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September 6 , 2005
Scienctists link genetic pathway to hearing development

BY Diana Goldman

EScientists are one step closer to understanding the genetic pathway involved in the development of hearing. New research findings, published online in the journal Nature Genetics, detail how sensory hair cells in the ear—the cells largely responsible for hearing—develop unique shapes that enable the
perception of sound.

Located in the spiraled cochlea, the hearing portion of the inner ear, the hair cells transform mechanical vibrations that enter the ear in the form of sound waves into chemical signals, which they then direct to the brain. Ping Chen, assistant professor of cell biology in the School of Medicine, and her colleagues found that the development of cochlea and hair cells is dependent on a genetic pathway called the PCP (planar cell polarity) pathway.

“This basic molecular pathway,” Chen said, “is involved in regulating many other aspects of embryonic development, in addition to the formation of the polarized structure of the auditory sensory organ.”

Although some species, including birds, are capable of regrowing them, mammals lack the ability to naturally regenerate hair cells. Thus individuals born with improperly developed hair cells, or those who lose them through trauma, disease, environmental factors or aging, cannot regain their hearing.

Reports from the National Institutes of Health (NIH) indicate that severe hearing impairment affects 28 million Americans. That number includes approximately 4,000 Americans who suffer each year from sudden deafness, and the roughly 12,000 children born annually with hearing impairment.

Scientists have been optimistic that, by discovering the genes involved in ear development, they could learn the molecular and genetic basis for some forms of deafness and offer hope for some degree of future hearing restoration. For the past two decades, scientists have understood that the unique asymmetrical shape of hair cells was an essential part of their proper function.

However, it was not clear which genes were involved in the development of this polarized shape within the cochlea. By using mouse models, Chen and her research team discovered that the PCP pathway is involved in shaping the cochlea and the sensory hair cells. Mutations within this genetic pathway affect the shape of the cochlea and the polarity of the sensory hair cells that are essential for hearing.

“Finding out which processes are involved in the formation of these polarized cells is an essential, fundamental issue for both developmental and cell biologists,” Chen said.

Chen’s study was done in cooperation with the University of California, San Diego School of Medicine and the House Ear Institute. Other Emory authors included Sharayne Mark, Xiaohui Zhang, Dong Qian, Seung-Jong Yoo, Kristen Radde-Gallwitz, Yanping Zhang and Xi Lin. The research was funded by the NIH and the Woodruff Foundation.

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