Sustained cadherin 23 expression in young and adult cochlea of normal and hearing-impaired mice.

Cadherin 23 encodes a single-pass transmembrane protein with 27 extracellular cadherin-domains and localizes to stereocilia where it functions as an inter-stereocilia link. Cadherin 23-deficient mice show congenital deafness in combination with circling behavior as a result of organizational defects in the stereocilia hair bundle; common inbred mouse strains carrying the hypomorphic Cdh23(753A) allele are highly susceptible to sensorineural hearing loss. Here, we show that an antibody (N1086) directed against the intracellular carboxyterminus reacts specifically with cadherin 23 and detects with high sensitivity the isoform devoid of the peptide encoded by exon 68 (CDH23Delta68). Cochlea, vestibule, eye, brain and testis produce the CDH23Delta68 isoform in abundance and form moieties with different molecular weight due to variations in glycosylation content. In the cochlea, CDH23Delta68 expression is highest at postnatal day 1 (P1) and P7; expression is down regulated through P14 and P21 and persists at a low steady-state level throughout adulthood (P160). Furthermore, CDH23Delta68 expression levels in young and adult cochlea are similar among normal and hearing deficient strains (C3HeB/FeJ, C57BL/6J and BUB/BnJ). Finally, by immunofluorescence using an antibody (Pb240) specific for ectodomain 14, we show that cadherin 23 localizes to stereocilia during hair bundle development in late gestation and early postnatal days. Cadherin 23-specific labeling becomes weaker as the hair bundle matures but faint labeling concentrated near the top of stereocilia is still detectable at P35. No labeling of cochlea stereocilia was observed with N1086. In conclusion, our data describe a cadherin 23-specific antibody with high affinity to the CDH23Delta68 isoform, reveal a dynamic cochlea expression and localization profile and show sustained cadherin 23 levels in adult cochlea of normal and hearing-impaired mice.