Characterization of two transgene insertional mutations at pirouette, a mouse deafness locus.

The mouse mutant 'pirouette' (pi) exhibits profound hearing loss and vestibular defects due to inheritance of a recessive mutation on chromosome 5. Dysfunction has been correlated with defects during maturation of sensory cells in the inner ear. As an initial step in characterizing pirouette at the genetic level, we have localized the candidate interval to a small region on central chromosome 5 by analysis of a congenic strain of pirouette mice. This region exhibits conserved synteny with human chromosome 4 and suggests that pirouette may be a genetic model of the human nonsyndromic deafness disorder DFNB25, which has been localized to 4p15.3-q12. In addition to the original spontaneous pirouette strain, we have identified and characterized 2 additional mouse strains with allelic mutations at the same locus. Analysis of the morphology in each of the 3 pirouette alleles indicated very similar early postnatal alterations in maturation of stereocilia and suggests that the gene affected in pirouette normally plays a role in building or maintaining these structures that are critical for sensory mechanotransduction.

Mutation of the novel gene Tmie results in sensory cell defects in the inner ear of spinner, a mouse model of human hearing loss DFNB6.

The recessive mutation at the mouse spinner (sr) locus results in hearing loss and vestibular dysfunction due to neuroepithelial defects in the inner ear. Using a positional cloning strategy, we have identified the mutant locus responsible for this pathology. The affected gene (Tmie) lies within a 40 kb deletion in the original sr allele. In a newly identified allele, Tmie contains a nonsense mutation expected to truncate the C-terminal end of its product. The 153 amino acid protein encoded by the gene shows no similarity to other known proteins, and is predicted to contain a signal peptide and at least one transmembrane domain. Tmie transcripts were identified in several tissues, including the cochlea. Loss of function of Tmie results in postnatal alterations of sensory hair cells in the cochlea, including defects in stereocilia, the apical projections of hair cells that are important in mechanotransduction of sound. These morphological defects are associated with a profound failure to develop normal auditory function. Consistent with a conserved role for this gene in the cochlea, the genetic mapping data presented here support human TMIE as the gene affected at DFNB6, a non-syndromic hearing loss locus. The spinner mutant is thus a valuable model for insight into mechanisms of human deafness and development of sensory cell function.

Mutations in a novel gene, TMIE, are associated with hearing loss linked to the DFNB6 locus.

We have identified five different homozygous recessive mutations in a novel gene, TMIE (transmembrane inner ear expressed gene), in affected members of consanguineous families segregating severe-to-profound prelingual deafness, consistent with linkage to DFNB6. The mutations include an insertion, a deletion, and three missense mutations, and they indicate that loss of function of TMIE causes hearing loss in humans. TMIE encodes a protein with 156 amino acids and exhibits no significant nucleotide or deduced amino acid sequence similarity to any other gene.