Manipulation of BK channel expression is sufficient to alter auditory hair cell thresholds in larval zebrafish

Abstract

Non-mammalian vertebrates rely on electrical resonance for frequency tuning in auditory hair cells. A key component of the resonance exhibited by these cells is an outward calcium-activated potassium current that flows through large-conductance calciumactivated potassium (BK) channels. Previous work in midshipman fish (Porichthys notatus) has shown that BK expression correlates with seasonal changes in hearing sensitivity and that pharmacologically blocking these channels replicates the natural decreases in sensitivity during the winter non-reproductive season. To test the hypothesis that reducing BK channel function is sufficient to change auditory thresholds in fish, morpholino oligonucleotides (MOs) were used in larval zebrafish (Danio rerio) to alter expression of slo1a and slo1b, duplicate genes coding for the pore-forming α-subunits of BK channels. Following MO injection, microphonic potentials were recorded from the inner ear of larvae. Quantitative real-time PCR was then used to determine the MO effect on slo1a and slo1b expression in these same fish. Knockdown of either slo1a or slo1b resulted in disrupted gene expression and increased auditory thresholds across the same range of frequencies of natural auditory plasticity observed in midshipman. We conclude that interference with the normal expression of individual slo1 genes is sufficient to increase auditory thresholds in zebrafish larvae and that changes in BK channel expression are a direct mechanism for regulation of peripheral hearing sensitivity among fishes.

Neuroendocrine control of seasonal plasticity in the auditory and vocal systems of fish

“…The first step has now been made in furthering our understanding of the ability of BK channel expression changes to shape auditory tuning by targeting slo1 gene expression in larval zebrafish. Consistent with the midshipman work [119], reduction of BK channel expression via use of morpholinos results in higher saccular thresholds than controls [120]. …”

Gene expression underlying enhanced, steroid-dependent auditory sensitivity of hair cell epithelium in a vocal fish

“…Among the ion channels upregulated in reproductive SE were large conductance, calcium-activated potassium (BK) channel transcripts (Table 5 , Additional file 2 ) that have been localized to saccular hair cells in midshipman, shown to vary in abundance across seasons and to regulate auditory sensitivity in midshipman adults and zebrafish larvae [ 12 , 61 ]. Numerous other potassium channel transcripts were also differentially regulated across seasons (Additional file 2 ), which may be necessary for the fine-tuning of auditory thresholds, as demonstrated in other vertebrates [ 62 ] and suggested by our auditory physiology studies of the SE [ 12 ].…”

A profile of auditory‐responsive neurons in the larval zebrafish brain

“…It is unknown whether this pathway is developed in larval zebrafish, as most studies of hearing in zebrafish have looked at juveniles or adults (Cervi, Poling, & Higgs, ; Higgs et al, ; Higgs, Souza, Wilkins, Presson, & Popper, ; Mueller, ; Wang et al, ). The few studies assessing larval hearing have used microphonic potentials to gauge responses in the ears' hair cells (Lu & DeSmidt, ; Rohmann, Tripp, Genova, & Bass, ; Yao et al, ), and this work has shown responses to tones ranging from 20 Hz to 400 Hz as early as 3 days postfertilization (dpf) (Yao et al, ). By 5–6 dpf, larvae startle to tones up to 1,000 Hz, although these responses require extremely strong stimuli (Bhandiwad, Zeddies, Raible, Rubel, & Sisneros, ).…”