Characterization of H-2 congenic strains using DNA markers

Fine haplotype structure of a chromosome 17 region in the laboratory and wild mouse

Extensive linkage disequilibrium among classical laboratory strains represents an obstacle in the high-resolution haplotype mapping of mouse quantitative trait loci (QTL). To determine the potential of wild-derived mouse strains for fine QTL mapping, we constructed a haplotype map of a 250-kb region of the t-complex on chromosome 17 containing the Hybrid sterility 1 (Hst1) gene. We resequenced 33 loci from up to 80 chromosomes of five mouse (sub)species. Trans-species single-nucleotide polymorphisms (SNPs) were rare between Mus m. musculus (Mmmu) and Mus m. domesticus (Mmd). The haplotypes in Mmmu and Mmd differed and therefore strains from these subspecies should not be combined for haplotype-associated mapping. The haplotypes of t-chromosomes differed from all non-t Mmmu and Mmd haplotypes. Half of the SNPs and SN indels but only one of seven longer rearrangements found in classical laboratory strains were useful for haplotype mapping in the wild-derived M. m. domesticus. The largest Mmd haplotype block contained three genes of a highly conserved synteny. The lengths of the haplotype blocks deduced from 36 domesticus chromosomes were in tens of kilobases, suggesting that the wild-derived Mmd strains are suitable for fine interval-specific mapping.

Insulin-like growth factor II receptor, transforming growth factor-beta, and Cdk4 expression and the developmental epigenetics of mouse palate morphogenesis and dysmorphogenesis

The B10/B10.A congenic mouse pair serves as a model for identifying specific genes related to morphogenesis and dysmorphogenesis of the embryonic palate and other organs. The present report describes our initial investigation of the Fraser-Juriloff paradigm, which proposes that susceptibility to malformation results from genetically determined differences in normal developmental patterns. Specifically, we evaluated the relationship between Igf2r gene expression, transforming growth factor-beta (TGF-beta) activation, and cdk4 gene expression. By using in situ hybridization, RNase protection assays, indirect immunofluorescence, Western blots, and bioassays, we show 1) the presence of insulin-like growth factor II (IGF-II), IGF-II receptor (IGF-IIR), IGF-IR, TGF-beta, plasminogen, plasminogen activators [urokinase plasminogen activator (uPA) and tissue plasminogen activator (tPA)], and Cdk4 in developing palates; 2) on embryonic day 14 (E14), which is a critical day for palatal growth, B10.A embryos have 82% greater IGF-IIR mRNA than B10; 3) on E14, B10.A embryonic palates have a 57% greater level of active TGF-beta2 than B10, although the total TGF-beta2 is nearly identical; and 4) on E14, B10 embryonic palates have a 52% greater level of Cdk4 mRNA than B10.A palates, a measure of cell cycle progression. Because cellular activation of latent TGF-beta appears to require binding to the mannose-6-phosphate (M6P) binding site of the IGF-IIR and is plasmin and plasminogen activator dependent, the positive correlation of IGF-IIR levels and active TGF-beta2 levels seems to be key. Thus, the strain variation of TGF-beta2/IGF-IIR-mediated growth inhibition in late G1 phase would appear to account for the slower growth and development of B10.A palates relative to B10. Elevated corticosteroid (CORT) exposure in E14 B10.A embryos significantly increases TGF-beta levels, 87% of which is TGF-beta2, as well as the levels of active TGF-beta, 64% of which is TGF-beta2. Without exogenous CORT, B10.A embryos do not have clefts; hence, we present an outline of pathogenesis: slower growing B10.A embryos have an up-regulation of IGF-IIR, which serves to sequester IGF-II from the growth-promoting IGF-IR and to bind more CORT-up-regulated, latent TGF-beta2 for subsequent plasmin-dependent activation; higher levels of TGF-beta2 signaling down-regulate Cdk4 and result in greater palatal growth inhibition at a critical stage of palatogenesis and, thus, cleft palate. We present an epigenetic model of information processing related to cell proliferation. The model is a dynamical network that uses continuous logic to learn its rules from changing conditions.

Developmental expression of insulin-like growth factor II receptor (IGF-IIR) in congenic mouse embryonic lungs: correlation between IGF-IIR mRNA and protein levels and heterochronic lung development

Embryonic lung maturation in the H-2 congenic pair, B10.A and B10, proceeds at different rates. The dependence of this heterochronic development on maternal haplotype suggests the involvement of a parentally imprinted gene. Since B10.A (H-2a) and B10 (H-2b) mice are genetically identical except for a 3-18 cM region of chromosome 17 that includes the H-2 complex, we sought a promising candidate gene(s) involved in regulating the rate of lung development from genes encoded in this region. The best candidate is the gene encoding the type II insulin-like growth factor receptor (IGF-IIR), whose ligand is the growth factor IGF-II. Only the maternal copy of this gene is expressed in postimplantation embryos. This receptor does not appear to transduce mitogenic signals; instead, IGF-IIR appears to regulate the levels of its ligand available to the growth-promoting type I IGF receptor (IGF-IR). Using in situ hybridization and indirect immunofluorescence, we demonstrate that IGF-IIR mRNA and protein are localized throughout the pulmonary mesenchyme, as well as in branching epithelia of the pseudoglandular and canalicular stages. We also examined the levels of IGF-IIR mRNA and protein expression by RNase protection assay and ligand blotting during the embryonic period of lung development in B10.A and B10 mice, and found that there is a highly significant positive correlation of IGF-IIR levels with progressive development in both strains. Further, slower-developing B10.A lungs contain significantly higher levels of IGF-IIR mRNA and protein than the more rapidly developing B10 lungs. These results suggest that haplotype-dependent elevation of IGF-IIR levels reduces the available concentration of IGF-II, resulting in a decreased rate of morphogenesis in B10.A mice. Heterochronic lung maturation, then, appears consequent to variable extracellular levels of this important growth factor. These results may be of clinical importance to predicting susceptibility to Respiratory Distress Syndrome in prenatal newborns.

Mouse H2 congenic intervals: analysis and use for mapping

In this study we exploit the unique genetic resource of inbred mouse major histocompatibility complex (H2) congenic and recombinant strains to construct a high-resolution map of microsatellite loci in and around the H2 region, as well as an independent genetic map of other loci on mouse Chromosome (Chr) 17. Microsatellite loci were analyzed in 11 C57BL/10 (B10) strains to determine the size of the congenic interval in each. The length of the congenic interval found in each strain varied widely. Interestingly, the intervals were generally smaller than statistical expectations. However, the observed congenic intervals were still sufficiently long that these strains and probably wild-derived H2 congenics are an important source of genetic variability. The staggered ends of the various congenic intervals and the recombinants were used to construct the map. This map will be useful for physical cloning and to help localize novel genes. As evidence of the mapping application of congenic strains, locational information was derived about Trp53-ps and Stl.

Identification of murine loci associated with susceptibility to chronic experimental autoimmune encephalomyelitis

B10.RIII mice develop chronic and relapsing experimental autoimmune encephalomyelitis (EAE) after immunization with the myelin basic protein (MBP) peptide 89-101. The disease is associated with the major histocompatibility complex (MHC) (eae1). We have now investigated the importance of non-MHC regions for the EAE susceptibility in a cross between RIIIS/J and B10.RIII mice which share the MHC region but differ in disease susceptibility. Linkage analysis using microsatellite markers spanning the genome identified a region (eae2) on chromosome 15 which showed linkage to disease (P = 0.0002). Our data also suggest linkage to a second region (eae3) on chromosome 3 (P = 0.0024), and provide evidence for locus interactions between eae2 and eae3. These results provide clues to the genetic basis of multiple sclerosis.

Cloning of the beta 2-microglobulin gene in the zebrafish

The beta 2-microglobulin (beta 2m) is a protein found in the serum in a free form and on the cell surface in a form noncovalently associated with the alpha chain of the class I major histocompatibility complex (Mhc) molecules. In mammals, the beta 2m-encoding gene (B2m) is found on a chromosome different from the Mhc proper. We have isolated and characterized the B2m gene of the zebrafish, Brachydanio rerio, family Cyprinidae. We obtained both cDNA and genomic clones of the Brre-B2m gene. The cDNA clones contained the entire coding sequence, the entire 3' untranslated (UT) region, and at least part of the 5'UT region. The genomic clone contained the entire Brre-B2m gene. The coding sequence specifies 97 amino acid residues of the mature protein so that the zebrafish beta 2m is two residues shorter than human and one residue shorter than cattle, fowl, or turkey beta 2m (codons at positions 85 and 86 have been deleted in the Brre-B2m gene). The amino acid and nucleotide sequence similarities between zebrafish and human beta 2m (B2m) are 45% and 59%, respectively. Approximately 24% of the positions are invariant and an additional 9% show only conservative substitutions in comparisons which include all known beta 2m sequences (fish, avian, and mammalian). Most of the conserved positions are in the beta strands (some 47% of the beta-strand positions are conserved in the three vertebrate classes). The Brre-B2m gene consists of four exons separated by three introns. All of the introns are considerably shorter than the corresponding introns in the mammalian B2m genes. The coding sequences of the cDNA and the genomic clones are almost identical but the sequences of the 3'UT regions differ at 1.7% of the sites, suggesting that the genes borne by these clones might have diverged at least 0.7 million years (my) ago. In contrast to the human B2m gene, the Brre-B2m gene shows no bias in the distribution of the CpG dinucleotides: the dinucleotides are distributed evenly along the entire available sequence. The haploid genome of the zebrafish contains only one copy of the B2m gene.

Major histocompatibility complex class II genes of zebrafish

Twenty cDNA clones derived from beta-chain-encoding class II genes of the zebrafish (Brachydanio rerio) major histocompatibility complex (MHC) have been sequenced. They fall into three groups identifying three loci of expressed genes. The length and organization of these genes are similar to those of their mammalian homologs. Amplification by polymerase chain reaction and sequencing of genomic DNA from zebrafish collected at different locations in India indicate the existence of a fourth group of sequences (fourth locus). A high degree of polymorphism at the B. rerio MHC loci and concentration of variability to the putative peptide-binding region of the beta 1-domain-encoding part of the gene are also indicated. Large genetic distances between alleles suggest trans-specific evolution of fish MHC polymorphism. Zebrafish genes appear to be derived from a different ancestor than the various class II gene families of other vertebrates. In spite of great sequence divergence between fish and mammalian MHC genes, there seems to be a striking conservation in their overall organization.

Polygenic influences on the length of oestrous cycles in inbred mice involve MHC alleles

Genetic influences on female reproductive cycles were analysed in histocompatibility-congenic strains of mice. Oestrous cycles of young, virgin mice of inbred-congenic strains, hybrid crosses (F1), and parental-hybrid backcrosses (F2) were monitored for 3 months. Oestrous cycles were categorized by length (inter-oestrous interval): 4, 5, 6, or 7-14 days. Mice with the following H-2 haplotypes had a greater proportion of 5-day oestrous cycles: H-2b, H-2r, H-2h2, H-2h4, and H-2i5. In contrast, the H-2k and H-2d haplotypes had mostly 4-day oestrous cycles. Influences of H-2 haplotype were seen on two genetic backgrounds, C57BL/10Sn and C3H. Non-H-2 alleles were also implied by different patterns of cycles between strains with the same H-2b haplotype: C57BL/10Sn with predominantly 5-day cycles vs. C57BL/6J with a mix of 4- and 5-day cycles. The genetic basis for strain differences was investigation in F1 hybrids and their backcrosses. F1 hybrids of an H-2b (C57BL/10Sn; 5-day cycles) and an H-2k (B10.BR; 4-day cycles) strain had mostly 5-day cycles, indicating dominance of an H-2b allele(s). However, F1 hybrids from the reciprocal B6 x B10 cross (both H-2b) also display a preponderance of 5-day cycles, indicating dominance of a non-H-2 autosomal allele from the C57BL/10Sn strain. Among F2 mice, a '4-day' phenotype segregated with homozygosity for the k haplotype (P < 0.05, chi 2). These findings demonstrate the influence of genetic differences at the major histocompatibility complex on oestrous cycles.

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 recombinant congenic strains--a novel genetic tool applied to the study of colon tumor development in the mouse

The development of tumors in mice is under multigenic control, but, in spite of considerable efforts, the identification of the genes involved has so far been unsuccessful, because of the insufficient resolution power of the available genetic tools. Therefore, a novel genetic tool, the RC (Recombinant Congenic) strains system, was designed. In this system, a series of RC strains is produced from two inbred strains, a "background" strain and a "donor" strain. Each RC strain contains a different small subset of genes from the donor strain and the majority of genes from the background strain. As a consequence, the individual genes of the donor strain which are involved in the genetic control of a multigenic trait, become separated into different RC strains, where they can be identified and studied individually. One of the RC strains series which we produced is made from the parental strains BALB/cHeA (background strain) and STS/A (donor strain). We describe the genetic composition of this BALB/cHeA-C-STS/A (CcS/Dem) series and show, using 45 genetic autosomal markers, that it does not deviate from the theoretical expectation. We studied the usefulness of the CcS/Dem RC strains for analysis of the genetics of colon tumor development. The two parental strains, BALB/cHeA and STS/A, are relatively resistant and highly susceptible, respectively, to the induction of colon tumors by 1,2-dimethylhydrazine (DMH). The individual RC strains differ widely in colon tumor development after DMH treatment; some are highly susceptible, while others are very resistant. This indicates that a limited number of genes with a major effect are responsible for the high susceptibility of the STS strain. Consequently, these genes can be mapped by further analysis of the susceptible RC strains. The differences between the RC strains were not limited to the number of tumors, but the RC strains differed also in size of the tumors and the relative susceptibility of the two sexes. Our data indicate that the number of tumors and the size of tumors are not controlled by the same genes. The genetics of these different aspects of colon tumorigenesis can also be studied by the RC strains. The DMH-treated mice of the parental strains and the RC strains also developed anal tumors and haemangiomas in varying numbers. The strain distribution pattern (SDP) of susceptibility for each of the three types of tumors induced by DMH is different, indicating that development of these tumors is under control of different, largely non-overlapping, sets of genes.(ABSTRACT TRUNCATED AT 400 WORDS)

Chronic experimental autoimmune encephalomyelitis induced by the 89-101 myelin basic protein peptide in B10RIII (H-2r) mice

Development of experimental allergic encephalomyelitis (EAE) in the SJL (H-2s) mice is associated with a T cell-dependent autoimmune response to the C-terminal part of the myelin basic protein (MBP). In this study the influence of both H-2 and non-H-2 genetic background on EAE induced with the MBP89-101 peptide is described. Analysis of different H-2q haplotype strains, B10G, B10Q, SWR and NFR/N, showed that the B10 background is relatively resistant to disease induction. Both SWR and NFR/N were susceptible to EAE showing that the H-2q haplotype is permissive for EAE development induced with MBP89-101 and that the T cell receptor (TcR) haplotype or complement C5 deficiency exert no significant influence on disease susceptibility. In a series of H-2-congenic strains on the B10 background only B10RIII (H-2r) mice were susceptible to EAE. The B10RIII mice developed a severe EAE with early onset and chronic progressive or relapsing course of disease. In addition, B10RIII mice treated with Freund's complete adjuvant and pertussis toxin alone showed an early monophasic disease. The clinical observations were confirmed by immunohistopathologic analysis of the central nervous system. In these studies, we also applied antibodies to different TcR V beta elements which showed no specific limitation of the used TcR among infiltrating T cells in the target tissue in any of the strains. It is concluded that an MBP peptide-specific disease can be induced in three different haplotypes and it is possible that shared structures between the As, Aq and Ar molecules are of importance for the trigger of encephalitogenic T cells with different TcR V elements. The presently described chronic EAE model induced in the B10RIII mice will be of value as a model for multiple sclerosis.

Limits of the distal inversion in the t complex of the house mouse: evidence from linkage disequilibria

The suppression of crossing-over and the consequent linkage disequilibrium of genetic markers within the t complex of the house mouse is caused by two large and two short inversions. The inversions encompass a region that is some 15 centiMorgans (cM) long in the homologous wild-type chromosome. The limits of the proximal inversions are reasonably well-defined, those of the distal inversions much less so. We have recently obtained seven new DNA markers (D17Tu) which in wild-type chromosomes map into the region presumably involved in the distal inversions of the t chromosomes. To find out whether the corresponding loci do indeed reside within the inversions, we have determined their variability among 26 complete and 12 partial t haplotypes. In addition, we also tested the same collection of t haplotypes for their variability at five D17Leh, Hba-ps4, Pim-1, and Crya-1 loci. The results suggest that the distal end of the most distal inversion lies between the loci D17Leh467 and D17Tu26. The proximal end of the large distal inversion was mapped to the region between the D17Tu43 and Hba-ps4 loci, but this assignment is rather ambiguous. The loci Pim-1, Crya-1, and the H-2 complex, which have been mapped between the Hba-ps4 and Grr within the large distal inversion, behave as if they recombine from time to time with their wild-type homologs.