Fig. 5. Hair cells are produced early and in excess in the Delta1 conditional knockout cochlea. Confocal optical sections of whole mounts of cochleas at E17.5. (A) In the apex of the wild-type mouse cochlea, stained with phalloidin, no hair cells are visible as yet. (B,B') In the apex of the cochlea of a Delta1 conditional knockout littermate, hair cells are already plainly visible and present in excess (arrow; B' shows detail). (C) Middle region of wild-type cochlea shows a narrow band of Jag1 staining, corresponding to the future sensory patch. (D) Delta1 conditional knockout shows a wider band of Jag1 staining, corresponding to the enlarged and precocious sensory patch, and suggesting an increase in the numbers of supporting cells (which are Jag1-positive) as well as hair cells (which are not). (E,F) A milder excess of hair cells is seen in the middle and basal parts of the Delta1 conditional knockout cochlea (F), with one extra row of outer hair cells and many more inner hair cells than in the littermate control (E). (G,H) Confocal optical sections of the middle region of the cochlea in a plane passing through the bodies of the supporting cells at a deeper level than the hair cells. The membranes of the supporting cells are stained with Jag1 antibody, and the mutant has slightly more of these cells per unit length of cochlea.