Fgf3 and Fgf8 dependent and independent transcription factors are required for otic placode specification
2003
The vertebrate inner ear develops from the otic placode, an ectodermal
thickening that forms adjacent to the presumptive hindbrain. Previous studies
have suggested that competent ectodermal cells respond to signals from
adjacent tissues to form the placode. Members of the Fgf family of growth
factors and the Dlx family of transcription factors have been implicated in
this signal-response pathway. We show that compromising Fgf3 and Fgf8
signaling blocks ear development; only a few scattered otic cells form.
Removal of dlx3b, dlx4b and sox9a genes together also blocks
ear development, although a few residual cells form an otic epithelium. These
cells fail to form if sox9b function is also blocked. Combined loss
of Fgf signaling and the three transcription factor genes, dlx3b,
dlx4b and sox9a , also completely eliminates all indications of
otic cells. Expression of sox9a but not dlx3b, dlx4b or
sox9b requires Fgf3 and Fgf8. Our results provide evidence for Fgf3-
and Fgf8-dependent and -independent genetic pathways for otic specification
and support the notion that Fgf3 and Fgf8 function to induce both the otic
placode and the epithelial organization of the otic vesicle.
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