A Role for diaphanous homolog 3 in the Mammalian Auditory System.

Abstract

Inherited deafness is a highly heterogeneous disorder that may be the result of mutations in any one of more than 100 genes. Although the chromosomal locations of these genes have been mapped, the specific gene identities are unknown for approximately half of them. The heterogeneity of inherited deafness is a testament to the complexity of the inner ear and reflects the number of processes and molecules that are involved in one of our most important senses for communicating with others and interacting with our surroundings.

Hearing research is beset with the same challenge as other fields of neuroscience: access to human tissue is extremely limited. Animal models, therefore, have become critical to the identification and confirmation of human deafness genes. Beyond gene identification and confirmation, animal models are also essential for identifying the underlying molecular mechanisms involved in hearing loss and in normal hearing.

This dissertation describes the identification of a gene mutation in the non-coding region of diaphanous homolog 3 that causes a form of human deafness known as auditory neuropathy. The 5’ UTR mutation results in 2- to 3-fold upregulation both in human lymphoblastoid cell lines of affected individuals and in an in vitro reporter assay. A Drosophila model demonstrates that expression of constitutively active diaphanous protein in the fly hearing organ results in impaired auditory responses. In addition, this dissertation describes the generation of a mouse model of diaphanous homolog 3 overexpression that recapitulates the delayed onset and progressive nature of the human auditory phenotype. Histological examination of the cochlear tissues of these mice reveals highly aberrant morphological characteristics of the inner hair cells, consistent with one of the cell types predicted to be affected in human auditory neuropathy. This dissertation also describes potential downstream effects of diaphanous homolog 3 overexpression on the expression of many other genes, as identified by microarray analysis. Identification of the molecular mechanisms responsible for this form of hearing loss will greatly enhance our understanding of the molecular basis of normal auditory function, with potential applications for prevention or treatment of auditory neuropathy.