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Mouse models of human cancers are important for understanding determinants of overt disease and for "preclinical" development of rational therapeutic strategies; for instance, based on macrodrugs. Chromosomal translocations underlie many human leukemias, sarcomas, and epithelial tumors. We have developed three technologies based on homologous recombination in mouse ES cells to mimic human chromosome translocations. The first, called the knockin method, allows creation of fusion genes like those typical of translocations of human leukemias and sarcomas. Two new conditional chromosomal translocation mimics have been developed. The first is a method for generating reciprocal chromosomal translocations de novo using Cre-loxP recombination (translocator mice). In some cases, there is incompatible gene orientation and the translocator model cannot be applied. We have developed a different model (invertor mice) for these situations. This method consists of introducing an inverted cDNA cassette into the intron of a target gene and bringing the cassette into the correct transcriptional orientation by Cre-loxP recombination. We describe experiments using the translocator model to generate MLL-mediated neoplasias and the invertor method to generate EWS-ERG-mediated cancer. These methods mimic the situation found in human chromosome translocations and provide the framework for design and study of human chromosomal translocations in mice.

The MRL-lpr/lpr mouse strain is a commonly used model of the human autoimmune disease systemic lupus erythematosus (SLE). Although much is known about the contribution of the lpr Fas mutation to B cell tolerance breakdown, the role of the genetic background of the MRL strain itself is less well explored. In this study, we use the MD4 anti-hen egg lysozyme Ig (Ig HEL ) transgenic system to explore B cell function in MRL1/1 and non-autoimmune mice. We demonstrate that MRL Ig HEL B cells show spontaneous hyperactivity in the absence of self-antigen, which is associated with low total B cell numbers but an expansion of the marginal zone B cell population. However, B cell anergy is normal in the presence of soluble lysozyme [soluble hen egg lysozyme (sHEL)], and MRL Ig HEL B cells undergo normal elimination in the presence of sHEL when competing with a polyclonal C57BL/6 B cell repertoire. We conclude that B cell hyperactivity may contribute to the autoimmune phenotype of MRL1/1 and MRL-lpr/lpr strains when it initiates antibody responses to rare or sequestered antigens that are below the threshold for tolerance induction, but that there is no B cell intrinsic defect in anergy in MRL mice.

To study the genetics of atopy systematically we established a mouse model that provides the general phenotype of atopy: the early response characteristic of IgE-dependent eczema or atopic dermatitis, and the diagnostic test of atopy, the skin-prick test. Using an immediate cutaneous hypersensitivity test (ICHS) against birch pollen extract we could classify A/J and C57BL/6 (B6) inbred mouse strains respectively as high responder and low responders. The F1 hybrids were found to be high responders with incomplete penetrance. Backcrossing F1 mice to the low responder B6 strain yielded three classes of responders, high, intermediate, and low. A genome-wide microsatellite screen of the backcross progeny disclosed suggestive linkage to a microsatellite marker on chromosome 6 close to the locus of the IL-5 receptor alpha chain. Its allelic variation in A/J and B6 strains was investigated and two major differences were detected. Firstly, a nucleotide exchange in the 5' untranslated region of B6 mRNA resulted in increased transcription/translation of a reporter construct. Higher expression of the receptor on the cell surface would be expected to favor an allergic immune response. Secondly, the two alleles are differentially spliced so as to yield two soluble isoforms in A/J mice versus one in B6 mice. Higher expression of soluble IL-5R would be expected to reduce the level of allergy through capture of IL-5. Thus both findings conform to the expectation based on susceptibility to atopy and thus identify the IL-5R alpha chain as a likely contributor to the genetics of atopy.

Background: Mouse models have been established mirroring key features of human bronchial asthma including airway hyperresponsiveness (AHR). Acute airway obstruction in response to an allergen challenge, however, remains to be demonstrated in these models. Objective: A mouse model of allergic lung inflammation was employed to analyze the development of specific (allergen-induced) and nonspecific (methacholine-induced) airway obstruction. Methods: Mice were sensitized to ovalbumin (OVA) and challenged with OVA aerosol twice each week during four weeks. Changes in lung functions were determined by noninvasive head-out body plethysmography. The development of acute airway obstruction after OVA challenge and AHR after methacholine aerosol application were assessed by a decrease in the mid-expiratory flow rate (EF50). Results: Two airway challenges were sufficient to induce AHR (5.7 vs. 15 mg/ml methacholine). Further OVA challenges reduced the baseline EF50 from 1.85 to 1.20 ml/s (4th week) and induced acute airway obstruction. The OVA-induced obstruction was maximal in the 4th week (EF50 = 0.91 ml/s). Conclusion: The development of acute airway obstruction in allergen-sensitized mice was demonstrated by means of head-out body plethysmography. In our model, AHR was observed before the development of airway obstruction.

Chronic skin colonization with Staphylococcus aureus is a well-known feature in atopic dermatitis. The aim of this study was to develop a human-SCID mouse model to analyze the possible role of bacterial superantigens in human allergic immune responses under in vivo conditions. SCID mice were reconstituted with peripheral blood mononuclear cells (between 2 and 9 x 10(7) cells per mouse) from atopic dermatitis patients sensitized to house dust mite allergen (Der p). Total and Der p specific antibody production required the following conditions: (i) injection of Der p; (ii) presence of CD14+ antigen-presenting cells; and (iii) IL-4 as shown by the inhibitory effect of human soluble IL-4 receptor on immunoglobulin E production. This model was used to study the immunomodulatory effects of the superantigen staphylococcal enterotoxin B in comparison with Der p. In intraperitoneally reconstituted human-SCID mice, topical treatment was ineffective in inducing skin inflammation. Therefore, additionally to intraperitoneal transfer, peripheral blood mononuclear cells from atopic donors were also injected intradermally. Such reconstituted SCID mice were then exposed via the skin to either Der p, staphylococcal enterotoxin B, or a combination of both. Maximal effects on epidermal inflammation and dermal T cell infiltration were obtained with staphylococcal enterotoxin B and Der p. Staphylococcal enterotoxin B alone was less effective and Der p only stimulated dermal T cell infiltration. These findings support the hypothesis that bacterial superantigens can act as trigger factors in allergic skin inflammation.

For a series of immunological diseases including asthma, inflammatory arthritis and experimental allergic encephalomyelitis the non-classical major histocompatibility complex (MHC) genetics of man and mouse has been making rapid progress. Information is available not only for the disease associations of individual candidate genes but also from the first genome scans. In both species the proinflammatory cytokine genes and/or their related receptors and inhibitors (IL-1, IL-1r, IL-1ra, IL-2, IL-6r, TNF-alpha), and to a lesser extent the anti-inflammatory cytokine IL-4 are implicated as candidate control elements. In contrast, genes for the signalling and adhesion CD molecules have so far been inconspicuous. Most of the polymorphisms so far detected have been in the regulatory sequences of these genes, rather than in the exons. It is suggested that the benefit conferred on an individual by greater flexibility in its immunoregulatory machinery may be responsible for maintaining this form of polymorphism.

To detect rare epigenetic effects associated with assisted reproduction, it is necessary to monitor methylation patterns of developmentally important genes in a few germ cells and individual embryos. Bisulfite treatment degrades DNA and reduces its complexity, rendering methylation analysis from small amounts of DNA extremely challenging. Here we describe a simple approach that allows determining the parent-specific methylation patterns of multiple genes in individual early embryos. Limiting dilution (LD) of bisulfite-treated DNA is combined with independent multiplex PCRs of single DNA target molecules to avoid amplification bias. Using this approach, we compared the methylation status of three imprinted (H19, Snrpn and Igf2r) and one pluripotency-related gene (Oct4) in three different groups of single mouse two-cell embryos. Standard in vitro fertilization of superovulated oocytes and the use of in vitro matured oocytes were not associated with significantly increased rates of stochastic single CpG methylation errors and epimutations (allele methylation errors), when compared with the in vivo produced controls. Similarly, we compared the methylation patterns of two imprinted genes (H19 and Snrpn) in individual mouse 16-cell embryos produced in vivo from superovulated and non-superovulated oocytes and did not observe major between-group differences. Using bovine oocytes and polar bodies as a model, we demonstrate that LD even allows the methylation analysis of multiple genes in single cells.

MLL-AF4 fusion is the most common consequence of chromosomal translocations in infant leukaemia and is associated with a poor prognosis. MLL-AF4 is thought to be required in haematopoietic stem cells to elicit leukaemia and may be involved in tumour phenotype specification as it is only found in B-cell tumours in humans. We have employed the invertor conditional technology to create a model of MLL-AF4, in which a floxed AF4 cDNA was knocked into Mll in the opposite orientation for transcription. Cell-specific Cre expression was used to generate Mll-AF4 expression. The mice develop exclusively B-cell lineage neoplasias, whether the Cre gene was controlled by B- or T-cell promoters, but of a more mature phenotype than normally observed in childhood leukaemia. These findings show that the MLL-AF4 fusion protein does not have a mandatory role in multi-potent haematopoietic stem cells to cause cancer and indicates that MLL-AF4 has an instructive function in the phenotype of the tumour.

Chromosomal translocations are primary events in tumorigenesis. Those involving the mixed lineage leukaemia (MLL) gene are found in various guises and it is unclear whether MLL fusions can affect haematopoietic differentiation. We have used a model in which chromosomal translocations are generated in mice de novo by Cre-loxP-mediated recombination (translocator mice) to compare the functionally relevant haematopoietic cell contexts for Mll fusions, namely pluripotent stem cells, semicommitted progenitors or committed cells. Translocations between Mll and Enl or Af9 cause myeloid neoplasias, initiating in pluripotent stem cells or multipotent myeloid progenitors. However, while Mll-Enl translocations can also cause leukaemia from T-cell progenitors, no tumours arose with Mll-Af9 translocations in the T-cell compartment. Furthermore, Mll-Enl translocations in T-cell progenitors can cause lineage reassignment into myeloid tumours. Therefore, a permissive cellular environment is required for oncogenicity of Mll-associated translocations and Mll fusions can influence haematopoietic lineage commitment.

The EWS-ERG fusion protein is found in human sarcomas with the chromosomal translocation t(21;22)(q22;q12), where the translocation is considered to be an initiating event in sarcoma formation within uncommitted mesenchymal cells, probably long-lived progenitors capable of self renewal. The fusion protein may not therefore have an oncogenic capability beyond these progenitors. To assess whether EWS-ERG can be a tumour initiator in cells other than mesenchymal cells, we have analysed Ews-ERG fusion protein function in a cellular environment not typical of that found in human cancers, namely, committed lymphoid cells. We have used Ews-ERG invertor mice having an inverted ERG cDNA cassette flanked by loxP sites knocked in the Ews intron 8, crossed with mice expressing Cre recombinase under the control of the Rag1 gene to give conditional, lymphoid-specific expression of the fusion protein. Clonal T cell neoplasias arose in these mice. This conditional Ews gene fusion model of tumourigenesis shows that Ews-ERG can cause haematopoietic tumours and the precursor cells are committed cells. Thus, Ews-ERG can function in cells that do not have to be pluripotent progenitors or mesenchymal cells., Using a mouse model, these authors study the potential of a known cancer-related gene to cause tumors in cells committed to different lineages.

Chromosomal1 translocations are key elements in tumor etiology, as these somatically created abnormal chromosomes have activated oncogenes where the chromosome breakpoints occur (for review, see Rabbitts 1994). Most often, gene fusions are caused by chromosomal translocations, which frequently break within the exons of the two involved chromosomes, allowing the transcription product to encompass the linked exons, for post-transcriptional processing to splice these exons to create a tumor-specific fusion mRNA and in turn fusion protein. This type of event is common in both leukemias and in sarcomas (Rabbitts 1994; Look 1997). The leukemias divide into chronic and acute forms of cancer. The translocation genes involved can be roughly categorized into distinct types, with those involved in acute leukemia often being transcription regulators (Cleary 1991) whose role as master genes in cell fate determination is a key element in their role in leukemias (Rabbitts 1991). Thus, activated oncogenes or gene fusions influence differentiation in cell-specific ways and the tropism of specific chromosomal translocations for specific cell types is a manifestation of this role.

The etiology of human tumors often involves chromosomal translocations. Models that emulate translocations are essential to understanding the determinants of frank malignancy, those dictating the restriction of translocations to specific lineages, and as a basis for development of rational therapeutic methods. We demonstrate that developmentally regulated Cre-loxP-mediated interchromosomal recombination between the Mll gene, whose human counterpart is involved in a spectrum of leukemias, and the Enl gene creates reciprocal chromosomal translocations that cause myeloid tumors. There is a rapid onset and high penetrance of leukemogenesis in these translocator mice, and high proportions of cells carrying chromosomal translocations can be found in bone marrow as early as 12 days after birth. This de novo strategy is a direct recapitulation of naturally occurring human cancer-associated translocations.

Atopic disorders are complex traits with a significant contribution of heritability. Several mouse models for atopic phenotypes such as allergen-induced and intrinsic asthma, atopic dermatitis and immediate cutaneous hypersensitivity have been used to systematically dissect the genetics of these diseases. Many of the chromosomal regions identified in genome-wide screens colocalize with linkage regions of autoimmune phenotypes suggesting common regulatory genes in combination (or addition) to disease-specific genes. Moreover, many of these regions correspond to regions found in the human system, thus strengthening the likelihood of a gene contributing to the phenotype. The role of individual candidate genes has been vigorously pursued in genetically modified mice by destruction or overexpression of the candidate gene. The complex interactions of multiple contributing genes may further be elucidated in randomly mutated mouse strains. Thus mouse models can contribute largely to the elucidation of disease genes.

Antigen-induced airway hyperresponsiveness and airway inflammation are features of both human asthma and animal models of this disease. The genesis of these key asthma phenotypes represents the summation of a complex cascade of immune responses. It is hypothesized that multiple cell types are involved in the induction, propagation, and maintenance of these immune processes. Several molecules have been reported to be essential for cell-cell interactions, inflammatory cell recruitment, and effector functions leading to the overall expression of the asthmatic phenotype. This review summarizes the genetic evidence supporting a role for these molecules in antigen-driven airway hyperresponsiveness and inflammation.

Asthma is a disease characterized by intermittent airway obstruction, inflammatory cell infiltrates, increased mucus production, lung epithelial remodeling, and airway hyperreactivity. The genetics of asthma, as investigated in animal models, is poorly understood. Because no animal model of asthma mimics all of the pathologic and physiological features of asthma, genetic studies have focused on several phenotypes, including intrinsic or native airway hyperreactivity. It is generally accepted that both genetic and environmental factors determine the phenotypic expression of this complex disease. The genetics of airway hyperresponsiveness, as investigated in the mouse, are presented in this review. The inbred mouse currently represents the most valuable genetic resource for understanding the factors that control this complex phenotype.

A method for the noninvasive measurement of airway responsiveness was validated in allergic BALB/c mice. With head-out body plethysmography and the decrease in tidal midexpiratory flow (EF50) as an indicator of airway obstruction, responses to inhaled methacholine (MCh) and the allergen ovalbumin were measured in conscious mice. Allergen-sensitized and -challenged mice developed airway hyperresponsiveness as measured by EF50 to aerosolized MCh compared with that in control animals. This response was associated with increased allergen-specific IgE and IgG1 production, increased levels of interleukin-4 and interleukin-5 in bronchoalveolar lavage fluid and eosinophilic lung inflammation. Ovalbumin aerosol challenge elicited no acute bronchoconstriction but resulted in a significant decline in EF50 baseline values 24 h after challenge in allergic mice. The decline in EF50 to MCh challenge correlated closely with simultaneous decreases in pulmonary conductance and dynamic compliance. The decrease in EF50 was partly inhibited by pretreatment with the inhaled β2-agonist salbutamol. We conclude that measurement of EF50 to inhaled bronchoconstrictors by head-out body plethysmography is a valid measure of airway hyperresponsiveness in mice.

To facilitate whole-genome scan experiments, we selected a panel of 128 microsatellite markers on the basis of spacing and polymorphism in the strains DBA/2, BALB/c, AKR, C57BL/6, C57BL/10, A/J, C3H, 129/J, SJL/J, JF1, and PWB. Many of the primer pairs were redesigned for better performance. The last four strains were not characterized previously using these markers. JF1 and PWB are particularly interesting for intersubspecific crosses offering high polymorphism. We provide allele size data for the markers on these strains and add them to the emerging radiation hybrid framework map, which is not continuous except for chromosome 17 and 13. Information on the interrelationships of strains is useful both because of the importance of polymorphism in designing crosses and the background in assessing phenotypes. Microsatellites offer a widely dispersed, selectively neutral set of characters that lends itself conceptually to parsimony methods of analysis. The microsatellite allele size data were recoded as binary discrete characters in such a way that adjacent sizes differ by one step. Trees were generated using a Wagner parsimony method. As expected, the non-Mus domesticus strains, PWB (musculus) and JF1 (molossinus), are excluded from the domesticus strains. Among the domesticus strains, C57BL/6 and C57BL/10 (derived from the same founding pair) form a strongly supported group, as do C3H, A/J, and BALB/c (derived from the Bagg albino stock). No unique branching order for SJL/J, AKR, and DBA/2 is strongly supported, which may reflect a complicated history. Strain 129/J is clearly placed as the most deeply diverged of thedomesticus strains represented.

Genetic predisposition and environmental factors modulate the expression of allergic phenotypes. The frequent allergic phenotype 'immediate cutaneous hypersensitivity' was established in mice as a model for atopy. Genetic dissection of this trait requires a robust procedure to assess the allergic phenotype. To this end, different mouse strains were immunized with birch pollen extract. Immediate cutaneous hypersensitivity reactions were induced through intradermal allergen exposure. Wheel formation was quantitated and expressed as a hypersensitivity score according to the bonitur method. This procedure identified A/J and C57BL/6 mice as high– and low–responder strains, respectively. Crosses of A/J and C57BL/6 mice should allow the characterization of mendelian factors responsible for the two extreme phenotypes identified here.

Bronchial asthma (BA) develops on the basis of a genetic predisposition and involves a characteristic sequence of changes in immune functions. In the immunopathogenesis, several phases can be distinguished: the initial stage is defined as the development of allergic sensitization. This step is dependent on: (i) T cell activation; (ii) IL-4 production; (iii) IgE synthesis; and (iv) mediator release by effector cells. The second phase of allergic inflammation as a consequence of the T cell dependent sensitization is characterized by IL-5 production and eosinophil activation and recruitment. Airway mucosa remodelling is the consequence of chronic inflammatory processes and represents the final stage of BA. In this article animal models will be discussed with regard to their relevance for these different phases in development of chronic allergic BA.