Molecular characterization of the carbon dioxide receptor in the oriental latrine fly, Chrysomya megacephala (Diptera: Calliphoridae)

The blowfly Chrysomya megacephala (Fabricius) (Diptera: Calliphoridae) cannot only act as a mechanical vector of various pathogens, but also infest man and animals causing human health problems and economic losses in the livestock and fish industries. As in other insects, olfaction of this species plays an important role in host location and is presumably mediated via transmembrane receptor signaling pathways. Here, we isolate and characterize CmegGr1 and CmegGr2, two new members of the chemosensory receptor gene family from C. megacephala. The open reading frames of CmegGr1 and CmegGr2 cDNA clones encode 453 and 486 amino acid residues, respectively. These two deduced proteins display high amino acid conservation with previously identified carbon dioxide (CO2) receptors, such as Drosophila melanogaster Gr21a/Gr63a and Anopheles gambiae s.s. Gr22/Gr24. Further sequence analysis showed that both proteins are consistent with their corresponding orthologs in the membrane topology prediction with some ambiguities in the location of N terminus and the number of transmembrane domains. The transcripts of CmegGr1 and CmegGr2 were detected in the major chemosensory organs including the antennae and proboscises with maxillary palps attached. These results suggest that CmegGr1 and CmegGr2 are likely to be the primary receptors for CO2 detection in C. megacephala. Knowledge of the molecular identity of the blowfly olfactory CO2 receptors may aid in the development of novel control strategies designed to take advantage of this unique and critical olfactory pathway.