Figure 8.

Model of Fgf20 function during development. A, Sox2 is expressed in the developing otocyst and is downstream of Notch signaling. Before Fgf20 expression, Sox2 levels are low as cochlear elongation occurs. B, Fgf20 expression acts downstream of Notch signaling and sweeps in a base to apex manner from E13.5 to E14.5. We hypothesize that Fgf20 is spatially expressed in the sensory domain and increases Sox2 expression to specify prosensory precursors in the developing cochlea. C, Fgf20 expression is transient and downregulates around E15. When Sox2 expression reaches a critical level in prosensory progenitors, they are able to differentiate into hair cells and support cells. S, Saccule; GER, greater epithelial ridge.