Gap junctional coupling is essential for epithelial repair in the avian cochlea.

The loss of auditory hair cells triggers repair responses within the population of nonsensory supporting cells. When hair cells are irreversibly lost from the mammalian cochlea, supporting cells expand to fill the resulting lesions in the sensory epithelium, an initial repair process that is dependent on gap junctional intercellular communication (GJIC). In the chicken cochlea (the basilar papilla or BP), dying hair cells are extruded from the epithelium and supporting cells expand to fill the lesions and then replace hair cells via mitotic and/or conversion mechanisms.

Gap junctions and connexins in the inner ear: their roles in homeostasis and deafness.

Purpose Of Review: Mutations in GJB2 and GJB6, the genes encoding the gap-junction proteins connexin 26 and connexin 30, are the most common cause of autosomal recessive nonsyndromic deafness in many populations across the world. In this review, we discuss current ideas about the roles of gap junctions in the inner ear and the implications of connexin mutations on auditory function.

Recent Findings: In recent years, a complex picture of the roles of gap junctions in cochlear physiology emerged.

Prolonged maturation of cochlear function in the barn owl after hatching.

Cochlear microphonics (CMs), which represent the electrical activity of hair cells, and compound action potentials (CAPs), which represent the activity of the auditory nerve, were recorded from the round window of the inner ear, in owlets aged between 5 and 97 days posthatching, i.e., from soon after hatching to beyond fledgling.

Molecular and functional characterization of gap junctions in the avian inner ear.

To analyze the fundamental role of gap junctions in the vertebrate inner ear, we examined molecular and functional characteristics of gap junctional communication (GJC) in the auditory and vestibular system of the chicken. By screening inner ear tissues for connexin isoforms using degenerate reverse transcription-PCR, we identified, in addition to chicken Cx43 (cCx43) and the inner-ear-specific cCx30, an as yet uncharacterized connexin predicted to be the ortholog of the mammalian Cx26. In situ hybridization indicated that cCx30 and cCx26 transcripts were both widely expressed in the cochlear duct and utricle in an overlapping pattern, suggesting coexpression of these isoforms similar to that in the mammalian inner ear.

Connexins and gap junctions in the inner ear.

Mutations in the genes for three different isotypes of the gap junction channel protein connexin are associated with deafness. This indicates an important role for gap junctions in auditory function and provides an opportunity to explore structure-function relationships in the connexin molecule. We have been examining the distribution of gap junctions and the pattern of connexin expression in the mature inner ear and during development, and the effect of specific mutations on the processing and functionality of the expressed connexin proteins in an in vitro system.