The genetic map around the tail kinks (tk) locus on mouse chromosome 9

Tail kinks (tk) is a classical mouse skeletal mutation, located on Chromosome (Chr) 9. As the first step for the positional cloning of the tk gene, we have established a genetic map of a region surrounding the tk locus by generating a backcross segregating for tk. From this backcross, 1004 progeny were analyzed for the coat-color phenotype of the proximally located dilute (d) gene and for the distally flanking microsatellite marker, D9Mit12. Fifty-six recombinants between d and tk and 75 recombinants between tk and D9Mit12 were identified, completing a panel of 130 recombinants including one double recombinant. This panel allowed us to map five microsatellite loci as well as d and Mod-1 with respect to tk. We show that one of the microsatellite markers mapped, D9Mit9, does not recombine at all with tk in our backcross. This indicates that the D9Mit9 locus will serve as a good starting point for a chromosomal walk to the tk gene.     

Evidence for the presence of insulin-dependent diabetes-associated alleles on the distal part of mouse chromosome 6

Type 1 diabetes (IDDM) is a complex disorder with multifactorial and polygenic etiology. A genome-wide screen performed in a BC1 cohort of a cross between the nonobese diabetic (NOD) mouse with the diabetes-resistant feral strain PWK detected a major locus contributing to diabetes development on the distal part of chromosome 6. Unlike the majority of other Idd loci identified in intraspecific crosses, susceptibility is associated with the presence of the PWK allele. Genetic linkage analysis of congenic lines segregating PWK chromosome 6 segments in a NOD background confirmed the presence of the Idd locus within this region. The genetic interval defined by analysis of congenic animals showed a peak of significant linkage (P = 0.0005) centered on an approximately 9-cM region lying between D6Mit11 and D6Mit25 genetic markers within distal mouse chromosome 6. [Genetic markers polymorphic between the NOD and PWK strains are available as a supplement at http://www.genome.org]     

Rbt (Rabo torcido), a new mouse skeletal mutation involved in anteroposterior patterning of the axial skeleton, maps close to the Ts (tail-short) locus and distal to the Sox9 locus on chromosome 11

Rbt (Rabo torcido) is a new semidominant mouse mutant with a variety of skeletal abnormalities. Heterozygous Rbt mutants display homeotic anteroposterior patterning problems along the axial skeleton that resemble Polycomb group and trithorax gene mutations. In addition, the Rbt mutant displays strong similarities to the phenotype observed in Ts (Tail-short), indicating also a homeotically transformed phenotype in these mice. We have mapped the Rbt locus to an interval of approximately 6 cM on mouse Chromosome (Chr) 11 between microsatellite markers D11Mit128 and D11Mit103. The Ts locus was mapped within a shorter interval of approximately 3 cM between D11Mit128 and D11Mit203. This indicates that Rbt and Ts may be allelic mutations. Sox9, the human homolog of which is responsible for the skeletal malformation syndrome campomelic dysplasia, was mapped proximal to D11Mit128. It is, therefore, unlikely that Ts and Rbt are mouse models for this human skeletal disorder.     

Expression of DCC protein in colorectal tumors and its relationship to tumor progression and metastasis

The strains BALB/cHeA (BALB/c) and STS/A (STS) differ in production of IL-4 and IL-10, two Th2 cytokines, after stimulation of spleen cells with Concanavalin A, STS being a low and BALB/c a high producer. We analyzed the genetic basis of this strain difference using the recombinant congenic (RC) strains of the BALB/c-c-STS/Dem (CcS/Dem) series. This series comprises 20 homozygous strains. Each CcS/Dem strain contains a different, random set of approximately 12. 5% genes of the "donor" strain STS and approximately 87.5% of the "background" strain BALB/c. We selected for further analysis the RC strain production intermediate between BALB/c and STS. In (CcS-20xBALB/c)F2 hybrids we found that different loci control expression of IL-4 and IL-10. Cypr1 (cytokine production 1) on chromosome 16 near D16Mit15 controls IL-4 production, whereas the production of IL-10 is influenced by loci Cypr2 near D1Mit14 and D1Mit227 on chromosome 1 and Cypr3 marked by D5Mit20 on chromosome 5. In addition, the relationship between the level of these two cytokines depends on the genotype of the F2 hybrids at a locus cora1 (correlation 1) on chromosome 5. This differential genetic regulation may be relevant for the understanding of biological effects of T-helper cells in mice of different genotypes.     

Doublefoot: a new mouse mutant affecting development of limbs and head

The mutant doublefoot, Dbf, of the mouse arose spontaneously, and was shown to be inherited as an autosomal dominant, mapping 9-13 cM proximal to leaden, In, on chromosome 1 and showing no recombination with the microsatellite markers D1Mit24 and D1Mit77. In heterozygotes the phenotype includes many extra toes on all four feet, and the tibia and fibula may be reduced and bowed. The head is shortened and broad and the eyes are held half-closed, and some animals develop hydrocephalus. The tail is kinked and abnormally thick, and the soles of the feet are swollen. Growth is retarded, viability is reduced, and reproduction is impaired in both sexes. Only about 30% of males are normally fertile, and testis weights and sperm counts may be reduced, although this appears not to be the main cause of poor fertility. In females vaginal opening is delayed and oestrous cycles are irregular, although the animals appear to respond to gonadotrophic hormones. Crosses of Dbf/+ x Dbf/+ are very poorly fertile. Prenatally, Dbf/+ heterozygotes can first be recognized at 11 1/2 days gestation by abnormally broad fore limb buds. Putative Dbf/Dbf homozygotes at 12 1/2 days have similar limbs defects and also split face, due to failure of the maxillae to fuse in the midline. Some homozygotes and a few putative heterozygotes have cranioschisis. At 13 1/2 days, the heads of homozygotes tend to bulge in the frontal region and a bleb of clear fluid is visible medially. At 14 1/2 days Dbf/Dbf fetuses may have oedema and some are dead. From 15 1/2 days onwards no live Dbf/Dbf fetuses have been found. The gene maps close to the locus of Pax3, but crossovers between Dbf and Pax3 have been found, ruling out the possibility that a gain-of-function mutation in Pax3 might be involved.     

Aphakia (ak), a mouse mutation affecting early eye development: fine mapping, consideration of candidate genes and altered Pax6 and Six3 gene expression pattern

The homozygous mouse mutant aphakia (ak) has been characterized by bilaterally aphakic eyes without a pupil [Varnum DS, Stevens, LC (1968): J Hered 59:147-150]. The mutation was mapped to chromosome 19 [Varnum DS, Stevens, LC (1975): Mouse News Lett 53:35]. Our linkage studies yielded a precise localization of the ak gene 0.6 +/- 0.3 cM proximal to the microsatellite marker D19Mit10 and 0.7 +/- 0.4 cM distal to D19Mit4 and D19Mit91. No recombination was found with the marker D19Mit9 among 418 backcross offspring tested. The developmental control gene Pax2 mapped 11.0 +/- 3.5 cM proximal to ak and is excluded as a candidate gene. Sequence analysis of Fgf8 and Chuk1, which are localized close to the marker D19Mit10, detected no mutations in the ak/ak mutants. Histological analysis of homozygous mutants suggested the arrest of lens development at the lens stalk stage, a transient morphological structure during the formation of the lens vesicle. In the lens remnants, Pax6 and Six3 are expressed, whereas in the persisting lens stalk only Pax6 was detected. The expression pattern of Pax2 appeared normal; Cryaa expression could not be detected. As a consequence of the arrested lens development, other ocular tissues that require for their development information from the intact lens, such as iris, ciliary muscle, retina, and vitreous body, are absent or formed abnormally.     

High-resolution mapping of a minor histocompatibility antigen gene on mouse chromosome 2

Minor histocompatibility (H) loci are significant tissue transplantation barriers but are poorly understood at the genetic and molecular level. We describe the construction of a high-resolution genetic map that positions a class II MHC-restricted minor H antigen locus and orders 12 other genes and genetic markers within the we-un interval of mouse Chromosome (Chr) 2. An intersubspecific backcross between B10.UW/Sn-H-3b and CAST/Ei, an inbred stock of Mus musculus castaneus, was used for this purpose. A total of 1168 backcross mice were generated, and 71 we-un recombinants were identified. Significant compression of the genetic map in males versus females and transmission distortion of CAST-derived we, un, and Aw genes were observed. Monoclonal T cell lines specific for two minor H alloantigens, Hd-1a and Hd-2a, encoded by gene(s) that map to the we-un interval were used to antigen type the backcross mice. The results suggest the Hd-1a and Hd-2a antigens are most likely encoded by a single gene, now referred to as H-3b. The determined gene order is we-0.09 +/- 0.09-Itp-0.62 +/- 0.23-D2Mit77-0.26 +/- 0.15-[Evi-4, Pcna, Prn-p]-0.26 +/- 0.15-Scg-1-0.44 +/- 0.19-[Bmp2a, D2Mit70]-0.09 +/-. 0.09-[D2Mit19, D2Mit46]-1.59 +/- 0.36-D2Mit28-0.97 +/- 0.28-D2Ler1-1.50 +/- 0.35-H-3b-0.26 +/- 0.15-un (% recombination +/- 1 SE). Because the average resolution of the backcross is 0.09 cM, the backcross panel should facilitate the physical mapping and molecular identification of a number of genes in this chromosome region.     

Tissue factor in the pathogenesis of atherosclerosis

The Otsuka Long-Evans Tokushima Fatty (OLETF) rat is an animal model for obese NIDDM. We performed a genome wide scan in F2 progenies obtained by crossing OLETF rats with two control strains, Long-Evans Tokushima Otsuka (LETO) and Fisher-344(F-344) rats. Since diabetes develops only in male progenies, we used only male F2 rats for the linkage studies.Highly significant linkage was observed between the phenotype, postprandial hyperglycemia and P-450ald locus on chromosome 1 and D7Mit 11 locus on chromosome 7. In addition, suggestive linkage was found between fasting glucose level and body weight and these two loci. Four other regions (D1Mit12, D2Mit11, D5Mgh14, and D17Arb1) on chromosome 1, 2, 5, and 17 were detected to influence body weight, fasting glucose level or postprandial hyperglycemia independently. We concluded that non-insulin-dependent diabetes mellitus(NIDDM) in OLETF rats is regulated by multiple genes which affect fasting, postprandial hyperglycemia, and obesity differently.     

Resistance to Leishmania major is linked to the H2 region on chromosome 17 and to chromosome 9

In Leishmaniasis, as in many infectious diseases, clinical manifestations are determined by the interaction between the genetics of the host and of the parasite. Here we describe studies mapping two loci controlling resistance to murine cutaneous leishmaniasis. Mice infected with L. major show marked genetic differences in disease manifestations: BALB/c mice are susceptible, exhibiting enlarging lesions that progress to systemic disease and death, whereas C57BL/6 are resistant, developing small, self-healing lesions. F2 animals from a C57BL/6 X BALB/c cross showed a continuous distribution of lesion score. Quantitative trait loci (QTL) have been mapped after a non-parametric QTL analysis on a genome-wide scan on 199 animals. QTLs identified were confirmed in a second cross of 271 animals. Linkage was confirmed to a chromosome 9 locus (D9Mit67-D9Mit71) and to a region including the H2 locus on chromosome 17. These have been named Imr2 and Imr1, respectively.     

Quantitative trait locus mapping of human blood pressure to a genetic region at or near the lipoprotein lipase gene locus on chromosome 8p22

Resistance to insulin-mediated glucose disposal is a common finding in patients with non-insulin-dependent diabetes mellitus (NIDDM), as well as in nondiabetic individuals with hypertension. In an effort to identify the generic loci responsible for variations in blood pressure in individuals at increased risk of insulin resistance, we studied the distribution of blood pressure in 48 Taiwanese families with NIDDM and conducted quantitative sib-pair linkage analysis with candidate loci for insulin resistance, lipid metabolism, and blood pressure control. We found no evidence for linkage of the angiotensin converting enzyme locus on chromosome 17, nor the angiotensinogen and renin loci on chromosome 1, with either systolic or diastolic blood pressures. In contrast, we obtained significant evidence for linkage or systolic blood pressure, but not diastolic blood pressure, to a genetic region at or near the lipoprotein lipase (LPL) locus on the short arm of chromosome 8 (P = 0.002, n = 125 sib-pairs, for the haplotype generated from two simple sequence repeat markers within the LPL gene). Further strengthening this linkage observation, two flanking marker loci for LPL locus, D8S261 (9 cM telomeric to LPL locus) and D8S282 (3 cM centromeric to LPL locus), also showed evidence for linkage with systolic blood pressure (P = 0.02 and 0.0002 for D8S261 and D8S282, respectively). Two additional centromeric markers (D8S133, 5 cM from LPL locus, and NEFL, 11 cM from LPL locus) yielded significant P values of 0.01 and 0.001, respectively. Allelic variation around the LPL gene locus accounted for as much as 52-73% of the total interindividual variation in systolic blood pressure levels in this data set. Thus, we have identified a genetic locus at or near the LPL gene locus which contributes to the variation of systolic blood pressure levels in nondiabetic family members at high risk for insulin resistance and NIDDM.     

Genetic basis for diabetes resistance in NOD/Wehi mice

The basis for diabetes resistance in low diabetes incidence NOD/Wehi mice was examined in a breeding study. NOD/Wehi mice were crossed with high diabetes incidence NOD/Lt mice producing F1 hybrid mice which expressed a low incidence of diabetes. To distinguish between genetic and environmental causes for diabetes resistance, these F1 mice were backcrossed to NOD/Lt mice resulting in BC1 hybrid mice which expressed an intermediate incidence of diabetes. Similar results were obtained by examining the severity of insulitis in the hybrid mice. As both the incidence of diabetes and severity of insulitis in the hybrid mice were consistent with a single dominant gene mediating diabetes resistance, an attempt to localize this gene was made. Although over 140 loci which display polymorphism amongst inbred strains were typed in both parental lines, only a single locus, D8Mit9, was found to differ. As heterozygotes at D8Mit9 were not over represented amongst 45 diabetic BC1 hybrid mice examined, it was concluded that a resistance gene was not linked to this locus.     

Can health care assistants replace student nurses?

Quantitative trait loci (QTLs) affecting body weight were investigated in the backcross population derived from diabetic BB/OK and spontaneously hypertensive rat (SHR). The F1 hybrids were backcrossed onto BB/OK rats, and QTL analysis was performed with the resulting backcross population on chromosomes 1, 3, 4, 10, 13 and 18. According to the stringent threshold for a lod score of 3.0, markers on chromosomes 1 and 4 were found to be linked with body weight. The QTL with a peak lod score (3.3) on chromosome 1 for a male population was located within the region flanked by loci Igf2 and D1Mgh12. On chromosome 4, linkage between the body weight and the region around the Npy locus was observed (lod score 3.1). The existence of the QTL on chromosome 4 affecting body weight was confirmed by congenic BB.LL rats, carrying chromosomal region of SHR (D4Mit6-Npy-Spr) on the genetic background of the BB/OK rat.     

Expression screening of a yeast artificial chromosome contig refines the location of the mouse H3a minor histocompatibility antigen gene

The H3 complex, on mouse Chromosome 2, is an important model locus for understanding mechanisms underlying non-self Ag recognition during tissue transplantation rejection between MHC-matched mouse strains. H3a is a minor histocompatibility Ag gene, located within H3, that encodes a polymorphic peptide alloantigen recognized by cytolytic T cells. Other genes within the complex include beta2-microglobulin and H3b. A yeast artificial chromosome (YAC) contig is described that spans the interval between D2Mit444 and D2Mit17, a region known to contain H3a. This contig refines the position of many genes and anonymous loci. In addition, 23 new sequence-tagged sites are described that further increase the genetic resolution surrounding H3a. A novel assay was developed to determine the location of H3a within the contig. Representative YACs were modified by retrofitting with a mammalian selectable marker, and then introduced by spheroplast fusion into mouse L cells. YAC-containing L cells were screened for the expression of the YAC-encoded H3a(a) Ag by using them as targets in a cell-mediated lympholysis assay with H3a(a)-specific CTLs. A single YAC carrying H3a was identified. Based on the location of this YAC within the contig, many candidate genes can be eliminated. The data position H3a between Tyro3 and Epb4.2, in close proximity to Capn3. These studies illustrate how genetic and genomic information can be exploited toward identifying genes encoding not only histocompatibility Ags, but also any autoantigen recognized by T cells.     

A new candidate site for a tumor suppressor gene involved in mouse thymic lymphomagenesis is located on the distal part of chromosome 4

In a previous work we provided preliminary evidence of the existence of a putative tumor suppressor gene region on the distal part of chromosome 4 in gamma-radiation-induced T-cell lymphomas of (C57BL/6J x RF/J) F1 hybrid mice. This region, named as TLSR2 (Thymic Lymphoma Suppressor Region 2), was located centered at D4Mit54. A more detailed allelotype analysis in the mentioned tumors with new informative microsatellites on distal chromosome 4 region, as well as in thymic lymphomas induced with gamma-rays in F1 hybrids generated from reciprocal crosses between the strains C57BL/6J and BALB/cJ, and having in mind the new map position of D4Mit205b, allowed us to confirm the existence of TLSR2 and to define it more precisely as centered at D4Mit205b. In addition, we identified a new candidate region, named as TLSR3 (Thymic Lymphoma Suppressor Region 3), located between the Mom-1 locus and D4Mit68, as the site of another putative tumor suppressor region involved in thymic lymphomagenesis.     

Chromosome 14 contains determinants that regulate susceptibility to Theiler's virus-induced demyelination in the mouse

Theiler's murine encephalomyelitis virus causes a chronic demyelinating disease in susceptible strains of mice that is similar to human multiple sclerosis. Several nonmajor histocompatibility complex-linked genes have been implicated as determinants of susceptibility or resistance to either demyelination or virus persistence. In this study, we used linkage analysis of major histocompatibility complex identical H-2d (DBA/2J x B10.D2) F2 intercross mice to identify loci associated with susceptibility to virus-induced demyelinating disease. In a 20-cM region on chromosome 14, we identified four markers, D14Mit54, D14Mit60, D14Mit61, and D14Mit90 that are significantly associated with demyelination. Because two peaks were identified, one near D14Mit54 and one near D14Mit90, it is possible that two loci in this region are involved in controlling demyelination.     

Complex genetic control of HDL levels in mice in response to an atherogenic diet. Coordinate regulation of HDL levels and bile acid metabolism

Inbred strains of mice differ in susceptibility to atherogenesis when challenged with a high fat, high cholesterol diet containing 0.5% cholic acid. Studies of recombinant inbred (RI) strains derived from the susceptible strain C57BL/6J (B6) and the resistant strains C3H/HeJ (C3H) and BALB/cJ have revealed an association between fatty streak lesion size and a decrease in high density lipoprotein (HDL) levels on the diet. To better understand the genetic factors contributing to HDL metabolism and atherogenesis in response to the diet, we studied mice derived from an intercross between B6 and C3H using a complete linkage map approach. A total of 185 female progeny were typed for 134 genetic markers spanning the mouse genome, resulting in an average interval of about 10 cM between markers. A locus on distal chromosome 1 containing the apolipoprotein AII gene was linked to HDL-cholesterol levels on both the chow and the atherogenic diets, but this locus did not contribute to the decrease in HDL-cholesterol in response to the diet. At least three distinct genetic loci, on chromosomes 3, 5, and 11, exhibited evidence of linkage to a decrease in HDL-cholesterol after a dietary challenge. Since a bile acid (cholic acid) is required for the diet induced changes in HDL levels and for atherogenesis in these strains, we examined cholesterol-7-alpha hydroxylase (C7AH) expression. Whereas B6 mice exhibited a large decrease in C7AH mRNA levels in response to the diet, C3H showed an increase. Among the intercross mice, multiple loci contributed to the regulation of C7AH mRNA levels in response to the diet, the most notable of which coincided with the loci on chromosomes 3, 5, and 11 controlling HDL levels in response to the diet. None of these loci were linked to the C7AH structural gene which we mapped to proximal chromosome 4. These studies reveal coordinate regulation of C7AH expression and HDL levels, and they indicate that the genetic factors controlling HDL levels are more complex than previously suggested by studies of RI strains. Furthermore, we observed that two of the loci for C7AH expression contributed to differences in gallstone formation between these strains.     

A high-resolution map in the chromosomal region surrounding the Lps locus

The Lps locus on mouse chromosome 4 controls host responsiveness to lipopolysaccharide, a major component of the outer membrane of Gram-negative bacteria. The C3H/HeJ inbred mouse strain is characterized by a mutant Lps allel (Lpsd) that renders it hyporesponsive to LPS and naturally tolerant of its lethal effects. To identify the Lps gene by a positional cloning strategy, we have generated a high-resolution linkage map of the chromosomal region surrounding this locus. We have analyzed a total of 1604 backcross mice from a preexisting interspecific backcross panel of 259 (Mus spretus x C57BL/6J)F1 x C57BL/6J and two novel panels of 597 (DBA/2J x C3H/HeJ)F1 x C3H/HeJ and 748 (C57BL/6J x C3H/HeJ)F1 x C3H/HeJ segregating at Lps. A total of 50 DNA markers have been mapped in a 11.8-cM span overlapping the Lps locus. This positions the Lps locus within a 1.1-cM interval, flanked proximally by a large cluster of markers, including three know genes (Cd301, Hxb, and Ambp), and distally by two microsatellite markers (D4Mit7/D4Mit178). The localization of the Lps locus is several centimorgans proximal to that previously assigned.     

The region responsible for stroke on chromosome 4 in the stroke-prone spontaneously hypertensive rat

To detect genetic loci responsible for stroke susceptibility, we produced 107 male F2 progenies crossed between stroke-prone spontaneously hypertensive rats (SHRSP/Izm) and normotensive Wistar Kyoto rats (WKY/Izm) and followed them up until they developed cerebral stroke. One hundred and twenty-five simple sequence repeat (SSR) markers were analyzed in these F2 rats. Nine of 107 F2 rats suffered from macroscopically overt stroke. In these 9 rats, the segregation ratio of 3 genotypes at 6 SSR marker loci on chromosomes 2, 4, 9, and 10 was highly distorted from the expected value (the observed sp/sp:sp/wky:wky/ wky ratio was either 6:3:0 or 6:2:1, while the expected was 1:2:1, p < 0.01 by chi 2 test). Further, the brain weight was significantly heavier (p < 0.001) in the F2 rats suffering from stroke, suggesting that the brain weight was a parameter for stroke. The brain weight of F2 rats cosegregated with D4Mit19, D4Mgh7, and D4Mgh8 (p = 0.0015, 0.0014, and 0.0040 by ANOVA, respectively) on chromosome 4 supporting genetic effects of this genetic loci on the pathogenesis of cerebral stroke. Blood pressure did not cosegregate with these markers on chromosome 4. These results suggest that a region on chromosome 4, independently of hypertension, determines genetic susceptibility to cerebral stroke.     

Autosomal dominant cerebellar ataxia type I in Martinique (French West Indies): genetic analysis of three unrelated SCA2 families

Autosomal dominant cerebellar ataxias (ADCAs) are a group of neurodegenerative disorders that are clinically and genetically heterogeneous. We report here a genetic linkage study, with five chromosome 12q markers, of three Martinican families with ADCA type 1, for which the spinocerebellar ataxia 1 (SCA1) locus was excluded. Linkage to the SCA2 locus was demonstrated with a maximal lead score of 6.64 at theta = 0.00 with marker D12S354. Recombinational events observed by haplotype reconstruction demonstrated that the SCA2 locus is located in an approximately 7-cM interval flanked by D12S105 and D12S79. Using the z(max)-1 method, multipoint analysis further reduced the candidate interval for SCA2 to a region of 5 cM. Two families shared a common haplotype at loci spanning 7 cM, which suggests a founder effect, whereas a different haplotype segregated with the disease in the third family. Finally, a mean anticipation of 12+/-14 years was found in parent-child couples, with no parental sex effect, suggesting that the disease might be caused by an expanded and unstable triplet repeat.     

Sucrose consumption in mice: major influence of two genetic loci affecting peripheral sensory responses

Individual variability in sucrose consumption is prominent in humans and other species. To investigate the genetic contribution to this complex behavior, we conducted behavioral, electrophysiological, and genetic studies, using male progeny of two inbred mouse strains (C57BL/6ByJ [B6] and 129/J [129]) and their F2 hybrids. Two loci on Chromosome (Chr) 4 were responsible for over 50% of the genetic variability in sucrose intake. These loci apparently modulated intake by altering peripheral neural responses to sucrose. One locus affected the response threshold, whereas the other affected the response magnitude. These findings suggest that the majority of difference in sucrose intake between male B6 and 129 mice is due to polymorphisms of two genes that influence receptor or peripheral nervous system activity.