by Vivienne Baillie Gerritsen

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For many, December - or the end of it - tends to be a time of year when keeping your balance becomes an ordeal. The cause: a seasonal numbing of the senses due to an exaggerated consumption of alcohol. Alcohol, however, is not the only substance which can play tricks on our sense of balance. An altered architecture of our inner ear can too. The intricate machinery that we carry around in our inner ear not only helps us to perceive sound but is also responsible for our sense of movement. Those who suffer from sea-sickness know all too well what this means.

Very small regions of our inner ear are capable of detecting both gravity and acceleration, two forces we spend our time dealing with. If we didn't, the simple act of moving our head would prove to be an experience you wouldn't like to repeat. At the heart of this perception of movement are small stones - or otoconia - and a protein: otopetrin. Otopetrin floats in the extracellular gelatinous matrix which surrounds these particular stones and is essential for the formation of calcium carbonate crystals, the stuff of otoconia.

Otoconia are located in the darkest recesses of our inner ear where they rest on tiny hairs. Any movement of our head makes the otoconia move, and their movement will, in turn, cause the hairs to move. The perception is then relayed to nerves and ultimately to the brain. When otopetrin is deficient, the formation of otoconia is impaired. Consequently, the perception of acceleration and gravity gets confused. When this happens in zebrafish for instance, they swim upside down!

The simple passing of time can bring on the degeneration or mal-positioning of otoconia thus causing dizziness or a loss of balance - the sort of benign troubles the elderly are prone to. Certain drugs are also the cause of otoconia degeneration and research is now focused on finding therapies which could improve their stability over time as well as enhance the biomineralization of remaining otoconia. Indeed, getting to know the mechanisms involved in otoconia synthesis could also lead to a better understanding of how bone is made - for without bone or otoconia, how could we fully enjoy a balanced life? Or a glass of champagne for that matter...

UniProt cross references
Otopetrin 1, Danio rerio (Zebrafish), Q7ZWK8
Otopetrin 1, Homo sapiens (Human), Q7RTM1
Also read the Protein Spotlight article: Ear of stone
Protein Spotlight (ISSN 1424-4721) is a monthly review written by the Swiss-Prot team of the SIB Swiss Institute of Bioinformatics. Spotlight articles describe a specific protein or family of proteins on an informal tone. Follow us: Subscribe · Twitter · Facebook