Drosophila hygrosensation requires the TRP channels water witch and nanchung

Abstract

The ability to detect variations in humidity is critical for many animals. Birds, reptiles and insects all show preferences for specific humidities that influence their mating, reproduction and geographic distribution. Because of their large surface area to volume ratio, insects are particularly sensitive to humidity, and its detection can influence their survival. Two types of hygroreceptors exist in insects: one responds to an increase (moist receptor) and the other to a reduction (dry receptor) in humidity. Although previous data indicated that mechanosensation might contribute to hygrosensation, the cellular basis of hygrosensation and the genes involved in detecting humidity remain unknown. To understand better the molecular bases of humidity sensing, we investigated several genes encoding channels associated with mechanosensation, thermosensing or water transport. Here we identify two Drosophila melanogaster transient receptor potential channels needed for sensing humidity: CG31284, named by us water witch (wtrw), which is required to detect moist air, and nanchung (nan), which is involved in detecting dry air. Neurons associated with specialized sensory hairs in the third segment of the antenna express these channels, and neurons expressing wtrw and nan project to central nervous system regions associated with mechanosensation. Construction of the hygrosensing system with opposing receptors may allow an organism to very sensitively detect changes in environmental humidity.

Humidity sensation requires both mechanosensory and thermosensory pathways in Caenorhabditis elegans

“…One set activates with moist air, and the other set responds to dry air. Similar moist and dry receptive neurons have been detected in the branched arista subsegment of the antennae in adult Drosophila (9). Removal of the arista or deletion of any one of three TRP channels expressed in the arista prevents hygrotaxis (5,9).…”

Flying the Fly: Long-range Flight Behavior of Drosophila melanogaster to Attractive Odors

“…Water has earlier been reported to be critically important for attraction to traps baited with synthetic fruit odors (Zhu et al 2003). Drosophila melanogaster sense water with gustatory receptor neurons on the proboscis, projecting into a specific region of the suboesophagal ganglion, and with hygrosensory neurons located on the antennae, projecting into the antennal mechanosensory centre (Fischler et al 2007;Liu et al 2007;Inoshita and Tanimura 2008). It is remarkable that stimuli from outside the antennal lobe, the olfactory center, generate or contribute to an upwind flight response in D. melanogaster.…”

Identification of ion channel genes in the Acyrthosiphon pisum genome

“…In flies, this gene is involved in larval thermotaxis (Rosenzweig et al, 2005). The other three Drosophila TRPA genes, pyrexia, waterwitch (CG31284) and painless (painless is somewhat divergent) are involved in responses to heat (Lee et al, 2005), humidity (Liu et al, 2007) and in mechanosensation/nociception (Goodman, 2003;Tracey et al, 2003), respectively. The best candidate for an orthologue to any of these genes in the aphid is for waterwitch where a putative orthologue seems to have been duplicated, with two copies adjacent to each other in the inverse orientation.…”

“…In flies, these genes are involved in sound perception (Kim et al, 2003) and the responses to humidity (Liu et al, 2007) and heat (Chentsova et al, 2002). The single insect member of the TRPM family is also conserved in the aphid.…”