The expression of a7 exhibits distinct spatiotemporal patterning in developing cochlear structures. Previously, we demonstrated the earliest expression of a7 in the developing embryo to be in rhombomeres 3 and 5 of the E9.0 embryo ). Thus, we initiated studies of a7 GFP staining at this time. From E9.5 through approximately E12.5, the otic and cochlear structures did not express detectable a7 GFP ( Fig. 2A and not shown, see . The earliest detected expression of a7 GFP in the cochlear structures was at E13.5 in cells of the spiral prominence (SP; Fig. 2B ). The SP retains a7 GFP expression throughout embryonic and post-natal development (see below). By E14.5 ( Fig. 2C and D) , a7 GFP expression extends to cells in the sensory domain of the lesser epithelial ridge near the site of the presumptive outer hair cells (OHC) and Deiters' cells (Morsli et al. 1998; Lanford et al. 1999; Kiernan et al. 2005a,b) . Light staining of the greater epithelium ridge was also present from E14.5 and thereafter, although this staining is inconsistently observed (Fig. 1B and C and not shown).