Sensory Perception

Dermal Light Detectors

Science Signaling  21 Dec 2010:
Vol. 3, Issue 153, pp. ec384
DOI: 10.1126/scisignal.3153ec384

Light sensing is not limited to animals with eyes, and even “sightless” animals respond to illumination. This ability to sense light can be critical to finding food or avoiding predation, which in fly larvae involves burrowing into food. Fly larvae have primitive light-sensing structures called Bolwig organs, which allow them to avoid light and burrow. However, as Garrity points out, once their anteriors are buried, how do they avoid winding up like the “ostrich with its head in the sand”? Xiang et al. show that larvae with the Bolwig organs ablated responded to high-intensity light (ultraviolet, violet, and blue, but not red or green), which activated calcium signaling and increased action potential frequency in class IV dendritic arborization neurons (class IV neurons) that have dendrites that provide complete coverage of the body wall. Class IV neurons also responded to light when isolated and cultured. Unexpectedly, the light response of the class IV neurons was normal when analyzed in flies with mutations in several genes encoding known light receptors or downstream signaling molecules, such as rhodopsins, cryptochrome, or phospholipase C. Instead, this form of light detection involved gustatory receptor 28b (Gr28b), which is the closest fly homolog of the G protein–coupled receptor that has been identified as a light receptor in the nematode Caenorhabditis elegans, and transient receptor potential A1 (TrpA1). Flies with mutations or knockdown of either of the encoding genes failed to exhibit a light response in the class IV neurons, and these manipulations prevented light avoidance in animals without Bolwig organs. Ablation of the class IV neurons decreased light avoidance behavior of larvae, even those with intact Bolwig organs. Analysis of the light avoidance response to different light intensities and wavelengths in larvae with either class IV neurons or Bolwig organs ablated indicated that the Bolwig organ responds to low-intensity light and the class IV neurons respond to high-intensity light. These results not only reveal a sensory process in flies but also provide evidence of another light-sensitive signal transduction pathway that remains to be fully elucidated.

Y. Xiang, Q. Yuan, N. Vogt, L. L. Looger, L. Y. Jan, Y. N. Jan, Light-avoidance-mediating photoreceptors tile the Drosophila larval body wall. Nature 468, 921–926 (2010). [PubMed]

P. A. Garrity, Feel the light. Nature 468, 900–901 (2010). [PubMed]