Hearing in Drosophila: development of Johnston's organ and emerging parallels to vertebrate ear development

In this review, I describe recent progress toward understanding the developmental genetics governing formation of the Drosophila auditory apparatus. The Drosophila auditory organ, Johnston's organ, is housed in the antenna. Intriguingly, key genes needed for specification or function of auditory cell types in the Drosophila antenna also are required for normal development or function of the vertebrate ear. These genes include distal-less, spalt and spalt-related, atonal, crinkled, nanchung and inactive, and prestin, and their vertebrate counterparts Dlx, spalt-like (sall), atonal homolog (ath), myosin VIIA, TRPV, and prestin, respectively. In addition, Drosophila auditory neurons recently were shown to serve actuating as well as transducing roles, much like their hair cell counterparts of the vertebrate cochlea. The emerging genetic and physiologic parallels have come as something of a surprise, because conventional wisdom holds that vertebrate and invertebrate hearing organs have separate evolutionary origins. The new findings raise the possibility that auditory organs are more ancient than previously thought and indicate that Drosophila is likely to be a powerful model system in which to gain insights regarding the etiologies of human deafness disorders.