Gutierrez A, Sanda T, Grebliunaite R, Carracedo A, Salmena L, Ahn Y, Dahlberg S, Neuberg D, Moreau LA, Winter SS, Larson R, Zhang J, Protopopov A, Chin L, Pandolfi PP, Silverman LB, Hunger SP, Sallan SE, Look AT. High frequency of PTEN, PI3K and AKT abnormalities in T cell acute lymphoblastic leukemia. Blood. 2009 Jul 16;114(3):647-50. Epub 2009 May 20.
Abstract
To more comprehensively assess the pathogenic contribution of the PTEN-PI3K-AKT pathway to T-cell acute lymphoblastic leukemia (T-ALL), we examined diagnostic DNA samples from children with T-ALL using array comparative genomic hybridization and sequence analysis. Alterations of PTEN, PI3K, or AKT were identified in 47.7% of 44 cases. There was a striking clustering of PTEN mutations in exon 7 in 12 cases, all of which were predicted to truncate the C2 domain without disrupting the phosphatase domain of PTEN. Induction chemotherapy failed to induce remission in 3 of the 4 patients whose lymphoblasts harbored PTEN deletions at the time of diagnosis, compared with none of the 12 patients with mutations of PTEN exon 7 (P = .007), suggesting that PTEN deletion has more adverse therapeutic consequences than mutational disruptions that preserve the phosphatase domain. These findings add significant support to the rationale for the development of therapies targeting the PTEN-PI3K-AKT pathway in T-ALL.
Rhodes J, Amsterdam A, Sanda T, Moreau LA, McKenna K, Heinrichs S, Ganem NJ, Ho KW, Neuberg DS, Johnston A, Ahn Y, Kutok JL, Hromas R, Wray J, Lee C, Murphy C, Radtke I, Downing JR, Fleming MD, MacConaill LE, Amatruda JF, Gutierrez A, Galinsky I, Stone RM, Ross EA, Pellman DS, Kanki JP, Look AT. Emi1 maintains genomic integrity during zebrafish embryogenesis and cooperates with p53 in tumor suppression.Mol Cell Biol. 2009 Nov;29(21):5911-22. Epub 2009 Aug 24.
Abstract
A growing body of evidence indicates that early mitotic inhibitor 1 (Emi1) is essential for genomic stability, but how this function relates to embryonic development and cancer pathogenesis remains unclear. We have identified a zebrafish mutant line in which deficient emi1 gene expression results in multilineage hematopoietic defects and widespread developmental defects that are p53 independent. Cell cycle analyses of Emi1-depleted zebrafish or human cells showed chromosomal rereplication, and metaphase preparations from mutant zebrafish embryos revealed rereplicated, unsegregated chromosomes and polyploidy. Furthermore, EMI1-depleted mammalian cells relied on topoisomerase II alpha-dependent mitotic decatenation to progress through metaphase. Interestingly, the loss of a single emi1 allele in the absence of p53 enhanced the susceptibility of adult fish to neural sheath tumorigenesis. Our results cast Emi1 as a critical regulator of genomic fidelity during embryogenesis and suggest that the factor may act as a tumor suppressor.
Sidi S, Sanda T, Kennedy RD, Hagen AT, Jette CA, Hoffmans R, Pascual J, Imamura S, Kishi S, Amatruda JF, Kanki JP, Green DR, D'Andrea AA, Look AT. Chk1 suppresses a caspase-2 apoptotic response to DNA damage that bypasses p53, Bcl-2, and caspase-3. Cell. 2008 May 30;133(5):864-77.
Abstract
Evasion of DNA damage-induced cell death, via mutation of the p53 tumor suppressor or overexpression of prosurvival Bcl-2 family proteins, is a key step toward malignant transformation and therapeutic resistance. We report that depletion or acute inhibition of checkpoint kinase 1 (Chk1) is sufficient to restore gamma-radiation-induced apoptosis in p53 mutant zebrafish embryos. Surprisingly, caspase-3 is not activated prior to DNA fragmentation, in contrast to classical intrinsic or extrinsic apoptosis. Rather, an alternative apoptotic program is engaged that cell autonomously requires atm (ataxia telangiectasia mutated), atr (ATM and Rad3-related) and caspase-2, and is not affected by p53 loss or overexpression of bcl-2/xl. Similarly, Chk1 inhibitor-treated human tumor cells hyperactivate ATM, ATR, and caspase-2 after gamma-radiation and trigger a caspase-2-dependent apoptotic program that bypasses p53 deficiency and excess Bcl-2. The evolutionarily conserved "Chk1-suppressed" pathway defines a novel apoptotic process, whose responsiveness to Chk1 inhibitors and insensitivity to p53 and BCL2 alterations have important implications for cancer therapy.
Jette CA, Flanagan AM, Ryan J, Pyati UJ, Carbonneau S, Stewart RA, Langenau DM, Look AT, Letai A. BIM and other BCL-2 family proteins exhibit cross-species conservation of function between zebrafish and mammals. Cell Death Differ. 2008 Jun;15(6):1063-72. Epub 2008 Apr 11.
Abstract
Here we investigate the function of zebrafish Bcl-2 family proteins and demonstrate important conservation of function across zebrafish and mammalian systems. We have isolated a zebrafish ortholog of mammalian BIM and show that it is the most toxic of the zebrafish BH3-only genes examined, sharing this characteristic with the mammalian BIM gene. The zebrafish bad gene shows a complete lack of embryonic lethality, but like mammalian BAD, its pro-apoptotic activity is regulated through phosphorylation of critical serines. We also found that the pattern of mitochondrial dysfunction observed by zebrafish BH3 domain peptides in a mammalian cytochrome c release assay recapitulates the pattern of embryonic lethality induced by the respective mRNA injections in vivo. In contrast to zebrafish Bim, Bid exhibited only weak binding to zebrafish Bcl-2 and moderate-to-weak overall lethality in zebrafish embryos and isolated mitochondria. Given that zebrafish Bcl-2 binds strongly to mammalian BID and BIM peptides and proteins, the protein identified as the zebrafish Bid ortholog has different properties than mammalian BID. Overall, our results demonstrate the high degree of functional conservation between zebrafish and mammalian Bcl-2 family proteins, thus validating the zebrafish as a model system to further dissect the molecular mechanisms that regulate apoptosis in future forward genetic and chemical modifier screens.
O'Neil J, Tchinda J, Gutierrez A, Moreau L, Maser RS, Wong KK, Li W, McKenna K, Liu XS, Feng B, Neuberg D, Silverman L, DeAngelo DJ, Kutok JL, Rothstein R, DePinho RA, Chin L, Lee C, Look AT. Alu elements mediate MYB gene tandem duplication in human T-ALL. J Exp Med. 2007 Dec 24;204(13):3059-66. Epub 2007 Dec 10
Abstract
Recent studies have demonstrated that the MYB oncogene is frequently duplicated in human T cell acute lymphoblastic leukemia (T-ALL). We find that the human MYB locus is flanked by 257-bp Alu repeats and that the duplication is mediated somatically by homologous recombination between the flanking Alu elements on sister chromatids. Nested long-range PCR analysis indicated a low frequency of homologous recombination leading to MYB tandem duplication in the peripheral blood mononuclear cells of approximately 50% of healthy individuals, none of whom had a MYB duplication in the germline. We conclude that Alu-mediated MYB tandem duplication occurs at low frequency during normal thymocyte development and is clonally selected during the molecular pathogenesis of human T-ALL.
Feng H, Langenau DM, Madge JA, Quinkertz A, Gutierrez A, Neuberg DS, Kanki JP, Look AT. Heat-shock induction of T-cell lymphoma/leukaemia in conditional Cre/lox-regulated transgenic zebrafish. Br J Haematol. 2007 Jul;138(2):169-75.
Abstract
The zebrafish is an ideal vertebrate model system to investigate the complex genetic basis of cancer because it has the capacity for in vivo tumour-cell imaging and forward genetic screens, and the molecular mechanisms regulating malignancy are remarkably conserved when compared with human. Our laboratory has previously generated transgenic zebrafish models that overexpress the mouse c-Myc gene fused to enhanced green fluorescent protein (EGFP) and develop T-cell acute lymphoblastic leukaemia (T-ALL) that recapitulates the human disease both molecularly and pathologically. Our previous models have been limited by disease onset prior to sexual maturity and by the low disease penetrance when conditional transgenic embryos are injected with Cre RNA. Here, we report a novel system in which compound transgenic fish expressed both Cre controlled by the heat-shock promoter and a rag2-promoter-regulated lox-dsRED2-lox-EGFP-mMyc cassette rag2-LDL-EMyc in developing T cells. After heat-shock treatment at 3 d postfertilisation (dpf) for 45 min at 37 degrees C, 81% of compound transgenic fish developed T-lymphoblastic lymphoma (T-LBL, mean latency 120 +/- 43 (standard deviation) days of life), which rapidly progressed to T-ALL. Heat-shock-regulated transgenic technology in zebrafish provides the missing link necessary to exploit the powerful genetic capacity of this organism to probe the multi-step molecular pathogenesis of leukaemia.
Grabher C, von Boehmer H, Look AT. Notch 1 activation in the molecular pathogenesis of T-cell acute lymphoblastic leukaemia. Nat Rev Cancer. 2006 May;6(5):347-59.
Abstract
The chromosomal translocation t(7;9) in human T-cell acute lymphoblastic leukaemia (T-ALL) results in deregulated expression of a truncated, activated form of Notch 1 (TAN1) under the control of the T-cell receptor-beta (TCRB) locus. Although TAN1 efficiently induces T-ALL in mouse models, t(7;9) is present in less than 1% of human T-ALL cases. The recent discovery of novel activating mutations in NOTCH1 in more than 50% of human T-ALL samples has made it clear that Notch 1 is far more important in human T-ALL pathogenesis than previously suspected.
Stewart RA, Arduini BL, Berghmans S, George RE, Kanki JP, Henion PD, Look AT. Zebrafish foxd3 is selectively required for neural crest specification, migration and survival. Dev Biol. 2006 Apr 1;292(1):174-88. Epub 2006 Feb 23.
Abstract
The vertebrate neural crest is a pluripotent cell population that generates a large variety of cell types, including peripheral neurons, cartilage and pigment cells. Mechanisms that control the patterning of the neural crest toward specific cell fates remain only partially understood. Zebrafish homozygous for the sympathetic mutation 1 (sym1) have defects in a subset of neural crest derivatives, such as peripheral neurons, glia and cartilage, but retain normal numbers of melanocytes. The sym1 mutation is a nucleotide deletion that disrupts the forkhead DNA-binding domain of the foxd3 gene, which encodes a conserved winged-helix transcription factor. We show that sym1 mutants have normal numbers of premigratory neural crest cells, but these cells express reduced levels of snai1b and sox10, implicating foxd3 as an essential regulator of these transcription factors in the premigratory neural crest. The onset of neural crest migration is also delayed in sym1 mutants, and there is a reduction in the number of migratory trunk neural crest cells, particularly along the medial migration pathway. TUNEL analysis revealed aberrant apoptosis localized to the hindbrain neural crest at the 15-somite stage, indicating a critical role for foxd3 in the survival of a subpopulation of neural crest cells. These results show that foxd3 selectively specifies premigratory neural crest cells for a neuronal, glial or cartilage fate, by inducing the expression of lineage-associated transcription factors in these cells and regulating their subsequent migration.
Langenau DM, Feng H, Berghmans S, Kanki JP, Kutok JL, Look AT. Cre/lox-regulated transgenic zebrafish model with conditional myc-induced T cell acute lymphoblastic leukemia. Proc Natl Acad Sci U S A. 2005 Apr 26;102(17):6068-73. Epub 2005 Apr 12.
Abstract
We have created a stable transgenic rag2-EGFP-mMyc zebrafish line that develops GFP-labeled T cell acute lymphoblastic leukemia (T-ALL), allowing visualization of the onset and spread of this disease. Here, we show that leukemias from this transgenic line are highly penetrant and render animals moribund by 80.7 +/- 17.6 days of life (+/-1 SD, range = 50-158 days). These T cell leukemias are clonally aneuploid, can be transplanted into irradiated recipient fish, and express the zebrafish orthologues of the human T-ALL oncogenes tal1/scl and lmo2, thus providing an animal model for the most prevalent molecular subgroup of human T-ALL. Because T-ALL develops very rapidly in rag2-EGFP-mMyc transgenic fish (in which "mMyc" represents mouse c-Myc), this line can only be maintained by in vitro fertilization. Thus, we have created a conditional transgene in which the EGFP-mMyc oncogene is preceded by a loxed dsRED2 gene and have generated stable rag2-loxP-dsRED2-loxP-EGFP-mMyc transgenic zebrafish lines, which have red fluorescent thymocytes and do not develop leukemia. Transgenic progeny from one of these lines can be induced to develop T-ALL by injecting Cre RNA into one-cell-stage embryos, demonstrating the utility of the Cre/lox system in the zebrafish and providing an essential step in preparing this model for chemical and genetic screens designed to identify modifiers of Myc-induced T-ALL.
Heinrichs S, Berman JN, Ortiz TM, Kornblau SM, Neuberg DS, Estey EH, Look AT. CD34+ cell selection is required to assess HOXA9 expression levels in patients with myelodysplastic syndrome. Br J Haematol. 2005 Jul;130(1):83-6.
Abstract
Overexpression of HOXA9 is linked to the molecular pathogenesis of acute myeloid leukaemia (AML) and myelodysplastic syndrome (MDS), conferring a poor prognosis. HOXA9 expression levels were analysed in the diagnostic bone marrow (BM) samples of 13 MDS patients. HOXA9 was expressed by CD34(+) BM cells at median levels 3.1-fold higher than in CD34(-) cells from the same patient and at median levels 4.3-fold higher than in CD34(+) cells from healthy donors. These results indicate that CD34(+) cell selection is required to accurately assess the expression levels of HOXA9 and related genes in the multipotential malignant progenitor cells of MDS patients.
Langenau DM, Ferrando AA, Traver D, Kutok JL, Hezel JP, Kanki JP, Zon LI, Look AT, Trede NS. In vivo tracking of T cell development, ablation, and engraftment in transgenic zebrafish. Proc Natl Acad Sci U S A. 2004 May 11;101(19):7369-74. Epub 2004 May 3.
Abstract
Transgenic zebrafish that express GFP under control of the T cell-specific tyrosine kinase (lck) promoter were used to analyze critical aspects of the immune system, including patterns of T cell development and T cell homing after transplant. GFP-labeled T cells could be ablated in larvae by either irradiation or dexamethasone added to the water, illustrating that T cells have evolutionarily conserved responses to chemical and radiation ablation. In transplant experiments, thymocytes from lck-GFP fish repopulated the thymus of irradiated wild-type fish only transiently, suggesting that the thymus contains only short-term thymic repopulating cells. By contrast, whole kidney marrow permanently reconstituted the T lymphoid compartment of irradiated wild-type fish, suggesting that long-term thymic repopulating cells reside in the kidney.
Yang HW, Kutok JL, Lee NH, Piao HY, Fletcher CD, Kanki JP, Look AT.
Targeted expression of human MYCN selectively causes pancreatic neuroendocrine tumors in transgenic zebrafish. Cancer Res. 2004 Oct 15;64(20):7256-62.
Abstract
The zebrafish model organism has been used extensively for studies of genetic pathways in development, indicating its potential applicability to cancer. Here we show that targeted expression of MYCN in cells of the pancreatic islet induces neuroendocrine carcinoma. Four transgenic fish developed abdominal tumors between 4 and 6 months of age, and histologic analysis revealed lobulated arrangements of neoplastic cells with expression of the MYCN transgene. The tumors also expressed insulin mRNA, and pancreatic exocrine cells and ducts were identified within the neoplasms, indicating a pancreatic origin for the tumor. Transmission electron microscopy revealed cytoplasmic, endocrine-dense core granules, analogous to those found in human neuroendocrine tumors. Our studies establish a zebrafish transgenic model of pancreatic neuroendocrine carcinoma, setting the stage to evaluate molecular pathways downstream of MYCN in this vertebrate forward genetic model system.
Langenau DM, Traver D, Ferrando AA, Kutok JL, Aster JC, Kanki JP, Lin S, Prochownik E, Trede NS, Zon LI, Look AT. Myc-induced T cell leukemia in transgenic zebrafish. Science. 2003 Feb 7;299(5608):887-90.
Abstract
The zebrafish is an attractive model organism for studying cancer development because of its genetic accessibility. Here we describe the induction of clonally derived T cell acute lymphoblastic leukemia in transgenic zebrafish expressing mouse c-myc under control of the zebrafish Rag2 promoter. Visualization of leukemic cells expressing a chimeric transgene encoding Myc fused to green fluorescent protein (GFP) revealed that leukemias arose in the thymus, spread locally into gill arches and retro-orbital soft tissue, and then disseminated into skeletal muscle and abdominal organs. Leukemic cells homed back to the thymus in irradiated fish transplanted with GFP-labeled leukemic lymphoblasts. This transgenic model provides a platform for drug screens and for genetic screens aimed at identifying mutations that suppress or enhance c-myc- induced carcinogenesis.
Hsu K, Look AT. Turning on a dimer: new insights into MLL chimeras. Cancer Cell. 2003 Aug;4(2):81-3.
Abstract
In this issue of Cancer Cell, demonstrate a novel mechanism for the oncogenic activity of MLL chimeric proteins. By providing coiled-coil or other dimerization domains, the cytoplasmic partners of MLL fusion proteins donate a platform for MLL homodimerization, allowing recruitment of accessory factors needed to activate the critical downstream targets, including selected subsets of the major HOX genes.
Abstract
To more comprehensively assess the pathogenic contribution of the PTEN-PI3K-AKT pathway to T-cell acute lymphoblastic leukemia (T-ALL), we examined diagnostic DNA samples from children with T-ALL using array comparative genomic hybridization and sequence analysis. Alterations of PTEN, PI3K, or AKT were identified in 47.7% of 44 cases. There was a striking clustering of PTEN mutations in exon 7 in 12 cases, all of which were predicted to truncate the C2 domain without disrupting the phosphatase domain of PTEN. Induction chemotherapy failed to induce remission in 3 of the 4 patients whose lymphoblasts harbored PTEN deletions at the time of diagnosis, compared with none of the 12 patients with mutations of PTEN exon 7 (P = .007), suggesting that PTEN deletion has more adverse therapeutic consequences than mutational disruptions that preserve the phosphatase domain. These findings add significant support to the rationale for the development of therapies targeting the PTEN-PI3K-AKT pathway in T-ALL.
Abstract
A growing body of evidence indicates that early mitotic inhibitor 1 (Emi1) is essential for genomic stability, but how this function relates to embryonic development and cancer pathogenesis remains unclear. We have identified a zebrafish mutant line in which deficient emi1 gene expression results in multilineage hematopoietic defects and widespread developmental defects that are p53 independent. Cell cycle analyses of Emi1-depleted zebrafish or human cells showed chromosomal rereplication, and metaphase preparations from mutant zebrafish embryos revealed rereplicated, unsegregated chromosomes and polyploidy. Furthermore, EMI1-depleted mammalian cells relied on topoisomerase II alpha-dependent mitotic decatenation to progress through metaphase. Interestingly, the loss of a single emi1 allele in the absence of p53 enhanced the susceptibility of adult fish to neural sheath tumorigenesis. Our results cast Emi1 as a critical regulator of genomic fidelity during embryogenesis and suggest that the factor may act as a tumor suppressor.
Abstract
Evasion of DNA damage-induced cell death, via mutation of the p53 tumor suppressor or overexpression of prosurvival Bcl-2 family proteins, is a key step toward malignant transformation and therapeutic resistance. We report that depletion or acute inhibition of checkpoint kinase 1 (Chk1) is sufficient to restore gamma-radiation-induced apoptosis in p53 mutant zebrafish embryos. Surprisingly, caspase-3 is not activated prior to DNA fragmentation, in contrast to classical intrinsic or extrinsic apoptosis. Rather, an alternative apoptotic program is engaged that cell autonomously requires atm (ataxia telangiectasia mutated), atr (ATM and Rad3-related) and caspase-2, and is not affected by p53 loss or overexpression of bcl-2/xl. Similarly, Chk1 inhibitor-treated human tumor cells hyperactivate ATM, ATR, and caspase-2 after gamma-radiation and trigger a caspase-2-dependent apoptotic program that bypasses p53 deficiency and excess Bcl-2. The evolutionarily conserved "Chk1-suppressed" pathway defines a novel apoptotic process, whose responsiveness to Chk1 inhibitors and insensitivity to p53 and BCL2 alterations have important implications for cancer therapy.
Abstract
Here we investigate the function of zebrafish Bcl-2 family proteins and demonstrate important conservation of function across zebrafish and mammalian systems. We have isolated a zebrafish ortholog of mammalian BIM and show that it is the most toxic of the zebrafish BH3-only genes examined, sharing this characteristic with the mammalian BIM gene. The zebrafish bad gene shows a complete lack of embryonic lethality, but like mammalian BAD, its pro-apoptotic activity is regulated through phosphorylation of critical serines. We also found that the pattern of mitochondrial dysfunction observed by zebrafish BH3 domain peptides in a mammalian cytochrome c release assay recapitulates the pattern of embryonic lethality induced by the respective mRNA injections in vivo. In contrast to zebrafish Bim, Bid exhibited only weak binding to zebrafish Bcl-2 and moderate-to-weak overall lethality in zebrafish embryos and isolated mitochondria. Given that zebrafish Bcl-2 binds strongly to mammalian BID and BIM peptides and proteins, the protein identified as the zebrafish Bid ortholog has different properties than mammalian BID. Overall, our results demonstrate the high degree of functional conservation between zebrafish and mammalian Bcl-2 family proteins, thus validating the zebrafish as a model system to further dissect the molecular mechanisms that regulate apoptosis in future forward genetic and chemical modifier screens.
Abstract
Recent studies have demonstrated that the MYB oncogene is frequently duplicated in human T cell acute lymphoblastic leukemia (T-ALL). We find that the human MYB locus is flanked by 257-bp Alu repeats and that the duplication is mediated somatically by homologous recombination between the flanking Alu elements on sister chromatids. Nested long-range PCR analysis indicated a low frequency of homologous recombination leading to MYB tandem duplication in the peripheral blood mononuclear cells of approximately 50% of healthy individuals, none of whom had a MYB duplication in the germline. We conclude that Alu-mediated MYB tandem duplication occurs at low frequency during normal thymocyte development and is clonally selected during the molecular pathogenesis of human T-ALL.
Abstract
The zebrafish is an ideal vertebrate model system to investigate the complex genetic basis of cancer because it has the capacity for in vivo tumour-cell imaging and forward genetic screens, and the molecular mechanisms regulating malignancy are remarkably conserved when compared with human. Our laboratory has previously generated transgenic zebrafish models that overexpress the mouse c-Myc gene fused to enhanced green fluorescent protein (EGFP) and develop T-cell acute lymphoblastic leukaemia (T-ALL) that recapitulates the human disease both molecularly and pathologically. Our previous models have been limited by disease onset prior to sexual maturity and by the low disease penetrance when conditional transgenic embryos are injected with Cre RNA. Here, we report a novel system in which compound transgenic fish expressed both Cre controlled by the heat-shock promoter and a rag2-promoter-regulated lox-dsRED2-lox-EGFP-mMyc cassette rag2-LDL-EMyc in developing T cells. After heat-shock treatment at 3 d postfertilisation (dpf) for 45 min at 37 degrees C, 81% of compound transgenic fish developed T-lymphoblastic lymphoma (T-LBL, mean latency 120 +/- 43 (standard deviation) days of life), which rapidly progressed to T-ALL. Heat-shock-regulated transgenic technology in zebrafish provides the missing link necessary to exploit the powerful genetic capacity of this organism to probe the multi-step molecular pathogenesis of leukaemia.
Abstract
The chromosomal translocation t(7;9) in human T-cell acute lymphoblastic leukaemia (T-ALL) results in deregulated expression of a truncated, activated form of Notch 1 (TAN1) under the control of the T-cell receptor-beta (TCRB) locus. Although TAN1 efficiently induces T-ALL in mouse models, t(7;9) is present in less than 1% of human T-ALL cases. The recent discovery of novel activating mutations in NOTCH1 in more than 50% of human T-ALL samples has made it clear that Notch 1 is far more important in human T-ALL pathogenesis than previously suspected.
Abstract
The vertebrate neural crest is a pluripotent cell population that generates a large variety of cell types, including peripheral neurons, cartilage and pigment cells. Mechanisms that control the patterning of the neural crest toward specific cell fates remain only partially understood. Zebrafish homozygous for the sympathetic mutation 1 (sym1) have defects in a subset of neural crest derivatives, such as peripheral neurons, glia and cartilage, but retain normal numbers of melanocytes. The sym1 mutation is a nucleotide deletion that disrupts the forkhead DNA-binding domain of the foxd3 gene, which encodes a conserved winged-helix transcription factor. We show that sym1 mutants have normal numbers of premigratory neural crest cells, but these cells express reduced levels of snai1b and sox10, implicating foxd3 as an essential regulator of these transcription factors in the premigratory neural crest. The onset of neural crest migration is also delayed in sym1 mutants, and there is a reduction in the number of migratory trunk neural crest cells, particularly along the medial migration pathway. TUNEL analysis revealed aberrant apoptosis localized to the hindbrain neural crest at the 15-somite stage, indicating a critical role for foxd3 in the survival of a subpopulation of neural crest cells. These results show that foxd3 selectively specifies premigratory neural crest cells for a neuronal, glial or cartilage fate, by inducing the expression of lineage-associated transcription factors in these cells and regulating their subsequent migration.
Abstract
We have created a stable transgenic rag2-EGFP-mMyc zebrafish line that develops GFP-labeled T cell acute lymphoblastic leukemia (T-ALL), allowing visualization of the onset and spread of this disease. Here, we show that leukemias from this transgenic line are highly penetrant and render animals moribund by 80.7 +/- 17.6 days of life (+/-1 SD, range = 50-158 days). These T cell leukemias are clonally aneuploid, can be transplanted into irradiated recipient fish, and express the zebrafish orthologues of the human T-ALL oncogenes tal1/scl and lmo2, thus providing an animal model for the most prevalent molecular subgroup of human T-ALL. Because T-ALL develops very rapidly in rag2-EGFP-mMyc transgenic fish (in which "mMyc" represents mouse c-Myc), this line can only be maintained by in vitro fertilization. Thus, we have created a conditional transgene in which the EGFP-mMyc oncogene is preceded by a loxed dsRED2 gene and have generated stable rag2-loxP-dsRED2-loxP-EGFP-mMyc transgenic zebrafish lines, which have red fluorescent thymocytes and do not develop leukemia. Transgenic progeny from one of these lines can be induced to develop T-ALL by injecting Cre RNA into one-cell-stage embryos, demonstrating the utility of the Cre/lox system in the zebrafish and providing an essential step in preparing this model for chemical and genetic screens designed to identify modifiers of Myc-induced T-ALL.
Abstract
Overexpression of HOXA9 is linked to the molecular pathogenesis of acute myeloid leukaemia (AML) and myelodysplastic syndrome (MDS), conferring a poor prognosis. HOXA9 expression levels were analysed in the diagnostic bone marrow (BM) samples of 13 MDS patients. HOXA9 was expressed by CD34(+) BM cells at median levels 3.1-fold higher than in CD34(-) cells from the same patient and at median levels 4.3-fold higher than in CD34(+) cells from healthy donors. These results indicate that CD34(+) cell selection is required to accurately assess the expression levels of HOXA9 and related genes in the multipotential malignant progenitor cells of MDS patients.
Abstract
Transgenic zebrafish that express GFP under control of the T cell-specific tyrosine kinase (lck) promoter were used to analyze critical aspects of the immune system, including patterns of T cell development and T cell homing after transplant. GFP-labeled T cells could be ablated in larvae by either irradiation or dexamethasone added to the water, illustrating that T cells have evolutionarily conserved responses to chemical and radiation ablation. In transplant experiments, thymocytes from lck-GFP fish repopulated the thymus of irradiated wild-type fish only transiently, suggesting that the thymus contains only short-term thymic repopulating cells. By contrast, whole kidney marrow permanently reconstituted the T lymphoid compartment of irradiated wild-type fish, suggesting that long-term thymic repopulating cells reside in the kidney.
Abstract
The zebrafish model organism has been used extensively for studies of genetic pathways in development, indicating its potential applicability to cancer. Here we show that targeted expression of MYCN in cells of the pancreatic islet induces neuroendocrine carcinoma. Four transgenic fish developed abdominal tumors between 4 and 6 months of age, and histologic analysis revealed lobulated arrangements of neoplastic cells with expression of the MYCN transgene. The tumors also expressed insulin mRNA, and pancreatic exocrine cells and ducts were identified within the neoplasms, indicating a pancreatic origin for the tumor. Transmission electron microscopy revealed cytoplasmic, endocrine-dense core granules, analogous to those found in human neuroendocrine tumors. Our studies establish a zebrafish transgenic model of pancreatic neuroendocrine carcinoma, setting the stage to evaluate molecular pathways downstream of MYCN in this vertebrate forward genetic model system.
Abstract
The zebrafish is an attractive model organism for studying cancer development because of its genetic accessibility. Here we describe the induction of clonally derived T cell acute lymphoblastic leukemia in transgenic zebrafish expressing mouse c-myc under control of the zebrafish Rag2 promoter. Visualization of leukemic cells expressing a chimeric transgene encoding Myc fused to green fluorescent protein (GFP) revealed that leukemias arose in the thymus, spread locally into gill arches and retro-orbital soft tissue, and then disseminated into skeletal muscle and abdominal organs. Leukemic cells homed back to the thymus in irradiated fish transplanted with GFP-labeled leukemic lymphoblasts. This transgenic model provides a platform for drug screens and for genetic screens aimed at identifying mutations that suppress or enhance c-myc- induced carcinogenesis.
Abstract
In this issue of Cancer Cell, demonstrate a novel mechanism for the oncogenic activity of MLL chimeric proteins. By providing coiled-coil or other dimerization domains, the cytoplasmic partners of MLL fusion proteins donate a platform for MLL homodimerization, allowing recruitment of accessory factors needed to activate the critical downstream targets, including selected subsets of the major HOX genes.
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