Press release: Hearing with rhodopsin and chemoreceptor proteins

Nr. 160/2012 - 31.08.2012

Scientists discover receptor proteins for light and odours in the Drosophila ear

(pug) Photo-, chemo-, and auditory receptor cells use different proteins for sensory stimulus detection: photoreceptors capture light with visual rhodopsins, chemoreceptors bind odorants with olfactory receptor proteins, and auditory receptors use ion channels to monitor sound-induced vibrations. Scientists of the University of Göttingen now discovered that all these different proteins coexist in the hearing organ of Drosophila and that the fly uses visual rhodopsins and olfactory receptor proteins for sound detection. The work, which was supported by the German Science Foundation and the Göttingen Collaborative Research Center “Molecular Mechanisms of Sensory Processing”, is reported in the current issue of Cell.

Hearing in Drosophila relies on 500 auditory receptor cells in the fly’s antenna. The formation of these cells is initiated by a gene which also directs the development of auditory receptor cells in human ears. By analyzing the genetic repertoire of the fly’s auditory receptor cells, the scientists discovered 274 gene products that are expressed in these cells. “Every fifth of these fly genes has a pendant in our genome that is a candidate human deafness gene,” says Professor Martin Göpfert, Head of the Department of Cellular Neurobiology at the University of Göttingen. “In addition to known genes from hearing, we uncovered many genes that had not been associated with hearing before, several of which encode proteins for olfaction and vision.”

To test whether chemo- and photoreceptor proteins are required for hearing, David Piepenbrock, Ph.D. student at Göttingen University, exposed hundreds of mutant flies to different sounds and examined what these flies hear. Most of the mutants had profound hearing deficits, documenting auditory roles for olfactory receptor proteins and visual rhodopsins. “Especially the auditory deficits in rhodopsin mutants were quite drastic,” says Piepenbrock. “If one rhodopsin was disrupted, the auditory receptor cells of these flies only responded to very loud sounds. When I disrupted two rhodopsin that, in the eye, detect light of different colors, also these responses to loud sound got lost and the flies were entirely deaf.” The auditory receptor cells of the fly, however, did not respond to flashes of light, indicating that rhodopsin function in the ear is independent of light.

“The discovery that rhodopsins and chemoreceptor proteins serve roles in hearing is evolutionarily interesting”, explains Professor Göpfert. “In the fly, auditory, photo- and certain chemoreceptor cells all seem to have evolved from a common ancestral cell. This protosensory cell was presumably closest to the auditory mechanoreceptors, so finding that these cells utilize rhodopsins and chemoreceptor proteins suggests that these molecules may already have served sensory functions before chemo- and photoreceptor cells diversified.” By probing the roles of photo- and chemoreceptor proteins in the fly’s hearing organ, the scientists now hope to gain insight into the ancestral roles of these proteins and the evolution of sensory signaling cascades.

Original publication: Pingkalai Senthilan et al. Drosophila auditory organ genes and genetic hearing defects. Cell (2012). http://www.cell.com/abstract/S0092-8674%2812%2900926-9

Contact:
Prof. Dr. Martin Göpfert
Georg-August-University of Göttingen
Biological Faculty
Department of Cellular Neurobiology
Julia-Lermontowa-Weg 3, 37077 Göttingen
Email: mgoepfe@gwdg.de
Internet: www.uni-goettingen.de/de/114662.html