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Anton Berns

Publications and source records attributed to Anton Berns.

At least 37 records · Page 2Linked to original sources
PubMed2004

The European dimension for the mouse genome mutagenesis program.

The European Mouse Mutagenesis Consortium is the European initiative contributing to the international effort on functional annotation of the mouse genome. Its objectives are to establish and integrate mutagenesis platforms, gene expression resources, phenotyping units, storage and distribution centers and bioinformatics resources. The combined efforts will accelerate our understanding of gene function and of human health and disease.

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PubMed2004

Mice deficient for all PIM kinases display reduced body size and impaired responses to hematopoietic growth factors.

The Pim family of proto-oncogenes encodes a distinct class of serine/threonine kinases consisting of PIM1, PIM2, and PIM3. Although the Pim genes are evolutionarily highly conserved, the contribution of PIM proteins to mammalian development is unclear. PIM1-deficient mice were previously described but showed only minor phenotypic aberrations. To assess the role of PIM proteins in mammalian physiology, compound Pim knockout mice were generated. Mice lacking expression of Pim1, Pim2, and Pim3 are viable and fertile. However, PIM-deficient mice show a profound reduction in body size at birth and throughout postnatal life. In addition, the in vitro response of distinct hematopoietic cell populations to growth factors is severely impaired. In particular, PIM proteins are required for the efficient proliferation of peripheral T lymphocytes mediated by synergistic T-cell receptor and interleukin-2 signaling. These results indicate that members of the PIM family of proteins are important but dispensable factors for growth factor signaling.

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PubMed2004

Unique and overlapping functions of pRb and p107 in the control of proliferation and differentiation in epidermis.

The retinoblastoma gene product, pRb, plays a crucial role in cell cycle regulation, differentiation and inhibition of oncogenic transformation. pRb and its closely related family members p107 and p130 perform exclusive and overlapping functions during mouse development. The embryonic lethality of Rb-null animals restricts the phenotypic analysis of these mice to mid-gestation embryogenesis. We employed the Cre/loxP system to study the function of Rb in adult mouse stratified epithelium. Rb(F19/F19);K14cre mice displayed hyperplasia and hyperkeratosis in the epidermis with increased proliferation and aberrant expression of differentiation markers. In vitro, pRb is essential for the maintainance of the postmitotic state of terminally differentiated keratinocytes, preventing cell cycle re-entry. However, p107 compensates for the effects of Rb loss as the phenotypic abnormalities of Rb(F19/F19);K14cre keratinocytes in vivo and in vitro become more severe with the concurrent loss of p107 alleles. p107 alone appears to be dispensable for all these phenotypic changes, as the presence of a single Rb allele in a p107-null background rescues all these alterations. Luciferase reporter experiments indicate that these phenotypic alterations might be mediated by increased E2F activity. Our findings support a model in which pRb in conjunction with p107 plays a central role in regulating epidermal homeostasis.

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PubMed2003

The generation of a conditional reporter that enables bioluminescence imaging of Cre/loxP-dependent tumorigenesis in mice.

The ability to noninvasively quantitate tumor burden from conditional (Cre/loxP-dependent) mouse cancer models would greatly increase their range of useful applications. We now report the generation of a reporter mouse that enables visualization of spontaneous tumor development from pre-existing conditional mouse tumor models via in vivo bioluminescence imaging. We demonstrate that bioluminescence can be "switched-on" in a Cre-dependent manner in every organ analyzed, and that this gives rise to between a 4 and 6-log increase in light emission per mg of wet tissue weight. Furthermore, we highlight the utility of this reporter by showing that it can be used as a sensitive means to measure spontaneous Kras2(v12)-induced lung tumorigenesis in a pre-existing mouse model of non-small cell lung cancer. Taken together, our results suggest that this reporter may be combined with a wide-range of other Cre/loxP tumor mouse models, irrespective of their tissue specificity and render them immediately amenable to longitudinal monitoring of tumor growth and therapeutic response with a noninvasive in vivo imaging approach.

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PubMed2003

Retroviral insertional mutagenesis: tagging cancer pathways.

Slow transforming retroviruses, such as the Moloney murine leukemia virus (M-MuLV), induce tumors upon infection of a host after a relatively long latency period. The underlying mechanism leading to cell transformation is the activation of proto-oncogenes or inactivation of tumor suppressor genes as a consequence of proviral insertions into the host genome. Cells carrying proviral insertions that confer a selective advantage will preferentially grow out. This means that proviral insertions mark genes contributing to tumorigenesis, as was demonstrated by the identification of numerous proto-oncogenes in retrovirally induced tumors in the past. Since cancer is a complex multistep process, the proviral insertions in one clone of tumor cells also represent oncogenic events that cooperate in tumorigenesis. Novel advances, such as the launch of the complete mouse genome, high-throughput isolation of proviral flanking sequences, and genetically modified animals have revolutionized proviral tagging into an elegant and efficient approach to identify signaling pathways that collaborate in cancer.

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PubMed2003

Induction of small cell lung cancer by somatic inactivation of both Trp53 and Rb1 in a conditional mouse model.

Small cell lung cancer (SCLC) is a highly aggressive human tumor with a more than 95% mortality rate. Its ontogeny and molecular pathogenesis remains poorly understood. We established a mouse model for neuroendocrine (NE) lung tumors by conditional inactivation of Rb1 and Trp53 in mouse lung epithelial cells. Mice carrying conditional alleles for both Rb1 and Trp53 developed with high incidence aggressive lung tumors with striking morphologic and immunophenotypic similarities to SCLC. Most of these tumors, which we designate MSCLC (murine small cell lung carcinoma), diffusely spread through the lung and gave rise to extrapulmonary metastases. In our model, inactivation of both Rb1 and p53 was a prerequisite for the pathogenesis of SCLC.

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PubMed2003

Rb and p107 are required for normal cerebellar development and granule cell survival but not for Purkinje cell persistence.

The involvement of the retinoblastoma gene product (Rb) and its family members (p107 and p130) in cell cycle exit and terminal differentiation of neural precursor cells has been demonstrated in vitro. To investigate the roles of Rb and p107 in growth, differentiation and apoptosis in the developing and mature cerebellum, we selectively inactivated either Rb alone or in combination with p107 in cerebellar precursor cells or in Purkinje cells. In our mouse models, we show that (1) Rb is required for differentiation, cell cycle exit and survival of granule cell precursors; (2) p107 can not fully compensate for the loss of Rb function in granule cells; (3) Rb and p107 are not required for differentiation and survival of Purkinje cells during embryonic and early postnatal development; (4) Rb function in Purkinje cells is cell autonomous; and (5) loss of Rb deficient CNS precursor cells is mediated by p53-independent apoptosis.

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PubMed2002

Proviral activation of the tumor suppressor E2a contributes to T cell lymphomagenesis in EmuMyc transgenic mice.

The basic helix-loop-helix factor E2A plays an important role in the development of B and T lymphocytes. In addition, E2a has been implicated as a gene with tumor suppressor activity, since mice deficient for E2a succumb to T cell lymphomas. We have performed retroviral tagging in EmuMyc transgenic mice to identify genes that contribute to lymphomagenesis. The EmuMyc transgenic mouse is a well-established model of a common translocation in human B cell lymphomas. Analyses of the proviral insertion sites in the MuLV-induced lymphomas revealed that a number of T cell lymphomas carried proviral insertions in the promoter region of E2a. These proviral insertions yield hybrid viral-E2a mRNAs resulting in a marked rise in E2A protein levels. The proviral insertions in E2a were predominantly of clonal origin indicating that E2a insertions are early events in these T cell lymphomas. The primary oncogenic effect of E2A is likely to be associated with enhancement of transcription of the c-Myc transgene via binding to the regulatory immunoglobulin enhancers. The results herein thus provide the first evidence that in a specific setting E2A overexpression can contribute to T-lymphomagenesis. This implies that E2a contains oncogenic features in addition to the previously described tumor suppressive properties.

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PubMed2002

High-throughput retroviral tagging to identify components of specific signaling pathways in cancer.

Genetic screens carried out in lower organisms such as yeast, Drosophila melanogaster and Caenorhabditis elegans have revealed many signaling pathways. For example, components of the RAS signaling cascade were identified using a mutant eye phenotype in D. melanogaster as a readout. Screening is usually based on enhancing or suppressing a phenotype by way of a known mutation in a particular signaling pathway. Such in vivo screens have been difficult to carry out in mammals, however, owing to their relatively long generation times and the limited number of animals that can be screened. Here we describe an in vivo mammalian genetic screen used to identify components of pathways contributing to oncogenic transformation. We applied retroviral insertional mutagenesis in Myc transgenic (E mu Myc) mice lacking expression of Pim1 and Pim2 to search for genes that can substitute for Pim1 and Pim2 in lymphomagenesis. We determined the chromosomal positions of 477 retroviral insertion sites (RISs) derived from 38 tumors from E mu Myc Pim1(-/-) Pim2(-/-) mice and 27 tumors from E mu Myc control mice using the Ensembl and Celera annotated mouse genome databases. There were 52 sites occupied by proviruses in more than one tumor. These common insertion sites (CISs) are likely to contain genes contributing to tumorigenesis. Comparison of the RISs in tumors of Pim-null mice with the RISs in tumors of E mu Myc control mice indicated that 10 of the 52 CISs belong to the Pim complementation group. In addition, we found that Pim3 is selectively activated in Pim-null tumor cells, which supports the validity of our approach.

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PubMed2002

Identification of oncogenes collaborating with p27Kip1 loss by insertional mutagenesis and high-throughput insertion site analysis.

The p27(Kip1) protein is a cyclin-dependent kinase inhibitor that blocks cell division in response to antimitogenic cues. p27 expression is reduced in many human cancers, and p27 functions as a tumor suppressor that exhibits haploinsufficiency in mice. Despite the well characterized role of p27 as a cyclin-dependent kinase inhibitor, its mechanism of tumor suppression is unknown. We used Moloney murine leukemia virus to induce lymphomas in p27+/+ and p27-/- mice and observed that lymphomagenesis was accelerated in the p27-/- animals. To identify candidate oncogenes that collaborate with p27 loss, we used a high-throughput strategy to sequence 277 viral insertion sites derived from two distinct sets of p27-/- lymphomas and determined their chromosomal location by comparison with the Celera and public (Ensembl) mouse genome databases. This analysis identified a remarkable number of putative protooncogenes in these lymphomas, which included loci that were novel as well as those that were overrepresented in p27-/- tumors. We found that Myc activations occurred more frequently in p27-/- lymphomas than in p27+/+ tumors. We also characterized insertions within two novel loci: (i) the Jun dimerization protein 2 gene (Jundp2), and (ii) an X-linked locus termed Xpcl1. Each of the loci that we found to be frequently involved in p27-/- lymphomas represents a candidate oncogene collaborating with p27 loss. This study illustrates the power of high-throughput insertion site analysis in cancer gene discovery.

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PubMed2002

Loss of p27(Kip1) but not p21(Cip1) decreases survival and synergizes with MYC in murine lymphomagenesis.

The cyclin-dependent kinase (CDK) inhibitors p21(Cip1) and p27(Kip1) are induced in response to anti-proliferative stimuli and block G(1)/S-phase progression through the inhibition of CDK2. Although the cyclin E-CDK2 pathway is often deregulated in tumors the relative contribution of p21(Cip1) and p27(Kip1) to tumorigenesis is still unclear. The MYC transcription factor is an important regulator of the G(1)/S transition and its expression is frequently altered in tumors. Previous reports suggested that p27(Kip1) is a crucial G(1) target of MYC. Our study shows that in mice, deficiency for p27(Kip1) but not p21(Cip1) results in decreased survival to retrovirally-induced lymphomagenesis. Importantly, in such p27(Kip1) deficient lymphomas an increased frequency of Myc activation is observed. p27(Kip1) deficiency was also shown to collaborate with MYC overexpression in transgenic lymphoma models. Thus, in vivo, the capacity of MYC to promote tumor growth is fully retained and even enhanced upon p27(Kip1) loss. We show that in lymphocytes, MYC overexpression and p27(Kip1) deficiency independently stimulate CDK2 activity and augment the fraction of cells in S phase, in support of their distinct roles in tumorigenesis.

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PubMed2002

Tumor formation in mice with somatic inactivation of the retinoblastoma gene in interphotoreceptor retinol binding protein-expressing cells.

The retinoblastoma suppressor gene product Rb has been assigned a critical role in cell cycle regulation, the induction of differentiation, and inhibition of oncogenic transformation. Inheritance of a mutant RB allele in humans is responsible for bilateral retinoblastoma, a malignant tumor of the retina. Trilateral retinoblastoma (TRB) is a rare variant of familial retinoblastoma in which, in addition to retinal tumors, tumors develop from the pineal gland, an organ ontologically related to the retina. Germline inactivation of Rb in mice leads to mid-gestational lethality with defects in erythropoeisis and neurogenesis. This embryonic lethality prohibits the analysis of Rb function in selected cell types at later stages of development or in the adult. Here, we describe the Cre-LoxP mediated somatic inactivation of Rb in a subset of neuroendocrine cells, including photoreceptor cells. We observed neuroendocrine tumors of the pineal and pituitary gland. These tumors invariably showed inactivation of Rb and Trp53. Remarkably, loss of Rb in photoreceptor cells does not lead to retinoblastoma or any phenotypic changes, not even when photoreceptor cells are made deficient in Rb, p107 and Trp53. Our results highlight the important differences that exist in tumor susceptibility between mice and man (e.g pineal gland) and question the photoreceptor cell origin of human retinoblastoma.

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PubMed2002

Noninvasive imaging of spontaneous retinoblastoma pathway-dependent tumors in mice.

Identification of the critical pathways involved in tumorigenesis should ultimately lead to the design of better anticancer agents that target specific components of the disrupted pathways. Murine models of spontaneous cancer in which tumor formation is dependent on defined genetic alterations provide a powerful test system for evaluating the therapeutic efficacy of pathway-specific antineoplastics. We have generated a conditional mouse model for retinoblastoma-dependent sporadic cancer that permits noninvasive monitoring of pituitary tumor development in live animals via in vivo bioluminescence imaging of luciferase expression. We show that the high sensitivity of bioluminescence imaging can be used for noninvasive detection of luciferase expression in pituitary glands from tumor-free animals and for in vivo quantitation of tumor burden over a large dynamic range. This mouse model permits longitudinal monitoring of tumor onset, progression, and response to therapy and may be used effectively for testing cancer prevention and treatment strategies based on therapeutics that specifically target the retinoblastoma pathway.

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PubMed2002

Controlling gene expression in the urothelium using transgenic mice with inducible bladder specific Cre-lox recombination.

PURPOSE: Clinical advances in bladder cancer would require the development of novel animal model systems closely mimicking human disease. We describe a system of conditional gene targeting using the Cre/loxP system that permits temporally controlled mutation of tumor suppressor genes in bladder urothelium. MATERIALS AND METHODS: Mice expressing Cre-ERT, a fusion between Cre-recombinase and a mutated hormone binding domain of the human estrogen receptor ERT, permit temporally and spatially controlled Cre mediated recombination in vivo by the topical application of 4-hydroxy-tamoxifen. Mice expressing Cre-ERT under transcriptional control of the ubiquitously expressed ROSA26 locus R26cre-ERT were crossbred with R26R mice that express the lacZ reporter gene after Cre mediated excision of a neo cassette in all cells of the adult mice. At 7 and 90 days after intravesical application of 1, 2, 5 and 10 mg. 4-hydroxy-tamoxifen the bladder was processed for X-Gal (Life Technologies, Rockville, Maryland) staining. RESULTS: At doses of 1, 2, 5 and 10 mg. 4-hydroxy-tamoxifen Cre mediated recombination was readily detected in the bladder urothelium in dose dependent fashion. Within the urothelium basal, suprabasal and superficial cells stained. Applying the 10 mg. dose resulted in widespread multifocal staining of the urothelium without recombination in the bladder wall or distant organs. CONCLUSIONS: The R26cre-ERT mouse can be used to induce multifocal somatic mutagenesis in the bladder urothelium in a promoter independent and time controlled manner. This model would enable us to study temporally controlled mutations of bladder cancer related tumor suppressor genes by crossbreeding with mice carrying floxed alleles for Rb, p53 and p16INK4a alone or in combination.

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PubMed2002

Conditional mouse models of sporadic cancer.

First-generation mouse tumour models, which used transgenic mice or conventional knockouts, are now being superseded by models that are based on conditional knockouts and mice that carry regulatable oncogenes. In these mice, somatic mutations can be induced in a tissue-specific and time-controlled fashion, which more faithfully mimics sporadic tumour formation. These second-generation models provide exciting new opportunities to gain insight into the contribution of known and unknown genes in the initiation, progression and treatment of cancer, and mimic human cancer better than ever before.

Alleles↗
PubMed2002

PTEN is essential for cell migration but not for fate determination and tumourigenesis in the cerebellum.

PTEN is a tumour suppressor gene involved in cell cycle control, apoptosis and mediation of adhesion and migration signalling. Germline mutations of PTEN in humans are associated with familial tumour syndromes, among them Cowden disease. Glioblastomas, highly malignant glial tumours of the central nervous system frequently show loss of PTEN. Recent reports have outlined some aspects of PTEN function in central nervous system development. Using a conditional gene disruption approach, we inactivated Pten in mice early during embryogenesis locally in a region specific fashion and later during postnatal development in a cell-specific manner, to study the role of PTEN in differentiation, migration and neoplastic transformation. We show that PTEN is required for the realisation of normal cerebellar architecture, for regulation of cell and organ size, and for proper neuronal and glial migration. However, PTEN is not required for cell differentiation and lack of PTEN is not sufficient to induce neoplastic transformation of neuronal or glial cells

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