Extracellular signaling molecules provide the vertebrate inner ear with positional information at multiple stages of its development to produce the required patterns of growth and differentiation necessary for the formation of the vestibulum and cochlea, the two inner ear organs responsible for sensing, balance and sound, respectively. In previous work, we identified roles for the secreted factors, Shh and Wnt1/Wnt3a, in the polarization of the mouse otic vesicle along its dorsal-ventral axis. Our studies determined that Shh, secreted from the notochord, signals directly to ventral regions of the otic epithelium to direct the outgrowth of the cochlear duct. Whereas, Wnt1/Wnt3a, secreted from the dorsal hindbrain, signals to the dorsal otocyst to regulate vestibular morphogenesis. In addition to these early roles, Hedgehog (Hh) and Wnt/2catenin signaling pathways are also active at critical junctures later in ear development when sensory epithelial progenitors are undergoing their specification and differentiation into hair cells and support cells. We now propose to investigate the specific requirements of Wnt/2catenin and Hh signaling pathways at later stages of inner ear development in the mouse, using a conditional gene targeting strategy that inactivates essential mediators of these pathways at defined periods of cochlear and vestibular development. Our conditional gene targeting approach takes advantage of our recent finding that Wnt responsive cells originating in the dorsal otocyst extend ventrally over time and contribute to the sensory epithelium of the cochlear duct. Using a tamoxifen inducible form of cre recombinase, expressed under the transcriptional control of a Wnt responsive Top promotor (TopcreER), floxed alleles of 2catenin and Smoothened will be inactivated in sensory epithelial progenitors. Preliminary results indicate that Wnt/2catenin signaling is required for the specification and/or differentiation of hair cells and support cells in the organ of corti and cristae of the semicircular canals. Experiments in this proposal will further elaborate on the mechanisms by which Wnt/2catenin and Hh signaling pathways function to mediate sensory cell fates in the inner ear. We have also developed a genetic recombination based strategy to indelibly mark Wnt responsive cells in the dorsal otocyst in order to trace their fates over the course of inner ear development. Additional experiments described in this proposal will test the hypothesis that hair cells and support cells in the organ of corti derive from a population of Wnt responsive progenitors in the dorsal otocyst. Results from these studies should improve our fundamental understanding of sensory development in auditory and vestibular regions of the inner ear.

Public Health Relevance

The auditory and vestibular structures of the inner ear mediate our senses of hearing and balance, respectively. Progress continues to be made in identifying the causes of hereditary forms of deafness and vestibular disease in humans. Nonetheless, a detailed understanding of the genetic pathways coordinating inner ear development remains limited. By elucidating the genetic networks regulating cell fate decisions in the inner ear, our studies should not only improve our fundamental understanding of this intricate organ, but also the pathogenesis of congenital forms of deafness.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
Research Project (R01)
Project #
5R01DC006254-10
Application #
8289320
Study Section
Special Emphasis Panel (ZRG1-IFCN-B (03))
Program Officer
Freeman, Nancy
Project Start
2003-08-01
Project End
2013-07-31
Budget Start
2012-08-01
Budget End
2013-07-31
Support Year
10
Fiscal Year
2012
Total Cost
$315,205
Indirect Cost
$111,562
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