Multi-omics analysis of ion channels expressed by chicken embryo vestibular type I and type II hair cells.

Balance and gaze rely on the rapid and accurate detection and signalling of head movements by vestibular type I and type II hair cells. Signal transduction and transmission involve several types of ion channels, which are acquired progressively during hair cell differentiation and whose identity is known only in part. In the present study, we adopted a multi-omics approach to identify the molecular nature of ion channels expressed by chicken vestibular hair cells between embryonic day 15 and embryonic day 21, the day of hatching, when both type I and II hair cells appear functionally mature. Type I hair cells are characterized by the expression of a low-voltage-activated outward rectifying K+ current, termed IKL. In adult mice, IKL is carried by the KV1.8 α-subunit, although it is still debatable whether the KV7.4 α-subunit contributes to IKL in immature mouse type I hair cells. In this study, no effect of linopirdine, a specific blocker of KV7 channels, was found in either immature or mature type I or II hair cells. Furthermore, whole-organ RT-PCR and transcriptome analysis showed no expression of the KV7.4 α-subunit transcript, while detecting the transcript for the KV1.8 subunit. Its expression in type I and II hair cells was finally confirmed by patch-sequencing experiments. Further analysis of the transcriptomes of individual hair cells revealed the presence of transcripts for several other α and auxiliary subunits of Na+, K+ and Ca2+ channels, which are, presumably, responsible for the ionic currents recorded in both birds and mammals.