A molecular genetic linkage map of mouse chromosome 7

The homology between mouse chromosome 7 and human chromosomes 11, 15, and 19 was examined using interspecific backcross animals derived from mating C3H/HeJ-gld/gld and Mus spretus mice. In an earlier study, we reported on the linkage relationships of 16 loci on mouse chromosome 7 and the homologous relationship between this chromosome and the myotonic dystrophy gene region on human chromosome 19. Segregation analyses were used to extend the gene linkage relationships on mouse chromosome 7 by an additional 21 loci. Seven of these genes (Cyp2a, D19F11S1h, Myod-1, Otf-2, Rnu1p70, Rnu2pa, and Xrcc-1) were previously unmapped in the mouse. Several potential mouse chromosome 7 genes (Mel, Hkr-1, Icam-1, Pvs) did not segregate with chromosome 7 markers, and provisional chromosomal assignments were made. This study establishes a detailed molecular genetic linkage map of mouse chromosome 7 that will be useful as a framework for determining linkage relationships of additional molecular markers and for identifying homologous disease genes in mice and humans.     

Physical and genetic mapping of a novel chromosome 19 ERCC1 marker showing close linkage with myotonic dystrophy.

Recent genetic linkage analyses have mapped the myotonic dystrophy locus to the region of 19q13.2-13.3 lying distal to the gene for creatine kinase subunit M (CKM). The human excision repair gene ERCC1 has also been mapped to this region of chromosome 19. A novel polymorphic DNA marker, pEO.8, has been isolated from a chromosome 19 ERCC1-containing cosmid that maps to a 300-kb NotI fragment encompassing both CKM and ERCC1. Genetic linkage analysis reveals close linkage between pEO.8 and myotonic dystrophy (DM) (zmax = 19.3, theta max = 0.01). Analysis of two key recombinant events suggests a mapping of DM distal to pEO.8 and CKM.     

The syntenic relationship of proximal mouse chromosome 7 and the myotonic dystrophy gene region on human chromosome 19q

The syntenic relationship of the myotonic dystrophy (DM) gene region on human chromosome 19q and proximal mouse chromosome 7 was examined using an interspecific backcross between C3H/HeJ-gld/gld mice and Mus spretus. Segregation analyses were used to order homologs of nine human loci linked with the DM gene. Their order from the centromere was Prkcg, [Apoe, Atpa-2, Ckmm, D19S19h, Ercc-2], Cyp2b, Mag, Lhb. Two other murine loci, D7Rp2 and Ngfg, were also positioned within this interval. Homologs for five human chromosome 11 and 15 loci (Calc, Fes, Hras-1, Igflr, Tyr) were localized within an 18-cM span telomeric to Lhb. Comparison of the gene orders indicates an inversion extending from Prkcg through the interval between Mag and Lhb. This study establishes a detailed map of proximal mouse chromosome 7 that will be useful in identifying and determining whether new human chromosome 19 probes are linked to the DM region.     

cDNA and genomic cloning of HRC, a human sarcoplasmic reticulum protein, and localization of the gene to human chromosome 19 and mouse chromosome 7

Histidine-rich calcium binding protein (HRC) is a luminal sarcoplasmic reticulum (SR) protein of 165 kDa identified by virtue of its ability to bind 125I-labeled low-density lipoprotein with high affinity after sodium dodecyl sulfate-polyacrylamide gel electrophoresis (Hofmann et al., J. Biol. Chem. 264: 8260-8270, 1989). Its role in SR function is unknown. In this report, the gene encoding human HRC was localized to human chromosome 19 and mouse chromosome 7 by hybridization of a human HRC cDNA fragment to a panel of somatic cell hybrids. Known synteny between a portion of human chromosome 19 and a portion of mouse chromosome 7 and in situ hybridization of a biotin-labeled HRC probe to human chromosomes suggest a localization to a region corresponding to 19q13.3. The locus for myotonic dystrophy resides in the region 19q13.2-13.3. Therefore, we considered HRC, a muscle-specific gene, to possibly represent a "candidate gene" for myotonic muscular dystrophy. As a first step toward localizing HRC in relation to the myotonic dystrophy locus, we report the cloning of the human HRC gene, its intron-exon organization, and characterization of several informative polymorphisms to be used in future linkage studies in families with myotonic dystrophy. Of particular interest is an Alu-associated poly-d(GA) sequence located in an intron in the middle of the gene, and two stretches of acidic amino acids in the coding region of exon 1 that vary in length among different individuals.     

A reordering of human chromosome 19 long-arm DNA markers and identification of markers flanking the myotonic dystrophy locus

The gene for myotonic dystrophy (DM), the most common form of adult muscular dystrophy, has previously been mapped to the proximal long arm of chromosome 19. We have conducted linkage analysis on 53 DM families (comprising 421 individuals) using seven DM-linked DNA markers. This analysis, combined with our somatic cell hybrid mapping panel data, places the DM locus more distal on the chromosome 19 long arm than previously thought. Further, we have been able to unequivocally identify DNA markers that flank the disease locus. The definition of a 10-cM region of chromosome 19 that contains the DM locus should prove useful in both the search for the causative gene and the molecular diagnosis of DM.     

High-resolution physical mapping of four microsatellite repeat markers near the RYR1 locus on chromosome 19q13.1 and apparent exclusion of the MHS locus from this region in two malignant hyperthermia susceptible families.

Malignant hyperthermia susceptibility (MHS) is a potentially lethal, hereditary disorder of skeletal muscle that may be triggered by inhalation anesthetics and depolarizing muscle relaxants. Defects in the gene encoding the ryanodine receptor (RYR1) localized on human chromosome 19q13.1 have been proposed to be responsible for MHS. Using a chromosome 19-specific human/hamster somatic cell hybrid mapping panel, we were able to determine that four closely linked microsatellite repeat markers bracket RYR1 with the order 19cen-D19S75-D19S191-RYR1-(D19S47, D19S190)-19ter. Application of the four markers to genetic studies of MHS showed recombination between the markers and MHS in two families, with linkage analysis apparently excluding the MHS locus from the RYR1 region of 19q13.1. These results therefore support the recent observations of genetic heterogeneity in MHS.     

Long-range restriction map of a region of human chromosome 19 containing the apolipoprotein genes,a CLL-associated translocation breakpoint,and two polymorphic MluI sites

Summary The apolipoprotein gene cluster on human chromosome 19 (APOC1, APOC2, APOE) has been localised by pulsed-field gel electrophoresis to within 200 kb of a chronic lymphocytic leukemia-associated translocation breakpoint. A restriction map covering 1300 kb around these loci has been constructed and contains two polymorphic MluI sites, which appear to show Mendelian inheritance. The orientation of the map on the chromosome has been established as 19cen CLL breakpoint-APOC2-19qter. Pedigree analysis using APOC2, a probe derived from the CLL breakpoint, and other localised markers on 19q suggests that the myotonic dystrophy locus is distal to APOC2 on 19q.     

Genetic and cytogenetic localisation of the homeo box containing genes on mouse chromosome 6 and human chromosome 7.

Probes from the m6 homeo box cluster were mapped to mouse chromosome 6 by somatic cell genetics, in situ hybridisation, and by a Mus spretus--Mus musculus backcross mapping system. In addition, the testis-specific homeo box containing cDNA, clone, HBT-1, has been mapped using the same back-cross system and the B X D recombinant inbred strain set. Close genetic and physical linkage between the m6 cluster and HBT-1 was demonstrated, positioning these sequences to the same local cluster of homeo box containing genes. The map location of this cluster between IgK and Tcrb coincides with the morphological mutation hypodactyly (Hd). Synteny has been observed between a region of mouse chromosome 6 and the long arm of human chromosome 7 encompassing the markers Cpa, Tcrb and Try-1. Here we localise human sequences hybridising to the mouse m6 probes to the short arm of chromosome 7, breaking the region of synteny.     

Regional localisations and linkage relationships of seven RFLPs and myotonic dystrophy on chromosome 19

Summary We have studied the genetic linkage relationships of seven DNA polymorphisms on chromosome 19, with each other and with the myotonic dystrophy locus. The DNA sequences were localised to various regions of the chromosome using translocations in somatic cell hybrids. These results provide the basis for a linkage map of most of chromosome 19, and suggest that the myotonic dystrophy locus is close to the centromere.     

A multipoint linkage map around the locus for myotonic dystrophy on chromosome 19

Employing 16 polymorphic DNA markers as well as the chromosome 19 centromere heteromorphism, we have performed a genetic linkage study in 26 families with myotonic dystrophy. Fourteen of these markers had been assigned previously to one of five different intervals of the 19cen-19q13.2 segment by using somatic cell hybrids. For the long arm of chromosome 19, a genetic map that encompasses 9 polymorphic markers and the DM gene has been constructed. Our studies indicate that the DM and CKMM genes map distal to the ApoC2-ApoE gene cluster and to the anonymous polymorphic markers D19S15 and D19S16, but proximal to the D19S22 marker. The orientation of DM and CKMM remains to be determined.     

A new polymorphic probe which defines the region of chromosome 19 containing the myotonic dystrophy locus

The region of human chromosome 19 which includes the myotonic dystrophy locus (DM) has recently been redefined by the tight linkage between it and the gene for muscle-specific creatine kinase (CKMM), which lies just proximal to DM. Utilizing human/hamster hybrid cell lines containing defined breakpoints within this region, we have assigned a number of new probes close to DM. Two of these probes, p134B and p134C, were isolated from a single cosmid clone (D19S51) and detect the same BglI RFLP; p134C detects an additional RFLP with the enzyme PstI. Analysis of these probes in the Centre d'Etude du Polymorphisme Humain families demonstrates tight linkage with a number of markers known to be proximal to DM. A two-point lod score of 6.34 at theta = .025 demonstrates the linkage of this probe to DM. Analysis of a DM individual previously shown to be recombinant for other tightly linked markers indicates that p134C is distal to DM. This result indicates that both the new probe and the existing group of proximal probes including CKMM and ERCC1 probably flank DM and define the genetic interval into which this mutation maps.     

The apolipoprotein CII gene: Subchromosomal localisation and linkage to the myotonic dystrophy locus

Summary The human apolipoprotein CII gene probe detects a restriction fragment length polymorphism located on chromosome 19. We have investigated the linkage of this polymorphism to the myotonic dystrophy locus in families. The two lici are closely linked with a maximum Lod score of 7.877 at 4% recombination. The close linkage and informativeness of the APOC2 polymorphism suggest that this probe may be of use for presymptomatic diagnosis of the myotonic dystrophy gene. The APOC2 gene was localised to the region 19p13–19q13 using somatic cell hybrids, providing further evidence that the myotonic dystrophy locus is situated in the central region of chromosome 19.     

Linkage relationships of the insulin receptor gene with the complement component 3, LDL receptor,apolipoprotein C2 and myotonic dystrophy loci on chromosome 19

Summary Myotonic dystrophy is associated with disturbances in the insulin response, possibly due to an abnormality of the insulin receptor. Both the myotonic dystrophy (DM) and insulin receptor (INSR) genes are on chromosome 19. Using a cloned gene probe for INSR, we have studied its linkage relationships with the DM locus and other chromosome 19 markers. The results show that INSR is not closely linked to DM, but is located very close to C3, in the region 19pter-19p13.2. This implies that the basic genetic defect which causes DM is not directly responsible for the disturbed insulin response in these patients.     

Construction of a detailed molecular map of the mouse X chromosome by microcloning and interspecific crosses.

A large number of microclones obtained by microdissection of the mouse X chromosome have been mapped using an interspecific Mus domesticus/Mus spretus cross. Clones displaying close linkage to a number of loci of known phenotype but unknown gene product, such as mdx (X-linked muscular dystrophy), have been obtained. Over a central 30 cM span of the mouse X chromosome, 17 clones have been mapped and ordered at a sufficient density to contemplate the complete physical mapping of this region that will aid in the isolation of a number of unidentified genes. Some of the mapped microclones detect moderately repetitive sequences that were clustered in several discrete regions of the mouse X chromosome.     

Genetic mapping in the region of the mouse X-inactivation center

The mouse X-inactivation center lies just distal to the T16H breakpoint. Utilizing pedigree analysis of backcross progeny from a Mus domesticus/Mus spretus interspecific cross, we have mapped a number of genetic loci, gene probes, microclones, and EagI linking clones distal to the T16H breakpoint. The genetic analysis provides a detailed genetic map in the vicinity of the mouse X-inactivation center. Comparative mapping data from the human X chromosome indicate that the most probable location of the mouse X-inactivation center is distal to Ccg-1 and in the region of the Pgk-1 locus. We report the assignment of two new loci, EM13 and DXSmh44, to the Ccg-1/Pgk-1 interval.     

Physical mapping and cloning of the proximal segment of the myotonic dystrophy gene region.

The myotonic dystrophy (DM) region has been recently shown to be bracketed by two key recombinant events. One recombinant occurs in a Dutch DM family, which maps the DM locus distal to the ERCC1 gene and D19S115 (pE0.8). The other recombinant event is in a French Canadian DM family, which maps DM proximal to D19S51 (p134c). To further resolve this region, we initiated a chromosome walk in a telomeric direction from pE0.8, a proximal marker tightly linked to DM, toward the genetic locus. An Alu-PCR approach to chromosome walking in a cosmid library from flow-sorted chromosome 19 was used to isolate DM region cosmids. This effort has resulted in the cloning of a 350-kb genomic contig of human chromosome 19q13.3. New genetic and physical mapping information has been generated using the newly cloned markers from this study. As a result of this new mapping information, the minimal area that is to contain the DM gene has been redefined. Approximately 200 kb of sequence between pE0.8 and the closest proximal marker to DM, pKEX0.8, that would have otherwise been screened for DM candidate genes, has been eliminated as containing the DM gene.     

Evidence for linkage of the central core disease locus to the proximal long arm of human chromosome 19

Central core disease of muscle (CCD; MIM 117000) is a rare inheritable myopathy that is frequently found in association with susceptibility to malignant hyperthermia (MHS). This observation has prompted us to perform a linkage study in CCD families using various chromosome 19q probes that are linked to the MHS locus and map close to the ryanodine receptor gene (RYR1), a strong MHS candidate gene. Our genetic linkage data support a location of the CCD gene on proximal 19q13.1 and thus suggest that CCD and MHS may be allelic.     

A multilocus linkage map of mouse chromosome 8

We present a genetic linkage map of mouse chromosome 8 that spans 53 cM and includes eight cloned loci. This map was derived from analysis of 100 progeny of an interspecific backcross between Mus spretus and Mus musculus domesticus. Genes that were mapped in this analysis include L7, Plat, Lpl, Ucp, Es, Mt-1, Um, and Tat. This analysis positions a new extremely proximal marker on chromosome 8, which is discussed as a potential candidate gene for the nervous locus. These linkage data will be useful for the mapping of additional loci on chromosome 8.