St. Jude Study Solves Mystery of Mammalian Ears
Editor: Scientists at St. Jude Children's Research Hospital have
answered a long-standing question about mammalian hair cells. Here's their
press release.
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Protein motor in cochlea hair cells dominates the process of sound
amplification in the mammalian ear, while movement of the cilia atop those
cells dominates the response in non-mammals
A 30-year scientific debate over how specialized cells in the inner ear
amplify sound in mammals appears to have been settled more in favor of
bouncing cell bodies rather than vibrating, hair-like cilia, according to
investigators at St. Jude Children's Research Hospital.
The finding could explain why dogs, cats, humans and other mammals have
such sensitive hearing and the ability to discriminate among frequencies.
The work also highlights the importance of basic hearing research in
studies into the causes of deafness. A report on this work appears in the
advanced online issue of "Proceedings of the National Academy of Science."
"Our discovery helps explain the mechanics of hearing and what might be
going wrong in some forms of deafness," said Jian Zuo, Ph.D., the paper's
senior author and associate member of the St. Jude Department of
Developmental Neurobiology. "There are a variety of causes of hearing
loss, including side effects of chemotherapy for cancer."
The long-standing argument centers around outer hair cells, which are
rod- shaped cells that respond to sound waves. Located in the fluid-filled
part of the inner ear called the cochlea, these outer hair cells sport
tufts of hair- like cilia that project into the fluid. The presence of
outer hair cells makes mammalian hearing more than 100 times better than
it would be if the cells were absent.
In mammals, the rod-shaped body of the outer hair cell contracts and
then vibrates in response to the sound waves, amplifying the sound. While
both mammals and non-mammals have cilia on their outer hair cells, only
mammalian outer hair cells have prestin, a protein "motor" that drives
this cellular contraction. This contraction pulls the tufts of cilia
downward, maximizing the force of their vibration. In mammals, both the
cilia and the cell itself vibrate. Thus far the question has been whether
the cilia are the main engine of sound amplification in both mammals and
non-mammals.
In the study, Zuo and his team conducted a complex series of studies
that showed in mammals that the role of somatic mobility driven by prestin
is not simply to modify the response of the outer hair cells' cilia to
incoming sound waves in the cochlea fluid. Instead, somatic motility
itself appears to dominate the amplification process in the mammalian
cochlea, while the cilia dominate amplification in non-mammals.
Other authors of this study include Jiangang Gao, Xudong Wu and Manish
Patel (St. Jude); Xiang Wang, Shuping Jia and David He (Creighton
University, Omaha, Neb.); Sal Aguinaga, Kristin Huynh, Keiji Matsuda, Jing
Zheng, MaryAnn Cheatham and Peter Dallos (Northwestern University,
Evanston, Ill.).
This work was supported in part by ALSAC, The Hugh Knowles Center and
the National Institutes of Health.
St. Jude Children's Research Hospital
St. Jude Children's Research Hospital is internationally recognized for
its pioneering work in finding cures and saving children with cancer and
other catastrophic diseases. Founded by late entertainer Danny Thomas and
based in Memphis, Tenn., St. Jude freely shares its discoveries with
scientific and medical communities around the world. No family ever pays
for treatments not covered by insurance, and families without insurance
are never asked to pay. St. Jude is financially supported by ALSAC, its
fundraising organization. For more information, please visit http://www.stjude.org.
