Fly ear on top and the human ear on the bottom. On the left, the overall structure of the ear. In the middle, the sensory organ and on the right, the individual cells which record sound waves. Venn diagram shows the number of genes known to be involved in deafness in mice, flies and humans, and how many they have in common. Credit: http://dx.doi.org/10.1016/j.cell.2012.08.007
25 September 2012
By Morag Lewis
Deafness is the most common form of sensory disorder; more than half of the population who are over 70 would benefit from a hearing aid. Despite this, there is still no medical treatment for hearing loss. One of the problems with studying hearing loss is that most of the genes involved in the development and function of the inner ear are still unknown. There are between 20,000 and 25,000 genes in the human genome involved in protein development , and it's thought that well over 500 of these are involved in deafness, yet fewer than 140 deafness genes have been identified.
I work on investigating novel genes involved in hearing loss. These are often a complete surprise to us, and operate in unexpected ways. For example, in 2009 we reported a microRNA responsible for hearing loss; this is a tiny gene that regulates lots of other genes, and it controls the maturation of the cells that detect sound (called "hair cells"). We are still working on the network of genes our microRNA regulates; we hope that this will help us discover more genes involved in deafness, some of which may be useful as targets for treatment for hearing loss.
We recently reviewed a paper (Senthilan et al, 2012) in Cell. This paper is particularly interesting because the experiments were carried out on the fruit fly. The fruit fly ear is called the Johnston's organ (JO), and it sits in part of the antenna (see figure). It looks very different to the mammalian ear (also in the figure), but nonetheless there are similarities, both functionally and genetically. The study looked at genes which work in the JO and investigated how the loss of those genes affected the fly. Losing some of the genes resulted in a totally deaf fly, while others affected just some aspects of the fly's hearing, and a few even enhanced its hearing.
The reason this paper is interesting to us, as researchers into mammalian hearing, is because so many of the genes are the same. The Venn diagram shows the overlap between mouse, human and fly genes involved in deafness. The single gene in the middle is Myo7a, the first mouse gene to be identified as underlying deafness. The long list of genes which work in the fly JO and affect fly hearing is a catalogue of interesting candidates for us to work from in the future. The more we understand the genetics of hearing, the better our chances of developing therapies to prevent or delay hearing loss.
Morag Lewis is a postdoc in Karen Steel’s team, studying the genetics of deafness more...
Morag A. Lewis, Karen P. Steel. 'A Cornucopia of Candidates for Deafness'
Cell, Volume 150, Issue 5, 31 August 2012, Pages 879-881 DOI: 10.1016/j.cell.2012.08.007.