| First Author | Ishikawa A | Year | 1996 |
| Journal | Mouse Genome | Volume | 94 |
| Issue | 4 | Pages | 871-3 |
| Mgi Jnum | J:38090 | Mgi Id | MGI:85479 |
| Citation | Ishikawa A, et al. (1996) Genetic mapping of the Rimy mutation on mouse Chromosome 11. Mouse Genome 94(4):871-3 |
| abstractText | Full text of Mouse Genome contribution: GENETIC MAPPING OF THE RIMY MUTATION ON MOUSE CHROMOSOME 11. Akira Ishikawa 1, 2 and Peter D. Keightley 1; 1 Institute of Cell, Animal and Population Biology, The University of Edinburgh, Edinburgh EH9 3JT, Scotland, and Laboratory of Animal Genetics, School of Agricultural Sciences, Nagoya University, Nagoya 464-01, Japan. Introduction The rimy mutation controlled by a single autosomal recessive gene (symbol rmy) has been found in a line under selection for increased body size in an inbred mouse strain C3H/He (1). Phenotypically rimy mice are characterised by a grey coat colour resulting from reduced phaeomelanin granules of the hair, 10-30% lower body weight than their normal littermates and infertility in mutant males (1). Grizzled (gr), a recessive coat colour mutation, is most similar in phenotype to rimy (1-3). However, in contrast to rimy, grizzled mice show a kinked tail and recover body weight after weaning (1-3). The gr gene is located on chromosome 10 (3), but the rmy gene has not yet been mapped. In this study, we report the chromosomal location of the rmy gene and the identification of microsatellite markers flanking rmy that will be useful for constructing a high-resolution map around the gene. Materials and Methods A total of 75 backcross progeny was produced from a cross between C3H/He-rmy females and (C3H/He-rmy females X C57BL/6J males) Fi males. Microsatellite markers were purchased from Research Genetics (Huntsville, AL, USA). PCR products were separated on 3.5% agarose gels and visualised by ethidium bromide staining. Our approach to mapping the rmy gene was divided into two parts. In the first part, a DNA pooling strategy (4) was used as a preliminary means of identifying microsatellite markers which may be linked to the rmy gene. Two separate DNA pools were made from all mutant and wild-type individuals in backcross progeny. Enrichment or diminution was investigated for C3H and C57BL alleles of each marker in the mutant DNA pool in comparison with the wild-type DNA pool. Two parental strains and the Fl hybrid were used as controls. In the second part, the entire backcross progeny was individually genotyped for the markers identified by the pooling analysis and the neighbouring markers. Linkage analysis was performed using Map Manager software (5). Results and Discussion The backcross progeny obtained consisted of 22 (29%) mutant and 53 (71%) wild-type mice. The segregation ratio departed significantly from the 1: 1 ratio expected for single autosomal recessive inheritance (X2-test, P < 0.001). This is probably due to the low prenatal or perinatal viability of mutant mice (1). The under-representation of the mutant mice does not affect the linkage analysis described below, as they are under-represented equally in recombinant and non-recombinant classes. Although we had linkage evidence that rmy is not allelic to gr (1), to confirm it we started linkage analysis on chromosome 10. At the same time we analysed microsatellite markers on chromosomes 11 to 13. Eight microsatellite markers on these chromosomes were typed for mutant and wild-type pools and controls. For the chromosome 11 marker D11Mit20, a diminution of the C57BL allele was clearly discernible in the mutant pool in comparison with the wild-type pool and Fl hybrid. For D11Mit132, the C57BL allele was not visible on agarose gels, whereas a strong enrichment of the C3H allele was observed in the mutant pool (data not shown). This marker showed evidence of close linkage to the rmy gene. In contrast, no differences were seen between the two pools for other six markers on chromosomes 10, 12 and 13 (data not shown). These results strongly suggested that the rmy gene is located on chromosome 11. Fig. 1. (Legend). (Left) Haplotype analysis of 75 backcross progeny. Each column shows a chromosomal haplotype inherited from the (C3H/He-rmy X C57BL/6J) F1 parent. Closed boxes represent C3H alleles and open boxes represent C57BL alleles. The number of backcross progeny carrying each haplotype is listed at the bottom of each column. (Right) Genetic map of the central region of mouse chromosome 11, showing the location of rmy in relation to linked microsatellite markers. Genetic distances (in cM +/- SE) between loci are indicated to the left of the map. Gene order was determined by minimising the number of double recombinants required to explain the allele distribution patterns. Figure 1 shows the haplotypes and the genetic map constructed from individual typing data. The mapping results indicate that rmy is located in the central region of chromosome 11, 5.3 cM distal to D11Mit242 and 1.3 cM proximal to D11Mit212. No recombinants were detected between rmy and D11Mit35 in the 75 backcross progeny typed (0 +/- 4.8 cM for 95% confidence interval). The order of microsatellite markers is consistent with that reported in the Mouse Genome Database (MGD) (6). The genetic distances between the markers are roughly 50% shorter than those in the MGD (6), but the latter distances are within the 95% confidence intervals of the former except for the distance between D11Mit212 and D11Mit132. Different crosses are known to vary in recombination frequencies even within the same chromosomal region, resulting from differences in chromosomal locations of recombinational hotspots among strains (7). Whether this is the reason for the shortened distances in our map is unclear. According to the MGD (6), no coat colour genes are reported on chromosome 11, while the Idd4 (insulin dependent diabetes susceptibility-4) gene and the Om (ovum mutant) gene are listed in the interval between D11Mit242 and D11Mit212 as candidate genes that could be involved in the body weight and viability phenotypes of rmy. Idd4 is unlikely to be involved because rimy mice having reduced body weight do not appear to exhibit diabetes. Om, causing preimplantation embryo lethality known as the DDK syndrome, is mapped 1.55 cM proximal to D11Mit35 (8), which is very closely linked to rmy (Fig.1) affecting prenatal or perinatal viability as mentioned earlier. Whether Om is actually responsible for the rimy phenotype will need further research. In summary, we revealed that the rmy gene resides in the central region of mouse chromosome 11. The closest microsatellite marker D11Mit35 has no recombinants with the rmy gene. One recombinant was identified for the distal marker D11Mit212. These closely linked markers should be useful for high-resolution mapping of the rmy gene. Acknowledgements We thank Dr. S. Horvat (Roslin Institute, Edinburgh) for advice and Professor W.G. Hill (ICAPB, The University of Edinburgh) for critical comments on the manuscript. AI wishes to thank the Ministry of Education, Science, Sports and Culture, Japan for financial support (an Overseas Research Scholarship). References (1) Keightley, P.D. and Hawkins, S. (1991). Mouse Genome 89: 410. (2) Bloom, J.L. and Falconer, D.S. (1966). Genetical Research 7: 159-167. (3) Kapfhamer, D. and Burmeister, M. (1994). Genomics 23: 635-642. (4) Taylor, B.A., Navin, A., and Phillips, S.J. (1994). Genomics 21: 626-632. (5) Manly, K.F. (1993). Mammalian Genome 4: 303-313. (6) Mouse Genome Database (MGD) 3.1. (1996). Mouse Genome Informatics, The Jackson Laboratory, Bar Harbor, Maine. World Wide Web (URL:http//www.informatics.jax.org/), February. (7) Silver, L.M. (ed.) (1995). Mouse Genetics: Concepts and Applications. Oxford University Press, Oxford. (8) Baldacci, P.A., Cohen-Tannoudji, M., Kress, C., Pournin, S., and Babinet, C. (1996). Mammalian Genome 7: 114-116. |
