The main objective of this research is to determine the identities, interactions and regulation of genes that participate in the development and/or function of the mouse peripheral auditory and vestibular systems. Previously, a gene trap screening strategy was employed to identify and mutate genes expressed in or adjacent to the developing inner ear. One of the genes found in the screen, Dusp6 is expressed in otic mesenchyme and encodes a dual-specificity protein phosphate that inactivates the mitogen-activated protein kinase, ERK, a downstream effectors of Fibroblast Growth Factor (FGF) signaling. FGFs play critical roles in many aspects of otic development and Dusp6 mRNA is not only expressed in many sites of FGF signaling, including otic sites, its expression also depends on FGF signaling. Furthermore, mice that lacks Dusp6 have partially penetrate postnatal lethality associated with small size and craniosynostosis. Affected animals also have ossicle and otic capsule abnormalities. The size and cranial phenotypes are characteristic to different extents of humans and mice with dominant activating mutations in FGF receptors. Hearing impairment is variably associated with the human mutations, but has not been evaluated in the mouse models. Taken together, these data suggest the hypothesis that DUSP6 is a partially redundant negative feedback regulator of FGF signaling during the development of otic and other tissues.
Three Specific Aims are proposed to test the hypothesis. First, the ontogeny and cellular basis of the otic phenotypes of Dusp6 null mutants will be characterized and the status of the inner ear will be determined. Next, expression analysis performed during the critical period for development of the Dusp6 phenotypes will be used to identify candidate FGF signaling pathways mediating those phenotypes. The otic phenotypes of mouse models of Pfeiffer (FGFR1), Apert (FGFR2) and Muenke (FGFR3) Syndromes will be compared with those of Dusp6 mutants and genetic interaction studies will be used to determine which of the FGFR signaling pathways are regulated by DUSP6. Finally, expression analysis will be used to evaluate other ERK phosphates for potential redundancy with Dusp6 and their roles in otic development will be defined genetically. As the mouse ear is very similar to that of humans, we expect that our studies will apply to human ear development and shed light on the genetic mechanisms, which perturbs it, leading to hearing and balance disorders. ? ?
