Fig. 3. The hair cells in the cochlea of the Jag1 conditional knockout have characteristics of inner hair cells. Confocal optical sections of whole mounts of the middle region of the cochlea at E17.5 are shown. (A) Control, stained with calretinin antibody. At this stage the inner hair cells (arrow) but not outer hair cells are calretinin-positive, and so are occasional inner pillar cells (arrowheads). (B) Jag1 conditional knockout cochlea. All the hair cells produced are stained for calretinin, as well as some adjacent cells (possibly inner pillar cells). (C) Control cochlea, stained with the nuclear dye DAPI and with phalloidin. A row of inner pillar cells with characteristic rectangular profiles can be seen in the wild type between the rows of inner (IHC) and outer hair cells (OHC). (D) In the Jag1 conditional knockout, cells with this morphology can be seen outside the disorganised rows of hair cells. The cells appear larger than in C merely because the plane of section is slightly different.