Expression of the connexin43-and connexin45-encoding genes in the developing and mature mouse inner ear

Intercellular communication through gap junctions is crucial for proper functioning of the inner ear. Indeed, mutations in several connexin genes have been found to cause hearing loss. In the inner ear, only the cell distributions of connexin30 and connexin26 have been well documented. We took advantage of the lacZ reporter gene in Cx43 and Cx45 knock-out mice to study the expression of the connexin43 and connexin45 genes during the inner ear development. Expression of Cx43 and Cx45 in the inner ear was detected from embryonic days 15.5 and 17.5, respectively. Until the 1st week of life, Cx43 was highly expressed in the connective tissues, and weakly expressed in the immature sensory epithelium of the cochlea. From postnatal day 8, however, Cx43 was almost exclusively expressed in the bone of the otic capsule. During embryogenesis, Cx45 was expressed in epithelial and connective inner ear tissues. From birth onwards, Cx45 expression could be detected in some inner ear capillaries. Vascular expression thereafter increased and persisted in the adult. In the mature inner ear, Cx45 was expressed in the entire vasculature. These results indicate that connexin43 and connexin45 play a role in the otic capsule bone and the inner ear vascular system, respectively.