We have demonstrated that the phenotype of the mouse mutant sex-linked fidget ( slf ) is caused by developmental malformations of the inner ear that result in hearing loss and vestibular dysfunction. Recently, pilot mapping experiments suggested that the mouse Brn4 / Pou3f4 gene co-segregated with the slf locus on the mouse X chromosome. These mapping data, in conjunction with the observation that the vertical head-shaking phenotype of slf mutants is identical to that observed in mice with a targeted deletion of the Brn4 gene, suggested that slf is a mutant allele of the Brn4 gene. In this paper, we have identified the nature of the slf mutation, and demonstrated that it is an X chromosomal inversion with one breakpoint close to Brn4. This inversion selectively eliminates the expression of the Brn4 gene in the developing inner ear, but not the neural tube. Finally, these results demonstrate that the slf mutation is a good mouse model for the most prevalent form of X-linked congenital deafness in man, which is associated with mutations in the human Brn4 ortholog, POU3F4.

Menkes' disease (MD) and occipital horn syndrome (OHS) are allelic X-linked disorders caused by mutations in the copper ion transporting ATPase, ATP7A. Genetic, phenotypic and biochemical data suggest that mottled mutants in the mouse, which range in severity and phenotype, are caused by mutations in Atp7a, the mouse homologue of ATP7A. As the only causal mutation in Atp7a has been reported in one very mild allele thought to be a model for OHS, Atp7aMo-blo (mottled blotchy), we sequenced the entire 4.5 kb coding region of three other mottled mutants, two of which are thought to be models for classical MD (AtpaMo-br, AtpaMo-13H) and one with a slightly milder phenotype (Atp7aMo-vbr). Although no causal mutation was found in Atp7aMo-13H, mutations which can be predicted to affect Atp7a function were identified in Atp7aMo-br and Atp7aMo-vbr. A 6 bp deletion of nucleotides 2478-2483, which can be predicted to affect the correct processing of the protein, was found in Atp7aMo-br and an A3189-->C nucleotide change, which results in lysine-->threonine amino acid substitution in the phosphorylation domain, was found in Atp7aMo-vbr. Thus we provide further proof that mottled mutants will provide excellent models for MD as well as OHS.

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