Fig. 3. Notch activity within a sensory patch acts cell-autonomously to inhibit hair-cell differentiation. (A) Whole-mount immunostaining in the utricle of an E9 embryo electroporated at stage HH 17 (E2.5) with the N^ICD-IRES-GFP construct. In this specimen, GFP-positive cells are clustered and form a patch completely devoid of hair cells. Around the GFP-positive region, hair cells differentiate normally. (B) Whole-mount immunostaining in the saccule of an E9 embryo electroporated at stage HH 17 (E2.5) with N^ICD-IRES-GFP construct. In this specimen, GFP-positive cells are mixed with GFP-negative (untransfected) cells. Two different GFP-positive regions are outlined (1, 2). In both regions, hair cell density is diminished compared with adjacent regions. In region 2, however, some HCA-positive cells (hair cells) can be seen in the central part of the transfected patch. (C) Careful examination of region 2 at higher magnification, and in z-series of optical sections (Z1 to Z4, from the apical surface of the epithelium to deeper planes) reveals that these HCA positive cells are all GFP-negative (arrowheads); only the cells transfected with the N^ICD-IRES-GFP construct are inhibited from differentiating as hair cells.