Polymorphism of T-cell receptor genes among laboratory and wild mice: diverse origins of laboratory mice

Mouse protein coding diversity: What's left to discover?

For over a century, mice have been used to model human disease, leading to many fundamental discoveries about mammalian biology and the development of new therapies. Mouse genetics research has been further catalysed by a plethora of genomic resources developed in the last 20 years, including the genome sequence of C57BL/6J and more recently the first draft reference genomes for 16 additional laboratory strains. Collectively, the comparison of these genomes highlights the extreme diversity that exists at loci associated with the immune system, pathogen response, and key sensory functions, which form the foundation for dissecting phenotypic traits in vivo. We review the current status of the mouse genome across the diversity of the mouse lineage and discuss the value of mice to understanding human disease.

T cell receptor-gamma allele-specific selection of V gamma 1/V delta 4 cells in the intestinal epithelium

Previous genetic analyses have shown that the relative representation of subsets of gammadelta intestinal intraepithelial lymphocytes (i-IELs) is influenced by genes linked to the TCRgamma, TCRdelta, and MHC loci. Here, we have analyzed V-gene use in gammadelta i-IELs from C57BL/6 (B6) and C57BL/10 (B10) mice and from their F(1) and F(2) progenies with a larger panel of Vgamma- and Vdelta-specific mAbs and have shown that the influence of TCRgamma-linked genes operates at two levels: one influencing the representation of Vgamma1 (or Vgamma7) i-IELs and other acting specifically on the Vgamma1/Vdelta4 i-IEL subset, which represents 3% and 15% of the gammadelta i-IELs in B6 and B10 mice, respectively. Analysis of mice transgenic for a rearranged Vgamma1Jgamma4Cgamma4 chain of B6 origin demonstrated that the TCRgamma-linked genes influencing the representation of the Vgamma1/Vdelta4 i-IEL subset are the structural genes of TCRgamma chains. This influence is allele specific and cell autonomous, as evidenced by the different behavior of Vgamma1/Vdelta4 cells bearing either parental allele in F(1) mice. The representation of Vgamma1/Vdelta4 cells among gammadelta thymocytes is similar in B6 and B10 mice, demonstrating that the Vdelta4 chain can pair well with both alleles of the Vgamma1Jgamma4Cgamma4 chain and strongly suggesting that a cellular selection mechanism is responsible for the observed differences. The Vgamma1-Jgamma4 junctional amino acid sequences of B6 Vgamma1/Vdelta4 i-IELs are diverse but display less variation in length than those found in similar cells from B10 mice, indicating that B6 Vgamma1/Vdelta4 cells are the target of this cellular selection event.

Low antibody responsiveness is found to be associated with resistance to chemical skin tumorigenesis in several lines of Biozzi mice

High and low antibody responder lines of mice from Selections I, III and G were assayed for two-step skin tumorigenesis using a protocol consisting in initiation with 7,12-dimethylbenz[a]anthracene (DMBA) and promotion with 12-O-tetradecanoylphorbol-13-acetate (TPA). Concordant results were obtained in the three selections: low antibody responder mice were shown to be significantly more resistant to tumor induction than the high responder counterparts. The difference was observed for all parameters: kinetics and percentages of tumor incidence and tumor multiplicity. The three bidirectional selective breeding experiments differed in several respects namely, the origin of the foundation populations, the antigens and immunization protocols used during the selection, as well as the breeding unit environments. Therefore, the consistent results relative to tumorigenesis strongly suggest that some of the alleles relevant to multispecific 'low' antibody production could contribute to the resistance to cutaneous chemical tumorigenesis.

Phylogenetic relationships among laboratory and wild-origin Mus musculus strains on the basis of genomic DNA RFLPs

Genetic distance measures between the laboratory mouse strains C57BL/6J and RF/J and the wild-origin Mus musculus mouse strains CAST/Ei, MOLF/Ei, POSCH I, and CZECH II were estimated by allelic patterns revealed by RFLP analysis. These results suggest phylogenetic relationships indicating that the mouse strains related to the subspecies M.m. domesticus (RF/J, POSCH I and C57BL/6J) are more closely related to the CAST/Ei strain (derived from M.m. castaneus) than to the strains CZECH II (M.m. musculus) and MOLF/Ei (M.m. molossinus). Furthermore, the hybrid strain C57BL/6J is more closely related to POSCH I (M.m. poschiavinus) than to RF/J as calculated by the method distance measures of Cavalli-Sforza and Edwards (Evolution 21,550, 1967), Nei's minimum (Am. Natural. 106,283, 1972) and unbiased minimum (Genetics 89,583, 1978), Edwards (Biometrics 27,873, 1971; Genetic Distance, p. 41, 1974) and Rogers modified (1986).

Characterization of a V kappa family in Mus musculus castaneus: sequence analysis

To examine genetic variation at immunoglobulin (Ig) multigene loci over short spans of evolutionary time, we have compared members of an Ig kappa chain variable (V kappa) region family from several mouse species. In this study, seven unique Igk-V24 family members have been isolated from Mus m. castaneus and characterized by nucleotide sequence determination for comparison to their counterparts in Mus m. domesticus (BALB/c), and Mus pahari, representing 1-2 million years of evolution in the former case and 5-8 million years in the latter. Parsimony, together with evolutionary distances calculated for various pairs of Igk-V24 family coding regions, relate all family members to a common progenitor existing roughly 24 million years ago (Mya). A significant portion of the M. m. castaneus family consists of pseudogene segments in various degrees of progressive degeneration. The substitution patterns and divergence rates for all gene segments are characteristic of their respective subsets, especially in the areas flanking the coding regions. Complex and variable patterns of diversity are seen in potentially expressed coding regions, which appear to reflect quite different selective pressures on various subregions within the V kappa protein domain. These results indicate that evolutionary pressures are operating at the level of family subsets, their individual members, and subregions within similar molecules.

New T-cell receptor gamma haplotypes in wild mice and evidence for limited Tcrg-V gene polymorphism

Tcrg gene polymorphism was investigated by Southern blot analysis on a panel of laboratory and wild mouse strains using a set of probes which identify all known Tcrg-V and -C genes. Only three haplotypes are found in laboratory mice: gA, gB, and gC which are represented by BALB/c, AKR, and DBA/2 prototypes respectively. gA and gC haplotypes are the most frequent among laboratory mice whereas gB is poorly represented. Seven new haplotypes are described among 23 wild mice corresponding to four Mus musculus subspecies (Mus mus domesticus, castaneus, musculus, and molossinus). However, only a few new alleles of individual genes are observed. Tcrg-V genes located at the 5' end of the Tcrg locus (V7 and V4) appear to be nonpolymorphic whereas two Tcrg-V3, -V5, -V6, -C4 and three Tcrg-V1, -V2, -C1, -C2, and -C3 specific restriction fragment length polymorphisms are detected. These results indicate a relatively high degree of conservation of Tcrg genes as compared to other members of the immunoglogulin (Ig) gene family and might be related to the specifity and function of gamma delta T cells. Several of the new haplotypes described here result from point mutations in noncoding Tcrg-V or -C gene-flanking regions. Recombinations may have also participated in the evolution of the Tcrg locus. Finally, these new Tcrg haplotypes are unequally distributed among the four M. m. subspecies and support the idea that the gA and gC haplotypes found in laboratory mice are inherited from M. m. domesticus whereas gB might originate from asian subspecies (castaneus, musculus or molossinus).

Polymorphisms distinguishing different mouse species and t haplotypes

Three anonymous chromosome 17 DNA markers, D17Tu36, D17Tu43, and D17Le66B, differentiate between house mouse species and/or between t chromosomes. The D17Tu36 probe, which maps near the Fu locus and to the In(17)4 on t chromosomes, identifies at least 15 haplotypes, each haplotype characterized by a particular combination of DNA fragments obtained after digestion with the Taq I restriction endonuclease. Ten of these haplotypes occur in Mus domesticus, while the remaining five occur in M. musculus. In each of these two species, one haplotype is borne by t chromosomes while the other haplotypes are present on non-t chromosomes. The D17Tu43 probe, which maps near the D17Leh122 locus and to the In(17)3 on t chromosomes, also identifies at least 15 haplotypes in Taq I DNA digests, of which nine occur in M. domesticus and six in M. musculus. One of the nine M. domesticus haplotypes is borne by t chromosomes, the other haplotypes are borne by non-t chromosomes; two of the six M. musculus haplotypes are borne by t chromosomes and the remaining four by non-t chromosomes. Some of the D17Tu43 haplotypes are widely distributed in a given species, while others appear to be population-specific. Exceptions to species-specificity are found only in a few mice captured near the M. domesticus-M. musculus hybrid zone or in t chromosomes that appear to be of hybrid origin. The D17Leh66B probe, which maps to the In(17)2, distinguishes three haplotypes of M. domesticus-derived t chromosomes and one haplotype of M. musculus-derived t chromosomes. Because of these characteristics, the three markers are well suited for the study of mouse population genetics in general and of t chromosome population genetics in particular. A preliminary survey of wild M. domesticus and M. musculus populations has not uncovered any evidence of widespread introgression of genes from one species to the other; possible minor introgressions were found only in the vicinity of the hybrid zone. Typing of inbred strains has revealed the contribution of only M. domesticus DNA to the chromosome 17 of the laboratory mouse.

The musculus-type Y Chromosome of the laboratory mouse is of Asian origin

Mus musculus domesticus, M.m. bactrianus, M.m. musculus, M.m. castaneus, and M.m. molossinus wild mice were investigated for polymorphisms of the Y Chromosome (Chr) genes Zinc finger-Y (Zfy) and Sex-determining region-Y (Sry). Zfy divided the Y Chrs of these mice into domesticus- (domesticus) and musculus-types (musculus, castaneus, molossinus). M.m. bactrianus specimens had both Y Chrs, possibly owing to the introgression of a musculus-type Y into this population. Sry identified a subpopulation of musculus-type Y chromosomes. This subpopulation, designated the molossinus-type, was found in M.m. molossinus, a M. musculus subspecies specimen from northern China (Changchun), and laboratory mice. The cumulative data suggest that M.m. musculus of northern China and Korea are a subpopulation distinct from M.m. musculus of Europe and central China and that this subpopulation invaded Japan, giving rise to M.m. molossinus. Furthermore, the data suggest that the musculus-type Y of the laboratory mouse originated from this subpopulation, corroborating early historical records reporting that Chinese and Japanese mice that were imported into Europe for the pet trade contributed to the genome of the laboratory mouse.

The contribution of non-MHC genes to susceptibility to autoimmune diseases

Genetic studies of experimental models of autoimmune diseases, including systemic lupus-like syndromes and organ-specific autoimmunity, provide major information on genetic control of autoimmune diseases. In addition to genes known to be linked to the major histocompatibility complex (MHC), these studies point to multiple genes located outside the MHC that influence the onset and the progression of autoimmune diseases. Identification of these genes and of their interrelationships is now a major task that will be facilitated by recent progress in molecular biology and gene mapping. Among candidate genes, antigen-receptor genes (i.e., immunoglobulin- and T-cell receptor genes) most likely contribute an important part of the autoimmune susceptibility in several of these animal models. Available linkage data suggest a similar involvement of these antigen-receptor genes in several human autoimmune diseases. In addition to a better understanding of pathogenic mechanisms associated with autoimmunity, the knowledge of these disease-predisposing genes is expected to permit a better classification of often complex syndromes as well as the design of new treatments.

T-cell receptor genes in tassel-eared squirrels (Sciurus aberti). I. Genetic polymorphism and divergence in the Abert and Kaibab subspecies

The role of environmental factors in the evolution and maintenance of diversity of antigen receptor gene families which participate in the immune response in mammals is inadequately understood. In order to elucidate the impact of these factors, we have undertaken the analysis of these gene families in the tassel-eared squirrel (Sciurus aberti) which has been separated into discrete subspecies by geographic barriers and whose food resources can be quantitated for estimating environmental quality. In this communication we describe the initial analysis of the complexity and polymorphism of sequences related to T-cell receptor (Tcr) alpha and beta chain genes in two subspecies, Sciurus aberti aberti (Abert) and Sciurus aberti kaibabensis (Kaibab) which have identical habitats and are separated by the Grand Canyon in Arizona, USA. Genomic blot analysis of 60 Abert and 62 Kaibab individuals collected over a 3-year period was performed with mouse Tcrb and Tcra cDNA probes. Sequences homologous to Tcrb-C, Tcrb-J1, and Tcrb-J2 genes were observed in all individuals from both subspecies; although Tcrb-J1 fragments were monomorphic. Tcrb-C and Tcrb-J2 fragments were polymorphic with both species- and subspecies-specific sequences. A single, monomorphic Tcra-C fragment was observed in addition to multiple Tcra-V fragments homologous to the mouse Tcra-V1 subfamily. Abert samples exhibited greater numbers of Tcra-V1 fragments as well as greater polymorphism than Kaibab samples. Heterozygosity estimates of Tcrb-C and Tcra-V1 sequences were determined for annually collected samples and compared with the yearly estimates of availability of hypogeous fungi, one of the major diet items of tassel-eared squirrels. In the Kaibab annual collections, Tcra-V1 heterozygosity declined with the decline in food resource, whereas heterozygosity of Tcrb-C sequences was inversely related to food resource. Similarly, a reduction in food resource for Abert squirrels in 1985 coincided with an increase in Tcrb-C heterozygosity in the same year. These results suggest that the diversity of gene families which participate in the immune response in mammals may be affected by environmental factors.

Polymorphism of Tcrb and Tcrg genes in Biozzi mice: segregation analysis of a new Tcrg haplotype with antibody responsiveness

Tcrb and Tcrg gene polymorphism was investigated in high (H) and low (L) responder Biozzi mice from selection I, II, and GS by Southern blot analysis with appropriate V and C probes. No polymorphism of the Tcrb haplotype was detected between H and L mice in all selections which were all found to be of the BALB/c type. The H-I and H-II g genotype was of BALB/c and DBA/2 type, respectively. In contrast, a new Tcrg haplotype shared by L-I and L-II mice was identified and characterized by C gamma 1, 2, 3, C gamma 4, V gamma 1, 2, 3, V gamma 5, and V gamma 6 restriction fragment length polymorphisms (RFLPs). Tcrg genotypes were not fixed in the GS selection and two additional new haplotypes were identified in two L-GS mice. An attempt was made to correlate the L-I g genotype with the low responder status by analyzing g haplotypes among highest and lowest responder (H-I X L-I)F2 hybrids immunized with sheep red blood cells (SRBC). No correlation was found in this segregation study, whereas a highly significant one was established with the H-2 haplotype, a locus already known to participate in the genetic control of H-I/L-I difference. The lack of correlation between SRBC response and the Tcrg genotype was consistent with the heterogenous g haplotypes found in mice of the GS selection. Together, the present results suggest that H and L mice have the same Tcrab potential repertoire and that T-cell receptor (Tcr) genes cannot be considered as immune response genes in this model. Our results also indicate that the F2 segregation analysis, given a polymorphic gene, is suitable for an investigation of its immune response functions.