The remodeling of the sensory cell region of the cochlear structure between E16.5 and E18.5 as suggested by the progression in changing a7 GFP expression was examined further. Through E16.5, all otic structures exhibit a similar a7 GFP expression pattern (Fig. 3A) . This was not the case in the E18.5 cochlear structure where the loss of a7 GFP expression by OHC and Deiters' cells and acquisition of staining by Hensen's cells was first observed in the most basal structures and it then appears in the more apical structures successive developmental stages ( Fig. 3B and C and not shown). This generates a striking contrast in a7 GFP expression between cochlear structures at the apex relative to the base with intermediary turns, exhibiting the progressive stages of this change in a7 GFP expression (Fig. 3B ). By P4, this gradient was not evident (not shown) and the mature a7 GFP expression pattern first observed in the E18.5 basal cochlear structures was present across the entire structure. In Fig. 3D , a diagram depicts the remodeling of a7 GFP expression seen in the E18.5 developing cochlear structure.