Nav: Home

Surprising discovery links sour taste to the inner ear's ability to sense balance

January 25, 2018

Scientists at the USC Dornsife College of Letters, Arts and Sciences have discovered an entirely new class of ion channels. These channels let protons (H+ ions) into cells, are important in the inner ear for balance, and are present in the taste cells that respond to sour flavors.

The findings were published Thursday, Jan. 25 in Science.

Protons control whether a solution is acidic or basic. They set pH. Not surprisingly, protons do not cross cell membranes; they must be transported across the membrane through special proteins like ion channels.

Although a gene encoding an ion channel that lets protons leave cells has been identified, whether one gene or several genes were necessary to form an ion channel that lets protons into cells was unknown. Now, research into sour taste has identified the otopetrin family of genes as encoding proton-conducting ion channels.

This gene family was originally identified as important for balance: mice with mutations in otopetrin 1 (Otop1) are called tilted (tlt) because they cannot right themselves. The function of the encoded protein and why mutations in the gene cause a vestibular defect are unknown. But while studying taste perception, a group led by Emily Liman, USC Dornsife professor of biological sciences, discovered that Otop1 encodes a proton channel, providing hints as to how otopetrin1 contributes to inner ear function and balance.

Because sour taste is the perception of acidic substances, which have a high concentration of protons, Liman predicted that sour taste cells have an ion channel that responds to or transports protons. Indeed, eight years ago, her lab used biophysical approaches to show that protons enter taste cells through a specialized proton channel in the cell membrane. The gene encoding this channel and the structural properties of the proton channel were unknown.

Liman's lab used a molecular genetics technique called RNAseq to identify which genes were specifically expressed in sour taste cells and not other types of taste cells. Graduate student Yu-Hsiang Tu then tested candidate genes one-by-one until he found one that produced a proton-conducting protein when introduced into cells that did not have any proton-conducting channels.

After Yu-Hsiang had tested more than three dozen candidates, Liman had all but given up. "When Yu-Hsiang called me in to the lab and showed me the otopetrin data, I could not believe we had finally found it," Liman said. "We had been looking for so many years."

In addition to Otop1, there are two other related genes in vertebrates (Otop2 and Otop3), and this gene family is represented in the fruit fly Drosophila melanogaster. Otopetrins are structurally different from all other ion channels, and all of the otopetrins form proton channels, suggesting that these proton-conducting channels are evolutionarily conserved. Each of the otopetrins has a distinct distribution in many tissues, including the tongue, ear, eye, nerves, reproductive organs, and digestive tract.

In the vestibular system, Otop1 is necessary for the formation and function of structures called otoconia, which are calcium carbonate crystals that sense gravity and acceleration. The investigators speculate that the otopetrins maintain the pH appropriate for formation of otoconia and that the defect in the tlt mice is due to a dysregulation of pH.

In the taste system, otopetrins may be involved in sensing acids as part of sour taste perception. The function of these proton channels in other tissues is unknown.

"We never in a million years expected that the molecule that we were looking for in taste cells would also be found in the vestibular system," Liman said. "This highlights the power of basic or fundamental research."
-end-
In addition to Liman and Tu, the authors of the study were Alexander J. Cooper, Bochuan Teng, Rui B. Chang, Daniel J. Artiga, Heather N. Turner, Eric M. Mulhall, Wenlei Ye, Andrew D. Smith.

The research was funded by the U.S. National Institutes of Health, grant no. 5R01DC013741 awarded to Emily Liman in 2015 for $2,200,032 and grant no. 5R21DC012747 in 2012 for $622,842.

About the USC Dornsife College

The USC Dana and David Dornsife College of Letters, Arts and Science is the heart of USC, with more than 900 faculty and 10,000 undergraduate and graduate students, 30 academic departments and 36 centers and institutes.

University of Southern California

Related Genes Articles:

Insomnia genes found
An international team of researchers has found, for the first time, seven risk genes for insomnia.
Genes affecting our communication skills relate to genes for psychiatric disorder
By screening thousands of individuals, an international team led by researchers of the Max Planck Institute for Psycholinguistics, the University of Bristol, the Broad Institute and the iPSYCH consortium has provided new insights into the relationship between genes that confer risk for autism or schizophrenia and genes that influence our ability to communicate during the course of development.
The fate of Neanderthal genes
The Neanderthals disappeared about 30,000 years ago, but little pieces of them live on in the form of DNA sequences scattered through the modern human genome.
Face shape is in the genes
Many of the characteristics that make up a person's face, such as nose size and face width, stem from specific genetic variations, reports John Shaffer of the University of Pittsburgh in Pennsylvania, and colleagues, in a study published on Aug.
Study finds hundreds of genes and genetic codes that regulate genes tied to alcoholism
Using rats carefully bred to either drink large amounts of alcohol or to spurn it, researchers at Indiana and Purdue universities have identified hundreds of genes that appear to play a role in increasing the desire to drink alcohol.
Reading between the genes
For a long time dismissed as 'junk DNA,' we now know that also the regions between the genes fulfill vital functions.
The silence of the genes
Research led by Dr. Keiji Tanimoto from the University of Tsukuba, Japan, has brought us closer to understanding the mechanisms underlying the phenomenon of genomic imprinting.
Why some genes are highly expressed
The DNA in our cells is folded into millions of small packets, like beads on a string, allowing our two-meter linear DNA genomes to fit into a nucleus of only about 0.01 mm in diameter.
Activating genes on demand
A new approach developed by Harvard geneticist George Church, Ph.D., can help uncover how tandem gene circuits dictate life processes, such as the healthy development of tissue or the triggering of a particular disease, and can also be used for directing precision stem cell differentiation for regenerative medicine and growing organ transplants.
Controlling genes with light
Researchers at Duke University have demonstrated a new way to activate genes with light, allowing precisely controlled and targeted genetic studies and applications.

Related Genes Reading:

Lewin's GENES XII
by Jocelyn E. Krebs (Author), Elliott S. Goldstein (Author), Stephen T. Kilpatrick (Author)

The Gene: An Intimate History
by Siddhartha Mukherjee (Author)

Dirty Genes: A Breakthrough Program to Treat the Root Cause of Illness and Optimize Your Health
by Ben Lynch ND. (Author)

The Genie in Your Genes: Epigenetic Medicine and the New Biology of Intention
by Dawson Church (Author)

Genetics: From Genes to Genomes
by Leland Hartwell Dr. (Author), Michael L. Goldberg Professor Dr. (Author), Janice Fischer (Author), Leroy Hood Dr. (Author)

Genetics: From Genes to Genomes, 5th edition
by Leland H. Hartwell (Author), Michael L. Goldberg (Author), Janice A. Fischer (Author), Leroy Hood (Author), Charles F. Aquadro (Author)

The Stranger in My Genes: A Memoir
by New England Historic Genealogical Society

The Society of Genes
by Itai Yanai (Author), Martin Lercher (Author)

Gen Z: The Culture, Beliefs and Motivations Shaping the Next Generation
by Barna Group (Author)

Super Genes: Unlock the Astonishing Power of Your DNA for Optimum Health and Well-Being
by Deepak Chopra M.D. (Author), Rudolph E. Tanzi Ph.D. (Author)

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Bias And Perception
How does bias distort our thinking, our listening, our beliefs... and even our search results? How can we fight it? This hour, TED speakers explore ideas about the unconscious biases that shape us. Guests include writer and broadcaster Yassmin Abdel-Magied, climatologist J. Marshall Shepherd, journalist Andreas Ekström, and experimental psychologist Tony Salvador.
Now Playing: Science for the People

#513 Dinosaur Tails
This week: dinosaurs! We're discussing dinosaur tails, bipedalism, paleontology public outreach, dinosaur MOOCs, and other neat dinosaur related things with Dr. Scott Persons from the University of Alberta, who is also the author of the book "Dinosaurs of the Alberta Badlands".