Genetic mapping of a Ptch1-associated rhabdomyosarcoma susceptibility locus on mouse chromosome 2

Mutations in the Patched (Ptch1) gene are responsible for various familial and sporadic cancers. Ptch1(neo67/+) mice, in which exons 6 and 7 are deleted, show genetic background-dependent susceptibility to the development of muscle tumors resembling human rhabdomyosarcoma (RMS); BALB/c (BALB) is a susceptible strain whereas C57BL/6 (B6) shows resistance. A genome-wide linkage analysis was carried out using Ptch1(neo67/+)mice produced from B6 x (BALB x B6) backcrosses to identify loci involved in the control of RMS susceptibility. Quantitative trait locus mapping with the censored tumor latency time as the quantitative parameter was used to detect a significant RMS susceptibility modifier locus, Parms1 (Patched-Associated RMS 1), on chromosome 2 between D2Mit37 and D2Mit102 (LRS = 10). A Kaplan-Meier survival curve revealed that mice with the B6/BALB genotype develop tumors more frequently and much faster as compared to mice homozygous for the B6 allele (P = 0.02). Additional loci not reaching linkage significance were also detected for medulloblastoma resistance.     

Congenic mapping and candidate gene analysis for streptozotocin-induced diabetes susceptibility locus on mouse chromosome 11

Streptozotocin (STZ) has been widely used to induce diabetes in rodents. Strain-dependent variation in susceptibility to STZ has been reported; however, the gene(s) responsible for STZ susceptibility has not been identified. Here, we utilized the A/J-11^SM consomic strain and a set of chromosome 11 (Chr. 11) congenic strains developed from A/J-11^SM to identify a candidate STZ-induced diabetes susceptibility gene. The A/J strain exhibited significantly higher susceptibility to STZ-induced diabetes than the A/J-11^SM strain, confirming the existence of a susceptibility locus on Chr. 11. We named this locus Stzds1 (STZ-induced diabetes susceptibility 1). Congenic mapping using the Chr. 11 congenic strains indicated that the Stzds1 locus was located between D11Mit163 (27.72 Mb) and D11Mit51 (36.39 Mb). The Mpg gene, which encodes N-methylpurine DNA glycosylase (MPG), a ubiquitous DNA repair enzyme responsible for the removal of alkylated base lesions in DNA, is located within the Stzds1 region. There is a close relationship between DNA alkylation at an early stage of STZ action and the function of MPG. A Sanger sequence analysis of the Mpg gene revealed five polymorphic sites in the A/J genome. One variant, p.Ala132Ser, was located in a highly conserved region among rodent species and in the minimal region for retained enzyme activity of MPG. It is likely that structural alteration of MPG caused by the p.Ala132Ser mutation elicits increased recognition and excision of alkylated base lesions in DNA by STZ.

     

Genome-wide mapping of susceptibility to coronary artery disease identifies a novel replicated locus on chromosome 17

Coronary artery disease (CAD) is a leading cause of death world-wide, and most cases have a complex, multifactorial aetiology that includes a substantial heritable component. Identification of new genes involved in CAD may inform pathogenesis and provide new therapeutic targets. The PROCARDIS study recruited 2,658 affected sibling pairs (ASPs) with onset of CAD before age 66 y from four European countries to map susceptibility loci for CAD. ASPs were defined as having CAD phenotype if both had CAD, or myocardial infarction (MI) phenotype if both had a MI. In a first study, involving a genome-wide linkage screen, tentative loci were mapped to Chromosomes 3 and 11 with the CAD phenotype (1,464 ASPs), and to Chromosome 17 with the MI phenotype (739 ASPs). In a second study, these loci were examined with a dense panel of grid-tightening markers in an independent set of families (1,194 CAD and 344 MI ASPs). This replication study showed a significant result on Chromosome 17 (MI phenotype; p = 0.009 after adjustment for three independent replication tests). An exclusion analysis suggests that further genes of effect size λ_sib > 1.24 are unlikely to exist in these populations of European ancestry. To our knowledge, this is the first genome-wide linkage analysis to map, and replicate, a CAD locus. The region on Chromosome 17 provides a compelling target within which to identify novel genes underlying CAD. Understanding the genetic aetiology of CAD may lead to novel preventative and/or therapeutic strategies.     

Deletion mapping of the medulloblastoma locus on chromosome 17p

Isochromosome 17q has previously been observed consistently in cytogenetic studies of medulloblastoma, the most common posterior fossa neoplasm in children. We performed a restriction fragment length polymorphism (RFLP) investigation of medulloblastoma which showed a loss of chromosome 17p sequences in 45% of these tumors. This finding was predictive of a poor clinical response to treatment. A contiguous panel of markers permitted mapping of the deletion to 17p12-p13.1, the same chromosomal region for which loss of alleles has been shown in tumor specimens from patients with colon cancer, and the same region to which the p53 gene has been mapped. This suggests that medulloblastoma is associated with a recessive oncogene on chromosome 17p that may be involved in the genesis of several embryologically unrelated neoplasms and that the absence of this gene in tumor tissue has prognostic significance.     

Multiple seizure susceptibility genes on chromosome 7 in SWXL-4 congenic mouse strains

The SWXL-4 recombinant inbred mouse strain is unusually sensitive to recurrent tonic-clonic seizures upon routine handling and to seizures induced by chemoconvulsants. In a conventional intercross with the ABP/Le strain, we previously mapped a SWXL-4-derived quantitative trait locus called Szf1 (seizure frequency 1) to Chromosome 7. In the present study, we confirm the existence of Szf1 in both an independent cross and a congenic strain. However, derivative congenic recombinant strains show that an interaction between at least two genes on Chromosome 7-each of which has a very small effect on its own-account for Szf1.     

Yeast artificial chromosome mapping of the cystinosis locus on chromosome 17p by fluorescence in situ hybridization

The gene locus for cystinosis has been mapped between markers D17S1583 and D17S1584 on the short arm of chromosome 17. Using markers encompassing the cystinosis region, we assigned different yeast artificial chromosome (YAC) clones previously identified by sequence tagged site (STS) screening to 17p13.3. Three of the clones hybridized to the target 17p gene region; one of these was chimeric, hybridizing both to chromosomes 3p and 5q; two of the YACs did not contain sequences of 17p13.3. Our physical mapping has identified candidate YACs as a first step towards a positional cloning approach. Received: 28 February 1996 / Revised: 3 May 1996     

Fine mapping of the schizophrenia susceptibility locus on chromosome 1q22

Schizophrenia is a serious neuropsychiatric illness estimated to affect approximately 1% of the general population. As part of a genome scan for schizophrenia susceptibility loci, we have previously reported a maximum heterogeneity four-point lod score of 6.50 on chromosome 1q21-22 in a group of 22 medium-sized Canadian families, selected for study because multiple relatives were clinically diagnosed with schizophrenia or schizoaffective disorder. We have now conducted fine mapping of this locus in the same set of individuals using 15 genetic markers spanning an approximately 15-cM interval. Parametric linkage analysis with GENEHUNTER v2.1 and VITESSE v2.0 produced a maximum multipoint heterogeneity lod score of 6.50, with a Zmax-1 support interval of <3 cM, corresponding to approximately 1 Mb. Physical mapping and sequence analysis from this region confirmed the presence of an approximately 81-kb tandem duplication, containing low-affinity IgG receptor genes and heat shock protein genes. The sequences of the two copies of this duplication are approximately 97% identical, which has led to the collapse of the two copies into one in the June 2002 NCBI Build 30 of the Human Genome. This duplication may be involved in genomic instability, leading to gene deletion, and so presents an intriguing candidate locus for schizophrenia susceptibility.     

Fine mapping of a sedative-hypnotic drug withdrawal locus on mouse chromosome 11

We have established that there is a considerable amount of common genetic influence on physiological dependence and associated withdrawal from sedative-hypnotic drugs including alcohol, benzodiazepines, barbiturates and inhalants. We previously mapped two loci responsible for 12 and 9% of the genetic variance in acute alcohol and pentobarbital withdrawal convulsion liability in mice, respectively, to an approximately 28-cM interval of proximal chromosome 11. Here, we narrow the position of these two loci to a 3-cM interval (8.8 Mb, containing 34 known and predicted genes) using haplotype analysis. These include genes encoding four subunits of the GABA(A) receptor, which is implicated as a pivotal component in sedative-hypnotic dependence and withdrawal. We report that the DBA/2J mouse strain, which exhibits severe withdrawal from sedative-hypnotic drugs, encodes a unique GABA(A) receptor gamma2 subunit variant compared with other standard inbred strains including the genetically similar DBA/1J strain. We also demonstrate that withdrawal from zolpidem, a benzodiazepine receptor agonist selective for alpha1 subunit containing GABA(A) receptors, is influenced by a chromosome 11 locus, suggesting that the same locus (gene) influences risk of alcohol, benzodiazepine and barbiturate withdrawal. Our results, together with recent knockout studies, point to the GABA(A) receptor gamma2 subunit gene (Gabrg2) as a promising candidate gene to underlie phenotypic differences in sedative-hypnotic physiological dependence and associated withdrawal episodes.     

Premature myocardial infarction novel susceptibility locus on chromosome 1P34-36 identified by genomewide linkage analysis

The most frequent causes of death and disability in the Western world are atherosclerotic coronary artery disease (CAD) and acute myocardial infarction (MI). This common disease is thought to have a polygenic basis with a complex interaction with environmental factors. Here, we report results of a genomewide search for susceptibility genes for MI in a well-characterized U.S. cohort consisting of 1,613 individuals in 428 multiplex families with familial premature CAD and MI: 712 with MI, 974 with CAD, and average age of onset of 44.4+/-9.7 years. Genotyping was performed at the National Heart, Lung, and Blood Institute Mammalian Genotyping Facility through use of 408 markers that span the entire human genome every 10 cM. Linkage analysis was performed with the modified Haseman-Elston regression model through use of the SIBPAL program. Three genomewide scans were conducted: single-point, multipoint, and multipoint performed on of white pedigrees only (92% of the cohort). One novel significant susceptibility locus was detected for MI on chromosomal region 1p34-36, with a multipoint allele-sharing P value of <10(-12) (LOD=11.68). Validation by use of a permutation test yielded a pointwise empirical P value of.00011 at this locus, which corresponds to a genomewide significance of P<.05. For the less restrictive phenotype of CAD, no genetic locus was detected, suggesting that CAD and MI may not share all susceptibility genes. The present study thus identifies a novel genetic-susceptibility locus for MI and provides a framework for the ultimate cloning of a gene for the complex disease MI.     

A new strain congenic for the Mtv-7/Mls-1 locus of mouse chromosome 1

Correspondence to: B. A. Taylor.     

Nonobese diabetic mouse congenic analysis reveals chromosome 11 locus contributing to diabetes susceptibility, macrophage STAT5 dysfunction, and granulocyte-macrophage colony-stimulating factor overproduction

Unstimulated monocytes of at-risk/type 1 diabetic humans and macrophages of the NOD mouse have markedly elevated autocrine GM-CSF production and persistent STAT5 phosphorylation. We analyzed the relationship between GM-CSF production and persistent STAT5 phosphorylation in NOD macrophages using reciprocal congenic mouse strains containing either diabetes-susceptible NOD (B6.NODC11), or diabetes-resistant C57L (NOD.LC11) loci on chromosome 11. These intervals contain the gene for GM-CSF (Csf2; 53.8 Mb) and those for STAT3, STAT5A, and STAT5B (Stat3, Stat5a, and Stat5b; 100.4-100.6 Mb). High GM-CSF production and persistent STAT5 phosphorylation in unactivated NOD macrophages can be linked to a region (44.9-55.7 Mb) containing the Csf2 gene, but not the Stat3/5a/5b genes. This locus, provisionally called Idd4.3, is upstream of the previously described Idd4.1 and Idd4.2 loci. Idd4.3 encodes an abundance of cytokine genes that use STAT5 in their macrophage activation signaling and contributes approximately 50% of the NOD.LC11 resistance to diabetes.     

Ahl3, a third locus on mouse chromosome 17 affecting age-related hearing loss

Genetic variation in humans probably plays a role in determining the range of individual susceptibility to age-related hearing loss (AHL), but no contributing loci have been identified because of the difficulties of dissecting complex traits in humans. This paper reports mapping of an AHL locus using a panel of consomic mice between C57BL/6J (B6) and MSM strains, which covered more than a half of chromosome sets. B6 strain exhibited AHL beginning at 10 months of age whereas MSM strain, derived from Japanese wild mice, had normal hearing throughout life. Individuals in the panel were examined with auditory brainstem response (ABR) at various months of age, revealing that one particular strain (B6-Chr17(MSM)) substituting the chromosome 17 with the MSM-derived one showed a prominent resistance, having still good hearing at 18 months of age. Subsequent mapping using 89 individuals in the cross between B6-Chr17(MSM) and B6 was performed, which showed a significant association of ABR thresholds with loci in the vicinity of D17Mit119. These results show a novel AHL-resistant locus, designated as Ahl3, on the chromosome 17.     

Mapping of the Sod-2 locus into the t complex on mouse chromosome 17

A human DNA probe specific for the superoxide dismutase gene was used to identify the corresponding mouse gene. Under the chosen hybridizing conditions, the probe detected DNA fragments most likely carrying the mouse Sod-2 gene. Mapping studies revealed that the Sod-2 gene resides in the proximal inversion of the t complex on mouse chromosome 17. All complete t haplotypes tested showed restriction fragment length polymorphism which is distinct from that found in all wild-type chromosomes tested. The Sod-2 locus maps in the same region as some of the loci that influence segregation of t chromosomes in male gametes. The possibility that the Sod-2 locus is related to some of the t-complex distorter or responder loci is discussed. The data indicate that the human homolog of the mouse t complex has split into two regions, the distal region remaining on the p arm of human chromosome 6, while the proximal region has been transposed to the telomeric region of this chromosome's q arm.     

Location ofMls locus on mouse chromosome 1

Linkage between theMls locus and the chromosome 1 markersDip-1 andald was detected using two sets of recombinant inbred strains. Linkage betweenMls andDip-1 was confirmed in the fifth and sixth backcross generations of an incipient congenic strain. The AKXL data indicate that the gene order isDip-1-ald-Mls. The recombination frequency betweenald andMls is estimated to be 0.07 ±0.05, based on the AKXL data. The recombination frequency betweenDip-1 andMls is estimated to be 0.18 ±0.04, based on all the available data.     

Genetic mapping of the lurcher locus on mouse chromosome 6 using an intersubspecific backcross.

The lurcher (Lc) mutant mouse strain exhibits postnatal degeneration of cerebellar Purkinje cells. We have typed progeny from an intersubspecific, phenotypic backcross at seven loci to develop a genetic linkage map which spans approximately 35 cM surrounding and including the Lc locus on mouse chromosome 6. [(Mus musculus castaneus x B6CBA-Aw-J/A-Lc)F1 x B6CBA-Aw-J/A]N2 progeny were scored visually for the lurcher phenotype and molecularly, through restriction fragment length polymorphism analysis, for six cloned markers. Two candidate genes, Npy and Pcp-1, which map to mouse chromosome 6 and which are expressed in the cerebellum, are demonstrated to be distinct from Lc. Three genes are shown to be closely linked to the Lc locus, and the map order cen-Cpa-Npy-Cbl-1-Lc-Igk, Fabpl-Pcp-1 is determined. The molecular genetic linkage map presented here represents progress toward isolating a clone of the Lc gene.     

Genetic mapping of thet-complex region on mouse chromosome 17 including theHybrid sterility-1 gene

t-haplotypes occupy a region on chromosome (Chr) 17 which slightly overlaps the ends of theT-H-2 interval. The wild-type form of this 14 centi-Morgan (cM) region was mapped in a multilocus backcross (C57BL/10-T×C3H)F₁×C57BL/10 using 15 DNA probes on Southern blots of the DNA extracted from 53 animals which were recombinants in theT-H-2 interval. Each recombinant was also progenytested to ascertain itsHybrid sterility-1 (Hst-1) genotype by crossing to PWB/Ph, aMus musculus-derived inbred strain. The limit of resolution of the cross was 0.27 cM. The map distances have been determined for the DNA loci in theT-H-2 interval and theHst-1 gene was mapped in close vicinity to theD17Rp17 locus.