphia chromosome-positive chronic myelogenous leukemia (CML). Retroviral transfer of the gene encoding P210bcr/abl into murine bone marrow induces a granulocytic leukemia that models the chronic phase of human CML. We have transferred the leukemic clone to syngeneic animals, albeit with surprising inefficiency, and have observed CML and clonally related acute leukemias of lymphoid or myeloid phenotype in some transplant recipients. These data show that murine CML can result from retroviral transfer of the bcr/abl gene into pluripotent hematopoietic stem cells, that infected clones repopulate poorly after adoptive transfer, and that these clones can give rise to acute leukemia, reflecting evolution to a phase resembling blast crisis in the human disease.

v-abl causes hematopoietic disease distinct from that caused by bcr-abl

v-abl, the oncogene transduced by Abelson murine leukemia virus, was first characterized by its ability to transform lymphoid cells. bcr-abl, the oncogene formed by a t(9;22) translocation thought to occur in human hematopoietic stem cells, is detectable in almost all cases of chronic myelogenous leukemia (CML), a malignancy of granulocytic cells. bcr-abl also causes a CML-like syndrome in mice whose bone-marrow cells are infected with a retrovirus transducing the gene. More recent reports have suggested that v-abl can, however, cause a disease similar to CML. We demonstrate here that v-abl, when transduced in a helper virus-containing system, causes disease similar to, but distinct from, the CML-like syndrome induced by bcr-abl. Animals whose bone marrow has been infected by v-abl virus develop modest splenomegaly, marked granulocytosis, and malignant disease of several hematopoietic cell types. Unlike animals with CML-like disease resulting from bcr-abl, the polymorphonuclear leukocytes from animals infected with a v-abl construct do not contain the v-abl provirus at a significant frequency. Histopathologic analysis also shows significant differences between the diseases caused by v-abl and bcr-abl.

Activation of phosphatidylinositol 3-kinase in cells expressing abl oncogene variants

A phosphoinositide kinase specific for the D-3 position of the inositol ring, phosphatidylinositol (PI) 3-kinase, associates with activated receptors for platelet-derived growth factor, insulin, and colony-stimulating factor 1, with products of the oncogenes src, fms, yes, crk, and with polyomavirus middle T antigen. Efficient fibroblast transformation by proteins of the abl and src oncogene families requires activation of their protein-tyrosine kinase activity and membrane association via an amino-terminal myristoylation. We have demonstrated that the PI 3-kinase directly associates with autophosphorylated, activated protein-tyrosine kinase variants of the abl protein. In vivo, this association leads to accumulation of the highly phosphorylated products of PI 3-kinase, PI-3,4-bisphosphate and PI-3,4,5-trisphosphate, only in myristoylated, transforming abl protein variants. Myristoylation thus appears to be required to recruit PI 3-kinase activity to the plasma membrane for in vivo activation and correlates with the mitogenicity of the abl protein variants.

Induction of chronic myelogenous leukemia in mice by the P210bcr/abl gene of the Philadelphia chromosome

In tumor cells from virtually all patients with chronic myelogenous leukemia, the Philadelphia chromosome, a fusion of chromosomes 9 and 22, directs the synthesis of the P210bcr/abl protein. The protein-tyrosine kinase activity and hybrid structure of P210bcr/abl are similar to the oncogene product of the Abelson murine leukemia virus, P160gag/v-abl, which induces acute lymphomas. To determine whether P210bcr/abl can induce chronic myelogenous leukemia, murine bone marrow was infected with a retrovirus encoding P210bcr/abl and transplanted into irradiated syngeneic recipients. Transplant recipients developed several hematologic malignancies; prominent among them was a myeloproliferative syndrome closely resembling the chronic phase of human chronic myelogenous leukemia. Tumor tissue from diseased mice harbored the provirus encoding P210bcr/abl. These results demonstrate that P210bcr/abl expression can induce chronic myelogenous leukemia. Retrovirus-mediated expression of the protein provides a murine model system for further analysis of the disease.

Induction of chronic myelogenous leukemia in mice by the P210bcr/abl gene of the Philadelphia chromosome

In tumor cells from virtually all patients with chronic myelogenous leukemia, the Philadelphia chromosome, a fusion of chromosomes 9 and 22, directs the synthesis of the P210bcr/abl protein. The protein-tyrosine kinase activity and hybrid structure of P210bcr/abl are similar to the oncogene product of the Abelson murine leukemia virus, P160gag/v-abl, which induces acute lymphomas. To determine whether P210bcr/abl can induce chronic myelogenous leukemia, murine bone marrow was infected with a retrovirus encoding P210bcr/abl and transplanted into irradiated syngeneic recipients. Transplant recipients developed several hematologic malignancies; prominent among them was a myeloproliferative syndrome closely resembling the chronic phase of human chronic myelogenous leukemia. Tumor tissue from diseased mice harbored the provirus encoding P210bcr/abl. These results demonstrate that P210bcr/abl expression can induce chronic myelogenous leukemia. Retrovirus-mediated expression of the protein provides a murine model system for further analysis of the disease.

Transformation of an interleukin 3-dependent hematopoietic cell line by the chronic myelogenous leukemia-specific P210bcr/abl protein

The P210bcr/abl protein is associated with virtually every case of human chronic myelogenous leukemia. Unlike the related P160gag/v-abl oncogene product of Abelson murine leukemia virus, P210bcr/abl does not transform NIH 3T3 fibroblasts. To assess whether P210bcr/abl might transform hematopoietic cell types, retroviral constructs encoding P210bcr/abl were used to infect the bone marrow-derived interleukin 3-dependent Ba/F3 cell line. As for P160gag/v-abl, cell lines expressing P210bcr/abl were growth factor independent and tumorigenic in nude mice. No evidence for autocrine production of interleukin 3 by factor-independent cell lines was found. These experiments establish that P210bcr/abl can transform hematopoietic cell types to tumorigenicity.

The CML-specific P210 bcr/abl protein, unlike v-abl, does not transform NIH/3T3 fibroblasts

The v-abl oncogene of the Abelson murine leukemia virus (A-MuLV) is known to efficiently transform NIH/3T3 fibroblasts in vitro and to cause an acute lymphosarcoma in susceptible murine hosts. The role of its relative, the bcr/abl gene product, in the etiology of human chronic myelogenous leukemia (CML) remains speculative. To assess the transforming properties of the bcr/abl gene product, complementary DNA clones encoding the CML-specific P210 bcr/abl protein were expressed in NIH/3T3 fibroblasts. In contrast to the v-abl oncogene product P160, the P210 bcr/abl gene product did not transform NIH/3T3 cells. Cell lines were isolated that expressed high levels of the P210 bcr/abl protein but were morphologically normal. During the course of these experiments, a transforming recombinant of bcr/abl was isolated which fuses gag determinants derived from helper virus to the NH2-terminus of the bcr/abl protein. This suggests that a property of viral gag sequences, probably myristylation-dependent membrane localization, must be provided to bcr/abl for it to transform fibroblasts.

Overlapping cDNA clones define the complete coding region for the P210c-abl gene product associated with chronic myelogenous leukemia cells containing the Philadelphia chromosome

The Philadelphia chromosome, observed in greater than 90% of patients with chronic myelogenous leukemia, results from a reciprocal translocation between chromosomes 9 and 22. The translocation breakpoint on chromosome 9 occurs near the ABL gene and correlates with the production of a chronic myelogenous leukemia-specific 8.5-kilobase ABL-related mRNA species accompanied by a structurally altered ABL protein (P210c-abl). The N-terminal sequence of the protein is derived from the BCR gene on chromosome 22. We have isolated overlapping cDNA clones from the K-562 cell line corresponding to approximately 8.5 kilobases of mRNA and have sequenced 2550 nucleotides at the 5' end. Our results indicate that the 5' end of the 8.5-kilobase mRNA consists of greater than 400 nucleotides of noncoding sequence that are greater than 80% G + C rich. Based on our sequence analysis, we propose that initiation of translation occurs at nucleotide 471, such that the initial 927 amino acids of P210c-abl are derived from BCR sequences. Our cDNA clones thus define the complete coding sequences for the P210c-abl gene product.

The chronic myelogenous leukemia-specific P210 protein is the product of the bcr/abl hybrid gene

Chronic myelogenous leukemia (CML) is a human disease associated with a consistent chromosomal translocation that results in sequences from the c-abl locus on chromosome 9 being fused to sequences in a breakpoint cluster region (bcr) on chromosome 22. CML cells have two novel products: an 8.5-kilobase RNA transcript containing both abl and bcr and a 210-kilodalton phosphoprotein (P210) recognized by v-abl-specific antisera. To test whether the P210 is the product of the novel 8.5-kilobase bcr/abl fusion transcript, antibodies were prepared against c-abl and bcr determinants. By using these reagents and v-abl-specific antisera, it was demonstrated that the P210 in CML cells is indeed the protein product of the 8.5-kilobase transcript. By analogy to the gag/abl fusion protein of Abelson murine leukemia virus, the replacement of amino terminal c-abl sequences by bcr sequences in P210 may create a transforming protein involved in CML. A 190-kilodalton phosphoprotein that is a candidate for the normal bcr protein was identified in both HeLa and K562 cells.

The chronic myelogenous leukemia-specific P210 protein is the product of the bcr/abl hybrid gene

Chronic myelogenous leukemia (CML) is a human disease associated with a consistent chromosomal translocation that results in sequences from the c-abl locus on chromosome 9 being fused to sequences in a breakpoint cluster region (bcr) on chromosome 22. CML cells have two novel products: an 8.5-kilobase RNA transcript containing both abl and bcr and a 210-kilodalton phosphoprotein (P210) recognized by v-abl-specific antisera. To test whether the P210 is the product of the novel 8.5-kilobase bcr/abl fusion transcript, antibodies were prepared against c-abl and bcr determinants. By using these reagents and v-abl-specific antisera, it was demonstrated that the P210 in CML cells is indeed the protein product of the 8.5-kilobase transcript. By analogy to the gag/abl fusion protein of Abelson murine leukemia virus, the replacement of amino terminal c-abl sequences by bcr sequences in P210 may create a transforming protein involved in CML. A 190-kilodalton phosphoprotein that is a candidate for the normal bcr protein was identified in both HeLa and K562 cells.

Alternative 5' exons in c-abl mRNA

The cellular abl proto-oncogene encodes a protein-tyrosine kinase and is expressed in many cell types in two or three mRNA size species. Four types of mouse c-abl cDNAs have been cloned from 70Z/3 lymphoid cells that have different 5' sequences encoding predicted N-terminal regions of 20-45 amino acids. One of the four cDNAs has a predicted N-terminal sequence of met-gly-gln in common with the gag N terminus of v-abl. The 5' heterogeneity appears to be generated by alternative addition of 5' exons onto a common set of 3' exons. Alternative splicing occurs at the same site at which bcr sequences join to abl sequences in the Philadelphia chromosome translocation.