High-Resolution Linkage Map of Mouse Chromosome 13 in the Vicinity of the Host Resistance LocusLgn1

Natural resistance of inbred mouse strains to infection withLegionella pneumophilais controlled by the expression of a single dominant gene on chromosome 13, designatedLgn1.The genetic difference atLgn1is phenotypically expressed as the presence or absence of intracellular replication ofL. pneumophilain host macrophages. In our effort to identify theLgn1gene by positional cloning, we have generated a high-resolution linkage map of theLgn1chromosomal region. For this, we have carried out extensive segregation analysis in a total of 1270 (A/J × C57BL/6J) × A/J informative backcross mice segregating the resistance allele of C57BL/6J and the susceptibility allele of A/J. Additional segregation analyses were carried out in three preexisting panels of C57BL/6J ×Mus spretusinterspecific backcross mice. A total of 39 DNA markers were mapped within an interval of approximately 30 cM overlapping theLgn1region. Combined pedigree analyses for the 5.4-cM segment overlappingLgn1indicated the locus order and the interlocus distances (in cM):D13Mit128–(1.4)–D13Mit194–(0.1)–D13Mit147–(0.9)–D13Mit36–(0.9)–D13Mit146–(0.2)–Lgn1/D13Mit37–(1.0)–D13Mit70.Additional genetic linkage studies of markers not informative in the A/J × C57BL/6J cross positionedD13Mit30, -72, -195,and-203, D13Gor4, D13Hun35,andMtap5in the immediate vicinity of theLgn1locus. The marker density and resolution of this genetic linkage map should allow the construction of a physical map of the region and the isolation of YAC clones overlapping the gene.     

A High-Resolution Map in the Chromosomal Region Surrounding theLpsLocus

TheLpslocus 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 mutantLpsallele (Lps^d) that renders it hyporesponsive to LPS and naturally tolerant of its lethal effects. To identify theLpsgene 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× C57BL/6J)F1 × C57BL/6J and two novel panels of 597 (DBA/2J × C3H/HeJ)F1 × C3H/HeJ and 748 (C57BL/6J × C3H/HeJ)F1 × C3H/HeJ segregating atLps.A total of 50 DNA markers have been mapped in a 11.8-cM span overlapping theLpslocus. This positions theLpslocus within a 1.1-cM interval, flanked proximally by a large cluster of markers, including three known genes (Cd30l, Hxb,andAmbp), and distally by two microsatellite markers (D4Mit7/D4Mit178). The localization of theLpslocus is several centimorgans proximal to that previously assigned.     

High-resolution linkage map in the vicinity of the Lp locus

Looptail (Lp) is a mutation that profoundly affects neurulation in mouse and is characterized by craniorachischisis, an open neural tube extending from the midbrain to the tail in embryos homozygous for the mutation. Lp maps to the distal portion of mouse chromosome 1, and as part of a positional cloning approach, we have generated a high-resolution linkage map of the Lp chromosomal region. For this, we have carried out extensive segregation analysis in a total of 706 backcross mice informative for Lp and derived from two crosses, (Lp/ + X SJL/J)F1 X SJL/J and (Lp/ + X SWR/J)F1 X SWR/J. In addition, 269 mice from a (Mus spretus X C57BL/6J)F1 X C57BL/6J interspecific backcross were also used to order marker loci and calculate intergene distances for this region. With these mice, a total of 28 DNA markers corresponding to either cloned genes or anonymous markers of the SSLP or SSCP-types were mapped within a 5-cM interval overlapping the Lp region, with the following locus order and interlocus distances (in cM): centromere-D1Mit110 / Atp1β1 / Cd3ζ / Cd3η / D1Mit145 — D1Hun14 / D1Mit15 — D1Mit111 / D1Mit112 — D1Mit114 — D1Mit148 / D1Mit205/ D1Mit36 / D1Mit146 / D1Mit147 / D1Mit270 / D1Hun13 — Fcgr2 — Mpp — Apoa2/Fcer1γ - Lp - D1Mit149 / Spna1/Fcer1α-Eph1-Hlx1/D1Mit62. These studies have allowed the delineation of a maximum genetic interval for Lp of 0.5 cM, a size amenable to physical mapping techniques.     

Assignment of a locus for mouse lung tumor susceptibility to proximal Chromosome 19

Previous studies have hypothesized that at least three genetic loci contribute to differences in pulmonary adenoma susceptibility between mouse strains A/J and C57BL/6J. One gene that may confer susceptibility to lung tumorigenesis is the Kras protooncogene. To identify other relevant loci involved in this polygenic trait, we determined tumor multiplicity in 56 randomly chosen N-ethyl-N-nitrosourea-treated (A/J×C57BL/6J) N1×C57BL/6 backcross (AB6N2) progeny and correlated it with genotypes at 77 microsatellite markers spanning the genome. A correlation of lung tumor multiplicity phenotypes with genotypes of microsatellite markers on distal Chromosome (Chr) 6 in the Kras region (Pas1) was confirmed, and a new region on Chr 19 (designated Pas3) was identified that also contributes to susceptibility. Linkage analysis on Chr 19 with 270 AB6N2 mice localized the region flanked by D19Mit42 and D19Mit19 that is most closely associated with lung tumor susceptibility. The Pas3 locus may be an enhancer of the susceptibility locus on Chr 6.     

Quantitative trait loci affecting growth in high growth (hg) mice

A genome-wide scan was performed in order to identify Quantitative Trait Loci (QTL) associated with growth in a population segregating high growth (hg), a partially recessive mutation that enhances growth rate and body size in the mouse. A sample of 262 hg/hg mice was selected from a C57BL/6J-hg/hg× CAST/EiJ F₂ cross and typed with 79 SSLP markers distributed across the genome. Eight significant loci were identified through interval mapping. Loci on Chromosomes (Chrs) 2 and 8 affected the growth rate of F₂ mice. Loci on Chr 2 and 11 affected growth rate and carcass lean mass (protein and ash). A locus on Chr 9 modified femur length and another one in Chr 17 affected both carcass lean mass and femur length, but none of these had significant effects on growth rate. Loci on Chrs 5 and 9 modified carcass fat content. Additive effects were positive for C57BL/6J alleles, except for the two loci affecting carcass fatness. Typing of selected markers in 274 +/+ F₂ mice revealed significant interactions between hg and other growth QTL, which were detected as changes in gene action (additive or dominant) and in allele substitution effects. Knowledge about interactions between loci, especially when major genes are involved, will help in the identification of positional candidate genes and in the understanding of the complex genetic regulation of growth rate and body size in mammals. Received: 29 June 2000 / Accepted: 22 November 2000     

Genetic analysis of alcohol intake in recombinant inbred and congenic strains derived from A/J and C57BL/6J progenitors

The objective of the present study was to map quantitative trait loci (QTL) for alcohol intake using A × B/B × A recombinant inbred (RI) and AcB/BcA recombinant congenic (RC) strains of mice that were independently derived from the A/J and C57BL/6J progenitors. Mice were screened for levels of alcohol consumption with four days of forced exposure to alcohol, followed by three weeks of free choice between water and a 10% alcohol solution. Alcohol consumption data previously collected for 27 A × B/B × A RI strains were reanalyzed using a larger marker set and composite interval mapping. The reanalysis found markers on Chromosome 2 (D2Mit74, 107 cM) (males and females) and on Chromosome 11 (Pmv22, 8 cM) (females only) that exceeded the threshold for significant loci, and found suggestive loci (in males) on Chromosomes 10 (D10 Mit126, 21 cM), 12 (D12Mit37, 1 cM), 15 (Pdgfb, 46.8 cM), and 16 (D16Mit125, 29 cM). An additional suggestive locus was identified in female RI mice on Chromosome 11 (D11Mit120, 47.5 cM). Composite interval mapping (CIM) analysis indicated that there was a significant association between loci at Pdgfb and D2Mit74 in both males and females. Analysis of the AcB/BcA RC strains identified 11 QTL on Chromosomes 2, 3, 5,6, 7, 8, 9, 10, 12, 13, and 15. QTL on Chromosomes 7, 10, 12, and 15 were identified in both the A × B/B × A RI and AcB/BcA RC strains of mice. Additional QTLs identified on Chromosomes 2, 3, 7, 11, and 15 overlap with those previously identified in the literature using strains of mice with a C57BL/6J progenitor.     

Mapping of the Gracile Axonal Dystrophy (gad) Gene to a Region between D5Mit197 and D5Mit113 on Proximal Mouse Chromosome 5

The gracile axonal dystrophy (gad) mouse, which shows hereditary sensory ataxia and motor paresis, has been morphologically characterized by the dying back type of axonal degeneration in the nerve terminals of dorsal root ganglion cells and motor neurons. In the present study, using an intraspecific backcross between gad and C57BL/6J mice, the gracile axonal dystrophy (gad) gene was mapped to a region between D5Mit197 and D5Mit113. Estimated distances between gad and D5Mit197 and between gad and D5Mit113 are 0.4 ± 0.3 and 5.0 ± 1.0 cM, respectively. The gene order was defined: centromere- D5Mit81-D5Mit233-D5Mit184/D5Mit254-D5Mit256-D5Mit197-gad-D5Mit113-D5Mit7 . The mouse map location of the gad locus appears to be in a region homologous to human 4p15-p16. Our present data suggest that the nearest flanking marker D5Mit197 provides a useful anchor for the isolation of the gad gene in a yeast artificial chromosome contig.     

TheCmv1Host Resistance Locus Is Closely Linked to theLy49Multigene Family within the Natural Killer Cell Gene Complex on Mouse Chromosome 6

Natural killer (NK) cells play important roles in controlling tumor cells and against a range of infectious organisms. Recent studies of mouse NK cell surface receptors, which may be involved in the specificity of NK cells, have shown that many of these molecules are encoded by theLy49andLy55(Nkrp1) multigene families that map to distal mouse chromosome 6. Also mapping to this NK cell gene complex (NKC) is the resistance locus,Cmv1,which is involved in genetically determined resistance to murine cytomegalovirus (MCMV). The aim of this study was to localizeCmv1more precisely in relation to other NKC loci by generating a high-resolution genetic map of the region. We have analyzed 1250 backcross mice comprising panels of 700 (BALB/c × C57BL/6J)F₁× BALB/c and 550 (A/J × C57BL/6J)F₁× A/J progeny. A total of 25 polymorphic genes or microsatellite markers were analyzed over a region of 10 map units fromD6Mit134toD6Mit59.TheCmv1phenotypes of mice recombinant in this interval were tested by infection with MCMV. The results obtained indicate that the functionally important NKC region is a tightly linked cluster of loci spanning at least 0.4 map units. Furthermore,Cmv1maps distal to, but very closely linked to, theLy49multigene family (<0.2 map units), suggesting that MCMV resistance may be conferred by MHC class I-specific NK cell receptors.     

An interstitial telomere array proximal to the distal telomere of mouse chromosome 13

Lambda clones of mouse DNA from BALB/c and C57BL/10, each containing an array of telomere hexamers, were localized by FISH to a region close to the telomere of Chr 13. Amplification of mouse genomic DNA with primers flanking SSRs within the cloned DNA showed several alleles, which were used to type eight sets of RI strains. The two lambda clones contained allelic versions of the interstitial telomere array, Tel-rs4, which is 495 bp in C57BL/10 and which includes a variety of sequence changes from the consensus telomere hexamer. Comparison of the segregation of the amplification products of the SSRs with the segregation of other loci in an interspecies backcross (C57BL/6JEi × SPRET/Ei) F₁× SPRET/Ei shows recombination suppression, possibly associated with ribosomal DNA sequences present on distal Chr 13 in Mus spretus, when compared with recombination in an interstrain backcross, (C57BL/6J × DBA/J) F₁× C57BL/6J, and with the MIT F₂ intercross. Analysis of recombination in females using a second interstrain backcross, (ICR/Ha × C57BL/6Ha) F₁× C57BL/6Ha, also indicates recombination suppression when compared with recombination in males of the same strains, using backcross C57BL/6Ha × (ICR/Ha × C57BL/6Ha) F₁. Thus, more than one cause may contribute to recombination suppression in this region. The combined order of the loci typed was D13Mit37–D13Mit30–D13Mit148–(D13Rp1, 2, 3, 4, Tel-rs4)–D13Mit53–D13Mit196–D13Mit77–(D13Mit78, 35). Data from crosses where apparently normal frequencies of recombination occur suggest that the telomere array is about 6 map units proximal to the most distal loci on Chr 13. This distance is consistent with evidence from markers identified in two YAC clones obtained from the region. Received: 24 September 1996/Accepted: 20 January 1997     

Genetic basis for unresponsiveness to lipopolysaccharide in C57BL/10Cr mice

The unresponsiveness to LPS detected in C57BL/10Cr mice is inherited as a recessive trait and is determined by an autosomal gene linked to theMup-1 locus on chromosome 4. Since no complementation for LPS responsiveness was observed in F₁ hybrid mice between C3H/HeJ and C57BL/10Cr, we conclude that C57BL/10Cr mice carry a defective allele at the sameLps locus, previously identified by the mutation detected in the C3H/HeJ strain.     

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.     

The immunoglobulin <Emphasis Type="Italic">IGHD</Emphasis> gene locus in C57BL/6 mice

Four immunoglobulin heavy chain diversity (IGHD) gene subgroups (DFL16, DSP2, DQ52, and DST4) have been identified previously in BALB/c mice. Although the locations of most IGHD genes have been established based on restriction map and Southern blot analysis, a complete mouse IGHD gene locus map at the sequence level is still not available. In addition, a previous restriction fragment length polymorphism study suggested that significant difference in the IGHD gene locus exists between C57BL/6 and BALB/c mice. The author has now analyzed the C57BL/6 mouse genomic data and established a complete map of the IGHD gene locus. All four IGHD subgroups previously identified in BALB/c mice were found to be present in C57BL/6 mice. However, unlike the BALB/c mice, which have at least 13 IGHD genes, the C57BL/6 genome contains only ten IGHD genes, which include one DFL16, six DSP2, one DQ52, and two DST4 genes. There are also differences in the coding regions of the DST4 and DQ52 genes between the two mouse strains.     

Strain distribution pattern in AXB and BXA recombinant inbred strains for loci on murine Chromosomes 10, 13, 17, and 18

Strain distribution patterns (SDPs) of selected loci previously mapped to murine Chromosomes (Chrs) 10, 13, 17, and 18 are reported for the AXB, BXA recombinant inbred (RI) strain set derived from the progenitor strains A/J (A) and C57BL/6J (B). The loci included the simple sequence length polymorphisms (D10Nds1, D10Mit2, D10Mit10, D10Mit14, D13Mit3, D13Nds1, D13Mit10, D13Mit13, D13Mit7, D13Mit11, D17Mit18, D17Mit10, D17Mit20, D17Mit3, D17Mit2, D18Mit17, D18Mit9, and D18Mit4), the restriction fragment length polymorphisms Pdea and Csfmr, and the biochemical marker AS-1. These loci were chosen because they map to genomic regions that had few or no genetic markers in the AXB, BXA RI set. Several of these loci also were typed in backcross progeny of matings of the (AXB)F₁ to strain A or B. The strain distribution patterns for chromosomes 10, 13, 17, and 18 are reported, and the gene order and map distances determined from the backcross data. The addition of these markers to the AXB, BXA RI strain set increases the genomic region over which linkage for new markers can be detected.     

Serological and complementation studies in four C57BL/6H-2 mutants

C57BL/6 (H-2 ^b ) mice, and four mutants (B6.C-H-2 ^ba , B6-H-2 ^bg1 , B6-H-2 ^bg2 , B6-H-2 ^bh ) derived from this strain after separate mutations had occurred at the same locus within theH-2 complex, were analyzed to determine whether the mutations had led to anyH-2 (or Ia) difference which could be detected serologically. The strains were typed directly with antisera specific for H-2K and H-2D public and private specificities and for the Ia specificities; quantitative absorption studies were also performed for the relevant H-2K^b, H-2D^d and Ia^b specificities. In no case was any quantitative or qualitative difference detected serologically between any of the strains. In addition, by using a variety of techniques to produce and assay for antibody, we failed to produce any antisera between the parental strains and the four mutants. TheH-2 mutations therefore appear to give rise to a type of antigenic specificity which is recognized byT cells and which generateT, but notB cell responses; nor are they recognized by H-2 or Ia alloantisera. The location of the mutating locus within theH-2 complex was shown by the complementation method to be within theK orIA region and not in theIB region, since crosses of the mutant strains with B10.A(4R) or D2.GD failed to complement for a subsequent C57BL/6 skin graft.     

A novel mouse Chromosome 2 congenic strain with obesity phenotypes

Linkage studies have identified many chromosomal regions containing obesity genes in mice. However, only a few of these quantitative trait loci (QTLs) have been used to guide the production of congenic mouse strains that retain obesity phenotypes. We seek to identify chromosomal regions containing obesity genes in the BSB model of spontaneous obesity because the BSB model is a multigenic obesity model. Previous studies identified QTLs on Chromosomes (Chrs) 2, 6, 7,12, and 15. BSB mice are made by backcross of lean C57BL/6J × Mus spretus. F₁s were backcrossed to C57BL/6J mice to produce BSB progeny. We have constructed a new BSB cross and produced congenic mice with obesity phenotypes by marker-directed selection called B6.S–D2Mit194–D2Mit311. We found a highly significant QTL for percentage body lipid on Chr 2 just proximal to the Agouti locus. Chr 2 congenics were constructed to determine whether the main effects would be detectable. We observed highly significant linkage of the Chr 2 congenic containing Agouti and containing markers distal to D2Mit311 and proximal to D2Mit194. Thus, this congenic contains approximately 14.6 cM or 30 Mb (about 1.1% of the spretus mouse genome) and several hundred genes. The obesity phenotype of the QTL is retained in the congenic. The congenic can now be used to model the genetic and physiological basis for a relatively simple, perhaps monogenic, obesity.     

Susceptibility to re-infection in C57BL/6 mice with recombinant strains of Toxoplasma gondii

This work reports results of re-infection of BALB/c and C57BL/6 mice with different recombinant strains of Toxoplasma gondii. Mice were prime-infected with the non-virulent D8 strain and challenged with virulent strains. PCR–RFLP of cS10-A6 genetic marker of T. gondii demonstrated that BALB/c mice were re-infected with the EGS strain, while C57BL/6 mice were re-infected with the EGS and CH3 strains. Levels of IFN-γ and IL-10 after D8 prime-infection were lower in C57BL/6 than in BALB/c mice. Brain inflammation after D8 prime-infection was more intense in C57BL/6 than in BALB/c mice. It was shown that re-infection depends on mice lineage and genotype of the strain used in the challenge.     

Overlapping mouse subcongenic strains successfully separate two linked body fat QTL on distal MMU 2

Background

Mouse chromosome 2 is linked to growth and body fat phenotypes in many mouse crosses. With the goal to identify the underlying genes regulating growth and body fat on mouse chromosome 2, we developed five overlapping subcongenic strains that contained CAST/EiJ donor regions in a C57BL/6J^hg/hg background (hg is a spontaneous deletion of 500 Kb on mouse chromosome 10). To fine map QTL on distal mouse chromosome 2 a total of 1,712 F2 mice from the five subcongenic strains, plus 278 F2 mice from the HG2D founder congenic strain were phenotyped and analyzed. Interval mapping (IM) and composite IM (CIM) were performed on body weight and body fat traits on a combination of SNP and microsatellite markers, which generated a high-density genotyping panel.

Results

Phenotypic analysis and interval mapping of total fat mass identified two QTL on distal mouse chromosome 2. One QTL between 150 and 161 Mb, Fatq2a, and the second between 173.3 and 175.6 Mb, Fatq2b. The two QTL reside in different congenic strains with significant total fat differences between homozygous cast/cast and b6/b6 littermates. Both of these QTL were previously identified only as a single QTL affecting body fat, Fatq2. Furthermore, through a novel approach referred here as replicated CIM, Fatq2b was mapped to the Gnas imprinted locus.

Conclusions

The integration of subcongenic strains, high-density genotyping, and CIM succesfully partitioned two previously linked QTL 20 Mb apart, and the strongest QTL, Fatq2b, was fine mapped to a ~2.3 Mb region interval encompassing the Gnas imprinted locus.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-014-1191-8) contains supplementary material, which is available to authorized users.     

Localization to chromosome 10 of a locus influencing morphine analgesia in crosses derived from C57BL/ and DBA/2 strains

A quantitative trait locus (QTL) was detected and mapped to proximal chromosome 10 near the markers Mpmv5 and D10Mit51 with a strong influence on morphine-induced analgesia in the BXD recombinant inbred (Rl) strains and in an F₂ cross (B6D2F2) between the BXD progenitor strains, C57BL/6 and DBA/2. A LOD score of 3.9 (p <. 00002) was seen for analgesia using the hot plate assay. Naloxone Bmax was also associated with this chromosome region in BXD RI mice. The mu opioid receptor gene (Oprm) has recently been mapped to this same chromosome region. The observation that several morphine-related traits and naloxone Bmax appear to be partly determined by this presumed single locus is consistent with the hypothesis that the mu opioid receptor gene, or one of its modulators, is the basis for the QTL.     

Unravelling the complex genetics of cleft lip in the mouse model

Nonsyndromic cleft lip in ``A' strain mice and humans is genetically complex and is distinct from isolated cleft palate. Cleft lip embryos recovered in 2.4% of 1485 first backcross (BC₁) segregants from a cross of A/WySnJ (24% cleft lip) and C57BL/6J (no cleft lip) in A/WySnJ mothers, and in testcrosses of 10 recombinant inbred (RI) strains (AXB/Pgn or BXA/Pgn), were used for gene mapping and for inference of genetic architecture. The A/WySnJ maternal genotype increased cleft lip risk in reciprocal crosses; the relevant genetic difference between AXB-6/Pgn (8%) and A/WySnJ (24%) is entirely maternal. A combination of new mapping panels (325 meioses), new markers, and a recombinant cleft lip embryo redefined the location of a recessive factor essential to cleft lip risk, clf1, and candidate genes Itgb3 and Crhr, to between D11Mit146/360 and D11Mit166/147. A screen of 54 YACs for 46 genes and SSLP loci located Wnt15, Wnt3, Crhr, Mtapt, Itgb3, Dlx3, and Dlx7 within the clf1 candidate region. The clf2 locus was newly mapped to Chromosome (Chr) 13 by a genome screen of BC₁ segregants, and further defined to a 4-cM region between D13Mit13/54 and D13Mit231 by strain distribution patterns of cleft lip liability and markers in testcrossed RI strains. Specific combinations of marker genotypes associated with cleft lip risk indicated that high risk in A/WySnJ mice is caused by epistatic interaction between clf1 and clf2 in the context of a genetic maternal effect. Human homologs of clf1 and clf2 are expected to be on 17q and 5q/9q. Received: 17 May 2000 / Accepted: 30 November 2000     

Submucosal gland distribution in the mouse has a genetic determination localized on Chromosome 9

Submucosal glands (SMG) are important secretory glands that are present in the major airways and bronchioles of humans. In mice the structure, cellular composition, and density of SMG are similar to those seen in humans, but the glands are present only in the trachea. Characterization of SMG is important as they secrete bacteriocidal products such as lactoferrin, lysozyme, and defensins believed to be of importance in the innate defense system. Serous cells in SMG are the primary site of cystic fibrosis transmembrane conductance regulator (CFTR) gene expression and the initial site of histological abnormality in cystic fibrosis (CF) individuals. In this study, we examined four inbred strains of mice (A/J, C57BL/6N, FVB/N, and BALB/CAnN) and revealed that the extent to which glands descend in the mouse trachea varied between inbred strains. In particular, the A/J and C57BL/6N strains exhibited few SMG extending further than the first or second intercartilaginous space (mean depth of 0.4 ± 0.11 and 1.5 ± 0.32 tracheal rings respectively) in the trachea, whereas the FVB/N and BALB/CAnN strains had SMG extending beyond the fourth space (mean depths of 3.3 ± 0.46 and 5.6 ± 0.45 rings respectively). We have previously shown that in congenic C57Bl/6N Cftr mutant mice (CF mice), the SMG are distributed more distally than in wild-type C57Bl/6N but are indistinguishable from BALB/CAnN wild-type or CF mice. The implication that SMG distribution is influenced by Cftr gene expression (or a gene closely linked to Cftr) led us to investigate the genetic difference between C57Bl6/N and BALB/CAnN mice. In recombinant inbred strain (RIS) analysis (with BALB/CJ and C57BL/6J progenitors), two loci were identified as being linked to the SMG phenotype (peak likelihood statistic levels of 8.8 and 9.9 on Chrs 9 and 10 respectively, indicating suggestive linkage). A subsequent segregation analysis of an F₂ intercross between the C57BL/6N and BALB/CAnN mice indicated that there were at least two major genetic factors responsible for SMG distribution. The loci indicated in the RI analysis were included in a targeted genome scan involving 235 F₂ intercross animals (C57BL/6N and BALB/CAnN strain intercross). The genome scan confirmed the locus on Chr 9 (between genetic markers D9Mit11 and D9Mit182), designated Smgd1, as significantly linked to the SMG distribution phenotype (peak LOD score 5.8) within a 95% confidence interval of 12 cM. Received: 26 June 2000 / Accepted: 18 September 2000