The senses of hearing and balance are mediated by the hair cells of the inner ear, sensory epithelial cells with specialized architectures optimized for the detection of movement. Hair cells detect motion via the mechanical deflection of a kinocilium and stereocilia bundle located at one edge of the apical cell surface. Only movements of the bundle towards the kinocilium generate an excitatory response. Consequently the proper polarization of the stereocilia bundle and coordination of bundle polarity between adjacent cells is necessary for accurate vestibular function. Auditory hair cells within the organ of Corti detect sound in a similar fashion and the bundle polarity of adjacent cells is also coordinated. This type of organization is called planar cell polarity (PCP) and has been described in a number of different tissues and species. Moreover, hair cells within the vestibular maculae are further organized into two groups with opposite bundle polarities patterned about an abrupt line of polarity reversal (LPR). This increases the range of detectable motion and sensitivity to motion in a single direction. However, despite the likely importance of stereocilia bundle polarity and hair cell patterning for vestibular function it is not known how bundle polarization is initiated and coordinated within the sensory epithelia. Within this research proposal the cellular mechanisms guiding the polarization of the stereocilia bundle and orientation of hair cells will be evaluated using a combination of transgenic, mutant and knockout mice. [The function of the essential polarity gene van gogh-like2 (vangl2) will be determined by analyzing hair cell PCP using a novel vangl2 knockout mouse (vangl2TMS). These results will be compared to the vangl2 mutant line looptail which has become a reference for inner ear PCP mutant analysis despite having semi-dominant phenotypic characteristics.] Next the cellular mechanism of Vangl2 function in coordinating bundle polarity between adjacent cells will be tested through the production and analysis of a vangl2 conditional knockout line (vangl2floxedATG) in which the polarity gene is deleted in a cell-specific manner. These experiments will determine whether polarity cues are propagated from cell to cell and whether vangl2 is necessary for initiating bundle polarity or maintaining bundle polarity during inner ear morphogenesis. In addition, other vangl2 mutations result in embryonic lethality and this will be avoided be generating ear-specific vangl2floxedATG conditional knockouts. These mice will enable a series of behavioral experiments to examine the effects of hair cell misorientation on vestibular and auditory function.

Public Health Relevance

Project Narrative The proper morphogenesis and organization of specialized inner ear sensory receptors called hair cells is necessary for hearing and balance, and the loss of these cells is the primary basis of age-related deafness and balance disorders. This project is designed to determine how hair cells are oriented and patterned within the within the vestibular maculae of the utricle and saccule. Understanding these events should reveal the basis of some forms of vestibular dysfunction and will define critical parameters that must be met by therapeutic approaches that rely upon introducing replacement hair cells into the mature inner ear.

National Institute of Health (NIH)
National Institute on Deafness and Other Communication Disorders (NIDCD)
Small Research Grants (R03)
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Special Emphasis Panel (ZDC1-SRB-Y (59))
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Cyr, Janet
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Johns Hopkins University
Schools of Medicine
United States
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