Fig. 5. Notch activity outside sensory patches can induce ectopic expression of multiple sensory-patch markers. (A) Cryosections of the cochlear duct from an E7 embryo electroporated at stage HH 13 (E2) with N^ICD-IRES-GFP. In the cochlear duct at this stage, TuJ1 staining is a feature of sensory progenitors and nascent hair cells (Molea et al., 1999), as seen in the proximal (upper) part of the basilar papilla. A cluster of N^ICD-IRES-GFP-positive cells is present in the lateral wall of the cochlear duct (arrow), which is normally devoid of hair cells. At high magnification (right panel), the cells of this cluster are seen to express high levels of TuJ1. (B) Whole-mount in-situ hybridisation for Bmp4 (red) and immunostaining for GFP (green) in vestibular epithelia of E5 embryos electroporated at stage HH 13 (E2) with N^ICD-IRES-GFP. The crista expresses Bmp4 in the normal fashion for a sensory patch, while a group of GFP-positive cells express Bmp4 ectopically (arrowheads). (C) Cryosections of the dorsal region of the posterior crista from an E7 embryo electroporated at stage HH 13 (E2) with N^ICD-IRES-GFP. Some of the N^ICD-IRES-GFP-transfected cells have differentiated as ectopic hair cells, labelled for HCS-1 (arrows). These cells were also positive for HCA (not shown). (D,E) Immunostaining of GFP and ß-III tubulin (TuJ1) in transverse paraffin sections of the inner ear from an E9 embryo electroporated at stage HH 13 (E2) with N^ICD-IRES-GFP. Left and right panels in D show the electroporated and non-electroporated sides of the embryo, respectively; nerve cells and neurites penetrating sensory patches are strongly TuJ1-positive (dorsal is up). On the electroporated side, in addition to the utricle, saccule and cochlear duct/basilar papilla, an extra epithelial region with a central lumen can be seen (asterisk). At higher magnification (J), TuJ1-positive nerve fibres from the vestibular ganglion are seen to contact the GFP-positive cells in the ectopic end-organ-like structure. BP, basilar papilla; CG, cochlear ganglion; NT, neural tube; S, saccule; U, utricle; VG, vestibular ganglion.