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Matthias Wabl

Publications and source records attributed to Matthias Wabl.

At least 19 recordsLinked to original sources
PubMed2006

Activation of an oncogenic microRNA cistron by provirus integration.

Retroviruses can cause tumors when they integrate near a protooncogene or tumor suppressor gene of the host. We infected >2,500 mice with the SL3-3 murine leukemia virus; in 22 resulting tumors, we found provirus integrations nearby or within the gene that contains the mir-17-92 microRNA (miRNA) cistron. Using quantitative real-time PCR, we showed that expression of miRNA was increased in these tumors, indicating that retroviral infection can induce expression of oncogenic miRNAs. Our results demonstrate that retroviral mutagenesis can be a potent tool for miRNA discovery.

Animals↗
PubMed2006

Slow, stochastic transgene repression with properties of a timer.

BACKGROUND: When gene expression varies unpredictably between genetically identical organisms, this is sometimes ascribed as stochastic. With the prevalence of retroviral vectors, stochastic repression is often observed and can complicate the interpretation of outcomes. But it may also faithfully reflect characteristics of sites in the genome. RESULTS: We created and identified several cell clones in which, within a given cell, retroviral transcription of a transgene was repressed heritably and essentially irreversibly. This repression was relatively slow; total repression in all cells took months. We observed the dynamics of repression and found that they were ergodic, that is, tending with a probability to a final state independent of previous conditions. Different positions of the transgene in the genome demonstrated different dynamics. At a position on mouse chromosome 9, repression abided by near perfect first-order kinetics and was highly reproducible, even under conditions where the number of cell generations per day varied. CONCLUSION: We propose that such a cell division independent 'off' mechanism could play a role in endogenous gene expression, potentially providing an epigenetically based timer for extended periods.

Animals↗
PubMed2005

A tumor-suppressor function for NFATc3 in T-cell lymphomagenesis by murine leukemia virus.

Nuclear factor of activated T cell (NFAT) transcription factors play a central role in differentiation, activation, and elimination of lymphocytes. We here report on the finding of provirus integration into the Nfatc3 locus in T-cell lymphomas induced by the murine lymphomagenic retrovirus SL3-3 and show that NFATc3 expression is repressed in these lymphomas. The provirus insertions are positioned close to the Nfatc3 promoter or a putative polyadenylated RNA (polyA) region. Furthermore, we demonstrate that NFATc3-deficient mice infected with SL3-3 develop T-cell lymphomas faster and with higher frequencies than wild-type mice or NFATc2-deficient mice. These results identify NFATc3 as a tumor suppressor for the development of murine T-cell lymphomas induced by the retrovirus SL3-3.

Animals↗
PubMed2005

Hypermutation rate normalized by chronological time.

It is generally believed that in cells undergoing Ig somatic hypermutation, more cell divisions result in more mutations. This is because DNA synthesis and replication is thought to play roles in the known mechanisms-cytidine deamination and subsequent conversion to thymidine, uracil-DNA glycosylase-mediated repair, mismatch repair, and DNA synthesis by error-prone polymerases. In this study, we manipulated the number of cell generations by varying the rate at which cultures of a mouse cell line were replenished with fresh medium. We found that the frequency of mutants does not necessarily increase with the number of cell generations. On the contrary, a greater number of divisions can lead to a lower frequency of mutants, indicating that cell division is not a rate-limiting step in the hypermutation process. Thus, when comparing mutation rates, we suggest that rates are more appropriately expressed as mutations per day than per cell generation.

Animals↗
PubMed2005

Somatic hypermutation and mismatch repair in non-B cells.

Mismatch repair contributes to hypermutation in B lymphocytes, both by increasing the frequency of mutations and by changing the mutational patterns. In this paper, we investigated whether or not mismatch repair influences activation-induced cytidine deaminase (AID)-mediated hypermutation in a non-B lymphocyte line. We did so by regulating expression of MutL homologue MLH 1, which is essential in mismatch repair, in a kidney cell line that had been transduced by an AID-containing vector. Whether or not MLH1 was expressed, we found no difference in the mutation rates of an indicator gene. We conclude that in order to contribute to hypermutation, mismatch repair needs additional factors that are present in activated B lymphocytes, but absent in the cell line investigated.

Adaptor Proteins, Signal Transducing↗
PubMed2005

Retroviral vectors to monitor somatic hypermutation.

The recent expansion of studies on hypermutation may benefit from a fast and uncomplicated way to measure mutation rates. In this paper we compare different retroviral vector designs for monitoring hypermutation in vivo. Retroviral vectors combine a high transduction rate with integration at random sites within the host cell genome, thus equalizing positional effects on the reporter gene. The vectors contain a reporter gene with a premature TAG termination codon; upon reversion, a full-length fluorescent protein is expressed. Any single point mutation at the amber codon activates the reporter--except the transition from G to A, which only creates the stop codon TAA. In the construct, the reporter gene is followed by an internal ribosome entry site and a second marker that allows selection of stably transduced cells. As a reporter gene, we tested the green and yellow fluorescence proteins (GFP and YFP); and various proteins with red fluorescence (dsRed). The second marker was either a drug resistance gene, or a second fluorescent protein. We also introduced various cis-acting enhancer elements into the reporter construct, to study the simultaneous activity of enhancers on transcription and hypermutation. We found that GFP as a reporter, combined with a drug selection marker, gave the most consistent and convenient mutation rate measurements. DsRed is a good alternative to GFP, but variants with greater fluorescence intensity are needed when combined with green fluorescence measurements. We also confirm that no immunoglobulin specific sequence is needed to target hypermutation. Depending on their position in these ectopically expressed constructs, enhancers can have positive or negative effects on hypermutation.

Animals↗
PubMed2004

Mutational activity in cell line WEHI-231.

The cell line WEHI-231 expresses activation-induced cytidine deaminase (AID), the enzyme that mediates hypermutation and immunoglobulin class switch recombination in activated B cells. Although both the cDNA sequence and protein expression of AID appear normal, the frequency of mutation at the endogenous immunoglobulin locus is low. In this report, we have tested the mutational activity of the cell line with three different indicator constructs. The first construct measures a composite rate of transversions of C to G and C to A, respectively. The second construct measures only transversion from C to G. The third measures the canonical AID activity, from C to U, which after cell replication can result in a C to T transition. We found that in WEHI-231, the C to G activity is 32- to 37-times lower than in the hypermutating cell line 18-81. The C to T activity is also much reduced, but only 12-fold. We suggest that the WEHI-231 lacks an activity that subverts the faithful repair of incipient C to U mutations.

Animals↗
PubMed2004

Autoreactivity and allelic inclusion in a B cell nuclear transfer mouse.

Lymphocytes typically express only one functional antigen receptor, a restriction contributed to by allelic exclusion. Here we have analyzed B lymphocyte development in offspring of a mouse generated by nuclear transfer using a single donor B lymphocyte. In this mouse, all immunoglobulin alleles were inherited as found in the donor lymphocyte. This donor cell had two rearranged immunoglobulin light chain alleles, both directing the synthesis of light chains that could form functional antigen receptors, one of which was autoreactive. Progeny mice carrying this immunoglobulin light chain allele produced mature B cells, some of which continued to express the autoreactive receptor but required another rearrangement to rescue them from negative selection. Such receptor editing failed to destroy expression of one original light chain allele, thereby recreating dual receptor expression on these surviving B cells. We suggest that autoreactive antibodies in serum of mice and humans are due in part to such 'passenger' receptors.

Alleles↗
PubMed2004

Directed molecular evolution by somatic hypermutation.

After rearrangement of immunoglobulin gene segments, the immune system evolves the antibody repertoire by mutating the immunoglobulin variable region at a high rate. While this somatic hypermutation was thought to occur only at the variable region, recent studies suggest that hypermutation can occur at locations throughout the genome. Building upon this notion, we sought to exploit this mechanism as a mutagenesis tool. We created a substrate based on GFP that could be screened using flow cytometry and showed that retroviral infection can deliver the transgene to genomic locations that support hypermutation. Infected cells generated various GFP mutants with increased fluorescence intensity and analysis revealed mutations not only at the chromophore, but also an unexpected mutation at a distant residue. Our results demonstrate in principle that immunoglobulin somatic hypermutation can be a potent means of mutagenesis. With appropriate selection conditions it may be utilized to evolve gene products with desired properties.

Amino Acid Sequence↗
PubMed2004

Precise dosage of an endogenous mutagen in the immune system.

Four decades ago, it was hypothesized that lymphocytes mutate the immunoglobulin loci at a rate much greater than the spontaneous rate. Over time this Ig somatic hypermutation became the prime example of in vivo, site-directed mutagenesis. But recent studies have demonstrated that this is not necessarily the case, and that hypermutation occurs not only at the Ig locus but also at various locations throughout the genome. Here, we propose that hypermutation can be genome-wide with minimal injury, if a sufficient mutation rate is coupled with strong clonal selection.

Animals↗
PubMed2004

Endogenous expression of activation-induced cytidine deaminase in cell line WEHI-231.

Because of its susceptibility to apoptosis on Ag receptor cross-linking, cells of the mouse cell line WEHI-231 have been classified as immature B cells. Surprisingly, however, the cell line expresses activation-induced cytidine deaminase, the enzyme that mediates hypermutation and Ig class switch recombination in activated B cells. Although both cDNA sequence and protein expression of activation-induced cytidine deaminase appear normal, the cell line does not hypermutate an indicator plasmid. For the readout, the indicator plasmid depends on the removal of deoxyuridine after transition from C to U and, therefore, on functional expression of uracil N-glycosylase 2, which is normal in WEHI-231. At the endogenous Ig locus, however, WEHI-231 does undergo the canonical hypermutation of G. C to A. T base pairs to some extent. The cell line also expresses the germline transcripts of the Ig gamma 2b, epsilon, and alpha loci, but it does not switch its IgM surface Ig.

Amino Acid Sequence↗
PubMed2004

DNA acrobats of the Ig class switch.

Small resting B lymphocytes all start out producing IgM Abs. Upon encountering Ag, the cells become activated and make a switch from IgM to other Ig classes. This class switch serves to distribute a particular V region to different Ig C regions. Each C region mediates a specialized effector function, and so, through switching, an organism can guide its Abs to various sites. Creating the new H chain requires loop-out and deletion of DNA between switch regions. These DNA acrobatics require transcription of the switch regions, presumably so that necessary factors can gain access to the DNA. These requisite switching factors include activation-induced cytidine deaminase and components of general DNA repair, including base excision repair, mismatch repair, and double-strand break repair. Despite much recent progress, not all important factors have been discovered, especially those that may guide recombination to a particular subclass.

Animals↗
PubMed2004

Genome-wide somatic hypermutation.

DNA mutagenesis is generally considered harmful. Yet activated B cells normally mutate the Ig loci. Because this somatic hypermutation is potentially dangerous, it has been hypothesized that mutations do not occur throughout the genome but instead are actively targeted to the Ig loci. Here we challenge this longstanding and widely accepted hypothesis. We demonstrate that hypermutation requires no Ig gene sequences. Instead, activation-induced cytidine deaminase and other trans-acting hypermutation factors may function as general mutators.

Cell Line↗
PubMed2004

A murine leukemia virus with Cre-LoxP excisible coding sequences allowing superinfection, transgene delivery, and generation of host genomic deletions.

BACKGROUND: To generate a replication-competent retrovirus that could be conditionally inactivated, we flanked the viral genes of the Akv murine leukemia virus with LoxP sites. This provirus can delete its envelope gene by LoxP/Cre mediated recombination and thereby allow superinfection of Cre recombinase expressing cells. RESULTS: In our studies, the virus repeatedly infected the cell and delivered multiple copies of the viral genome to the host genome; the superinfected cells expressed a viral transgene on average twenty times more than non-superinfected cells. The insertion of multiple LoxP sites into the cellular genome also led to genomic deletions, as demonstrated by comparative genome hybridization. CONCLUSION: We envision that this technology may be particularly valuable for delivering transgenes and/or causing deletions.

3T3 Cells↗
PubMed2004

DNA-PKcs function regulated specifically by protein phosphatase 5.

Unrepaired DNA double-strand breaks can lead to apoptosis or tumorigenesis. In mammals double-strand breaks are repaired mainly by nonhomologous end-joining mediated by the DNA-PK complex. The core protein of this complex, DNA-PKcs, is a DNA-dependent serine/threonine kinase that phosphorylates protein targets as well as itself. Although the (auto)phosphorylation activity has been shown to be essential for repair of both random double-strand breaks and induced breaks at the immunoglobulin locus, the corresponding phosphatase has been elusive. In fact, to date, none of the putative phosphatases in DNA double-strand break repair has been identified. Here we show that protein phosphatase 5 interacts with DNA-PKcs and dephosphorylates with surprising specificity at least two functional sites. Cells with either hypo- or hyperphosphorylation of DNA-PKcs at these sites show increased radiation sensitivity.

Animals↗
PubMed2003

Inhibitory coreceptors activated by antigens but not by anti-Ig heavy chain antibodies install requirement of costimulation through CD40 for survival and proliferation of B cells.

Ag-induced B cell proliferation in vivo requires a costimulatory signal through CD40, whereas B cell Ag receptor (BCR) ligation by anti-Ig H chain Abs, such as anti-Ig micro H chain Ab and anti-Ig delta H chain Ab, alone induces proliferation of B cells in vitro, even in the absence of CD40 ligation. In this study, we demonstrate that CD40 signaling is required for survival and proliferation of B cells stimulated by protein Ags in vitro as well as in vivo. This indicates that the in vitro system represents B cell activation in vivo, and that protein Ags generate BCR signaling distinct from that by anti-Ig H chain Abs. Indeed, BCR ligation by Ags, but not by anti-Ig H chain Abs, efficiently phosphorylates the inhibitory coreceptors CD22 and CD72. When these coreceptors are activated, anti-Ig H chain Ab-stimulated B cells can survive and proliferate only in the presence of CD40 signaling. Conversely, treatment of Ag-stimulated B cells with anti-CD72 mAb blocks CD72 phosphorylation and induces proliferation, even in the absence of CD40 signaling. These results strongly suggest that activation of B cells by anti-Ig H chain Abs involves their ability to silence the inhibitory coreceptors, and that the inhibitory coreceptors install requirement of CD40 signaling for survival and proliferation of Ag-stimulated B cells.

Animals↗
PubMed2002

SWAP-70-deficient mast cells are impaired in development and IgE-mediated degranulation.

Cross-linking of the high-affinity IgE receptor (FcepsilonRI) on mast cell activates signaling pathways that trigger degranulation and the release of multiple pro-inflammatory mediators. Mature,immature and precursor mast cells are degranulation competent. We show here that the signaling protein SWAP-70 has a function in mast cell biology. While not found in many cell types, we find that apart from B cells, mast cells also express SWAP-70. In activated B cells, SWAP-70 shuttles between cytoplasm and nucleus, but in mast cells it is confined to the cytoplasm. SWAP-70(ko/ko) (double knockout) mice have reduced numbers of mature mast cells, and these are degranulation competent. However, although immature mast cells from SWAP-70(ko/ko) mice respond normally to SCF and IL-3 and have functional granules, their FcepsilonRI-mediated degranulation is inhibited. Thus, in mast cells SWAP-70 plays a role both in establishing the initial competence to degranulate and to develop into mature mast cells.

Animals↗