Fig. 1.

A schematic model showing diverse roles of FGF signaling in cochlear development. In the E11.5 cochlea, FGF9 expressed in non-sensory epithelium and FGF20 in sensory epithelium signal to FGFR1 and FGFR2 within the surrounding mesenchyme to regulate cochlear progenitor proliferation. Around E14.5–E15.5, FGF20 expressed within the Sox2 prosensory domain signal to FGFR1 expressed in the lateral edge of the prosensory domain to regulate the differentiation of outer hair cells and supporting cells. Around E16.5, FGF8 expressed by inner hair cells signal to FGFR3 in outer hair cells and supporting cells to regulate the pillar cell differentiation.