Hereditary inner ear disease is prevalent and has significant implications for quality of life. There is currently no available clinical cure for hereditary inner ear disease. The mouse serves as an ideal mammalian model for understanding genetic inner ear disease and for developing therapeutic measures. Mouse models have facilitated the discovery of genes that underlie hereditary disease in humans, have made it possible to study the role of these genes in inner ear development and function, and hold great promise as models for developing treatments for hereditary inner ear disease. This grant application builds on our discovery that mutations in the unconventional myosin gene, Myo15, are responsible for profound congenital deafness and vestibular dysfunction in two spontaneous mouse mutants: shaker 2 and shaker 2J, and in humans with DFNB3. We used these mouse models to demonstrate the long-term structural and functional phenotypic correction of deafness with a transgene expressing Myo15. We characterized the development of pathology in Myo15, Myo6, Myo7a, pirouette, and whirlin deficient mutants, double heterozygotes and double mutants. Although there is no enhanced risk of age related hearing loss in double heterozygotes, these studies revealed unique functions of each myosin gene, and suggested the possibility that MYO15 has other functions besides transportation of whirlin to the stereocilia tips. We established adenoviral vectors for gene therapy and a database of genes exhibiting differential expression in the cochlea between weaning and adulthood in normal and Myo15 mutant mice. These studies laid a sound foundation for the goals of this grant. There are multiple isoforms of MYO15 that are generated by alternative splicing, including the presence or absence of a large proline-rich region N-terminal to the motor domain of MYO15. We hypothesize that this proline-rich region is important for protein-protein interactions necessary for hearing. We have generated a mouse model that recapitulates a human mutation in the proline-rich domain using knock-in technology. These mutants have profound congenital deafness, hair bundle pathology that is distinct from shaker 2 and shaker 2J mice, and apparently normal vestibular function. We propose a structure-function analysis that will reveal the importance of MYO15 isoforms in the development and function of the cochlea using mutant alleles, cell culture and cochlear explant assays. We will conduct a classical genetic analysis to evaluate interactions between mutant alleles and identify interacting proteins. Our investigative team has a track record for accomplishments resulting from cross-disciplinary collaboration, bringing together experts in otolaryngology, microscopy, physiology, and developmental genetics. This team will enable us to exploit the animal models fully to understand the mechanisms of inner ear disease and has the potential to identify novel genes essential for normal hearing.

Public Health Relevance

Deafness is a common birth defect, affecting about 1 birth in 2000. About half of these children are affected because of genetic reasons, and there is no known cure or prevention. Myosin 15 is a molecular motor protein that is important for normal hearing. Mutations in this gene cause deafness in humans and mice. In this grant proposal we seek to identify other proteins that Myosin 15 interacts with and to use mouse models to identify the pathological changes caused by human mutations.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
Research Project (R01)
Project #
5R01DC005053-09
Application #
8305687
Study Section
Auditory System Study Section (AUD)
Program Officer
Watson, Bracie
Project Start
2001-08-01
Project End
2014-08-31
Budget Start
2012-09-01
Budget End
2013-08-31
Support Year
9
Fiscal Year
2012
Total Cost
$302,497
Indirect Cost
$79,100
Name
University of Michigan Ann Arbor
Department
Genetics
Type
Schools of Medicine
DUNS #
073133571
City
Ann Arbor
State
MI
Country
United States
Zip Code
48109
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Karolyi, I Jill; Dootz, Gary A; Halsey, Karin et al. (2007) Dietary thyroid hormone replacement ameliorates hearing deficits in hypothyroid mice. Mamm Genome 18:596-608
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Cha, K B; Karolyi, I J; Hunt, A et al. (2004) Skeletal dysplasia and male infertility locus on mouse chromosome 9. Genomics 83:951-60
Karolyi, I Jill; Probst, Frank J; Beyer, Lisa et al. (2003) Myo15 function is distinct from Myo6, Myo7a and pirouette genes in development of cochlear stereocilia. Hum Mol Genet 12:2797-805

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