Lack of FGF20 results in undifferentiated lateral compartment cells.

(A) Co-immunostaining of E-Cadherin and Myo6 showing that E-Cadherin stains lateral compartment cells in Fgf20^βGal/+ cochlea (A, upper). In Fgf20^βGal/βGal cochlea, E-Cadherin stains all lateral compartment cells including cells localized in the region between sensory patches (A, lower, arrow). (B) Co-immunostaining of Sox2 and phalloidin showing that Sox2 labels supporting cells in Fgf20^βGal/+ cochlea (B, upper). In Fgf20^βGal/βGal cochlea, the region between patches was marked by strong Sox2 staining (B, lower, arrows). (C) Co-immunostaining of p27 and phalloidin showing that p27 stains supporting cells in Fgf20^βGal/+cochlea (C, upper). In Fgf20^βGal/βGal cochlea, the region between patches was marked by strong p27 staining (C, lower, arrows). (D) Co-immunostaining of Sox2 and Prox1 of Fgf20^βGal/βGal explants treated with or without FGF9. Without FGF9 treatment (left), Sox2+/Prox1− cells were localized in the region between sensory patches (arrows). Treatment of Fgf20^βGal/βGal explants with FGF9 induced Sox2+/Prox1− cells to express Prox1 (right).