Date of Award

2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Cell & Molecular Biology

First Advisor

Douglas J. Epstein

Abstract

Hearing loss is the most common form of congenital birth defect, affecting an estimated

35 million children worldwide. To date, nearly 100 genes have been identified which

contribute to a deafness phenotype in humans, however, many cases remain in which a

causative mutation has yet to be found. In addition, the exact mechanism by which

hearing loss occurs in the presence of many of these mutations is still not understood.

This is due, in part, to the complex nature of the development and function of the

cochlear duct, the organ of hearing. The cochlea undergoes an intricate morphogenetic

development and requires the proper specification and maintenance of dozens of

different cell types in order to function correctly. In the mature duct, an interplay between

mechanotransducing sensory hair cells, supporting pillar and Dieters' cells, and

generation of electrochemical potential by the stria vascularis are necessary to respond

to sound stimuli. We utilized exome and RNA-sequencing experiments combined with

mouse genetics in order to discover novel genes that play roles in cochlear

development and function. Exome sequencing of families with profound hearing loss

uncovered mutations in Epithelial Splicing Regulatory Protein 1 (ESRP1), a critical

regulator of alternative mRNA splicing. Analysis of Esrp1 mutant mice revealed a

shortened cochlear duct, delay in hair cell differentiation and maturation, and loss of the

stria vascularis due to inappropriate Fgf ligand usage, stemming from an alternatively

spliced receptor, in these cells. To identify additional regulators of inner ear development

we performed an RNA-seq experiment comparing the gene expression profiles of control

and Smoecko otic vesicles, which lack a cochlear duct. This generated a dataset of

hundreds of cochlear enriched transcripts including Growth Arrest Specific 2 (Gas2) a

cytoskeletal binding protein with the potential to act as a regulator of cochlear

development. We generated a Gas2 null mouse line and discovered that these animals

have severe hearing impairment likely due to defects in microtubule organization in the

pillar cells. Taken together, these studies implicate Esrp1 and Gas2 as novel hearing

loss genes that regulate aspects of cochlear development and function.

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Additional Files

Rohacek dissertation Table 2-1 Esrp1 dependent alternative splicing events in the cochlear epithelium.xlsx (133 kB)

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