Fig. 3. Targeted deletion of Fgf8 leads to a disruption in pillar cell development. (A) Lumenal suface of the OC from a littermate control at E18.5. Hair cell stereocilia and cell boundaries labeled with phalloidin (Phal, green) and PCs labeled with anti-p75^ntr (red). The row of IHCs and first row of OHCs (OHC1) are indicated. (B) Lumenal surface from an Fgf8^2,3n/flox; Foxg1^cre/+ mouse. Note the disrupted growth of the PCs and close approximation of the IHCs to OHCs. (C,D) Red channels from A and B, respectively, illustrating PC morphology. (D) PCs are missing or underdeveloped in Fgf8^2,3n/flox; Foxg1^cre/+ mice. (E) Cross-section through a control OC at E18.5 showing two PCs (asterisks) extending a lumenal projection between the IHC and first row OHC (numbered). Magnification of the boxed region (inset) illustrates the morphology of the projection, with a red line to indicate the lateral boundary of the IHC and a green line to indicate the medial boundary of the first row OHC. (F) Cross-section through an Fgf8^2,3n/flox; Foxg1^cre/+ OC illustrating a stunted lumenal PC projection (magnified in inset). (G) Average ITO distances (see text for details), as a measure of the degree of PC development, in control and Fgf8^2,3n/flox; Foxg1^cre/+ cochleae. Error bars indicate s.e.m. ^*, P<0.001. (H) In situ hybridization using a probe specific to the deleted region of Fgf8 in control and Fgf8^2,3n/flox; Foxg1^cre/+ cochleae. Arrowhead points to the row of labeled IHCs in the control; no such labeling is apparent in the Fgf8^2,3n/flox; Foxg1^cre/+ cochlea. Both cochleae have been intentionally over-reacted to ensure complete detection of Fgf8 expression. Scale bars: 20 µm in A-D; 10 µm in E,F.