Misregulation of intercellular signaling disrupts inner ear morphogenesis in human subjects and animal models, leading to hearing and balance disorders. Normal morphogenesis of the inner ear's membranous labyrinth requires temporal integration of regional and cell fate specification with changes in cell behavior. Past work has begun to identify changes in otocyst gene expression downstream of signals, including BMP, FGF and SHH, but much less is known about the cell behaviors driving morphogenesis and how these behaviors are coordinated temporally with progressive restriction of cell fates to generate the mature vestibular and cochlear compartments. Using temporally and spatially controlled loss- and gain-of-function in chick and mouse embryos, we propose to test the general hypothesis that BMP/TGFss, FGF and HH signaling are integrated to regulate otocyst regional and cell fate specification and cell behavior to initiate normal morphogenesis of the vestibular and cochlear compartments of the developing membranous labyrinth. Our preliminary data provide proof-of-principle for our approach. In control chick embryos, we identified a columnar-to-squamous cell shape change in the dorsolateral otocyst epithelium that occurs concomitant with thinning and expansion to form the primordial canal pouch. Spatiotemporally controlled loss- and gain-of-function experiments showed that BMP/SMAD signaling is both necessary and sufficient for this cell shape change. In addition, similar chick misexpression experiments revealed a common intersection point regulating BMP/SHH signaling during early otocyst dorsoventral patterning and morphogenesis. In mouse, we found that otocyst-derived FGF3 and FGF10 signals, in addition to their well-known roles in vestibular morphogenesis, are required to initiate cochlear morphogenesis. However, these epithelial signals are not required for early otocyst regional patterning, which is normal in FGF-deficient otocysts. Therefore, we propose to test the specific hypotheses that 1) temporal integration of BMP/TGFss, FGF and HH signaling controls three key early steps of otocyst morphogenesis: primordial canal outgrowth, subdivision of the primordium into vertical and lateral canal pouches and initial cochlear outgrowth, and 2) that such signaling coordinates otocyst regional and/or cell fate specification with changes in relevant cell behaviors. Our proposal takes advantage of the unique expertise of a team of established investigators using state-of-the-art molecular genetic and embryologic techniques in two animal models with complementary strengths that will illuminate important differences and similarities in mechanisms driving key morphogenetic steps downstream of growth factor signaling. This will advance the field by providing a novel understanding of how signaling pathways are integrated to control initiation of vestibular and cochlear morphogenesis, and how these signals coordinate specification of cell fate and changes in cell behavior to initiate and sculpt a normally functioning membranous labyrinth. Such information provides an essential foundation for understanding and ultimately preventing human hearing loss.
Hearing loss is the most common human sensory deficit and can be caused by mutations that change the levels of growth factor signaling during development. We are using mice and chick embryos as experimental models to study the roles of growth factor signaling during inner ear formation. Our studies are expected to contribute knowledge that will likely be useful for developing new approaches for preventing, diagnosing, and treating hearing loss.
|Ohta, Sho; Schoenwolf, Gary C (2018) Dorsoventral differences in cAMP levels and correlated changes in the subcellular distribution of the PKA catalytic domain, provide further evidence that PKA signaling coordinates dorsoventral patterning of the otocyst. Dev Growth Differ 60:431-441|
|Ohta, Sho; Schoenwolf, Gary C (2018) Hearing crosstalk: the molecular conversation orchestrating inner ear dorsoventral patterning. Wiley Interdiscip Rev Dev Biol 7:|
|Olaya-Sánchez, Daniel; Sánchez-Guardado, Luis Óscar; Ohta, Sho et al. (2017) Fgf3 and Fgf16 expression patterns define spatial and temporal domains in the developing chick inner ear. Brain Struct Funct 222:131-149|
|Nishitani, Allison M; Ohta, Sho; Yung, Andrea R et al. (2017) Distinct functions for netrin 1 in chicken and murine semicircular canal morphogenesis. Development 144:3349-3360|
|Ohta, Sho; Wang, Baolin; Mansour, Suzanne L et al. (2016) SHH ventralizes the otocyst by maintaining basal PKA activity and regulating GLI3 signaling. Dev Biol 420:100-109|
|Hung, Irene H; Schoenwolf, Gary C; Lewandoski, Mark et al. (2016) A combined series of Fgf9 and Fgf18 mutant alleles identifies unique and redundant roles in skeletal development. Dev Biol 411:72-84|
|Ohta, Sho; Wang, Baolin; Mansour, Suzanne L et al. (2016) BMP regulates regional gene expression in the dorsal otocyst through canonical and non-canonical intracellular pathways. Development 143:2228-37|
|Urness, Lisa D; Wang, Xiaofen; Shibata, Shumei et al. (2015) Fgf10 is required for specification of non-sensory regions of the cochlear epithelium. Dev Biol 400:59-71|
|Jackson, Abigail; Kasah, Sahrunizam; Mansour, Suzanne L et al. (2014) Endoderm-specific deletion of Tbx1 reveals an FGF-independent role for Tbx1 in pharyngeal apparatus morphogenesis. Dev Dyn 243:1143-51|
|Ohta, Sho; Mansour, Suzanne L; Schoenwolf, Gary C (2010) BMP/SMAD signaling regulates the cell behaviors that drive the initial dorsal-specific regional morphogenesis of the otocyst. Dev Biol 347:369-81|
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