| First Author | Sonin NV | Year | 1996 |
| Journal | Mouse Genome | Volume | 94 |
| Issue | 2 | Pages | 491-3 |
| Mgi Jnum | J:33865 | Mgi Id | MGI:81358 |
| Citation | Sonin NV, et al. (1996) Molecular mapping of the mouse Gy mutation on Chromosome X. Mouse Genome 94(2):491-3 |
| abstractText | Full text of Mouse Genome contribution: MOLECULAR MAPPING OF THE MOUSE Gy MUTATION ON CHROMOSOME X N.V. Sonin,1 R.T. Taggart,(1, 3) M.H. Meyer,2 and R.A. Meyer, Jr.2. 1Department of Obstetrics and Gynecology and 2Department of Orthopaedic Surgery, Carolinas Medical Center, P.O. Box 32861, Charlotte, NC 28232-2861; 3Present address: Div. of Genetics, Children's Hospital, 936 Delaware Ave., Buffalo, NY 14209 Introduction Two closely linked hypophosphatemic genes, Gy and Hyp. are known on the mouse X chromosome (1, 2). Both genes are fully dominant for hypophosphatemia, but the hemizygous Gy males are more severely affected by abnormal skeletal development (3). The Gy and Hyp phenotypes are similar to the human disease X-linked hypophosphatemia (gene symbol HYP) (3). The human HYP gene was previously localized to chromosome Xp22.1-p22.2 (4, 5). This region of the human X chromosome is homologous to the distal part of the mouse X chromosome where Gy and Hyp are located (6). A candidate gene, PEX, has been proposed for the human disease (7). The mouse Hyp locus has been placed on a molecular genetic map on which the closest marker Cbx-rsl was 2 cM distant from Hyp (8). However, no detailed map exists for the Gy mutation. A single normal mouse found in a linkage study suggests that Gy and Hyp are mutations of separate, but closely linked, genes (2). However, the exact distance between them is not known, nor is it established as to which is distal to the other. The present work was designed to construct such a map for Gy and to identify markers closely linked to this locus that will be useful for positional cloning of the gene. High resolution mapping of both Gy and Hyp may also help to identify the exact distance between the loci and the correct gene order. Materials and Methods Heterozygous female Gy B6C3H mice (B6C3H is a hybrid between C57BL/6J and C3H/HeSnJ (3)) were crossed to normal BALB/cJ male mice. Among the Fl progeny, female Gy mice were identified by low plasma phosphate levels, decreased body weight, and short tails (3). These Gy B6C3H/BALB female mice were backcrossed to normal BALB/cJ male mice. The offspring of this second cross were scored for segregation of the Gy gene and for a number of microsatellite molecular markers (9), using the polymerase chain reaction and primer pairs from Research Genetics (Huntsville, AL). Results DXMit microsatellite markers were chosen for their proximity to the Gy region on the mouse X chromosome and for their polymorphism between B6C3H and BALB/c. Four widely spaced markers were initially screened. Two were found to be distant from Gy. DXMit67 was analyzed in the first 48 mice. It was found to be 4 +/- cM centromeric to DXMit36 and was not explored further. Likewise DXMit31 was screened in the first 174 mice, was found to be 1.7 +/- 1.7 cM telomeric to DXMit5, and was not explored further. Gy was found to be between DXMit36 and DXMit5. A total of 389 progeny were scored for segregation of DXMit36, Gy and DXMit5. A total of 22 key recombinants were found which were then scored for: DXMit80, DXMit98, DXMit99, DXMit121, DXMit153, and DXMit178. The recombination fractions were calculated and are listed in Table 1. Fig. 1 shows the backcross haplotypes and the genetic map constructed from our data. No double crossover events were observed within the 389 progeny, therefore the order of the Gy locus and the microsatellite markers could be assigned with certainty. The closest markers to Gy were DXMit80 and DXMit178 which had 1 recombination with Gy within the 389 observations. DXMit80 and DXMit178 did not recombine with each other. Table 1. Number of Recombinants and Recombination Fractions between Loci on Chromosome X of the Mouse DXMit36: DXMit 36: -; 153: 2; 98: 8; 80; 178: 12; Gy: 13; DXMit 99: 18; 121: 21; 5: 22. DXMit153: DXMit 36: 0.5; 153: -; 98: 6; 80; 178: 10; Gy: 11; DXMit 99: 16; 121: 19; 5: 20. DXMit98: DXMit 36: 2.1; 153: 1.5; 98: -; 80; 178: 4; Gy: 5; DXMit 99: 10; 121: 13; 5: 14. DXMit80; 178: DXMit 36: 3.1; 153: 2.6; 98: 1.0; 80; 178: -; Gy: 1; DXMit 99: 6; 121: 9; 5: 10. Gy: DXMit 36: 3.3; 153: 2.8; 98: 1.3; 80; 178: 0.3; Gy: -; DXMit 99: 5; 121: 8; 5: 9. DXMit99: DXMit 36: 4.6; 153: 4.1; 98: 2.6; 80; 178: 1.5; Gy: 1.3; DXMit 99: -; 121: 3; 5: 4. DXMit121: DXMit 36: 5.4; 153: 4.9; 98: 3.3; 80; 178: 2.3; Gy: 2.1; DXMit 99: 0.8; 121: -; 5: 1. DXMit5: DXMit 36: 5.7; 153: 5.1; 98: 3.6; 80; 178: 2.6; Gy: 2.3; DXMit 99: 1.0; 121: 0.3; 5: -. The upper right of the body of the table shows the number of recombinations within each pair of markers in the 389 animals tested. DXMit80 and DXMit178 were not separated by recombination and are listed together. The lower left shows the recombination fraction (in %). SE of the estimated recombination fraction ranges from 0.3 +/- 0.3% to 5.7 +/- 1.2%. Fig. 1. (Legend) (Left) Analysis of backcross haplotypes. Each column represents a chromosomal haplotype that was inherited from the (B6C3H/BALB Gy/ +) parent. The number of progeny of each haplotype is indicted below each column. Open boxes represent the BALBb alleles and closed boxes represent the B6C3Hh alleles as determined by PCR for the markers indicated to the left. (Right) Genetic map of the distal region of mouse chromosome X, demonstrating the location of the Gy locus. Markers scored are indicated to the right. The distances between Gy and each of the markers are given to the left. DXMit67 wa s found to be 4 +/- 3 cM centromeric to DXMit36 and is not plotted. Discussion This is the first determination of the order and the genetic distance of the Gy mutation with respect to molecular markers. These data show that the Gy locus resides within a 1.6 cM interval flanked on the distal side by the marker DXMit99 and on the proximal side by the markers DXMit80 and DXMit178. Based on a calculated recombination frequency of 0.3%, these two markers are the closest to the Gy locus. We can not compare this map with the map for the mouse Hyp locus (8) because different markers were used in the two studies. We are currently repeating our study with the Hyp gene. When both maps are available, this will facilitate determination of the relative position of Gy and Hyp. This will give a better estimate of the distance between Gy and Hyp and will also determine which is more distal on the X chromosome. While microsatellite markers have been mapped to each other, there is less certainty about their alignment to maps of phenotypic genes, such as Gy. Recent maps show Gy to be 7 cM distal to DXMit28 (10). Since DXMit28 and DXMit99 are tightly linked and since we find Gy to be proximal to DXMit99 by 1.3 cM, the alignment between these markers may be off by 8 cM. In summary, we report a high resolution map of the Gy gene on the X chromosome of the mouse. The closest microsatellite markers, DXMit80 and DXMit178, are 0.3 cM proximal to Gy. The present map provides entry points for positional cloning of the Gy gene. These data are also the first report of the correct order for several of these new microsatellite markers. Acknowledgements The authors thank Ms. K. Greene for her technical assistance and Ms. C. Ayers for her secretarial assistance. We also thank Dr. D. Price for his valuable discussion and support. References 1. Eicher EM, Southard JL, Scriver CR, Glorieux FH 1976. Proc Natl Acad Sci USA 73:4667-4671. 2. Lyon MF, Scriver CR, Baker LR, Tenenhouse HS, Kronick J, Mandla S 1986. Proc Natl Acad Sci USA 83:4899-4903. 3. 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