Aminoglycoside Damage and Hair Cell Regeneration in the Chicken Utricle
In this study, we present a systematic characterization of hair cell loss and regeneration in the chicken utricle in vivo. A single unilateral surgical delivery of streptomycin caused robust decline of hair cell numbers in striolar as well as extrastriolar regions, which in the striola was detected very early, 6 h post-insult. During the initial 12 h of damage response, we observed global repression of DNA replication, in contrast to the natural, mitotic hair cell production in undamaged control utricles. Regeneration of hair cells in striolar and extrastriolar regions occurred via high rates of asymmetric supporting cell divisions, accompanied by delayed replenishment by symmetric division. While asymmetric division of supporting cells is the main regenerative response to aminoglycoside damage, the detection of symmetric divisions supports the concept of direct transdifferentiation where supporting cells need to be replenished after their phenotypic conversion into new hair cells. Supporting cell divisions appear to be well coordinated because total supporting cell numbers throughout the regenerative process were invariant, despite the initial large-scale loss of hair cells. We conclude that a single ototoxic drug application provides an experimental framework to study the precise onset and timing of utricle hair cell regeneration in vivo. Our findings indicate that initial triggers and signaling events occur already within a few hours after aminoglycoside exposure. Direct transdifferentiation and asymmetric division of supporting cells to generate new hair cells subsequently happen largely in parallel and persist for several days.
Keywordscell cycle EdU inner ear otic S-phase vestibular
A special thank you to Stephanie Jensen (Stanford Veterinary Service Center) for her exceptional help and support in establishing the surgery protocol; to Jialin Shang (University of Washington) for assistance with tissue preparation; to J. David Dickman (Baylor) and Mark Warchol (Washington University) for consulting and enthusing discussions; and to Amanda Janesick, Giovanni H Diaz, and Byron H. Hartman for equally enthusing discussions and comments on the manuscript.
Compliance with Ethical Standards
Animal procedures were approved by the Stanford University Institutional Animal Care and Use Committee (IACUC).
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