SEM unravels how hearing develops


Rebecca Pool

Wednesday, January 8, 2020 - 09:30
Image: Electron microscopy images reveals mature hair bundles in the inner ear of mice.
SEM and fluorescence microscopy and have shed new light onto the development of hair bundles, the intricately complex assemblies in the inner ear responsible for hearing.
New results from Dr Jocelyn Krey, at the Oregon Hearing Research Center and the Vollum Institute at Oregon Health & Science University, US, and colleagues, reveal that hearing develops in tandem with form and function.
The latest studies point to how scientists might develop techniques to regenerate hair cells and reverse hearing loss, with results potentially focusing future hearing loss reversal research on early development.
Hair bundles are precisely arranged cellular structures deep within the spiral cavity of the inner ear. 
Together, the structures convert vibrational energy into electrical signals in the brain that translate into the sensation of hearing.
Once lost - whether by loud noise, toxins, disease or ageing - the bundles do not naturally regenerate in people and other mammals.
However, new results from Krey and colleagues provide important clues that may help researchers develop new techniques to regenerate hair cells and reverse hearing loss.
Investigations on mice revealed that the development of hair bundles occurs in a feedback loop, in which form follows function and function drives form.
Image-scanning microscopy with Airyscan detection and SEM allowed the researchers to examine a stereocilia in a hair bundle.
Electron microscopy image shows the classic stair-stepping form of mature hair bundles in the inner ear of mice.
Analyses showed that stereocilia, roughly 100 of which are assembled into a hair bundle, widen simultaneously with the onset of mechanotransduction, the action of converting mechanical signals in the form of sound into electrical signals measured within the brain.
The stereocilia only elongated to their mature lengths after transduction had been established, indicating that form and function are mutually reinforcing.
"We've been looking at these as separate pathways," says Krey. “But in the course of this research, we observed the change in form occurs at the same time as the conversion of mechanical to electrical signals. So we're seeing these happen together, and feeding each other in a way we hadn't seen before."
Krey and colleagues discovered when they examined mice lacking transduction or used a compound to block transduction, the animals did not develop the classic staircase-shaped form of mature hair bundles.
The researchers say the study suggests that new techniques to reverse hearing loss should focus on the critical importance of early development.
"In the future, with the rapid development of gene editing tools like CRISPR, we will be able to turn on genes at will," highlights Professor Peter Barr-Gillespie also from the Oregon Hearing Research Center and senior scientist in the Vollum Institute. "I have no doubt we will be there in 5 or 10 years."
Research is published in Current Biology.
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