Fig. 6. Fgf17 inhibits development of outer hair cells and Deiters cells. (A,B) Low-magnification view of p75^ntr expression (red) in (A) a control explant and (B) in an explant treated with 300 ng/ml Fgf17 for 5 days. (C) High-magnification of a control OC. Cell surfaces and stereocilia are labeled with phalloidin (green), p75^ntr-positive PCs in red. (D) High magnification of an Fgf17-treated explant. IHCs are present, but the OHC region appears undifferentiated and is positive for p75^ntr (red). (E-F') Lumenal views of the OC from E14 mouse cochlear explants after 6 DIV. (E) PCs, positive for both p75^ntr (green) and ß-actin (red), appear as a yellow line between IHCs and OHCs [myosin VI (Myo6) in blue]. (E') ß-actin alone. (F) OHC numbers are reduced and p75^ntr expression is increased (green) in the OHC region in Fgf17-treated explants. At the extreme lateral edge, a second band of ß-actin expression (red in F, arrow) appears. (F') ß-actin alone. (G) An Fgf17-treated explant with few OHCs (numbered). Most cells in the OHC region are positive for p75^ntr (red). (G') p75^ntr expression alone. OHC positions are indicated with numbered circles. (H-I') High magnification of individual examples of OHCs from Fgf17-treated explants. Stereocilia and cell boundaries are indicated in green, p75^ntr in red. Asterisks in G-I' indicate cells adjacent to OHCs that have downregulated expression of p75^ntr. Scale bars: 200 µm in A,B; 50 µm in C,D; 20 µm in E-F'; 25 µm in G,G'; 20 µm in H-I'.