Diversity Supplement: Radomski: Impact of a DFNA20 Gamma Actin Mutation in the Mechanotransduction-Dependent Stereocilia Remodeling

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Description

PROJECT SUMMARY/ABSTRACT Inner ear hair cells have actin-filled projections on their apical surface that are highly organized in rows of increasing heights known as hair bundles. These microvilli-like structures are known as stereocilia, and they have mechano-electrical transduction (MET) channels at their tips. Thus, the stereocilia bundles are the sites where sound-induced vibrations and head motions are converted into electrical signals. Velez-Ortega et al. (Elife, 2017) previously showed that the actin cytoskeleton at the stereocilia tips exhibits MET-dependent remodeling, and that a constant entry of calcium through MET channels (which are partially open at rest) was crucial to maintain the stability of auditory stereocilia. The stereocilia actin cytoskeleton is made up of two actin isoforms, beta and gamma, which are produced by two separate genes. It was previously shown that hair cells can develop stereocilia bundles in the absence of either beta or gamma actin, but these hair cells quickly degenerate causing hearing loss (Perrin et al., PLoS Genet, 2010). Therefore, both actin isoforms are required for stereocilia maintenance throughout the lifetime of vertebrates. Here, we hypothesize that a specific mutation in the gamma actin gene that leads to progressive hearing loss in humans and mice causes increased MET-dependent remodeling of the actin cytoskeleton in auditory stereocilia. To test this, Aim 1 will explore MET-dependent changes to the morphology of stereocilia via scanning electron microscopy after the exposure to MET channel blockers or an increase in intracellular calcium buffering with BAPTA-AM in auditory hair cells of mice with the gamma actin mutation and littermate controls. Given that beta and gamma actin exhibit different rates of polymerization and depolymerization in the presence of calcium (Bergeron et al., J Biol Chem, 2010), Aim 2 will evaluate MET-dependent changes to the ratio of both actin isoforms in the stereocilia and cuticular plate of auditory hair cells from the mutant mice and littermate controls using immunohistochemistry and high-resolution confocal microscopy. Results from this supplement might uncover the molecular mechanism that triggers stereocilia degeneration in congenital deafness due to mutations in the gamma actin gene.
StatusActive
Effective start/end date6/7/235/31/28

Funding

  • National Institute on Deafness & Other Communications

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