(A) PTK7 expression has no effect on JNK activation in vitro. HEK293T cells were transfected either with PTK7, Fz3 or both and assayed for c-Jun phosphorylation. (B–C”) In the middle turn of E17.5 OC (50% cochlear length), pJNK localization (red) in the Ptk7−/− OC (C–C”) was similar to the control (B–B”). Green, phalloidin staining. (D–F) Basal region (15% cochlear length) of E18.5 Ptk7−/− (D), Jnk1−/− (E) and Jnk1−/−; Ptk7−/− (F) cochleae stained with phalloidin (green) and acetylated tubulin (red). Quantifications of bundle orientation of OHC3s are shown to the right. White arrowheads indicate the row of pillar cells; orange arrowheads indicate the OHC3 row. Brackets indicate OHC rows. Lateral is up in all micrographs. Scale bars, B-C’, 6 µm; B”,C”, 2 µm; D–F, 10 µm.