AbstractThe development of the mammalian inner ear involves a complex series of cell‐cell and cell‐extracellular matrix interactions. These interactions are likely to be mediated by families of adhesion molecules, including the integrins. We have studied the expression of three integrin subunits known to be expressed on epithelia in a number of tissues (namely, α3, α6, and β4) during the development of the murine inner ear. At E10.5, both α3 and α6 were expressed in the epithelial layers of the otocyst. The expression of α6 was concentrated in an anterioventral region of the epithelium and in a proportion of the cells forming the cochlear‐vestibular and facial ganglia. By E12.5, α6 showed a more restricted expression, confined mainly to the pro‐sensory epithelia and the neural processes from the cochlear‐vestibular ganglion. In contrast, α3 was expressed in epithelia adjacent to the pro‐sensory areas. This reciprocal expression pattern was maintained until birth. Between birth and P6, a switch in expression occurred such that α3 was upregulated and α6 was downregulated in the sensory epithelia of both the auditory and vestibular systems. At this stage, α3 was expressed in all the epithelia lining the scala media, thus defining the endolymph compartment. The expression of β4 was restricted to epithelial/mesenchymal borders throughout the developmental stages studied, suggesting that α6 expression observed within the epithelium and neuronal tissue was α6β1. The early expression and changing pattern of α3 and α6 integrins during development of the mammalian inner ear suggests that they may be involved in the molecular processes that define epithelial boundaries and guide sensory innervation. J. Comp. Neurol. 445:122–132, 2002. © 2002 Wiley‐Liss, Inc.