Mosquito vision: molecular evolution and functional characterization of the opsins in Anopheles gambiae and Aedes aegypti

A novel strategy to reduce incidence of vector-borne diseases involves manipulating mosquito vision to disrupt mating, host detection or oviposition. An understanding of mosquito vision is fundamental to explore the feasibility of this approach. Opsins are proteins that interact with photons to initiate a phototransduction signaling cascade, involved with a visual response. Typically, insects have three classes of opsins to visualize ultraviolet, short, or long light wavelengths and a pteropsin gene, which is believed to regulate circadian rhythm. Previously, we identified 11 and 10 opsin genes in Anopheles gambiae and Aedes aegypti, respectively. Here, newly available expressed sequence tag (EST) data and homology-based analyses were used to improve opsin annotations. Analysis of A. aegypti revealed that all opsins are expressed in all sexes and stages, the exception being op 5 which is expressed only in females. Expression of all opsins except op7 and op11 was confirmed in A. gambiae adults using a real time quantitative RT-PCR approach. In situ hybridization of op3 and op8 in the eye of A. aegypti was consistent with that reported for orthologs in Drosophila melanogaster. Phylogentic analyses using ~300 opsin gene sequences from invertebrates and vertebrates revealed that mosquitoes have orthologs of the three visual opsins and the non-visual pteropsin. Long wavelength opsins have expanded in mosquitoes; perhaps this is tied to their visual needs during periods of low light intensity when they are most active. Future research is aimed at characterizing the spectral sensitivity of mosquitoes opsins.