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 I_KL. In adult mice, I_KL is carried by the K_V1.8 α-subunit, although it is still debatable whether the K_V7.4 α-subunit contributes to I_KL in immature mouse type I hair cells. In this study, no effect of linopirdine, a specific blocker of K_V7 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 K_V7.4 α-subunit transcript, while detecting the transcript for the K_V1.8 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.