International Mammalian Genome Society

The 13th International Mouse Genome Conference
October 31-November 3, 1999

Table of Contents * Structure * Bioinformatics * Sequence * Mapping * New Tools * Gene Discovery * Developmental * Mutagenesis * Functional Genomics

G20 Mapping of Modifier Gene for Mouse Preaxial Polydactylous Mutantion, Rim4

Hiroshi Masuya1, Tomoko Sagai2, Motohisa Takahashi3, Toshihiko Ogura3, and Toshihiko Shiroishi1,2. 1Mouse Functional Genomics Reserch Group, RIKEN Genomic Sciences Center; 2Mammalian Genetics Laboratory, National Institute of Genetics; 3Nara Institute of Science and Technology

The anteroposterior axis patterning in vertebral limb morphogenesis is established by the formation of the zone of polarizing activity (ZPA) at the posterior margin of limb buds. The Sonic hedgehog (Shh) gene is expressed exclusively at the posterior margin of limb buds, and it mediates the polarizing activity. A preaxial polydactyly mutant Rim4 that arose spontaneously in the C57BL/10 background shows ectopic expression of Shh at the anterior margin of the limb bud and results in mirror-image duplication of the digits. Crossing the Rim4 heterozygotes with an inbred strain, MSM, completely suppresses the Rim4 phenotype, while crossing the same mice with the NZB strain demonstrates almost a full penetrance of the phenotype. In this study, we carried out mapping of the modifier gene for Rim4, based on the polymorphism between the MSM and NZB strains. As a result, a major modifier gene was mapped to chromosome 2, closely linked to Aristaless-like4 (Alx4) that is the causative gene of another preaxial polydactyly mutation, Strongs luxoid (lst). Double heterozygotes of Rim4 and lstJ showed a more severe polydactyly phenotype than that of the heterozygotes of either single mutation. We found three amino acid substitutions in the Alx4 gene between the MSM and NZB alleles. All these results suggest the possibility that genetic interaction between Rim4 and Alx4 genes plays a key role in establishing anteroposterior axis formation in limb development.


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