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Abstract
Prestin is an integral membrane motor protein located in outer hair cells of the mammalian cochlea. It is responsible for electromotility and required for cochlear amplification. Although prestin works in a cycle-by-cycle mode up to frequencies of at least 79 kHz, it is not known whether or not prestin is required for the extreme high frequencies used by echolocating species. Cetaceans are known to possess a prestin coding gene. However, the expression and distribution pattern of the protein in the cetacean cochlea has not been determined, and the contribution of prestin to echolocation has not yet been resolved. Here we report the expression of the protein prestin in five species of echolocating whales and two species of echolocating bats. Positive labeling in the basolateral membrane of outer hair cells, using three anti-prestin antibodies, was found all along the cochlear spiral in echolocating species. These findings provide morphological evidence that prestin can have a role in cochlear amplification in the basolateral membrane up to 120–180 kHz. In addition, labeling of the cochlea with a combination of anti-prestin, anti-neurofilament, anti-myosin VI and/or phalloidin and DAPI will be useful for detecting potential recent cases of noise-induced hearing loss in stranded cetaceans. This study improves our understanding of the mechanisms involved in sound transduction in echolocating mammals, as well as describing an optimized methodology for detecting cases of hearing loss in stranded marine mammals.
Highlights
The mammalian cochlea contains two types of auditory sensory cells, the inner hair cells (IHCs) and the outer hair cells (OHCs) that are arranged in one single row of IHCs and three rows of OHCs along the organ of Corti, or hearing organ
Positive labeling for prestin was observed in OHCs basolateral membrane in toothed whales (Figures 2–4), as well as in the two species of bats (Parnell’s mustached bat and Seba’s short-tailed bat, Figure 5) all along the cochlear spiral
We only show here the results for harbor porpoise (Figure 2), beluga whale (Figure 3), bottlenose dolphin (Figure 4) and Seba’s short tailed and mustached bat (Figure 5), we obtained the same pattern in the other species
Summary
The mammalian cochlea contains two types of auditory sensory cells, the inner hair cells (IHCs) and the outer hair cells (OHCs) that are arranged in one single row of IHCs and three rows of OHCs along the organ of Corti, or hearing organ. While OHCs amplify the incoming sound stimulation within the cochlea and are essential for the exquisite frequency selectivity and sensitivity, IHCs transduce the acoustic stimulation into the release of glutamate onto the afferent auditory nerve fibers. To achieve these tasks, both hair cell types differ in their molecular and protein composition. Prestin is a member of the membrane transporter superfamily of SLC26A proteins It is expressed on the whole basolateral membrane of OHCs of terrestrial mammals [2, 3] and undergoes a conformational change at a high rate when detecting changes in the membrane potential [(4), reviewed in [5,6,7]]
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