Mapping of an insulin-dependent diabetes locus, Idd9, in NOD mice to chromosome 4

The Role of NOD Mice in Type 1 Diabetes Research: Lessons from the Past and Recommendations for the Future

For more than 35 years, the NOD mouse has been the primary animal model for studying autoimmune diabetes. During this time, striking similarities to the human disease have been uncovered. In both species, unusual polymorphisms in a major histocompatibility complex (MHC) class II molecule confer the most disease risk, disease is caused by perturbations by the same genes or different genes in the same biological pathways and that diabetes onset is preceded by the presence of circulating autoreactive T cells and autoantibodies that recognize many of the same islet antigens. However, the relevance of the NOD model is frequently challenged due to past failures translating therapies from NOD mice to humans and because the appearance of insulitis in mice and some patients is different. Nevertheless, the NOD mouse remains a pillar of autoimmune diabetes research for its usefulness as a preclinical model and because it provides access to invasive procedures as well as tissues that are rarely procured from patients or controls. The current article is focused on approaches to improve the NOD mouse by addressing reasons why immune therapies have failed to translate from mice to humans. We also propose new strategies for mixing and editing the NOD genome to improve the model in ways that will better advance our understanding of human diabetes. As proof of concept, we report that diabetes is completely suppressed in a knock-in NOD strain with a serine to aspartic acid substitution at position 57 in the MHC class II Aβ. This supports that similar non-aspartic acid substitutions at residue 57 of variants of the human class II HLA-DQβ homolog confer diabetes risk.

A recombination hotspot leads to sequence variability within a novel gene (AK005651) and contributes to type 1 diabetes susceptibility

More than 25 loci have been linked to type 1 diabetes (T1D) in the nonobese diabetic (NOD) mouse, but identification of the underlying genes remains challenging. We describe here the positional cloning of a T1D susceptibility locus, Idd11, located on mouse chromosome 4. Sequence analysis of a series of congenic NOD mouse strains over a critical 6.9-kb interval in these mice and in 25 inbred strains identified several haplotypes, including a unique NOD haplotype, associated with varying levels of T1D susceptibility. Haplotype diversity within this interval between congenic NOD mouse strains was due to a recombination hotspot that generated four crossover breakpoints, including one with a complex conversion tract. The Idd11 haplotype and recombination hotspot are located within a predicted gene of unknown function, which exhibits decreased expression in relevant tissues of NOD mice. Notably, it was the recombination hotspot that aided our mapping of Idd11 and confirms that recombination hotspots can create genetic variation affecting a common polygenic disease. This finding has implications for human genetic association studies, which may be affected by the approximately 33,000 estimated hotspots in the genome.

Emerging roles for B lymphocytes in Type 1 diabetes

Self-reactive B lymphocytes play two main pathological roles in autoimmune diseases: as secretors of autoantibodies and as specialized antigen-presenting cells that present self-components to autoreactive T lymphocytes. In recognition of these roles, recent clinical trials have utilized B-lymphocyte-depleting monoclonal antibodies to treat various autoimmune diseases, with encouraging results in those where humoral autoimmunity is clearly important. Surprisingly, recent results in animal models suggest that B-lymphocyte depletion may also be effective in the treatment of T-lymphocyte-mediated autoimmune diseases, such as Type 1 diabetes (T1D). This article reviews the experimental evidence that has uncovered pathogenic as well as regulatory roles for B lymphocytes in the prodrome of T1D and how this information is being used to develop novel therapeutic strategies to treat the disease.

Genetic Control of Susceptibility to Autoimmune Gastritis

A familial component to the tendency to develop autoimmune gastritis has long been recognized. Although linkage to certain HLA alleles and an association with the endocrine autoimmune diseases thyroiditis and type 1 diabetes have been reported, little further progress has been achieved in clinical studies. In contrast, the mouse model of gastritis induced in the BALB/c strain by thymectomy in the third day of life has identified four linkage regions; two on distal chromosome 4 (Gasa1 and Gasa2), one on chromosome 6 (Gasa3) and one in the H2 (Gasa4). Three of these four genes colocalize with NOD mouse diabetes susceptibility genes--the strongest concordance identified to date between any two autoimmune diseases--reflecting the association between autoimmune diabetes and type 1 gastritis in humans.

Localization of Idd11 is not associated with thymus and nkt cell abnormalities in NOD mice

Congenic mouse strains provide a unique resource for genetic dissection and biological characterization of chromosomal regions associated with diabetes progression in the nonobese diabetic (NOD) mouse. Idd11, a mouse diabetes susceptibility locus, was previously localized to a region on chromosome 4. Comparison of a panel of subcongenic NOD mouse strains with different intervals derived from the nondiabetic C57BL/6 (B6) strain now maps Idd11 to an approximately 8-Mb interval. B6-derived intervals protected congenic NOD mice from diabetes onset, even though lymphocytic infiltration of pancreatic islets was similar to that found in NOD mice. In addition, neither thymic structural irregularities nor NKT cell deficiencies were ameliorated in diabetes-resistant congenic NOD mice, indicating that Idd11 does not contribute to these abnormalities, which do not need to be corrected to prevent disease.

Sex-Specific Effect of Insulin-Dependent Diabetes 4 on Regulation of Diabetes Pathogenesis in the Nonobese Diabetic Mouse

Many human autoimmune diseases are more frequent in females than males, and their clinical severity is affected by sex hormone levels. A strong female bias is also observed in the NOD mouse model of type I diabetes (T1D). In both NOD mice and humans, T1D displays complex polygenic inheritance and T cell-mediated autoimmune pathogenesis. The identities of many of the insulin-dependent diabetes (Idd) loci, their influence on specific stages of autoimmune pathogenesis, and sex-specific effects of Idd loci in the NOD model are not well understood. To address these questions, we analyzed cyclophosphamide-accelerated T1D (CY-T1D) that causes disease with high and similar frequencies in male and female NOD mice, but not in diabetes-resistant animals, including the nonobese diabetes-resistant (NOR) strain. In this study we show by genetic linkage analysis of (NOD x NOR) x NOD backcross mice that progression to severe islet inflammation after CY treatment was controlled by the Idd4 and Idd9 loci. Congenic strains on both the NOD and NOR backgrounds confirmed the roles of Idd4 and Idd9 in CY-T1D susceptibility and revealed the contribution of a third locus, Idd5. Importantly, we show that the three loci acted at distinct stages of islet inflammation and disease progression. Among these three loci, Idd4 alleles alone displayed striking sex-specific behavior in CY-accelerated disease. Additional studies will be required to address the question of whether a sex-specific effect of Idd4, observed in this study, is also present in the spontaneous model of the disease with striking female bias.

Understanding the human condition: experimental strategies in mammalian genetics

Mice have become the mammalian model of choice for the application of genetics in biomedical research due to the evolutionary conservation of physiological systems and their attendant pathologies among all mammals as well as the exceptional power of genetic research technologies in the species. Beginning from aberrant phenotypes, a large number of mouse mutants and natural polymorphisms have been cloned, providing much information about the molecular basis of physiological processes. Additionally, the variable expression of these mutations in different inbred strain backgrounds has demonstrated the importance of modifier genes, which are also susceptible to cloning. Research efforts are keeping pace with these developments. In the area of gene discovery, large, government-funded mutagenesis programs now exist, and as a matter of great practical importance, recent evidence suggests that the same genes may be involved in the natural polymorphisms affecting disease in mice and humans. In parallel, dramatic advances are also being made in our ability to measure physiological processes in mice, and the advent of expression profiling promises revolutionary advances in understanding phenotype at the molecular level. Gene-driven approaches have relied on engineering the mouse genome, including adding, subtracting, and replacing genes and, most recently, the ability to control gene activity reversibly. Together, these multiple advances in our technical abilities have created extraordinary opportunities for future discovery.

Genetic heterogeneity of autoimmune disorders in the nonobese diabetic mouse

The nonobese diabetic mouse is highly susceptible not only to diabetes but to several autoimmune diseases, and one might suspect that these are controlled by a shared set of genes. However, based on various gene-segregation experiments, it seems that only a few loci are shared and that each disorder is influenced also by a unique set of genes.

Genetic analysis of autoimmune sialadenitis in nonobese diabetic mice: a major susceptibility region on chromosome 1

The nonobese diabetic (NOD) mouse strain provides a good study model for Sjögren's syndrome (SS). The genetic control of SS was investigated in this model using different matings, including a (NOD x C57BL/6 (B6))F(2) cross, a (NOD x NZW)F(2) cross, and ((NOD x B6) x NOD) backcross. Multiple and different loci were detected depending on parent strain combination and sex. Despite significant complexity, two main features were prominent. First, the middle region of chromosome 1 (chr.1) was detected in all crosses. Its effect was most visible in the (NOD x B6)F(2) cross and dominated over that of other loci, including those mapping on chr.8, 9, 10, and 16; the effect of these minor loci was observed only in the absence of the NOD haplotype on chr.1. Most critically, the chr.1 region was sufficient to trigger an SS-like inflammatory infiltrate of salivary glands as shown by the study of a new C57BL/6 congenic strain carrying a restricted segment derived from NOD chr.1. Second, several chromosomal regions were previously associated with NOD autoimmune phenotypes, including Iddm (chr.1, 2, 3, 9, and 17, corresponding to Idd5, Idd13, Idd3, Idd2, and Idd1, respectively), accounting for the strong linkage previously reported between insulitis and sialitis, and autoantibody production (chr.10 and 16, corresponding to Bana2 and Bah2, respectively). Interestingly, only two loci were detected in the (NOD x NZW)F(2) cross, on chr.1 in females and on chr.7 in males, probably because of the latent autoimmune predisposition of the NZW strain. Altogether these findings reflect the complexity and heterogeneity of human SS.

Association study between CD30 and CD30 ligand genes and type 1 diabetes in the Japanese population

CD30-CD30 ligand (CD30L) signal transduction appears to protect against autoimmune diabetes by preventing expansion of autoreactive T cells and suppressing Th1-cytokine response. The purpose of this study was to determine whether CD30 or CD30L genes serve as a novel susceptibility gene for type 1 diabetes in humans. We screened CD30 and CD30L genes for polymorphisms in Japanese patients with type 1 diabetes and control subjects. Then, association studies were performed between each of the identified polymorphisms and type 1 diabetes. Direct-sequencing analysis of the CD30 and CD30L genes revealed four polymorphisms: one in the CD30 gene (-201G/A from the transcription start site), and three in the CD30L gene [CA repeat in the promoter, 276G/A in the exon 3, -73T/C in the intron 3 (IVS3 -73T/C)]. Association studies revealed no association between the CD30 and CD30L genes and type 1 diabetes in the whole population. In the female and male subpopulations, however, the frequency of (CA)(9) allele of the CD30L gene promoter or T allele of IVS3 -73T/C polymorphism in the CD30L gene was slightly higher in female patients with type 1 diabetes than that in control females. In conclusion, we could not find significant association between CD30 or CD30L genes and type 1 diabetes, but (CA)(9) allele in the promotor or T allele of -73T/C in intron 3 in CD30L gene might play a minor role in the pathogenesis of type 1 diabetes, only in the Japanese female population.

The NOD mouse as a model of SLE

In addition to developing a high incidence of type 1 diabetes caused by a specific autoimmune response against pancreatic beta cells in the islets of Langerhans, NOD mice also demonstrate spontaneous autoimmunity to other targets including the thymus, adrenal gland, salivary glands, thyroid, testis, nuclear components and red blood cells. Moreover, treatment of pre-diabetic NOD mice with an intravenous dose of heat killed Mycobacterium bovis (M. bovis; bacillus Calmette-Guèrin (BCG)) protects them from developing type 1 diabetes, but instead precipitates an autoimmune rheumatic disease similar to systemic lupus erythematosus (SLE), characterised by accelerated and increased incidence of haemolytic anaemia (HA), anti-nuclear autoantibody (ANA) production, exacerbation of sialadenitis, and the appearance of immune complex-mediated glomerulonephritis (GN). The reciprocal switching between the two phenotypes by a single environmental trigger (mycobacterial exposure) raised the possibility that genetic susceptibility for type 1 diabetes and SLE may be conferred by a single collection of genes in the NOD mouse. This review will focus on the genetic components predisposing NOD mice to SLE induced by BCG treatment and compare them to previously determined diabetes susceptibility genes in this strain and SLE susceptibility genes in the BXSB, MRL and the New Zealand mouse strains.

The genetic control of sialadenitis versus arthritis in a NOD.QxB10.Q F2 cross

The non-obese diabetic (NOD) mouse spontaneously develops diabetes and sialadenitis. The sialadenitis is characterized by histopathological changes in salivary glands and functional deficit similar to Sjögren's syndrome. In humans, Sjögren's syndrome could be associated with other connective tissue disorders, such as rheumatoid arthritis. In the present study the genetic control of sialadenitis in mice was compared to that of arthritis. We have previously reported a NOD locus, identified in an F2 cross with the H2(q) congenic NOD (NOD.Q) and C57BL/10.Q (B10.Q) strains, that promoted susceptibility to collagen-induced arthritis. The sialadenitis in NOD.Q showed a similar histological phenotype as in NOD, whereas no submandibular gland infiltration was found in B10.Q. The development of sialadenitis was independent of immunization with type II collagen and established arthritis. To identify the genetic control of sialadenitis, a gene segregation experiment was performed on an (NOD.QxB10.Q)F2 cross and genetic mapping of 353 F2 mice revealed one significant locus associated with sialadenitis on chromosome 4, LOD score 4.7. The NOD.Q allele-mediated susceptibility under a recessive inheritance pattern. The genetic control of sialadenitis seemed to be unique in comparison to diabetes and arthritis, as no loci associated with these diseases have been identified at the same location.

Genetic, physical, and comparative map of the subtelomeric region of mouse Chromosome 4

The subtelomeric region of mouse chromosome (Chr) 4 harbors loci with effects on behavior, development, and disease susceptibility. Regions near the telomeres are more difficult to map and characterize than other areas because of the unique features of subtelomeric DNA. As a result of these problems, the available mapping information for this part of mouse Chr 4 was insufficient to pursue candidate gene evaluation. Therefore, we sought to characterize the area in greater detail by creating a comprehensive genetic, physical, and comparative map. We constructed a genetic map that contained 30 markers and covered 13.3 cM; then we created a 1.2-Mb sequence-ready BAC contig, representing a 5.1-cM area, and sequenced a 246-kb mouse BAC from this contig. The resulting sequence, as well as approximately 40 kb of previously deposited genomic sequence, yielded a total of 284 kb of sequence, which contained over 20 putative genes. These putative genes were confirmed by matching ESTs or cDNA in the public databases to the genomic sequence and/or by direct sequencing of cDNA. Comparative genome sequence analysis demonstrated conserved synteny between the mouse and the human genomes (1p36.3). DNA from two strains of mice (C57BL/6ByJ and 129P3/J) was sequenced to detect single nucleotide polymorphisms (SNPs). The frequency of SNPs in this region was more than threefold higher than the genome-wide average for comparable mouse strains (129/Sv and C57BL/6J). The resulting SNP map, in conjunction with the sequence annotation and with physical and genetic maps, provides a detailed description of this gene-rich region. These data will facilitate genetic and comparative mapping studies and identification of a large number of novel candidate genes for the trait loci mapped to this region.

Genetic control of collagen-induced arthritis in a cross with NOD and C57BL/10 mice is dependent on gene regions encoding complement factor 5 and FcgammaRIIb and is not associated with loci controlling diabetes

The nonobese diabetic (NOD) mouse spontaneously develops autoimmune-mediated diseases such as diabetes and Sjögren's syndrome. To investigate whether NOD genes also promote autoimmune-mediated arthritis we established a NOD strain with an MHC class II fragment containing the A(q) class II gene predisposing for collagen induced arthritis (NOD.Q). However, this mouse was resistant to arthritis in contrast to other A(q) expressing strains such as B10.Q and DBA/1. To determine the major resistance factor/s, a genetic analysis was performed. (NOD.Q x B10.Q)F1 mice were resistant, whereas 27% of the (NOD.Q x B10.Q)F2 mice developed severe arthritis. Genetic mapping of 353 F2 mice revealed two loci associated with arthritis. One locus was found on chromosome 2 (LOD score 9.8), at the location of the complement factor 5 (C5) gene. The susceptibility allele was from B10.Q, which contains a productive C5 encoding gene in contrast to NOD.Q. The other significant locus was found on chromosome 1 (LOD score 5.6) close to the Fc-gamma receptor IIb gene, where NOD carried the susceptible allele. An interaction between the two loci was observed, indicating that they operate on the same or on interacting pathways. The genetic control of arthritis is unique in comparison to diabetes, since none of these loci have been identified in analysis of diabetes susceptibility.

Single QTL effects, epistasis, and pleiotropy account for two-thirds of the phenotypic F(2) variance of growth and obesity in DU6i x DBA/2 mice

Genes influencing body weight and composition and serum concentrations of leptin, insulin, and insulin-like growth factor I (IGF-I) in nonfasting animals were mapped in an intercross of the extreme high-growth mouse line DU6i and the inbred line DBA/2. Significant loci with major effects (F > 7.07) for body weight, obesity, and muscle weight were found on chromosomes 1, 4, 5, 7, 11, 12, 13, and 17, for leptin on chromosome 14, for insulin on chromosome 4, and for IGF-I on chromosome 10 at the Igf1 gene locus itself and on chromosome 18. Significant interaction between different quantitative trait loci (QTL) positions was observed (P < 0.01). Evidence was found that loci having small direct effect on growth or obesity contribute to the obese phenotype by gene-gene interaction. The effects of QTLs, epistasis, and pleiotropy account for 64% and 63% of the phenotypic variance of body weight and fat accumulation and for over 32% of muscle weight and serum concentrations of leptin, and IGF-I in the F(2) population of DU6i x DBA/2 mice. [The quantitative trait loci described in this paper have been submitted to the Mouse Genome Database.]

Single QTL Effects, Epistasis, and Pleiotropy Account for Two-thirds of the Phenotypic F2 Variance of Growth and Obesity in DU6i x DBA/2 Mice

Genes influencing body weight and composition and serum concentrations of leptin, insulin, and insulin-like growth factor I (IGF-I) in nonfasting animals were mapped in an intercross of the extreme high-growth mouse line DU6i and the inbred line DBA/2. Significant loci with major effects (F > 7.07) for body weight, obesity, and muscle weight were found on chromosomes 1, 4, 5, 7, 11, 12, 13, and 17, for leptin on chromosome 14, for insulin on chromosome 4, and for IGF-I on chromosome 10 at the Igf1 gene locus itself and on chromosome 18. Significant interaction between different quantitative trait loci (QTL) positions was observed (P < 0.01). Evidence was found that loci having small direct effect on growth or obesity contribute to the obese phenotype by gene–gene interaction. The effects of QTLs, epistasis, and pleiotropy account for 64% and 63% of the phenotypic variance of body weight and fat accumulation and for over 32% of muscle weight and serum concentrations of leptin, and IGF-I in the F2 population of DU6i x DBA/2 mice.

[The quantitative trait loci described in this paper have been submitted to the Mouse Genome Database.]

Linkage analysis of systemic lupus erythematosus induced in diabetes-prone nonobese diabetic mice by Mycobacterium bovis

Systemic lupus erythematosus induced by Mycobacterium bovis in diabetes-prone nonobese diabetic mice was mapped in a backcross to the BALB/c strain. The subphenotypes-hemolytic anemia, antinuclear autoantibodies, and glomerular immune complex deposition-did not cosegregate, and linkage analysis for each trait was performed independently. Hemolytic anemia mapped to two loci: Bah1 at the MHC on chromosome 17 and Bah2 on distal chromosome 16. Antinuclear autoantibodies mapped to three loci: Bana1 at the MHC on chromosome 17, Bana2 on chromosome 10, and Bana3 on distal chromosome 1. Glomerular immune complex deposition did not show significant linkage to any genomic region. Mapping of autoantibodies (Coombs' or antinuclear autoantibodies) identified two loci: Babs1 at the MHC and Babs2 on distal chromosome 1. It has previously been reported that genes conferring susceptibility to different autoimmune diseases map nonrandomly to defined regions of the genome. One possible explanation for this clustering is that some alleles at loci within these regions confer susceptibility to multiple autoimmune diseases-the "common gene" hypothesis. With the exception of the H2, this study failed to provide direct support for the common gene hypothesis, because the loci identified as conferring susceptibility to systemic lupus erythematosus did not colocalize with those previously implicated in diabetes. However, three of the four regions identified had been previously implicated in other autoimmune diseases.

Derivation of diabetes-resistant congenic lines from the nonobese diabetic mouse

Autoimmune diabetes is a polygenic disease process in man and rodents. To identify and characterize genes involved in the pathogenesis of diabetes in nonobese diabetic (NOD) mice, we initiated a repetitive backcross of diabetes-resistant C57L/J mice onto the NOD strain. This breeding scheme was based on the premise that selection for the trait of disease resistance among genetically mixed mice could be used to maintain transmission of nonpermissive alleles from the diabetes-resistant strain at critical diabetes susceptibility loci. Each of the three recombinant congenic mouse lines derived by this strategy retains a unique constellation of C57L/J-derived DNA segments. Consistent with the involvement of different genetic loci, the pancreatic histology of disease-resistant mice differs from that in NOD mice in a line-specific manner. Functional studies using these lines demonstrate that pathogenesis of autoimmune diabetes is a multistep process which can be blocked at a minimum of three critical, genetically determined points.

The NOD Idd9 genetic interval influences the pathogenicity of insulitis and contains molecular variants of Cd30, Tnfr2, and Cd137

Previous analyses of NOD mice have shown that some genes control the development of both insulitis and diabetes, while other loci influence diabetes without reducing insulitis. Evidence for the existence of a gene only influencing diabetes, Idd9 on mouse chromosome 4, is provided here by the development of a novel congenic mouse strain, NOD.B10 Idd9. NOD.B10 Idd9 mice display profound resistance to diabetes even though nearly all develop insulitis. Subcongenic analysis has demonstrated that alleles of at least three B10 genes, Idd9.1, Idd9.2, and Idd9.3 are required to produce Idd9-mediated diabetes resistance. Candidate genes with amino acid differences between the NOD and B10 strains have been localized to the 5.6 cM Idd9.2 interval (Tnfr2, Cd30) and to the 2.0 cM Idd9.3 interval (Cd137).

Genetic basis of autoimmune sialadenitis in MRL/lpr lupus-prone mice: additive and hierarchical properties of polygenic inheritance

OBJECTIVE

To clarify the mode of inheritance of autoimmune sialadenitis in MRL/MpJ-lpr/lpr (MRL/lpr) lupus-prone mice and identify the susceptibility loci.

METHODS

MRL/lpr, C3H/HeJ-lpr/lpr (C3H/lpr), (MRL/lpr x C3H/lpr)F1 intercross, and MRL/lpr x (MRL/lpr x C3H/lpr)F1 backcross mice were prepared, and sialadenitis in individual mice was analyzed by histopathologic grading. The genomic DNA of the backcross mice was examined by simple sequence-length polymorphism analysis, and the highly associated polymorphic microsatellite markers with sialadenitis were determined as sialadenitis susceptibility loci.

RESULTS

Four susceptible gene loci recessively associated with sialadenitis were mapped on chromosomes 10, 18, 4, and 1, respectively. These loci manifested additive and hierarchical properties in the development of sialadenitis.

CONCLUSION

The results indicate that sialadenitis in MRL/lpr mice is under the control of polygenic inheritance, possibly involving allelic polymorphism.

A Major Linkage Region on Distal Chromosome 4 Confers Susceptibility to Mouse Autoimmune Gastritis

Although much is known about the pathology of human chronic atrophic (type A, autoimmune) gastritis, its cause is poorly understood. Mouse experimental autoimmune gastritis (EAG) is a CD4+ T cell-mediated organ-specific autoimmune disease of the stomach that is induced by neonatal thymectomy of BALB/c mice. It has many features similar to human autoimmune gastritis. To obtain a greater understanding of the genetic components predisposing to autoimmune gastritis, a linkage analysis study was performed on (BALB/cCrSlc × C57BL/6)F2 intercross mice using 126 microsatellite markers covering 95% of the autosomal genome. Two regions with linkage to EAG were identified on distal chromosome 4 and were designated Gasa1 and Gasa2. The Gasa1 gene maps within the same chromosomal segment as the type 1 diabetes and systemic lupus erythematosus susceptibility genes Idd11 and Nba1, respectively. Gasa2 is the more telomeric of the two genes and was mapped within the same chromosomal segment as the type 1 diabetes susceptibility gene Idd9. In addition, there was evidence of quantitative trait locus controlling autoantibody titer within the telomeric segment of chromosome 4. The clustering of genes conferring susceptibility to EAG with those conferring susceptibility to type 1 diabetes is consistent with the coinheritance of gastritis and diabetes within human families. This is the first linkage analysis study of autoimmune gastritis in any organism and as such makes an important and novel contribution to our understanding of the etiology of this disease.

The mouse tumor necrosis factor receptor 2 gene: genomic structure and characterization of the two transcripts

The mouse TNFR2 gene has been cloned, sequenced, and characterized as a gene spanning >44 kb of the genome. By alignment of five genomic clones we have established that TNFR2 consists of 10 exons and 9 introns with exons ranging in size from 35 bp to 2.6 kb and introns ranging from 322 bp to >16 kb. All splice acceptor and donor sites conform to the canonical AG/GT rule. The translation initiation and termination sites are located in exon 1 and 10, respectively. Although TNFR2 lacks a canonical TATA box, the gene is transcribed from a unique start site located 70 bp upstream of the ATG initiation codon that conforms to the consensus Inr motif. Several cis-elements for transcription factors were identified in the 5' flanking region, including NF-1, Sp-1, AP2, gamma-IRE, and NF-kappaBeta motifs. Functional analysis indicates that the region -705/-412 contains a negative cis-acting element and that the minimal promoter contains motifs that confer LPS inducibility. Two mouse TNFR2 mRNAs of 3.2 and 4.1 kb are detected by Northern blot analysis, but until now their origin has not been explained. No evidence of alternative splicing of the coding exons was found. However, hybridization studies and amplification of cDNA ends suggest the use of a noncanonical polyadenylation signal in the untranslated region of exon 10. A comparative analysis of the 3' untranslated regions of the human and mouse TNFR2 genes shows highly divergent 3' ends. The possibility of an ancestral mouse TNFR2 mRNA similar to the short transcript is discussed.

Genetic control of diabetes progression

Autoimmune diabetes in both the human and the nonobese diabetic mouse has elaborate genetics; in the latter case, the disease is influenced by at least 15-20 loci. We anticipated that the genetics would be simpler in the BDC2.5 T cell receptor transgenic mouse model of diabetes, wherein many T cells express a particular diabetogenic specificity. Initiation of insulitis in this model was the same on the two genetic backgrounds analyzed, but the kinetics and penetrance of diabetes were strikingly different, permitting us to focus on genetic influences during a defined window of disease progression. The differences correlated with variations in five genomic intervals, certain ones of which have been previously implicated in susceptibility to autoimmune disease. This reductionist approach indeed simplified the analysis of diabetes susceptibility loci.

Immunogenetics and the cause of autoimmune disease

Autoimmune disease results from the action of environmental factors on a predisposed genotype. In this review, the role of genetic susceptibility in the aetiology of autoimmune disease is examined. As the genetics of autoimmune diabetes has been studied more intensively than that of other autoimmune diseases, supporting evidence is drawn principally from that example. Autoimmune diseases are not inherited as entities but as constitutions which confer an increased probability of developing disease. It is proposed that there are two components to autoimmune disease susceptibility. One confers susceptibility to autoimmunity per se, while the other determines tissue specificity. In this review, the concept of liability is introduced as a tool used in quantitative genetics and is applied to the analysis of autoimmune diabetes by considering a threshold model. In this example, empirically derived incidence figures are used to calculate heritability which is a relative measure of the influence of genetics and environmental factors. The validity of applying the concept of liability to diabetes is confirmed by examining the values of heritability calculated from empirical data obtained from different kindred relationships, and by confirming that the assumptions on which liability is based are supported by recent gene mapping data. Finally, the physiological significance of liability is considered and its significance to the cause of autoimmunity discussed.

Production of congenic mouse strains carrying NOD-derived diabetogenic genetic intervals: an approach for the genetic dissection of complex traits

Insulin-dependent (Type 1) diabetes (IDD) in the NOD mouse is inherited as a complex polygenic trait making the identification of susceptibility genes difficult. Currently none of the non-MHC IDD susceptibility genes in NOD have been identified. In this paper we describe the congenic mouse approach that we are using for the dissection of complex traits, such as IDD. We produced a series of six congenic strains carrying NOD-derived diabetogenic genomic intervals, which were previously identified by linkage analysis, on a resistant background. These congenic strains were produced for the purpose of characterizing the function of each of these genes, alone and in combinations, in IDD pathogenesis and to allow fine mapping of the NOD IDD susceptibility genes. Histological examination of pancreata from 6 to 8-month-old congenic mice reveals that intervals on Chromosomes (Chrs) 1 and 17, but not 3, 6, and 11, contain NOD-derived genes that can increase the trafficking of mononuclear cells into the pancreas. Insulitis was observed only very rarely, even in older congenic mice, indicating that multiple genes are required for this phenotype. These results demonstrate the utility of this congenic approach for the study of complex genetic traits.

Self and non-self antigen in diabetic autoimmunity: molecules and mechanisms

In this article, we have summarized current facts, models and views of the autoimmunity that leads to destruction of insulin-producing beta-cells and consequent Type 1 (insulin-dependent) diabetes mellitus. The presence of strong susceptibility and resistance gene loci distinguishes this condition from other autoimmune disorders, but environmental disease factors must conspire to produce disease. The mapping of most of the genetic risk (or disease resistance) to specific alleles in the major histocompatibility locus (MHC class II) has direct functional implications for our understanding of autoimmunity in diabetes and directly implies that presentation of a likely narrow set of peptides is critical to the development of diabetic autoimmunity. While many core scientific questions remain to be answered, current insight into the disease process is beginning to have direct clinical impact with concerted efforts towards disease prevention or intervention by immunological means. In this process, identification of the critical antigenic epitopes recognized by diabetes-associated T cells has achieved highest priority.

Resistance alleles at two non-major histocompatibility complex-linked insulin-dependent diabetes loci on chromosome 3, Idd3 and Idd10, protect nonobese diabetic mice from diabetes

Development of diabetes in NOD mice is polygenic and dependent on both major histocompatibility complex (MHC)-linked and non-MHC-linked insulin-dependent diabetes (Idd) genes. In (F1 x NOD) backcross analyses using the B10.H-2g7 or B6.PL-Thy1a strains as the outcross partner, we previously identified several non-MHC Idd loci, including two located on chromosome 3 (Idd3 and Idd10). In the current study, we report that protection from diabetes is observed in NOD congenic strains having B6.PL-Thy1a- or B10-derived alleles at Idd3 or Idd10. It is important to note that only partial protection is provided by two doses of the resistance allele at either Idd3 or Idd10. However, nearly complete protection from diabetes is achieved when resistance alleles are expressed at both loci. Development of these congenic strains has allowed Idd3 to be localized between Glut2 and D3Mit6, close to the Il2 locus.