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First published online 17 September 2008
doi: 10.1242/dev.026674

Development 135, 3415-3424 (2008)
Published by The Company of Biologists 2008
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Progressive restriction of otic fate: the role of FGF and Wnt in resolving inner ear potential

Sabine Freter1,2, Yuko Muta1, Siu-Shan Mak1, Silke Rinkwitz2 and Raj K. Ladher1,*

1 Laboratory for Sensory Development, RIKEN Center for Developmental Biology, 2-2-3 Minatojima-Minamimachi, Chuo-ku, Kobe 650-0047, Japan.
2 Neurogenetics Group, Carl of Ossietzky University, Oldenburg 26111, Germany.

* Author for correspondence (e-mail: raj-ladher{at}cdb.riken.jp)

Accepted 1 September 2008

The development of the vertebrate inner ear is an emergent process. Its progression from a relatively simple disk of thickened epithelium within head ectoderm into a complex organ capable of sensing sound and balance is controlled by sequential molecular and cellular interactions. Fibroblast growth factor (FGF) and Wnt signals emanating from mesoderm and neural ectoderm have been shown to direct inner ear fate. However, the role of these multiple signals during inner ear induction is unclear. We demonstrate that the action of the FGFs and Wnts is sequential, and that their roles support a model of hierarchical fate decisions that progressively restrict the developmental potential of the ectoderm until otic commitment. We show that signalling by Fgf3 and Fgf19 is required to initiate a proliferative progenitor region that is a precursor to both the inner ear and the neurogenic epibranchial placodes. Significantly, we find that only after FGF action is attenuated can the subsequent action of Wnt signalling allow otic differentiation to proceed. In addition, gain and loss of function of Wnt-signalling components show a role for this signalling in repressing epibranchial fate. This interplay of signalling factors ensures the correct and ordered differentiation of both inner ear and epibranchial systems.

Key words: Inner ear, Epibranchial, Sensory placode, Fibroblast growth factor, Wnt






© The Company of Biologists Ltd 2008