Mouse serum amyloid P-component (SAP) levels controlled by a locus on chromosome 1

Recombinant inbred strains were used to demonstrate the existence of a major locus on chromosome 1, designated Sap, which controls the endogenous concentration of the mouse acute phase reactant, serum amyloid P-component (SAP). Levels of SAP were associated with alleles at the Ly-9 locus in two sets of RI strains: BXD (C57BL/6J × DBA/2) and BXH (C57BL/6J × C3H/HeJ). Low endogenous levels of SAP were present in the C57BL/6J progenitor strain and in most of the RI strains which inherited the Ly-9 ^ballele. High levels of SAP were present in the DBA/2J and C3H/HeJ progenitors and in most of the RI strains which inherited the Ly-9 ^aallele. In the BXD strains 91% of the genetic variation of SAP levels was accounted for by segregation at the Ly-9 locus while an additional 9% was attributed to genetic factors unlinked to Ly-9. In the BXH strains the percentage of genetic variation accounted for by Ly-9 segregation was reduced to 46%, while 54% was accounted for by other genetic factors. Because of background genetic variation it was not possible to detect any crossovers between Sap and Ly-9. However, in the BXD strains the linkage between Sap and Ly-9 appears to be quite close. The B6.C-H-25 ^ccongenic strain, which carries a segment of BALB/c chromosome 1 including the minor histocompatibility locus H-25 on a C57BL/6By background, had the same endogenous SAP level as the BALB/c donor strain.     

A genome-wide set of congenic mouse strains derived from DBA/2J on a C57BL/6J background

In the analysis of complex traits, congenic strains are powerful tools because they allow characterization of a single locus in the absence of genetic variation throughout the remainder of the genome. Here, we report the construction and initial characterization of a genome-wide panel of congenic strains derived from the donor strain DBA/2J on the background strain C57BL/6J. For many strains, we have carried out high-density SNP genotyping to precisely map the congenic interval and to identify any contaminating regions. Certain strains exhibit striking variation in litter size and in the ratio of females to males. We illustrate the utility of the set by "Mendelizing" the complex trait of myocardial calcification. These 65 strains cover more than 95% of the autosomal genome and should facilitate the analysis of the many genetic trait differences that have been reported between these parental strains.     

Susceptibility to Seizure-Induced Excitotoxic Cell Death Is Regulated by an Epistatic Interaction between Chr 18 (Sicd1) and Chr 15 (Sicd2) Loci in Mice

Seizure-induced cell death is believed to be regulated by multiple genetic components in addition to numerous external factors. We previously defined quantitative trait loci that control susceptibility to seizure-induced cell death in FVB/NJ (susceptible) and C57BL/6J (resistant) mice. Two of these quantitative trait loci assigned to chromosomes 18 (Sicd1) and 15 (Sicd2), control seizure-induced cell death resistance. In this study, through the use of a series of novel congenic strains containing the Sicd1 and Sicd2 congenic strains and different combinations of the Sicd1 or Sicd2 sub region(s), respectively, we defined these genetic interactions. We generated a double congenic strain, which contains the two C57BL/6J differential segments from chromosome 18 and 15, to determine how these two segments interact with one another. Phenotypic comparison between FVB-like littermates and the double congenic FVB.B6-Sicd1/Sicd2 strain identified an additive effect with respect to resistance to seizure-induced excitotoxic cell death. It thus appears that C57BL/6J alleles located on chromosomes 18 and 15 interact epistatically in an additive manner to control the extent of seizure-induced excitotoxic cell death. Three interval-specific congenic lines were developed, in which either segments of C57BL/6J Chr 18 or C57BL/6J Chr 15 were introduced in the FVB/NJ genetic background, and progeny were treated with kainate and examined for the extent of seizure-induced cell death. All of the interval-specific congenic lines exhibited reduced cell death in both area CA3 and the dentate hilus, associated with the C57BL/6J phenotype. These experiments demonstrate functional interactions between Sicd1 and Sicd2 that improve resistance to seizure-induced excitotoxic cell death, validating the critical role played by gene-gene interactions in excitotoxic cell death.     

Susceptibility to a mouse acquired immunodeficiency syndrome is influenced by theH-2

The development of a mouse acquired immunodeficiency syndrome (MAIDS) induced following LP-BM5 MuLV infection depends on host genetic factors. Susceptible mice, such as C57BL/6J mice, develop a profound impairment of lymphoproliferative response to mitogens and hyperplasia of lymphoid organs and succumb to infection within 6 months. These changes do not occur in resistant mice, such as A/J mice. Resistance to MAIDS is a dominant trait since (C57BL/6JxA/J)F₁ hybrid mice did not develop any immune dysfunctions following infection. Genetic regulation of the trait of resistance/susceptibility to MAIDS was determined in AXB/BXA recombinant inbred (RI) mouse strains (derived from resistant A/J and susceptible C57BL/6J progenitors). Two different criteria were used to determine their resistance or susceptibility to developing MAIDS: the gross pathologic evaluation of lymphoid organs at 13–15 weeks of infection, and survival. RI mouse strains segregated into two non-overlapping groups. The first group did not develop any significant pathology, and these mouse strains were considered as resistant to MAIDS. The second group showed the virus-induced pathological changes as well as an immunological dysfunction as seen in C57BL/6J progenitor mice, and these strains were thus considered as susceptible to MAIDS. This bimodal strain distribution pattern of resistance/susceptibility to MAIDS among the RI strains suggests that this phenotype is controlled by a single gene. Linkage analysis with other allelic markers showed a strong association between resistance/susceptibility to MAIDS and theH-2 complex. Possession of theH-2 ^b haplotype derived from C57BL/6J mice was associated with susceptibility to MAIDS, while theH-2 ^a haplotype conferred resistance to the disease. This finding was confirmed by demonstrating thatH-2 ^a congenics on the susceptible C57BL/10 background were as resistant to MAIDS as A/J mice which donated theH-2 ^a locus. Gene(s) within theH-2 complex thus represent the major regulatory mechanism of resistance/susceptibility to MAIDS.     

Congenic mice reveal genetic epistasis and overlapping disease loci for autoimmune diabetes and listeriosis

The nonobese diabetic (NOD) mouse strain serves as a genomic standard for assessing how allelic variation for insulin-dependent diabetes (Idd) loci affects the development of autoimmune diabetes. We previously demonstrated that C57BL/6 (B6) mice harbor a more diabetogenic allele than NOD mice for the Idd14 locus when introduced onto the NOD genetic background. New congenic NOD mouse strains, harboring smaller B6-derived intervals on chromosome 13, now localize Idd14 to an ~18-Mb interval and reveal a new locus, Idd31. Notably, the B6 allele for Idd31 confers protection against diabetes, but only in the absence of the diabetogenic B6 allele for Idd14, indicating genetic epistasis between these two loci. Moreover, congenic mice that are more susceptible to diabetes are more resistant to Listeria monocytogenes infection. This result co-localizes Idd14 and Listr2, a resistance locus for listeriosis, to the same genomic interval and indicates that congenic NOD mice may also be useful for localizing resistance loci for infectious disease.     

Segregation of a QTL cluster for home-cage activity using a new mapping method based on regression analysis of congenic mouse strains

Recent genetic studies have shown that genetic loci with significant effects in whole-genome quantitative trait loci (QTL) analyses were lost or weakened in congenic strains. Characterisation of the genetic basis of this attenuated QTL effect is important to our understanding of the genetic mechanisms of complex traits. We previously found that a consomic strain, B6-Chr6C^MSM, which carries chromosome 6 of a wild-derived strain MSM/Ms on the genetic background of C57BL/6J, exhibited lower home-cage activity than C57BL/6J. In the present study, we conducted a composite interval QTL analysis using the F2 mice derived from a cross between C57BL/6J and B6-Chr6C^MSM. We found one QTL peak that spans 17.6 Mbp of chromosome 6. A subconsomic strain that covers the entire QTL region also showed lower home-cage activity at the same level as the consomic strain. We developed 15 congenic strains, each of which carries a shorter MSM/Ms-derived chromosomal segment from the subconsomic strain. Given that the results of home-cage activity tests on the congenic strains cannot be explained by a simple single-gene model, we applied regression analysis to segregate the multiple genetic loci. The results revealed three loci (loci 1–3) that have the effect of reducing home-cage activity and one locus (locus 4) that increases activity. We also found that the combination of loci 3 and 4 cancels out the effects of the congenic strains, which indicates the existence of a genetic mechanism related to the loss of QTLs.     

Congenic strains provide evidence that a mapped locus on chromosome 15 influences excitotoxic cell death

Inbred strains of mice differ in their susceptibility to excitotoxin‐induced cell death, but the genetic basis of individual variation is unknown. Prior studies with crosses of the FVB/NJ (seizure‐induced cell death susceptible) mouse and the seizure‐induced cell death resistant mouse, C57BL/6J, showed the presence of three quantitative trait loci (QTLs), named seizure‐induced cell death 1 (Sicd1) to Sicd3. To better localize and characterize the Sicd2 locus, two reciprocal congenic mouse strains were created. While the B6.FVB‐Sicd2 congenic mouse was without effect on modifying susceptibility to seizure‐induced excitotoxic cell death, the FVB.B6‐Sicd2 congenic mouse, in which the chromosome (Chr) 15 region of C57BL/6J was introgressed into FVB/NJ, showed reduced seizure‐induced excitotoxic cell death following kainate administration. Phenotypic comparison between FVB and the congenic FVB.B6‐Sicd2 strain confirmed that the Sicd2 interval harbors gene(s) conferring strong protection against seizure‐induced excitotoxic cell death. Interval‐specific congenic lines (ISCLs) that encompass Sicd2 on Chr 15 were generated and were used to fine‐map this QTL. Resultant progeny were treated with kainate and examined for the extent of seizure‐induced cell death in order to deduce the Sicd2 genotypes of the recombinants through linkage analysis. All of the ISCLs exhibited reduced cell death associated with the C57BL/6J phenotype; however, ISCL‐2 showed the most dramatic reduction in seizure‐induced cell death in both area CA3 and in the dentate hilus. These findings confirm the existence of polymorphic loci within the reduced critical region of Sicd2 that regulate the severity of seizure‐induced cell death.     

Trypanosoma cruzi: role of the immune response in the natural resistance of inbred strains of mice.

Nine inbred strains of mice were challenged with 10⁴ or 10⁵ trypomastigotes of the Brazil strain of Trypanosoma cruzi. A spectrum of resistance was evident ranging from highly susceptible strains, e.g., C3H, which developed high parasitemias and died within 3 to 4 weeks, to resistant strains, e.g., C57BL/10, which developed low parasitemias and survived. Impairment of the immune system in resistant C57BL/10 mice by X-irradiation, splenectomy, or treatment with silica led to high, often fatal parasitemias. Athymic nude mice, in particular, attained exceptionally high parasitemias before dying. The immune response appears to be necessary for survival and to play a role in the natural resistance of some mouse strains by effectively eliminating parasites and minimizing parasitemia. Using congenic strains of mice, it was shown that the principal genetic determinant of resistance is not associated with their H-2 haplotype.     

Regulation of resistance to leprosy by chromosome 1 locus in the mouse

Mice of different inbred strains vary in their resistance to intravenous infection with Mycobacterium lepraemurium (MLM). The mean survival time of MLM-infected A/J and DBA/2 mice is significantly longer than that of similarly infected C57BL/6 and BALB/c mice. The typing of AXB/BXA recombinant inbred strains (A = A/J, B = C57BL/6) for the trait of relative resistance/susceptibility to MLM revealed a perfect match with the strain distribution pattern of resistance/susceptibility to Mycobacterium bovis (BCG), the trait which is controlled by the Bcg (Ity, Lsh) locus on chromosome 1. The control, by this gene, of response to MLM was further confirmed by the demonstration that BALB/c-Bcg ^r congenic mice,which carry the DBA/2-derived Bcg ^r (resistant) allele on chromosome 1, are significantly more resistant to MLM infection than their BALB/c (Bcg ^s , susceptible) counterparts.     

Host defenses in experimental scrub typhus: mapping the gene that controls natural resistance in mice

Natural resistance of mice to lethal ifections of Rickettsia tsutsugamushi, strain Gilliam, is controlled by a single, autosomal, dominant gene, which we have designated Ric, with r and s representing the resistant nd susceptible alleles, respectively. Using three sets of recombinant inbred mouse strains (BXD, BXH, and BXJ), the Ric locus was mapped to Chromosome 5 closely linked to the retinal degeneration (rd) locus. This linkage was confirmed by a backcross analysis. Based on the RI strains and the C57BL/6Ty-le congenic strain (the only proven Ric-rd cross-over), we estimate the recombination frequency between Ric and rd to be 0.015. Three presumptive Ric-rd recombinants detected among 93 backcross mice may represent caes of incomplete penetrance of the resistance allele rather than recombination. Analyis of th C57BL/6JTy-le congenic strain indicates that Ric is proximal to rd on Chromosome 5. If so, the correct gene order is Pgm-1-W-Ric-rd-Gus.     

Genome-wide screening for genetic loci associated with noise-induced hearing loss

Noise-induced hearing loss (NIHL) is one of the more common sources of environmentally induced hearing loss in adults. In a mouse model, Castaneous (CAST/Ei) is an inbred strain that is resistant to NIHL, while the C57BL/6J strain is susceptible. We have used the genome-tagged mice (GTM) library of congenic strains, carrying defined segments of the CAST/Ei genome introgressed onto the C57BL/6J background, to search for loci modifying the noise-induced damage seen in the C57BL/6J strain. NIHL was induced by exposing 6-8-week old mice to 108 dB SPL intensity noise. We tested the hearing of each mouse strain up to 23 days after noise exposure using auditory brainstem response (ABR). This study identifies a number of genetic loci that modify the initial response to damaging noise, as well as long-term recovery. The data suggest that multiple alleles within the CAST/Ei genome modify the pathogenesis of NIHL and that screening congenic libraries for loci that underlie traits of interest can be easily carried out in a high-throughput fashion.     

Genetic Determination of the Developmental Program for Mouse Liver β-GALACTOSIDASE: Involvement of Sites Proximate to and Distant from the Structural Gene

The identification and mode of action of genetic loci that program gene expression during development are important for understanding differentiation in higher organisms. Previous work from this laboratory has identified two patterns for the postnatal development of liver beta-galactosidase among inbred mouse strains: type I, where activity levels remain constant after about 30 days of age, is found in strains DBA/2J, CBA/J, and BALB/cJ, among others; type II, where activity levels increase between 25 and 50 days of age to reach a new adult level, is found in strain C57BL/6J and related strains. It has been shown that the type I vs. type II developmental difference between strains C57BL/6J and DBA/2J is due to variation at a locus, Bgl-t, that maps with the beta-galactosidase complex, [Bgl], on chromosome 9. In the present study, we have confirmed the existence of Bgl-t as a temporal locus within [Bgl] by analysis of both a congenic strain carrying the beta-galactosidase complex of strain CBA/J in the C57BL/6J genetic background and a cross of strains CBA/J and C57BL/6J. The existence of additional temporal loci for beta-galactosidase that segregate independently of the structural gene and participate in determination of the type I vs. type II difference was revealed by analysis of: (1) a congenic strain containing the beta-galactosidase complex of strain BALB/cJ in the C57BL/10Sn background; (2) recombinant inbred lines derived from progenitor strains C57BL/6ByJ and BALB/cByJ; and (3) a genetic cross between strains C57BL/6ByJ and BALB/cByJ. Thus, for these pairs of strains, the type I vs. type II developmental difference is due to variation at a temporal locus (or loci) unlinked to the enzyme structural gene, and not at Bgl-t. These facts, together with information gathered from an examination of the distribution of beta-galactosidase phenotypes among over 100 inbred strains (Breen, Lusis and Paigen 1977), have led us to conclude that the postnatal developmental pattern for liver beta-galactosidase is determined by a set of interacting temporal genes. One of these, Bgl-t, is located within [Bgl], and one or more are separable from [Bgl] by recombination. A possible mode of interaction among the temporal and instructural loci is suggested.     

Resistance to HSV-1 in the mouse is governed by two major,independently segregating,non-H-2 loci

Earlier studies showed that genetic resistance of adult, inbred strains of mice to Herpes Simplex Virus-type 1 (HSV-1) is a dominant genetic trait. The present studies were undertaken to determine the number of genetic loci involved and whether they were found within the major histocompatibility complex,H-2, of the mouse. Challenge with HSV-1 of progeny of mice backcrossed to moderately susceptible BALB/c mice, of progeny of mice backcrossed to very susceptible A/J strain mice, and of progeny of the F-2 cross using (C57BL/6 × A/J)F₁ mice indicated that two major loci were responsible for resistance. The backcrosses to BALB/c mice suggested that additional genes on this background enhanced resistance, while further backcrosses with the A/J mice indicated that other genes on the A/J background (or the lack thereof) reduced resistance. Studies with congenic mice showed that genes within theH-2 did not influence resistance or susceptibility.     

Analysis of reciprocal congenic lines reveals the C3H/HeJ genome to be highly resistant to ApcMin intestinal tumorigenesis

Genetic background affects polyp development in the Multiple intestinal neoplasia (Apc(Min)) mouse model. The Modifier of Min 1 (Mom1) locus accounts for approximately 50% of the variation in polyp multiplicity. We generated reciprocal congenic lines, such that the recipient C57BL/6J (B6) strain carries a donor C3H/HeJ (C3H) Mom1 allele, and the recipient C3H strain carries a donor B6 Mom1 allele. Hybrid progeny from congenic females mated to B6 Apc(Min/+) males were analyzed. A single C3H Mom1 locus on the B6 background reduced small intestinal polyp numbers by 50% and colon polyp incidence by 66% compared to their susceptible B6 Mom1(S/S)Apc(Min/+) siblings. These findings show that the C3H genome contains a resistant Mom1(R) locus. The reciprocal congenic line, which carries the susceptible B6 Mom1(S) locus on the C3H background, reduced small intestinal polyp numbers by 80% and colon polyp incidence by 95% compared to B6 Mom1(S/S)Apc(Min/+) mice. These data demonstrate that unidentified modifiers in the C3H strain can suppress intestinal polyp multiplicity in Apc(Min/+) mice, and act in the absence of a resistant Mom1(R) locus.     

A Locus for Circadian Period of Locomotor Activity on Mouse Proximal Chromosome 3

Lengthened circadian period of locomotor activity is a characteristic of a congenic strain of mice carrying a nonsense mutation in exon 5 of the carbonic anhydrase II gene, car2. The null mutation in car2 is located on a DBA/2J inbred strain insert on proximal chromosome 3, on an otherwise C57BL/6J genomic background. Since reducing the size of the congenic region would narrow the possible candidate genes for period, two recombinant congenic strains (R1 and R2) were developed from the original congenic strain. These new congenic strains were assessed for period, genetic composition, and the presence of immunoreactive carbonic anhydrase II. R1 mice were homozygous DBA/2J for the distal portion of the original DBA/2J insert, while R2 mice were homozygous DBA/2J for the proximal portion. R1 mice had a significantly lengthened period compared to R2 mice and wild-type C57BL/6J mice, indicating that the gene(s) affecting period is likely found within the reduced DBA/2J insert (?1 cM) in the R1 mice. The R1 mice also possessed the null mutation in car2. This study confirmed the presence of a gene(s) affecting period on proximal chromosome 3 and significantly reduced the size of the congenic region and the number of candidate genes. Future studies will focus on identifying the gene influencing period.     

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.Deceased, Aug. 8, 1994.     

Genetic analysis of testis weight and fertility in an interspecies hybrid congenic strain for Chromosome X

A hybrid congenic strain, C57BL/6J.SPRET-Hprt ^a , carrying 17 map units of Chromosome (Chr) X from Mus spretus on a background of C57BL/6J, has the novel phenotype of low fertility associated with small testis weight. In histological cross-section, many of the tubules in the testes of these congenic mice are empty except for Sertoli cells, while the other tubules appear to be normal. The gene, interspecific hybrid testis weight 1 (Ihtw1) causing this phenotype, has been fine mapped by using the strategy of generating subcongenic strains from recombinants within the congenic region. Genetic and phenotypic analysis of the subcongenic strains has defined a critical region of 1.8 map units for Ihtw1. This region of the genetic map is orthologous to the region on human Chr X containing the gene for the Borjeson-Forssman-Lehman syndrome, an inherited disease in which males show microorchidism. Received: 12 June 2000 / Accepted: 8 September 2000     

Dissection of multigenic obesity traits in congenic mouse strains

Previous quantitative trait locus mapping (QTL) identified multigenic obesity (MOB) loci on mouse Chromosome (Chr) 2 that influence the interrelated phenotypes of obesity, insulin resistance, and dyslipidemia. To better localize and characterize the MOB locus, three congenic mouse strains were created. Overlapping genomic intervals from the lean CAST/Ei (CAST) strain were introgressed onto an obesity-susceptible C57BL/6 (BL6) background to create proximal (15 Mb–73 Mb), middle (63 Mb–165 Mb), and distal (83 Mb–182 Mb) congenic strains. The congenic strains showed differences in obesity, insulin, and lipid traits consistent with the original QTL analysis for the locus. Importantly, characterization of the MOB congenics localized the effects of genes that underlie obesity-related traits to an introgressed interval (73–83 Mb) unique to the middle MOB congenic. Conversely, significant differences between the lipid and insulin profiles of the middle and distal MOB congenics implicated the presence of at least two genes that underlie these traits. When fed an atherogenic diet, several traits associated with metabolic syndrome were observed in the distal MOB congenic, while alterations in plasma lipoproteins were observed in the middle MOB congenic strain.     

Genetic analysis of the diabetes-prone C57BLKS/J mouse strain reveals genetic contribution from multiple strains

The C57BLKS/J (BKS) inbred mouse strain is a widely used animal model of type 2 diabetes. In the presence of the diabetes (db) mutation, obese BKS-db mice develop severe diabetes. Genetic studies of diabetes-susceptibility in this strain are facilitated by the fact that BKS is a genetic composite between the diabetes-resistant C57BL/6J (B6) and susceptible DBA/2J (DBA) strains. On this basis, it has been hypothesized that diabetes-susceptibility in BKS is conferred by DBA-derived alleles. However, recent studies revealed non-B6/non-DBA genetic material in BKS. To identify the origin of this genetic component, we generated a genomic map of BKS using 537 microsatellite markers. Our results demonstrate that, in addition to B6 and DBA, BKS contains alleles from at least three other strains, including 129, C57BL/10 and an unidentified mouse strain. We also analyzed two congenic strains, B6-db and BKS-db, which are widely used for the genetic mapping of diabetes-susceptibility loci. We identified several donor-derived genomic regions introduced during the generation of these congenic strains. In summary, our study reveals novel aspects of the genetic fine-structure of BKS and related strains and facilitates the identification of diabetes-susceptibility loci in this mouse model.     

Localization of Idd11 using NOD congenic mouse strains: elimination of Slc9a1 as a candidate gene

 Type 1 diabetes is a multigenic autoimmune disease, the genetic basis for which is perhaps best characterized in the nonobese diabetic (NOD) mouse model. We previously located a NOD diabetes susceptibility locus, designated Idd11, on mouse Chromosome (Chr) 4 by analyzing diabetic backcross mice produced after crossing NOD/Lt with the nondiabetic resistant strain C57BL/6 (B6) strain. In order to confirm Idd11 and further refine its location, three NOD congenic mouse strains with different B6 derived intervals within Chr 4 were generated. Two of the congenic strains had a significant decrease in the cumulative incidence of diabetes compared with NOD/Lt control mice. The third NOD congenic strain, containing a B6 interval surrounding the Slc9a1 locus, was not protected against diabetes. These results define a new distal boundary for Idd11 and eliminate the Slc9a1 gene as a candidate. The Idd11 locus has now been definitively mapped to a 13cM interval on mouse Chr 4. Received: 15 May 1999 / Revised: 25 September 1999