Cilia-mediated Hedgehog signaling controls form and function in the mammalian larynx

Nearly all animals communicateusing sound. In many cases these sounds are in the form of a voice, which in mammals is generated by a specialized organ in the throat called the larynx. Millions of people throughout the world have voice defects that make it difficult for them to communicate. Such defects are distinct from speech defects such as stuttering, and instead result from an inability to control the pitch or volume of the voice. This has a huge impact because our voice is so central to our quality of life. A wide range of human birth defects that are caused by genetic mutations are known to result in voice problems. These include disorders in which the Hedgehog signaling pathway, which allows cells to exchange information, is defective. Projections called cilia that are found on the outside of many cells transmit Hedgehogsignals, and birth defects that affect the cilia (called ciliopathies) also often result in voice problems. Although the shape of the larynxhas a crucial effect on voice, relatively little is known about how it develops in embryos. Mice are often studied to investigate how human embryos develop. By studying mouse embryos that had genetic mutations similar to those seen in humans with ciliopathies, Tabler, Rigney et al. now show that many different tissues interact in complex ways to form the larynx. A specific group of cells known as the neural crestwas particularly important. The neural cresthelps to form the face and skull and an excess of these cells causes face and skull defects in individuals with ciliopathies. Tabler, Rigney et al. show that having too many neural crestcells can also contribute towards defects in the larynxof mice with ciliopathies, despite the larynxbeing in the neck. Further investigation showed that the Hedgehog signaling pathwaywas required for the larynxto develop properly. Furthermore, recordings of the vocalizations of the mutant mice showed that they had defective voices, thus linking the defects in the shape of the larynxwith changes in the vocalizations that the mice made. Overall, Tabler, Rigney et al. show that mice can be used to investigate how the genes that control the shape of the larynxaffect the voice. The next step will be to use mice to investigate other genetic defects that cause voice defects in humans. Further research in other animals could also help us to understand how the larynxhas evolved.