Light-avoidance-mediating photoreceptors tile the Drosophila larval body wall

Photoreceptors for visual perception, phototaxis or light avoidance are typically clustered in eyes or related structures such as the Bolwig organ of Drosophila larvae. Unexpectedly, we found that the class IV dendritic arborization neurons of Drosophila melanogaster larvae respond to ultraviolet, violet and blue light, and are major mediators of light avoidance, particularly at high intensities. These class IV dendritic arborization neurons, which are present in every body segment, have dendrites tiling the larval body wall nearly completely without redundancy. Dendritic illumination activates class IV dendritic arborization neurons. These novel photoreceptors use phototransduction machinery distinct from other photoreceptors in Drosophila and enable larvae to sense light exposure over their entire bodies and move out of danger. Light sensing outside the eyes is common in many animals, usually confined to specialized organs. But now the entire body wall of the Drosophila fruitfly larva has been found to be blanketed with blue and ultraviolet light-sensing neuronal dendrites, which are essential for the maggot's innate light-avoidance behaviour. The phototransduction machinery used by these neurons is distinct from other Drosophila photoreceptor molecules, but similar to a system identified in nematode neurons. Light sensing outside the eyes is common in many animals but is usually confined to specialized organs. Here, the entire body wall of the fruitfly larva is found to be tiled with blue- and ultraviolet-light sensing neuronal dendrites, which are essential for the larva's innate light-avoidance behaviour. The phototransduction machinery used by these neurons is distinct from other Drosophila photoreceptor molecules but similar to a system recently identified in nematode neurons.