The mouse cochlea derives from the ventral extension of the otic vesicle. Over the course of several days during embryonic development, this outgrowth undergoes a complex sequence of morphogenetic changes resulting in its lengthening, coiling and differential patterning into sensory and nonsensory cell types that are essential for hearing (Groves and Fekete, 2012). Congenital malformations of the cochlea often lead to deafness, emphasizing the importance of a thorough understanding of its development (Jackler et al., 1987). We previously described a critical function of the Sonic hedgehog (Shh) signaling pathway in promoting ventral identity within the otic vesicle that is necessary for the subsequent outgrowth of the cochlear duct (Riccomagno et al., 2002;Bok et al., 2007b;Brown and Epstein, 2011). Mouse embryos lacking Shh, or carrying an ear conditional knockout of Smoothened (Smoecko), an essential Shh signal transduction component, exhibit cochlear agenesis. We also classified several transcription factors with key roles in cochlear development as either transcriptional targets (Pax2, Otx2, Gata3) or effectors (Gli2, Gli3) of Shh signaling within the ventral otic epithelium. However, despite these advances, a detailed understanding of the mechanism by which Shh dependent transcription factors promote cochlear duct outgrowth remains unclear, primarily since the genes acting downstream in this transcriptional cascade have yet to be determined. To identify novel targets of Shh signaling we compared the genome-wide expression profiles of control and Smoecko inner ears at E11.5, when the cochlea anlage is evident, and uncovered an intriguing set of Shh responsive genes with a combination of known and previously uncharacterized roles in cochlear morphogenesis. Interestingly, several of these genes maintain their expression at later stages of development within the prosensory domain of the cochlear duct, raising the possibility that Shh signaling is priming the presumptive sensory epithelium for subsequent steps in its development. We propose to characterize the ventral otic gene set according to the following experimental plan: classify their spatiotemporal patterns of expression and dependency on Shh signaling (Aim 1);decode their cis-regulatory architecture (Aim 2);and assess their functional contribution to cochlear development (Aim 3). The results of these experiments should advance our fundamental understanding of the molecular and cellular mechanisms underlying cochlear morphogenesis and cell fate specification within the inner ear.

Public Health Relevance

Congenital malformations of the inner ear are a significant cause of deafness and vestibular dysfunction in humans. Experiments in this grant proposal are strongly motivated by the premise that a detailed understanding of the cellular and molecular mechanisms underlying inner ear development should not only improve our fundamental knowledge of how this complex structure is assembled, but may also profoundly improve the way inner ear disorders are treated in the future.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
Research Project (R01)
Project #
2R01DC006254-11A1
Application #
8629843
Study Section
Auditory System Study Section (AUD)
Program Officer
Freeman, Nancy
Project Start
2003-08-01
Project End
2018-11-30
Budget Start
2013-12-01
Budget End
2014-11-30
Support Year
11
Fiscal Year
2014
Total Cost
$418,590
Indirect Cost
$154,096
Name
University of Pennsylvania
Department
Genetics
Type
Schools of Medicine
DUNS #
042250712
City
Philadelphia
State
PA
Country
United States
Zip Code
19104
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Brown, Alexander S; Epstein, Douglas J (2011) Otic ablation of smoothened reveals direct and indirect requirements for Hedgehog signaling in inner ear development. Development 138:3967-76
Bok, Jinwoong; Dolson, Diane K; Hill, Patrick et al. (2007) Opposing gradients of Gli repressor and activators mediate Shh signaling along the dorsoventral axis of the inner ear. Development 134:1713-22
Pachikara, Abraham; Dolson, Diane K; Martinu, Lenka et al. (2007) Activation of Class I transcription factors by low level Sonic hedgehog signaling is mediated by Gli2-dependent and independent mechanisms. Dev Biol 305:52-62
Cohen, Ethan David; Wang, Zhishan; Lepore, John J et al. (2007) Wnt/beta-catenin signaling promotes expansion of Isl-1-positive cardiac progenitor cells through regulation of FGF signaling. J Clin Invest 117:1794-804
Riccomagno, Martin M; Takada, Shinji; Epstein, Douglas J (2005) Wnt-dependent regulation of inner ear morphogenesis is balanced by the opposing and supporting roles of Shh. Genes Dev 19:1612-23