Search PubMed⌕ Search

Biomedical subjects

A Berns

Publications and source records attributed to A Berns.

At least 55 records · Page 3Linked to original sources
PubMed1997

Pertubation of B and T cell development and predisposition to lymphomagenesis in Emu Bmi1 transgenic mice require the Bmi1 RING finger.

Proviral activation of the Bmi1 gene has implicated Bmi1 as a collaborator of c-Myc in lymphomagenesis. To determine the effect of Bmi1 overexpression on hematopoiesis and lymphomagenesis transgenic mice were generated that overexpress different forms of the Bmi1 protein in their lymphoid compartment. Emu Bmi1 transgenic mice, overexpressing the wild type Bmi1 protein showed a perturbed lymphoid development and were highly susceptible to B and T cell lymphomagenesis. Mutational analysis of the Bmi1 protein demonstrated that the conserved N-terminal RING finger and central part of Bmi1 are essential for its oncogenic potential whereas the C-terminal Pro-Ser rich region is not required. We have used provirus tagging in the Emu Bmi1 mice to identify genes that cooperate with Bmi1 in lymphomagenesis. MoMLV infection in Emu Bmi1 transgenic mice accelerated lymphoma development. Proviral activation of the Pim and Myc genes but not the Gfi1 gene were frequently observed in these tumors. These results demonstrate that Bmi1 is a potent oncogene and suggest that it plays an important role in early lymphoid development.

Animals↗
PubMed1997

Bcl-2 reduces lymphomagenesis in deltaV-TCRbeta transgenic mice.

Overexpression of the bcl-2 oncogene in the lymphoid compartment of transgenic mice prolongs the lifespan of lymphocytes and leads to a low incidence of lymphomas at later age. Transgenic mice carrying a mutated T-cell receptor lacking the variable domain (deltaV-TCRbeta) suffer from lymphocyte depletion and are highly predisposed to lymphoma development. We intercrossed Bcl-2-Ig and deltaV-TCRbeta transgenic mice to assess whether Bcl-2 could synergize with deltaV-TCRbeta in tumorigenesis as reported previously for other oncogenes. Surprisingly, bitransgenic deltaV-TCRbeta; bcl-2-Ig mice showed a reduction in the incidence of lymphomas. Analyses of prelymphomatous mice showed that Bcl-2 restored some of the phenotypic aberrations caused by the deltaV-TCRbeta transgene in the lymphoid compartment. The inhibitory activity of Bcl-2 on deltaVTCRbeta-induced lymphomagenesis was not observed when both transgenes were crossed into the RAG-1-/- background suggesting an important role for more mature lymphocytes in this phenomenon. These results show that, depending on the specific conditions, overexpression of Bcl-2 can both promote as well as impair lymphoma development.

Animals↗
PubMed1997

Cre-mediated somatic site-specific recombination in mice.

Conditional mutant mice equipped with heterologous recombination systems (Cre/lox or Flp/frt) are promising for studying tissue-specific gene function and for designing better models of human diseases. The utility of these mice depends on the cell target specificity, on the efficiency and on the control over timing of gene (in)activation. We have explored the utility of adenoviral vectors and transgenic mice expressing Cre under the control of tissue-specific promoters to achieve Cre/lox-mediated somatic recombination of the LacZ reporter gene, using a newly generated flox LacZ mouse strain. When adeno Cre viruses were administered via different routes, recombination and expression of LacZ was detected in a wide range of tissues. Whereas in liverbeta-galactosidase activity was quickly lost by turnover of expressing cells, even though the recombined allele was retained,beta-galactosidase in other tissues persisted for many months. Our data indicate that the flox LacZ transgenic line can be utilized effectively to monitor the level and functionality of Cre protein produced upon infection with adeno Cre virus or upon crossbreeding with different Cre transgenic lines.

Actins↗
PubMed1997

Overexpression of the FosB2 gene in thymocytes causes aberrant development of T cells and thymic epithelial cells.

We have examined the role of the AP-1 transcription factor on thymocyte maturation and thymus architecture by overexpressing FosB2 in transgenic mice. FosB2 is a naturally occurring splice variant of the FosB2 gene, encoding a truncated protein which lacks two domains necessary for transcriptional activation. The expression of FosB2 in the thymocytes severely affected their maturation and the structure of the whole thymus: the phenotype developed slowly during the first months of life, resulting in a progressive expansion of the medulla and concomitant reduction of the cortex. CD4+ thymocytes represented the major thymocyte population, whereas the CD4+ 8+ thymocytes were virtually absent. This phenotype appeared to be an intrinsic property of bone marrow derived cells, as it could be reproduced in bone marrow chimaeric mice. This pathology was very reminiscent to that observed in mice overexpressing c-Fos in thymic epithelium: also in that case the thymus underwent with age a progressive expansion of the epithelium and major changes in the ratio of thymocyte subsets, but the phenotype appeared to be an intrinsic property of the epithelial cells since it could not be reproduced by transgenic bone marrow transplantation. We speculate that both overexpression of FosB2 in thymocytes and overexpression of c-Fos in thymic epithelium results in aberrant signaling between thymocytes and stroma, that ultimately alters the thymic micromilieu, leading to this severe pathology.

Age Factors↗
PubMed1997

Activation of a novel proto-oncogene, Frat1, contributes to progression of mouse T-cell lymphomas.

Acceleration of lymphomagenesis in oncogene-bearing transgenic mice by slow-transforming retroviruses has proven a valuable tool in identifying cooperating oncogenes. We have modified this protocol to search for genes that can collaborate effectively with the transgene in later stages of tumor development. Propagation of tumors induced by Moloney murine leukemia virus (M-MuLV) in E mu-Pim1 or H2-K-myc transgenic mice by transplantation to syngeneic hosts permitted proviral tagging of 'progression' genes. Molecular cloning of common proviral insertion sites that were detected preferentially in transplanted tumors led to the identification of a novel gene, designated Frat1. The initial selection for integrations near Frat1 occurs in primary tumor cells that have already acquired proviruses in other common insertion sites, yielding primary lymphomas that contain only a minor fraction of tumor cells with an activated Frat1 allele. Transplantation of such primary lymphomas allows for a further expansion of tumor cell clones carrying a proviral insertion near Frat1, resulting in detectable Frat1 rearrangements in 17% of the transplanted E mu-Pim1 tumors and 30% of the transplanted H2-K-myc tumors, respectively. We have cloned and sequenced both the mouse Frat1 gene and its human counterpart. The proteins encoded by Frat1 and FRAT1 are highly homologous and their functions are thus far unknown. Tumor cell lines with high expression of Myc and Pim1 acquired an additional selective advantage in vivo upon infection with a Frat1-IRES-lacZ retrovirus, thus underscoring the role of Frat1 in tumor progression, and the ability of Frat1 to collaborate with Pim1 and Myc in lymphomagenesis.

Amino Acid Sequence↗
PubMed1997

Immunological defects in mice with a targeted disruption in Bcl-3.

The proto-oncogene bcl-3 is a member of the IkappaB family. The Bcl-3 protein is known to interact specifically with the p50 and p52 subunits of NFkappaB. However, the function of this interaction is not well understood. To determine the in vivo role of Bcl-3, mice were generated that lack the bcl-3 gene, Bcl 3(-/-). Here we report that Bcl 3(-/-) mice appear developmentally normal, but exhibit severe defects in humoral immune responses and protection from in vivo pathogenic challenges. Relative to wild-type mice, Bcl 3(-/-) mice are unable to clear L. monocytogenes and are more susceptible to infection with S. pneumoniae. This phenotype is similar to that observed in the p50(-/-) mice and the cross between the Bcl-3(-/-) and p50(-/-) mice generates animals with an enhanced phenotype. In accordance with the observed defects in their immune response, the Bcl 3(-/-) mice have normal immunoglobulin levels before and after immunization, but fail to produce antigen-specific antibodies. Additionally, spleens from Bcl-3(-/-) mice are abnormal and void of germinal centers. In contrast, the p50(-/-) mice have normal germinal centers. We propose that in in vivo, Bcl-3 can function independently of p50.

Animals↗
PubMed1997

Identification of Bmi1-interacting proteins as constituents of a multimeric mammalian polycomb complex.

The Bmi1 gene has been identified as a mouse Polycomb group (Pc-G) gene implicated in the regulation of Hox gene expression. Here we describe the characterization of a Bmi binding protein Mph1, which shares similarity to Drosophila polyhomeotic. Coimmunoprecipitation experiments indicate that Bmi1 and Mph1, as well as the Mel18 and M33 proteins described previously, are constituents of a multimeric protein complex in mouse embryos and human cells. A central domain of Bmi1 interacts with the carboxyl terminus of Mph1, whereas a conserved alpha-helical domain in the Mph1 protein is required for its homodimerization. Transgenic mice overexpressing various mutant Bmi1 proteins demonstrate that the central domain of Bmil is required for the induction of anterior transformations of the axial skeleton. Bmi1, M33, and Mph1 show an overlapping speckled distribution in interphase nuclei. These data provide molecular evidence for the existence of a mammalian Polycomb complex.

Amino Acid Sequence↗
PubMed1997

Characterization of pal-1, a common proviral insertion site in murine leukemia virus-induced lymphomas of c-myc and Pim-1 transgenic mice.

Insertional mutagenesis with Moloney murine leukemia virus (MoMLV) in c-myc and Pim-1 transgenic mice permits the identification of oncogenes that collaborate with the transgenes in lymphomagenesis. The recently identified common insertion site pal-1, in MoMLV-induced lymphomas, is located in a region in which several independent integration clusters are found: eis-1, gfi-1, and evi-5. Proviral insertions of MoMLV in the different integration clusters upregulate the transcriptional activity of the Gfi-1 gene, which is located within the pal-1 locus. The eis-1/pal-1/gfi-1/evi-5 locus serves as a target for MoMLV proviral insertions in pre-B-cell lymphomas of Emu-myc transgenic mice (20%) and in T-cell lymphomas of H-2K-myc (75%) and Emu-pim-1 (93%) transgenic mice. Many tumors overexpress both Gfi-1 as well as Myc and Pim gene family members, indicating that Gfi-1 collaborates with Myc and Pim in lymphomagenesis. Proviral integrations in the previously identified insertion site bmi-1 are, however, mutually exclusive with integrations in the eis-1/pal-1/gfi-1/evi-5 locus. This finding suggests that Bmi-1 and Gfi-1 belong to the same complementation group in lymphoid transformation.

Amino Acid Sequence↗
PubMed1996

Domains of the TCR beta-chain required for early thymocyte development.

The T cell receptor beta (TCR beta) chain controls the developmental transition from CD4-CD8- to CD4+8+thymocytes. We show that the extracellular constant region and the transmembrane region, but not the variable domain or cytoplasmic tail of the TCR beta chain are required for this differentiation step. TCR beta mutant chains lacking the cytoplasmic tail can be found at the cell surface both in functional TCR/CD3 complexes and in a GPI-anchored monomeric form indicating that the cytoplasmic tail of the TCR beta chain functions as an ER retention signal. The concordance between cell surface expression of the mutant chains as TCR/CD3 complexes and their capacity to mediate thymocyte differentiation supports the CD3 mediated feedback model in which preTCR/CD3 complexes control the developmental transition from CD4-CD8- to CD4+CD8+thymocytes.

Animals↗
PubMed1996

Oncogenic potential of a pre-T cell receptor lacking the TCR beta variable domain.

In transgenic mice expressing a mutated T cell receptor (TCR) beta chain lacking the variable domain (DeltaV-TCRbeta) T cell differentiation is arrested at the CD4+ CD8+ thymocyte stage. Here, we report that these transgenic animals develop CD4+, CD8+, IL-2 receptor alpha-positive T cell lymphomas at a very high incidence. Introduction of a normal TCRbeta gene into the DeltaV-TCRbeta transgenic mice drastically reduces the tumor incidence, while crossing the DeltaV-TCRbeta transgene onto a recombinase-deficient RAG-1-/- background does not prevent tumor development. Therefore, the induction of T cell lymphomas is a property of the mutated TCRbeta chain. The DeltaV-TCRbeta chain appears at the cell surface as a disulfide-linked DeltaV-TCRbeta/pTalpha dimer in association with CD3gamma and -episilon, but not with CD3delta. This mutated preTCR/CD3 complex is shown to induce pre-T cell proliferation and differentiation, but does not permit formation of a normally sized CD4+8+ thymic compartment. DeltaV-TCRbeta transgenic mice frequently show an expansion of CD4+8+, IL-2 receptor alpha+ pre-T cells early in life. These cells likely represent the population that is subject to oncogenic transformation.

Amino Acid Sequence↗
PubMed1996

Biosynthesis of major histocompatibility complex molecules and generation of T cells in Ii TAP1 double-mutant mice.

Major histocompatibility complex (MHC) class I and II molecules are loaded with peptides in distinct subcellular compartments. The transporter associated with antigen processing (TAP) is responsible for delivering peptides derived from cytosolic proteins to the endoplasmic reticulum, where they bind to class I molecules, while the invariant chain (Ii) directs class II molecules to endosomal compartments, where they bind peptides originating mostly from exogenous sources. Mice carrying null mutations of the TAP1 or Ii genes (TAP10) or Ii0, respectively) have been useful tools for elucidating the two MHC/peptide loading pathways. To evaluate to what extent these pathways functionally intersect, we have studied the biosynthesis of MHC molecules and the generation of T cells in Ii0TAP10 double-mutant mice. We find that the assembly and expression of class II molecules in Ii0 and Ii0TAP10 animals are indistinguishable and that formation and display of class I molecules is the same in TAP10 and Ii0TAP10 animals. Thymic selection in the double mutants is as expected, with reduced numbers of both CD4+ CD8- and CD4- CD8+ thymocyte compartments. Surprisingly, lymph node T-cell populations look almost normal; we propose that population expansion of peripheral T cells normalizes the numbers of CD4+ and CD8+ cells in Ii0TAP10 mice.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Complementation tagging of cooperating oncogenes in knockout mice.

Gene disruption and overexpression in mice can be combined with proviral tagging to investigate the biochemical pathways in which oncogenes act. The phenomenon of oncogene collaboration permits a focussed genetic approach analogous to the strategies employed in suppressor screens in invertebrates and yeast. We illustrate here its application to investigating the action of the pim kinases in tumorigenesis. However, it should be possible to utilize this strategy for dissecting a much wider range of biochemical pathways in mammalian systems.

Animals↗
PubMed1996

The Polycomb-group homolog Bmi-1 is a regulator of murine Hox gene expression.

Drosophila homeotic genes and vertebrate Hox genes are involved in the anteroposterior organization of the developing embryo. In Drosophila, the Polycomb- and trithorax-group genes are required to maintain the homeotic genes throughout development in the repressed or activated state, respectively. The murine Bmi-1 proto-oncogene was shown to exhibit homology to the Polycomb-group gene Posteior sex combs. Mice lacking the Bmi-1 gene revealed posterior transformations along the axial skeleton, whereas transgenic mice overexpressing Bmi-1 display anterior transformations. We have analysed the expression patterns of several Hox genes by RNA in situ hybridization on serial sections of 11.5- and 12.5-day Bmi-1 null mutant embryos. Furthermore, we have analysed the expression of a Hoxc-8/LacZ fusion gene in younger embryos. Our analyses show that Bmi-1 is involved in the repression of a subset of Hox genes from different clusters from at least day 9.5 onwards. We discuss the possibility that members of the murine Polycomb-group can form multimeric protein complexes of different compositions with varying affinity or specificity for different subsets of Hox genes.

Age Factors↗
PubMed1996

Abnormal myotonic dystrophy protein kinase levels produce only mild myopathy in mice.

Myotonic dystrophy (DM) is commonly associated with CTG repeat expansions within the gene for DM-protein kinase (DMPK). The effect of altered expression levels of DMPK, which is ubiquitously expressed in all muscle cell lineages during development, was examined by disrupting the endogenous Dmpk gene and overexpressing a normal human DMPK transgene in mice. Nullizygous (-/-) mice showed only inconsistent and minor size changes in head and neck muscle fibres at older age, animals with the highest DMPK transgene expression showed hypertrophic cardiomyopathy and enhanced neonatal mortality. However, both models lack other frequent DM symptoms including the fibre-type dependent atrophy, myotonia, cataract and male-infertility. These results strengthen the contention that simple loss- or gain-of-expression of DMPK is not the only crucial requirement for development of the disease.

Animals↗
PubMed1995

Inactivation of the mouse Msh2 gene results in mismatch repair deficiency, methylation tolerance, hyperrecombination, and predisposition to cancer.

To investigate the role of the presumed DNA mismatch repair (MMR) gene Msh2 in genome stability and tumorigenesis, we have generated cells and mice that are deficient for the gene. Msh2-deficient cells have lost mismatch binding and have acquired microsatellite instability, a mutator phenotype, and tolerance to methylating agents. Moreover, in these cells, homologous recombination has lost dependence on complete identity between interacting DNA sequences, suggesting that Msh2 is involved in safeguarding the genome from promiscuous recombination. Msh2-deficient mice display no major abnormalities, but a significant fraction develops lymphomas at an early age. Thus, Msh2 is involved in MMR, controlling several aspects of genome stability; loss of MMR-controlled genome stability predisposes to cancer.

Animals↗
PubMed1995

Proviral tagging in E mu-myc transgenic mice lacking the Pim-1 proto-oncogene leads to compensatory activation of Pim-2.

The Pim-1 proto-oncogene is one of the most potent collaborators of the myc proto-oncogenes in inducing lymphomagenesis in mice. Contrary to the profound effects when overexpressed in vivo, Pim-1-deficient mice showed only subtle phenotypic alterations, which could indicate the presence of redundantly acting genes. In line with this, a PCR-based screen has led to the identification of a closely homologous gene, Pim-2. The X-linked Pim-2 gene is 53% identical to Pim-1 at the amino acid level and shares substrate preference and the usage of non-AUG initiation codons with Pim-1. We have used these data to test whether the strong synergistic interaction between Pim-1 and c-myc can be utilized to gain access to Pim-1 compensatory pathways. We reasoned that, upon proviral tagging in compound mutant mice (E mu-myc/Pim-1-/- mice), the selective advantage of cells carrying provirally activated genes, that act downstream from or parallel to Pim-1, would increase. We show here that this is the case. A dramatic increase (from 15 to 80%) was found in the frequency of proviral activation of the Pim-2 gene. These data show that the described strategy of 'complementation tagging' represents a powerful new tool to identify components of pathways involved in processes as complex as multistep tumorigenesis.

Amino Acid Sequence↗