SUMMARY
The assembly and maintenance of actin-based mechanosensitive stereocilia in the cochlea is critical for lifelong hearing. Myosin-15 (MYO15) is hypothesized to modulate stereocilia height by trafficking actin regulatory proteins to their tip compartments, where actin polymerization must be precisely controlled during development. We identified a mutation (p.D1647G) in the MYO15 motor-domain that initially maintained trafficking, but caused progressive hearing loss by stunting stereocilia growth, revealing an additional function for MYO15. Consistent with its maintenance of tip trafficking in vivo, purified p.D1647G MYO15 modestly reduced actin-stimulated ATPase activity in vitro. Using ensemble and single-filament fluorescence in vitro assays, we demonstrated that wild-type MYO15 directly accelerated actin filament polymerization by driving nucleation, whilst p.D1647G MYO15 blocked this activity. Collectively, our studies suggest direct actin nucleation by MYO15 at the stereocilia tip is necessary for elongation in vivo, and that this is a primary mechanism disrupted in DFNB3 hereditary human hearing loss.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
References updated to include companion manuscript on bioRxiv (Gong et al) https://doi.org/10.1101/2021.07.09.451843